WorldWideScience

Sample records for debonding

  1. Non-Uniform Compressive Strength of Debonded Sandwich Panels

    DEFF Research Database (Denmark)

    Nøkkentved, Alexandros; Lundsgaard-Larsen, Christian; Berggreen, Carl Christian

    2005-01-01

    debonds show a considerable strength reduction with increasing debond diameter, with failure mechanisms varying between fast debond propagation and wrinkling-introduced face compression failure for large and small debonds, respectively. Residual strength predictions are based on intact panel testing...

  2. Buckling driven debonding in sandwich columns

    DEFF Research Database (Denmark)

    Østergaard, Rasmus Christian

    2008-01-01

    results from two mechanisms: (a) interaction of local debond buckling and global buckling and (b) the development of a damaged zone at the debond crack tip. Based on the pronounced imperfection sensitivity, the author predicts that an experimental measurement of the strength of sandwich structures may......A compression loaded sandwich column that contains a debond is analyzed using a geometrically non-linear finite element model. The model includes a cohesive zone along one face sheet/core interface whereby the debond can extend by interface crack growth. Two geometrical imperfections are introduced...

  3. Two Models of Adhesive Debonding of Sylgard

    Energy Technology Data Exchange (ETDEWEB)

    Stevens, Ralph Robert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-03-14

    This report begins with a brief summary of the range of modeling methods used to simulate adhesive debonding. Then the mechanical simulation of the blister debonding test, and the thermomechanical simulation of the potted hemisphere problem are described. For both simulations, details of the chosen modeling techniques, and the reasons for choosing them (and rejecting alternate modeling approaches) will be discussed.

  4. Debonding of perticles in anisotropic materials

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang

    2003-01-01

    is calculated. For increased triaxiality the onset of matrix-particle debonding occurs at a significantly reduced overall strain of the cell. The point of initial debonding is nearly unaffected by variations of the shape of the inclusions, but complete debonding occurs earlier if the inclusions are elongated......Effects of geometrical anisotropy as well as plastic anisotropy are studied in relation to debonding of rigid inclusions embedded in a metal. Full finite strain analyses are carried out for a cell model under plane strain conditions, and the average overall stress-strain response of the cell...... perpendicular to the main tensile direction. The same effect is observed, if the spacing of the inclusions is larger in the main tensile direction than in the transverse direction. For the orientations of plastic anisotropy considered, the debonding initiates and grows at a much lower overall strain than...

  5. Particle debonding using different yield criteria

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang; Kuroda, Mitsutoshi

    2004-01-01

    Effects of plastic anisotropy in relation to debonding of rigid inclusions embedded in an elastic-viscoplastic metal are studied. Full finite strain analyses are carried out for plane cells assuming plane stress or plane strain. The overall stress strain response is calculated, when the cell......-matrix debonding. Keeping all material parameters fixed, the material response of the plane strain cell is considerably affected, due to debonding at a much reduced overall plastic strain compared to the corresponding plane stress cell. (C) 2004 Elsevier SAS. All rights reserved....... extent and shape of the particular yield function considered. The required overall straining of the cell for debonding initiation is related to the extent of the yield surfaces, since a high yield stress promotes debonding. Additionally, the maximum overall stress level for the cell is lower for the Hill...

  6. Reactive Nanocomposites for Controllable Adhesive Debonding

    Science.gov (United States)

    2011-08-01

    technologies include shape memory alloy (SMA)-based approach, a chemical foaming agent (CFA) approach, and a reactive nanocomposite (RNC) approach. SMA...anofoil (a) Component 1 Thermoset Adhesive Component 2 Nano-coating (b) Figure 2. Debonding approach where (a) freestanding...J. Controlled Adhesive Debonding of RAH-66 Comanche Chines Using Shape Memory Alloys ; ARL-TR-2937; U.S. Army Research Laboratory: Aberdeen Proving

  7. Damage assessment of compression loaded debond damaged sandwich panels

    DEFF Research Database (Denmark)

    Moslemian, Ramin; Berggreen, Christian; Quispitupa, Amilcar

    2010-01-01

    with an implanted circular face/core debond. Compression tests were conducted on intact sandwich panels and panels with an implanted circular face/core debond with three different types of foam core materials (PVC H130, PVC H250 and PMI 51-IG). The strains and out-of-plane displacements of the debonded region were...

  8. Interfacial debonding of ice-asphalt concrete

    Energy Technology Data Exchange (ETDEWEB)

    Tazawa, E.; Mizoue, Y. (Hiroshima Univ., Hiroshima (Japan)); Kojima, T. (Hitachi Chemical Co. Ltd., Tokyo (Japan))

    1992-09-20

    Series of experimental investigations were carried out to clarify the bonding mechanism between ice and asphalt and to develop a new technique to reduce bonding resistance. The surface bonding resistance was measured by three methods and the main variables taken into consideration have been surface energy, surface roughness and stiffness of asphalt. Surface energy was varied by using various water repellents and the stiffness of the concrete was varied by mixing rubber particles. Correlations of the three variables were studied and the following results have been obtained. Decreasing of surface energy and increasing of deformability of asphalt concrete has been the effective method to decrease the bonding between ice and asphalt. For the case of water repellent coated surface, shear debonding strength has been linearly related to the energy required for debonding by dynamic tension and the shear debonding strength has decreased with the decrease in roughness of pavement. In the case of surface without using repellent, shear debonding strength has not been influenced by surface energy and roughness of pavement. 6 refs., 16 figs., 7 tabs.

  9. Analysis of Smart Composite Structures Including Debonding

    Science.gov (United States)

    Chattopadhyay, Aditi; Seeley, Charles E.

    1997-01-01

    Smart composite structures with distributed sensors and actuators have the capability to actively respond to a changing environment while offering significant weight savings and additional passive controllability through ply tailoring. Piezoelectric sensing and actuation of composite laminates is the most promising concept due to the static and dynamic control capabilities. Essential to the implementation of these smart composites are the development of accurate and efficient modeling techniques and experimental validation. This research addresses each of these important topics. A refined higher order theory is developed to model composite structures with surface bonded or embedded piezoelectric transducers. These transducers are used as both sensors and actuators for closed loop control. The theory accurately captures the transverse shear deformation through the thickness of the smart composite laminate while satisfying stress free boundary conditions on the free surfaces. The theory is extended to include the effect of debonding at the actuator-laminate interface. The developed analytical model is implemented using the finite element method utilizing an induced strain approach for computational efficiency. This allows general laminate geometries and boundary conditions to be analyzed. The state space control equations are developed to allow flexibility in the design of the control system. Circuit concepts are also discussed. Static and dynamic results of smart composite structures, obtained using the higher order theory, are correlated with available analytical data. Comparisons, including debonded laminates, are also made with a general purpose finite element code and available experimental data. Overall, very good agreement is observed. Convergence of the finite element implementation of the higher order theory is shown with exact solutions. Additional results demonstrate the utility of the developed theory to study piezoelectric actuation of composite

  10. Residual Strength of In-plane Loaded Debonded Sandwich Panels

    DEFF Research Database (Denmark)

    Berggreen, Carl Christian; Simonsen, Bo Cerup

    2005-01-01

    This paper presents a FEM based numerical model for prediction of residual strength of damaged sandwich panels. As demonstrated, the model can predict the maximum load carrying capacity of real-life panels with debond damages, where the failure is governed by face-sheet buckling followed by debond...

  11. Comparison of two different debonding techniques in orthodontic treatment.

    Science.gov (United States)

    Piccoli, Luca; Migliau, Guido; Besharat, Laith Konstantinos; Di Carlo, Stefano; Pompa, Giorgio; Di Giorgio, Roberto

    2017-01-01

    The purpose of this research is to investigate whether and how the adhesive bond failure site varied in relation to the material used for the orthodontic bonding and debonding technique applied. Two different methods of orthodontic debonding were included in our survey; cutters for orthodontics and debonding plier. Three different materials for the adhesion of the bracket: composite light curing, self-curing composite and glass ionomer cement. The remaining amount of adhesive on the tooth surface is an important parameter that gives information on how the location of the posting site varied during the debonding. 60 dental elements, maxillary and mandibular, previously extracted for orthodontic reasons, as well as periodontal, were included in our research. We investigated a possible significant correlation between different variables (debonding technique and materials for membership) and the ARI index. The use of orthodontic cutters or debonding pliers does not affect the adhesive bond failure site and both techniques have a tendency to leave a significant amount of adhesive on the surface enamel. In the resin-reinforced glass ionomer cements, detachment occurs at the interface enamel-adhesive and this pattern of detachment increases the risk of the enamel damage during debonding. In both types of composite resins (photopolymerizable or self-curing), the detachment occurs at the interface bracketing adhesive. In this case the amount of remaining adhesive material on the tooth must be removed with further methods, which in addition, increase the risk of iatrogenic injury as well as the working hours.

  12. Requirements of frictional debonding at fiber/matrix interfaces for tough ceramic composites

    Science.gov (United States)

    Hsueh, Chun-Hway

    1992-11-01

    Optimum toughening of fiber-reinforced ceramic composites requires debonding at fiber/matrix interfaces and subsequent frictional sliding between the fibers and the matrix as the main crack extends through the composite. Criteria of both interfacial debonding vs fiber fracture, and frictional debonding vs frictionless debonding, are illustrated. To achieve interfacial debonding, the ratio of the fiber strength to the interfacial shear strength must exceed a critical value; to achieve a frictional interface after interfacial debonding, the ratio of the interfacial residual clamping stress to the interfacial shear strength must also exceed a critical value. While interfacial debonding is not sensitive to Poisson's effect, the frictional interface is sensitive to Poisson's effect.

  13. Debonding characteristics of adhesively bonded woven Kevlar composites

    Science.gov (United States)

    Mall, S.; Johnson, W. S.

    1988-01-01

    The fatigue damage mechanism of an adhesively bonded joint between fabric reinforced composite adherends was investigated with cracked-lap-shear specimens. Two bonded systems were studied: fabric Kevlar 49/5208 epoxy adherends bonded together with either EC 3445 or FM-300 adhesive. For each bonded system, two specimen geometries were tested. In all specimens tested, fatigue damage occurred in the form of cyclic debonding; however, the woven Kevlar specimens gave significantly slower debond growth rates and higher fracture toughness than previously found in the nonwoven adherend specimens. The surfaces for the woven adherends were not smooth; rather, they had regular crests (high spots) and troughs (low spots) due to the weave pattern. Radiographs of the specimens and examination of their failure surfaces revealed that fiber bridging occurred between the crests of the two adherends in the debonded region. The observed improvements in debond growth resistance and static fracture toughness are attributed to this bridging.

  14. Effect of Stitching on Debonding in Composite Structural Elements

    Science.gov (United States)

    Raju, I. S.; Glaessgen, E. H.

    2001-01-01

    Stitched multiaxial warp knit materials have been suggested as viable alternatives to laminated prepreg materials for large aircraft structures such as wing skins. Analyses have been developed to quantify the effectiveness of stitching for reducing strain energy release rates in skin-stiffener debond, lap joint and sandwich debond configurations. Strain energy release rates were computed using the virtual crack closure technique. In all configurations, the stitches were shown to significantly reduce the strain energy release rate.

  15. The use of easily debondable orthodontic adhesives with ceramic brackets.

    Science.gov (United States)

    Ryu, Chiyako; Namura, Yasuhiro; Tsuruoka, Takashi; Hama, Tomohiko; Kaji, Kaori; Shimizu, Noriyoshi

    2011-01-01

    We experimentally produced an easily debondable orthodontic adhesive (EDA) containing heat-expandable microcapsules. The purpose of this in vitro study was to evaluate the best debondable condition when EDA was used for ceramic brackets. Shear bond strengths were measured before and after heating and were compared statistically. Temperatures of the bracket base and pulp wall were also examined during heating. Bond strengths of EDA containing 30 wt% and 40 wt% heat-expandable microcapsules were 13.4 and 12.9 MPa, respectively and decreased significantly to 3.8 and 3.7 MPa, respectively, after heating. The temperature of the pulp wall increased 1.8-3.6°C after heating, less than that required to induce pulp damage. Based on the results, we conclude that heating for 8 s during debonding of ceramic brackets bonded using EDA containing 40 wt% heat-expandable microcapsules is the most effective and safest method for the enamel and pulp.

  16. Bracket debonding by mid-infrared laser radiation

    International Nuclear Information System (INIS)

    Jelínková, H; Šulc, J; Koranda, P; Němec, M; Dostálová, T; Hofmanova, P

    2009-01-01

    The purpose of the study was to determine the proper laser radiation for ceramic bracket debonding and the investigation of the tooth root temperature injury. The debonding was investigated by diode-pumped continuously running Tm:YAP and Nd:YAG lasers, and by GaAs laser diode generating radiation with the wavelengths 1.997 μm, 1.444 μm, and 0.808 μm, respectively. The possibility of brackets removal by laser radiation was investigated together with the tooth and, it specifically, root temperature rise. From the results it follows that continuously running diode pumped Tm:YAG or Nd:YAG laser generating wavelengths 1.997 μm or 1.444 μm, respectively, having the output power 1 W can be good candidates for ceramic brackets debonding

  17. Debonding of epoxy from glass in irradiated laminates

    International Nuclear Information System (INIS)

    Klabunde, C.E.; Coltman, R.R. Jr.

    1982-01-01

    Glass-fabric-filled epoxies irradiated at 4.7 K and examined at room temperature by 20x stereomicroscopy showed an internal flaw structure which increasingly filled the sample as the γ-dose was increased. These flaws were determined to be areas where the plastic had debonded from the glass fibers. The extent of this process correlated well with the dose-dependent loss of mechanical strength. Evidence is reported for a similar mechanism in polyimides although visible flaws have not yet been produced. Possible mechanisms for debonding are suggested. New experiments are also suggested to clarify further the failure mechanism

  18. Comparison of the Debonding Characteristics of Conventional and New Debonding Instrument used for Ceramic, Composite and Metallic Brackets - An Invitro Study.

    Science.gov (United States)

    Choudhary, Garima; Gill, Vikas; Reddy, Y N N; Sanadhya, Sudhanshu; Aapaliya, Pankaj; Sharma, Nidhi

    2014-07-01

    Debonding procedure is time consuming and damaging to the enamel if performed with improper technique. Various debonding methods include: the conventional methods that use pliers or wrenches, an ultrasonic method, electrothermal devices, air pressure impulse devices, diamond burs to grind the brackets off the tooth surface and lasers. Among all these methods, using debonding pliers is most convenient and effective method but has been reported to cause damage to the teeth. Recently, a New Debonding Instrument designed specifically for ceramic and composite brackets has been introduced. As this is a new instrument, little information is available on efficacy of this instrument. The purpose of this study was to evaluate the debonding characteristics of both "the conventional debonding Pliers" and "the New debonding instrument" when removing ceramic, composite and metallic brackets. One Hundred Thirty eight extracted maxillary premolar teeth were collected and divided into two Groups: Group A and Group B (n = 69) respectively. They were further divided into 3 subGroups (n = 23) each according to the types of brackets to be bonded. In subGroups A1 and B1{stainless steel};A2 and B2{ceramic};A3 and B3{composite}adhesive precoated maxillary premolar brackets were used. Among them {ceramic and composite} adhesive pre-coated maxillary premolar brackets were bonded. All the teeth were etched using 37% phosphoric acid for 15 seconds and the brackets were bonded using Transbond XT primer. Brackets were debonded using Conventional Debonding Plier and New Debonding Instrument (Group B). After debonding, the enamel surface of each tooth was examined under stereo microscope (10X magnifications). Amodifiedadhesive remnant index (ARI) was used to quantify the amount of remaining adhesive on each tooth. The observations demonstrate that the results of New Debonding Instrument for debonding of metal, ceramic and composite brackets were statistically significantly different (p = 0

  19. Comparison of the Debonding Characteristics of Conventional and New Debonding Instrument used for Ceramic, Composite and Metallic Brackets – An Invitro Study

    Science.gov (United States)

    Gill, Vikas; Reddy, Y. N. N.; Sanadhya, Sudhanshu; Aapaliya, Pankaj; Sharma, Nidhi

    2014-01-01

    Background: Debonding procedure is time consuming and damaging to the enamel if performed with improper technique. Various debonding methods include: the conventional methods that use pliers or wrenches, an ultrasonic method, electrothermal devices, air pressure impulse devices, diamond burs to grind the brackets off the tooth surface and lasers. Among all these methods, using debonding pliers is most convenient and effective method but has been reported to cause damage to the teeth. Recently, a New Debonding Instrument designed specifically for ceramic and composite brackets has been introduced. As this is a new instrument, little information is available on efficacy of this instrument. The purpose of this study was to evaluate the debonding characteristics of both “the conventional debonding Pliers” and “the New debonding instrument” when removing ceramic, composite and metallic brackets. Materials and Methods: One Hundred Thirty eight extracted maxillary premolar teeth were collected and divided into two Groups: Group A and Group B (n = 69) respectively. They were further divided into 3 subGroups (n = 23) each according to the types of brackets to be bonded. In subGroups A1 and B1{stainless steel};A2 and B2{ceramic};A3 and B3{composite}adhesive precoated maxillary premolar brackets were used. Among them {ceramic and composite} adhesive pre-coated maxillary premolar brackets were bonded. All the teeth were etched using 37% phosphoric acid for 15 seconds and the brackets were bonded using Transbond XT primer. Brackets were debonded using Conventional Debonding Plier and New Debonding Instrument (Group B). After debonding, the enamel surface of each tooth was examined under stereo microscope (10X magnifications). Amodifiedadhesive remnant index (ARI) was used to quantify the amount of remaining adhesive on each tooth. Results: The observations demonstrate that the results of New Debonding Instrument for debonding of metal, ceramic and composite brackets

  20. Buckling and Fracture Investigation of Debonded Sandwich Columns: An Experimental and Numerical Study

    DEFF Research Database (Denmark)

    Berggreen, Christian; Carlsson, Leif A.; Avilés, F.

    2008-01-01

    An experimental and numerical study of in-plane compression of foam core sandwich columns with implanted trough width face/core debond is presented. Experiments were conducted for columns with two different face thicknesses over different cores and debond lengths. The debonded region was monitore...

  1. Failure Investigation of Debonded Sandwich Columns: An Experimental and Numerical Study

    DEFF Research Database (Denmark)

    Moslemian, Ramin; Berggreen, Christian; Carlsson, Leif A.

    2009-01-01

    Failure of compression loaded sandwich columns with an implanted through-width face/core debond is examined. Compression tests were conducted on sandwich columns containing implemented face/core debonds. The strains and out-of-plane displacements of the debonded region were monitored using the di...

  2. Elastic interaction of partially debonded circular inclusions. I. Theoretical solution

    DEFF Research Database (Denmark)

    Kushch, V.I.; Shmegera, S.V.; Mishnaevsky, Leon

    2010-01-01

    and provides a simple and rapidly convergent iterative algorithm. The presented numerical data show an accuracy and numerical efficiency of the proposed method and discover the way and extent to which the elastic interaction between the partially debonded inclusions affects the local fields, stress intensity...... factors and the energy release rate at the interface crack tips....

  3. Debonding failure and size effects in micro reinforced composites

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang; Niordson, Christian Frithiof

    2010-01-01

    -plastic formulation. Bi-axially loaded unit cells are used and failure is modeled using a cohesive zone at the reinforcement interface. During debonding a sudden stress drop in the overall average stress–strain response is observed. Adaptive higher-order boundary conditions are imposed at the reinforcement interface...... for realistically modeling the restrictions on moving dislocations as debonding occurs. It is found that the influence of the imposed higher-order boundary conditions at the interface is minor. If strain-gradient effects are accounted for a void with a smooth shape develops at the reinforcement interface while...... a smaller void having a sharp tip nucleates if strain-gradient effects are excluded. Using orthogonalization of the plastic strain gradient with three corresponding material length scales it is found that, the first length scale dominates the evaluated overall average stress–strain response, the second one...

  4. Debonding analyses in anisotropic materials with strain- gradient effects

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang

    2012-01-01

    A unit cell approach is adopted to numerically analyze the effect of plastic anisotropy on damage evolution in a micro-reinforced composite. The matrix material exhibit size effects and a visco-plastic anisotropic strain gradient plasticity model accounting for such size effects is adopted....... A conventional cohesive law is extended such that both the average as well as the jump in plastic strain across the fiber-matrix interface are accounted for. Results are shown for both conventional isotropic and anisotropic materials as well as for higher order isotropic and anisotropic materials...... with and without debonding. Generally, the strain gradient enhanced material exhibits higher load carry capacity compared to the corresponding conventional material. A sudden stress drop occurs in the macroscopic stress-strain response curve due to fiber-matrix debonding and the results show that a change in yield...

  5. Laser debonding of ceramic orthodontic brackets: a theoretical approach

    Science.gov (United States)

    Kearney, Kristine L.; Marangoni, Roy D.; Rickabaugh, Jeff L.

    1992-06-01

    Ceramic brackets are an esthetic substitute for conventional stainless steel brackets in orthodontic patients. However, ceramic brackets are more brittle and have higher bond strengths which can lead to bracket breakage and enamel damage during debonding. It has been demonstrated that various lasers can facilitate ceramic bracket removal. One mechanism with the laser is through the softening of the bracket adhesive. The high energy density from the laser on the bracket and adhesive can have a resultant deleterious thermal effect on the pulp of the tooth which may lead to pulpal death. A theoretical computer model of bracket, adhesive, enamel and dentin has been generated for predicting heat flow through this system. Heat fluxes at varying intensities and modes have been input into the program and the resultant temperatures at various points or nodes were determined. Further pursuit should lead to optimum parameters for laser debonding which would have minimal effects on the pulp.

  6. Comparison between two methods for resin removing after bracket debonding

    OpenAIRE

    Marchi, Rodrigo De; Marchi, Luciana Manzotti De; Terada, Raquel Sano Suga; Terada, Hélio Hissashi

    2012-01-01

    OBJECTIVE: The aim of this study was to assess - using scanning electron microscopy (SEM) - the effectiveness of two abrasive discs, one made from silicon and one from aluminum oxide, in removing adhesive remnants (AR) after debonding orthodontic brackets. METHODS: Ten randomly selected bovine teeth were used, i.e., 2 in the control group, and the other 8 divided into two groups, which had orthodontic brackets bonded to their surface with Concise Orthodontic Adhesive (3M). The following metho...

  7. Prototype to measure bracket debonding force in vivo

    Directory of Open Access Journals (Sweden)

    Jéssika Lagni Tonus

    Full Text Available ABSTRACT Introduction: Material biodegradation that occurs in the mouth may interfere in the bonding strength between the bracket and the enamel, causing lower bond strength values in vivo, in comparison with in vitro studies. Objective: To develop a prototype to measure bracket debonding force in vivo and to evaluate, in vitro, the bond strength obtained with the prototype. Methods: A original plier (3M Unitek was modified by adding one strain gauge directly connected to its claw. An electronic circuit performed the reading of the strain gauge, and the software installed in a computer recorded the values of the bracket debonding force, in kgf. Orthodontic brackets were bonded to the facial surface of 30 bovine incisors with adhesive materials. In Group 1 (n = 15, debonding was carried out with the prototype, while tensile bond strength testing was performed in Group 2 (n = 15. A universal testing machine was used for the second group. The adhesive remnant index (ARI was recorded. Results: According to Student’s t test (α = 0.05, Group 1 (2.96 MPa and Group 2 (3.08 MPa were not significantly different. ARI score of 3 was predominant in the two groups. Conclusion: The prototype proved to be reliable for obtaining in vivo bond strength values for orthodontic brackets.

  8. Prototype to measure bracket debonding force in vivo

    Science.gov (United States)

    Tonus, Jéssika Lagni; Manfroi, Fernanda Borguetti; Borges, Gilberto Antonio; Grigolo, Eduardo Correa; Helegda, Sérgio; Spohr, Ana Maria

    2017-01-01

    ABSTRACT Introduction: Material biodegradation that occurs in the mouth may interfere in the bonding strength between the bracket and the enamel, causing lower bond strength values in vivo, in comparison with in vitro studies. Objective: To develop a prototype to measure bracket debonding force in vivo and to evaluate, in vitro, the bond strength obtained with the prototype. Methods: A original plier (3M Unitek) was modified by adding one strain gauge directly connected to its claw. An electronic circuit performed the reading of the strain gauge, and the software installed in a computer recorded the values of the bracket debonding force, in kgf. Orthodontic brackets were bonded to the facial surface of 30 bovine incisors with adhesive materials. In Group 1 (n = 15), debonding was carried out with the prototype, while tensile bond strength testing was performed in Group 2 (n = 15). A universal testing machine was used for the second group. The adhesive remnant index (ARI) was recorded. Results: According to Student’s t test (α = 0.05), Group 1 (2.96 MPa) and Group 2 (3.08 MPa) were not significantly different. ARI score of 3 was predominant in the two groups. Conclusion: The prototype proved to be reliable for obtaining in vivo bond strength values for orthodontic brackets. PMID:28444011

  9. Modeling of a partially debonded piezoelectric actuator in smart composite laminates

    International Nuclear Information System (INIS)

    Huang, Bin; Soo Kim, Heung; Ho Yoon, Gil

    2015-01-01

    A partially debonded piezoelectric actuator in smart composite laminates was modeled using an improved layerwise displacement field and Heaviside unit step functions. The finite element method with four node plate element and the extended Hamilton principle were used to derive the governing equation. The effects of actuator debonding on the smart composite laminate were investigated in both the frequency and time domains. The frequency and transient responses were obtained using the mode superposition method and the Newmark time integration algorithm, respectively. Two partial actuator debonding cases were studied to investigate the debonding effects on the actuation capability of the piezoelectric actuator. The effect of actuator debonding on the natural frequencies was subtler, but severe reductions of the actuation ability were observed in both the frequency and time responses, especially in the edge debonded actuator case. The results provided confirmation that the proposed modeling could be used in virtual experiments of actuator failure in smart composite laminates. (paper)

  10. Numerical simulation of progressive debonding in fiber reinforced composite under transverse loading

    DEFF Research Database (Denmark)

    Kushch, V.; Shmegera, S.V.; Brøndsted, Povl

    2011-01-01

    . Then, the effect on debonding progress of local stress redistribution due to interaction between the fibers was studied in the framework of two-inclusion model. Simulation of progressive debonding in fiber reinforced composite using the many-fiber models of composite has been performed. It has been...... shown that the developed model provides detailed analysis of the progressive debonding phenomenon including the interface crack cluster formation, overall stiffness reduction and induced anisotropy of the effective elastic moduli of composite....

  11. The Relationship between Rebar-Debonding and Cracking in Reinforced Concrete

    DEFF Research Database (Denmark)

    Thybo, Anna Emilie A.; Stang, Henrik; Olesen, John Forbes

    2012-01-01

    and the CMOD, indicating that if the debonding length has a significant influence on the risk of corrosion initiation and propagation (as indicated in the literature), then CMOD cannot be used alone as corrosion risk indicator. A limited parametric study has been performed and it has been shown that the shear...... strength of the interface has a significant influence on the debonding length. The cover layer – on the other hand – has relatively little influence on the debonding lengths....

  12. Debonding of short fibres among particulates in a metal matrix composite

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2003-01-01

    of differently shaped fibres or particulates in each unit cell. thus representing debonding of a relatively long discontinuous fibre among particulates that do not debond. Interfacial failure is modelled in terms of a cohesive zone model that accounts for decohesion by normal separation as well as by tangential...... separation. It is found that the evolution of failure can depend rather strongly on the distribution of particulates around a fibre subject to debonding. (C) 2003 Elsevier Ltd. All rights reserved....

  13. A randomized controlled trial to assess the pain associated with the debond of orthodontic fixed appliances

    Science.gov (United States)

    Mangnall, Louise A R; Dietrich, Thomas; Scholey, John M

    2013-01-01

    Objective: To determine patient experience of pain during treatment with fixed orthodontic appliances, expectations of pain during debond and whether biting on a soft acrylic wafer during debond decreases pain experience. Design: Multicentre randomized controlled trial. Setting: Three UK hospital based orthodontic departments: Mid-Staffordshire NHS Foundation Trust, Birmingham Dental Hospital and University Hospital of North Staffordshire. Materials and methods: Ninety patients were randomly allocated to either the control (n = 45) or wafer group (n = 45). A visual analogue scale-based questionnaire was completed pre-debond to determine pain experience during treatment and expectations of pain during debond. The appliances were debonded and those in the wafer group bit on a soft acrylic wafer. A second questionnaire was completed post-debond to assess the pain experienced. Results: Biting on an acrylic wafer significantly reduced the pain experienced when debonding the posterior teeth (P≤0·05). Thirty-nine per cent found the lower anterior teeth the most painful. The expected pain was significantly greater than that actually experienced (P≤0·0001). Greater pain during treatment correlated with increased expectations and increased actually experienced pain (P≤0·0001). Conclusions: Biting on a soft acrylic wafer during debond of the posterior teeth reduces the pain experienced. The lower anterior teeth are the most painful. The pain expected is significantly greater than actually experienced. Patients who had greater pain during treatment expected and experienced greater pain at debond. PMID:24009318

  14. 3D in situ observations of glass fibre/matrix interfacial debonding

    DEFF Research Database (Denmark)

    Martyniuk, Karolina; Sørensen, Bent F.; Modregger, Peter

    2013-01-01

    X-ray microtomography was used for 3D in situ observations of the evolution of fibre/matrix interfacial debonding. A specimen with a single fibre oriented perpendicular to the tensile direction was tested at a synchrotron facility using a special loading rig which allowed for applying a load...... transverse to the fibre. Three distinguishable damage stages were observed: (i) interfacial debond initiation at the free surface, (ii) debond propagation from the surface into the specimen and (iii) unstable debonding along the full length of the scanned volume. The high resolution microtomography provides...

  15. Quantitative analysis of enamel on debonded orthodontic brackets.

    Science.gov (United States)

    Cochrane, Nathan J; Lo, Thomas W G; Adams, Geoffrey G; Schneider, Paul M

    2017-09-01

    Iatrogenic damage to the tooth surface in the form of enamel tearouts can occur during removal of fixed orthodontic appliances. The aim of this study was to assess debonded metal and ceramic brackets attached with a variety of bonding materials to determine how frequently this type of damage occurs. Eighty-one patients close to finishing fixed orthodontic treatment were recruited. They had metal brackets bonded with composite resin and a 2-step etch-and-bond technique or ceramic brackets bonded with composite resin and a 2-step etch-and- bond technique, and composite resin with a self-etching primer or resin-modified glass ionomer cement. Debonded brackets were examined by backscattered scanning electron microscopy with energy dispersive x-ray spectroscopy to determine the presence and area of enamel on the base pad. Of the 486 brackets collected, 26.1% exhibited enamel on the bonding material on the bracket base pad. The incidences of enamel tearouts for each group were metal brackets, 13.3%; ceramic brackets, 30.2%; composite resin with self-etching primer, 38.2%; and resin-modified glass ionomer cement, 21.2%. The percentage of the bracket base pad covered in enamel was highly variable, ranging from 0% to 46.1%. Enamel damage regularly occurred during the debonding process with the degree of damage being highly variable. Damage occurred more frequently when ceramic brackets were used (31.9%) compared with metal brackets (13.3%). Removal of ceramic brackets bonded with resin-modified glass ionomer cement resulted in less damage compared with the resin bonding systems. Copyright © 2017 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.

  16. Fracture Analysis of Debonded Sandwich Columns Under Axial Compression

    DEFF Research Database (Denmark)

    May, A.; Avilés, F.; Berggreen, Christian

    A sandwich structure consists of two strong and stiff face sheets bonded to a weak low density core. The large separation between the face sheets provides increased bending rigidity and strength at low weight cost. Thus, sandwich structures frequently present better mechanical properties than...... monolithic structures of the same weight. The vast range of applications of such materials includes wind turbines, marine, and aerospace industries. In this work, geometrically nonlinear finite element analysis is conducted to investigate the fracture parameters and debond propagation of sandwich columns...

  17. Residual Strength Prediction of Debond Damaged Sandwich Panels

    DEFF Research Database (Denmark)

    Berggreen, Carl Christian

    followed by debond growth. The developed theoretical procedure is an extension of the Crack Surface Displacement method, here denoted the Crack Surface Displacement Extrapolation method. The method is first developed in 2D and then extended to 3D by use of a number of realistic assumptions...... for the considered configurations. Comparison of the theoretical predictions to two series of large-scale experiments with loadings (uniform and non-uniform in-plane compression) comparable with real life loading scenarios for sandwich ships shows that the model is indeed able to predict the failure modes...

  18. A Debonded Sandwich Specimen Under Mixed Mode Bending (MMB)

    DEFF Research Database (Denmark)

    Quispitupa, Amilcar; Berggreen, Christian; Carlsson, Leif A.

    2008-01-01

    Face/core interface crack propagation in sandwich specimens is analyzed. A thorough analysis of the typical failure modes in sandwich composites was performed in order to design the MMB specimen to promote face/core debond fracture. Displacement, compliance and energy release rate expressions...... for the MMB specimen were derived from a superposition analysis. An experimental verification of the methodology proposed was performed using MMB sandwich specimens with H100 PVC foam core and E-glass/polyester non-crimp quadro-axial [0/45/90/-45]s DBLT-850 faces. Different mixed mode loadings were applied...

  19. DEBONDING OF CERAMIC BRACKETS BY ER:YAG LASER

    Directory of Open Access Journals (Sweden)

    Fidan ALAKUŞ-SABUNCUOĞLU

    2016-04-01

    Full Text Available Purpose: The objective of the present study is to evaluate the effects of Er:YAG laser debonding of ceramic brackets on the bond strength and the amount of adhesive resin remnant. Materials and Methods: Twenty human mandibular incisors were randomly divided into two groups of 10 and polycrystalline ceramic brackets (Transcend series 6000, 3M Unitek, Monrovia, CA, USA were bonded on enamel surfaces. Group 1 was the control group in which no laser application was performed prior to the shear bond strength (SBS testing. In Group 2, Er:YAG was applied in 3W power for 6 seconds using the scanning method. The brackets were tested for SBS with an Instron universal testing machine and results were expressed in megapascals (MPa. The amount of adhesive remnant was evaluated with Adhesive Remnant Index (ARI. One-way analysis of variance and Tukey’s post-hoc tests were used for statistical analysis. Results: Mean ± standard deviation of SBS values in the control group was 13.42 ±1.23 MPa and 8.47 ±0.71 MPa in the Er:YAG group and this difference was statistically significant (p<0.05. The evaluation of ARI scores demonstrated more adhesive was left on the enamel surface with Er:YAG group. Conclusion: 3W power Er:YAG laser application with the scanning method to polycrystalline ceramic brackets demonstrated lower bond strengths and higher ARI scores during the debonding procedure.

  20. Variations in enamel damage after debonding of two different bracket base designs: An in vitro study.

    Science.gov (United States)

    Ahangar Atashi, Mohammad Hossein; Sadr Haghighi, Amir Hooman; Nastarin, Parastou; Ahangar Atashi, Sina

    2018-01-01

    Background. Bracket base design is a factor influencing shear bond strength. High shear bond strength leads to enamel crack formation during debonding. The aim of this study was to compare enamel damage variations, including the number and length of enamel cracks after debonding of two different base designs. Methods. Eighty-eight extracted human premolars were randomly divided into2 groups (n=44). The teeth in each group were bonded by two types of brackets with different base designs: 80-gauge mesh design versus anchor pylon design with pylons for adhesive retention. The number and length of enamel cracks before bonding and after debonding were evaluated under an optical stereomicroscope ×40 in both groups. Mann-Whitney U test was used to compare the number of cracks between the two groups. ANCOVA was used for comparison of crack lengths after and before debonding in each group and between the two groups. Results. There was a significant increase in enamel crack length and numbers in each group after debonding. There was no significant difference in enamel crack numbers after debonding between the two groups, whereas the length of enamel cracks was significantly greater in anchor pylon base design after debonding. Conclusion. Bracket bases with pylon design for adhesive retention caused more iatrogenic debonding damage to enamel surface.

  1. Debonding Patch Detection in FRP-Strengthened Materials with Fiber-Optic Interferometer

    Institute of Scientific and Technical Information of China (English)

    Xu Ying; Wang Dexiang; Tang Tianyou; Lu Miaomiao

    2017-01-01

    The interfacial debonding in fiber-reinforced plastic(FRP) strengthened repair material will affect the bonding strength and lead to failure of the repair without warning.Unfortunately the interfacial damage is normally invisible and often in the form of a patch rather than a through-width crack.Therefore,a debonding patch detection technique based on fiber optic interferometry is proposed.A quasi impulse loading is applied with a rubberhead hammer and the total elongation of a surface mounted optical fiber along the length of the repair material is measured as a function of load position.When a debonding patch is present,the induced sudden slope or sign change on the plot of fiber integral strain v.s.load position will reveal the extent and the location of the debonded area.The results of the study indicate that the proposed technique is applicable for debonding patch detection in repaired members under various support conditions.

  2. Cracking in concrete-debonding length at the concrete/steel interface

    OpenAIRE

    Kjeldby, Liv Brox

    2016-01-01

    Investigation of the debonding length at the concrete/steel interface have been investigated based on different types of cracks in concrete. Different methods for investigation have been used in the laboratory.

  3. An Intelligent Strain Gauge with Debond Detection and Temperature Compensation

    Science.gov (United States)

    Jensen, Scott L.

    2012-01-01

    The harsh rocket propulsion test environment will expose any inadequacies associated with preexisting instrumentation technologies, and the criticality for collecting reliable test data justifies investigating any encountered data anomalies. Novel concepts for improved systems are often conceived during the high scrutiny investigations by individuals with an in-depth knowledge from maintaining critical test operations. The Intelligent Strain Gauge concept was conceived while performing these kinds of activities. However, the novel concepts are often unexplored even if it has the potential for advancing the current state of the art. Maturing these kinds of concepts is often considered to be a tangential development or a research project which are both normally abandoned within the propulsion-oriented environment. It is also difficult to justify these kinds of projects as a facility enhancement because facility developments are only accepted for mature and proven technologies. Fortunately, the CIF program has provided an avenue for bringing the Intelligent Strain Gauge to fruition. Two types of fully functional smart strain gauges capable of performing reliable and sensitive debond detection have been successfully produced. Ordinary gauges are designed to provide test article data and they lack the ability to supply information concerning the gauge itself. A gauge is considered to be a smart gauge when it provides supplementary data relating other relevant attributes for performing diagnostic function or producing enhanced data. The developed strain gauges provide supplementary signals by measuring strain and temperature through embedded Karma and nickel chromium (NiCr) alloy elements. Intelligently interpreting the supplementary data into valuable information can be performed manually, however, integrating this functionality into an automatic system is considered to be an intelligent gauge. This was achieved while maintaining a very low mass. The low mass enables

  4. Delamination-Debond Behaviour of Composite T- Joints in Wind Turbine Blades

    International Nuclear Information System (INIS)

    Gulasik, H; Coker, D

    2014-01-01

    Wind turbine industry utilizes composite materials in turbine blade structural designs because of their high strength/stiffness to weight ratio. T-joint is one of the design configurations of composite wind turbine blades. T-joints consist of a skin panel and a stiffener co-bonded or co-cured together with a filler material between them. T-joints are prone to delaminations between skin/stiffener plies and debonds between skin-stiffener-filler interfaces. In this study, delamination/debond behavior of a co-bonded composite T-joint is investigated under 0° pull load condition by 2D finite element method. Using Abaqus® commercial FE software, zero-thickness cohesive elements are used to simulate delamination/debond in ply interfaces and bonding lines. Pulling load at 0° is applied and load-displacement behavior and failure scenario are observed. The failure sequence consists of debonding of filler/stringer interface during one load drop followed by a second drop in which the 2nd filler/stringer debonds, filler/skin debonding and skin delamination leading to total loss of load carrying capacity. This type of failure initiation has been observed widely in the literature. When the debond strength is increased 30%, failure pattern is found to change in addition to increasing the load capacity by 200% before total loss of loading carrying capacity occurs. Failure initiation and propagation behavior, initial and max failure loads and stress fields are affected by the property change. In all cases mixed-mode crack tip loading is observed in the failure initiation and propagation stages. In this paper, the detailed delamination/debonding history in T-joints is predicted with cohesive elements for the first time

  5. Effects of various debonding and adhesive clearance methods on enamel surface: an in vitro study

    OpenAIRE

    Fan, Xiao-Chuan; Chen, Li; Huang, Xiao-Feng

    2017-01-01

    Background The purpose of this study was to evaluate orthodontic debonding methods by comparing the surface roughness and enamel morphology of teeth after applying two different debonding methods and three different polishing techniques. Methods Forty eight human maxillary premolars, extracted for orthodontic reasons, were randomly divided into three groups. Brackets were bonded to teeth with RMGIC (Fuji Ortho LC, GC, Tokyo, Japan) (two groups, n?=?18 each) after acid etching (30s), light cur...

  6. 3-D FEM Modeling of fiber/matrix interface debonding in UD composites including surface effects

    International Nuclear Information System (INIS)

    Pupurs, A; Varna, J

    2012-01-01

    Fiber/matrix interface debond growth is one of the main mechanisms of damage evolution in unidirectional (UD) polymer composites. Because for polymer composites the fiber strain to failure is smaller than for the matrix multiple fiber breaks occur at random positions when high mechanical stress is applied to the composite. The energy released due to each fiber break is usually larger than necessary for the creation of a fiber break therefore a partial debonding of fiber/matrix interface is typically observed. Thus the stiffness reduction of UD composite is contributed both from the fiber breaks and from the interface debonds. The aim of this paper is to analyze the debond growth in carbon fiber/epoxy and glass fiber/epoxy UD composites using fracture mechanics principles by calculation of energy release rate G II . A 3-D FEM model is developed for calculation of energy release rate for fiber/matrix interface debonds at different locations in the composite including the composite surface region where the stress state differs from the one in the bulk composite. In the model individual partially debonded fiber is surrounded by matrix region and embedded in a homogenized composite.

  7. Evaluation of enamel damages following orthodontic bracket debonding in fluorosed teeth bonded with adhesion promoter.

    Science.gov (United States)

    Baherimoghadam, Tahreh; Akbarian, Sahar; Rasouli, Reza; Naseri, Navid

    2016-01-01

    To evaluate shear bond strength (SBS) of the orthodontic brackets bonded to fluorosed and nonfluorosed teeth using Light Bond with and without adhesion promoters and compare their enamel damages following debonding. In this study, 30 fluorosed (Thylstrup and Fejerskov Index = 4-5) and 30 nonfluorosed teeth were randomly distributed between two subgroups according to the bonding materials: Group 1, fluorosed teeth bonded with Light Bond; Group 2, fluorosed teeth bonded with adhesion promoters and Light Bond; Group 3, nonfluorosed teeth bonded with Light Bond; Group 4, nonfluorosed bonded with adhesion promoters and Light Bond. After bonding, the SBS of the brackets was tested with a universal testing machine. Stereomicroscopic evaluation was performed by unbiased stereology in all teeth to determine the amount of adhesive remnants and the number and length of enamel cracks before bonding and after debonding. The data were analyzed using two-way analysis of variance, Kruskal-Wallis, Wilcoxon Signed Rank, and Mann-Whitney test. While fluorosis reduced the SBS of orthodontic bracket (P = 0.017), Enhance Locus Ceruleus LC significantly increased the SBS of the orthodontic bracket in fluorosed and nonfluorosed teeth (P = 0.039). Significant increasing in the number and length of enamel crack after debonding was found in all four groups. There were no significant differences in the length of enamel crack increased after debonding among four groups (P = 0.768) while increasing in the number of enamel cracks after debonding was significantly different among the four groups (P = 0.023). Teeth in Group 2 showed the highest enamel damages among four groups following debonding. Adhesion promoters could improve the bond strength of orthodontic brackets, but conservative debonding methods for decreasing enamel damages would be necessary.

  8. Comparison between two methods for resin removing after bracket debonding

    Directory of Open Access Journals (Sweden)

    Rodrigo De Marchi

    2012-12-01

    Full Text Available OBJECTIVE: The aim of this study was to assess - using scanning electron microscopy (SEM - the effectiveness of two abrasive discs, one made from silicon and one from aluminum oxide, in removing adhesive remnants (AR after debonding orthodontic brackets. METHODS: Ten randomly selected bovine teeth were used, i.e., 2 in the control group, and the other 8 divided into two groups, which had orthodontic brackets bonded to their surface with Concise Orthodontic Adhesive (3M. The following methods were employed - in one single step - to remove AR after debracketing: Group A, Optimize discs (TDV and Group B, Onegloss discs (Shofu, used at low speed. After removing the AR with the aforementioned methods, the teeth were prepared to undergo SEM analysis, and photographs were taken of the enamel surface with 50x magnification. Six examiners evaluated the photographs applying the Zachrisson and Årtun enamel surface index (ESI system (1979. RESULTS: Group A exhibited minor scratches on the enamel surface as well as some AR in some of the photographs, while Group B showed a smoother surface, little or no AR and some abrasion marks in the photographs. No statistically significant differences were found between the two methods and the control group. CONCLUSIONS: The two abrasive discs were effective in removing the AR after bracket debonding in one single step.OBJETIVO: o objetivo deste trabalho foi avaliar, por microscopia eletrônica de varredura, a eficácia de dois discos abrasivos de silicone e óxido de alumínio para a remoção da resina remanescente após a descolagem de braquetes ortodônticos. MÉTODOS: foram utilizados 10 dentes bovinos selecionados aleatoriamente, sendo 2 para o grupo controle e os demais divididos em dois grupos, os quais receberam colagem de braquetes ortodônticos com resina ortodôntica Concise (3M. Os métodos de remoção da resina após a descolagem dos acessórios ortodônticos em apenas uma etapa foram: Grupo A - disco

  9. Investigation of actuator debonding effects on active control in smart composite laminates

    Directory of Open Access Journals (Sweden)

    Bin Huang

    2015-04-01

    Full Text Available This article presents a numerical study of active vibration control of smart composite laminates in the presence of actuator debonding failures. A comparison between the smart composite laminates with healthy actuator and various partially debonded actuator cases is performed to investigate the debonding effects on the vibration suppression. The improved layerwise theory with Heaviside’s unit step function is adopted to model the displacement field with actuator debonding failure. The higher order electric potential field is adopted to describe the potential variation through the thickness. The finite element method–based formulations are derived using the plate element, taking into consideration the electro-mechanical coupling effect. The reduced-order model is represented by the state-space form and further for the vibration suppression using a simple constant gain velocity feedback control strategy. For the purpose of demonstration, a 16-layer cross-ply substrate laminate ([0/90]4s is employed for the numerical study. The results show that the actuator debonding affects the closed-loop frequencies, active damping ratios, and efficiency of vibration suppression.

  10. Fatigue Debond Growth in Sandwich Structures Loaded in Mixed Mode Bending (MMB)

    DEFF Research Database (Denmark)

    Quispitupa, Amilcar; Berggreen, Christian; Carlsson, Leif A.

    2008-01-01

    Static and cyclic debond growth in sandwich specimens loaded in mixed mode bending (MMB) is examined. The MMB sandwich specimens were manufactured using H100 PVC foam core and E-glass/polyester non-crimp quadro-axial [0/45/90/-45]s DBLT-850 face sheets. Static test were performed to determine...... the fracture toughness of the debonded sandwich specimens at different mixed mode loadings. The mixed mode ratio (mode I to mode II) was controlled by changing the lever arm distance of the MMB test rig. Compliance technique and visual inspection was employed to measure the crack length during fatigue. Fatigue...... tests were performed at 90% of the static fracture toughness at a loading ratio of R=0.1. Fatigue results revealed higher debond crack growth rates when the lever arm distance was increased. For some specimens, the crack propagated just below the face/core interface in the foam core and for others...

  11. Nonlocal plasticity effects on fibre debonding in a whisker-reinforced metal

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Tvergaard, Viggo

    2002-01-01

    Numerical cell-model analyses for the matrix-fibre debonding in a metal matrix composite are used to study the effect of a characteristic material length in the plasticity description of the matrix material deformations. Characteristic material lengths are already present in the model problem...... in the problem. The nonlocal plasticity effect tends to increase the stress level at a given overall strain, which clearly tends to promote the onset of debonding......., in the form of fibre sizes and the length associated with the debonding process, so the nonlocal plasticity model brings in an additional material length. The analyses for metal reinforced by aligned short fibres are used to obtain an understanding of the interaction of the different length scales...

  12. Novel Predictive Model of the Debonding Strength for Masonry Members Retrofitted with FRP

    Directory of Open Access Journals (Sweden)

    Iman Mansouri

    2016-11-01

    Full Text Available Strengthening of masonry members using externally bonded (EB fiber-reinforced polymer (FRP composites has become a famous structural strengthening method over the past decade due to the popular advantages of FRP composites, including their high strength-to-weight ratio and excellent corrosion resistance. In this study, gene expression programming (GEP, as a novel tool, has been used to predict the debonding strength of retrofitted masonry members. The predictions of the new debonding resistance model, as well as several other models, are evaluated by comparing their estimates with experimental results of a large test database. The results indicate that the new model has the best efficiency among the models examined and represents an improvement to other models. The root mean square errors (RMSE of the best empirical Kashyap model in training and test data were, respectively, reduced by 51.7% and 41.3% using the GEP model in estimating debonding strength.

  13. Research on Debonding Defects in Thermal Barrier Coatings Structure by Thermal-Wave Radar Imaging (TWRI)

    Science.gov (United States)

    Wang, Fei; Liu, Junyan; Mohummad, Oliullah; Wang, Yang

    2018-06-01

    In this paper, thermal-wave radar imaging (TWRI) is introduced to detect debonding defects in SiC-coated Ni-based superalloy plates. Linear frequency modulation signal (chirp) is used as the excitation signal which has a large time-bandwidth product. Artificial debonding defects in SiC coating are excited by the laser beam with the light intensity modulated by a chirp signal. Cross-correlation algorithm and chirp lock-in algorithm are introduced to extract the thermal-wave signal characteristic. The comparative experiment between TWRI reflection mode and transmission mode was carried out. Experiments are conducted to investigate the influence of laser power density, chirp period, and excitation frequency. Experimental results illustrate that chirp lock-in phase has a better detection capability than other characteristic parameters. TWRI can effectively detect simulated debonding defects of SiC-coated Ni-based superalloy plates.

  14. Intermediate Crack Induced Debonding in Concrete Beams Strengthened with CFRP Plates - An Experimental Study

    DEFF Research Database (Denmark)

    Rusinowski, Piotr Michal; Täljsten, Björn

    2009-01-01

    , ductility and even durability. Design of structural strengthening applications using externally bonded FRP composites is usually based on conventional design approaches with improvement to account for the presence and characteristics of the FRP material. Non-conventional design issues that are specific...... of the strengthening method. End-peeling has governed a large interest and several debonding models have been presented. However, interfacial peeling at flexural cracks has not attained the same focus – even though this debonding failure is most likely more common. This paper presents laboratory tests of concrete...... beams strengthened in flexure with CFRP epoxy bonded plates. Wrapping with CFRP sheets was applied in order to try to localize the failure initiation. Concrete cracking as well as debonding initiation and propagation was possible to observe with help of advanced optical measuring system and high speed...

  15. Face/core debond fatigue crack growth characterization using the sandwich mixed mode bending specimen

    DEFF Research Database (Denmark)

    Manca, Marcello; Quispitupa, Amilcar; Berggreen, Christian

    2012-01-01

    Face/core fatigue crack growth in foam-cored sandwich composites is examined using the mixed mode bending (MMB) test method. The mixed mode loading at the debond crack tip is controlled by changing the load application point in the MMB test fixture. Sandwich specimens were manufactured using H45...... and H100 PVC foam cores and E-glass/polyester face sheets. All specimens were pre-cracked in order to define a sharp crack front. The static debond fracture toughness for each material configuration was measured at different mode-mixity phase angles. Fatigue tests were performed at 80% of the static...

  16. Debonding analyses of closely spaced Z-pins bridging an unbonded interface

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang

    2009-01-01

    In this study the plasticity, the spatial stress distribution and the debonding behavior of a metallic Z-pin bridging the unbonded interface between two substrates of an elasto-plastic material subjected to shear loading (mode II) are analyzed numerically by the finite element method taking full...... account of finite strains. For a weakly bonded Z-pin perpendicular to the substrates the overall average stress-strain response depicts a rather sudden stress drop which is not seen for stronger interfaces in the load range investigated. This stress drop is caused by dual debonding at different locations...

  17. Impact of nanohydroxyapatite on enamel surface roughness and color change after orthodontic debonding

    OpenAIRE

    Shabnam Ajami; Hamid Reza Pakshir; Neda Babanouri

    2016-01-01

    Abstract Background The aim of this prospective in vitro study was to evaluate the effect of nanohydroxyapatite (nanoHAP) serum on the enamel surface roughness and tooth color stability after orthodontic debonding procedure. Methods The crowns of 30 premolars were embedded in acrylic blocks with a 4 mm × 5-mm-sized window on the middle third of buccal surfaces. Primary roughness values were evaluated by an atomic force microscope (AFM). After bracket debonding, and polishing procedures, the s...

  18. Breakage and debonding of short brittle fibres among particulates in a metal matrix

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2004-01-01

    or fracture of a relatively long discontinuous fibre among particulates that do not fail. A cohesive zone model that accounts for normal separation as well as tangential separation is used to represent debonding, while fibre fracture is represented by a critical value of the average tensile stress on a cross......The competition of failure by fibre cracking or decohesion of the fibre-matrix interface is analysed for aluminium reinforced by aligned, short SiC fibres. An axisymmetric unit-cell model containing a number of differently shaped fibres or particulates is used here to represent failure by debonding...

  19. Experimental research into the relation between the peeling angle and the debonding of CFRP laminates bonded to concrete

    NARCIS (Netherlands)

    Klamer, E.L.

    2004-01-01

    CFRP is a relatively new, innovative strengthening material to strengthen reinforced concrete structures. Main issue, when strengthening a concrete structure is the debonding of CFRP. Although a lot of research has been carried out into the debonding behavior, still some questions remain open. In

  20. Nd:YAG Laser-aided ceramic brackets debonding: Effects on shear bond strength and enamel surface

    Science.gov (United States)

    Han, Xianglong; Liu, Xiaolin; Bai, Ding; Meng, Yao; Huang, Lan

    2008-11-01

    In order to evaluate the efficiency of Nd:YAG laser-aided ceramic brackets debonding technique, both ceramic brackets and metallic brackets were bonded with orthodontic adhesive to 30 freshly extracted premolars. The specimens were divided into three groups, 10 in each, according to the brackets employed and the debonding techniques used: (1) metallic brackets with shear debonding force, (2) ceramic brackets with shear debonding force, and (3) ceramic brackets with Nd:YAG laser irradiation. The result showed that laser irradiation could diminish shear bond strength (SBS) significantly and produce the most desired ARI scores. Moreover, scanning electron microscopy investigation displayed that laser-aided technique induced little enamel scratch or loss. It was concluded that Nd:YAG laser could facilitate the debonding of ceramic brackets and diminish the amount of remnant adhesive without damaging enamel structure.

  1. Nd:YAG Laser-aided ceramic brackets debonding: Effects on shear bond strength and enamel surface

    International Nuclear Information System (INIS)

    Han Xianglong; Liu Xiaolin; Bai Ding; Meng Yao; Huang Lan

    2008-01-01

    In order to evaluate the efficiency of Nd:YAG laser-aided ceramic brackets debonding technique, both ceramic brackets and metallic brackets were bonded with orthodontic adhesive to 30 freshly extracted premolars. The specimens were divided into three groups, 10 in each, according to the brackets employed and the debonding techniques used: (1) metallic brackets with shear debonding force, (2) ceramic brackets with shear debonding force, and (3) ceramic brackets with Nd:YAG laser irradiation. The result showed that laser irradiation could diminish shear bond strength (SBS) significantly and produce the most desired ARI scores. Moreover, scanning electron microscopy investigation displayed that laser-aided technique induced little enamel scratch or loss. It was concluded that Nd:YAG laser could facilitate the debonding of ceramic brackets and diminish the amount of remnant adhesive without damaging enamel structure

  2. Nd:YAG Laser-aided ceramic brackets debonding: Effects on shear bond strength and enamel surface

    Energy Technology Data Exchange (ETDEWEB)

    Han Xianglong [State Key Laboratory of Oral Diseases, Sichuan University, Chengdu 610041 (China); Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 (China); Liu Xiaolin [Department of Orthodontics, Stomatology Hospital, Dalian University, Dalian 116021 (China); Bai Ding [State Key Laboratory of Oral Diseases, Sichuan University, Chengdu 610041 (China); Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 (China)], E-mail: baiding88@hotmail.com; Meng Yao; Huang Lan [Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 (China)

    2008-11-15

    In order to evaluate the efficiency of Nd:YAG laser-aided ceramic brackets debonding technique, both ceramic brackets and metallic brackets were bonded with orthodontic adhesive to 30 freshly extracted premolars. The specimens were divided into three groups, 10 in each, according to the brackets employed and the debonding techniques used: (1) metallic brackets with shear debonding force, (2) ceramic brackets with shear debonding force, and (3) ceramic brackets with Nd:YAG laser irradiation. The result showed that laser irradiation could diminish shear bond strength (SBS) significantly and produce the most desired ARI scores. Moreover, scanning electron microscopy investigation displayed that laser-aided technique induced little enamel scratch or loss. It was concluded that Nd:YAG laser could facilitate the debonding of ceramic brackets and diminish the amount of remnant adhesive without damaging enamel structure.

  3. Mechanism of bonding and debonding using surface activated bonding method with Si intermediate layer

    Science.gov (United States)

    Takeuchi, Kai; Fujino, Masahisa; Matsumoto, Yoshiie; Suga, Tadatomo

    2018-04-01

    Techniques of handling thin and fragile substrates in a high-temperature process are highly required for the fabrication of semiconductor devices including thin film transistors (TFTs). In our previous study, we proposed applying the surface activated bonding (SAB) method using Si intermediate layers to the bonding and debonding of glass substrates. The SAB method has successfully bonded glass substrates at room temperature, and the substrates have been debonded after heating at 450 °C, in which TFTs are fabricated on thin glass substrates for LC display devices. In this study, we conducted the bonding and debonding of Si and glass in order to understand the mechanism in the proposed process. Si substrates are also successfully bonded to glass substrates at room temperature and debonded after heating at 450 °C using the proposed bonding process. By the composition analysis of bonding interfaces, it is clarified that the absorbed water on the glass forms interfacial voids and cause the decrease in bond strength.

  4. A Maximum Entropy Approach to Assess Debonding in Honeycomb aluminum Plates

    Directory of Open Access Journals (Sweden)

    Viviana Meruane

    2014-05-01

    Full Text Available Honeycomb sandwich structures are used in a wide variety of applications. Nevertheless, due to manufacturing defects or impact loads, these structures can be subject to imperfect bonding or debonding between the skin and the honeycomb core. The presence of debonding reduces the bending stiffness of the composite panel, which causes detectable changes in its vibration characteristics. This article presents a new supervised learning algorithm to identify debonded regions in aluminum honeycomb panels. The algorithm uses a linear approximation method handled by a statistical inference model based on the maximum-entropy principle. The merits of this new approach are twofold: training is avoided and data is processed in a period of time that is comparable to the one of neural networks. The honeycomb panels are modeled with finite elements using a simplified three-layer shell model. The adhesive layer between the skin and core is modeled using linear springs, the rigidities of which are reduced in debonded sectors. The algorithm is validated using experimental data of an aluminum honeycomb panel under different damage scenarios.

  5. Fatigue de-bond growth in adhesively bonded single lap joints

    Indian Academy of Sciences (India)

    3Department of Aerospace Engineering, Indian Institute of Science,. Bangalore 560012 ... experimental work, specimens were fabricated and fatigue de-bond growth tests were conducted at a ... such as the stress intensity factor, are related to fatigue crack growth. ..... American Society for Testing and Materials, Philadelphia.

  6. Failure of uniformly compression loaded debond damaged sandwich panels — An experimental and numerical study

    DEFF Research Database (Denmark)

    Moslemian, Ramin; Quispitupa, Amilcar; Berggreen, Christian

    2012-01-01

    This paper deals with the failure of compression-loaded sandwich panels with an implanted circular face/core debond. Uniform compression tests were conducted on intact sandwich panels with three different types of core material (H130, H250 and PMI) and on similar panels with circular face...

  7. Finite Element Analysis of Interfacial Debonding in Copper/Diamond Composites for Thermal Management Applications.

    Science.gov (United States)

    Zain-Ul-Abdein, Muhammad; Ijaz, Hassan; Saleem, Waqas; Raza, Kabeer; Mahfouz, Abdullah Salmeen Bin; Mabrouki, Tarek

    2017-07-02

    Copper/diamond (Cu/D) composites are famous in thermal management applications for their high thermal conductivity values. They, however, offer some interface related problems like high thermal boundary resistance and excessive debonding. This paper investigates interfacial debonding in Cu/D composites subjected to steady-state and transient thermal cyclic loading. A micro-scale finite element (FE) model was developed from a SEM image of the Cu/20 vol % D composite sample. Several test cases were assumed with respect to the direction of heat flow and the boundary interactions between Cu/uncoated diamonds and Cu/Cr-coated diamonds. It was observed that the debonding behavior varied as a result of the differences in the coefficients of thermal expansions (CTEs) among Cu, diamond, and Cr. Moreover, the separation of interfaces had a direct influence upon the equivalent stress state of the Cu-matrix, since diamond particles only deformed elastically. It was revealed through a fully coupled thermo-mechanical FE analysis that repeated heating and cooling cycles resulted in an extremely high stress state within the Cu-matrix along the diamond interface. Since these stresses lead to interfacial debonding, their computation through numerical means may help in determining the service life of heat sinks for a given application beforehand.

  8. A fiber optic Doppler sensor and its application in debonding detection for composite structures.

    Science.gov (United States)

    Li, Fucai; Murayama, Hideaki; Kageyama, Kazuro; Meng, Guang; Ohsawa, Isamu; Shirai, Takehiro

    2010-01-01

    Debonding is one of the most important damage forms in fiber-reinforced composite structures. This work was devoted to the debonding damage detection of lap splice joints in carbon fiber reinforced plastic (CFRP) structures, which is based on guided ultrasonic wave signals captured by using fiber optic Doppler (FOD) sensor with spiral shape. Interferometers based on two types of laser sources, namely the He-Ne laser and the infrared semiconductor laser, are proposed and compared in this study for the purpose of measuring Doppler frequency shift of the FOD sensor. Locations of the FOD sensors are optimized based on mechanical characteristics of lap splice joint. The FOD sensors are subsequently used to detect the guided ultrasonic waves propagating in the CFRP structures. By taking advantage of signal processing approaches, features of the guided wave signals can be revealed. The results demonstrate that debonding in the lap splice joint results in arrival time delay of the first package in the guided wave signals, which can be the characteristic for debonding damage inspection and damage extent estimation.

  9. Loss of surface enamel after bracket debonding : An in-vivo and ex-vivo evaluation

    NARCIS (Netherlands)

    Pont, Huib Berghauser; Özcan, Mutlu; Bagis, Bora; Ren, Yijin

    2010-01-01

    INTRODUCTION: The objective of this study was to evaluate the surface enamel after bracket debonding and residual resin removal. METHODS: Thirty patients (female, 20; male, 10; mean age, 18.4 years) who completed orthodontic treatment with fixed appliances (Twin Brackets, 3M Unitek, Monrovia, Calif)

  10. Modelling and Vibration Control of Beams with Partially Debonded Active Constrained Layer Damping Patch

    Science.gov (United States)

    SUN, D.; TONG, L.

    2002-05-01

    A detailed model for the beams with partially debonded active constraining damping (ACLD) treatment is presented. In this model, the transverse displacement of the constraining layer is considered to be non-identical to that of the host structure. In the perfect bonding region, the viscoelastic core is modelled to carry both peel and shear stresses, while in the debonding area, it is assumed that no peel and shear stresses be transferred between the host beam and the constraining layer. The adhesive layer between the piezoelectric sensor and the host beam is also considered in this model. In active control, the positive position feedback control is employed to control the first mode of the beam. Based on this model, the incompatibility of the transverse displacements of the active constraining layer and the host beam is investigated. The passive and active damping behaviors of the ACLD patch with different thicknesses, locations and lengths are examined. Moreover, the effects of debonding of the damping layer on both passive and active control are examined via a simulation example. The results show that the incompatibility of the transverse displacements is remarkable in the regions near the ends of the ACLD patch especially for the high order vibration modes. It is found that a thinner damping layer may lead to larger shear strain and consequently results in a larger passive and active damping. In addition to the thickness of the damping layer, its length and location are also key factors to the hybrid control. The numerical results unveil that edge debonding can lead to a reduction of both passive and active damping, and the hybrid damping may be more sensitive to the debonding of the damping layer than the passive damping.

  11. Void initiation from interfacial debonding of spherical silicon particles inside a silicon-copper nanocomposite: a molecular dynamics study

    Science.gov (United States)

    Cui, Yi; Chen, Zengtao

    2017-02-01

    Silicon particles with diameters from 1.9 nm to 30 nm are embedded in a face-centered-cubic copper matrix to form nanocomposite specimens for simulation. The interfacial debonding of silicon particles from the copper matrix and the subsequent growth of nucleated voids are studied via molecular dynamics (MD). The MD results are examined from several different perspectives. The overall mechanical performance is monitored by the average stress-strain response and the accumulated porosity. The ‘relatively farthest-traveled’ atoms are identified to characterize the onset of interfacial debonding. The relative displacement field is plotted to illustrate both subsequent interfacial debonding and the growth of a nucleated void facilitated by a dislocation network. Our results indicate that the initiation of interfacial debonding is due to the accumulated surface stress if the matrix is initially dislocation-free. However, pre-existing dislocations can make a considerable difference. In either case, the dislocation emission also contributes to the subsequent debonding process. As for the size effect, the debonding of relatively larger particles causes a drop in the stress-strain curve. The volume fraction of second-phase particles is found to be more influential than the size of the simulation box on the onset of interfacial debonding. The volume fraction of second-phase particles also affects the shape of the nucleated void and, therefore, influences the stress response of the composite.

  12. Effects of various debonding and adhesive clearance methods on enamel surface: an in vitro study.

    Science.gov (United States)

    Fan, Xiao-Chuan; Chen, Li; Huang, Xiao-Feng

    2017-02-27

    The purpose of this study was to evaluate orthodontic debonding methods by comparing the surface roughness and enamel morphology of teeth after applying two different debonding methods and three different polishing techniques. Forty eight human maxillary premolars, extracted for orthodontic reasons, were randomly divided into three groups. Brackets were bonded to teeth with RMGIC (Fuji Ortho LC, GC, Tokyo, Japan) (two groups, n = 18 each) after acid etching (30s), light cured for 40 s, exposed to thermocycling, then underwent 2 different bracket debonding methods: debonding pliers (Shinye, Hangzhou, China) or enamel chisel (Jinzhong, Shanghai, China); the third group (n = 12) comprised of untreated controls, with normal enamel surface roughness. In each debonded group, three cleanup techniques (n = 6 each) were tested, including (I) diamond bur (TC11EF, MANI, Tochigi, Japan) and One-Gloss (Midi, Shofu, Kyoto, Japan), (II) a Super-Snap disk (Shofu, Kyoto, Japan), and (III) One-Gloss polisher. The debonding methods were compared using the modified adhesive remnant index (ARI, 1-5). Cleanup efficiencies were assessed by recording operating times. Enamel surfaces were qualitatively and quantitatively evaluated with scanning electron microscopy (SEM) and surface roughness tester, respectively. Two surface roughness variables were evaluated: Ra (average roughness) and Rz (10-point height of irregularities). The ARI scores of debonded teeth were similar with debonding pliers and enamel chisel (Chi-square = 2.19, P > 0.05). There were significant differences between mean operating time in each group (F = 52.615, P One-Gloss took the shortest operating time (37.92 ± 3.82 s), followed by the Super-Snap disk (56.67 ± 7.52 s), and the One-Gloss polisher (63.50 ± 6.99 s). SEM appearance provided by the One-Gloss polisher was the closest to the intact enamel surface, and surface roughness (Ra: 0.082 ± 0.046 μm; Rz: 0.499

  13. Estimation of debonded area in bearing babbitt metal by C-Scan method

    Energy Technology Data Exchange (ETDEWEB)

    Jung, Gye-jo; Park, Sang-ki [Korea Electric Power Research Inst., Taejeon (Korea); Cha, Seok-ju [Korea South Eastern Power Corp., Seoul (Korea). GEN Sector; Park, Young-woo [Chungnam National Univ., Taejeon (Korea). Mechatronics

    2006-07-01

    The debonding area which had a complex boundary was imaged with a immersion technique, and the acoustic image was compared with the actual area. The amplitude information from focused transducer can discriminate between a defected boundary area and a sound interface of dissimilar metal. The shape of irregular boundary and area was processed by a histogram equalization, after that, through the clustering and labelling, it makes the defect area cleared. Each pixel has ultrasonic intensity rate and represents a position data. The estimation error in measuring debonding area was within 4% by image processing technique. The validity of this immersion method and image equalizing technique has been done for the inspection of power plant turbine's thrust bearings. (orig.)

  14. Face/core mixed mode debond fracture toughness characterization using the modified TSD test method

    DEFF Research Database (Denmark)

    Berggreen, Christian; Quispitupa, Amilcar; Costache, Andrei

    2014-01-01

    The modified tilted sandwich debond (TSD) test method is used to examine face/core debond fracture toughness of sandwich specimens with glass/polyester face sheets and PVC H45 and H100 foam cores over a large range of mode-mixities. The modification was achieved by reinforcing the loaded face sheet....... The fracture process was inspected visually during and after testing. For specimens with H45 core the crack propagated in the core. For specimens with an H100 core, the crack propagated between the resin-rich layer and the face sheet. © The Author(s) 2013 Reprints and permissions: sagepub...... with a steel bar, and fracture testing of the test specimens was conducted over a range of tilt angles. The fracture toughness exhibited mode-mixity phase angle dependence, especially for mode II dominated loadings; although, the fracture toughness remained quite constant for mode I dominated crack loadings...

  15. Preparation and Characterization of Electrochemical Devices for Energy Storage and Debonding

    OpenAIRE

    Leijonmarck, Simon

    2013-01-01

    Within the framework of this thesis, three innovative electrochemical devices have been studied. A part of the work is devoted to an already existing device, laminates which are debonded by the application of a voltage. This type of material can potentially be used in a wide range of applications, including adhesive joints in vehicles to both reduce the total weight and to simplify the disassembly after end-of-life, enabling an inexpensive recycling process. Although already a functioning dev...

  16. Thermotransduction and heat stress in dental structures during orthodontic debonding : Effectiveness of various cooling strategies.

    Science.gov (United States)

    Kley, Philipp; Frentzen, Matthias; Küpper, Katharina; Braun, Andreas; Kecsmar, Susann; Jäger, Andreas; Wolf, Michael

    2016-05-01

    Recent studies have indicated possible thermal damage to pulpal tissue during orthodontic debonding. This study aimed to analyze the thermal loads acting upon dental structures and their transfer to the pulp during orthodontic debonding. Specific goals were to analyze temperature changes in local dental tissues, thermotransduction to the pulp cavity, and the effectiveness of common cooling strategies and of simulated intrapulpal circulation. Metal brackets were bonded to five extracted human molars and subsequently removed. While a carbide bur was applied to debond the residual composite from the tooth surface, various cooling strategies (no/air/water cooling) were employed with or without simulated intrapulpal circulation, accompanied by temperature measurements with a thermographic infrared camera on the enamel surface and with measuring probes in the pulp cavity. Appropriate evaluation software was used to calculate the enamel-to-pulp temperature gradients and for statistical analysis. Significant differences in temperature rise and heat development over time, both on the enamel surfaces and in the pulp cavities were found. The mean temperature rises associated with no/air/water cooling were 90.7/46.6/9.2 °C on the enamel surface versus 9/8/4.6 °C inside the pulp. However, thermotransduction from enamel to pulp remained below 10 % of the surface measurements in all groups. Simulated intrapulpal microcirculation was found to significantly reduce intrapulpal temperature levels. During debonding of residual bracket adhesives, provided that a carbide bur is properly used, our data indicate a low risk of reaching critical intrapulpal temperatures even in the absence of dedicated cooling and no risk if the instrumentation is accompanied by air or water cooling.

  17. Effect of fiber positioning on mixed-mode fracture of interfacial debonding in composites

    DEFF Research Database (Denmark)

    Ashouri Vajari, Danial; Sørensen, Bent F.; Legarth, Brian Nyvang

    2015-01-01

    along the interface is due to mixed mode I/II fracture. The aim of this study is to explore ways to stabilize the early stage of debonding so that it becomes possible to determine the mixed mode interfacial fracture properties for the entire mode-mixity range by in-situ observations. Therefore...... instead of a single fiber in order to ease the characterization of interfacial properties. [All rights reserved Elsevier]....

  18. Effect of dental bleaching after bracket bonding and debonding using three different adhesive systems

    Directory of Open Access Journals (Sweden)

    Lucianna de Oliveira Gomes

    2013-04-01

    Full Text Available OBJECTIVE: To evaluate the influence of bonding and debonding of orthodontic brackets on dental in-home bleaching, taking into account three different adhesive systems. METHODS: Forty-four bovine incisors were divided into four groups according to the primer system used for orthodontic bracket bonding. Following the debonding of orthodontic brackets, the teeth were stored in staining solution for 96 hours. Then, teeth were whitened using 10% carbamide peroxide for two weeks at a 6-hour-a-day regime. Standardized digital photographs were taken at the following intervals: T0 (initial; T1 (after debonding; T2 (after pigmentation; T3, T4 and T5 representing 1, 7, and 14 days of bleaching. Repeatability and stability tests were carried out to check the method accuracy. Images were analyzed using Adobe Photoshop 7.0 software considering (L*a*b*color coordinate values and a modified color difference total (Δ;E'. RESULTS: The results of this study (ANOVA and Tukey; p < 0.01 demonstrated that after 7 days of bleaching, experimental groups showed significantly less teeth whitening compared to the control group. However, there were no significant color differences between the groups after 14 days, according to values of lightness (L*. CONCLUSIONS: Regardless of the adhesive primer system applied, bonding and debonding of orthodontic brackets alters the outcome of tooth whitening in the first 7 days of bleaching, however it has no influence on the whitening of the dental structure after 14 days of in-home dental bleaching with 10% carbamide peroxide.

  19. Comparative study of dental enamel loss after debonding braces by analytical scanning electron microscopy (SEM).

    Science.gov (United States)

    Rodríguez-Chávez, Jacqueline Adelina; Arenas-Alatorre, Jesús; Belio-Reyes, Irma Araceli

    2017-07-01

    Clinical procedures when shear forces are applied to brackets suggest adhesion forces between 2.8 and 10.0 MPa as appropriate. In this study dental enamel was evaluated by scanning electron microscopy (SEM) before and after removing the brackets. Thirty bicuspids (previous prophylaxis) with metallic brackets (Roth Inovation 0.022 GAC), Transbond Plus SEP 3M Unitek adhesive and Transbond XT 3M resin were used. The samples were preserved to 37°C during 24 hr and submited to tangential forces with the Instron Universal machine 1.0 mm/min speed load strength resistance debonding. Also the Adhesive Remanent Index (ARI) test was made, evaluating the bracket base and the bicuspid surface. All the bracket SEM images were processed with AutoCAD to determine the enamel detached area. The average value was 6.86 MPa (SD ± 3.2 MPa). ARI value 1= 63.3%, value 2= 20%, value 3= 13.3% and 33% presented value 0. All those samples with dental enamel loss, presented different situations as fractures, ledges, horizontal, and vertical loss in some cases, and some scratch lines. There is no association between the debonding resistance and enamel presence. Less than half of the remanent adhesive on the dental enamel was present in most of the samples when the ARI test was applied. When the resin area increases, the debonding resistance also increases, and when the enamel loss increases, the resin free metallic area of the bracket base decreases in the debonding. © 2017 Wiley Periodicals, Inc.

  20. Elastic interaction of partially debonded circular inclusions. II. Application to fibrous composite

    DEFF Research Database (Denmark)

    Kushch, V.I.; Shmegera, S.V.; Mishnaevsky, Leon

    2011-01-01

    have been solved to check an accuracy and numerical efficiency of the method. An effect of interface crack density on the effective elastic moduli of periodic and random structure FRC with interface damage has been evaluated. The developed approach provides a detailed analysis of the progressive...... debonding phenomenon including the interface cracks cluster formation, overall stiffness reduction and damage-induced anisotropy of the effective elastic moduli of composite....

  1. The prognostic value of visually assessing enamel microcracks: Do debonding and adhesive removal contribute to their increase?

    Science.gov (United States)

    Dumbryte, Irma; Jonavicius, Tomas; Linkeviciene, Laura; Linkevicius, Tomas; Peciuliene, Vytaute; Malinauskas, Mangirdas

    2016-05-01

    To find a correlation between the severity of enamel microcracks (EMCs) and their increase during debonding and residual adhesive removal (RAR). Following their examination with scanning electron microscopy (SEM), 90 extracted human premolars were divided into three groups of 30: group 1, teeth having pronounced EMCs (visible with the naked eye under normal room illumination); group 2, teeth showing weak EMCs (not apparent under normal room illumination but visible by SEM); and group 3, a control group. EMCs have been classified into weak and pronounced, based on their visibility. Metal brackets (MB) and ceramic brackets (CB), 15 of each type, were bonded to all the teeth from groups 1 and 2. Debonding was performed with pliers, followed by RAR. The location, length, and width of the longest EMCs were measured using SEM before and after debonding. The mean overall width (Woverall) was higher for pronounced EMCs before and after debonding CB (P < .05), and after the removal of MB. Pronounced EMCs showed greater length values using both types of brackets. After debonding, the increase in Woverall of pronounced EMCs was 0.57 µm with MB (P < .05) and 0.30 µm with CB; for weak EMCs, - 0.32 µm with MB and 0.30 µm with CB. Although the teeth having pronounced EMCs showed higher width and length values, this did not predispose to greater EMCs increase after debonding MB and CB followed by RAR.

  2. Dynamic debonding in layered structures: a coupled ALE-cohesive approach

    Directory of Open Access Journals (Sweden)

    Marco Francesco Funari

    2017-07-01

    Full Text Available . A computational formulation able to simulate crack initiation and growth in layered structural systems is proposed. In order to identify the position of the onset interfacial defects and their dynamic debonding mechanisms, a moving mesh strategy, based on Arbitrary Lagrangian-Eulerian (ALE approach, is combined with a cohesive interface methodology, in which weak based moving connections are implemented by using a finite element formulation. The numerical formulation has been implemented by means of separate steps, concerned, at first, to identify the correct position of the crack onset and, subsequently, the growth by changing the computational geometry of the interfaces. In order to verify the accuracy and to validate the proposed methodology, comparisons with experimental and numerical results are developed. In particular, results, in terms of location and speed of the debonding front, obtained by the proposed model, are compared with the ones arising from the literature. Moreover, a parametric study in terms of geometrical characteristics of the layered structure are developed. The investigation reveals the impact of the stiffening of the reinforced strip and of adhesive thickness on the dynamic debonding mechanisms.

  3. Anchorage strength models for end-debonding predictions in RC beams strengthened with FRP composites

    Science.gov (United States)

    Nardini, V.; Guadagnini, M.; Valluzzi, M. R.

    2008-05-01

    The increase in the flexural capacity of RC beams obtained by externally bonding FRP composites to their tension side is often limited by the premature and brittle debonding of the external reinforcement. An in-depth understanding of this complex failure mechanism, however, has not yet been achieved. With specific regard to end-debonding failure modes, extensive experimental observations reported in the literature highlight the important distinction, often neglected in strength models proposed by researchers, between the peel-off and rip-off end-debonding types of failure. The peel-off failure is generally characterized by a failure plane located within the first few millimetres of the concrete cover, whilst the rip-off failure penetrates deeper into the concrete cover and propagates along the tensile steel reinforcement. A new rip-off strength model is described in this paper. The model proposed is based on the Chen and Teng peel-off model and relies upon additional theoretical considerations. The influence of the amount of the internal tensile steel reinforcement and the effective anchorage length of FRP are considered and discussed. The validity of the new model is analyzed further through comparisons with test results, findings of a numerical investigation, and a parametric study. The new rip-off strength model is assessed against a database comprising results from 62 beams tested by various researchers and is shown to yield less conservative results.

  4. Ensemble variational Bayes tensor factorization for super resolution of CFRP debond detection

    Science.gov (United States)

    Lu, Peng; Gao, Bin; Feng, Qizhi; Yang, Yang; Woo, W. L.; Tian, Gui Yun

    2017-09-01

    The carbon fiber reinforced polymer (CFRP) is widely used in aircraft and wind turbine blades. The common type of CFRP defect is debond. Optical pulse thermographic nondestructive evaluation (OPTNDE) and relevant thermal feature extraction algorithms are generally used to detect the debond. However, the resolution of detection performance remain as challenges. In this paper, the ensemble variational Bayes tensor factorization has been proposed to conduct super resolution of the debond detection. The algorithm is based on the framework of variational Bayes tensor factorization and it constructs spatial-transient multi-layer mining structure which can significantly enhance the contrast ratio between the defective regions and sound regions. In order to quantitatively evaluate the results, the event based F-score is computed. The different information regions of the extracted thermal patterns are considered as different events and the purpose is to objectively evaluate the detectability for different algorithms. Experimental tests and comparative studies have been conducted to prove the efficacy of the proposed method.

  5. Effect of adhesive remnant removal on enamel topography after bracket debonding

    Directory of Open Access Journals (Sweden)

    Larissa Adrian Meira Cardoso

    2014-12-01

    Full Text Available INTRODUCTION: At orthodontic treatment completion, knowledge about the effects of adhesive remnant removal on enamel is paramount.OBJECTIVE: This study aimed at assessing the effect of different adhesive remnant removal methods on enamel topography (ESI and surface roughness (Ra after bracket debonding and polishing.METHODS: A total of 50 human premolars were selected and divided into five groups according to the method used for adhesive remnant removal: high speed tungsten carbide bur (TCB, Sof-Lex discs (SL, adhesive removing plier (PL, ultrasound (US and Fiberglass burs (FB. Metal brackets were bonded with Transbond XT, stored at 37oC for 24 hours before debonding with adhesive removing plier. Subsequently, removal methods were carried out followed by polishing with pumice paste. Qualitative and quantitative analyses were conducted with pre-bonding, post-debonding and post-polishing analyses. Results were submitted to statistical analysis with F test (ANOVA and Tukey's (Ra as well as with Kruskal-Wallis and Bonferroni tests (ESI (P < 0.05.RESULTS: US Ra and ESI were significantly greater than TCB, SL, PL and FB. Polishing minimized Ra and ESI in the SL and FB groups.CONCLUSION: Adhesive remnant removal with SL and FB associated with polishing are recommended due to causing little damage to the enamel.

  6. Effect of reinforcing steel debonding on RC frame performance in resisting progressive collapse

    Directory of Open Access Journals (Sweden)

    Waleed Mohamed Elsayed

    2016-12-01

    Full Text Available This paper presents the experimental program performed to study the effect of reinforcing steel debonding on progressive collapse resistance of moment resisting frame designed and detailed in accordance with the Egyptian code provisions for seismic design. Half-scale specimens of the first story were extracted from the frame structure prototype. Each specimen represented a two-bay beam resulting from the removal of middle supporting column of the lower floor. In all specimens, the exterior two short columns were restrained against horizontal and vertical displacements and a monotonic vertical load was applied on the middle column stub to simulate the vertical load of the upper stories. Gradually increasing vertical load at the location of the removed column is continuously applied and increased up to failure. The cracking patterns, strains and the deformations at selected locations of reinforcing steel and concrete are recorded for further analysis. Different debonded reinforcement ratios, places and length are examined in this study to evaluate its effect on the collapse resistance performance of the frame. The effect of debonding on the distribution of reinforcing steel strain is evaluated. The nonlinear response of the frame to the removal of the column is evaluated and the amount of energy absorbed during the course of deformation is calculated.

  7. Can pulpal floor debonding be detected from occlusal surface displacement in composite restorations?

    Science.gov (United States)

    Novaes, João Batista; Talma, Elissa; Las Casas, Estevam Barbosa; Aregawi, Wondwosen; Kolstad, Lauren Wickham; Mantell, Sue; Wang, Yan; Fok, Alex

    2018-01-01

    Polymerization shrinkage of resin composite restorations can cause debonding at the tooth-restoration interface. Theory based on the mechanics of materials predicts that debonding at the pulpal floor would half the shrinkage displacement at the occlusal surface. The aim of this study is to test this theory and to examine the possibility of detecting subsurface resin composite restoration debonding by measuring the superficial shrinkage displacements. A commercial dental resin composite with linear shrinkage strain of 0.8% was used to restore 2 groups of 5 model Class-II cavities (8-mm long, 4-mm wide and 4-mm deep) in aluminum blocks (8-mm thick, 10-mm wide and 14-mm tall). Group I had the restorations bonded to all cavity surfaces, while Group II had the restorations not bonded to the cavity floor to simulate debonding. One of the proximal surfaces of each specimen was sprayed with fine carbon powder to allow surface displacement measurement by Digital Image Correlation. Images of the speckled surface were taken before and after cure for displacement calculation. The experiment was simulated using finite element analysis (FEA) for comparison. Group I showed a maximum occlusal displacement of 34.7±6.7μm and a center of contraction (COC) near the pulpal floor. Group II had a COC coinciding with the geometric center and showed a maximum occlusal displacement of 17.4±3.8μm. The difference between the two groups was statistically significant (p-value=0.0007). Similar results were obtained by FEA. The theoretical shrinkage displacement was 44.6 and 22.3μm for Group I and II, respectively. The lower experimental displacements were probably caused by slumping of the resin composite before cure and deformation of the adhesive layer. The results confirmed that the occlusal shrinkage displacement of a resin composite restoration was reduced significantly by pulpal floor debonding. Recent in vitro studies seem to indicate that this reduction in shrinkage displacement

  8. Effects of 445-nm Diode Laser-Assisted Debonding of Self-Ligating Ceramic Brackets on Shear Bond Strength.

    Science.gov (United States)

    Stein, Steffen; Hellak, Andreas; Schauseil, Michael; Korbmacher-Steiner, Heike; Braun, Andreas

    2018-01-01

    The aim of this study was to measure the effect of irradiation with a novel 445-nm diode laser on the shear bond strength (SBS) of ceramic brackets before debonding. Thirty ceramic brackets (In-Ovation ® C, GAC) were bonded in standard manner to the planed and polished buccal enamel surfaces of 30 caries-free human third molars. Each tooth was randomly allocated to the laser or control group, with 15 samples per group. The brackets in the laser group were irradiated with the diode laser (SIROLaser Blue ® ; Sirona) on three sides of the bracket bases for 5 sec each (lateral-coronal-lateral, a total of 15 sec) immediately before debonding. SBS values were measured for the laser group and control group. To assess the adhesive remnant index (ARI) and the degree of enamel fractures, micrographs of the enamel surface were taken with 10-fold magnification after debonding. The SBS values were significantly lower statistically in the laser group in comparison with the control group (p bracket fractures or enamel fractures occurred in either group after debonding. Irradiation of ceramic brackets with the novel diode laser before debonding significantly reduces the SBS values. This is of clinical importance, as it means that the risk of damage to the teeth, bracket fractures, and the overall treatment time can be reduced.

  9. Comparison of multiple rebond shear strengths of debonded brackets after preparation with sandblasting and CO2 laser

    Directory of Open Access Journals (Sweden)

    Mojgan Kachoei

    2016-08-01

    Full Text Available Background. Failure of orthodontic bracket bonds is a common occurrence during orthodontic treatment. Different techniques have been suggested in the literature to remove resin residues from the bracket bases and enamel surfaces to prepare the surfaces again after debonding. This study attempted to compare multiple rebond shear strengths (SBS of debonded brackets following preparation with sandblasting and CO2 laser. Methods. The brackets were bonded on 30 human and bovine maxillary central incisors using self-curing composite resin. SBS was measured using Hounsfield testing machine. The brackets were rebonded for two other times after composite resin residues on their surfaces were removed, either with air abrasion or CO2 laser. The debonded brackets and enamel surfaces were also evaluated after each debonding procedure under a stereomicroscope in order to determine adhesive remnant index (ARI. SBS of debonded brackets after each step were compared between sandblast and CO2 laser groups. Results. We observed significant differences in SBS values between pre-recycling and first (P = 0.04, second (P = 0.007 and third recycling (P = 0.007 with laser. Recycling with sandblasting resulted in a decrease in SBS after the first and second recycling procedure; however, the SBS increased after the third recycling procedure, with no significant differences. Conclusion. SBS of brackets after recycling with sandblasting and laser beams was not significantly different, and both were at a favorable level. However, repeating the recycling procedure with sandblasting resulted in more favorable SBS compared to laser.

  10. Intrapulpal Temperature Increase During Er:YAG Laser-Aided Debonding of Ceramic Brackets.

    Science.gov (United States)

    Yilanci, Hilal; Yildirim, Zeynep Beyza; Ramoglu, Sabri Ilhan

    2017-04-01

    The purpose of this study was to evaluate the temperature changes in the pulp chamber while using a newly introduced application of Er:YAG laser to debond ceramic brackets in a study model with a pulpal circulation with and without thermocycled samples. An esthetic alternative to stainless steel brackets, ceramic brackets have been proposed. However, because of their low fracture resistance and high bond strengths, ceramic brackets can cause a problem when they are being removed using conventional techniques. Experimental Groups A and B were established for samples with or without thermocycling. The same 20 maxillary central incisor and 20 premolar teeth were used in both groups. Pulpal blood microcirculation was simulated using an apparatus described in a previous study. Monocrystalline brackets were bonded by using Transbond XT. In Group A, brackets were debonded using the Er:YAG laser (600 mJ, 2 Hz, long pulse, and no air or water spray) after being stored in distilled water for 24 h. In Group B, brackets were debonded using the same laser system as that used in Group A after being stored in distilled water for 24 h and then thermocycled for a total of 5000 cycles between 5°C and 55°C. The laser irradiation duration and intrapulpal temperature changes were measured. In Group B, the intrapulpal temperature increase of the central incisors was significantly higher than that of the premolar teeth. In the central incisor and premolar teeth groups, there were no statistically significant difference between Groups A and B (p > 0.05). A positive correlation was found between laser irradiation duration and temperature increase (p brackets. This method can be used safely under the consideration of intrapulpal temperature changes.

  11. Micromechanical Analyses of Debonding and Matrix Cracking in Dual-Phase Materials

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang; Yang, Qingda

    2016-01-01

    Failure in elastic dual-phase materials under transverse tension is studied numerically. Cohesive zones represent failure along the interface and the augmented finite element method (A-FEM) is used for matrix cracking. Matrix cracks are formed at an angle of 55 deg - 60 deg relative to the loading...... direction, which is in good agreement with experiments. Matrix cracks initiate at the tip of the debond, and for equi-biaxial loading cracks are formed at both tips. For elliptical reinforcement the matrix cracks initiate at the narrow end of the ellipse. The load carrying capacity is highest for ligaments...

  12. Development of an easy-debonding orthodontic adhesive using thermal heating.

    Science.gov (United States)

    Tsuruoka, Takashi; Namura, Yasuhiro; Shimizu, Noriyoshi

    2007-01-01

    We produced experimentally a new bonding material that consisted of a mixture of a base resin (4-META/MMA-TBB resin adhesive) and thermoexpandable microcapsules for safe, easy debonding. Microcapsules in the base resin would start expansion at 80 degrees C, leading to a remarkable decrease in bond strength. Stainless steel brackets were bonded to bovine permanent mandibular incisors using bonding materials containing the microcapsules at different contents. After thermal cycling or heating, the shear bond strength of the brackets was measured. Shear bond strength of the bonding materials containing 30-40 wt% microcapsules decreased to about one-third or one-fifth that of the base resin on heating. Heating the brackets for eight seconds increased the temperature in the pulp chamber by 2 degrees C, which should not induce pulp damage. Results obtained suggested that the new bonding material should prove useful for removing brackets easily at the time of bracket debonding without any pain or enamel cracks, while maintaining the bonding strength during active orthodontic treatment.

  13. A consistency assessment of coupled cohesive zone models for mixed-mode debonding problems

    Directory of Open Access Journals (Sweden)

    R. Dimitri

    2014-07-01

    Full Text Available Due to their simplicity, cohesive zone models (CZMs are very attractive to describe mixed-mode failure and debonding processes of materials and interfaces. Although a large number of coupled CZMs have been proposed, and despite the extensive related literature, little attention has been devoted to ensuring the consistency of these models for mixed-mode conditions, primarily in a thermodynamical sense. A lack of consistency may affect the local or global response of a mechanical system. This contribution deals with the consistency check for some widely used exponential and bilinear mixed-mode CZMs. The coupling effect on stresses and energy dissipation is first investigated and the path-dependance of the mixed-mode debonding work of separation is analitically evaluated. Analytical predictions are also compared with results from numerical implementations, where the interface is described with zero-thickness contact elements. A node-to-segment strategy is here adopted, which incorporates decohesion and contact within a unified framework. A new thermodynamically consistent mixed-mode CZ model based on a reformulation of the Xu-Needleman model as modified by van den Bosch et al. is finally proposed and derived by applying the Coleman and Noll procedure in accordance with the second law of thermodynamics. The model holds monolithically for loading and unloading processes, as well as for decohesion and contact, and its performance is demonstrated through suitable examples.

  14. Enamel cracks evaluation - A method to predict tooth surface damage during the debonding.

    Science.gov (United States)

    Dumbryte, Irma; Jonavicius, Tomas; Linkeviciene, Laura; Linkevicius, Tomas; Peciuliene, Vytaute; Malinauskas, Mangirdas

    2015-01-01

    The objective of this in vitro study was to evaluate the effect of the enamel cracks on the tooth damage during the debonding. Measurements of the cracks characteristics (visibility, direction, length, and location) were performed utilizing a scanning electron microscopy (SEM) technique and mathematically derived formulas (x=h/30, l=n*x) before and following the removal of mechanically retained metal and ceramic brackets. The likelihood of having greater extent enamel defects was higher for the teeth with pronounced cracks (odds vatios, OR=3.728), increased when the crack was located in more than one zone of the tooth (OR=1.998), and the inclination did not exceed 30-45° (OR=0.505). Using ceramic brackets the risk of greater amount tooth structure defects raised 1.45 times (OR=1.450). Enamel crack showing all these characteristics at the beginning of the orthodontic treatment and the use of ceramic brackets might predispose to higher risk of greater extent tooth surface damage after the debonding by 20.4%.

  15. Three-dimensional quantitative analysis of adhesive remnants and enamel loss resulting from debonding orthodontic molar tubes

    OpenAIRE

    Janiszewska-Olszowska, Joanna; Tandecka, Katarzyna; Szatkiewicz, Tomasz; Sporniak-Tutak, Katarzyna; Grocholewicz, Katarzyna

    2014-01-01

    Aims Presenting a new method for direct, quantitative analysis of enamel surface. Measurement of adhesive remnants and enamel loss resulting from debonding molar tubes. Material and methods Buccal surfaces of fifteen extracted human molars were directly scanned with an optic blue-light 3D scanner to the nearest 2 μm. After 20 s etching molar tubes were bonded and after 24 h storing in 0.9% saline - debonded. Then 3D scanning was repeated. Superimposition and comparison were proceeded and shap...

  16. Detection of Interfacial Debonding in a Rubber-Steel-Layered Structure Using Active Sensing Enabled by Embedded Piezoceramic Transducers.

    Science.gov (United States)

    Feng, Qian; Kong, Qingzhao; Jiang, Jian; Liang, Yabin; Song, Gangbing

    2017-09-01

    Rubber-steel-layered structures are used in many engineering applications. Laminated rubber-steel bearing, as a type of seismic isolation device, is one of the most important applications of the rubber-steel-layered structures. Interfacial debonding in rubber-steel-layered structures is a typical failure mode, which can severely reduce their load-bearing capacity. In this paper, the authors developed a simple but effective active sensing approach using embedded piezoceramic transducers to provide an in-situ detection of the interfacial debonding between the rubber layers and steel plates. A sandwiched rubber-steel-layered specimen, consisting of one rubber layer and two steel plates, was fabricated as the test specimen. A novel installation technique, which allows the piezoceramic transducers to be fully embedded into the steel plates without changing the geometry and the surface conditions of the plates, was also developed in this research. The active sensing approach, in which designed stress waves can propagate between a pair of the embedded piezoceramic transducers (one as an actuator and the other one as a sensor), was employed to detect the steel-rubber debonding. When the rubber-steel debonding occurs, the debonded interfaces will attenuate the propagating stress wave, so that the amplitude of the received signal will decrease. The rubber-steel debonding was generated by pulling the two steel plates in opposite directions in a material-testing machine. The changes of the received signal before and after the debonding were characterized in a time domain and further quantified by using a wavelet packet-based energy index. Experiments on the healthy rubber-steel-layered specimen reveal that the piezoceramic-induced stress wave can propagate through the rubber layer. The destructive test on the specimen demonstrates that the piezoceramic-based active sensing approach can effectively detect the rubber-steel debonding failure in real time. The active sensing

  17. Evaluation of failure characteristics and bond strength after ceramic and polycarbonate bracket debonding : effect of bracket base silanization

    NARCIS (Netherlands)

    Ozcan, M.; Finnema, K.; Ybema, A.

    The objectives of this study were to evaluate the effect of silanization on the failure type and shear-peel bond strength (SBS) of ceramic and polycarbonate brackets, and to determine the type of failure when debonded with either a universal testing machine or orthodontic pliers. Silanized and

  18. A Fracture-Based Criterion for Debonding Strength of Adhesive-Bonded Double-Strap Steel Joints

    Directory of Open Access Journals (Sweden)

    Prawit Santisukpotha

    2012-01-01

    Full Text Available This paper addresses the debonding strength of adhesive-bonded double-strap steel joints. A fracture-based criterion was formulated in terms of a stress singularity parameter, i.e., the stress intensity factor, which governs the magnitude of a singular stress field near the joint ends. No existing crack was assumed. A total of 24 steel joint specimens were tested under constant amplitude fatigue loadings at stress ratio of 0.2 and frequency of 2 Hz. The joint stiffness ratio was slightly less than one to control the maximum adhesive stresses at the joint ends. To detect the debonding, a simple and practical technique was developed. The test results showed that the interfacial failure near the steel/adhesive corner was a dominant failure mode. The failure was brittle and the debonding life was governed by the crack initiation stage. The finite element analysis was employed to calculate the stress intensity factors and investigate the effects of the adhesive layer thickness, lap length and joint stiffness ratio on the debonding strength.

  19. Thermo-mechanical stress analysis in platelet reinforced composites with bonded and debonded platelet end

    International Nuclear Information System (INIS)

    Fattahi, A. M.; Moaddab, E.; Bibishahrbanoei, N.

    2015-01-01

    An analytical model has been performed to analyze the stress transfer in platelet reinforced composite subjected to both tensile loading and residual thermal stresses. Two sets of the matrix/platelet displacement solutions, which were called respectively as the far-field solution and the transient solution, were exactly derived based on the theory of elasticity. These two sets of the displacement solutions were then superposed to obtain simplified analytical expressions for the matrix/platelet stress field components. The main difference with the previous works here were that the thermal residual stresses were considered in this article. The analytical results obtained here are then validated by the FEM modeling. Interestingly, good agreements are found between the analytical and numerical predictions. Another superiority of the proposed analytical model was in its capability of solving problems with platelet/matrix debonding defect.

  20. Examination of ceramic/enamel interfacial debonding using acoustic emission and optical coherence tomography.

    Science.gov (United States)

    Lin, Chun-Li; Kuo, Wen-Chuan; Chang, Yen-Hsiang; Yu, Jin-Jie; Lin, Yun-Chu

    2014-08-01

    This study investigates monitored micro-crack growth and damage in the ceramic/enamel adhesive interface using the acoustic emission (AE) technique with optical coherence tomography (OCT) under fatigue shear testing. Shear bond strength (SBS) was measured first with eight prepared ceramic/enamel adhesive specimens under static loads. The fatigue shear testing was performed with three specimens at each cyclic load according to a modified ISO14801 method, applying at 80%, 75%, 70%, and 65% of the SBS to monitor interface debonding. The number of cycles at each load was recorded until ceramic/enamel adhesive interface debonding occurred. The AE technique was used to detect micro-crack signals in static and fatigue shear bond tests. The results showed that the average SBS value in the static tests was 18.07 ± 1.72 MPa (mean ± standard deviation), expressed in Newton's at 56.77 ± 5.40N. The average number of fatigue cycles in which ceramic/enamel interface damage was detected in 80%, 75%, 70% and 65% of the SBS were 41, 410, 8141 and 76,541, respectively. The acoustic behavior varied according to the applied load level. Events were emitted during 65% and 70% fatigue tests. A good correlation was observed between the crack location in OCT images and the number of AE signal hits. The AE technique combined with OCT images as a pre-clinical assessment tool to determine the integrity of cemented load bearing restored ceramic material. Sustainable cyclic load stresses in ceramic/enamel bonded specimens were substantially lower than the measured SBS. Predicted S-N curve showed that the maximum endured load was 10.98 MPa (about 34.48 N) passing 10(6) fatigue cyclic. Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  1. Enamel Surface Roughness after Debonding of Orthodontic Brackets and Various Clean-Up Techniques

    Directory of Open Access Journals (Sweden)

    Farzaneh Ahrari

    2013-01-01

    Full Text Available Objective: This study aimed to evaluate enamel roughness after adhesive removal using different burs and an Er:YAG laser.Materials and Methods: The buccal surfaces of forty human premolars were sealed by two layers of nail varnish, except for a circular area of 3 mm in diameter on the middle third. The enamel surfaces were initially subjected to profilometry analysis and four parameters of surface irregularity (Ra, Rq, Rt and Rz were recorded. Following bracket bonding and debonding, adhesive remnants were removed by tungsten carbide burs in low- or high- speed handpieces (group 1 and 2, respectively, an ultrafine diamond bur (group 3 or an Er:YAG laser (250 mJ, long pulse, 4 Hz (group 4, and surface roughness parameters were measured again. Then, the buccal surfaces were polished and the third profilometry measurements were performed.Results: The specimens that were cleaned with a low speed tungsten carbide bur showed no significant difference in surface irregularity between the different treatment stages (p>0.05. Surface roughness increased significantly after clean-up with the diamond bur and the Er:YAG laser (p<0.01. In comparison between groups, adhesive removal with tungsten carbide burs at slow- or high-speed handpieces produced the lowest, while enamel clean-up with the Er:YAG laser caused the highest values of roughness measurements (P<0.05.Conclusion: Under the study conditions, application of the ultrafine diamond bur or the Er:YAG laser caused irreversible enamel damage on tooth surface, and thus these methods could not be recommended for removing adhesive remnants after debonding of orthodontic brackets.

  2. An Optical Interferometric Triaxial Displacement Sensor for Structural Health Monitoring: Characterization of Sliding and Debonding for a Delamination Process.

    Science.gov (United States)

    Zhu, Chen; Chen, Yizheng; Zhuang, Yiyang; Du, Yang; Gerald, Rex E; Tang, Yan; Huang, Jie

    2017-11-22

    This paper presents an extrinsic Fabry-Perot interferometer-based optical fiber sensor (EFPI) for measuring three-dimensional (3D) displacements, including interfacial sliding and debonding during delamination. The idea employs three spatially arranged EFPIs as the sensing elements. In our sensor, the three EFPIs are formed by three endfaces of three optical fibers and their corresponding inclined mirrors. Two coincident roof-like metallic structures are used to support the three fibers and the three mirrors, respectively. Our sensor was calibrated and then used to monitor interfacial sliding and debonding between a long square brick of mortar and its support structure (i.e., a steel base plate) during the drying/curing process. This robust and easy-to-manufacture triaxial EFPI-based 3D displacement sensor has great potential in structural health monitoring, the construction industry, oil well monitoring, and geotechnology.

  3. An Optical Interferometric Triaxial Displacement Sensor for Structural Health Monitoring: Characterization of Sliding and Debonding for a Delamination Process

    Directory of Open Access Journals (Sweden)

    Chen Zhu

    2017-11-01

    Full Text Available This paper presents an extrinsic Fabry–Perot interferometer-based optical fiber sensor (EFPI for measuring three-dimensional (3D displacements, including interfacial sliding and debonding during delamination. The idea employs three spatially arranged EFPIs as the sensing elements. In our sensor, the three EFPIs are formed by three endfaces of three optical fibers and their corresponding inclined mirrors. Two coincident roof-like metallic structures are used to support the three fibers and the three mirrors, respectively. Our sensor was calibrated and then used to monitor interfacial sliding and debonding between a long square brick of mortar and its support structure (i.e., a steel base plate during the drying/curing process. This robust and easy-to-manufacture triaxial EFPI-based 3D displacement sensor has great potential in structural health monitoring, the construction industry, oil well monitoring, and geotechnology.

  4. Easy Debonding of Ceramic Brackets Bonded with a Light-Cured Orthodontic Adhesive Containing Microcapsules with a CO2 Laser.

    Science.gov (United States)

    Arima, Shiori; Namura, Yasuhiro; Tamura, Takahiko; Shimizu, Noriyoshi

    2018-03-01

    An easy debonding method for ceramic brackets using a light-cured Bis-GMA resin containing heat-expandable microcapsules and CO 2 laser was investigated. Ceramic brackets are used frequently in orthodontic treatment because of their desirable esthetic properties. However, the application of heavy force to ceramic brackets in debonding can fracture the tooth enamel and ceramic brackets, causing tooth pain. In total, 60 freshly extracted bovine permanent mandibular incisors were divided randomly into 10 groups of 6 specimens each, corresponding to the number of variables tested. Ceramic brackets were bonded to bovine permanent mandibular incisors using an orthodontic bonding agent containing heat-expandable microcapsules at different levels (0-30 wt%) and resin composite paste, and cured by a curing device. The bond strengths were measured before and after CO 2 laser irradiation, and the temperature increase in the pulp chamber in fresh human first premolars was also evaluated. With CO 2 laser irradiation for 5 sec to the bracket, the bond strength in the 25% microcapsule group decreased significantly, to ∼0.17-fold, compared with that of the no-laser group (p brackets, with less debonding time and enamel damage.

  5. Modeling and simulation of the debonding process of composite solid propellants

    Science.gov (United States)

    Feng, Tao; Xu, Jin-sheng; Han, Long; Chen, Xiong

    2017-07-01

    In order to study the damage evolution law of composite solid propellants, the molecular dynamics particle filled algorithm was used to establish the mesoscopic structure model of HTPB(Hydroxyl-terminated polybutadiene) propellants. The cohesive element method was employed for the adhesion interface between AP(Ammonium perchlorate) particle and HTPB matrix and the bilinear cohesive zone model was used to describe the mechanical response of the interface elements. The inversion analysis method based on Hooke-Jeeves optimization algorithm was employed to identify the parameters of cohesive zone model(CZM) of the particle/binder interface. Then, the optimized parameters were applied to the commercial finite element software ABAQUS to simulate the damage evolution process for AP particle and HTPB matrix, including the initiation, development, gathering and macroscopic crack. Finally, the stress-strain simulation curve was compared with the experiment curves. The result shows that the bilinear cohesive zone model can accurately describe the debonding and fracture process between the AP particles and HTPB matrix under the uniaxial tension loading.

  6. Ballistic protection performance of curved armor systems with or without debondings/delaminations

    International Nuclear Information System (INIS)

    Tan, Ping

    2014-01-01

    Highlights: • Influence of pre-existing defect in an armor system on its ballistic performance. • Development of finite element models for the ballistic performance of armor systems. • Prediction of the ballistic limit and back face deformation of curved armor systems. - Abstract: In order to discern how pre-existing defects such as single or multiple debondings/delaminations in a curved armor system may affect its ballistic protection performance, two-dimensional axial finite element models were generated using the commercial software ANSYS/Autodyn. The armor systems considered in this investigation are composed of boron carbide front component and Kevlar/epoxy backing component. They are assumed to be perfectly bonded at the interface without defects. The parametric study shows that for the cases considered, the maximum back face deformation of a curved armor system with or without defects is more sensitive to its curvature, material properties of the ceramic front component, and pre-existing defect size and location than the ballistic limit velocity. Additionally, both the ballistic limit velocity and maximum back face deformation are significantly affected by the backing component thickness, front/backing component thickness ratio and the number of delaminations

  7. THE INFLUENCE OF SHRINKAGE AND MOISTURE DIFFUSION ON IDEALIZED TOOTH STRUCTURE INVOLVING DEBONDING DAMAGE

    Institute of Scientific and Technical Information of China (English)

    FanJianping; TangChak-Yin

    2005-01-01

    This study highlights the joint effect of early polymerization shrinkage and longtermmoisture diffusion on the behavior of the restoration-tooth structure. The interphase debonding between particle and polymer resin in dental composite is taken into account by introducing the damage variable. The idealized model is designed and constructed for representing the restorationtooth structure, which consists of enamel, dentin, composite and interphase, each considered as homogenous material. The simulation is carried out using the general-purpose finite element software package, ABAQUS incorporated with a user subroutine for definition of damaged material behavior. The influence of Young's moduli of composite and interphase on stress and displacement is discussed. The compensating effect of water sorption on the polymerization shrinkage is examined with and without involving damage evolution. A comparison is made between the influence of hyper-, equi- and hypo-water sorption. Interfacial failure in the specific regions as well as cuspal movement has been predicated. The damage evolving in dental composite reduces the rigidity of composite, thus in turn reducing consequent stress and increasing consequent displacement. The development of stresses at the restoration-tooth interface can have a detrimental effect on the longevity of a restoration.

  8. Implementation of Ultrasonic Immersion Technique for Babbitt Metal Debonding in Turbine Bearing

    International Nuclear Information System (INIS)

    Jung, Gye Jo; Park, Sang Ki; Cho, Yong Sang; Park, Byung Cheol; Kil, Doo Song

    2004-01-01

    This study is aimed for the implementation of ultrasonic method to assess the reliability of turbine bearings. A modified ultrasonic immersion technique was carried out in both laboratory experiment and field application. From the laboratory results, we confirmed that the condition of interface layer between the babbitt and base metal be monitored by the C-Scan. The C-scan image by the ultrasonic immersion test can be used successfully to observe the condition of interface layer. The testing with a focused transducer provides a promising approach for estimating the extent of the damaged region and observing the interface layer effectively. The difference of the ultrasonic reflection ratio between the bonding and debonding area at the interface layer is one of the key parameters for assessing the extent of the damaged area; additionally, the reflection amplitude exhibits a favorable correlation with the overall damage level. The technique developed in this study was applied to the inspection of the turbine bearings at several power plants in Korea whereby the applicability in the field can be ascertained

  9. Implementation of Ultrasonic Immersion Technique for Babbitt Metal Debonding in Turbine Bearing

    Energy Technology Data Exchange (ETDEWEB)

    Jung, Gye Jo; Park, Sang Ki; Cho, Yong Sang; Park, Byung Cheol; Kil, Doo Song [Korea Electric Power Research Institute, Daejeon (Korea, Republic of)

    2004-08-15

    This study is aimed for the implementation of ultrasonic method to assess the reliability of turbine bearings. A modified ultrasonic immersion technique was carried out in both laboratory experiment and field application. From the laboratory results, we confirmed that the condition of interface layer between the babbitt and base metal be monitored by the C-Scan. The C-scan image by the ultrasonic immersion test can be used successfully to observe the condition of interface layer. The testing with a focused transducer provides a promising approach for estimating the extent of the damaged region and observing the interface layer effectively. The difference of the ultrasonic reflection ratio between the bonding and debonding area at the interface layer is one of the key parameters for assessing the extent of the damaged area; additionally, the reflection amplitude exhibits a favorable correlation with the overall damage level. The technique developed in this study was applied to the inspection of the turbine bearings at several power plants in Korea whereby the applicability in the field can be ascertained

  10. Efficiency of different protocols for enamel clean-up after bracket debonding: an in vitro study

    Directory of Open Access Journals (Sweden)

    Lara Carvalho Freitas Sigilião

    2015-10-01

    Full Text Available Objective: This study aimed to assess the efficiency of six protocols for cleaning-up tooth enamel after bracket debonding.Methods:A total of 60 premolars were divided into six groups, according to the tools used for clean-up: 12-blade bur at low speed (G12L, 12-blade bur at high speed (G12H, 30-blade bur at low speed (G30L, DU10CO ORTHO polisher (GDU, Renew System (GR and Diagloss polisher (GD. Mean roughness (Ra and mean roughness depth (Rz of enamel surface were analyzed with a profilometer. Paired t-test was used to assess Ra and Rz before and after enamel clean-up. ANOVA/Tukey tests were used for intergroup comparison. The duration of removal procedures was recorded. The association between time and variation in enamel roughness (∆Ra, ∆Rz were evaluated by Pearson's correlation test. Enamel topography was assessed by scanning electron microscopy (SEM.Results:In Groups G12L and G12H, original enamel roughness did not change significantly. In Groups G30L, GDU, GR and GD, a smoother surface (p < 0.05 was found after clean-up. In Groups G30L and GD, the protocols used were more time-consuming than those used in the other groups. Negative and moderate correlation was observed between time and (∆Ra, ∆Rz; Ra and (∆Ra, ∆Rz; Rz (r = - 0.445, r = - 0.475, p < 0.01.Conclusion:All enamel clean-up protocols were efficient because they did not result in increased surface roughness. The longer the time spent performing the protocol, the lower the surface roughness.

  11. Interface debonding characterization by image correlation integrated with Double Cantilever Beam kinematics

    KAUST Repository

    Blaysat, Benoît

    2015-03-01

    A procedure is proposed for the identification of spatial interfacial traction profiles of peel loaded Double Cantilever Beam (DCB) samples, from which the corresponding traction-separation relation is extracted. The procedure draws upon recent developments in the area of non-contact optical techniques and makes use of so-called Integrated Digital Image Correlation (I-DIC) concepts. The distinctive feature of the I-DIC approach proposed herein is that the unknown degrees of freedom are not displacements or rotations, but the set of interfacial fracture properties describing the traction profile. A closed-form theoretical model is developed to reconstruct a mechanically admissible displacement field representing the deformation of the adhering layers during debonding in the DCB fracture test. The proposed modeling accounts for the spatial traction profile along the interface between the adherends using few degrees of freedom, i.e. crack tip position, maximum stress and size of the process zone. By minimizing the correlation residual with respect to the degrees of freedom, the full set of interfacial fracture properties is obtained through a one-step algorithm, revealing a substantial gain in terms of computational efficiency and robustness. It is shown that the identified traction profile can be effectively combined with the crack opening displacement to extract the corresponding traction-separation relation, i.e. the key input data for any cohesive zone model (CZM). The proposed procedure is validated by post-processing virtually deformed images generated through the finite element method. The robustness with respect to noisy data, as well as the low sensitivity to the initial guess, are demonstrated.

  12. Three-dimensional quantitative analysis of adhesive remnants and enamel loss resulting from debonding orthodontic molar tubes.

    Science.gov (United States)

    Janiszewska-Olszowska, Joanna; Tandecka, Katarzyna; Szatkiewicz, Tomasz; Sporniak-Tutak, Katarzyna; Grocholewicz, Katarzyna

    2014-09-10

    Presenting a new method for direct, quantitative analysis of enamel surface. Measurement of adhesive remnants and enamel loss resulting from debonding molar tubes. Buccal surfaces of fifteen extracted human molars were directly scanned with an optic blue-light 3D scanner to the nearest 2 μm. After 20 s etching molar tubes were bonded and after 24 h storing in 0.9% saline - debonded. Then 3D scanning was repeated. Superimposition and comparison were proceeded and shape alterations of the entire objects were analyzed using specialized computer software. Residual adhesive heights as well as enamel loss depths have been obtained for the entire buccal surfaces. Residual adhesive volume and enamel loss volume have been calculated for every tooth. The maximum height of adhesive remaining on enamel surface was 0.76 mm and the volume on particular teeth ranged from 0.047 mm3 to 4.16 mm3. The median adhesive remnant volume was 0.988 mm3. Mean depths of enamel loss for particular teeth ranged from 0.0076 mm to 0.0416 mm. Highest maximum depth of enamel loss was 0.207 mm. Median volume of enamel loss was 0.104 mm3 and maximum volume was 1.484 mm3. Blue-light 3D scanning is able to provide direct precise scans of the enamel surface, which can be superimposed in order to calculate shape alterations. Debonding molar tubes leaves a certain amount of adhesive remnants on the enamel, however the interface fracture pattern varies for particular teeth and areas of enamel loss are present as well.

  13. Diagnosing the severity of buccal caries lesions in orthodontic patients at de-bonding using digital photographs.

    Science.gov (United States)

    Almosa, Naif A; Lundgren, Ted; Bresin, Andrea; Birkhed, Dowen; Kjellberg, Heidrun

    2014-08-01

    The aims of this study were (1) to evaluate the severity of buccal caries lesions according to the International Caries Detection and Assessment System (ICDAS) criteria via scoring buccal caries lesions on digital photographs at the time of de-bonding and (2) to compare this method with clinical examination. In total, 89 patients treated with upper and lower fixed appliances were clinically examined immediately after de-bonding by the first author and buccal caries were scored according to the ICDAS-II. Close-up digital photographs were taken of 245 teeth with different buccal caries lesion scores according to the ICDAS-II. Thirteen postgraduate orthodontics students independently scored the buccal caries lesions in the digital photographs using the modified clinical criteria (ICDAS-II). Intra- and inter-examiner reliabilities were evaluated by calculating the weighted kappa. To evaluate the validity of diagnosing the severity of buccal caries lesions using digital photographs compared to clinical examination, Spearman's correlation coefficient was calculated. Intra-examiner reliability and the reliability between each examiner and the clinical examination showed moderate-to-excellent agreement, with kappa values of 0.52-0.83. Scoring buccal caries lesions via clinical examinations and scoring via photographs were well correlated according to the modified ICDAS-II criteria (Spearman's correlation coefficient, 0.76). Thus, scoring buccal caries lesions on digital photographs according to ICDAS-II criteria is a reliable and valid method for assessing the severity of buccal caries lesions.

  14. Qualitative and quantitative evaluation of human dental enamel after bracket debonding: a noncontact three-dimensional optical profilometry analysis.

    Science.gov (United States)

    Ferreira, Fabiano G; Nouer, Darcy F; Silva, Nelson P; Garbui, Ivana U; Correr-Sobrinho, Lourenço; Nouer, Paulo R A

    2014-09-01

    The aim of this study was to undertake a qualitative and quantitative evaluation of changes on enamel surfaces after debonding of brackets followed by finishing procedures, using a high-resolution three-dimensional optical profiler and to investigate the accuracy of the technique. The labial surfaces of 36 extracted upper central incisors were examined. Before bonding, the enamel surfaces were subjected to profilometry, recording four amplitude parameters. Brackets were then bonded using two types of light-cured orthodontic adhesive: composite resin and resin-modified glass ionomer cement. Finishing was performed by three different methods: pumice on a rubber cup, fine and ultrafine aluminum oxide discs, and microfine diamond cups followed by silicon carbide brushes. The samples were subsequently re-analyzed by profilometry. Wilcoxon signed-rank test, Kruskal-Wallis test (p enamel roughness when diamond cups followed by silicon carbide brushes were used to finish surfaces that had remnants of resin-modified glass ionomer adhesive and when pumice was used to finish surfaces that had traces of composite resin. Enamel loss was minimal. The 3D optical profilometry technique was able to provide accurate qualitative and quantitative assessment of changes on the enamel surface after debonding. Morphological changes in the topography of dental surfaces, especially if related to enamel loss and roughness, are of considerable clinical importance. The quantitative evaluation method used herein enables a more comprehensive understanding of the effects of orthodontic bonding on teeth.

  15. Experimental and simulation of split semi-torus key in PVC foam core to improve the debonding resistance of composite sandwich panel

    Science.gov (United States)

    Juliyana, M.; Santhana Krishnan, R.

    2018-02-01

    The sandwich composite panels consisting of facesheet and core material are used as a primary structural member for aerospace, civil and marine areas due to its high stiffness to weight ratio. But the debonding nature of facesheet from the foam core under shear loading conditions leads to failure of the composite structure. To inhibit the debonding, an innovative methodology of introducing semi-torus key is used in the present study. The polyvinyl chloride foam core(PVC) is grooved and filled with semi-torus shaped chopped strand prepregs which are sandwiched between alternate layers of woven roven(WR) and chopped strand mat(CSM) skins by vacuum infusion process. The sandwich panel manufactured with semi-torus keys is evaluated regarding experimental and numerical simulations under shear loading conditions. The present innovative concept delays the debonding between face-sheet and foam core with enhancement the shear load carrying capability as the initial stiffness is higher than the conventional model. Also, the shear behaviour of the proposed concept is in good agreement with experimental results. The split semi-torus keys sustain the shear failure resulting in resistance to debonding capability.

  16. Fatigue resistance, debonding force, and failure type of fiber-reinforced composite, polyethylene ribbon-reinforced, and braided stainless steel wire lingual retainers in vitro

    NARCIS (Netherlands)

    Foek, Dave Lie Sam; Yetkiner, Enver; Ozcan, Mutlu

    Objective: To analyze the fatigue resistance, debonding force, and failure type of fiber-reinforced composite, polyethylene ribbon-reinforced, and braided stainless steel wire lingual retainers in vitro. Methods: Roots of human mandibular central incisors were covered with silicone, mimicking the

  17. Simulation of debonding in Al/epoxy T-peel joints using a potential-based cohesive zone model

    KAUST Repository

    Alfano, Marco; Furgiuele, Franco; Lubineau, Gilles; Paulino, Glaucio H.

    2011-01-01

    In this work, a cohesive zone model of fracture is employed to study debonding in plastically deforming Al/epoxy T-peel joints. In order to model the adhesion between the bonded metal strips, the Park-Paulino-Roesler (PPR) potential based cohesive model (J Mech Phys Solids, 2009;57:891-908) is employed, and interface elements are implemented in a finite element com-mercial code. A study on the influence of the cohesive properties (i.e. cohesive strength, fracture energy, shape parameter and slope indicator) on the predicted peel-force versus displacement plots reveals that the numerical results are mostly sensitive to cohesive strength and fracture energy. In turn, these parameters are tuned until a match between experimental and simulated load displacement curves is achieved.

  18. Simulation of debonding in Al/epoxy T-peel joints using a potential-based cohesive zone model

    KAUST Repository

    Alfano, Marco

    2011-06-10

    In this work, a cohesive zone model of fracture is employed to study debonding in plastically deforming Al/epoxy T-peel joints. In order to model the adhesion between the bonded metal strips, the Park-Paulino-Roesler (PPR) potential based cohesive model (J Mech Phys Solids, 2009;57:891-908) is employed, and interface elements are implemented in a finite element com-mercial code. A study on the influence of the cohesive properties (i.e. cohesive strength, fracture energy, shape parameter and slope indicator) on the predicted peel-force versus displacement plots reveals that the numerical results are mostly sensitive to cohesive strength and fracture energy. In turn, these parameters are tuned until a match between experimental and simulated load displacement curves is achieved.

  19. Shear bond strength and debonding characteristics of metal and ceramic brackets bonded with conventional acid-etch and self-etch primer systems: An in-vivo study.

    Science.gov (United States)

    Mirzakouchaki, Behnam; Shirazi, Sajjad; Sharghi, Reza; Shirazi, Samaneh; Moghimi, Mahsan; Shahrbaf, Shirin

    2016-02-01

    Different in-vitro studies have reported various results regarding shear bond strength (SBS) of orthodontic brackets when SEP technique is compared to conventional system. This in-vivo study was designed to compare the effect of conventional acid-etching and self-etching primer adhesive (SEP) systems on SBS and debonding characteristics of metal and ceramic orthodontic brackets. 120 intact first maxillary and mandibular premolars of 30 orthodontic patients were selected and bonded with metal and ceramic brackets using conventional acid-etch or self-etch primer system. The bonded brackets were incorporated into the wire during the study period to simulate the real orthodontic treatment condition. The teeth were extracted and debonded after 30 days. The SBS, debonding characteristics and adhesive remnant indices (ARI) were determined in all groups. The mean SBS of metal brackets was 10.63±1.42 MPa in conventional and 9.38±1.53 MPa in SEP system, (P=0.004). No statistically significant difference was noted between conventional and SEP systems in ceramic brackets. The frequency of 1, 2 and 3 ARI scores and debonding within the adhesive were the most common among all groups. No statistically significant difference was observed regarding ARI or failure mode of debonded specimens in different brackets or bonding systems. The SBS of metal brackets bonded using conventional system was significantly higher than SEP system, although the SBS of SEP system was clinically acceptable. No significant difference was found between conventional and SEP systems used with ceramic brackets. Total SBS of metal brackets was significantly higher than ceramic brackets. Due to adequate SBS of SEP system in bonding the metal brackets, it can be used as an alternative for conventional system. Shear bond strength, Orthodontic brackets, Adhesive remnant index, self-etch.

  20. Effect of Surface Treatment on Enamel Cracks After Orthodontic Bracket Debonding: Er,Cr:YSGG Laser-Etching Versus Acid-Etching

    Science.gov (United States)

    Ghaffari, Hassanali; Mirhashemi, Amirhossein; Baherimoghadam, Tahereh; Azmi, Amir

    2017-01-01

    Objectives: This study sought to compare enamel cracks after orthodontic bracket debonding in the surfaces prepared with erbium, chromium: yttrium-scandium-galliumgarnet (Er,Cr:YSGG) laser and the conventional acid-etching technique. Materials and Methods: This in-vitro experimental study was conducted on 60 sound human premolars extracted for orthodontic purposes. The teeth were randomly divided into two groups (n=30). The teeth in group A were etched with 37% phosphoric acid gel, while the teeth in group B were subjected to Er,Cr:YSGG laser irradiation (gold handpiece, MZ8 tip, 50Hz, 4.5W, 60μs, 80% water and 60% air). Orthodontic brackets were bonded to the enamel surfaces and were then debonded in both groups. The samples were inspected under a stereomicroscope at ×38 magnification to assess the number and length of enamel cracks before bonding and after debonding. Independent-samples t-test was used to compare the frequency of enamel cracks in the two groups. Levene’s test was applied to assess the equality of variances. Results: No significant difference was noted in the frequency or length of enamel cracks between the two groups after debonding (P>0.05). Conclusions: Despite the same results of the frequency and length of enamel cracks in the two groups and by considering the side effects of acid-etching (demineralization and formation of white spot lesions), Er,Cr:YSGG laser may be used as an alternative to acid-etching for enamel surface preparation prior to bracket bonding. PMID:29296111

  1. Debonding damage analysis in composite-masonry strengthening systems with polymer- and mortar-based matrix by means of the acoustic emission technique

    International Nuclear Information System (INIS)

    Verstrynge, E; Wevers, M; Ghiassi, B; Lourenço, P B

    2016-01-01

    Different types of strengthening systems, based on fiber reinforced materials, are under investigation for external strengthening of historic masonry structures. A full characterization of the bond behavior and of the short- and long-term failure mechanisms is crucial to ensure effective design, compatibility with the historic substrate and durability of the strengthening solution. Therein, non-destructive techniques are essential for bond characterization, durability assessment and on-site condition monitoring. In this paper, the acoustic emission (AE) technique is evaluated for debonding characterization and localization on fiber reinforced polymer (FRP) and steel reinforced grout-strengthened clay bricks. Both types of strengthening systems are subjected to accelerated ageing tests under thermal cycles and to single-lap shear bond tests. During the reported experimental campaign, AE data from the accelerated ageing tests demonstrated the thermal incompatibility between brick and epoxy-bonded FRP composites, and debonding damage was successfully detected, characterized and located. In addition, a qualitative comparison is made with digital image correlation and infrared thermography, in view of efficient on-site debonding detection. (paper)

  2. In Situ Tomography of Microcracking in Cross Ply Carbon Fiber Composites with Pre-existing Debonding Damage

    KAUST Repository

    Traudes, Daniel

    2012-07-01

    Carbon fiber based composites are an essential material in weight-critical applications such as in the aerospace industry. However, these materials are susceptible to damage such as matrix microcracking and fiber/matrix debonding (diffuse damage), which occurs at stresses much lower than the failure stress. A T700/M21 [0/90]s laminate was tensile loaded to introduce diffuse damage and prepared for a study on the initiation of transverse microcracks. The material was tensile loaded in a [+45/-45]s orientation to induce diffuse damage. A diffuse damage indicator was developed by measuring the decrease in shear stiffness. Samples with diffuse damage levels of 0, 0.05, 0.10, 0.15, 0.20, and 0.25 were prepared to be tensile tested in a [0/90]s orientation to induce microcracks. A successful development of the microcracking test procedure was performed. The edge of the material was studied with optical microscopy and x-ray to establish the structure of the fiber bundle geometry when undamaged. A sample containing microcracks was treated with diiodomethane dye penetrant, which successfully highlighted microcracks during x-ray imaging. The application time was not sufficient to produce consistent x-ray images over time, so a 45 minute soak time was recommended instead. The same damaged sample was subjected to a tomographic scan without a dye penetrant and while unloaded. Transverse microcracks were successfully identified from the data, although the results were not clean enough and likely omitted some smaller microcracks. Results are expected to be cleaner if performed during tensile testing. Future tensile testing will quantify the induced crack density of samples containing various degrees of initial diffuse damage, either using x-rays with a dye penetrant or using x-ray microtomography.

  3. Effects of inside spallation of a coating on the debonding of its interface with a substrate subjected to a laser shock

    CERN Document Server

    Boustie, M; Romain, J P; Jeandin, M

    2002-01-01

    When applying a laser shock to a substrate with a coating in order to test the adhesion strength of the interface, traction can be generated not only at the interface, but also within the materials. The effects of a possible rupture of these materials prior to the debonding is analysed by shock wave propagation mechanisms and experimentally evidenced for plasma sprayed coatings of alumina on an aluminium substrate. An estimate of the bond strength and the spall strength of the coating is obtained by numerical simulation.

  4. Effects of inside spallation of a coating on the debonding of its interface with a substrate subjected to a laser shock

    International Nuclear Information System (INIS)

    Boustie, M; Auroux, E; Romain, J P; Jeandin, M

    2002-01-01

    When applying a laser shock to a substrate with a coating in order to test the adhesion strength of the interface, traction can be generated not only at the interface, but also within the materials. The effects of a possible rupture of these materials prior to the debonding is analysed by shock wave propagation mechanisms and experimentally evidenced for plasma sprayed coatings of alumina on an aluminium substrate. An estimate of the bond strength and the spall strength of the coating is obtained by numerical simulation

  5. Effects of inside spallation of a coating on the debonding of its interface with a substrate subjected to a laser shock

    Energy Technology Data Exchange (ETDEWEB)

    Boustie, M [Centre National de la Recherche Scientifique, Laboratoire de Combustion et de Detonique, ENSMA, BP 40109, 86961 Futuroscope-Chasseneuil (France); Auroux, E [Centre National de la Recherche Scientifique, Laboratoire de Combustion et de Detonique, ENSMA, BP 40109, 86961 Futuroscope-Chasseneuil (France); Romain, J P [Centre National de la Recherche Scientifique, Laboratoire de Combustion et de Detonique, ENSMA, BP 40109, 86961 Futuroscope-Chasseneuil (France); Jeandin, M [Centre des Materiaux Pierre Marie Fourt, Ecole Nationale Superieure des Mines de Paris, 91003 Evry (France)

    2002-11-11

    When applying a laser shock to a substrate with a coating in order to test the adhesion strength of the interface, traction can be generated not only at the interface, but also within the materials. The effects of a possible rupture of these materials prior to the debonding is analysed by shock wave propagation mechanisms and experimentally evidenced for plasma sprayed coatings of alumina on an aluminium substrate. An estimate of the bond strength and the spall strength of the coating is obtained by numerical simulation.

  6. Evaluation of enamel surface after bracket debonding and polishing Avaliação da superfície do esmalte dentário após a remoção do braquete e polimento

    Directory of Open Access Journals (Sweden)

    Lilian Maria Brisque Pignatta

    2012-08-01

    Full Text Available INTRODUCTION: Preserving the dental enamel structure during removal of orthodontic accessories is a clinician's obligation. Hence the search for an evidence based debonding protocol. OBJECTIVE: to evaluate and compare, by means of scanning electron microscopy (SEM, the effects of four different protocols of bracket debonding and subsequent polishing on enamel surface, and to propose a protocol that minimizes damage to enamel surface. METHODS: Twelve bovine permanent incisors were divided into four groups according to the instrument used for debonding and removal of the adhesive remnant. In groups 1 and 2, brackets were debonded with a straight debonding plier (Ormco Corp., Glendora, California, USA, and in groups 3 and 4, debonding was performed with the instrument Lift-Off (3M Unitek, Monrovia, California, USA. In groups 1 and 3, the adhesive remnant was removed using a long adhesive removing plier (Ormco Corp., Glendora, California, USA and in groups 2 and 4, residual adhesive was removed with a tungsten carbide bur (Beavers Dental at high-speed. After each stage of debonding and polishing, enamel surfaces were replicated and electron micrographs were obtained with 50 and 200X magnification. RESULTS: All four protocols of debonding and polishing caused enamel irregularities. CONCLUSION: Debonding brackets with straight debonding plier, removal of adhesive remnant with a tungsten carbide bur and polishing with pumice and rubber cup was found to be the protocol that caused less damage to enamel surface, therefore this protocol is suggested for debonding brackets.INTRODUÇÃO: a preservação da estrutura de esmalte após a remoção dos acessórios ortodônticos é obrigação do clínico. Portanto, procura-se um protocolo de descolagem com bases científicas. OBJETIVO: objetivou-se avaliar por microscopia eletrônica de varredura (MEV a influência de quatro protocolos de remoção de braquetes e polimento da superfície do esmalte e propor um

  7. Comparison of PZT and FBG sensing technologies for debonding detection on reinforced concrete beams strengthened with external CFRP strips subjected to bending loads

    Directory of Open Access Journals (Sweden)

    Sevillano, E.

    2016-06-01

    Full Text Available The development of monitoring technologies particularly suitable to be used with novel CFRP strengthening techniques has gained great attention in recent years. However, in spite of the high performance of these advanced composite materials in the strengthening and repairing of structures in service, they are usually associated with brittle and sudden failure mainly caused by debonding phenomena, originated either at the CFRP-plate end or at the intermediate areas in the vicinity of flexural cracks in the RC beam. Thus, it is highly recommended for these structures to be monitored in order to ensure their integrity while in service. Specifically, the feasibility of smart sensing technologies such as Fiber Bragg Grating (FBG sensors and piezo-impedance transducers (PZT has been studied. To the knowledge of the authors, none serious study has been carried out until now concerned to the topic of damage detection due to debonding in rehabilitated structures with CFRP composites.El desarrollo de tecnologías de monitorización aplicables junto con las novedosas técnicas de refuerzo basadas en materiales CFRP ha recibido una atención creciente los últimos años. Sin embargo, a pesar del alto rendimiento de estos avanzados materiales compuestos en la reparación y refuerzo de estructuras en servicio, están habitualmente asociados a fallos frágiles y repentinos causados principalmente por fenómenos de despegue, originados bien en los extremos del refuerzo, bien en áreas intermedias en las proximidades de grietas de flexión existentes en la viga. Por tanto, es altamente recomendable monitorizar estas soluciones estructurales de cara a garantizar su integridad en servicio. Específicamente, se ha estudiado la viabilidad de sensores inteligentes tales como los sensores Fiber Bragg Grating (FBG o los transductores piezoeléctricos (PZT. Hasta donde los autores saben, no se han realizado estudios serios hasta la fecha abordando la detección de da

  8. A Signal Decomposition Method for Ultrasonic Guided Wave Generated from Debonding Combining Smoothed Pseudo Wigner-Ville Distribution and Vold–Kalman Filter Order Tracking

    Directory of Open Access Journals (Sweden)

    Junhua Wu

    2017-01-01

    Full Text Available Carbon fibre composites have a promising application future of the vehicle, due to its excellent physical properties. Debonding is a major defect of the material. Analyses of wave packets are critical for identification of the defect on ultrasonic nondestructive evaluation and testing. In order to isolate different components of ultrasonic guided waves (GWs, a signal decomposition algorithm combining Smoothed Pseudo Wigner-Ville distribution and Vold–Kalman filter order tracking is presented. In the algorithm, the time-frequency distribution of GW is first obtained by using Smoothed Pseudo Wigner-Ville distribution. The frequencies of different modes are computed based on summation of the time-frequency coefficients in the frequency direction. On the basis of these frequencies, isolation of different modes is done by Vold–Kalman filter order tracking. The results of the simulation signal and the experimental signal reveal that the presented algorithm succeeds in decomposing the multicomponent signal into monocomponents. Even though components overlap in corresponding Fourier spectrum, they can be isolated by using the presented algorithm. So the frequency resolution of the presented method is promising. Based on this, we can do research about defect identification, calculation of the defect size, and locating the position of the defect.

  9. Avaliação da superfície da porcelana após a descolagem de braquetes ortodônticos Porcelain surface evaluation after debonding of orthodontic brackets

    Directory of Open Access Journals (Sweden)

    André Moreira Mattos

    2006-10-01

    Full Text Available OBJETIVO: o objetivo deste trabalho foi avaliar a influência do tempo de condicionamento ácido em superfície de porcelana e o estado desta após a descolagem de braquetes ortodônticos. METODOLOGIA: foram utilizadas 20 amostras de porcelana feldspática para esmalte (Duceram-LFC divididas em 2 grupos de acordo com o tempo de condicionamento com ácido fluorídico 10% (15 segundos e 1 minuto. Após o ataque ácido, foi aplicado silano (3M Scotchbond, adesivo resinoso (Optibond Solo Plus e resina (Fill Magic nestas superfícies. A descolagem foi realizada através de força de cisalhamento numa máquina universal de ensaios (DL 500 - EMIC calibrada com velocidade fixa de 0,5mm/minuto. O índice do adesivo remanescente (ARI nas superfícies cerâmicas e o estado destas após a remoção dos braquetes foram avaliados através de fotos digitais. RESULTADOS: no grupo 15 segundos, a força de adesão média foi de 3,63MPa, significantemente inferior à do grupo 1 minuto, que foi de 7,18MPa (pAIM: the aim of this study was to evaluate the influence of acid conditioning time in porcelain surface and its characteristics after debonding of orthodontic brackets. METHODS: twenty samples of feldspathic porcelain for enamel (Duceram-LFC were divided in 2 groups according with the amount of time of acid conditioning with hydrofluoric acid 10% (15 seconds and 1 minute. After acid etching, it was applied silane (3M Scotchbond, adhesive (Optibond Solo Plus and resin (Fill Magic in these surfaces. The debonding was done with shear strength through a universal testing machine (DL 500 - EMIC calibrated with a fixed speed of 0.5mm/minute. The adhesive remnant index (ARI in the porcelain surfaces and their characteristics after removal of the brackets were evaluated through digital pictures. RESULTS: in the 15 seconds group, the mean bond strength was 3.63Mpa, significantly lower than the 1 minute group, that was 7.18Mpa (p<0.0001. All fractures during debonding

  10. Avaliação da resistência adesiva e do padrão de descolagem de diferentes sistemas de colagem de braquetes associados à clorexidina Evaluation of the bond strength and debonding pattern of different bracket bonding systems associated with chlorhexidine

    Directory of Open Access Journals (Sweden)

    Jorge Luís de Oliveira Ribeiro

    2008-08-01

    Full Text Available OBJETIVOS: o objetivo deste estudo in vitro foi avaliar a resistência adesiva e o padrão de descolagem de diferentes sistemas de colagem de braquetes (Sistema Transbond XT / 3M-Unitek e Sistema Enlight / Ormco cujos respectivos adesivos foram pré-misturados ao verniz de clorexidina (Cervitec / Ivoclar-Vivadent. METODOLOGIA: a amostra utilizada foi constituída por 60 pré-molares humanos, extraídos por indicações ortodônticas, incluídos em cilindros de PVC e divididos aleatoriamente em quatro grupos: grupo 1 - Sistema Transbond XT conforme prescrito pelo fabricante; grupo 2 - Sistema Transbond XT associado a verniz de clorexidina; grupo 3 - Sistema Enlight conforme prescrito pelo fabricante; grupo 4 - Sistema Enlight associado a verniz de clorexidina. A resistência adesiva foi avaliada pelo teste de cisalhamento na máquina de ensaios universal EMIC (0,5mm/min; o padrão de descolagem foi avaliado, através da lupa estereoscópica STEMI 2000-C / Zeiss (20x, pela observação do Índice de Adesivo Remanescente (IAR na superfície do esmalte dentário, após a descolagem dos braquetes. RESULTADOS: não houve diferença estatisticamente significante (p AIM: The objective of this in vitro study was to evaluate the bond strength and the debonding pattern of different bracket bonding systems (Transbond XT System / 3M-Unitek and Enlight System / Ormco whose respective adhesives were pre-mixed with chlorhexidine varnish (Cervitec / Ivoclar-Vivadent. METHODS: The sample used consisted of sixty human pre-molars extracted for orthodontic purposes, included in PVC cylinder and randomly divided in four experimental groups: group 1 - Transbond XT System according to the manufacturer’s instructions; group 2 - Transbond XT System combined with chlorhexidine varnish; group 3 - Enlight System according to the manufacturer’s instructions; group 4 - Enlight System combined with chlorhexidine varnish. The bond strength evaluation was obtained through

  11. Delamination and debonding failure of laminated composite T-joints

    NARCIS (Netherlands)

    Cui, H.

    2014-01-01

    Composites are increasingly being used in aerospace, automotive and other industries. The T-joint (also named stringer stiffened skin) is a typical connection, broadly used in thin-walled structures, such as the wing and fuselage of aircraft. This thesis presents the analysis of the delamination and

  12. Non-Uniform Compressive Strength of Debonded Sandwich Panels

    DEFF Research Database (Denmark)

    Berggreen, Carl Christian; Simonsen, Bo Cerup

    2005-01-01

    .(2005)., shows that the model is indeed able to predict the failure modes and the residual strength of damaged panels with accuracy sufficient for practical applications. This opens up for a number of important engineering applications, for example risk-based inspection and repair schemes....

  13. Quantifying the debonding of inclusions through tomography and computational homology.

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Wei-Yang; Johnson, George C. (University of California, Berkeley, Berkeley, CA); Mota, Alejandro; Foulk, James W., III; Jin, Huiqing

    2010-09-01

    This report describes a Laboratory Directed Research and Development (LDRD) project to use of synchrotron-radiation computed tomography (SRCT) data to determine the conditions and mechanisms that lead to void nucleation in rolled alloys. The Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory (LBNL) has provided SRCT data of a few specimens of 7075-T7351 aluminum plate (widely used for aerospace applications) stretched to failure, loaded in directions perpendicular and parallel to the rolling direction. The resolution of SRCT data is 900nm, which allows elucidation of the mechanisms governing void growth and coalescence. This resolution is not fine enough, however, for nucleation. We propose the use statistics and image processing techniques to obtain sub-resolution scale information from these data, and thus determine where in the specimen and when during the loading program nucleation occurs and the mechanisms that lead to it. Quantitative analysis of the tomography data, however, leads to the conclusion that the reconstruction process compromises the information obtained from the scans. Alternate, more powerful reconstruction algorithms are needed to address this problem, but those fall beyond the scope of this project.

  14. Fracture Mechanics Analysis of Reinforced DCB Sandwich Debond Specimen Loaded by Moments

    DEFF Research Database (Denmark)

    Saseendran, Vishnu; Berggreen, Christian; Carlsson, Leif A.

    2018-01-01

    a pure moment loading is considered. The J-integral coupled with laminate beam theory is employed to derive closed-form expression for the energy releaserate in terms of the applied moments, geometry, and material properties .A scalar quantityωis obtained to express the mode-mixity phase angle...

  15. Interface debonding characterization by image correlation integrated with Double Cantilever Beam kinematics

    KAUST Repository

    Blaysat, Benoî t; Hoefnagels, Johan P.M.; Lubineau, Gilles; Alfano, Marco; Geers, Marc G D

    2015-01-01

    are not displacements or rotations, but the set of interfacial fracture properties describing the traction profile. A closed-form theoretical model is developed to reconstruct a mechanically admissible displacement field representing the deformation of the adhering

  16. Effects of debonds and face sheet damage in GRP sandwich panels in naval ships

    DEFF Research Database (Denmark)

    Hayman, B.; Berggreen, Christian; Quispitupa, Amilcar

    2009-01-01

    Sandwich construction with face sheets of fibre-reinforced plastics (FRP) and a core of polymer foam or balsa wood offer a lightweight construction that is well suited to naval and other vessels for high-speed operation or where payload considerations require that the structural weight be minimised...

  17. Experiments and Analyses for Determining Fibre/Matrix Interface Parameters – Understanding Debonding Problems

    DEFF Research Database (Denmark)

    Raghavalu Thirumalai, Durai Prabhakaran; Gupta, Mohit; Lilholt, Hans

    2013-01-01

    A new experimental technique is developed to monitor the initiation and propagation of adebond crack during a fibre pull-out experiment. The advanced experimental setup consists of a high resolution video camera and a laser extensometer mounted at a tensile test machine. The test setup enables...... strain ΔεT, accounting for initial residual stresses. Specimens of a single steel fibre embedded centrally in a polyester matrix are tested using the experimental setup and the model. A practical experimental procedure for establishing the interface parameters is suggested, and an example demonstrates...

  18. Methods for removal of resin remaining after debonding of orthodontic brackets: A literature review

    Directory of Open Access Journals (Sweden)

    Mateus Rodrigues Tonetto

    2014-01-01

    Full Text Available The removal of resin debris and/or resin cement from the enamel surface without causing iatrogenic is the main objective when removing the orthodontic brackets. Some factors such as the time required for removal, damage to the tooth structure, are essential factors for the clinician at the time of removal. Various techniques are used for the removal of orthodontic brackets after the treatment; it is known that the use of clinical procedures such as the use of diamond burs and some pliers removers can damage the structure of the enamel, often depending on the bond strength that should be taken into consideration at the time of removal. This literature review aims to gather the most relevant studies that can clarify the clinical technique, which may be more suitable for removal of the brackets.

  19. Characterization of enamel surface after orthodontic brackets debonding: an in vitro study

    OpenAIRE

    Peixoto, A.; Mesquita, M. F.; Costa, H. N.; Carvalho, P. A.; Manso, A.

    2015-01-01

    Abstract of the poster presented at the SPMicros Congress “Microscopy in Research” - XLVII Annual Congress of the Portuguese Society for Microscopy. Egas Moniz, Monte de Caparica, 9-10 December 2013. PEst-OE/CTM-UI0084/2011 grant (Fundação para a Ciência e a Tecnologia)

  20. Analytical Model for Fictitious Crack Propagation in Reinforced Concrete Beams without Debonding

    DEFF Research Database (Denmark)

    Ulfkjær, J. P.; Brincker, Rune

    1994-01-01

    , the crack growth is further simplified by introducing a continuous layer of springs at the midsection mainly representing a simplified material response around the fracture zone. In the reinforcement the strain condition is assumed to be equal to the strain condition in the concrete. the important question...

  1. Cracking and debonding of a thin fiber reinforced concrete overlay : research brief.

    Science.gov (United States)

    2017-03-01

    Experimental tests found that the tensile interfacial energy : increased with fiber-reinforcement. Also bond tests indicated : that interfacial fracture occurred through the overlay mixture and : was proportional to the number of fibers which interse...

  2. Evaluation of one-step micro polishers for residual resin removal after debonding on fluorosed teeth

    Directory of Open Access Journals (Sweden)

    Padmalatha Challa

    2014-01-01

    Full Text Available Aim and objectives: To evaluate the effectiveness of one step micro polishers for residual resin removal on fluorosed teeth using scanning electron microscope (SEM. Methods and Material: 55 teeth with mild to moderate fluorosis were selected with five teeth as control. Metal brackets were bonded onto 50 teeth which were divided into 5 groups. The finishing and polishing methods which were tested include tungsten carbide burs (TCB, multistep finishing system (Sof-Lex, one step polishers (PoGo and combination of TCB with multistep and one step polishing systems. After resin removal, all the samples were examined under SEM for assessment of the enamel surface. Results: The enamel surface was closest to untouched enamel in samples finished with the PoGo one step polishers followed by Sof-Lex multistep finishing system. However, they took the longest time to finish. TCB required the shortest time for residual resin removal. Conclusions: All polishing systems produce a certain degree of damage to the enamel surface with the smoothest surface being produced by one step polishers on fluorosed teeth.

  3. Modeling Interfaces Through an Extension of Continuum Mechanics to the Nanoscale with Application to Fracture and Debonding of Composites

    National Research Council Canada - National Science Library

    Walton, Jay R; Sendova, Tsvetanka

    2008-01-01

    .... In contrast to classical fracture theories, the new theory predicts bounded crack tip stresses and strains by including a novel boundary condition arising from the jump momentum balance enforced...

  4. Surface roughness of debonded straight-tapered stems in cemented THA reduces subsidence but not cement damage

    NARCIS (Netherlands)

    Verdonschot, N.J.J.; Huiskes, H.W.J.

    1998-01-01

    Although stress analyses have shown that the mechanical endurance of cemented femoral THA reconstructions is served by stems that firmly bond to their cement mantles, retrieval studies suggest that this may be difficult to achieve. Clinical studies with roentgen stereophotogrammetric analyses have

  5. Full-field ultrasonic inspection for a composite sandwich plate skin-core debonding detection using laser-based ultrasonics

    Science.gov (United States)

    Chong, See Yenn; Victor, Jared J.; Todd, Michael D.

    2017-04-01

    In this paper, a full-field ultrasonic guided wave method is proposed to inspect a composite sandwich specimen made for an aircraft engine nacelle. The back skin/core interface of the specimen is built with two fabricated disbond defects (diameters of 12.7 mm and 25.4 mm) by removing areas of the adhesive used to bond the back skin to the core. A laser ultrasonic interrogation system (LUIS) incorporated with a disbond detection algorithm is developed. The system consists of a 1-kHz laser ultrasonic scanning system and a single fixed ultrasonic sensor to interrogate ultrasonic guided waves in the sandwich specimen. The interest area of 400 mm × 400 mm is scanned at a 0.5 mm scan interval. The corresponding full-field ultrasonic data is obtained and generated in the three-dimensional (3-D) space-time domain. Then, the 3-D full-field ultrasonic data is Fourier transformed and the ultrasonic frequency spectra are analyzed to determine the dominant frequency that is sensitive to the disbond defects. Continuous wavelet transform (CWT) based on fast Fourier transform (FFT) is implemented as a single-frequency bandpass filter to filter the full-field ultrasonic data in the 3-D space-time domain at the selected dominant frequency. The LUIS has shown the ability to detect the disbond with diameters of 11 mm and 23 mm which match to the pre-determined disbond sizes well. For future research, a robust signal processing algorithm and a model-based matched filter will be investigated to make the detection process autonomous and improve detectability

  6. Comparative Evaluation of Shear Bond Strength and Debonding Characteristics using Conventional Halogen Light Curing Unit and LED Light Curing Unit: An in vitro Study

    Directory of Open Access Journals (Sweden)

    Amit Bhardwaj

    2013-01-01

    Conclusion: The result of this study showed promise for the orthodontic application of LED as light curing units and 20 seconds of exposure time is adequate for both LED and Halogen light, since increasing the curing time to 40 seconds showed no significant difference.

  7. The Role of Interphase on Micro- to Macroscopic Responses and Prediction for Initiation of Debonding Damage of Glass—Fiber Reinforced Polycarbonate

    OpenAIRE

    Esmaeili , N.; Tomita , Y.

    2008-01-01

    Abstract A computational model based on large-deformation finite element method (FEM) analysis is developed and used to evaluate the interaction between the microstructure and the heterogeneous deformation behavior of ternary composites on micro- to macroscopic scales. To uncover the influence of the plastic interphase layer on the stress?strain behavior of the three-phase system under constant strain-rate loading, the analyses of two different types of polymers with different Pois...

  8. An Investigation of Interfacial Fatigue in Fiber Reinforced Composites

    Science.gov (United States)

    Yanhua, Chen; Zhifei, Shi

    2005-09-01

    Based on the shear-lag model and the modified degradation formula for coefficient of friction, the interfacial fatigue and debonding for fiber reinforced composites under cyclic loading are studied. The loading condition is chosen as the kind that is the most frequently used in fiber-pull-out experiments. The stress components in the debonded and bonded regions are obtained according to the maximum and minimum applied loading. By the aid of theory of fracture mechanics and Paris formula, the governing equation is solved numerically and the interfacial debonding is simulated. The relationships between the parameters (such as the debond rate, debond length, debond force) and the number of cycles are obtained.

  9. Effect of the precrack preparation with an ultrasonic instrument on the ceramic bracket removal

    Directory of Open Access Journals (Sweden)

    Yen-Liang Chen

    2015-08-01

    Conclusion: The ultrasonic precrack preparation can significantly decrease the debonding force and may guide the bracket debonding through a favorable fracture plane without damage to either the bracket or the enamel.

  10. A Comparison of an Acid Primer (Clearfil Liner Bond 2V with Other Conventional Etchants on the Shear Bond Strength and the Bracket—Adhesive Failure Mode: An ex vivo Study

    Directory of Open Access Journals (Sweden)

    Ashish Garg

    2013-01-01

    Results and conclusion: The results of the study indicated that acidic primer containing both the enamel etchant and primer have adequate bond strength with decreased residual adhesive left on the enamel surface after debonding, thereby maintaining a sound unblemished enamel surface after debonding orthodontic brackets and less chances of iatrogenic enamel fracture and crazing along with decreased chairside time.

  11. 76 FR 24832 - Airworthiness Directives; Airbus Model A330-201, -202, -203, -223, and -243 Airplanes, A330-300...

    Science.gov (United States)

    2011-05-03

    ... include vacuum loss and elasticity laminate checker inspections for damage including de-bonding between... exist or develop on other products of the same type design. Differences Between This AD and the MCAI or... elasticity laminate checker inspection on the trailing edge area (Area 2) for damage including de-bonding...

  12. Clinical Survival of Rebonded Brackets with Different ARI Scores

    Directory of Open Access Journals (Sweden)

    Mohammad Hossein Ahangar Atashi

    2016-01-01

    Full Text Available Introduction: Bracket debonding is one of the most common events in orthodontics. The aim of the present study was to quantitatively compare clinical survival of rebonded brackets with different ARI scores with new brackets rebonding. Materials and Methods: The subjects in the present study consisted of 74 patients with 76 debonded brackets on maxillary first and second premolars. After refreshing the bracket base of the debonded brackets, they were assigned in two groups: group A with 27 brackets of ARI≥4 and group B with 28 brackets of ARI≤2. In 21 cases, new brackets were used (group C. The frequency of the debonding in each rebonded group during treatment was calculated in intervals of 6,12,18 mounths after onset of bracket rebonding . Chi-squared test was used to compare the frequency of debonded brackets. Results: The frequency of debonded brackets was significantly higher in group B (ARI≤2 than those of groups A (ARI≥4 and C (new brackets. The number of debonded brackets were not significantly different between groups A (ARI≥4 and C (new brackets. Conclusion: Rebonding strength of debonded brackets in those that the failure is presented between adhesive and enamel (ARI≥4 could be clinically acceptable with no need to use new brackets.    Key words: dental bonding; orthodontic brackets; prevalence

  13. Nde of Frp Wrapped Columns Using Infrared Thermography

    Science.gov (United States)

    Halabe, Udaya B.; Dutta, Shasanka Shekhar; GangaRao, Hota V. S.

    2008-02-01

    This paper investigates the feasibility of using Infrared Thermography (IRT) for detecting debonds in Fiber Reinforced Polymer (FRP) wrapped columns. Laboratory tests were conducted on FRP wrapped concrete cylinders of size 6″×12″ (152.4 mm×304.8 mm) in which air-filled and water-filled debonds of various sizes were placed underneath the FRP wraps. Air-filled debonds were made by cutting plastic sheets into the desired sizes whereas water-filled debonds were made by filling water in custom made polyethylene pouches. Both carbon and glass fiber reinforced wraps were considered in this study. Infrared tests were conducted using a fully radiometric digital infrared camera which was successful in detecting air-filled as well as water-filled subsurface debonds. In addition to the laboratory testing, two field trips were made to Moorefield, West Virginia for detecting subsurface debonds in FRP wrapped timber piles of a railroad bridge using infrared testing. The results revealed that infrared thermography can be used as an effective nondestructive evaluation tool for detecting subsurface debonds in structural components wrapped with carbon or glass reinforced composite fabrics.

  14. Mechanisms of Probe Tack Adhesion of Model Acrylic Elastomers

    Science.gov (United States)

    Lakrout, Hamed; Creton, Costantino; Ahn, Dongchan; Shull, Kenneth R.

    1997-03-01

    The adhesion mechanisms of model acrylate homopolymers and copolymers are studied with an instrumented probe tack test. A video camera positioned under the transparent glass substrate records the bonding and debonding process while the force displacement curve is acquired. This setup allows to couple the observation of the cavitation and fibrillation mechanisms, occurring during the debonding of the film from the stainless steel probe, with the mechanical measurement of stress and strain. The transitions between different debonding mechanisms are critically dicussed in terms of the bulk and surface properties of the adhesive and its molecular structure.

  15. Damage identification in composite panels using guided waves

    NARCIS (Netherlands)

    Loendersloot, R.; Moix-Bonet, M.

    2015-01-01

    A methodology for the identification of barely visible impact damage using guided waves on a typical aircraft composite structure is implemented. Delaminations and debondings have been introduced in two stiffened panels by means of impact loads.

  16. Evaluation of Roadway Subsurface Drainage on Rural Routes

    Science.gov (United States)

    2017-09-01

    Excess moisture has been identified as a cause for stripping, raveling, debonding, and rutting in flexible pavement [ODOT, 2016a]. The Ohio Department of Transportation (ODOT) has been getting substantially less than the expected 15 year service life...

  17. Polypropylene–clay composite prepared from Indian bentonite

    Indian Academy of Sciences (India)

    WINTEC

    composites have recently found applications in packaging, automotive ... process using xylene as the solvent. Solvent ... Particle size distribution curve for clay, bentonite. Table 2. .... greater probability of debonding due to the poor interfa-.

  18. Tuning Material and Component Properties to Reduce Weight and Increase Blastworthiness of a Notional V-Hull Structure

    Science.gov (United States)

    2015-04-24

    debonding, matrix cracking , and fiber breakage have been considered for creating blast mitigation configurations [17]. For similar purposes...to demonstrate a process for identifying suitable stiffness, inertia , and damping characteristics of the various components. In addition to the

  19. Automated Damage Assessment System for Ballistic Protective Inserts Using Low Frequency Ultrasonics

    National Research Council Canada - National Science Library

    Godinez-Azcuaga, Valery F; Ozevin, Didem; Finlayson, Richard D; Colanto, David

    2006-01-01

    .... Radiography and low frequency ultrasonics are two methods that can provide information about the condition of a BPI, with respect to cracking and porosity in the ceramic plate and debonding between layers...

  20. Stress Analysis and Strength Prediction of Adhesively Bonded Composite Joints

    National Research Council Canada - National Science Library

    Rastogi, Naveen

    1998-01-01

    .... Further, the submodeling technique available in the commercial finite element package ABAQUS is explored to study the three-dimensional stress field in the vicinity of joint edges and debond cracks...

  1. Modeling the Monotonic and Cyclic Tensile Stress-Strain Behavior of 2D and 2.5D Woven C/SiC Ceramic-Matrix Composites

    Science.gov (United States)

    Li, L. B.

    2018-05-01

    The deformation of 2D and 2.5 C/SiC woven ceramic-matrix composites (CMCs) in monotonic and cyclic loadings has been investigated. Statistical matrix multicracking and fiber failure models and the fracture mechanics interface debonding approach are used to determine the spacing of matrix cracks, the debonded length of interface, and the fraction of broken fibers. The effects of fiber volume fraction and fiber Weibull modulus on the damage evolution in the composites and on their tensile stress-strain curves are analyzed. When matrix multicracking and fiber/matrix interface debonding occur, the fiber slippage relative to the matrix in the debonded interface region of the 0° warp yarns is the main reason for the emergance of stress-strain hysteresis loops for 2D and 2.5D woven CMCs. A model of these loops is developed, and histeresis loops for the composites in cyclic loadings/unloadings are predicted.

  2. Interfacial bonding and friction in silicon carbide (filament)-reinforced ceramic- and glass-matrix composites

    International Nuclear Information System (INIS)

    Bright, J.D.; Shetty, D.K.

    1989-01-01

    This paper reports interfacial shear strength and interfacial sliding friction stress assessed in unidirectional SiC-filament-reinforced reaction-bonded silicon nitride (RBSN) and borosilicate glass composites and 0/90 cross-ply reinforced borosilicate glass composite using a fiber pushout test technique. The interface debonding load and the maximum sliding friction load were measured for varying lengths of the embedded fibers by continuously monitoring the load during debonding and pushout of single fibers in finite-thickness specimens. The dependences of the debonding load and the maximum sliding friction load on the initial embedded lengths of the fibers were in agreement with nonlinear shear-lag models. An iterative regression procedure was used to evaluate the interfacial properties, shear debond strength (τ d ), and sliding friction stress (τ f ), from the embedded fiber length dependences of the debonding load and the maximum frictional sliding load, respectively. The shear-lag model and the analysis of sliding friction permit explicit evaluation of a coefficient of sliding friction (μ) and a residual compressive stress on the interface (σ 0 ). The cross-ply composite showed a significantly higher coefficient of interfacial friction as compared to the unidirectional composites

  3. Damage of the Interface Between an Orthodontic Bracket and Enamel - the Effect of Some Elastic Properties of the Adhesive Material

    Science.gov (United States)

    Durgesh, B. H.; Alkheraif, A. A.; Al Sharawy, M.; Varrela, J.; Vallittu, P. K.

    2016-01-01

    The aim of this study was to investigate the magnitude of debonding stress of an orthodontic bracket bonded to the enamel with resin systems having different elastic properties. For the same purpose, sixty human premolars were randomly divided into four groups according to the adhesive system used for bonding brackets: G Fix flowable resin (GFI) with Everstick NET (ESN), GFI, G Aenial Universal Flow (GAU) with ESN, and GAU. The brackets were stressed in the occlusogingival direction on a universal testing machine. The values of debonding load and displacement were determined at the point of debonding. The elastic modulus of the tested materials was determined using nanoindentation. An analysis of variance showed a significant difference in the loads required to debond the bracket among the groups tested. The GAU group had the highest elastic modulus, followed by the GFI and ESN groups. ARI (Adhesive Remnant Index) scores demonstrated more remnants of the adhesive material on the bracket surface with adhesives having a higher elastic modulus. Taking into consideration results of the present in-vitro study, it can be concluded that the incorporation of a glass-fiber-reinforced composite resin (FRC) with a low elastic modulus between the orthodontic bracket and enamel increases the debonding force and strain more than with adhesive systems having a higher elastic modulus.

  4. Effect of Fiber Poisson Contraction on Matrix Multicracking Evolution of Fiber-Reinforced Ceramic-Matrix Composites

    Science.gov (United States)

    Longbiao, Li

    2015-12-01

    An analytical methodology has been developed to investigate the effect of fiber Poisson contraction on matrix multicracking evolution of fiber-reinforced ceramic-matrix composites (CMCs). The modified shear-lag model incorporated with the Coulomb friction law is adopted to solve the stress distribution in the interface slip region and intact region of the damaged composite. The critical matrix strain energy criterion which presupposes the existence of an ultimate or critical strain energy limit beyond which the matrix fails has been adopted to describe matrix multicracking of CMCs. As more energy is placed into the composite, matrix fractures and the interface debonding occurs to dissipate the extra energy. The interface debonded length under the process of matrix multicracking is obtained by treating the interface debonding as a particular crack propagation problem along the fiber/matrix interface. The effects of the interfacial frictional coefficient, fiber Poisson ratio, fiber volume fraction, interface debonded energy and cycle number on the interface debonding and matrix multicracking evolution have been analyzed. The theoretical results are compared with experimental data of unidirectional SiC/CAS, SiC/CAS-II and SiC/Borosilicate composites.

  5. Influence of bruxism on survival of porcelain laminate veneers.

    Science.gov (United States)

    Granell-Ruíz, Maria; Agustín-Panadero, Rubén; Fons-Font, Antonio; Román-Rodríguez, Juan-Luis; Solá-Ruíz, María-Fernanda

    2014-09-01

    This study aims to determine whether bruxism and the use of occlusal splints affect the survival of porcelain laminate veneers in patients treated with this technique. Restorations were made in 70 patients, including 30 patients with some type of parafunctional habit. A total of 323 veneers were placed, 170 in patients with bruxism activity, and the remaining 153 in patients without it. A clinical examination determined the presence or absence of ceramic failure (cracks, fractures and debonding) of the restorations; these incidents were analyzed for association with bruxism and the use of splints. Analysis of the ceramic failures showed that of the 13 fractures and 29 debonding that were present in our study, 8 fractures and 22 debonding were related to the presence of bruxism. Porcelain laminate veneers are a predictable treatment option that provides excellent results, recognizing a higher risk of failure in patients with bruxism activity. The use of occlusal splints reduces the risk of fractures.

  6. An experimental and theoretical investigation of stick-slip, steady-state and roughness dominated sliding in fiber-reinforced composites

    International Nuclear Information System (INIS)

    Mackin, T.J.

    1995-01-01

    The mechanical properties of fiber reinforced composites depends strongly upon the properties of the fiber/matrix interface. Enhanced fracture resistance and strain to failure are synonymous with debonding and sliding of the reinforcement phase. Thus, the two key properties of the composite are the interfacial toughness and the post-debond sliding stress. After debonding a variety of interfacial sliding phenomena are noted, including: stick-slip, steady-state, and roughness dominated sliding. The interfacial properties, including the coefficient of friction, the radial clamping pressure, asperity amplitude, the elastic properties of the constituents, and the compliance of the test machine, each play a role in the operative sliding phenomenon. Experiments have been conducted to explore each of these phenomena. In addition, models have been developed that rationalize all of the observed behavior

  7. Evaluation of the adhesive layer of blast tube by using ultrasound

    Energy Technology Data Exchange (ETDEWEB)

    Park, Joon Soo; Song, Sung Jin; Kim, Young H.; Cho, Hyun [Sungkyunkwan University, Seoul (Korea, Republic of); Lim, Soo Yong; Yun, Nam Gyun [Agency Defence Development, Daejeon (Korea, Republic of); Lee, Jeong Ki [Korea Inspection and Engineering Co., LTD, Daejeon (Korea, Republic of); Park, Young Joo [Hankuk Fiber Co., LTD, Milyang (Korea, Republic of)

    2003-07-01

    Ultrasonic testing method has been developed to evaluated adhesive layers in blast tube for the reliability of the rocket. The main objective of the present work was to find debonding and uncharged state between steel and FRP layers. We distinguish the debonding and uncharged state using the resonance method in the adhesive layers. It was found that the higher magnitude of ultrasound is reflected for the uncharged area in frequency domain, and shown good agreements with experimental results. The traditional ultrasonic pulse-echo method offers good implements for the distinction debonding area. The nondestructive testing results were compared with the micrography of destructive testing. As results, ultrasonic testing could be utilized for the evaluation of adhesive layer in the blast tube.

  8. Evaluation of the adhesive layer of blast tube using ultrasound

    Energy Technology Data Exchange (ETDEWEB)

    Park, Joon Soo; Song, Sung Jin; Kim, Young Hwan; Cho, Hyun [Dept. of Machanical Engineering, Sungkyunkwan University, Seoul (Korea, Republic of); Lim, Soo Yong; Yun, Nam Gyun [Agency for Defense Development, Daejeon (Korea, Republic of); Lee, Jeong Ki [Korea Inspection and Engineering Co., Ltd, Seoul (Korea, Republic of); Park, Young Joo [Hankuk Fiber Group, Milyang (Korea, Republic of)

    2003-05-15

    Ultrasonic testing method has been developed to evaluate adhesive layers in blast tube for the reliability of the rocket. The main objective of the present work was to find debonding and uncharged state between steel and FRP layers. We distinguish the debonding and uncharged state using the resonance method in the adhesive layers. It was found that the higher magnitude of ultrasound is reflected for the uncharged area in frequency domain, and shown good agreements with experimental results. The traditional ultrasonic pulse-echo method offers good implements for the distinction debonding area. The nondestructive testing results were compared with the micrography of destructive testing. As results, ultrasonic testing could be utilized for the evaluation of adhesive layer in the blast tube.

  9. The effect of pretreatment with fluoride on the tensile strength of orthodontic bonding

    International Nuclear Information System (INIS)

    Wang, W.N.; Sheen, D.H.

    1991-01-01

    White spot decalcifications and caries occurring adjacent to bonded orthodontic brackets have long been a concern to orthodontists. One procedure suggested to overcome this problem is fluoride treatment prior to bonding. The purpose of this study was to compare the tensile bond strength of orthodontic self-cured resin from Concise on teeth rinsed 4 minutes in 1.23% APF with untreated controls. Measurements were made on an Instron machine. Debonding interfaces were observed with a scanning electron microscope and energy dispersive x-ray spectrometry. Distributions were calculated. The tensile bond strengths of the fluoride-treated teeth and the untreated teeth were not significantly different. The debonding interfaces between resin and bracket base, within the resin itself, and between enamel and resin were similar in the two experimental groups. However, greater enamel detachment was seen within the fluoride pretreatment group. So while fluoride pretreatment does not significantly affect tensile bond strength, it may cause enamel detachment after debonding

  10. Fracture Characterization of Sandwich Face/Core Interfaces

    DEFF Research Database (Denmark)

    Manca, Marcello

    of load transfer between the faces and the core layer is lost, the debonds are considered as primary damage initiators. Under fatigue loading the debonds may evolve into cracks that cause a reduction in structural performance and consequent failure. At present most structural design is based on “life-time...... of sandwich structures is defects that are introduced in the manufacturing process. It is inevitable that areas of the face sheets will not fully adhere to the core resulting in defects known as “debonds”. Debonds can also be induced in-service due to e.g. localised impact loading or overloading. As the means...... such result it is important to devise new experimental and analytical techniques to establish the multi-mode fracture characteristics of sandwich plate structures and accordingly develop methods to inhibit defect propagation. This thesis deals with characterization of fracture between face and core...

  11. Supramolecular Cross-Links in Poly(alkyl methacrylate) Copolymers and Their Impact on the Mechanical and Reversible Adhesive Properties.

    Science.gov (United States)

    Heinzmann, Christian; Salz, Ulrich; Moszner, Norbert; Fiore, Gina L; Weder, Christoph

    2015-06-24

    Hydrogen-bonded, side-chain-functionalized supramolecular poly(alkyl methacrylate)s were investigated as light- and temperature-responsive reversible adhesives that are useful for bonding and debonding on demand applications. Here, 2-hydroxyethyl methacrylate (HEMA) was functionalized with 2-ureido-4[1H]pyrimidinone (UPy) via a hexamethylenediisocyanate (HMDI) linker, to create a monomer (UPy-HMDI-HEMA) that serves to form supramolecular cross-links by way of forming quadruple hydrogen bonded dimers. UPy-HMDI-HEMA was copolymerized with either hexyl methacrylate or butyl methacrylate to create copolymers comprising 2.5, 5, or 10 mol % of the cross-linker. The mechanical properties of all (co)polymers were investigated with stress-strain experiments and dynamic mechanical analysis. Furthermore, the adhesive properties were studied at temperatures between 20 and 60 °C by testing single lap joints formed with stainless steel substrates. It was found that increasing the concentration of the UPy-HMDI-HEMA cross-linker leads to improved mechanical and adhesive properties at elevated temperatures. Concurrently, the reversibility of the bond formation remained unaffected, where rebonded samples displayed the same adhesive strength as regularly bonded samples. Debonding on demand abilities were also tested exemplarily for one copolymer, which for light-induced debonding experiments was blended with a UV-absorber that served as light-heat converter. Single lap joints were subjected to a constant force and heated or irradiated with UV light until debonding occurred. The necessary debonding temperature was comparable for direct heating and UV irradiation and varied between 28 and 82 °C, depending on the applied force. The latter also influenced the debonding time, which under the chosen conditions ranged from 30 s to 12 min.

  12. Comparison of Different Energy Levels of Er:YAG Laser Regarding Intrapulpal Temperature Change During Safe Ceramic Bracket Removal.

    Science.gov (United States)

    Nalbantgil, Didem; Tozlu, Murat; Oztoprak, Mehmet Oguz

    2018-04-01

    This study was done to compare the intrapulpal temperature change generated by different energy levels of Er:YAG laser used during debonding of ceramic brackets and find the most suitable level for clinical use. Eighty polycrystalline alumina brackets were bonded on bovine incisor teeth, which were randomly divided into 4 groups of 20. One group was assigned as control. In the study groups, after laser exposure with 2, 4, or 6 Watt energy levels, brackets were debonded using an Instron Universal Testing machine. Adhesive remnant index (ARI) scores were recorded to evaluate the site of debonding. To assess intrapulpal thermal increase, 60 human premolar teeth that were prepared in the same way, at the same energy levels, by a thermocouple were used. When the debonding forces, intrapulpal temperature increases, and ARI of the groups were examined, statistically significant difference was observed between the groups. Mean temperature increases of 0.67°C ± 0.12°C, 1.25°C ± 0.16°C, and 2.36°C ± 0.23°C were recorded for the 2, 4, and 6 Watt laser groups. The mean shear bond strength was 21.35 ± 3.43 megapascals (MPa) for the control group, whereas they were 8.79 ± 2.47, 3.28 ± 0.73, and 2.46 ± 0.54 MPa for the 2, 4, and 6 Watt laser groups, respectively. Four watts is the most efficient and safe energy level to be used, utilizing Er:YAG laser with water cooling spray for 6 sec by scanning method during debonding of polycrystalline alumina brackets without any carbonization effects and detrimental temperature changes at debond sites.

  13. Adhesive performance of precoated brackets after expiration.

    Science.gov (United States)

    Cloud, Cayce C; Trojan, Terry M; Suliman, Sam N; Tantbirojn, Daranee; Versluis, Antheunis

    2016-03-01

    To evaluate adhesive performance in terms of debonding forces of precoated metal and ceramic brackets 4 years after expiration. Buccal and lingual surfaces of embedded extracted maxillary premolars were etched with 34% Tooth Conditioner Gel (Dentsply Caulk, Milford, Del), rinsed, and dried. Transbond MIP (3M Unitek, Monrovia, Calif) was applied prior to placing adhesive precoated brackets (APC II Victory stainless steel and APC Plus Clarity ceramic brackets, 3M Unitek). The preexpiration brackets had 29-35 months before, and the postexpiration brackets were 45-52 months past, their expiration dates. Sample size was 17-21 per group. Debonding forces were determined by subjecting the bonded brackets to a shear force in a universal testing machine. Debonding forces were compared using two-way ANOVA. Debonded surfaces were examined under a stereomicroscope to determine failure modes, which were compared using the chi-square test. No statistically significant difference was found in debonding forces (P  =  .8581) or failure modes (P  =  .4538) between expired and unexpired brackets. Metal brackets required statistically significantly higher debonding forces than did ceramic brackets (P  =  .0001). For both expired and unexpired brackets, failure modes were mostly cohesive in the adhesive layer for ceramic brackets, and mixed between adhesive and cohesive failure in the adhesive layer for metal brackets. Adhesive precoated brackets did not have any reduction in enamel-adhesion properties up to 4 years after their expiration date. Extended shelf life testing for precoated dental brackets may be worth considering.

  14. Development and Validation of a Constitutive Model for Dental Composites during the Curing Process

    Science.gov (United States)

    Wickham Kolstad, Lauren

    Debonding is a critical failure of a dental composites used for dental restorations. Debonding of dental composites can be determined by comparing the shrinkage stress of to the debonding strength of the adhesive that bonds it to the tooth surface. It is difficult to measure shrinkage stress experimentally. In this study, finite element analysis is used to predict the stress in the composite during cure. A new constitutive law is presented that will allow composite developers to evaluate composite shrinkage stress at early stages in the material development. Shrinkage stress and shrinkage strain experimental data were gathered for three dental resins, Z250, Z350, and P90. Experimental data were used to develop a constitutive model for the Young's modulus as a function of time of the dental composite during cure. A Maxwell model, spring and dashpot in series, was used to simulate the composite. The compliance of the shrinkage stress device was also taken into account by including a spring in series with the Maxwell model. A coefficient of thermal expansion was also determined for internal loading of the composite by dividing shrinkage strain by time. Three FEA models are presented. A spring-disk model validates that the constitutive law is self-consistent. A quarter cuspal deflection model uses separate experimental data to verify that the constitutive law is valid. Finally, an axisymmetric tooth model is used to predict interfacial stresses in the composite. These stresses are compared to the debonding strength to check if the composite debonds. The new constitutive model accurately predicted cuspal deflection data. Predictions for interfacial bond stress in the tooth model compare favorably with debonding characteristics observed in practice for dental resins.

  15. Explicit modeling the progressive interface damage in fibrous composite: Analytical vs. numerical approach

    DEFF Research Database (Denmark)

    Kushch, V.I.; Shmegera, S.V.; Mishnaevsky, Leon

    2011-01-01

    of the multiple inclusion problem by means of complex potentials. The second, finite element model of FRC is based on the cohesive zone model of interface. Simulation of progressive debonding in FRC using the many-fiber models of composite has been performed. The advantageous features and applicability areas...... of both models are discussed. It has been shown that the developed models provide detailed analysis of the progressive debonding phenomena including the interface crack cluster formation, overall stiffness reduction and induced anisotropy of the effective elastic moduli of composite....

  16. Treatment of post-orthodontic white spot lesions with casein phosphopeptide-stabilised amorphous calcium phosphate

    DEFF Research Database (Denmark)

    Bröchner, Ann; Christensen, Carsten; Kristensen, Bjarne

    2010-01-01

    This study aims to investigate the effect of topical applications of 10% casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on white spot lesions (WSL) detected after treatment with fixed orthodontic appliances. Sixty healthy adolescents with >/=1 clinically visible WSL at debonding were...... findings were largely reflected by the clinical scores. No side effects were reported. Topical treatment of white spot lesions after debonding of orthodontic appliances with a casein phosphopeptide-stabilised amorphous calcium phosphate agent resulted in significantly reduced fluorescence and a reduced...

  17. Prestressed CFRP Fabrics for Flexural Strengthening of Concrete Beams with an Easy Prestressing Technique

    Science.gov (United States)

    Şakar, G.; Tanarslan, H. M.

    2014-09-01

    It is proposed to use prestressed CFRP plates for strengthening in order to prevent their debonding and thus to increase their strengthening efficiency. For this purpose, and easy-to-use piece of equipment was created. To determine the effectiveness of this method, an experimental program was carried out, and the effect of prestressed CFRP on the behavior and ultimate strength of reinforced concrete beams was examined in threepoint bending tests. A remarkable increase in their strength with debonding was seen for every specimen to which a prestressed CFRP plate had been applied.

  18. Tuneable adhesion through novel binder technologies

    NARCIS (Netherlands)

    Wouters, M.E.L.; Burghoorn, M.M.A.; Ingenhut, B.; Timmer, K.; Rentrop, C.H.A.; Bots, T.L.; Oosterhuis, G.; Fischer, H.R.

    2011-01-01

    A reversible crosslinking mechanism enabling bonding and debonding of adhesives and coatings based on Diels-Alder chemistry is described. The Diels-Alder compounds form a covalently crosslinked network at low temperatures that break at elevated temperatures. As a result, the adhesive exhibits good

  19. A new theoretical model of the quasistatic single-fiber pullout problem: Analysis of stress field

    DEFF Research Database (Denmark)

    Qing, Hai

    2013-01-01

    with respect to the axial direction is neglected for shear stress-strain relationship. The general solutions of the axial and radial displacements in both fibre and matrix are obtained in explicit forms. In the debonded region, a modified Coulomb's friction law, in which the frictional coefficient...

  20. Behaviour of E-glass fibre reinforced vinylester resin composites ...

    Indian Academy of Sciences (India)

    A well-defined impact fatigue (S–N) behaviour, having a progressive endurance below the threshold single cycle impact fracture stress with decreasing applied stress has been demonstrated. Fractographic analysis revealed fracture by primary debonding having fibre breakage and pullout at the tensile zone, but a shear ...

  1. Experimental and numerical study of the micro-mechanical failure in composites

    DEFF Research Database (Denmark)

    Ashouri Vajari, Danial; Martyniuk, Karolina; Sørensen, Bent F.

    2013-01-01

    The fibre/matrix interfacial debonding is found to be the first microscale failure mechanism leading to subsequent macroscale transverse cracks in composite materials under tensile load. In this paper, the micromechanical interface failure in fiber-reinforced composites is studied experimentally ...

  2. A quasistatic mixed-mode delamination model

    Czech Academy of Sciences Publication Activity Database

    Roubíček, Tomáš; Mantič, V.; Panagiotopoulos, C.G.

    2013-01-01

    Roč. 6, č. 2 (2013), s. 591-610 ISSN 1937-1632 R&D Projects: GA ČR GAP201/10/0357 Institutional support: RVO:61388998 Keywords : rate-independent interface fracture * inelastic debonding * interface plasticity Subject RIV: BA - General Mathematics http://aimsciences.org/journals/pdfs.jsp?paperID=7907&mode=full

  3. Improving the durability of the optical fiber sensor based on strain transfer analysis

    Science.gov (United States)

    Wang, Huaping; Jiang, Lizhong; Xiang, Ping

    2018-05-01

    To realize the reliable and long-term strain detection, the durability of optical fiber sensors has attracted more and more attention. The packaging technique has been considered as an effective method, which can enhance the survival ratios of optical fiber sensors to resist the harsh construction and service environment in civil engineering. To monitor the internal strain of structures, the embedded installation is adopted. Due to the different material properties between host material and the protective layer, the monitored structure embedded with sensors can be regarded as a typical model containing inclusions. Interfacial characteristic between the sensor and host material exists obviously, and the contacted interface is prone to debonding failure induced by the large interfacial shear stress. To recognize the local interfacial debonding damage and extend the effective life cycle of the embedded sensor, strain transfer analysis of a general three-layered sensing model is conducted to investigate the failure mechanism. The perturbation of the embedded sensor on the local strain field of host material is discussed. Based on the theoretical analysis, the distribution of the interfacial shear stress along the sensing length is characterized and adopted for the diagnosis of local interfacial debonding, and the sensitive parameters influencing the interfacial shear stress are also investigated. The research in this paper explores the interfacial debonding failure mechanism of embedded sensors based on the strain transfer analysis and provides theoretical basis for enhancing the interfacial bonding properties and improving the durability of embedded optical fiber sensors.

  4. Effect of One-Step and Multi-Steps Polishing System on Enamel Roughness

    Directory of Open Access Journals (Sweden)

    Cynthia Sumali

    2013-07-01

    Full Text Available Normal 0 false false false MicrosoftInternetExplorer4 The final procedures of orthodontic treatment are bracket debonding and cleaning the remaining adhesive. Multi-step polishing system is the most common method used. The disadvantage of that system is long working time, because of the stages that should be done. Therefore, dental material manufacturer make an improvement to the system, to reduce several stages into one stage only. This new system is known as one-step polishing system. Objective: To compare the effect of one-step and multi-step polishing system on enamel roughness after orthodontic bracket debonding. Methods: Randomized control trial was conducted included twenty-eight maxillary premolar randomized into two polishing system; one-step OptraPol (Ivoclar, Vivadent and multi-step AstroPol (Ivoclar, Vivadent. After bracket debonding, the remaining adhesive on each group was cleaned by subjective polishing system for ninety seconds using low speed handpiece. The enamel roughness was subjected to profilometer, registering two roughness parameters (Ra, Rz. Independent t-test was used to analyze the mean score of enamel roughness in each group. Results: There was no significant difference of enamel roughness between one-step and multi-step polishing system (p>0.005. Conclusion: One-step polishing system can produce a similar enamel roughness to multi-step polishing system after bracket debonding and adhesive cleaning.DOI: 10.14693/jdi.v19i3.136

  5. Examining Thermally Sprayed Coats By Fluorescence Microscopy

    Science.gov (United States)

    Street, Kenneth W., Jr.; Leonhardt, Todd A.

    1994-01-01

    True flaws distinquished from those induced by preparation of specimens. Fluorescence microscopy reveals debonding, porosity, cracks, and other flaws in specimens of thermally sprayed coating materials. Specimen illuminated, and dye it contains fluoresces, emitting light at different wavelength. Filters emphasize contrast between excitation light and emission light. Specimen viewed directly or photographed on color film.

  6. Effect of immediate and delayed dentin sealing on the fracture strength, failure type and Weilbull characteristics of lithiumdisilicate laminate veneers

    NARCIS (Netherlands)

    Gresnigt, Marco M.M.; Cune, Marco S.; de Roos, Joanne G.; Özcan, Mutlu

    OBJECTIVES: Adhesion on dentin is less reliable than on enamel, which could affect the durability of laminate veneers (LV). Immediate dentin sealing (IDS) is suggested instead of delayed dentin sealing (DDS) to overcome hypersensitivity and prevent debonding from dentin. This study evaluated the

  7. Reactive transport of CO2-rich fluids in simulated wellbore interfaces : Flow-through experiments on the 1–6 m length scale

    NARCIS (Netherlands)

    Wolterbeek, Timotheus K.T.; Peach, Colin J.; Raoof, Amir; Spiers, Christopher J.

    2016-01-01

    Debonding at casing-cement interfaces poses a leakage pathway risk that may compromise well integrity in CO2 storage systems. The present study addresses the effects of long-range, CO2-induced, reactive transport on the conductance of such interfacial pathways. This is done by means of reactive

  8. Adhesive Properties of Bonded Orthodontic Retainers to Enamel : Stainless Steel Wire vs Fiber-reinforced Composites

    NARCIS (Netherlands)

    Foek, Dave Lie Sam; Krebs, Eliza; Sandham, John; Ozcan, Mutlu

    2009-01-01

    Purpose: The objectives of this study were to compare the bond strength of a stainless steel orthodontic wire vs various fiber-reinforced composites (FRC) used as orthodontic retainers on enamel, analyze the failure types after debonding, and investigate the influence of different application

  9. Design Analysis of the Mixed Mode Bending Sandwich Specimen

    DEFF Research Database (Denmark)

    Quispitupa, Amilcar; Berggreen, Christian; Carlsson, Leif A.

    2010-01-01

    A design analysis of the mixed mode bending (MMB) sandwich specimen for face–core interface fracture characterization is presented. An analysis of the competing failure modes in the foam cored sandwich specimens is performed in order to achieve face–core debond fracture prior to other failure modes...... for the chosen geometries and mixed mode loading conditions....

  10. State of residual stress in laser-deposited ceramic composite coatings on aluminum alloys

    NARCIS (Netherlands)

    Kadolkar, P. B.; Watkins, T. R.; De Hosson, J. Th. M.; Kooi, B. J.; Dahotre, N. B.

    The nature and magnitude of the residual stresses within laser-deposited titanium carbide (TiC) coatings on 2024 and 6061 aluminum (Al) alloys were investigated. Macro- and micro-stresses within the coatings were determined using an X-ray diffraction method. Owing to increased debonding between the

  11. Melt Drawing/Coating of Oxide Fibers for Composite Materials Applications

    National Research Council Canada - National Science Library

    Weber, J

    1996-01-01

    .... Fiber coatings were formed by pulsed excimer laser ablation. Push-out tests on coated fibers imbedded in a ceramic matrix gave small values of the debonding shear strength, tau d 25 MPa, for fibers coated with 2 MgO-SiO2 (enstatite...

  12. A practical approach to fracture analysis at the trailing edge of wind turbine rotor blades

    DEFF Research Database (Denmark)

    Eder, Martin Alexander; Bitsche, Robert; Nielsen, Magda

    2014-01-01

    Wind turbine rotor blades are commonly manufactured from composite materials by a moulding process. Typically, the wind turbine blade is produced in two halves, which are eventually adhesively joined along their edges. Investigations of operating wind turbine blades show that debonding...

  13. Modeling of Sylgard Adhesive Strength

    Energy Technology Data Exchange (ETDEWEB)

    Stevens, Ralph Robert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-02-03

    Sylgard is the name of a silicone elastomeric potting material manufactured by Dow Corning Corporation.1 Although the manufacturer cites its low adhesive strength as a feature of this product, thin layers of Sylgard do in fact have a non-negligible strength, which has been measured in recent tensile and shear debonding tests. The adhesive strength of thin layers of Sylgard potting material can be important in applications in which components having signi cantly di erent thermal expansion properties are potted together, and the potted assembly is subjected to temperature changes. The tensile and shear tractions developed on the potted surfaces of the components can cause signi cant internal stresses, particularly for components made of low-strength materials with a high area-to-volume ratio. This report is organized as follows: recent Sylgard debonding tests are rst brie y summarized, with particular attention to the adhesion between Sylgard and PBX 9501, and also between Sylgard and aluminum. Next, the type of numerical model that will be used to simulate the debonding behavior exhibited in these tests is described. Then the calibration of the debonding model will be illustrated. Finally, the method by which the model parameters are adjusted (scaled) to be applicable to other, non- tested bond thicknesses is summarized, and all parameters of the model (scaled and unscaled) are presented so that other investigators can reproduce all of the simulations described in this report as well as simulations of the application of interest.

  14. Failure phenomena in fibre-reinforced composites. Part 6: a finite element study of stress concentrations in unidirectional carbon fibre-reinforced epoxy composites

    NARCIS (Netherlands)

    van den Heuvel, P.W.J.; Goutianos, S.; Young, R.J.; Peijs, A.A.J.M.

    2004-01-01

    A three-dimensional (3-D) finite element (FE) analysis of the stress situation around a fibre break in a unidirectional carbon fibre-reinforced epoxy composite has been performed. Two cases were considered: (i) good fibre/matrix adhesion and (ii) fibre/matrix debonding. In the case of good adhesion,

  15. Repeated bonding of fixed retainer increases the risk of enamel fracture.

    Science.gov (United States)

    Chinvipas, Netrporn; Hasegawa, Yuh; Terada, Kazuto

    2014-01-01

    The aim of this study was to investigate the influences of repeated bonding, using 2 different orthodontic adhesive systems, on the shear bond strength (SBS) and the enamel surface morphology. Sixty premolars were divided into 2 groups (n = 30), and either Transbond XT (T group) or Fuji Ortho LC (F group) adhesives were used. SBS was measured 24 h after bonding, using a universal testing machine. Then, the enamel surfaces were investigated and the mode of failure was described using adhesive remnant index (ARI) scores. After each debonding, 10 teeth from each group were examined by scanning electron microscopy to determine the penetration of adhesives, the length of resin tags, and the state of the enamel surface. The other teeth were subjected to two more bonding/debonding procedures. In T group, the second debonding sequences had significantly higher bond strengths than the other sequences. The length of resin tags was greatest in the second debonding sequence, although there was no significant difference. In F group, the SBS increased with further rebonding and the failure mode tended towards cohesive failure. In both groups, the ARI scores increased with rebonding. Enamel loss could have occurred with both adhesives, although the surfaces appeared unchanged to the naked eye. From this study, we suggest that enamel damage caused by repeated bonding is of concern. To prevent bond failure, we should pay attention to the adhesion method used for bondable retainers.

  16. Appendix B

    DEFF Research Database (Denmark)

    Christensen, F. A.; Brincker, Rune

    1999-01-01

    In this appendix the failure behaviour of lightly reinforced concrete beams is investigated. A numerical model based on the fictitious crack approach according to Hillerborg [1] is established in order to estimate the load-deflection curve for lightly reinforced concrete beams. The debonding...

  17. Mechanical aspects of degree of cement bonding and implant wedge effect.

    Science.gov (United States)

    Yoon, Yong-San; Oxland, Thomas R; Hodgson, Antony J; Duncan, Clive P; Masri, Bassam A; Choi, Donok

    2008-11-01

    The degree of bonding between the femoral stem and cement in total hip replacement remains controversial. Our objective was to determine the wedge effect by debonding and stem taper angle on the structural behavior of axisymmetric stem-cement-bone cylinder models. Stainless steel tapered plugs with a rough (i.e. bonded) or smooth (i.e. debonded) surface finish were used to emulate the femoral stem. Three different stem taper angles (5 degrees , 7.5 degrees , 10 degrees ) were used for the debonded constructs. Non-tapered and tapered (7.5 degrees ) aluminum cylindrical shells were used to emulate the diaphyseal and metaphyseal segments of the femur. The cement-aluminum cylinder interface was designed to have a shear strength that simulated bone-cement interfaces ( approximately 8MPa). The test involved applying axial compression at a rate of 0.02mm/s until failure. Six specimens were tested for each combination of the variables. Finite element analysis was used to enhance the understanding of the wedge effect. The debonded stems sustained about twice as much load as the bonded stem, regardless of taper angle. The metaphyseal model carried 35-50% greater loads than the diaphyseal models and the stem taper produced significant differences. Based on the finite element analysis, failure was most probably by shear at the cement-bone interface. Our results in this simplified model suggest that smooth (i.e. debonded) stems have greater failure loads and will incur less slippage or shear failure at the cement-bone interface than rough (i.e. bonded) stems.

  18. Suitability of orthodontic brackets for rebonding and reworking following removal by air pressure pulses and conventional debracketing techniques.

    Science.gov (United States)

    Knösel, Michael; Mattysek, Simone; Jung, Klaus; Kubein-Meesenburg, Dietmar; Sadat-Khonsari, Reza; Ziebolz, Dirk

    2010-07-01

    To test the null hypothesis that there are no significant differences in the reusability of debonded brackets with regard to debonding technique and adhesive used. Ninety-six osteotomed third molars were randomly assigned to two study groups (n = 48) for bonding of a 0.018-inch bracket (Ormesh, Ormco) with either a composite adhesive (Mono-Lok2; RMO) or a glass ionomer cement (GIC; Fuji Ortho LC;GC). Each of these two groups were then randomly divided into four subgroups (n = 12) according to the method of debonding using (1) bracket removal pliers (BRP; Dentaurum), (2) a side cutter (SC; Dentaurum), (3) a lift-off debracketing instrument (LODI; 3M-Unitek), or (4) an air pressure pulse device (CoronaFlex; KaVo). The brackets were subsequently assessed visually for reusability and reworkability with 2x magnification and by pull testing with a 0.017- x 0.025-inch steel archwire. The proportions of reusable brackets were individually compared in terms of mode of removal and with regard to adhesives using the Fisher exact test (alpha = 5%). The null hypothesis was rejected. Not taking into account the debonding method, brackets bonded with GIC were judged to a significant extent (81%; n = 39; P < .01) to be reworkable compared with those bonded with composite (56%; n = 27). All brackets in both adhesive groups removed with either the LODI or the CoronaFlex were found to be reusable, whereas 79% (46%) of the brackets removed with the BRP (SC) were not. The proportion of reusable brackets differed significantly between modes of removal (P < .01). With regard to bracket reusability, the SC and the BRP cannot be recommended for debonding brackets, especially in combination with a composite adhesive.

  19. Linear rheology of cross-linked polypropylene oxide as a pressure sensitive adhesive

    DEFF Research Database (Denmark)

    Jensen, Mette Krog; Bach, A.; Hassager, Ole

    2009-01-01

    are carefully considered. Two main mechanisms must be considered when studying adhesives, that is the debonding and bonding mechanisms. Linear rheology is used to study the debonding mechanisms to gain better understanding of the peeling process of the PSAs. A variety of PSAs are prepared by mixing a linear......-linked networks. The adhesive performance was tested with 90 degrees peel tests at three peel rates and thicknesses, and it was observed that the peel force varies with r, M and f and also the peel rate. The fundamental viscoelastic parameters that govern the PSA performance of cross-linked systems were used...... to state an empirical relation for the peel force. The relation is combining the peel force with the loss tangent at the peel frequency and the equilibrium modulus. Based on this, basic guidelines for selecting the appropriate polymer/cross-linker system to achieve the target performance are given....

  20. Characterization of Impact Damage in Ultra-High Performance Concrete Using Spatially Correlated Nanoindentation/SEM/EDX

    Science.gov (United States)

    Moser, R. D.; Allison, P. G.; Chandler, M. Q.

    2013-12-01

    Little work has been done to study the fundamental material behaviors and failure mechanisms of cement-based materials including ordinary Portland cement concrete and ultra-high performance concretes (UHPCs) under high strain impact and penetration loads at lower length scales. These high strain rate loadings have many possible effects on UHPCs at the microscale and nanoscale, including alterations in the hydration state and bonding present in phases such as calcium silicate hydrate, in addition to fracture and debonding. In this work, the possible chemical and physical changes in UHPCs subjected to high strain rate impact and penetration loads were investigated using a novel technique wherein nanoindentation measurements were spatially correlated with images using scanning electron microscopy and chemical composition using energy dispersive x-ray microanalysis. Results indicate that impact degrades both the elastic modulus and indentation hardness of UHPCs, and in particular hydrated phases, with damage likely occurring due to microfracturing and debonding.

  1. Interfacial (Fiber-matrix) Properties of High-strength Mortar (150 MPa) from Fiber Pullout

    DEFF Research Database (Denmark)

    Shannag, M.J.; Brincker, Rune; Hansen, Will

    1996-01-01

     The steel fiber-matrix properties of high-strength mortar (150 MPa), such as DSP (densified small particle), are obtained and compared to an ordinary strength mortar (40 MPa) using a specially designed fiber pullout apparatus. A new method for estimating the debonding energy of the interfacial z......-strength DSP mortar has significantly improved interfacial properties compared to ordinary strength mortar. These results are important in the understanding of the role of steel fibers in improving the tensile properties of high-strength, brittle, cement-matrix composites....... The steel fiber-matrix properties of high-strength mortar (150 MPa), such as DSP (densified small particle), are obtained and compared to an ordinary strength mortar (40 MPa) using a specially designed fiber pullout apparatus. A new method for estimating the debonding energy of the interfacial...

  2. Damage assessment in a sandwich panel based on full-field vibration measurements

    Science.gov (United States)

    Seguel, F.; Meruane, V.

    2018-03-01

    Different studies have demonstrated that vibration characteristics are sensitive to debonding in composite structures. Nevertheless, one of the main restrictions of vibration measurements is the number of degrees of freedom that can be acquired simultaneously, which restricts the size of the damage that can be identified. Recent studies have shown that it is possible to use high-speed three-dimensional (3-D) digital image correlation (DIC) techniques for full-field vibration measurements. With this technique, it is possible to take measurements at thousands of points on the surface of a structure with a single snapshot. The present article investigates the application of full-field vibration measurements in the debonding assessment of an aluminium honeycomb sandwich panel. Experimental data from an aluminium honeycomb panel containing different damage scenarios is acquired by a high-speed 3-D DIC system; four methodologies to compute damage indices are evaluated: mode shape curvatures, uniform load surface, modal strain energy and gapped smoothing.

  3. Fibre-matrix bond strength studies of glass, ceramic, and metal matrix composites

    Science.gov (United States)

    Grande, D. H.; Mandell, J. F.; Hong, K. C. C.

    1988-01-01

    An indentation test technique for compressively loading the ends of individual fibers to produce debonding has been applied to metal, glass, and glass-ceramic matrix composites; bond strength values at debond initiation are calculated using a finite-element model. Results are correlated with composite longitudinal and interlaminar shear behavior for carbon and Nicalon fiber-reinforced glasses and glass-ceramics including the effects of matrix modifications, processing conditions, and high-temperature oxidation embrittlement. The data indicate that significant bonding to improve off-axis and shear properties can be tolerated before the longitudinal behavior becomes brittle. Residual stress and other mechanical bonding effects are important, but improved analyses and multiaxial interfacial failure criteria are needed to adequately interpret bond strength data in terms of composite performance.

  4. Fluorescence microscopy for the characterization of structural integrity

    Science.gov (United States)

    Street, Kenneth W.; Leonhardt, Todd A.

    1991-01-01

    The absorption characteristics of light and the optical technique of fluorescence microscopy for enhancing metallographic interpretation are presented. Characterization of thermally sprayed coatings by optical microscopy suffers because of the tendency for misidentification of the microstructure produced by metallographic preparation. Gray scale, in bright field microscopy, is frequently the only means of differentiating the actual structural details of porosity, cracking, and debonding of coatings. Fluorescence microscopy is a technique that helps to distinguish the artifacts of metallographic preparation (pullout, cracking, debonding) from the microstructure of the specimen by color contrasting structural differences. Alternative instrumentation and the use of other dye systems are also discussed. The combination of epoxy vacuum infiltration with fluorescence microscopy to verify microstructural defects is an effective means to characterize advanced materials and to assess structural integrity.

  5. Nondestructive Evaluation of Carbon Fiber Reinforced Polymer Composites Using Reflective Terahertz Imaging

    Directory of Open Access Journals (Sweden)

    Jin Zhang

    2016-06-01

    Full Text Available Terahertz (THz time-domain spectroscopy (TDS imaging is considered a nondestructive evaluation method for composite materials used for examining various defects of carbon fiber reinforced polymer (CFRP composites and fire-retardant coatings in the reflective imaging modality. We demonstrate that hidden defects simulated by Teflon artificial inserts are imaged clearly in the perpendicular polarization mode. The THz TDS technique is also used to measure the thickness of thin fire-retardant coatings on CFRP composites with a typical accuracy of about 10 micrometers. In addition, coating debonding is successfully imaged based on the time-delay difference of the time-domain waveforms between closely adhered and debonded sample locations.

  6. Interfacial characterization of CVI-SiC/SiC composites

    International Nuclear Information System (INIS)

    Yang, W.; Kohyama, A.; Noda, T.; Katoh, Y.; Hinoki, T.; Araki, H.; Yu, J.

    2002-01-01

    The mechanical properties of the interfaces of two families of chemical vapor infiltration SiC/SiC composites, advanced Tyranno-SA and Hi-Nicalon fibers reinforced SiC/SiC composites with various carbon and SiC/C interlayers, were investigated by single fiber push-out/push-back tests. Interfacial debonding and fibers sliding mainly occurred adjacent to the first carbon layer on the fibers. The interfacial debonding strengths and frictional stresses for both Tyranno-SA/SiC and Hi-Nicalon/SiC composites were correlated with the first carbon layer thickness. Tyranno-SA/SiC composites exhibited much larger interfacial frictional stresses compared to Hi-Nicalon/SiC composites. This was assumed to be mainly contributed by the rather rough surface of the Tyranno-SA fiber

  7. Bonding techniques for flexural strengthening of R.C. beams using CFRP laminates

    Directory of Open Access Journals (Sweden)

    Alaa Morsy

    2013-09-01

    Full Text Available This paper presents an experimental study of an alternative method of attaching FRP laminates to reinforced concrete beams by the way of fasting steel rivets through the FRP laminate and concrete substrate. Five full scale R.C. beams were casted and strengthened in flexural using FRP laminate bonded with conventional epoxy and compared with other beams strengthened with FRP laminate and bonded with fastener “steel rivets” of 50 mm length and 10 mm diameter. Based on experimental evidence the beam strengthened with conventional bonding methods failed due to de-bonding with about 13% increase over the un-strengthened beam. On the other hand, the beams strengthened with FRP laminate and bonded by four steel fastener rivets only failed by de-bonding also but at higher flexural capacity with increase 19% over the un-strengthened beam.

  8. Face/core interface fracture characterization of mixed mode bending sandwich specimens

    DEFF Research Database (Denmark)

    Quispitupa, Amilcar; Berggreen, Christian; Carlsson, L.A.

    2011-01-01

    and PVC H45, H100 and H250 foam core materials were evaluated. A methodology to perform precracking on fracture specimens in order to achieve a sharp and representative crack front is outlined. The mixed mode loading was controlled in the mixed mode bending (MMB) test rig by changing the loading......Debonding of the core from the face sheets is a critical failure mode in sandwich structures. This paper presents an experimental study on face/core debond fracture of foam core sandwich specimens under a wide range of mixed mode loading conditions. Sandwich beams with E‐glass fibre face sheets...... application point (lever arm distance). Finite element analysis was performed to determine the mode‐mixity at the crack tip. The results showed that the face/core interface fracture toughness increased with increased mode II loading. Post failure analysis of the fractured specimens revealed that the crack...

  9. Stress distribution in a transversely loaded cross-shaped single fiber SCS-6/Ti-6Al-4V composite

    International Nuclear Information System (INIS)

    Warrier, S.G.; Gundel, D.B.; Majumdar, B.S.; Miracle, D.B.

    1996-01-01

    In most structural applications utilizing fiber reinforced metal matrix composites (MMCs), the mechanical response normal to the fiber direction has to be considered. The transverse response is very sensitive to the interface bond strength, which has commonly been determined by testing straight-sided 90 degree specimens and interpreting debond initiation from the knee in the stress-strain curve as well as from a sudden drop in the Poisson's ratio. In an attempt to modify the debond initiation site to an internal location free of uncharacteristic states of stress, a cross-shaped specimen has been developed. Experiments conducted by Gundel et al. indicated that this geometry was successful in obtaining the appropriate crack initiation site. In the present study, finite element analysis (FEA) was done on the cross-shaped specimen to obtain the stress distribution in the composite under transverse loading, in an effort to corroborate the success of this geometry in determining the true transverse response of the composite

  10. Quantitative defects detection in wind turbine blade using optical infrared thermography

    Energy Technology Data Exchange (ETDEWEB)

    Kwaon, Koo Ahn [School of Aerospace System Engineering, UST, Daejeon (Korea, Republic of); Choi, Man Yong; Park, Hee Sang; Park, Jeong Hak; Huh, Yong Hak; Choi, Won Jai [Safety Measurement Center, Korea Research Institute of Standards and Science, Daejeon (Korea, Republic of)

    2015-02-15

    A wind turbine blade is an important component in wind-power generation, and is generally exposed to harsh environmental conditions. Ultrasonic inspection is mainly used to inspect such blades, but it has been difficult to quantify defect sizes in complicated composite structures. Recently, active infrared thermography has been widely studied for inspecting composite structures, in which thermal energy is applied to an object, and an infrared camera detects the energy emitted from it. In this paper, a calibration method for active optical lock-in thermography is proposed to quantify the size. Inclusion, debonding and wrinkle defects, created in a wind blade for 100 kW wind power generation, were all successfully detected using this method. In particular, a 50.0 mm debonding defect was sized with 98.0% accuracy.

  11. A micromechanics model for bread dough

    Science.gov (United States)

    Mohammed, M. A. P.; Tarleton, E.; Charalambides, M. N.; Williams, J. G.

    2015-01-01

    The mechanical behaviour of dough and gluten was studied in an effort to investigate whether bread dough can be treated as a two phase (starch and gluten) composite material. The dough and gluten show rate dependent behaviour under tension, compression and shear tests, and non-linear unloading-reloading curves under cyclic compression tests. There is evidence from cryo-Scanning Electron Microscopy (SEM) that damage in the form of debonding between starch and gluten occurs when the sample is stretched. A composite finite element model was developed using starch as filler and gluten as matrix. The interaction between the starch and gluten was modelled as cohesive contact. The finite element analysis predictions agree with trends seen in experimental test data on dough and gluten, further evidence that debonding of starch and gluten is a possible damage mechanism in dough.

  12. A micromechanics model for bread dough

    International Nuclear Information System (INIS)

    Mohammed, M. A. P; Tarleton, E.; Charalambides, M. N.; Williams, J. G.

    2015-01-01

    The mechanical behaviour of dough and gluten was studied in an effort to investigate whether bread dough can be treated as a two phase (starch and gluten) composite material. The dough and gluten show rate dependent behaviour under tension, compression and shear tests, and non-linear unloading-reloading curves under cyclic compression tests. There is evidence from cryo-Scanning Electron Microscopy (SEM) that damage in the form of debonding between starch and gluten occurs when the sample is stretched. A composite finite element model was developed using starch as filler and gluten as matrix. The interaction between the starch and gluten was modelled as cohesive contact. The finite element analysis predictions agree with trends seen in experimental test data on dough and gluten, further evidence that debonding of starch and gluten is a possible damage mechanism in dough

  13. A micromechanics model for bread dough

    Energy Technology Data Exchange (ETDEWEB)

    Mohammed, M. A. P; Tarleton, E.; Charalambides, M. N.; Williams, J. G. [Imperial College London, Mechanical Engineering Department, London SW7 2AZ (United Kingdom)

    2015-01-22

    The mechanical behaviour of dough and gluten was studied in an effort to investigate whether bread dough can be treated as a two phase (starch and gluten) composite material. The dough and gluten show rate dependent behaviour under tension, compression and shear tests, and non-linear unloading-reloading curves under cyclic compression tests. There is evidence from cryo-Scanning Electron Microscopy (SEM) that damage in the form of debonding between starch and gluten occurs when the sample is stretched. A composite finite element model was developed using starch as filler and gluten as matrix. The interaction between the starch and gluten was modelled as cohesive contact. The finite element analysis predictions agree with trends seen in experimental test data on dough and gluten, further evidence that debonding of starch and gluten is a possible damage mechanism in dough.

  14. Strengthening of Shear Walls

    DEFF Research Database (Denmark)

    Hansen, Christian Skodborg

    The theory for concrete structures strengthened with fiber reinforced polymer materials has been developing for approximately two decades, and there are at the present time numerous guidelines covering strengthening of many commonly encountered structural building elements. Strengthening of in...... that describes a unit width strip of a strengthened disk. The unit width strip is named a strengthened concrete tension member and contains a single tensile crack and four debonding cracks. Analysis of the member results in closed form expressions for the load-crack opening relationship. Further analysis...... of the response, results in the ability to determine and characterize the two-way crack propagation, i.e. the relationship between tensile cracking in the concrete and interface debonding between strengthening and concrete. Using the load-crack opening relationship from the strengthened concrete tension member...

  15. Energetic versus maximally-dissipative local solutions of a quasi-static rate-independent mixed-mode delamination model

    Czech Academy of Sciences Publication Activity Database

    Vodička, R.; Mantič, V.; Roubíček, Tomáš

    2014-01-01

    Roč. 49, č. 12 (2014), s. 2933-2963 ISSN 0025-6455 R&D Projects: GA ČR GAP201/10/0357 Institutional support: RVO:61388998 Keywords : adhesive contact * debonding interface fracture * interface damage Subject RIV: BA - General Mathematics Impact factor: 1.949, year: 2014 http://link.springer.com/article/10.1007/s11012-014-0045-4?no-access=true

  16. Microleakage of composite crowns luted on CAD/CAM-milled human molars: a new method for standardized in vitro tests.

    Science.gov (United States)

    Schlenz, Maximiliane Amelie; Schmidt, Alexander; Rehmann, Peter; Niem, Thomas; Wöstmann, Bernd

    2018-04-24

    To investigate debonding of full crowns made of CAD/CAM composites, CAD/CAM technology was applied to manufacture standardized test abutments to increase the reproducibility of human teeth used in in vitro studies. A virtual test abutment and the corresponding virtual crown were designed and two STL data sets were generated. Sixty-four human third molars and CAD/CAM blocks were milled using a CNC machine. Crowns of four different composite blocks (Lava Ultimate (LU), Brilliant Crios (BC), Cerasmart (CS), Experimental (EX)) were adhesively bonded with their corresponding luting system (LU: Scotchbond Universal/RelyX Ultimate; BC: One Coat 7 Universal/DuoCem; CS: G-PremioBond/G-Cem LinkForce; EX: Experimental-Bond/Experimental-Luting-Cement). Half of the specimens were chemical-cured (CC) and the others were light-cured (LC). Afterwards, specimens were artificially aged in a chewing simulator (WL-tec, 1 million cycles, 50-500 N, 2 Hz, 37 °C). Finally, a dye penetration test was used to detect debonding. For inspection, the specimens were sliced, and penetration depth was measured with a digital microscope. Data were analyzed with the Mann-Whitney U test. No cases of total debonding were observed after cyclic loading. However, the LC specimens showed a significantly lower amount of leakage than the CC ones (p CAD/CAM technology in highly standardized test abutments for in vitro testing. For CAD/CAM composites, light curing should be performed. The success of a restoration depends on the long-term sealing ability of the luting materials, which avoids debonding along with microleakage. For CAD/CAM composites, separate light curing of the adhesive and luting composite is highly recommended.

  17. Ceramographic Examinations of Irradiated AGR-1 Fuel Compacts

    Energy Technology Data Exchange (ETDEWEB)

    Paul Demkowicz; Scott Ploger; John Hunn

    2012-05-01

    The AGR 1 experiment involved irradiating 72 cylindrical fuel compacts containing tri-structural isotropic (TRISO)-coated particles to a peak burnup of 19.5% fissions per initial metal atom with no in-pile failures observed out of almost 300,000 particles. Five irradiated AGR 1 fuel compacts were selected for microscopy that span a range of irradiation conditions (temperature, burnup, and fast fluence). These five compacts also included all four TRISO coating variations irradiated in the AGR experiment. The five compacts were cross-sectioned both transversely and longitudinally, mounted, ground, and polished after development of careful techniques for preserving particle structures against preparation damage. Approximately 40 to 80 particles within each cross section were exposed near enough to mid-plane for optical microscopy of kernel, buffer, and coating behavior. The microstructural analysis focused on kernel swelling and porosity, buffer densification and fracture, debonding between the buffer and inner pyrolytic carbon (IPyC) layers, and fractures in the IPyC and SiC layers. Three basic particle morphologies were established according to the extent of bonding between the buffer and IPyC layers: complete debonding along the interface (Type A), no debonding along the interface (Type B), and partial debonding (Type AB). These basic morphologies were subdivided according to whether the buffer stayed intact or fractured. The resulting six characteristic morphologies were used to classify particles within each cross section, but no spatial patterns were clearly observed in any of the cross-sectional morphology maps. Although positions of particle types appeared random within compacts, examining a total of 830 classified particles allowed other relationships among morphological types to be established.

  18. Shear Bond Strength of Metal Brackets to Zirconia Conditioned with Various Primer-Adhesive Systems

    Science.gov (United States)

    2016-07-01

    adhesion to ceramic crowns through chemical bonding presents a risk of prosthesis surface damage at debond (Falkensammer et al., 2013). When bonding...enamel. Traditional protocol associated with attaching brackets to enamel must be altered for ceramic crowns due to the dissimilarity in composition. The...Uniform Services University of the Health Sciences In Partial Fulfillment Of the Requirements For the Degree of MASTER OF SCIENCE By Michael

  19. Recent Developments in Assessing Microstructure-Sensitive Early Stage Fatigue of Polycrystals (Postprint)

    Science.gov (United States)

    2014-04-01

    can strongly affect formation of fatigue cracks. El Bartali et al. [7] quantified plastic strain at the grain scale in a duplex stainless steel and mea...finite ele- ment models for 304L stainless steel using EBSD measurements ta- ken on successive slices of microstructure through the thickness. Their work...inclusions in martensitic gear steel in the context of 3D polycrystal plasticity and nonlocal FIPs. Coupled effects of inclusion fracture/debonding and

  20. Ceramographic Examinations of Irradiated AGR-1 Fuel Compacts

    International Nuclear Information System (INIS)

    Demkowicz, Paul; Ploger, Scott; Hunn, John

    2012-01-01

    The AGR 1 experiment involved irradiating 72 cylindrical fuel compacts containing tri-structural isotropic (TRISO)-coated particles to a peak burnup of 19.5% fissions per initial metal atom with no in-pile failures observed out of almost 300,000 particles. Five irradiated AGR 1 fuel compacts were selected for microscopy that span a range of irradiation conditions (temperature, burnup, and fast fluence). These five compacts also included all four TRISO coating variations irradiated in the AGR experiment. The five compacts were cross-sectioned both transversely and longitudinally, mounted, ground, and polished after development of careful techniques for preserving particle structures against preparation damage. Approximately 40 to 80 particles within each cross section were exposed near enough to mid-plane for optical microscopy of kernel, buffer, and coating behavior. The microstructural analysis focused on kernel swelling and porosity, buffer densification and fracture, debonding between the buffer and inner pyrolytic carbon (IPyC) layers, and fractures in the IPyC and SiC layers. Three basic particle morphologies were established according to the extent of bonding between the buffer and IPyC layers: complete debonding along the interface (Type A), no debonding along the interface (Type B), and partial debonding (Type AB). These basic morphologies were subdivided according to whether the buffer stayed intact or fractured. The resulting six characteristic morphologies were used to classify particles within each cross section, but no spatial patterns were clearly observed in any of the cross-sectional morphology maps. Although positions of particle types appeared random within compacts, examining a total of 830 classified particles allowed other relationships among morphological types to be established.

  1. Sprayable Aerogel Bead Compositions With High Shear Flow Resistance and High Thermal Insulation Value

    Science.gov (United States)

    Ou, Danny; Trifu, Roxana; Caggiano, Gregory

    2013-01-01

    A sprayable aerogel insulation has been developed that has good mechanical integrity and lower thermal conductivity than incumbent polyurethane spray-on foam insulation, at similar or lower areal densities, to prevent insulation cracking and debonding in an effort to eliminate the generation of inflight debris. This new, lightweight aerogel under bead form can be used as insulation in various thermal management systems that require low mass and volume, such as cryogenic storage tanks, pipelines, space platforms, and launch vehicles.

  2. Tailoring Sandwich Face/Core Interfaces for Improved Damage Tolerance

    DEFF Research Database (Denmark)

    Lundsgaard-Larsen, Christian; Berggreen, Christian; Carlsson, Leif A.

    2010-01-01

    A face/core debond in a sandwich structure may propagate in the interface or kink into either the face or core. It is found that certain modifications of the face/core interface region influence the kinking behavior, which is studied experimentally in the present paper. A sandwich double cantilever....... The transition points where the crack kinks are identified and the influence of four various interface design modifications on the propagation path and fracture resistance are investigated....

  3. Effects of vacuum thermal cycling on mechanical and physical properties of high performance carbon/bismaleimide composite

    International Nuclear Information System (INIS)

    Yu Qi; Chen Ping; Gao Yu; Mu Jujie; Chen Yongwu; Lu Chun; Liu Dong

    2011-01-01

    Highlights: → The level of cross-links was improved to a certain extent. → The thermal stability was firstly improved and then decreased. → The transverse and longitudinal CTE were both determined by the degree of interfacial debonding. → The mass loss ratio increases firstly and then reaches a plateau value. → The surface morphology was altered and the surface roughness increased firstly and then decreased. → The transverse tensile strength was reduced. → The flexural strength increased firstly and then decreased to a plateau value. → The ILSS increased firstly and then decreased to a plateau value. - Abstract: The aim of this article was to investigate the effects of vacuum thermal cycling on mechanical and physical properties of high performance carbon/bismaleimide (BMI) composites used in aerospace. The changes in dynamic mechanical properties and thermal stability were characterized by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), respectively. The changes in linear coefficient of thermal expansion (CTE) were measured in directions perpendicular and parallel to the fiber direction, respectively. The outgassing behavior of the composites were examined. The evolution of surface morphology and surface roughness were observed by atomic force microscopy (AFM). Changes in mechanical properties including transverse tensile strength, flexural strength and interlaminar shear strength (ILSS) were measured. The results indicated that the vacuum thermal cycling could improve the crosslinking degree and the thermal stability of resin matrix to a certain extent, and induce matrix outgassing and thermal stress, thereby leading to the mass loss and the interfacial debonding of the composite. The degradation in transverse tensile strength was caused by joint effects of the matrix outgassing and the interfacial debonding, while the changes in flexural strength and ILSS were affected by a competing effect between the crosslinking degree

  4. The Effect of Two Soft Drinks on Bracket Bond Strength and on Intact and Sealed Enamel: An In Vitro Study

    OpenAIRE

    Pasha, Azam; Sindhu, D; Nayak, Rabindra S; Mamatha, J; Chaitra, K R; Vishwakarma, Swati

    2015-01-01

    Background and Objectives: This study was conducted to evaluate the effect of two soft drinks, Coca-Cola and Mirinda orange on bracket bond strength, on adhesive remnant on teeth after debonding the bracket, and to observe by means of scanning electron microscope (SEM) the effect of these drinks on intact and sealed enamel. Methods: 120 non-carious maxillary premolar teeth already extracted for Orthodontic purposes were taken and divided into three groups, i.e., Coca-Cola drink, Mirinda orang...

  5. Towards Rational Design Method for Strengthening of Concrete Structures by External Bonding

    Directory of Open Access Journals (Sweden)

    Furuuchi H.

    2012-01-01

    Full Text Available Many infrastructures need to be repaired or strengthened due to various reasons, such as unexpected deterioration and changes in performance requirement. This paper presents the following recent achievements by the authors’ group on design method for flexural strengthening of concrete structures by external bonding; (i fracture characteristics of interface between substrate concrete and cementitious overlay, (ii crack spacing of flexural strengthened beams, which affects debonding strength, (iii strengths of intermediate crack (IC debonding and end peeling, (iv strength of concrete cover separation, and (v effectiveness of strengthening by external bonding. A unified approach for flexural strengthening by steel plate, fiber reinforced polymer lami¬nate and cementitious overlay, for both intermediate crack (IC debonding, including end peeling, and concrete cover separation is pre¬sented with consideration of crack spacing in the streng¬thened members. Appropriate interfacial rough¬¬¬ness to achieve efficient interface bond property is clari¬fied and the concept of effectiveness of strengthen¬ing is proposed for better strengthening design.

  6. Probabilistic failure analysis of bone using a finite element model of mineral-collagen composites.

    Science.gov (United States)

    Dong, X Neil; Guda, Teja; Millwater, Harry R; Wang, Xiaodu

    2009-02-09

    Microdamage accumulation is a major pathway for energy dissipation during the post-yield deformation of bone. In this study, a two-dimensional probabilistic finite element model of a mineral-collagen composite was developed to investigate the influence of the tissue and ultrastructural properties of bone on the evolution of microdamage from an initial defect in tension. The probabilistic failure analyses indicated that the microdamage progression would be along the plane of the initial defect when the debonding at mineral-collagen interfaces was either absent or limited in the vicinity of the defect. In this case, the formation of a linear microcrack would be facilitated. However, the microdamage progression would be scattered away from the initial defect plane if interfacial debonding takes place at a large scale. This would suggest the possible formation of diffuse damage. In addition to interfacial debonding, the sensitivity analyses indicated that the microdamage progression was also dependent on the other material and ultrastructural properties of bone. The intensity of stress concentration accompanied with microdamage progression was more sensitive to the elastic modulus of the mineral phase and the nonlinearity of the collagen phase, whereas the scattering of failure location was largely dependent on the mineral to collagen ratio and the nonlinearity of the collagen phase. The findings of this study may help understanding the post-yield behavior of bone at the ultrastructural level and shed light on the underlying mechanism of bone fractures.

  7. Microstructure Deformation and Fracture Mechanism of Highly Filled Polymer Composites under Large Tensile Deformation

    International Nuclear Information System (INIS)

    Tao Zhangjiang; Ping Songdan; Mei Zhang; Cheng Zhaipeng

    2013-01-01

    The microstructure deformation and fracture mechanisms of particulate-filled polymer composites were studied based on microstructure observations in this paper. By using in-situ tensile test system under scanning electron microscopy, three different composites composed of polymer binder filled by three different types of particles, namely Al particles, AP particles and HMX particles, with the same total filler content were tested. The roles of initial microstructure damage and particle type on the microstructure deformation and damage are highlighted. The results show that microstructure damage starts with the growth of the initial microvoids within the binders or along the binder/particle interfaces. With the increase of strain, the microstructure damages including debonding at the particle/binder interface and tearing of the binder lead to microvoid coalescence, and finally cause an abrupt fracture of the samples. Coarse particles lead to an increase of debonding at the particle/binder interface both in the initial state and during the loading process, and angular particles promote interface debonding during the loading process.

  8. Interfacial damage identification of steel and concrete composite beams based on piezoceramic wave method.

    Science.gov (United States)

    Yan, Shi; Dai, Yong; Zhao, Putian; Liu, Weiling

    2018-01-01

    Steel-concrete composite structures are playing an increasingly important role in economic construction because of a series of advantages of great stiffness, good seismic performance, steel material saving, cost efficiency, convenient construction, etc. However, in service process, due to the long-term effects of environmental impacts and dynamic loading, interfaces of a composite structure might generate debonding cracks, relative slips or separations, and so on, lowering the composite effect of the composite structure. In this paper, the piezoceramics (PZT) are used as transducers to perform experiments on interface debonding slips and separations of composite beams, respectively, aimed at proposing an interface damage identification model and a relevant damage detection innovation method based on PZT wave technology. One part of various PZT patches was embedded in concrete as "smart aggregates," and another part of the PZT patches was pasted on the surface of the steel beam flange, forming a sensor array. A push-out test for four specimens was carried out and experimental results showed that, under the action of the external loading, the received signal amplitudes will increasingly decrease with increase of debonding slips along the interface. The proposed signal energy-based interface damage detection algorithm is highly efficient in surface state evaluations of composite beams.

  9. Using Finite Model Analysis and Out of Hot Cell Surrogate Rod Testing to Analyze High Burnup Used Nuclear Fuel Mechanical Properties

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jy-An John [ORNL; Jiang, Hao [ORNL; Wang, Hong [ORNL

    2014-07-01

    Based on a series of FEA simulations, the discussions and the conclusions concerning the impact of the interface bonding efficiency to SNF vibration integrity are provided in this report; this includes the moment carrying capacity distribution between pellets and clad, and the impact of cohesion bonding on the flexural rigidity of the surrogate rod system. As progressive de-bonding occurs at the pellet-pellet interfaces and at the pellet-clad interface, the load ratio of the bending moment carrying capacity gradually shifts from the pellets to the clad; the clad starts to carry a significant portion of the bending moment resistance until reaching the full de-bonding state at the pellet-pellet interface regions. This results in localized plastic deformation of the clad at the pellet-pellet-clad interface region; the associated plastic deformations of SS clad leads to a significant degradation in the stiffness of the surrogate rod. For instance, the flexural rigidity was reduced by 39% from the perfect bond state to the de-bonded state at the pellet-pellet interfaces.

  10. On the improved adhesion of NiTi wires embedded in polyester and vinylester resins

    Directory of Open Access Journals (Sweden)

    Mattia Merlin

    2015-01-01

    Full Text Available This paper discusses the effect of different surface treatments on shape memory alloy wires embedded in PolyEster (PE and VinylEster (VE polymeric matrices. In particular, two types of chemical etching and a chemical bonding with a silane coupling agent have been performed on the surfaces of the wires. Pull-out tests have been carried out on samples made from a specifically designed Teflon mould. Considering the best results of the pull-out tests obtained with PE resin, the debonding induced by strain recovery of 4%, 5% and 6% pre-strained NiTi wires has been evaluated with the wires being subjected to different surface treatment conditions and then being embedded in the PE matrix. The results prove that the wires functionalised and embedded in the PE resin show the maximum pull-out forces and the highest interfacial adhesion. Finally, it has been found that debonding induced by strain recovery is strongly related to the propagation towards the radial direction of sharp cracks at the debonding region.

  11. Thermal fatigue testing of a diffusion-bonded beryllium divertor mock-up under ITER relevant conditions

    International Nuclear Information System (INIS)

    Youchison, D.L.; Guiniiatouline, R.; Watson, R.D.

    1994-01-01

    Thermal response and thermal fatigue tests of four 5 mm thick beryllium tiles on a Russian divertor mock-up were completed on the Electron Beam Test System at Sandia National Laboratories. The beryllium tiles were diffusion bonded onto an OFHC copper saddleblock and a DSCu (MAGT) tube containing a porous coating. Thermal response tests were performed on the tiles to an absorbed heat flux of 5 MW/m 2 and surface temperatures near 300 degrees C using 1.4 MPa water at 5.0 m/s flow velocity and an inlet temperature of 8-15 degrees C. One tile was exposed to incrementally increasing heat fluxes up to 9.5 MW/m 2 and surface temperatures up to 690 degrees C before debonding at 10 MW/m 2 . A third tile debonded after 9200 thermal fatigue cycles at 5 MW/m 2 , while another debonded after 6800 cycles. In all cases, fatigue failure occurred in the intermetallic layers between the beryllium and copper. No fatigue cracking of the bulk beryllium was observed. During thermal cycling, a gradual loss of porous coating produced increasing sample temperatures. These experiments indicate that diffusion-bonded beryllium tiles can survive several thousand thermal cycles under ITER relevant conditions without failure. However, the reliability of the diffusion bonded Joint remains a serious issue

  12. Probabilistic analysis of the influence of the bonding degree of the stem-cement interface in the performance of cemented hip prostheses.

    Science.gov (United States)

    Pérez, M A; Grasa, J; García-Aznar, J M; Bea, J A; Doblaré, M

    2006-01-01

    The long-term behavior of the stem-cement interface is one of the most frequent topics of discussion in the design of cemented total hip replacements, especially with regards to the process of damage accumulation in the cement layer. This effect is analyzed here comparing two different situations of the interface: completely bonded and debonded with friction. This comparative analysis is performed using a probabilistic computational approach that considers the variability and uncertainty of determinant factors that directly compromise the damage accumulation in the cement mantle. This stochastic technique is based on the combination of probabilistic finite elements (PFEM) and a cumulative damage approach known as B-model. Three random variables were considered: muscle and joint contact forces at the hip (both for walking and stair climbing), cement damage and fatigue properties of the cement. The results predicted that the regions with higher failure probability in the bulk cement are completely different depending on the stem-cement interface characteristics. In a bonded interface, critical sites appeared at the distal and medial parts of the cement, while for debonded interfaces, the critical regions were found distally and proximally. In bonded interfaces, the failure probability was higher than in debonded ones. The same conclusion may be established for stair climbing in comparison with walking activity.

  13. Analysis of factors influencing the bond strength in roll bonding processes

    Science.gov (United States)

    Khaledi, Kavan; Wulfinghoff, Stephan; Reese, Stefanie

    2018-05-01

    Cold Roll Bonding (CRB) is recognized as an industrial technique in which the metal sheets are joined together in order to produce laminate metal composites. In this technique, a metallurgical bond resulting from severe plastic deformation is formed between the rolled metallic layers. The main objective of this paper is to analyse different factors which may affect the bond formation in rolling processes. To achieve this goal, first, an interface model is employed which describes both the bonding and debonding. In this model, the bond strength evolution between the metallic layers is calculated based on the film theory of bonding. On the other hand, the debonding process is modelled by means of a bilinear cohesive zone model. In the numerical section, different scenarios are taken into account to model the roll bonding process of metal sheets. The numerical simulation includes the modelling of joining during the roll bonding process followed by debonding in a Double Cantilever Beam (DCB) peeling test. In all simulations, the metallic layers are regarded as elastoplastic materials subjected to large plastic deformations. Finally, the effects of some important factors on the bond formation are numerically investigated.

  14. Effect of Thermal Distress on Residual Behavior of CFRP-Strengthened Steel Beams Including Periodic Unbonded Zones

    Directory of Open Access Journals (Sweden)

    Isamu Yoshitake

    2015-11-01

    Full Text Available This paper presents the residual behavior of wide-flange steel beams strengthened with high-modulus carbon fiber-reinforced polymer (CFRP laminates subjected to thermal loading. Because the coefficients of thermal expansion of the steel and the CFRP are different, temperature-induced distress may take place along their interface. Periodic unbonded zones are considered to represent local interfacial damage. Five test categories are designed depending on the size of the unbonded zones from 10 to 50 mm, and corresponding beams are loaded until failure occurs after exposing to a cyclic temperature range of ΔT = 25 °C (−10 to 15 °C up to 84 days. The composite action between the CFRP and the steel substrate is preserved until yielding of the beams happens, regardless of the thermal cycling and periodic unbonded zones. The initiation and progression of CFRP debonding become apparent as the beams are further loaded, particularly at geometric discontinuities in the vicinity of the unbonded zones along the interface. A simple analytical model is employed to predict the interfacial stress of the strengthened beams. A threshold temperature difference of ΔT = 30 °C is estimated for the initiation and progression of CFRP debonding. Multiple debonding-progression stages in conjunction with the extent of thermal distress appear to exist. It is recommended that high-modulus CFRP be restrictively used for strengthening steel members potentially exposed to a wide temperature variation range.

  15. Mechanical properties of polypropylene/calcium carbonate nanocomposites

    Directory of Open Access Journals (Sweden)

    Daniel Eiras

    2009-01-01

    Full Text Available The aim of this work was to study the influence of calcium carbonate nanoparticles in both tensile and impact mechanical properties of a polypropylene homopolymer. Four compositions of PP/CaCO3 nanocomposites were prepared in a co-rotational twin screw extruder machine with calcium carbonate content of 3, 5, 7 and 10 wt. (% The tests included SEM analyzes together with EDS analyzer and FTIR spectroscopy for calcium carbonate, tensile and impact tests for PP and the nanocomposites. The results showed an increase in PP elastic modulus and a little increase in yield stress. Brittle-to-ductile transition temperature was reduced and the impact resistance increased with the addition of nanoparticles. From the stress-strain curves we determined the occurrence of debonding process before yielding leading to stress softening. Debonding stress was determined from stress-strain curves corresponding to stress in 1% strain. We concluded that the tensile properties depend on the surface contact area of nanoparticles and on their dispersion. Finally we believe that the toughening was due to the formation of diffuse shear because of debonding process.

  16. Bond strength of stainless steel orthodontic brackets bonded to prefabricated acrylic teeth.

    Science.gov (United States)

    Wan Abdul Razak, Wan Salbiah; Sherriff, Martyn; Bister, Dirk; Seehra, Jadbinder

    2017-06-01

    The purpose of this in-vitro study was to evaluate the force to debond stainless steel orthodontic brackets bonded to acrylic teeth using different combinations of adhesive and surface treatments. One hundred prefabricated upper lateral incisor acrylic teeth were divided into 4 equal groups: Transbond XT® adhesive only (Group 1, control), Transbond XT® adhesive with sandblasting (Group 2), Transbond XT® adhesive with abrasion / + methyl methacrylate (MMA) (Group 3) and Triad® Gel only (Group 4). The force in Newtons (N) to debond the brackets was measured. One-way analysis of variance (ANOVA) and pairwise multi-comparison of means (Šidak's adjustment) were undertaken. The highest force to debond was recorded for Group 2 (275.7 N; SD 89.0) followed by Group 3 (241.9 N; SD 76.0), Group 1 (142.7 N; SD 36.7) and Group 4 (67.9 N; SD 21.1). Significant differences in bond strength measurements between the experimental groups were detected. Mean force values for the groups revealed no significant differences between Group 2 and Group 3 (p>0.05). Both sandblasting and surface abrasion/+ application of methyl methacrylate (MMA) in combination with Transbond XT® adhesive are recommended for bonding stainless orthodontic brackets to acrylic teeth.

  17. Comparison of Microleakage under Rebonded Stainless Steel Orthodontic Brackets Using Two Methods of Adhesive Removal: Sandblast and Laser.

    Science.gov (United States)

    Tudehzaeim, Mohamad Hossein; Yassaei, Soghra; Taherimoghadam, Shohreh

    2015-02-01

    Debonding is a common occurrence in orthodontic treatment and a considerable number of orthodontists prefer to rebond the detached brackets because of economic issues. The aim of this study was to compare the microleakage beneath rebonded stainless steel brackets using two methods of adhesive removal namely sandblast and laser. Sixty human premolar teeth were randomly divided into three groups. Following bonding the brackets, group 1 served as the control group. Brackets in groups 2 and 3 were debonded, and adhesive removal from the bracket bases was done by means of sandblasting and Er-YAG laser, respectively. After rebonding, teeth in each group were stained with 2% methylene blue for 24 hours, sectioned and examined under a stereomicroscope. Marginal microleakage at the adhesive-enamel and bracket-adhesive interfaces in the occlusal and gingival margins was determined. Statistical analysis was done using the Kruskal-Wallis test. Comparison of the microleakage scores among the three groups revealed no statistically significant difference (P > 0.05). At the enamel-adhesive interface, the gingival margins in all groups showed higher microleakage while in the adhesive-bracket interface, the occlusal margin exhibited greater microleakage. Er-YAG laser irradiation and sandblasting for adhesive removal from the debonded brackets yielded clinically acceptable microleakage scores.

  18. Stress transfer around a broken fiber in unidirectional fiber-reinforced composites considering matrix damage evolution and interface slipping

    Science.gov (United States)

    Yang, Zhong; Zhang, BoMing; Zhao, Lin; Sun, XinYang

    2011-02-01

    A shear-lag model is applied to study the stress transfer around a broken fiber within unidirectional fiber-reinforced composites (FRC) subjected to uniaxial tensile loading along the fiber direction. The matrix damage and interfacial debonding, which are the main failure modes, are considered in the model. The maximum stress criterion with the linear damage evolution theory is used for the matrix. The slipping friction stress is considered in the interfacial debonding region using Coulomb friction theory, in which interfacial clamping stress comes from radial residual stress and mismatch of Poisson's ratios of constituents (fiber and matrix). The stress distributions in the fiber and matrix are obtained by the shear-lag theory added with boundary conditions, which includes force continuity and displacement compatibility constraints in the broken and neighboring intact fibers. The result gives axial stress distribution in fibers and shear stress in the interface and compares the theory reasonably well with the measurement by a polarized light microscope. The relation curves between damage, debonding and ineffective region lengths with external strain loading are obtained.

  19. Tensile Properties and Fracture Behavior of a Powder-Thixoformed 2024Al/SiCp Composite at Elevated Temperatures

    Directory of Open Access Journals (Sweden)

    Pubo Li

    2017-10-01

    Full Text Available In the present work, the tensile properties and fracture behavior of a 2024Al composite reinforced with 10 vol % SiCp and fabricated via powder thixoforming (PT were studied at temperatures ranging from 25 °C to 300 °C with a strain rate of 0.05 s−1, as well as the PT 2024 alloy. The results indicated that the tensile strengths of both the PT materials were all decreased with increasing the temperature, but the decrease rate of the composite was smaller than that of the 2024 alloy, and the composite exhibited higher tensile strength than that of the 2024 alloy at all of the employed testing temperatures due to the strengthening role of SiCp. Increasing temperature was beneficial for enhancing the ductility of materials, and the maximum elongation was reached at 250 °C. The elongation decrease over 250 °C was attributed to the cavity formation due to the debonding of the SiCp/Al interface and the fracturing of the matrix between SiCp. The fracture of the composite at room temperature initiated from the fracture of SiCp and the debonding of the SiCp/Al interface, but that at high temperatures was dominated by void nucleation and growth in the matrix besides the interface debonding.

  20. How Is the Enamel Affected by Different Orthodontic Bonding Agents and Polishing Techniques?

    Directory of Open Access Journals (Sweden)

    Farzin Heravi

    2015-10-01

    Full Text Available Objectives: The objective of this study was to assess the effect of new bonding techniques on enamel surface.Materials and Methods: Sixty upper central incisors were randomly divided into two equal groups. In the first group, metal brackets were bonded using Trans- bondXT and, in the second group, the same brackets were bonded with MaxcemElite. The shear bond strength (SBS of both agents to enamel was measured and the number and length of enamel cracks before bonding, after debonding and after polishing were compared. The number of visible cracks and the adhesive remnant index (ARI scores in each group were also measured.Results: There were significantly more enamel cracks in the Transbond XT group after debonding and polishing compared to the Maxcem Elite group. There was no significant difference in the length of enamel cracks between the two groups; but, in each group, a significant increase in the length of enamel cracks was noticeable after debonding. Polishing did not cause any statistically significant change in crack length. The SBS of Maxcem Elite was significantly lower than that of Transbond XT (95% confidence interval.Conclusion: Maxcem Elite offers clinically acceptable bond strength and can thus be used as a routine adhesive for orthodontic purposes since it is less likely todamage the enamel.

  1. Enamel microcracks in terms of orthodontic treatment: A novel method for their detection and evaluation.

    Science.gov (United States)

    Dumbryte, Irma; Linkeviciene, Laura; Linkevicius, Tomas; Malinauskas, Mangirdas

    2017-07-26

    The study aimed at introducing current available techniques for enamel microcracks (EMCs) detection, and presenting a method for direct quantitative analysis of an individual EMC. Measurements of the detailed EMCs characteristics (location, length, and width) were taken from the reconstructed images of the buccal tooth surface (teeth extracted from two age groups of patients) employing a scanning electron microscopy (SEM) and our derived formulas before and after ceramic brackets removal. Measured parameters of EMCs for younger age group were 2.41 µm (width), 3.68 mm (length) before and 2.73 µm, 3.90 mm after debonding; for older -4.03 µm, 4.35 mm before and 4.80 µm, 4.37 mm after brackets removal. Following debonding EMCs increased for both groups, however the changes in width and length were statistically insignificant. Regardless of the age group, proposed method enabled precise detection of the same EMC before and after debonding, and quantitative examination of its characteristics.

  2. How Is the Enamel Affected by Different Orthodontic Bonding Agents and Polishing Techniques?

    Science.gov (United States)

    Heravi, Farzin; Shafaee, Hooman; Abdollahi, Mojtaba; Rashed, Roozbeh

    2015-03-01

    The objective of this study was to assess the effect of new bonding techniques on enamel surface. Sixty upper central incisors were randomly divided into two equal groups. In the first group, metal brackets were bonded using TransbondXT and, in the second group, the same brackets were bonded with Maxcem Elite. The shear bond strength (SBS) of both agents to enamel was measured and the number and length of enamel cracks before bonding, after debonding and after polishing were compared. The number of visible cracks and the adhesive remnant index (ARI) scores in each group were also measured. There were significantly more enamel cracks in the Transbond XT group after debonding and polishing compared to the Maxcem Elite group. There was no significant difference in the length of enamel cracks between the two groups; but, in each group, a significant increase in the length of enamel cracks was noticeable after debonding. Polishing did not cause any statistically significant change in crack length. The SBS of Maxcem Elite was significantly lower than that of Transbond XT (95% confidence interval). Maxcem Elite offers clinically acceptable bond strength and can thus be used as a routine adhesive for orthodontic purposes since it is less likely to damage the enamel.

  3. Research on the fracture behavior of PBX under static tension

    Directory of Open Access Journals (Sweden)

    Hu Guo

    2014-06-01

    Full Text Available The fracture behavior of polymer-bonded explosive (PBX seriously affects the safety and reliability of weapon system. The effects of interface debonding and initial meso-damage on the fracture behavior of PBX under quasi-static tension are studied using numerical method. A two-dimensional representative volume element (RVE is established based on Voronoi model in which the component contents could be regulated and the particles are randomly distributed. A nonlinear damage model of polymer matrix relative to matrix depth between particles is constructed. The results show that the simulated strain-stress relation is coincident with experiment data. It is found that interface debonding leads to the nucleation and propagation of meso-cracks, and a main crack approximately perpendicular to the loading direction is generated finally. The interface debonding tends to occur in the interface perpendicular to the loading direction. There seems to be a phenomenon that strain softening and hardening alternatively appear around peak stress of stress and strain curve. It is shown that the initial damages of intragranular and interfacial cracks both decrease the modulus and failure stress, and the main crack tends to propagate toward the initial meso-cracks.

  4. Porcelain surface alterations and refinishing after use of two orthodontic bonding methods.

    Science.gov (United States)

    Herion, Drew T; Ferracane, Jack L; Covell, David A

    2010-01-01

    To compare porcelain surfaces at debonding after use of two surface preparation methods and to evaluate a method for restoring the surface. Lava Ceram feldspathic porcelain discs (n = 40) underwent one of two surface treatments prior to bonding orthodontic brackets. Half the discs had sandblasting, hydrofluoric acid, and silane (SB + HF + S), and the other half, phosphoric acid and silane (PA + S). Brackets were debonded using bracket removing pliers, and resin was removed with a 12-fluted carbide bur. The surface was refinished using a porcelain polishing kit, followed by diamond polishing paste. Measurements for surface roughness (Ra), gloss, and color were made before bonding (baseline), after debonding, and after each step of refinishing. Surfaces were also examined by scanning electron microscopy (SEM). Data was analyzed with 2-way ANOVA followed by Tukey HSD tests (alpha = 0.05). The SB + HF + S bonding method increased Ra (0.160 to 1.121 microm), decreased gloss (41.3 to 3.7) and altered color (DeltaE = 4.37; P gloss (41.7 to 38.0) and color (DeltaE = 0.50). The measurements and SEM observations showed that changes were fully restored to baseline with refinishing. The PA + S method caused significantly less damage to porcelain than the SB + HF + S method. The refinishing protocol fully restored the porcelain surfaces.

  5. Effect of Various Finishing Procedures on the Reflectivity (Shine) of Tooth Enamel - An In-vitro Study.

    Science.gov (United States)

    Patil, Harshal Ashok; Chitko, Shrikant Shrinivas; Kerudi, Veerendra Virupaxappa; Maheshwari, Amit Ratanlal; Patil, Neeraj Suresh; Tekale, Pawankumar Dnyandeo; Gore, Ketan Ashorao; Zope, Amit Ashok

    2016-08-01

    Reflectivity of an object is a good parameter for surface finish. As the patient evaluates finishing as a function of gloss/reflectivity/shine an attempt is made here to evaluate changes in surface finish with custom made reflectometer. The aim of the present study was to study the effect of various procedures during orthodontic treatment on the shine of enamel, using a custom made reflectometer. Sixty one extracted premolars were collected and each tooth was mounted on acrylic block. Reflectivity of the teeth was measured as compared to standard before any procedure. One tooth was kept as standard throughout the study. Sixty teeth were acid etched. Reflectivity was measured on custom made reflectometer and readings recorded. Same procedure was repeated after debonding. Then 60 samples were divided into three groups: Group 1 - Tungsten Carbide, Group 2 - Astropol, Group 3- Sof-Lex disc depending upon the finishing method after debonding and reflectivity was measured. The mean percentage of reflectivity after acid etching was 31.4%, debonding 45.5%, Tungsten carbide bur finishing (Group 1) was 58.3%, Astropol (Group 2) 72.8%, and Sof-Lex disc (Group 3) 84.4% as that to the standard. There was statistically very highly significant (p Group 2> Group 1. The primary goal was to restore the enamel to its original state after orthodontic treatment. The methods tested in this study could not restore the original enamel reflectivity.

  6. Experimental Study on Fatigue Behaviour of BFRP-Concrete Bond Interfaces under Bending Load

    Directory of Open Access Journals (Sweden)

    Jianhe Xie

    2018-01-01

    Full Text Available Basalt fiber reinforced polymer (BFRP composites are increasingly being used to retrofit concrete structures by external bonding. For such strengthened members, the BFRP-concrete interface plays the crucial role of transferring stresses. This study aims to investigate the fatigue behaviour of the interface under bending load. A series of tests were conducted on BFRP-concrete bonded joint, including static, fatigue, and postfatigue loading. The fatigue failure modes, the development of deflection, the evolution of BFRP strains, and the propagation of interfacial cracks were analysed. In addition, the debonding-induced fatigue life of BFRP-concrete bonded joints was studied. Finally, a new model of fatigue life was proposed by defining the effective fatigue bond stress. The results showed that the fatigue experience has a significant effect on the BFRP strength especially near the root of concrete transverse crack and on the bond performance of the adhesive near the interface crack tip. There are two main fatigue failure modes: BFRP rupture and BFRP debonding. The fatigue damage development of the bond interface has three stages: rapid, stable, and unstable growth. The proposed model for the debonding-induced fatigue life is more conservative for the BFRP-concrete bonded joints under pure shear load than for those under bending load.

  7. Laser all-ceramic crown removal and pulpal temperature--a laboratory proof-of-principle study.

    Science.gov (United States)

    Rechmann, P; Buu, N C H; Rechmann, B M T; Finzen, F C

    2015-11-01

    The objective of this proof-of-principle laboratory pilot study was to evaluate the temperature increase in the pulp chamber in a worst case scenario during Er:YAG laser debonding of all-ceramic crowns. Twenty extracted molars were prepared to receive all-ceramic IPS E.max CAD full contour crowns. The crowns were bonded to the teeth with Ivoclar Multilink Automix. Times for laser debonding and temperature rise in the pulp chamber using micro-thermocouples were measured. The Er:YAG was used with 560 mJ/pulse. The irradiation was applied at a distance of 5 mm from the crown surface. Additional air-water spray for cooling was utilized. Each all-ceramic crown was successfully laser debonded with an average debonding time of 135 ± 35 s. No crown fractured, and no damage to the underlying dentin was detected. The bonding cement deteriorated, but no carbonization at the dentin/cement interface occurred. The temperature rise in the pulp chamber averaged 5.4° ± 2.2 °C. During 8 out of the 20 crown removals, the temperature rise exceeded 5.5 °C, lasting 5 to 43 s (average 18.8 ± 11.6 s). A temperature rise of 11.5 °C occurred only once, while seven times the temperature rise was limited to 6.8 ± 0.5 °C. Temperature rises above 5.5 °C occurred only when the laser was applied from one side and additional cooling from the side opposite the irradiation. Er:YAG laser energy can successfully be used to efficiently debond all-ceramic crowns from natural teeth. Temperature rises exceeding 5.5 °C only occur when an additional air/water cooling from a dental syringe is inaccurately directed. To avoid possible thermal damage and to allow further heat diffusion, clinically temperature-reduced water might be applied.

  8. Hierarchical micro- and nanofabrication by pattern-directed contact instabilities of thin viscoelastic films

    Science.gov (United States)

    Ghosh, Abir; Bandyopadhyay, Dipankar; Sarkar, Jayati; Sharma, Ashutosh

    2017-12-01

    A surface of a thin viscoelastic film forms spinodal patterns when brought in contact proximity of another surface due to the dominance of destabilizing intermolecular interaction over the stabilizing elastic and surface tension forces. In this study, we theoretically explore such contact instabilities of a thin viscoelastic film, wherein the patterns generated on the surface of the film is developed with the help of a contactor decorated with periodic physical, chemical, and physicochemical features on the surface. The nonlinear analysis shown here considers the movement of the patterned contactor during the adhesion and debonding processes, which is unlike most of the previous works where the contactor is considered to be stationary. The simulations reveal that the amplitude and periodicity of the patterns decorated on the contactor together with the contactor speed can be the key parameters to stimulate pattern formation on the film surface alongside causing changeover of the various modes of debonding of the surfaces. In particular, the ratio of the elastic to viscous compliances of the film is found to play a critical role to stimulate the changeover of the modes from catastrophic to peeling or coalescence. The study uncovers that a higher wettability contrast across the patterned contactor leads to the catastrophic collapse of the patterns decorated on the film surface when the contactor debonds at a moderate speed. In comparison, a moderately high wettability contrast alongside a faster withdrawal speed of the contactor results in the gradual peeling of columns during the debonding cycle. Remarkably, a higher withdrawal speed of the contactor from the film-proximity can increase the aspect ratio of the patterns fabricated on the film surface to about fourfold during the peeling mode of debonding. The results show the importance of the usage of patterned contactors, their controlled movement, and extent of elastic to viscous compliance ratio of the film for

  9. The Effect of Artificial Aging on The Bond Strength of Heat-activated Acrylic Resin to Surface-treated Nickel-chromium-beryllium Alloy.

    Science.gov (United States)

    Al Jabbari, Youssef S; Zinelis, Spiros; Al Taweel, Sara M; Nagy, William W

    2016-01-01

    The debonding load of heat-activated polymethylmethacrylate (PMMA) denture base resin material to a nickel-chromium-beryllium (Ni-Cr-Be) alloy conditioned by three different surface treatments and utilizing two different commercial bonding systems was investigated. Denture resin (Lucitone-199) was bonded to Ni-Cr-Be alloy specimens treated with Metal Primer II, the Rocatec system with opaquer and the Rocatec system without opaquer. Denture base resin specimens bonded to non-treated sandblasted Ni-Cr-Be alloy were used as controls. Twenty samples for each treatment condition (80 specimens) were tested. The 80 specimens were divided into two categories, thermocycled and non-thermocycled, containing four groups of ten specimens each. The non-thermocycled specimens were tested after 48 hours' storage in room temperature water. The thermocycled specimens were tested after 2,000 cycles in 4°C and 55°C water baths. The debonding load was calculated in Newtons (N), and collected data were subjected by non parametric test Kruskal-Wallis One Way Analysis of Variance on Ranks and Dunn's post hoc test at the α = 0.05. The Metal Primer II and Rocatec system without opaquer groups produced significantly higher bond strengths (119.9 and 67.6 N), respectively, than did the sandblasted and Rocatec system with opaquer groups, where the bond strengths were 2.6 N and 0 N, respectively. The Metal Primer II was significantly different from all other groups (P<0.05). The bond strengths of all groups were significantly decreased (P<0.05) after thermocycling. Although thermocycling had a detrimental effect on the debonding load of all surface treatments tested, the Metal Primer II system provided higher values among all bonding systems tested, before and after thermocycling.

  10. Bond strength of orthodontic light-cured resin-modified glass ionomer cement.

    Science.gov (United States)

    Cheng, Hsiang Yu; Chen, Chien Hsiu; Li, Chuan Li; Tsai, Hung Huey; Chou, Ta Hsiung; Wang, Wei Nan

    2011-04-01

    The purpose of this study was to compare the bond strengths and debonded interfaces achieved with light-cured resin-modified glass ionomer cement (RMGIC) and conventional light-cured composite resin. In addition, the effects of acid etching and water contamination were examined. One hundred human premolars were randomly divided into five equal groups. The mini Dyna-lock upper premolar bracket was selected for testing. The first four groups were treated with light-cured RMGIC with or without 15 per cent phosphoric acid-etching treatment and with or without water contamination preceding bracket bonding. The control samples were treated with the conventional light-cured Transbond composite resin under acid etching and without water contamination. Subsequently, the brackets were debonded by tensile force using an Instron machine. The modified adhesive remnant index (ARI) scores were assigned to the bracket base of the debonded interfaces using a scanning electron microscope. The bond strength and modified ARI scores were determined and analysed statistically by one-way analysis of variance and chi-square test. Under all four conditions, the bond strength of the light-cure RMGIC was equal to or higher than that of the conventional composite resin. The highest bond strength was achieved when using RMGIC with acid etching but without water contamination. The modified ARI scores were 2 for Fuji Ortho LC and 3 for Transbond. No enamel detachment was found in any group. Fifteen per cent phosphoric acid etching without moistening the enamel of Fuji Ortho LC provided the more favourable bond strength. Enamel surfaces, with or without water contamination and with or without acid etching, had the same or a greater bond strength than Transbond.

  11. An in vitro Evaluation of Shear Bond Strength of Adhesive Precoated Brackets

    Directory of Open Access Journals (Sweden)

    A S Sibi

    2014-01-01

    Full Text Available Newer materials have been introduced in the field of orthodontics to improve clinical efficacy as well as to simplify the technique. In an effort to reduce the time and steps to bond orthodontic attachments, adhesive precoated (APC brackets were introduced. In this study, an attempt is made to evaluate the shear bond strength (SBS and debonding behavior of APC brackets compared with uncoated ceramic brackets. A total of 60 human premolar teeth were divided into two groups of 30 each, bonded with APC ceramic brackets and uncoated ceramic brackets. Group I bonded with APC brackets as prescribed by the manufacturers and group II was bonded with conventional bonding using Turbobond. After bonding, sthe samples were kept in distilled water at 37°C for 24 hours and a universal testing mechine was used to apply an occlusal shear force at a speed of 0.5 mm/min. The shear bond strength of the groups was compared using Student t-test and the debonding behavior were compared using Mann-Whitney′s U test. Mean shear bond strength and standard deviation of the groups were group I - 9.09 ± 2.5 MPa and group II - 12.95 ± 2.81 MPa. There were significant differences in bond strength observed between the two groups. The debonding behavior showed an adhesive remnant index score of 0.90 ± 0.08 for group I and 1.10 ± 0.04 for group II, which indicates there is significant difference between each other. When considering the values required for optimum bond strength, APC brackets in this study showed adequate bond strength and could be used for routine clinical use.

  12. Finite Element Modelling and Analysis of Damage Detection Methodology in Piezo Electric Sensor and Actuator Integrated Sandwich Cantilever Beam

    Science.gov (United States)

    Pradeep, K. R.; Thomas, A. M.; Basker, V. T.

    2018-03-01

    Structural health monitoring (SHM) is an essential component of futuristic civil, mechanical and aerospace structures. It detects the damages in system or give warning about the degradation of structure by evaluating performance parameters. This is achieved by the integration of sensors and actuators into the structure. Study of damage detection process in piezoelectric sensor and actuator integrated sandwich cantilever beam is carried out in this paper. Possible skin-core debond at the root of the cantilever beam is simulated and compared with undamaged case. The beam is actuated using piezoelectric actuators and performance differences are evaluated using Polyvinylidene fluoride (PVDF) sensors. The methodology utilized is the voltage/strain response of the damaged versus undamaged beam against transient actuation. Finite element model of piezo-beam is simulated in ANSYSTM using 8 noded coupled field element, with nodal degrees of freedoms are translations in the x, y directions and voltage. An aluminium sandwich beam with a length of 800mm, thickness of core 22.86mm and thickness of skin 0.3mm is considered. Skin-core debond is simulated in the model as unmerged nodes. Reduction in the fundamental frequency of the damaged beam is found to be negligible. But the voltage response of the PVDF sensor under transient excitation shows significantly visible change indicating the debond. Piezo electric based damage detection system is an effective tool for the damage detection of aerospace and civil structural system having inaccessible/critical locations and enables online monitoring possibilities as the power requirement is minimal.

  13. Microscopic analysis of irradiated AGR-1 coated particle fuel compacts

    Energy Technology Data Exchange (ETDEWEB)

    Ploger, Scott A., E-mail: scott.ploger@inl.gov [Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-3855 (United States); Demkowicz, Paul A. [Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-3855 (United States); Hunn, John D.; Kehn, Jay S. [Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6093 (United States)

    2014-05-01

    The AGR-1 experiment involved irradiation of 72 TRISO-coated particle fuel compacts to a peak compact-average burnup of 19.5% FIMA with no in-pile failures observed out of 3 × 10{sup 5} total particles. Irradiated AGR-1 fuel compacts have been cross-sectioned and analyzed with optical microscopy to characterize kernel, buffer, and coating behavior. Six compacts have been examined, spanning a range of irradiation conditions (burnup, fast fluence, and irradiation temperature) and including all four TRISO coating variations irradiated in the AGR-1 experiment. The cylindrical specimens were sectioned both transversely and longitudinally, then polished to expose from 36 to 79 individual particles near midplane on each mount. The analysis focused primarily on kernel swelling and porosity, buffer densification and fracturing, buffer–IPyC debonding, and fractures in the IPyC and SiC layers. Characteristic morphologies have been identified, 981 particles have been classified, and spatial distributions of particle types have been mapped. No significant spatial patterns were discovered in these cross sections. However, some trends were found between morphological types and certain behavioral aspects. Buffer fractures were found in 23% of the particles, and these fractures often resulted in unconstrained kernel protrusion into the open cavities. Fractured buffers and buffers that stayed bonded to IPyC layers appear related to larger pore size in kernels. Buffer–IPyC interface integrity evidently factored into initiation of rare IPyC fractures. Fractures through part of the SiC layer were found in only four classified particles, all in conjunction with IPyC–SiC debonding. Compiled results suggest that the deliberate coating fabrication variations influenced the frequencies of IPyC fractures and IPyC–SiC debonds.

  14. The influence of size and structure of metal orthodontic bracket base on bond strength on tooth enamel

    Directory of Open Access Journals (Sweden)

    Mitić Vladimir

    2009-01-01

    Full Text Available Introduction. The factors which may influence the bond strength of the applied orthodontic brackets on the tooth surface are the size and structure of the bracket base. Objective. The aim of the paper was to investigate the influence of size and shape of different types of brackets on bond strength on the enamel and analyze the remaining quality of adhesive material on the tooth surface after debonding of orthodontic brackets (adhesive remnant index - ARI. Methods. In this study, three types of metal brackets of different sizes and shapes of Dentaurum manufacturer were used (Utratrimm, Equilibrium 2, Discovery, Dentaurum, Inspringen, Germany. The brackets were applied onto the middle part of the anatomic crowns of buccal surfaces of 30 premolars extracted for orthodontic reasons. In addition, the pre-treatment of teeth by 37% orthophosphoric acid and adhesive material System1+ (Dentaurum, Germany were used. Results. The mean value of the bonded brackets bond strength of Discovery type after debonding was 8.67±0.32 MPa, while the value of the bonded brackets bond strength of Equilibrium 2 type amounted to 8.62±0.22 MPa. The value of the bonded brackets bond strength of Ultratrimm type after debonding was 8.22±0.49 MPa. There were no statistical differences in the values of bond strength regarding all three groups of the investigated orthodontic brackets (F=4.56; p<0.05. Conclusion. The base size and design of metal orthodontic brackets did not play a significant role in bond strength, while the values of ARI index were identical in all three investigated groups.

  15. Efficacy of 2 finishing protocols in the quality of orthodontic treatment outcome.

    Science.gov (United States)

    Stock, Gregory J; McNamara, James A; Baccetti, Tiziano

    2011-11-01

    The objectives of this prospective clinical study were to evaluate the quality of treatment outcomes achieved with a complex orthodontic finishing protocol involving serpentine wires and a tooth positioner, and to compare it with the outcomes of a standard finishing protocol involving archwire bends used to detail the occlusion near the end of active treatment. The complex finishing protocol sample consisted of 34 consecutively treated patients; 1 week before debonding, their molar bands were removed, and serpentine wires were placed; this was followed by active wear of a tooth positioner for up to 1 month after debonding. The standard finishing protocol group consisted of 34 patients; their dental arches were detailed with archwire bends and vertical elastics. The objective grading system of the American Board of Orthodontics was used to quantify the quality of the finish at each time point. The Wilcoxon signed rank test was used to compare changes in the complex finishing protocol; the Mann-Whitney U test was used to compare changes between groups. The complex finishing protocol group experienced a clinically significant improvement in objective grading system scores after treatment with the positioner. Mild improvement in posterior space closure was noted after molar band removal, but no improvement in the occlusion was observed after placement of the serpentine wires. Patients managed with the complex finishing protocol also had a lower objective grading system score (14.7) at the end of active treatment than did patients undergoing the standard finishing protocol (23.0). Tooth positioners caused a clinically significant improvement in interocclusal contacts, interproximal contacts, and net objective grading system score; mild improvement in posterior band space was noted after molar band removal 1 week before debond. Copyright © 2011 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

  16. Evaluation of enamel micro-cracks characteristics after removal of metal brackets in adult patients.

    Science.gov (United States)

    Dumbryte, Irma; Linkeviciene, Laura; Malinauskas, Mangirdas; Linkevicius, Tomas; Peciuliene, Vytaute; Tikuisis, Kristupas

    2013-06-01

    The purpose of this study was to evaluate and compare enamel micro-crack characteristics of adult patients before and after removal of metal brackets. After the examination with scanning electron microscopy (SEM), 45 extracted human teeth were divided into three groups of equal size: group 1, the teeth having enamel micro-cracks, group 2, the teeth without initial enamel micro-cracks, and group 3, control group to study the effect of dehydration on existing micro-cracks or formation of new ones. For all the teeth in groups 1 and 2, the same bonding and debonding procedures of metal brackets were conducted. The length and width of the longest enamel micro-crack were measured for all the teeth before and after removal of metal brackets. The changes in the location of the micro-cracks were also evaluated. In group 3, teeth were subjected to the same analysis but not bonded. The mean overall width of micro-cracks after removal of metal brackets was 3.82 μm greater than before bonding procedure (P cracks in first zone (cervical third) and third zone (occlusal third) after debonding procedure (P enamel micro-cracks were found in 6 of 15 (40 per cent) examined teeth. Greatest changes in the width of enamel micro-cracks after debonding procedure appear in the cervical third of the tooth. On the basis of this result, the dentist must pay extra care and attention to this specific area of enamel during removal of metal brackets in adult patients.

  17. The Effect of High Concentration and Small Size of Nanodiamonds on the Strength of Interface and Fracture Properties in Epoxy Nanocomposite

    Directory of Open Access Journals (Sweden)

    Yasir A. Haleem

    2016-06-01

    Full Text Available The concentration and small size of nanodiamonds (NDs plays a crucial role in the mechanical performance of epoxy-based nanocomposites by modifying the interface strength. Herein, we systemically analyzed the relation between the high concentration and small size of ND and the fracture properties of its epoxy-based nanocomposites. It was observed that there is a two-fold increase in fracture toughness and a three-fold increase in fracture energy. Rationally, functionalized-NDs (F-NDs showed a much better performance for the nanocomposite than pristine NDs (P-NDs because of additional functional groups on its surface. The F-ND/epoxy nanocomposites exhibited rougher surface in contrast with the P-ND/epoxy, indicating the presence of a strong interface. We found that the interfaces in F-ND/epoxy nanocomposites at high concentrations of NDs overlap by making a web, which can efficiently hinder further crack propagation. In addition, the de-bonding in P-ND/epoxy nanocomposites occurred at the interface with the appearance of plastic voids or semi-naked particles, whereas the de-bonding for F-ND/epoxy nanocomposites happened within the epoxy molecular network instead of the interface. Because of the strong interface in F-ND/epoxy nanocomposites, at high concentrations the de-bonding within the epoxy molecular network may lead to subsequent cracks, parallel to the parent crack, via crack splitting which results in a fiber-like structure on the fracture surface. The plastic void growth, crack deflection and subsequent crack growth were correlated to higher values of fracture toughness and fracture energy in F-ND/epoxy nanocomposites.

  18. Assessment of Composite Delamination Self-Healing Via Micro-Encapsulation

    Science.gov (United States)

    O'Brien, T. Kevin; White, Scott R.

    2008-01-01

    Composite skin/stringer flange debond specimens manufactured from composite prepreg containing interleaf layers with a polymer based healing agent encapsulated in thin walled spheres were tested. As a crack develops and grows in the base polymer, the spheres fracture releasing the healing agent. The agent reacts with catalyst and polymerizes healing the crack. In addition, through-thickness reinforcement, in the form of pultruded carbon z-pins were included near the flange tips to improve the resistance to debonding. Specimens were manufactured with 14 plies in the skin and 10 plies in the stiffener flange. Three-point bend tests were performed to measure the skin/stiffener debonding strength and the recovered strength after healing. The first three tests performed indicated no healing following unloading and reloading. Micrographs showed that delaminations could migrate to the top of the interleaf layer due to the asymmetric loading, and hence, bypass most of the embedded capsules. For two subsequent tests, specimens were clamped in reverse bending before reloading. In one case, healing was observed as evidenced by healing agent that leaked to the specimen edge forming a visible "scar". The residual strength measured upon reloading was 96% of the original strength indicating healing had occurred. Hence, self-healing is possible in fiber reinforced composite material under controlled conditions, i.e., given enough time and contact with pressure on the crack surfaces. The micro-encapsulation technique may prove more robust when capsule sizes can be produced that are small enough to be embedded in the matrix resin without the need for using an interleaf layer. However, in either configuration, the amount of healing that can occur may be limited to the volume of healing agent available relative to the crack volume that must be filled.

  19. Mechanism-Based Design for High-Temperature, High-Performance Composites. Book 2

    Science.gov (United States)

    1997-09-01

    0790’ specimen. 52 CO Q. CO CO s 00 D) c TD C CD H c ’E o 350 300 - 250 i^^^^^^w^^^^cs^^^^N^^^^^^^^^^^^^^^ 200 - 150 100 i i...equation x = 3P/ 4BD , where P, B and D are the load, thickness and depth of the specimen, respec- tively, (b) Micrograph showing delamination cracks...strains in the following manner. The total strain of the composite is given by the weighted sum of the average fiber strain in the debonded portion, td

  20. A simple beam model to analyse the durability of adhesively bonded tile floorings in presence of shrinkage

    Directory of Open Access Journals (Sweden)

    S. de Miranda

    2014-07-01

    Full Text Available A simple beam model for the evaluation of tile debonding due to substrate shrinkage is presented. The tile-adhesive-substrate package is modeled as an Euler-Bernoulli beam laying on a two-layer elastic foundation. An effective discrete model for inter-tile grouting is introduced with the aim of modelling workmanship defects due to partial filled groutings. The model is validated using the results of a 2D FE model. Different defect configurations and adhesive typologies are analysed, focusing the attention on the prediction of normal stresses in the adhesive layer under the assumption of Mode I failure of the adhesive.

  1. The Processing and Mechanical Properties of High Temperature/High Performance Composites. Book 2, Section 2: Strength and Fracture Resistance

    Science.gov (United States)

    1989-10-15

    anavlysis *(the omtd*delcno data, this WOarIncfancel lower the slope of she lotig cw t(i3) an h 1~ 0= ~ulidme fta seen. Consequently, the MAO analysis hat...ftypcal micromet ad aer) W nile ti moratt:uekt fro Fg.Alisth raliatontht omlee crcmfretil Whgesn a clexinvaantitie ar eo esenIolrfom deondisqunliely toin...Corp. West Palm Beach, FL ABSTRACT The effects of reinforcement debonding and work hardening on ductile reinforcement toughening of r.TiAl have been

  2. Fatigue damage propagation in unidirectional glass fibre reinforced composites

    DEFF Research Database (Denmark)

    Hansen, Jens Zangenberg; Alzamora Guzman, Vladimir Joel; Østergaard, R.C.

    2012-01-01

    bundles. The underlying mechanisms are examined using digital microscopy, and it is postulated that fatigue damage initiates due to stress concentrations between the backing (transverse) layer and the unidirectional layer, followed by a cyclic fretting and axial fibre debonding. This fretting mechanism......Damage progression in unidirectional glass fibre reinforced composites exposed to tension fatigue is investigated, and a quantitative explanation is given for the observed stiffness loss. The stiffness degradation during fatigue is directly related to fibre breaks in the load-carrying axial fibre...... needs further attention and understanding in order to improve the fatigue life-time of glass fibre reinforced composites....

  3. New generation of plasma-sprayed mullite coatings on silicon carbide

    Science.gov (United States)

    Lee, Kang N.; Miller, Robert A.; Jacobson, Nathan S.

    1995-01-01

    Mullite is promising as a protective coating for silicon-based ceramics in aggressive high-temperature environments. Conventionally plasma-sprayed mullite on SiC tends to crack and debond on thermal cycling. It is shown that this behavior is due to the presence of amorphous mullite in the conventionally sprayed mullite. Heating the SiC substrate during the plasma spraying eliminated the amorphous phase and produced coatings with dramatically improved properties. The new coating exhibits excellent adherence and crack resistance under thermal cycling between room temperature and 1000 to 1400 C. Preliminary tests showed good resistance to Na2CO3-induced hot corrosion.

  4. Handbook of 3D integration

    CERN Document Server

    Garrou , Philip; Ramm , Peter

    2014-01-01

    Edited by key figures in 3D integration and written by top authors from high-tech companies and renowned research institutions, this book covers the intricate details of 3D process technology.As such, the main focus is on silicon via formation, bonding and debonding, thinning, via reveal and backside processing, both from a technological and a materials science perspective. The last part of the book is concerned with assessing and enhancing the reliability of the 3D integrated devices, which is a prerequisite for the large-scale implementation of this emerging technology. Invaluable reading fo

  5. Interfacial Micromechanics in Fibrous Composites: Design, Evaluation, and Models

    Science.gov (United States)

    Lei, Zhenkun; Li, Xuan; Qin, Fuyong; Qiu, Wei

    2014-01-01

    Recent advances of interfacial micromechanics in fiber reinforced composites using micro-Raman spectroscopy are given. The faced mechanical problems for interface design in fibrous composites are elaborated from three optimization ways: material, interface, and computation. Some reasons are depicted that the interfacial evaluation methods are difficult to guarantee the integrity, repeatability, and consistency. Micro-Raman study on the fiber interface failure behavior and the main interface mechanical problems in fibrous composites are summarized, including interfacial stress transfer, strength criterion of interface debonding and failure, fiber bridging, frictional slip, slip transition, and friction reloading. The theoretical models of above interface mechanical problems are given. PMID:24977189

  6. Failure Surface Analysis of Polyimide/Titanium Notched Coating Adhesion Specimens

    Energy Technology Data Exchange (ETDEWEB)

    GIUNTA,RACHEL K.; KANDER,RONALD G.

    2000-12-18

    Adhesively bonded joints of LaRC{trademark} PETI-5, a phenylethynyl-terminated polyimide, with chromic acid anodized titanium were fabricated and debonded interfacially. The adhesive-substrate failure surfaces were investigated using several surface analysis techniques. From Auger spectroscopy, field emission scanning electron microscopy, and atomic force microscopy studies, polymer appears to be penetrating the pores of the anodized substrate to a depth of approximately 100 nm. From x-ray photoelectron spectroscopy data, the polymer penetrating the pores appears to be in electrical contact with the titanium substrate, leading to differential charging. These analyses confirm that the polymer is becoming mechanically interlocked within the substrate surface.

  7. Computer Tomography Analysis of Fastrac Composite Thrust Chamber Assemblies

    Science.gov (United States)

    Beshears, Ronald D.

    2000-01-01

    Computed tomography (CT) inspection has been integrated into the production process for NASA's Fastrac composite thrust chamber assemblies (TCAs). CT has been proven to be uniquely qualified to detect the known critical flaw for these nozzles, liner cracks that are adjacent to debonds between the liner and overwrap. CT is also being used as a process monitoring tool through analysis of low density indications in the nozzle overwraps. 3d reconstruction of CT images to produce models of flawed areas is being used to give program engineers better insight into the location and nature of nozzle flaws.

  8. Investigation on fracture behavior and mechanisms of DGEBF toughened by CTBN

    Science.gov (United States)

    Wang, Lulu; Tan, Yefa; Wang, Haitao; Gao, Li; Xiao, Chufan

    2018-05-01

    Carboxyl-terminated butadiene-co-acrylonitrile (CTBN) was used as the toughener to improve the mechanical performance and fracture toughness of diglycidyl ether of bisphenol F (DGEBF) by prereacted approach. The results show that the chemical bonding interface was formed between DGEBF and CTBN particles in the prepolymerization reaction process, which remarkably enhances the fracture toughness of the composites. Based on the qualitative and quantitative analyses, it shows the main toughening mechanisms are the plastic shear banding effect resulted from the plastic deformation of the EP matrix and the plastic void expansion because of the debonding of CTBN particles from the EP matrix.

  9. Deformation properties of highly plastic fissured Palaeogene clay - Lack of stress memory?

    DEFF Research Database (Denmark)

    Krogsbøll, Anette; Hededal, Ole; Foged, Niels Nielsen

    2012-01-01

    are evaluated based on the degree of debonding caused by natural processes insitu as compared to processes induced during severe loading and unloading in laboratory. A long term oedometer test on Lillebælt Clay with a series of loading and unloading cycles was carried out. The test results are used to evaluate......The geological preconsolidation of the Palaeogene clays in Denmark is estimated to 5-8 MPa or more, whereas laboratory and field experiences indicate values between 100 and 3000 kPa. Presumably, the high plasticity clay loses its memory of earlier preloads due to swelling, or as an effect...

  10. Interfaces between a fibre and its matrix

    DEFF Research Database (Denmark)

    Lilholt, Hans; Sørensen, Bent F.

    2017-01-01

    in polyester matrix. The analysis of existing experimental literature data is demonstrated for steel fibres in epoxy matrix and for tungsten wires in copper matrix. These latter incomplete analyses show that some results can be obtained even if all three experimental parameters are not recorded....... parameters (applied load, debond length and relative fibre/matrix displacement) are rather similar for these test modes. A simplified analysis allows the direct determination of the three interface parameters from two plots for the experimental data. The complete analysis is demonstrated for steel fibres...

  11. Fatigue crack growth behavior and AE signal recognition from a composite patch repaired Ai thein plate

    International Nuclear Information System (INIS)

    Kim, Sung Jin; Kwon, Oh Yang

    2004-01-01

    The fatigue crack growth behavior of a fatigue-cracked and patch-repaired AA2024-T3 plate has been monitored. It was found that the overall crack growth rate was reduced and the crack propagation into the adjacent hole was also retarded. Signals due to crack growth after patch-repair and those due to debonding of the plate-patch interface were discriminated each other by using principal component analysis. The former showed higher center frequency and lower amplitude, whereas the latter showed longer rise time, lower frequency and higher amplitude.

  12. State of residual stress in laser-deposited ceramic composite coatings on aluminum alloys

    OpenAIRE

    Kadolkar, P. B.; Watkins, T. R.; De Hosson, J. Th. M.; Kooi, B. J.; Dahotre, N. B.

    2007-01-01

    The nature and magnitude of the residual stresses within laser-deposited titanium carbide (TiC) coatings on 2024 and 6061 aluminum (Al) alloys were investigated. Macro- and micro-stresses within the coatings were determined using an X-ray diffraction method. Owing to increased debonding between the coating and the substrate, the macro-stresses were found to be compressive and to decrease in magnitude with increasing processing speed. The origin of the macro- and micro-stresses is discussed. T...

  13. FaceSheet Push-off Tests to Determine Composite Sandwich Toughness at Cryogenic Temperatures

    Science.gov (United States)

    Gates, Thomas S.; Herring, Helen M.

    2001-01-01

    A new novel test method, associated analysis, and experimental procedures are developed to investigate the toughness of the facesheet-to-core interface of a sandwich material at cryogenic temperatures. The test method is designed to simulate the failure mode associated with facesheet debonding from high levels of gas pressure in the sandwich core. The effects of specimen orientation are considered, and the results of toughness measurements are presented. Comparisons are made between room and liquid nitrogen (-196 C) test temperatures. It was determined that the test method is insensitive to specimen facesheet orientation and strain energy release rate increases with a decrease in the test temperature.

  14. Evaluation of the effect of three innovative recyling methods on the shear bond strength of stainless steel brackets-an in vitro study.

    Science.gov (United States)

    Gupta, Neeraj; Kumar, Dilip; Palla, Aparna

    2017-04-01

    Orthodontists are commonly faced with the decision of what to do with debonded or inaccurately positioned brackets. An economical option to this dilemma is to recycle the brackets. Many recycling methods have been proposed, but the optimal bond strength of these recycled brackets needs further evaluation. Objectives: To evaluate and compare the effect of three recycling methods: (i) Sandblasting (ii) Sandblasting / direct flaming (iii) Sandblasting /direct flaming /acid bath solution on shear bond strength (SBS) of stainless steel brackets. Eighty human premolars were bonded with premolar stainless steel brackets as per manufacturer's instructions. The teeth were divided into 4 groups (n=20): Recycling and initial debonding was not done in Control group (Group I). After initial bonding, the brackets in the rest of the three experimental groups were debonded and recycled by following methods: (i) Sandblasting (Group II) (ii) Sandblasting /direct flaming (Group III) (iii) Sandblasting /direct flaming /acid bath solution (Group IV). Further the recycled brackets were bonded. The specimens were then subjected to testing in a Universal machine. The evaluation of the variation of the shear bond strength (SBS) among test groups was done using one-way ANOVA test and inter-experimental group comparison was done by Newman-Keuls multiple post hoc procedure. Group I (8.6510±1.3943MPa) showed the highest bond strength followed by Group II (5.0185±0.9758MPa), Group IV (2.30±0.65MPa) and Group III (2.0455± 0.6196MPa). Statistically significant variations existed in the shear bond strength (SBS) in all groups analyzed except between Group III and Group IV. The following conclusions were drawn from the study: 1. Shear bond strength of new brackets is significantly higher than the recycled brackets. 2. Brackets sandblasted with 90µm aluminium oxide particle air-abrasion showed significantly higher shear bond strength compared to direct flaming/sandblasting and direct flaming

  15. Digital device in postextraction implantology : a clinical case presentation

    OpenAIRE

    Borgonovo, A..E.; Rigaldo, F.; Battaglia, D.; Re, D.; Giannì, A.B.

    2014-01-01

    Aim. The aim of this work is to describe a case of immediate implant placement after extraction of the upper right first premolar, with the use of CAD/CAM technology, which allows an early digital impression of the implant site with an intraoral scanner (MHT 3D Progress, Verona, Italy). Case Report. A 46-year-old female was referred with a disorder caused by continuous debonding of the prosthetic crown on the upper right first premolar. Clinically, there were no signs, and the evaluation of t...

  16. Design, fabrication, and testing of an ultrasonic de-icing system for helicopter rotor blades

    Science.gov (United States)

    Palacios, Jose Luis

    A low-power, non-thermal ultrasonic de-icing system is introduced as a possible substitute for current electro-thermal systems. The system generates delaminating ultrasonic transverse shear stresses at the interface of accreted ice. A PZT-4 disk driven at 28.5 KHz (radial resonance of the disk) instantaneously de-bonds 2 mm thick freezer ice layers. The ice layers are accreted to a 0.7 mm thick, 30.4 cm x 30.4 cm steel plate at an environment temperature of -20°C. A power input of 50 Watts is applied to the actuator (50 V, 19.6 KV/m), which translates to a de-icing power of 0.07 W/cm2. A finite element model of the actuator bonded to the isotropic plate is used to guide the design of the system, and predicts the transverse shear stresses at the ice interface. Wind tunnel icing tests were conducted to demonstrate the potential use of the proposed system under impact icing conditions. Both glaze ice and rime ice were generated on steel and composite plates by changing the cloud conditions of the wind tunnel. Continuous ultrasonic vibration prevented impact ice formation around the actuator location at an input power not exceeding 0.18 W/cm 2 (1.2 W/in2). As ice thickness reached a critical thickness of approximately 1.2 mm, shedding occurred on those locations where ultrasonic transverse shear stresses exceeded the shear adhesion strength of the ice. Finite element transverse shear stress predictions correlate with observed experimental impact ice de-bonding behavior. To increase the traveling distance of propagating ultrasonic waves, ultrasonic shear horizontal wave modes are studied. Wave modes providing large modal interface transverse shear stress concentration coefficients (ISCC) between the host structure (0.7 mm thick steel plate) and accreted ice (2.5 mm thick ice layer) are identified and investigated for a potential increase in the wave propagation distance. Ultrasonic actuators able to trigger these optimum wave modes are designed and fabricated. Despite

  17. Fracture analysis of adhesive joints in wind turbine blades

    DEFF Research Database (Denmark)

    Eder, Martin Alexander; Bitsche, Robert

    2015-01-01

    Modern wind turbine rotor blades are usually made from fibre-reinforced composite subcomponents. In the final assembly stage, these subcomponents are bonded together by several adhesive joints. One important adhesive joint is situated at the trailing edge, which refers to the downstream edge where...... the air-flow rejoins and leaves the blade. Maintenance inspections of wind turbine rotor blades show that among other forms of damage, local debonding of the shells along the trailing edge is a frequent failure type. The cause of trailing edge failure in wind turbine blades is complex, and detailed...

  18. A comparison of shear bond strength of orthodontic brackets bonded with four different orthodontic adhesives

    Science.gov (United States)

    Sharma, Sudhir; Tandon, Pradeep; Nagar, Amit; Singh, Gyan P; Singh, Alka; Chugh, Vinay K

    2014-01-01

    Objectives: The objective of this study is to compare the shear bond strength (SBS) of stainless steel (SS) orthodontic brackets bonded with four different orthodontic adhesives. Materials and Methods: Eighty newly extracted premolars were bonded to 0.022 SS brackets (Ormco, Scafati, Italy) and equally divided into four groups based on adhesive used: (1) Rely-a-Bond (self-cure adhesive, Reliance Orthodontic Product, Inc., Illinois, USA), (2) Transbond XT (light-cure adhesive, 3M Unitek, CA, USA), (3) Transbond Plus (sixth generation self-etch primer, 3M Unitek, CA, USA) with Transbond XT (4) Xeno V (seventh generation self-etch primer, Dentsply, Konstanz, Germany) with Xeno Ortho (light-cure adhesive, Dentsply, Konstanz, Germany) adhesive. Brackets were debonded with a universal testing machine (Model No. 3382 Instron Corp., Canton, Mass, USA). The adhesive remnant index (ARI) was recordedIn addition, the conditioned enamel surfaces were observed under a scanning electron microscope (SEM). Results: Transbond XT (15.49 MPa) attained the highest bond strength. Self-etching adhesives (Xeno V, 13.51 MPa; Transbond Plus, 11.57 MPa) showed clinically acceptable SBS values and almost clean enamel surface after debonding. The analysis of variance (F = 11.85, P adhesives left on the tooth) to be the most prevalent in Transbond XT (40%), followed by Rely-a-Bond (30%), Transbond Plus with Transbond XT (15%), and Xeno V with Xeno Ortho (10%). Under SEM, enamel surfaces after debonding of the brackets appeared porous when an acid-etching process was performed on the surfaces of Rely-a-Bond and Transbond XT, whereas with self-etching primers enamel presented smooth and almost clean surfaces (Transbond Plus and Xeno V group). Conclusion: All adhesives yielded SBS values higher than the recommended bond strength (5.9-7–8 MPa), Seventh generation self-etching primer Xeno V with Xeno Ortho showed clinically acceptable SBS and the least amount of residual adhesive left on the

  19. On the failure analysis of bondlines: Stress or energy based fracture criteria?

    DEFF Research Database (Denmark)

    Anyfantis, Konstantinos

    2014-01-01

    that characterizes a given bondline, both its cohesive strength and fracture toughness material parameters must be experimentally defined. Based on these properties, failure analysis of the bondline can be done either through stress- or energy-based criteria. The aim of this work is to investigate the effectiveness...... to classify the wide range of bondlines with respect to the failure theory that best describes the debonding process. Cohesive length scale effects are first demonstrated by modeling end notch flexure geometries and later by modeling double strap joint geometries within the framework of a wide numerical...

  20. Measurement of Localized Corrosion Rates at Inclusion Particles in AA7075 by In Situ Three Dimensional (3D) X-ray Synchrotron Tomography

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Sudhanshu S.; Williams, Jason J.; Stannard, Tyler J.; Xiao, Xianghui; De Carlo, Francesco; Chawla, Nikhilesh

    2016-03-01

    In situ X-ray synchrotron tomography was used to measure the localized corrosion rate of Mg2Si particles present in 7075 aluminum alloys in deionized ultra-filtered (DIUF) water. The evolution of hydrogen bubbles was captured as a function of time and the measured volume was used to calculate the local corrosion rate of Mg2Si particles. It was shown that in the absence of chloride ions, stress was needed to create fresh particle surfaces, either by fracture or debonding, to initiate corrosion at the particles.

  1. Experimental study on mechanical behavior of fiber/matrix interface in metal matrix composite

    International Nuclear Information System (INIS)

    Wang, Q.; Chiang, F.P.

    1994-01-01

    The technique SIEM(Speckle Interferometry with Electron Microscopy) was employed to quantitatively measure the deformation on the fiber/matrix interface in SCS-6/Ti-6-4 composite at a microscale level. The displacement field within the fiber/matrix interphase zone was determined by in-situ observation with sensitivity of 0.003(microm). The macro-mechanical properties were compared with micro-mechanical behavior. It is shown that the strength in the interphase zone is weaker than the matrix tensile strength. The deformation process can be characterized by the uniform deformation, interface strain concentration and debond, and matrix plastic deformation

  2. Nonlinear soil-structure interaction analysis of SIMQUAKE II. Final report

    International Nuclear Information System (INIS)

    Vaughan, D.K.; Isenberg, J.

    1982-04-01

    This report describes an analytic method for modeling of soil-structure interaction (SSI) for nuclear power plants in earthquakes and discusses its application to SSI analyses of SIMQUAKE II. The method is general and can be used to simulate a three-dimensional structural geometry, nonlinear site characteristics and arbitrary input ground shaking. The analytic approach uses the soil island concept to reduce SSI models to manageable size and cost. Nonlinear constitutive behavior of the soil is represented by the nonlinear, kinematic cap model. In addition, a debonding-rebonding soil-structure interface model is utilized to represent nonlinear effects which singificantly alter structural response in the SIMQUAKE tests. STEALTH, an explicit finite difference code, is used to perform the dynamic, soil-structure interaction analyses. Several two-dimensional posttest SSI analyses of model containment structures in SIMQUAKE II are performed and results compared with measured data. These analyses qualify the analytic method. They also show the importance of including debonding-rebonding at the soil-structure interface. Sensitivity of structural response to compaction characteristics of backfill material is indicated

  3. A study of TiB2/TiB gradient coating by laser cladding on titanium alloy

    Science.gov (United States)

    Lin, Yinghua; Lei, Yongping; Li, Xueqiao; Zhi, Xiaohui; Fu, Hanguang

    2016-07-01

    TiB2/TiB gradient coating has been fabricated by a laser cladding technique on the surface of a Ti-6Al-4V substrate using TiB2 powder as the cladding material. The microstructure and mechanical properties of the gradient coating were analyzed by SEM, EPMA, XRD, TEM and an instrument to measure hardness. With the increasing distance from the coating surface, the content of TiB2 particles gradually decreased, but the content of TiB short fibers gradually increased. Meanwhile, the micro-hardness and the elastic modulus of the TiB2/TiB coating showed a gradient decreasing trend, but the fracture toughness showed a gradient increasing trend. The fracture toughness of the TiB2/TiB coating between the center and the bottom was improved, primarily due to the debonding of TiB2 particles and the high fracture of TiB short fibers, and the fracture position of TiB short fiber can be moved to an adjacent position. However, the debonding of TiB2 particles was difficult to achieve at the surface of the TiB2/TiB coating.

  4. Sliding wear behavior of E-glass-epoxy/MWCNT composites: An experimental assessment

    Directory of Open Access Journals (Sweden)

    Ravindranadh Bobbili

    2016-03-01

    Full Text Available This investigation has evaluated the sliding wear properties of E-glass-epoxy/MWCNT (multiwalled carbon nanotube composite and Epoxy/MWCNT composite. Four different reinforcements (0, 0.5,1 and 1.5 wt % of MWCNTs are dispersed into an epoxy resin. Design of experiments (DOE and Analysis of variance (ANOVA are employed to understand the relationship between control factors (Percentage of reinforcement, Sliding distance, Sliding velocity and Normal load and response measures (specific wear rate and friction coefficient. The control variables such as sliding distance (300, 600, 900 and 1200 m and normal loads of 10, 15, 20 and 25 N and at sliding velocities of 1, 2, 3 and 4 m/s are chosen for this study. It is observed that that the specific wear rate and friction coefficient can be reduced by the addition of MWCNTs. Scanning electron microscopy (SEM is used to observe the worn surfaces of the samples. Compared with neat epoxy, the composites with MWCNTs showed a lower mass loss, friction coefficient and wear rate and these parameters decreased with the increase of MWCNT percentage. Microscopic investigation of worn out sample fracture surface has revealed that fiber debonding happens when the stresses at the fiber matrix interface exceeds the interfacial strength, causing the fiber to debond from the matrix. The optimum control variables have been derived to reduce both wear and friction coefficient of composites.

  5. Survival of anterior cantilevered all-ceramic resin-bonded fixed dental prostheses made from zirconia ceramic.

    Science.gov (United States)

    Sasse, Martin; Kern, Matthias

    2014-06-01

    This study evaluated the clinical outcome of all-ceramic resin-bonded fixed dental prostheses (RBFDPs) with a cantilevered single-retainer design made from zirconia ceramic. Forty-two anterior RBFDPs with a cantilevered single-retainer design were made from yttrium oxide-stabilized zirconium oxide ceramic. RBFDPs were inserted using Panavia 21 TC as luting agent after air-abrasion of the ceramic bonding surface. During a mean observation time of 61.8 months two debondings occurred. Both RBFDPs were rebonded using Panavia 21 TC and are still in function. A caries lesion was detected at one abutment tooth during recall and was treated with a composite filling. Therefore, the overall six-year failure-free rate according to Kaplan-Meier was 91.1%. If only debonding was defined as failure the survival rate increased to 95.2%. Since all RBFDPs are still in function the overall survival rate was 100% after six years. Cantilevered zirconia ceramic RBFDPs showed promising results within the observation period. Single-retainer resin-bonded fixed dental prostheses made from zirconia ceramic show very good mid-term clinical survival rates. They should therefore be considered as a viable treatment alternative for the replacement of single missing anterior teeth especially as compared to an implant therapy. Copyright © 2014 Elsevier Ltd. All rights reserved.

  6. Deposit Probe Measurements in Large Biomass-Fired Grate Boilers and Pulverized-Fuel Boilers

    DEFF Research Database (Denmark)

    Hansen, Stine Broholm; Jensen, Peter Arendt; Jappe Frandsen, Flemming

    2014-01-01

    A number of full-scale deposit probe measuring campaigns conducted in grate-fired and suspension-fired boilers, fired with biomass, have been reviewed and compared. The influence of operational parameters on the chemistry of ash and deposits, on deposit build-up rates, and on shedding behavior has...... of the deposits formed is determined by the fly ash composition and the flue gas temperature; increases in the local flue gas temperature lead to higher contents of Si and Ca and lower contents of Cl in the deposits. The net deposit build-up rates in grate-fired and suspension-fired boilers are at similar levels....../wood-firing in suspension-fired boilers, shedding occurred by debonding with incomplete removal at flue gas temperatures of 600–1000 °C and by debonding with complete removal during wood-firing in suspension-fired boilers at high flue gas temperatures (1300 °C). Shedding events were not observed during wood suspension...

  7. Application of the laser spallation technique to the measurement of the adhesion strength of tungsten carbide coatings on superalloy substrates

    Energy Technology Data Exchange (ETDEWEB)

    Boustie, M.; Aoroux, E.; Romain, J.-P. [Ecole Nationale Superieure de Mecanique et d' Aerotechnique (ENSMA), 86 - Futuroscope (FR). Lab. de Combustion et de Detonique (LCD)

    2000-10-01

    High power pulsed lasers are used to induce shock waves in Hastelloy X targets coated with tungsten carbide of 70 {mu}m and 50 {mu}m thickness. In suitable irradiation conditions, a debonding of the substrate/coating interface due to the generation of tensile stresses is observed. Experimental results are analyzed with the use of numerical simulations yielding the stress history at interface and its dependence on laser pulse intensity up to 600 GW/cm{sup 2} with 1 ns and 3 ns durations under direct irradiation, and 23 ns with water confinement. As a consequence of shock decay during the propagation through the substrate, a strong variation of incident intensity results in a small variation of tensile stress. This allows an accurate determination of the debonding threshold which is found in the range of 1.0 to 1.3 GPa for short laser pulses (1 and 3 ns) and 0.5 to 0.6 GPa for long laser pulses (23 ns confined). (orig.)

  8. The properties degradation of exposed GFRP roof

    Science.gov (United States)

    Zainudin, Mohammad; Diharjo, Kuncoro; Kaavessina, Mujtahid; Setyanto, Djoko

    2018-02-01

    There is much consideration of roof selection as a protector of a building against the outside weather, such as lightweight, strong stiff, corrosion resistant and guarantee for the availability of products. Based on these considerations, glass fiber reinforced polymer (GFRP) roof is a roof which can fulfill the requirement. The objective of this research is to investigate the degradation of physical and mechanical properties of GFRP roof exposed in outside weather. This GFRP roof composite was produced using a sheet molding compound (SMC) supplied by PT Intec Persada, Tangerang, Indonesia. There are two kinds GFRP roofs evaluated in this research that are GFRP roof exposed within 7 years and new GFRP roof that has not been exposed. The GFRP roofs were cut manually for preparing the specimens for hardness test, tensile test, SEM and FTIR test. The results show that the GFRP roof exposed within 7 years had the degradation of properties compared to the new GFRP roof. The exposed GFRP roof had lower strength and hardness compared to the new GFRP roof. The SEM observation indicates that exposed GFRP roof had the debonding of fiber on the surface, and in contrast, there are no debonding of fiber in the new GFRP roof surface. It can be recommended that the exposed GFRP roof may be repaired to enhance its performance and can re-increase its properties using the coating.

  9. A Study on the Embedment Effect in the Soil-Structure Interaction Analysis of the APR1400

    International Nuclear Information System (INIS)

    Young-Sun Jang; Kwang-Ho Joo; Chong-Hak Kim

    2002-01-01

    The SSI (Soil-Structure Interaction) analyses are being performed for the APR1400 (Advanced Power Reactor 1400 MWe, Old name - KNGR; Korean Next Generation Reactor) design, because the APR1400 is developed as a Standard Nuclear Power Plant concept enveloping suitable soil conditions. For the SSI analyses, SASSI program which adopts the Flexible Volume Method is used. In the SSI analyses, there can be uncertainties by Bond and De-bond problem between the structure and lateral soil elements. According to ASCE Standard 4, one method to address this concern is to assume no connectivity between structure and lateral soil over the upper half of the embedment of 20 ft (6 m), whichever is less. This study is performed as a part of the parametric analyses for the APR1400 seismic analyses to address the concern of the potential embedment effect on the in-structure response spectra due to connectivity between structure and lateral soil. In this study, 4 model cases are analyzed to check the potential embedment effect - Full connection, 20 ft no connectivity which is defined as a minimum De-bond depth of the soil in ASCE Standard 4 and 26.5 ft no connectivity between structure and lateral soil over the upper half of the embedment. Last one is full no connection for only reference. The in-structure response spectra are compared with the response spectra without considering the embedment effect. (authors)

  10. Longevity of metal-ceramic crowns cemented with self-adhesive resin cement: a prospective clinical study

    Directory of Open Access Journals (Sweden)

    Lucas Pradebon BRONDANI

    2017-04-01

    Full Text Available Abstract Resin cements are often used for single crown cementation due to their physical properties. Self-adhesive resin cements gained widespread due to their simplified technique compared to regular resin cement. However, there is lacking clinical evidence about the long-term behavior of this material. The aim of this prospective clinical trial was to assess the survival rates of metal-ceramic crowns cemented with self-adhesive resin cement up to six years. One hundred and twenty-nine subjects received 152 metal-ceramic crowns. The cementation procedures were standardized and performed by previously trained operators. The crowns were assessed as to primary outcome (debonding and FDI criteria. Statistical analysis was performed using Kaplan-Meier statistics and descriptive analysis. Three failures occurred (debonding, resulting in a 97.6% survival rate. FDI criteria assessment resulted in scores 1 and 2 (acceptable clinical evaluation for all surviving crowns. The use of self-adhesive resin cement is a feasible alternative for metal-ceramic crowns cementation, achieving high and adequate survival rates.

  11. Longevity of metal-ceramic crowns cemented with self-adhesive resin cement: a prospective clinical study

    Science.gov (United States)

    Brondani, Lucas Pradebon; Pereira-Cenci, Tatiana; Wandsher, Vinicius Felipe; Pereira, Gabriel Kalil; Valandro, Luis Felipe; Bergoli, César Dalmolin

    2017-04-10

    Resin cements are often used for single crown cementation due to their physical properties. Self-adhesive resin cements gained widespread due to their simplified technique compared to regular resin cement. However, there is lacking clinical evidence about the long-term behavior of this material. The aim of this prospective clinical trial was to assess the survival rates of metal-ceramic crowns cemented with self-adhesive resin cement up to six years. One hundred and twenty-nine subjects received 152 metal-ceramic crowns. The cementation procedures were standardized and performed by previously trained operators. The crowns were assessed as to primary outcome (debonding) and FDI criteria. Statistical analysis was performed using Kaplan-Meier statistics and descriptive analysis. Three failures occurred (debonding), resulting in a 97.6% survival rate. FDI criteria assessment resulted in scores 1 and 2 (acceptable clinical evaluation) for all surviving crowns. The use of self-adhesive resin cement is a feasible alternative for metal-ceramic crowns cementation, achieving high and adequate survival rates.

  12. Volume growth during uniaxial tension of particle-filled elastomers at various temperatures - Experiments and modelling

    Science.gov (United States)

    Ilseng, Arne; Skallerud, Bjørn H.; Clausen, Arild H.

    2017-10-01

    A common presumption for elastomeric material behaviour is incompressibility, however, the inclusion of filler particles might give rise to matrix-particle decohesion and subsequent volume growth. In this article, the volumetric deformation accompanying uniaxial tension of particle-filled elastomeric materials at low temperatures is studied. An experimental set-up enabling full-field deformation measurements is outlined and novel data are reported on the significant volume growth accompanying uniaxial tension of two HNBR and one FKM compounds at temperatures of - 18 , 0, and 23 °C. The volumetric deformation was found to increase with reduced temperature for all compounds. To explain the observed dilatation, in situ scanning electron microscopy was used to inspect matrix-particle debonding occurring at the surface of the materials. A new constitutive model, combining the Bergström-Boyce visco-hyperelastic formulation with a Gurson flow potential function is outlined to account for the observed debonding effects in a numerical framework. The proposed model is shown to provide a good correspondence to the experimental data, including the volumetric response, for the tested FKM compound at all temperature levels.

  13. Mechanical Properties of Abutments: Resin-Bonded Glass Fiber-Reinforced Versus Titanium.

    Science.gov (United States)

    Bassi, Mirko Andreasi; Bedini, Rosells; Pecci, Raffaela; Ioppolo, Pietro; Laritano, Dorina; Carinci, Francesco

    2016-01-01

    The clinical success and longevity of endosseous implants, after their prosthetic finalization, mainly depends on mechanical factors. Excessive mechanical stress has been shown to cause initial bone loss around implants in the presence of a rigid implant-prosthetic connection. The implant abutments are manufactured with high elastic modulus materials such as titanium, steel, precious alloys, or esthetic ceramics. These materials do not absorb any type of shock from the chewing loads or ensure protection of the bone-implant interface, especially when the esthetic restorative material is ceramic rather than composite resin. The mechanical resistance to cyclical load was evaluated in a tooth-colored fiber-reinforced abutment prototype (TCFRA) and compared to that of a similarly shaped titanium abutment (TA). Eight TCFRAs and eight TAs were adhesively cemented on as many titanium implants. The swinging the two types of abutments showed during the application of sinusoidal load was also analyzed. In the TA group, fracture and deformation occurred in 12.5% of samples, while debonding occurred in 62.5%. In the TCFRA group, only debonding was present, in 37.5% of samples. In comparison to the TAs, the TCFRAs exhibited greater swinging during the application of sinusoidal load. In the TA group extrusion prevailed, whereas in the TCFRA group intrusion was more frequent. TCFRA demonstrated a greater elasticity than did TAs to the flexural load, absorbing part of the transversal load applied on the fixture during the chewing function and thus reducing the stress on the bone-implant interface.

  14. Revisiting the generalized scaling law for adhesion: role of compliance and extension to progressive failure.

    Science.gov (United States)

    Mojdehi, Ahmad R; Holmes, Douglas P; Dillard, David A

    2017-10-25

    A generalized scaling law, based on the classical fracture mechanics approach, is developed to predict the bond strength of adhesive systems. The proposed scaling relationship depends on the rate of change of debond area with compliance, rather than the ratio of area to compliance. This distinction can have a profound impact on the expected bond strength of systems, particularly when the failure mechanism changes or the compliance of the load train increases. Based on the classical fracture mechanics approach for rate-independent materials, the load train compliance should not affect the force capacity of the adhesive system, whereas when the area to compliance ratio is used as the scaling parameter, it directly influences the bond strength, making it necessary to distinguish compliance contributions. To verify the scaling relationship, single lap shear tests were performed for a given pressure sensitive adhesive (PSA) tape specimens with different bond areas, number of backing layers, and load train compliance. The shear lag model was used to derive closed-form relationships for the system compliance and its derivative with respect to the debond area. Digital image correlation (DIC) is implemented to verify the non-uniform shear stress distribution obtained from the shear lag model in a lap shear geometry. The results obtained from this approach could lead to a better understanding of the relationship between bond strength and the geometry and mechanical properties of adhesive systems.

  15. Combustion chemical vapor deposition (CCVD) of LaPO4 monazite and beta-alumina on alumina fibers for ceramic matrix composites

    International Nuclear Information System (INIS)

    Hwang, T.J.; Hendrick, M.R.; Shao, H.; Hornis, H.G.; Hunt, A.T.

    1998-01-01

    This research used the low cost, open atmosphere combustion chemical vapor deposition (CCVD SM ) method to efficiently deposit protective coatings onto alumina fibers (3M Nextel TM 610) for use in ceramic matrix composites (CMCs). La-monazite (LaPO 4 ) and beta-alumina were the primary candidate debonding coating materials investigated. The coated fibers provide thermochemical stability, as well as desired debonding/sliding interface characteristics to the CMC. Dense and uniform La-phosphate coatings were obtained at deposition temperatures as low as 900-1000 C with minimal degradation of fibers. However, all of the β-alumina phases required high deposition temperatures and, thus, could not be applied onto the Nextel TM 610 alumina fibers. The fibers appeared to have complete and relatively uniform coatings around individual filaments when 420 and 1260 filament tows were coated via the CCVD process. Fibers up to 3 feet long were fed through the deposition flame in the laboratory of MicroCoating Technologies (MCT). TEM analyses performed at Wright-Patterson AFB on the CCVD coated fibers showed a 10-30 nm thick La-rich layer at the fiber/coating interface, and a layer of columnar monazite 0.1-1 μm thick covered with sooty carbon of <50 nm thick on the outside. A single strength test on CCVD coated fibers performed by 3M showed that the strength value fell in the higher end of data from other CVD coated samples. (orig.)

  16. Electroplating chromium on CVD SiC and SiCf-SiC advanced cladding via PyC compatibility coating

    Science.gov (United States)

    Ang, Caen; Kemery, Craig; Katoh, Yutai

    2018-05-01

    Electroplating Cr on SiC using a pyrolytic carbon (PyC) bond coat is demonstrated as an innovative concept for coating of advanced fuel cladding. The quantification of coating stress, SEM morphology, XRD phase analysis, and debonding test of the coating on CVD SiC and SiCf-SiC is shown. The residual tensile stress (by ASTM B975) of electroplated Cr is > 1 GPa prior to stress relaxation by microcracking. The stress can remove the PyC/Cr layer from SiC. Surface etching of ∼20 μm and roughening to Ra > 2 μm (by SEM observation) was necessary for successful adhesion. The debonding strength (by ASTM D4541) of the coating on SiC slightly improved from 3.6 ± 1.4 MPa to 5.9 ± 0.8 MPa after surface etching or machining. However, this improvement is limited due to the absence of an interphase, and integrated CVI processing may be required for further advancement.

  17. Facile synthesis of main-chain degradable block copolymers for performance enhanced dismantlable adhesion.

    Science.gov (United States)

    Sato, Eriko; Hagihara, Takashi; Matsumoto, Akikazu

    2012-04-01

    Block copolymers consisting of readily degradable polyperoxides and non-degradable vinyl polymers as the block segments were successfully synthesized by reversible chain transfer catalyzed polymerization, which is one of living radical polymerization techniques. The block copolymers showed characteristic morphology and wettability being different from the polymer blends. When block copolymers containing polyperoxide and polymethacrylate blocks were heated below 150 °C, the polyperoxide blocks were completely degraded and the polymethacrylate blocks were recovered without degradation. Block copolymers containing a poly(2-ethylhexyl methacrylate) block were then investigated as a dismantlable adhesion material, which requires adequate bonding strength during use and easy debonding on demand. Among the several block copolymers, the one consisting of poly(2-ethylhexyl methacrylate) and polyperoxide from methyl sorbate (PPMS) (M(n) = 4900) exhibited good performance as a pressure-sensitive adhesive (PSA). After heating the test specimens in a temperature range from 60 to 100 °C, PSA performance, which was evaluated by 180° peel strength and shear holding power measurements, was significantly diminished. Especially, after heating at 100 °C for 1 h, spontaneous debonding of some test specimens was observed because of the evolution of volatile acetaldehyde from PPMS.

  18. Fiscal 2000 technology trend survey. Survey of technology trend relating to next-generation metal-based material compatible with inverse manufacturing leading to energy use rationalization; 2000 nendo gijutsu doko chosa hokokusho. Energy shiyo gorika ni kakawaru inverse manufacturing ni tekigoushita jisedai kinzoku kei zairyo ni kansuru gijutsu doko chosa

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2001-03-01

    For the construction of a recycling system consuming less energy and therefore higher in efficiency, studies were made about the feasibility of metallic material developing/recycling systems more congruent with the objective through the application of inverse manufacturing (IM). Concerning metallic materials and recycling technologies, steel, aluminum alloys, and magnesium alloys were taken up, and a survey was made of hazardous elements in steel materials, unification of materials to constitute aluminum alloy parts, yield of magnesium in die casting, and the like. In the survey of recycling of automobiles, it was pointed out that the treatment of resin-based shredder dust was posing problems and that the use of metallic materials high in recyclability was essential to IM. In conclusion, three propositions were presented, which involved technologies for the advanced use of magnesium alloys as materials leading to the realization of IM, the development of recycling-oriented general-purpose alloys (with Mg and Al as mother metals), and the development of functional bonding technology enabling debonding (debondable bonding technology). (NEDO)

  19. Mechanical properties of resin glass fiber-reinforced abutment in comparison to titanium abutment

    Science.gov (United States)

    Andreasi Bassi, Mirko; Bedini, Rossella; Pecci, Raffella; Ioppolo, Pietro; Lauritano, Dorina; Carinci, Francesco

    2015-01-01

    Purpose: So far, definitive implant abutments have been performed with high elastic modulus materials, which prevented any type of shock absorption of the chewing loads and as a consequence, the protection of the bone-fixture interface. This is particularly the case when the esthetic restorative material chosen is ceramic rather than composite resin. The adoption of an anisotropic abutment, characterized by an elastic deformability, could allow decreasing the impulse of chewing forces transmitted to the crestal bone. Materials and Methods: According to research protocol, the mechanical resistance to cyclical load was evaluated in a tooth-colored fiber-reinforced abutment (TCFRA) prototype and compared to that of a titanium abutment (TA), thus eight TCFRAs and eight TAs were adhesively cemented on as many titanium implants. The swinging that the two types of abutments showed during the application of sinusoidal load was also analyzed. Results: In the TA group, both fracture and deformation occurred in 12.5% of samples while debonding 62.5%. In the TCFRA group, only debonding was present in 37.5% of samples. In comparison to the TAs, the TCFRAs exhibited a greater swinging during the application of sinusoidal load. In the TA group, the extrusion prevailed, whereas in the TCFRA group, the intrusion was more frequent. Conclusion: The greater elasticity of TCFRA to the flexural load allows absorbing part of the transversal load applied on the fixture during the chewing function, thus reducing the stress on the bone-implant interface. PMID:26229266

  20. ′Metal to resin′: A comparative evaluation of conventional band and loop space maintainer with the fiber reinforced composite resin space maintainer in children

    Directory of Open Access Journals (Sweden)

    A Garg

    2014-01-01

    Full Text Available Aims: To compare the clinical efficacy of two space maintainers namely, conventional band and loop and Fiber Reinforced Composite Resin (FRCR space maintainers . Subjects and Methods: Thirty healthy children, aged 5 to 8 years were selected having at least two deciduous molars in different quadrants indicated for extraction or lost previously. FRCR space maintainer was placed in one quadrant and in the other quadrant band and loop space maintainer was cemented. All the patients were recalled at 1 st , 3 rd , and 6 th months for evaluation of both types of space maintainer. Patient acceptability, time taken, and clinical efficacy was recorded. Statistical analysis used: The observations thus obtained were subjected to statistical analysis using Chi- square test and Mann-Whitney U test. Results: Patient acceptability was greater in Group I (FRCR in comparison to Group II (band and loop space maintainer. The time taken by Group I was significantly lower as compared to that of Group II. In Group I, debonding of enamel, composite was the most common complication leading to failure followed by debonding of fiber composite. In Group II, cement loss was the most common complication leading to failure followed by slippage of band and fracture of loop. The success rates of Groups I and Group II weares 63.3% and 36.7%, respectively. Conclusion: The study concluded that FRCRFiber Reinforced Composite Resin (Ribbond space maintainers can be considered as viable alternative to the conventional band and loop space maintainers.

  1. Microbial decontamination of some chicken meat products by gamma irradiation

    International Nuclear Information System (INIS)

    Afifi, E.A.; El-Nashaby, F.M.

    2001-01-01

    This investigation aims to study the possibility of using gamma irradiation for microbial decontamination of some chicken meat products (Luncheon, Burger and debonded minced chicken) which are produced by three companies (Halwany Bros.(H)-Faragalla (F) and Egypco (E)). The samples were purchased from local supermarkets and examined for the presence of Salmonella spp. and Staphylococcus aureus. The examination illustrated that all examined samples were positive for Staphylococcus aureus. While Luncheon (F), Burger (H) and debonded minced chicken (E) were only positive for Salmonella spp. Therefore, these product samples were gamma irradiated at 0, 3, 6 and 9 kGy. The effects of radiation treatments and cold storage (5+,-1 degree) on the total volatile basic nitrogen (T.V.B.N.), microbiological quality and sensory properties of samples under investigation were studied. The results indicated that 3kGy dose of gamma irradiation completely destroyed Staphylococcus aureus and Salmonella spp. and caused slight increase in (T.V.B.N.) content for all samples. A gradual increase in total bacteria, molds and yeast and T. V. B. N. during storage were observed, while 6 kGy dose was also sufficient for destroying Salmonella spp. and Staphylococcus aureus in all chicken meat products under investigation without any detectable effects on the sensory properties of these products and increased the shelf-life of luncheon, burger and minced for 8, 4 and 3 weeks respectively as compared with 4, 2 and 1 weeks for control samples

  2. Analysis of syntactic foam – GFRP sandwich composites for flexural loads

    Science.gov (United States)

    Paul, Daniel; Velmurugan, R.; Jayaganthan, R.; Gupta, N. K.; Manzhirov, A. V.

    2018-04-01

    The use of glass microballoon (GMB) — epoxy syntactic foams as a sandwich core material is studied. The skins and foam core are fabricated and joined instantaneously unlike the procedures followed in the previous studies. Each successive layer of the sandwich is fabricated when the previous layer is in a semi-gelled state. These sandwich samples are characterized for their properties under flexural loading. The failure modes and mechanical properties are carefully investigated. The change in fabrication technique results in a significant increase in the load bearing pattern of the sandwich. In earlier studies, debonding was found to occur prematurely since the bonding between the skins and core is the weakest plane. Using the current technique, core cracking occurs first, followed by skin fiber breaking and debonding happens at the end. This ensures that the load carrying phase of the structure is extended considerably. The sandwich is also analytically studied using Reddy’s higher order shear deformation theory. A higher order theory is selected as the sandwich can no longer be considered as a thin beam and thus shear effects also need to be considered in addition to bending effects.

  3. Examination of fracture surfaces using focused ion beam milling

    International Nuclear Information System (INIS)

    Cairney, J.M.; Munroe, P.R.; Schneibel, J.H.

    2000-01-01

    Composite materials consisting of an iron aluminide matrix with composition approximately Fe-40at%Al, reinforced with a volume fraction of 40--70% ceramic particles (TiC, WC, TiB 2 or ZrB 2 ), are currently being developed. Focused ion beam milling is a relatively new tool to materials science. It uses a high resolution (<5nm), energetic beam of gallium ions to selectively sputter regions of a material, whilst also functioning as a scanning ion microscope. The milling accuracy is of the order of the beam size allowing very precise sectioning to be carried out. The focused ion beam can be used to prepare highly localized cross sections which reveal the internal sub-structure of materials, avoiding detrimental processes such as deformation, or closing of existing cracks by mechanical abrasion. An area is milled from the sample such that, upon tilting, the internal structure can be imaged. The focused ion beam therefore offers a unique opportunity to examine cross-sections of the fracture surfaces in FeAl-based composites. In the present study, the focused ion beam was used to obtain cross-sections of fracture surfaces in two composite materials, in order to examine the extent of interfacial debonding and matrix deformation, thus providing more information about the mode of fracture. These cross-sections were prepared at regions where significant debonding was observed

  4. Concrete Infill Monitoring in Concrete-Filled FRP Tubes Using a PZT-Based Ultrasonic Time-of-Flight Method.

    Science.gov (United States)

    Luo, Mingzhang; Li, Weijie; Hei, Chuang; Song, Gangbing

    2016-12-07

    Concrete-filled fiber-reinforced polymer tubes (CFFTs) have attracted interest for their structural applications in corrosive environments. However, a weak interfacial strength between the fiber-reinforced polymer (FRP) tube and the concrete infill may develop due to concrete shrinkage and inadequate concrete compaction during concrete casting, which will destroy the confinement effect and thereby reduce the load bearing capacity of a CFFT. In this paper, the lead zirconate titanate (PZT)-based ultrasonic time-of-flight (TOF) method was adopted to assess the concrete infill condition of CFFTs. The basic idea of this method is that the velocity of the ultrasonic wave propagation in the FRP material is about half of that in concrete material. Any voids or debonding created along the interface between the FRP tube and the concrete will delay the arrival time between the pairs of PZT transducers. A comparison of the arrival times of the PZT pairs between the intact and the defected CFFT was made to assess the severity of the voids or the debonding. The feasibility of the methodology was analyzed using a finite-difference time-domain-based numerical simulation. Experiments were setup to validate the numerical results, which showed good agreement with the numerical findings. The results showed that the ultrasonic time-of-flight method is able to detect the concrete infill condition of CFFTs.

  5. FRP-RC Beam in Shear: Mechanical Model and Assessment Procedure for Pseudo-Ductile Behavior

    Directory of Open Access Journals (Sweden)

    Floriana Petrone

    2014-07-01

    Full Text Available This work deals with the development of a mechanics-based shear model for reinforced concrete (RC elements strengthened in shear with fiber-reinforced polymer (FRP and a design/assessment procedure capable of predicting the failure sequence of resisting elements: the yielding of existing transverse steel ties and the debonding of FRP sheets/strips, while checking the corresponding compressive stress in concrete. The research aims at the definition of an accurate capacity equation, consistent with the requirement of the pseudo-ductile shear behavior of structural elements, that is, transverse steel ties yield before FRP debonding and concrete crushing. For the purpose of validating the proposed model, an extended parametric study and a comparison against experimental results have been conducted: it is proven that the common accepted rule of assuming the shear capacity of RC members strengthened in shear with FRP as the sum of the maximum contribution of both FRP and stirrups can lead to an unsafe overestimation of the shear capacity. This issue has been pointed out by some authors, when comparing experimental shear capacity values with the theoretical ones, but without giving a convincing explanation of that. In this sense, the proposed model represents also a valid instrument to better understand the mechanical behavior of FRP-RC beams in shear and to calculate their actual shear capacity.

  6. Delamination of plasters applied to historical masonry walls: analysis by acoustic emission technique and numerical model

    Science.gov (United States)

    Grazzini, A.; Lacidogna, G.; Valente, S.; Accornero, F.

    2018-06-01

    Masonry walls of historical buildings are subject to rising damp effects due to capillary or rain infiltrations, which in the time produce decay and delamination of historical plasters. In the restoration of masonry buildings, the plaster detachment frequently occurs because of mechanical incompatibility in repair mortar. An innovative laboratory procedure is described for test mechanical adhesion of new repair mortars. Compression static tests were carried out on composite specimens stone block-repair mortar, which specific geometry can test the de-bonding process of mortar in adherence with a stone masonry structure. The acoustic emission (AE) technique was employed for estimating the amount of energy released from fracture propagation in adherence surface between mortar and stone. A numerical simulation was elaborated based on the cohesive crack model. The evolution of detachment process of mortar in a coupled stone brick-mortar system was analysed by triangulation of AE signals, which can improve the numerical model and predict the type of failure in the adhesion surface of repair plaster. Through the cohesive crack model, it was possible to interpret theoretically the de-bonding phenomena occurring at the interface between stone block and mortar. Therefore, the mechanical behaviour of the interface is characterized.

  7. Susceptibility to scratch surface damage of wollastonite- and talc-containing polypropylene micrometric composites

    International Nuclear Information System (INIS)

    Hadal, R.; Dasari, A.; Rohrmann, J.; Misra, R.D.K.

    2004-01-01

    The paper describes the effect of wollastonite and talc on the scratch deformation behavior of low and high crystallinity polypropylenes under identical test conditions. The vertical resolution of atomic force microscopy and lateral resolution of scanning electron microscopy is utilized to examine the characteristics of scratch damage. Contrary to the expectations that high crystallinity and stiffness of polypropylene composites should increase resistance to scratch deformation, the susceptibility to mechanical deformation depends on bonding of mineral particles to the polymer matrix. Scratch deformed regions in neat polypropylenes were free of voids and grooves, while reinforced-polypropylenes exhibited voids and debonding/detachment of filler particles. The severity of plastic deformation in reinforced polypropylenes is a function of debonding/detachment of mineral particles, which is comparatively more for talc-reinforced polypropylenes than wollastonite-reinforced polypropylenes because of the layered structure of talc that encourages delamination. Usage of coating and coupling agents improved the resistance to scratch deformation by promoting adhesion and bonding between the reinforcement and matrix

  8. Assessment of the changes in quality of life of patients with class II and III deformities during and after orthodontic-surgical treatment.

    Science.gov (United States)

    Baherimoghaddam, T; Tabrizi, R; Naseri, N; Pouzesh, A; Oshagh, M; Torkan, S

    2016-04-01

    The aim of this longitudinal study was to assess and compare the oral health-related quality of life (OHRQoL) of patients with class II and III deformities during and after orthodontic-surgical treatment. Thirty class III and 28 class II patients were evaluated at baseline (T0), just prior to surgery (T1), at 6 months after surgery (T2), and at 12 months after debonding (T3). OHRQoL was assessed using the Oral Health Impact Profile (OHIP-14). Friedman two-way analysis of variance and the Wilcoxon signed-rank test were performed to compare the relative changes in OHRQoL during treatment. Significant changes in the overall OHIP-14 scores were observed during and after orthodontic-surgical treatment in both groups. During the pre-surgical stage, psychological discomfort and psychological disability decreased in class III patients, and class II patients experienced a significant deterioration in psychological discomfort during the same period. Six months after surgery, patients in both groups showed improvements in psychological discomfort, social disability, and handicap. Physical disability and functional limitation showed further improvement at 12 months after debonding in class II patients. This study reaffirms that orthodontic-surgical treatment has a significant effect on the OHRQoL of class III and class II patients. Copyright © 2015 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

  9. Adhesion of nickel–titanium shape memory alloy wires to thermoplastic materials: theory and experiments

    International Nuclear Information System (INIS)

    Antico, F C; Zavattieri, P D; Hector Jr, L G; Mance, A; Rodgers, W R; Okonski, D A

    2012-01-01

    We present a combined experimental/theoretical study aimed at enhancing adhesion between a NiTi wire and a thermoplastic polyolefin (TPO) matrix in which it is embedded. NiTi wire surfaces were subjected to the following surface treatments prior to pull-out tests: (i) treatment with an acid etch or chemical conversion coating and (ii) application of a surface microgeometry to enhance mechanical interlocking between the wire and the TPO matrix. Nanometer to micron-scale NiTi wire surface features were examined with atomic force microscopy. The extent to which each treatment increased the pull-out force was quantified. Existing theoretical models of wire pull-out based upon strength of materials and linear elastic fracture mechanics are reviewed. Results from a finite element model (FEM), wherein the NiTi/TPO matrix interface is modeled with a cohesive zone model, suggest that the interface behavior strongly depends on the cohesive energy. The FEM model properly accounts for energy dissipation at the debonding front and inelastic deformation in a NiTi wire during pull-out. We demonstrate that residual stresses from the molding process significantly influence mode mixity at the debonding front. (paper)

  10. Single fiber push-out characterization of interfacial mechanical properties in unidirectional CVI-C/SiC composites by the nano-indentation technique

    Science.gov (United States)

    Zhang, Lifeng; Ren, Chengzu; Zhou, Changling; Xu, Hongzhao; Jin, Xinmin

    2015-12-01

    The characterization of interfaces in woven ceramic matrix composites is one of the most challenging problems in composite application. In this investigation, a new model material consisting of the chemical vapor infiltration unidirectional C/SiC composites with PyC fiber coating were prepared and evaluated to predict the interfacial mechanic properties of woven composites. Single fiber push-out/push-back tests with the Berkovich indenter were conducted on the thin sliced specimens using nano-indentation technique. To give a detailed illustration of the interfacial crack propagation and failure mechanism, each sector during the push-out process was analyzed at length. The test results show that there is no detectable difference between testing a fiber in a direct vicinity to an already tested fiber and testing a fiber in vicinity to not-pushed fibers. Moreover, the interface debonding and fiber sliding mainly occur at the PyC coating, and both the fiber and surrounding matrix have no plastic deformation throughout the process. Obtained from the load-displacement curve, the interfacial debonding strength (IDS) and friction stress (IFS) amount to, respectively, 35 ± 5 MPa and 10 ± 1 MPa. Based on the findings, the interfacial properties with PyC fiber coating can be predicted. Furthermore, it is expected to provide a useful guideline for the design, evaluation and optimal application of CVI-C/SiC.

  11. Can 10% hydrofluoric acid be used for reconditioning of orthodontic brackets?

    Science.gov (United States)

    Pompeo, Daniela D; Rosário, Henrique D; Lopes, Beatriz Mv; Cesar, Paulo F; Paranhos, Luiz Renato

    2016-01-01

    Bracket debonding is a common problem during orthodontic treatment. This type of failure is associated to masticatory forces, poor adhesion, and the need for repositioning the piece. The objective of this work was to compare the shear bond strength of debonded brackets that were reconditioned using different protocols (alumina blasting versus hydrofluoric etching). This was an in vitro experimental study with 45 stainless steel orthodontic brackets. They were randomly divided into three groups: (1) New brackets (n = 15), (2) brackets reconditioned using 10% hydrofluoric acid for 60 s (n = 15), and (3) brackets reconditioned by aluminum oxide blasting until complete removal of the remaining resin (n = 15). In Groups 2 and 3, the insertion of composite resin proceeded in two stages to simulate a type of bracket failure in which the bonding resin was left at the bracket base. For the shear test, the assembly composed by the metallic support, and specimen was taken to the Instron universal testing machine in which the specimens were loaded using a semicircle-shaped active tip in the region of the bonding interface parallel to the surface of the bracket at a speed of 0.5 mm/min. The data were subjected to D'Agostino's normality test to have their distribution checked. Analysis of variance and Tukey's test (P brackets) showed higher bond strength than that obtained for the group treated with hydrofluoric acid (Group 2, P brackets. Nevertheless, the reconditioning technique using 10% fluoridric acid for 60 s was not efficient for clinical use.

  12. Bond efficacy of recycled orthodontic brackets: A comparative in vitro evaluation of two methods.

    Science.gov (United States)

    Shetty, Vikram; Shekatkar, Yash; Kumbhat, Neesu; Gautam, G; Karbelkar, Shalan; Vandekar, Meghna

    2015-01-01

    Recycling of orthodontic brackets in developing orthodontic economies is an extremely common procedure. Bonding protocols and reliability of these brackets is, however, questionable, and still the subject of research. The aim was to evaluate and compare the shear bond strength of brackets recycled with sandblasting and silicoating. Ninety extracted human premolars were bonded with 0.022" SS brackets (American Orthodontics, Sheboygan USA) and then debonded. The debonded brackets were divided into three groups of 30 each. Group I: Sandblasting with 50-μm aluminum oxide (control group) Group II: Sandblasting with 50-μm aluminum oxide followed by metal primer application Group III: Silicoating with 30-μm Cojet sand followed by silane application and rebonded with Transbond XT. The sandblasted brackets and silicoated brackets were viewed under the scanning electron microscope, immediately after surface conditioning before rebonding. The shear bond strength with each group was tested. One-way analysis of variance, post-hoc Scheffe multiple comparison tests. The results showed that sandblasting created more irregularities and deeper erosions while silica coating created superficial irregularities and shallow erosions.

  13. Stability of extraction space closure.

    Science.gov (United States)

    Garib, Daniela Gamba; Bressane, Larissa Borges; Janson, Guilherme; Gribel, Bruno Frazão

    2016-01-01

    The objectives of this study were to evaluate the prevalence and long-term behavior of extraction space reopening in patients with Class I malocclusion and to identify some associated factors. A sample of 43 patients met the inclusion criteria. Dental casts at the onset of treatment, after treatment, and 1 and 5 years after debonding were used. Initial and final cephalometric radiographs were used to measure the amount of incisor retraction. Cochran tests were used to compare the numbers of open and closed extraction spaces after treatment and at 1 and 5 years after debonding (P space reopening with t tests. Of the sample, 30.23% had extraction space reopening. The frequency of open spaces significantly increased between the final and the 1-year posttreatment dental casts and decreased between the casts at 1 and 5 years posttreatment. Patients with space reopening had less initial anterior crowding and greater amounts of mandibular incisor retraction during treatment. There was a high prevalence of space reopening 1 year after treatment. However, these spaces tended to decrease by 5 years after treatment. Copyright © 2016 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.

  14. High resolution X-ray imaging of bone-implant interface by large area flat-panel detector

    International Nuclear Information System (INIS)

    Kytyr, D; Jirousek, O; Dammer, J

    2011-01-01

    The aim of the research was to investigate the cemented bone-implant interface behavior (cement layer degradation and bone-cement interface debonding) with emphasis on imaging techniques suitable to detect the early defects in the cement layer. To simulate in vivo conditions a human pelvic bone was implanted with polyurethane acetabular cup using commercial acrylic bone cement. The implanted cup was then loaded in a custom hip simulator to initiate fatigue crack propagation in the bone cement. The pelvic bone was then repetitively scanned in a micro-tomography device. Reconstructed tomography images showed failure processes that occurred in the cement layer during the first 250,000 cycles. A failure in cemented acetabular implant - debonding, crumbling and smeared cracks - has been found to be at the bone-cement interface. Use of micro-focus source and high resolution flat panel detector of large physical dimensions allowed to reconstruct the micro-structural models suitable for investigation of migration, micro-motions and consecutive loosening of the implant. The large area flat panel detector with physical dimensions 120 x 120mm with 50μm pixel size provided a superior image quality compared to clinical CT systems with 300-150μm pixel size.

  15. Loading Analysis of Composite Wind Turbine Blade for Fatigue Life Prediction of Adhesively Bonded Root Joint

    Science.gov (United States)

    Salimi-Majd, Davood; Azimzadeh, Vahid; Mohammadi, Bijan

    2015-06-01

    Nowadays wind energy is widely used as a non-polluting cost-effective renewable energy resource. During the lifetime of a composite wind turbine which is about 20 years, the rotor blades are subjected to different cyclic loads such as aerodynamics, centrifugal and gravitational forces. These loading conditions, cause to fatigue failure of the blade at the adhesively bonded root joint, where the highest bending moments will occur and consequently, is the most critical zone of the blade. So it is important to estimate the fatigue life of the root joint. The cohesive zone model is one of the best methods for prediction of initiation and propagation of debonding at the root joint. The advantage of this method is the possibility of modeling the debonding without any requirement to the remeshing. However in order to use this approach, it is necessary to analyze the cyclic loading condition at the root joint. For this purpose after implementing a cohesive interface element in the Ansys finite element software, one blade of a horizontal axis wind turbine with 46 m rotor diameter was modelled in full scale. Then after applying loads on the blade under different condition of the blade in a full rotation, the critical condition of the blade is obtained based on the delamination index and also the load ratio on the root joint in fatigue cycles is calculated. These data are the inputs for fatigue damage growth analysis of the root joint by using CZM approach that will be investigated in future work.

  16. Meso-Scale Progressive Damage Behavior Characterization of Triaxial Braided Composites under Quasi-Static Tensile Load

    Science.gov (United States)

    Ren, Yiru; Zhang, Songjun; Jiang, Hongyong; Xiang, Jinwu

    2018-04-01

    Based on continuum damage mechanics (CDM), a sophisticated 3D meso-scale finite element (FE) model is proposed to characterize the progressive damage behavior of 2D Triaxial Braided Composites (2DTBC) with 60° braiding angle under quasi-static tensile load. The modified Von Mises strength criterion and 3D Hashin failure criterion are used to predict the damage initiation of the pure matrix and fiber tows. A combining interface damage and friction constitutive model is applied to predict the interface damage behavior. Murakami-Ohno stiffness degradation scheme is employed to predict the damage evolution process of each constituent. Coupling with the ordinary and translational symmetry boundary conditions, the tensile elastic response including tensile strength and failure strain of 2DTBC are in good agreement with the available experiment data. The numerical results show that the main failure modes of the composites under axial tensile load are pure matrix cracking, fiber and matrix tension failure in bias fiber tows, matrix tension failure in axial fiber tows and interface debonding; the main failure modes of the composites subjected to transverse tensile load are free-edge effect, matrix tension failure in bias fiber tows and interface debonding.

  17. Effect of Temperature Variation on Bond Characteristics between CFRP and Steel Plate

    Directory of Open Access Journals (Sweden)

    Shan Li

    2016-01-01

    Full Text Available In recent years, application of carbon fiber reinforced polymer (CFRP composite materials in the strengthening of existing reinforced concrete structures has gained widespread attention, but the retrofitting of metallic buildings and bridges with CFRP is still in its early stages. In real life, these structures are possibly subjected to dry and hot climate. Therefore, it is necessary to understand the bond behavior between CFRP and steel at different temperatures. To examine the bond between CFRP and steel under hot climate, a total of twenty-one double strap joints divided into 7 groups were tested to failure at constant temperatures from 27°C to 120°C in this paper. The results showed that the joint failure mode changed from debonding along between steel and adhesive interface failure to debonding along between CFRP and adhesive interface failure as the temperature increased beyond the glass transition temperature (Tg of the adhesive. The load carrying capacity decreased significantly at temperatures approaching or exceeding Tg. The interfacial fracture energy showed a similar degradation trend. Analytical models of the ultimate bearing capacity, interfacial fracture energy, and bond-slip relationship of CFRP-steel interface at elevated temperatures were presented.

  18. Concrete Infill Monitoring in Concrete-Filled FRP Tubes Using a PZT-Based Ultrasonic Time-of-Flight Method

    Science.gov (United States)

    Luo, Mingzhang; Li, Weijie; Hei, Chuang; Song, Gangbing

    2016-01-01

    Concrete-filled fiber-reinforced polymer tubes (CFFTs) have attracted interest for their structural applications in corrosive environments. However, a weak interfacial strength between the fiber-reinforced polymer (FRP) tube and the concrete infill may develop due to concrete shrinkage and inadequate concrete compaction during concrete casting, which will destroy the confinement effect and thereby reduce the load bearing capacity of a CFFT. In this paper, the lead zirconate titanate (PZT)-based ultrasonic time-of-flight (TOF) method was adopted to assess the concrete infill condition of CFFTs. The basic idea of this method is that the velocity of the ultrasonic wave propagation in the FRP material is about half of that in concrete material. Any voids or debonding created along the interface between the FRP tube and the concrete will delay the arrival time between the pairs of PZT transducers. A comparison of the arrival times of the PZT pairs between the intact and the defected CFFT was made to assess the severity of the voids or the debonding. The feasibility of the methodology was analyzed using a finite-difference time-domain-based numerical simulation. Experiments were setup to validate the numerical results, which showed good agreement with the numerical findings. The results showed that the ultrasonic time-of-flight method is able to detect the concrete infill condition of CFFTs. PMID:27941617

  19. Continuous Modeling Technique of Fiber Pullout from a Cement Matrix with Different Interface Mechanical Properties Using Finite Element Program

    Directory of Open Access Journals (Sweden)

    Leandro Ferreira Friedrich

    Full Text Available Abstract Fiber-matrix interface performance has a great influence on the mechanical properties of fiber reinforced composite. This influence is mainly presented during fiber pullout from the matrix. As fiber pullout process consists of fiber debonding stage and pullout stage which involve complex contact problem, numerical modeling is a best way to investigate the interface influence. Although many numerical research works have been conducted, practical and effective technique suitable for continuous modeling of fiber pullout process is still scarce. The reason is in that numerical divergence frequently happens, leading to the modeling interruption. By interacting the popular finite element program ANSYS with the MATLAB, we proposed continuous modeling technique and realized modeling of fiber pullout from cement matrix with desired interface mechanical performance. For debonding process, we used interface elements with cohesive surface traction and exponential failure behavior. For pullout process, we switched interface elements to spring elements with variable stiffness, which is related to the interface shear stress as a function of the interface slip displacement. For both processes, the results obtained are very good in comparison with other numerical or analytical models and experimental tests. We suggest using the present technique to model toughening achieved by randomly distributed fibers.

  20. Mechanical Behavior of Steel Fiber-Reinforced Concrete Beams Bonded with External Carbon Fiber Sheets.

    Science.gov (United States)

    Gribniak, Viktor; Tamulenas, Vytautas; Ng, Pui-Lam; Arnautov, Aleksandr K; Gudonis, Eugenijus; Misiunaite, Ieva

    2017-06-17

    This study investigates the mechanical behavior of steel fiber-reinforced concrete (SFRC) beams internally reinforced with steel bars and externally bonded with carbon fiber-reinforced polymer (CFRP) sheets fixed by adhesive and hybrid jointing techniques. In particular, attention is paid to the load resistance and failure modes of composite beams. The steel fibers were used to avoiding the rip-off failure of the concrete cover. The CFRP sheets were fixed to the concrete surface by epoxy adhesive as well as combined with various configurations of small-diameter steel pins for mechanical fastening to form a hybrid connection. Such hybrid jointing techniques were found to be particularly advantageous in avoiding brittle debonding failure, by promoting progressive failure within the hybrid joints. The use of CFRP sheets was also effective in suppressing the localization of the discrete cracks. The development of the crack pattern was monitored using the digital image correlation method. As revealed from the image analyses, with an appropriate layout of the steel pins, brittle failure of the concrete-carbon fiber interface could be effectively prevented. Inverse analysis of the moment-curvature diagrams was conducted, and it was found that a simplified tension-stiffening model with a constant residual stress level at 90% of the strength of the SFRC is adequate for numerically simulating the deformation behavior of beams up to the debonding of the CFRP sheets.

  1. Flexural properties of treated and untreated kenaf/epoxy composites

    International Nuclear Information System (INIS)

    Yousif, B.F.; Shalwan, A.; Chin, C.W.; Ming, K.C.

    2012-01-01

    Graphical abstract: Untreated kenaf fibre/epoxy composites. Treated kenaf fibre/epoxy composites. Highlights: ► Treatment of kenaf fibres with 6% NaOH has improved the flexural properties of epoxy composites. ► Interfacial adhesion of the natural fibres is controlled by the microstructure of the fibres. ► Kenaf fibres have a potential to replace glass fibres for flexural applications. -- Abstract: In the current work, flexural properties of unidirectional long kenaf fibre reinforced epoxy (KFRE) composites are studied. The kenaf fibres were prepared into two types as untreated and treated (with 6% NaOH). The failure mechanism and damage features of the materials were categorized with the surface observation by scanning electron microscope (SEM). The results revealed that reinforcement of epoxy with treated kenaf fibres increased the flexural strength of the composite by about 36%, while, untreated fibres introduced 20% improvement. This was mainly due to the high improvement of the chemical treatment (NaOH) on the interfacial adhesion of the fibres and the porosity of the composites which prevented the debonding, detachments or pull out of fibres. For untreated KFRE, the fracture mechanisms were debonding, tearing, detachments and pull out of fibres. The developed composite exhibited superior properties compared to the previous composites based on natural and synthetic fibres.

  2. Shear bond strength and enamel fracture behavior of ceramic brackets Fascination® and Fascination®2.

    Science.gov (United States)

    Gittner, Robert; Müller-Hartwich, Ralf; Engel, Sylvia; Jost-Brinkmann, Paul-Georg

    2012-01-01

    The purpose of this study was to compare the shear bond strength and incidence of enamel fractures of the ceramic brackets Fascination® and Fascination®2. A total of 360 teeth (180 first upper bicuspids and 180 lower incisors) were stored in 96% ethanol, while 360 other teeth (180 first upper bicuspids and 180 lower incisors) were stored in 0.1% thymol. All 720 teeth were bonded one-half each with Fascination® and Fascination®2 brackets using three different adhesives and three different light curing units. The teeth were debonded with a debonding-device according to DIN EN ISO 10477 using a universal testing machine with a crosshead speed of 1 mm per minute. The enamel surface was then examined stereomicroscopically (10x and 40x magnification). The non-parametric Mann-Whitney U test was used, since the data were not normally distributed. The Fascination®2 brackets provided significantly lower shear bond strength than Fascination® brackets (p = 0.003). Fascination® brackets demonstrated significantly fewer, smaller enamel fractures than Fascination®2 brackets (p = 0.012). The lower shear bond strength of the Fascination®2 brackets is clinically acceptable, but our study's experimental design did not enable us to prove whether this is clinically associated with a lower risk of enamel fracture.

  3. The effect of weak interface on transverse properties of a ceramic matrix composite

    Science.gov (United States)

    Shimansky, R. A.; Hahn, H. T.; Salamon, N. J.

    1990-01-01

    Experimental studies conducted at NASA Lewis on SiC reaction-bonded Si3N4 composite system showed that transverse stiffness and strength were much lower than those predicted from existing analytical models based on good interfacial bonding. It was believed that weakened interfaces were responsible for the decrease in tranverse properties. To support this claim, a two-dimensional FEM analysis was performed for a transverse representative volume element. Specifically, the effect of fiber/matrix displacement compatibility at the interface was studied under both tensile and compressive transverse loadings. Interface debonding was represented using active gap elements connecting the fiber and matrix. The analyses show that the transverse tensile strength and stiffness are best predicted when a debonded interface is assumed for the composite. In fact, the measured properties can be predicted by simply replacing the fibers by voids. Thus, it is found that little or no interfacial bonding exists in the composite, and that an elastic analysis can predict the transverse stiffness and strength.

  4. Flexural Strengthening of RC Slabs with Prestressed CFRP Strips Using Different Anchorage Systems

    Directory of Open Access Journals (Sweden)

    José Sena-Cruz

    2015-10-01

    Full Text Available Externally Bonded Reinforcement (EBR technique has been widely used for flexural strengthening of concrete structures by using carbon fiber-reinforced polymers (CFRP. EBR technique offers several structural advantages when the CFRP material is prestressed. This paper presents an experimental and numerical study on reinforced (RC slabs strengthened in flexure with prestressed CFRP strips as a structural strengthening system. The strips are applied as an externally bonded reinforcement (EBR and anchored with either a mechanical or a gradient anchorage. The former foresees metallic anchorage plates fixed to the concrete substrate, while the latter is based on an accelerated epoxy resin curing followed by a segment-wise prestress force decrease at the strip ends. Both anchorage systems, in combination with different CFRP strip geometries, were subjected to static loading tests. It could be demonstrated that the composite strip’s performance is better exploited when prestressing is used, with slightly higher overall load carrying capacities for mechanical anchorages than for the gradient anchorage. The performed investigations by means of a cross-section analysis supported the experimental observation that in case a mechanical anchorage is used, progressive strip debonding changes the fully bonded configuration to an unbonded end-anchored system. The inclusion of defined debonding criteria for both the anchorage zones and free length between the anchorage regions allowed to precisely capture the ultimate loading forces.

  5. Crack identification for reinforced concrete using PZT based smart rebar active sensing diagnostic network

    Science.gov (United States)

    Song, N. N.; Wu, F.

    2016-04-01

    An active sensing diagnostic system using PZT based smart rebar for SHM of RC structure has been currently under investigation. Previous test results showed that the system could detect the de-bond of concrete from reinforcement, and the diagnostic signals were increased exponentially with the de-bonding size. Previous study also showed that the smart rebar could function well like regular reinforcement to undertake tension stresses. In this study, a smart rebar network has been used to detect the crack damage of concrete based on guided waves. Experimental test has been carried out for the study. In the test, concrete beams with 2 reinforcements have been built. 8 sets of PZT elements were mounted onto the reinforcement bars in an optimized way to form an active sensing diagnostic system. A 90 kHz 5-cycle Hanning-windowed tone burst was used as input. Multiple cracks have been generated on the concrete structures. Through the guided bulk waves propagating in the structures from actuators and sensors mounted from different bars, crack damage could be detected clearly. Cases for both single and multiple cracks were tested. Different crack depths from the surface and different crack numbers have been studied. Test result shows that the amplitude of sensor output signals is deceased linearly with a propagating crack, and is decreased exponentially with increased crack numbers. From the study, the active sensing diagnostic system using PZT based smart rebar network shows a promising way to provide concrete crack damage information through the "talk" among sensors.

  6. Evaluation of Shear Bond Strength of Orthodontic Brackets Bonded with Nano-filled Composites

    Directory of Open Access Journals (Sweden)

    Mohammad Sadegh Ahmad Akhoundi

    2013-01-01

    Full Text Available Objectives: The purpose of this study was to evaluate the shear bond strength (SBS of orthodontic brackets bonded with two types of nano-composites in comparison to a conventional orthodontic composite. Materials and Methods: Sixty extracted human first premolars were randomly divided into 3 groups each containing 20 teeth. In group I, a conventional orthodontic composite (Transbond XT was used to bond the brackets, while two nano-composites (Filtek TM Supreme XT and AELITE Aesthetic Enamel were used in groups II and III respectively. The teeth were stored in distilled water at 37°C for 24 hours, thermocycled in distilled water and debonded with a universal testing machine at a crosshead speed of 1 mm/min. The adhesive remnant index (ARI was also evaluated using a stereomicroscope. Results: AELITE Aesthetic Enamel nano-composite revealed a SBS value of 8.44±2.09 MPa, which was higher than Transbond XT (6.91± 2.13 and Filtek TM Supreme XT (6.04± 2.01. Statistical analysis revealed a significant difference between groups II and III (P 0.05. Evaluation of ARI showed that Transbond XT left fewer adhesive remains on teeth after debonding. Conclusion: Results of this study indicate that the aforementioned nano-composites can be successfully used for bonding orthodontic brackets.

  7. Evaluation of shear bond strength of orthodontic brackets bonded with nano-filled composites.

    Science.gov (United States)

    Chalipa, Javad; Akhondi, Mohammad Sadegh Ahmad; Arab, Sepideh; Kharrazifard, Mohammad Javad; Ahmadyar, Maryam

    2013-09-01

    The purpose of this study was to evaluate the shear bond strength (SBS) of orthodontic brackets bonded with two types of nano-composites in comparison to a conventional orthodontic composite. Sixty extracted human first premolars were randomly divided into 3 groups each containing 20 teeth. In group I, a conventional orthodontic composite (Transbond XT) was used to bond the brackets, while two nano-composites (Filtek TM Supreme XT and AELITE Aesthetic Enamel) were used in groups II and III respectively. The teeth were stored in distilled water at 37°C for 24 hours, thermocycled in distilled water and debonded with a universal testing machine at a crosshead speed of 1 mm/min. The adhesive remnant index (ARI) was also evaluated using a stereomicroscope. AELITE Aesthetic Enamel nano-composite revealed a SBS value of 8.44±2.09 MPa, which was higher than Transbond XT (6.91±2.13) and Filtek TM Supreme XT (6.04±2.01). Statistical analysis revealed a significant difference between groups II and III (P 0.05). Evaluation of ARI showed that Transbond XT left fewer adhesive remains on teeth after debonding. Results of this study indicate that the aforementioned nano-composites can be successfully used for bonding orthodontic brackets.

  8. Effect of carbonated hydroxyapatite incorporated advanced platelet rich fibrin intrasulcular injection on the alkaline phosphatase level during orthodontic relapse

    Science.gov (United States)

    Alhasyimi, Ananto Ali; Pudyani, Pinandi Sri; Asmara, Widya; Ana, Ika Dewi

    2018-02-01

    Nowadays, relapse in orthodontic treatment is considered very important because of high incidence of relapse after the treatment. Alkaline phosphatase (ALP) as a biomarker of bone formation will decrease in compression sites during relapse after orthodontic tooth movement. In this situation, manipulating alveolar bone remodeling to increase ALP level is considered one of the new strategies to prevent relapse properly. In the field of tissue engineering, in this study, carbonated hydroxyapatite (CHA) is expected to have the ability to incorporate advanced platelet rich fibrin (aPRF). Next, CHA will retain the aPRF containing various growth factors (GF) until it reaches into a specific targeted area, gradually degraded, and deliver the GF in a controlled manner to prevent relapse. Here, gingival crevicular fluid (GCF) of 45 samples (n=45) were collected and levels of ALP were analyzed using UV-Vis 6300 Spectrophotometer at 405 nm wavelength. We found that there is a significant difference of ALP levels (p<0.05) in GCF between treatments and control groups. ALP level was elevated significantly in CHA and CHA-aPRF groups at days 7 and 14 after debonding compared with the control groups. The peak level of ALP was observed at days 14 after debonding in groups C (0.789 ± 0.039 U/mg). Therefore, it can be concluded that the application of hydrogel CHA with controlled release manner incorporated aPRF enhances bone regeneration by increasing ALP level.

  9. Assessment of Composite Delamination Self-Healing Under Cyclic Loading

    Science.gov (United States)

    O'Brien, T. Kevin

    2009-01-01

    Recently, the promise of self-healing materials for enhanced autonomous durability has been introduced using a micro-encapsulation technique where a polymer based healing agent is encapsulated in thin walled spheres and embedded into a base polymer along with a catalyst phase. For this study, composite skin-stiffener flange debonding specimens were manufactured from composite prepreg containing interleaf layers with a polymer based healing agent encapsulated in thin-walled spheres. Constant amplitude fatigue tests in three-point bending showed the effect of self-healing on the fatigue response of the skin-stiffener flange coupons. After the cycling that created debonding, fatigue tests were held at the mean load for 24 hours. For roughly half the specimens tested, when the cyclic loading was resumed a decrease in compliance (increase in stiffness) was observed, indicating that some healing had occurred. However, with continued cycling, the specimen compliance eventually increased to the original level before the hold, indicating that the damage had returned to its original state. As was noted in a prevoius study conducted with specimens tested under monotonically increasing loads to failure, healing achieved via the micro-encapsulation technique may be limited to the volume of healing agent available relative to the crack volume.

  10. Survival of all-ceramic restorations after a minimum follow-up of five years: A systematic review.

    Science.gov (United States)

    Araujo, Nara Santos; Moda, Mariana Dias; Silva, Ebele Adaobi; Zavanelli, Adriana Cristina; Mazaro, José Vitor Quinelli; Pellizzer, Eduardo Piza

    2016-01-01

    The purpose of this systematic review was to compare the survival and complication rates of all-ceramic restorations after a minimum follow-up time of 5 years. A comprehensive search of studies published from 2005 to November 2015 and listed in the PubMed/MEDLINE, Scopus, and Cochrane Library databases was performed in accordance with the PRISMA statement. Two reviewers independently analyzed the abstracts. Relevant studies were selected according to predetermined inclusion criteria. Twenty-nine studies were selected for the final analysis from an initial yield of 514. Only four studies fulfilled the requirement of having a randomized design, and 25 studies were prospective with a mean follow-up period of 5 to 16 years. Overall, the 5-year complication rates were low. The most frequent complications were secondary caries, endodontic problems, ceramic fractures, ceramic chipping, and loss of retention. This systematic review showed that all-ceramic restorations fabricated using the correct clinical protocol have an adequate clinical survival for at least 5 years of clinical service with very low complication rates. Minor ceramic chipping and debonding did not affect the longevity of the restorations. Long-term clinical performance of all-ceramic restorations manufactured using various ceramic systems provides clinical evidence of complications and long-term management of these restorations. Available evidence indicates the effectiveness of many ceramic systems for numerous clinical applications. Correct planning and a rigorous technical execution protocol increase clinical success. Studies of ceramic prostheses indicate more problems with ceramic failure and debonding.

  11. A mechanics approach to the study of pressure sensitive adhesives and human skin for transdermal drug delivery applications

    Science.gov (United States)

    Taub, Marc Barry

    Transdermal drug delivery is an alternative approach to the systemic delivery of pharmaceuticals where drugs are administered through the skin and absorbed percutaneously. This method of delivery offers several advantages over more traditional routes; most notably, the avoidance of the fast-pass metabolism of the liver and gut, the ability to offer controlled release rates, and the possibility for novel devices. Pressure sensitive adhesives (PSAs) are used to bond transdermal drug delivery devices to the skin because of their good initial and long-term adhesion, clean removability, and skin and drug compatibility. However, an understanding of the mechanics of adhesion to the dermal layer, together with quantitative and reproducible test methods for measuring adhesion, have been lacking. This study utilizes a mechanics-based approach to quantify the interfacial adhesion of PSAs bonded to selected substrates, including human dermal tissue. The delamination of PSA layers is associated with cavitation in the PSA followed by the formation of an extensive cohesive zone behind the debond tip. A quantitative metrology was developed to assess the adhesion and delamination of PSAs, such that it could be possible to easily distinguish between the adhesive characteristics of different PSA compositions and to provide a quantitative basis from which the reliability of adhesive layers bonded to substrates could be studied. A mechanics-based model was also developed to predict debonding in terms of the relevant energy dissipation mechanisms active during this process. As failure of transdermal devices may occur cohesively within the PSA layer, adhesively at the interface between the PSA and the skin, or cohesively between the corneocytes that comprise the outermost layer of the skin, it was also necessary to explore the mechanical and fracture properties of human skin. The out-of-plane delamination of corneocytes was studied by determining the strain energy release rate during

  12. Effect of the probiotic bacterium Lactobacillus reuteri on white spot lesion development in orthodontic patients.

    Science.gov (United States)

    Gizani, Sotiria; Petsi, Georgia; Twetman, Svante; Caroni, Crys; Makou, Margarita; Papagianoulis, Lisa

    2016-02-01

    The purpose of the study is to evaluate the effect of daily intake of lozenges containing probiotic bacteria on white spot lesion (WSL) formation as well as on salivary lactobacilli (LB) and mutans streptococci (MS) counts, in patients undergoing orthodontic treatment with fixed appliances. A randomized double-blind placebo-controlled study design with two parallel arms was employed. Patients (n = 85, mean age 15.9 years) with maxillary braces on at least eight anterior teeth and a remaining treatment period of 7-24 months were finally enrolled and randomly allocated to a test or placebo group. Subjects in the test group were instructed to take one probiotic lozenge containing two strains of Lactobacillus reuteri once daily. An identical lozenge without active bacteria was used in the placebo group. Dental plaque, WSL, and salivary MS and LB levels were recorded at baseline and immediately after debonding. The groups were balanced at baseline. The mean duration of the intervention was 17 months and the total dropout rate was 10 per cent. There were no differences in the incidence of WSL between the groups at debonding. The patients had generally a neglected oral hygiene, both at baseline and at the follow-up. The levels of salivary LB were significantly reduced in both groups (P < 0.05) at the time of debonding compared with baseline, while no alterations of the MS counts were unveiled. WSL were scored from photos that may not fully mirror the clinical situation. Chair-side tests estimate the counts of selected bacteria in saliva and do not reflect the entire microbiota. The invention was implemented approximately 6 months after the onset of the fixed appliances and some lesions may have been present at bonding. Daily intake of probiotic lozenges did not seem to affect the development of WSL during orthodontic treatment with fixed appliances. © The Author 2015. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved

  13. Dental compensation for skeletal Class III malocclusion by isolated extraction of mandibular teeth. Part 1: Occlusal situation 12 years after completion of active treatment.

    Science.gov (United States)

    Zimmer, Bernd; Schenk-Kazan, Sarah

    2015-05-01

    The purpose of this work was to statistically evaluate the outcomes achieved by isolated extraction of mandibular teeth (second premolars or first molars) for Class III compensation. Part A of the study dealt with the quality of outcomes at the end of active treatment, using weighted Peer Assessment Rating (PAR) scores determined on the basis of casts for 25 (14 female and 11 male) consecutive patients aged 16 ± 1.7 years at the time of debonding. These results were compared to the scores in a randomly selected control group of 25 (14 female and 11 male) patients who were 14.7 ± 1.9 years old at debonding. Part B evaluated the long-term stability of the outcomes based on 12 (all of them female) patients available for examination after a mean of 11.8 years. The mean weighted PAR scores obtained in both study parts were analyzed for statistical differences using a two-tailed paired Student's t-test at a significance level of p ≤ 0.05. Mean weighted PAR scores of 4.76 ± 3.94 and 3.92 ± 3.44 were obtained in the Class III extraction group and the control group, respectively, at the end of active treatment. This difference was not significant (p = 0.49). Among the 12 longitudinal patients, the mean score increased from 4 ± 3.46 at debonding to 6.25 ± 3.67 by the end of the 11.8-year follow-up period. This difference was significant (p = 0.0008). Treatment of Class III anomalies by isolated extraction of lower premolars or molars can yield PAR scores similar to those achieved by standard therapies. These scores, while increasing significantly, remained at a clinically acceptable level over 11.8 years. Hence this treatment modality--intended for cases that border on requiring orthognathic surgery--may also be recommended from a long-term point of view.

  14. Prediction of thermal and mechanical stress-strain responses of TMC's subjected to complex TMF histories

    Science.gov (United States)

    Johnson, W. S.; Mirdamadi, M.

    1994-01-01

    This paper presents an experimental and analytical evaluation of cross-plied laminates of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) matrix reinforced with continuous silicon-carbide fibers (SCS-6) subjected to a complex TMF loading profile. Thermomechanical fatigue test techniques were developed to conduct a simulation of a generic hypersonic flight profile. A micromechanical analysis was used. The analysis predicts the stress-strain response of the laminate and of the constituents in each ply during thermal and mechanical cycling by using only constituent properties as input. The fiber was modeled as elastic with transverse orthotropic and temperature-dependent properties. The matrix was modeled using a thermoviscoplastic constitutive relation. The fiber transverse modulus was reduced in the analysis to simulate the fiber-matrix interface failures. Excellent correlation was found between measured and predicted laminate stress-strain response due to generic hypersonic flight profile when fiber debonding was modeled.

  15. Fracture and flaking off behavior of coated layer of DyBCO coated conductor under applied tensile strain

    International Nuclear Information System (INIS)

    Arai, T.; Shin, J.K.; Matsubayashi, H.; Ochiai, S.; Okuda, H.; Osamura, K.; Prusseit, W.

    2009-01-01

    The tensile behavior of the DyBa 2 Cu 3 O 7-δ (DyBCO) coated conductor with MgO buffer layer deposited on the Hastelloy C-276 substrate by inclined substrate deposition (ISD) was studied. The tensile stress-strain curve showed a flat region, characterized by the discontinuous yielding of the substrate due to the Lueders band extension from the gripped portions of the sample. In the area where the Lueders band had passed, the coating layer showed severe multiple transverse cracking due to the localized plastic deformation of the substrate. The flaking off of the coating layers took place at high applied strain, due to the buckling fracture of the coated layers in the sample width direction, accompanied by the interfacial debonding.

  16. Brutal crack propagation in dynamic fracture: industrial application to the length of the crack arrest

    International Nuclear Information System (INIS)

    Dumouchel, P.E.

    2008-03-01

    This research thesis aims at understanding and analysing some mechanisms involved in the dynamic failure under various loadings which are notably present in industrial environment, and more particularly in some parts of EDF's plants where networks of micro-cracks may steadily grow: heterogeneous zones, defects under coating. The author presents a simplified model based on the de-bonding of a film to understand the mechanisms of a sudden failure under a quasi-static loading. He develops a similar model to explore the influence of a defect on crack propagation under a quasi-static loading, and then under a sudden loading. This model is then generalized to the case of several defects, and more particularly very small defects. Finally, the author gives a numerical interpretation of a sudden propagation under quasi-static loading

  17. Effects of anomalies on fracture processes of graphite fiber reinforced aluminum composite

    International Nuclear Information System (INIS)

    Su, J.; Wu, G.H.; Li, Y.; Gou, H.S.; Chen, G.H.; Xiu, Z.Y.

    2011-01-01

    To determine the effects of anomalies on fracture processes of graphite fiber reinforced aluminum composite (Gr f /Al), unidirectional Gr f /Al specimens embedded with inclusions and aluminum-rich areas (Al-rich) were chosen for bending test. Fracture processes and fracture surfaces of anomaly-embedded specimens were analyzed by scanning electron microscopy in situ observation. The micromechanisms of fracture process are as following: interface layer between inclusions and composite is fractured by stress concentration in front of crack tip, and cracks connect voids in inclusions, resulting in failure of inclusion-embedded specimens immediately. However, Al-rich eases stress concentration in bending specimens and crack is blunted by Al-rich/composite interface debonding and friction during fracture process.

  18. Acoustic emission characteristics during bending fracture process of piezoelectric composite actuators

    International Nuclear Information System (INIS)

    Woo, Sung Choong; Goo, Nam Seo

    2006-01-01

    The objective of this study is to investigate the damage mechanisms in a thin monolithic PZT wafer and an asymmetrically laminated piezoelectric composite actuator (PCA) under bending loading by the acoustic emission (AE) technique. Fracture surface examinations were conducted using a scanning electron microscope (SEM) and an optical microscope. Using the fabricated PCAs, correlations were established between the observed damage growth mechanisms and the AE results in terms of the AE amplitude and dominant frequency band which was processed by fast Fourier transform (FFT). These correlations can be used to monitor the damage evolution in the plate-type piezoelectric composite actuators exhibiting multiple modes of damage. Results from this study revealed that the AE technique is a powerful and effective tool for identifying damage mechanisms such as brittle fracture in the PZT, matrix cracking, fiber-matrix debonding, fiber breakage and delamination between the PZT layer and fiber composite layer in the asymmetrically laminated PCAs.

  19. Comparative study of postoperative stability between conventional orthognathic surgery and a surgery-first orthognathic approach after bilateral sagittal split ramus osteotomy for skeletal class III correction.

    Science.gov (United States)

    Mah, Deuk-Hyun; Kim, Su-Gwan; Oh, Ji-Su; You, Jae-Seek; Jung, Seo-Yun; Kim, Won-Gi; Yu, Kyung-Hwan

    2017-02-01

    The purpose of this study is to compare the postoperative stability of conventional orthognathic surgery to a surgery-first orthognathic approach after bilateral sagittal split ramus osteotomy (BSSRO). The study included 20 patients who underwent BSSRO for skeletal class III conventional orthognathic surgery and 20 patients who underwent a surgery-first orthognathic approach. Serial lateral cephalograms were analyzed to identify skeletal changes before surgery (T0), immediately after surgery (T1), and after surgery (T2, after 1 year or at debonding). The amount of relapse of the mandible in the conventional orthognathic surgery group from T1 to T2 was 2.23±0.92 mm ( P surgery-first orthognathic approach group from T1 to T2 was 3.49±1.71 mm ( P surgery-first orthognathic approach. Therefore, careful planning and skeletal stability should be considered in orthognathic surgery.

  20. Viscoelastic analysis of a dental metal-ceramic system

    Science.gov (United States)

    Özüpek, Şebnem; Ünlü, Utku Cemal

    2012-11-01

    Porcelain-fused-to-metal (PFM) restorations used in prosthetic dentistry contain thermal stresses which develop during the cooling phase after firing. These thermal stresses coupled with the stresses produced by mechanical loads may be the dominant reasons for failures in clinical situations. For an accurate calculation of these stresses, viscoelastic behavior of ceramics at high temperatures should not be ignored. In this study, the finite element technique is used to evaluate the effect of viscoelasticity on stress distributions of a three-point flexure test specimen, which is the current international standard, ISO 9693, to characterize the interfacial bond strength of metal-ceramic restorative systems. Results indicate that the probability of interfacial debonding due to normal tensile stress is higher than that due to shear stress. This conclusion suggests modification of ISO 9693 bond strength definition from one in terms of the shear stress only to that accounting for both normal and shear stresses.

  1. Quantitative X-ray determination of CFRP micro structures

    International Nuclear Information System (INIS)

    Hentschel, Manfred P.; Mueller, Bernd R.; Lange, Axel; Wald, Oliver

    2008-01-01

    Beyond imaging the mass distribution of materials by X-ray absorption techniques recent synchrotron and laboratory X-ray refraction techniques provide interface contrast imaging of micro structures. This is of specific relevance to carbon fibre composites (CFRP) which constitute advanced aerospace components. Apart from merely finding isolated flaws like cracks or pores within the natural high interface density only the quantitative measurement of the differences after defined mechanical treatment provides a reliable understanding of the related macroscopic properties. The contribution of the fibre matrix interface of CFRP laminates to the mechanical properties is investigated by relating the mechanical damage to the additional fibre debonding after impact and fatigue. Composites of industrially sized carbon fibres for aerospace applications and of unsized fibres are compared. (orig.)

  2. Numerical insight into the micromechanics of jet erosion of a cohesive granular material

    Directory of Open Access Journals (Sweden)

    Cuéllar Pablo

    2017-01-01

    Full Text Available Here we investigate the physical mechanisms behind the surface erosion of a cohesive granular soil induced by an impinging jet by means of numerical simulations coupling fluid and grains at the microscale. The 2D numerical model combines the Discrete Element and Lattice Boltzmann methods (DEM-LBM and accounts for the granular cohesion with a contact model featuring a paraboloidal yield surface. Here we review first the hydrodynamical conditions imposed by the fluid jet on a solid granular packing, turning then the attention to the impact of cohesion on the erosion kinetics. Finally, the use of an additional subcritical debonding damage model based on the work of Silvani and co-workers provides a novel insight into the internal solicitation of the cohesive granular sample by the impinging jet.

  3. Numerical insight into the micromechanics of jet erosion of a cohesive granular material

    Science.gov (United States)

    Cuéllar, Pablo; Benseghier, Zeyd; Luu, Li-Hua; Bonelli, Stéphane; Delenne, Jean-Yves; Radjaï, Farhang; Philippe, Pierre

    2017-06-01

    Here we investigate the physical mechanisms behind the surface erosion of a cohesive granular soil induced by an impinging jet by means of numerical simulations coupling fluid and grains at the microscale. The 2D numerical model combines the Discrete Element and Lattice Boltzmann methods (DEM-LBM) and accounts for the granular cohesion with a contact model featuring a paraboloidal yield surface. Here we review first the hydrodynamical conditions imposed by the fluid jet on a solid granular packing, turning then the attention to the impact of cohesion on the erosion kinetics. Finally, the use of an additional subcritical debonding damage model based on the work of Silvani and co-workers provides a novel insight into the internal solicitation of the cohesive granular sample by the impinging jet.

  4. A numerical insight into elastomer normally closed micro valve actuation with cohesive interfacial cracking modelling

    Science.gov (United States)

    Wang, Dongyang; Ba, Dechun; Hao, Ming; Duan, Qihui; Liu, Kun; Mei, Qi

    2018-05-01

    Pneumatic NC (normally closed) valves are widely used in high density microfluidics systems. To improve actuation reliability, the actuation pressure needs to be reduced. In this work, we utilize 3D FEM (finite element method) modelling to get an insight into the valve actuation process numerically. Specifically, the progressive debonding process at the elastomer interface is simulated with CZM (cohesive zone model) method. To minimize the actuation pressure, the V-shape design has been investigated and compared with a normal straight design. The geometrical effects of valve shape has been elaborated, in terms of valve actuation pressure. Based on our simulated results, we formulate the main concerns for micro valve design and fabrication, which is significant for minimizing actuation pressures and ensuring reliable operation.

  5. Cohesive zone model for direct silicon wafer bonding

    Science.gov (United States)

    Kubair, D. V.; Spearing, S. M.

    2007-05-01

    Direct silicon wafer bonding and decohesion are simulated using a spectral scheme in conjunction with a rate-dependent cohesive model. The cohesive model is derived assuming the presence of a thin continuum liquid layer at the interface. Cohesive tractions due to the presence of a liquid meniscus always tend to reduce the separation distance between the wafers, thereby opposing debonding, while assisting the bonding process. In the absence of the rate-dependence effects the energy needed to bond a pair of wafers is equal to that needed to separate them. When rate-dependence is considered in the cohesive law, the experimentally observed asymmetry in the energetics can be explained. The derived cohesive model has the potential to form a bridge between experiments and a multiscale-modelling approach to understand the mechanics of wafer bonding.

  6. Constitutional equations of thermal stresses of particle-reinforced composite

    International Nuclear Information System (INIS)

    Asakawa, Atsushi; Noda, Naotake; Tohgo, Keiichiro; Tsuji, Tomoaki.

    1994-01-01

    Functionally gradient materials (FGM) have been developed as ultrahigh-heat-resistant materials in aircraft, space engineering and nuclear fields. In the heat-resistant FGM which contain particles (ceramics) in the matrix (metal), the matrix will be subjected to plastic deformation, particles will be debonded, and finally cracks will be generated. The constitutive equations of FGM which take into account the damage process and change in temperature are necessary in order to solve these phenomena. In this paper, the constitutive equations of particle-reinforced composites with consideration of the damage process and change in temperature are estimated by the equivalent inclusion method in terms of elastoplasticity. The stress-strain relations and the coefficients of linear thermal expansion of the composites (Al-PSZ and Ti-PSZ) are calculated in ultrahigh temperature. (author)

  7. Damage characterization and modeling of a 7075-T651 aluminum plate

    International Nuclear Information System (INIS)

    Jordon, J.B.; Horstemeyer, M.F.; Solanki, K.; Bernard, J.D.; Berry, J.T.; Williams, T.N.

    2009-01-01

    In this paper, the damage-induced anisotropy arising from material microstructure heterogeneities at two different length scales was characterized and modeled for a wrought aluminum alloy. Experiments were performed on a 7075-T651 aluminum alloy plate using sub-standard tensile specimens in three different orientations with respect to the rolling direction. Scanning electron microscopy was employed to characterize the stereology of the final damage state in terms of cracked and or debonded particles. A physically motivated internal state variable continuum model was used to predict fracture by incorporating material microstructural features. The continuum model showed good comparisons to the experimental data by capturing the damage-induced anisotropic material response. Estimations of the mechanical stress-strain response, material damage histories, and final failure were numerically calculated and experimentally validated thus demonstrating that the final failure state was strongly dependent on the constituent particle morphology.

  8. Role of Stress Factors on the Adhesion of Interfaces in R2R Fabricated Organic Photovoltaics

    DEFF Research Database (Denmark)

    Corazza, Michael; Rolston, Nicholas; Dauskardt, Reinhold H.

    2016-01-01

    adhesion properties. Depth profiling analysis on the fractured samples reveals interdiffusion of layers in the structure, which results in the increase of adhesion and change of the debond path. It is shown that through diffusion and intermixing of internal interfaces coupled stresses can increase......The role of the common stress factors such as high temperature, humidity,and UV irradiation on interface adhesion of roll-to-roll fabricated organic photovoltaic (OPV) devices is investigated. The samples range from bare front electrodes to complete devices. It is shown that applying single stress...... or combinations of stresses onto the samples variably affect the adhesion properties of the different interfaces in the OPV device. It is revealed that while the exposure of the complete devices to the stresses results in the loss of photovoltaic performance, some interfaces in the devices present improved...

  9. Influence of intermetallic particles on short fatigue crack initiation in AA2050-T8 and AA7050-T7451

    Directory of Open Access Journals (Sweden)

    Nizery Erembert

    2014-06-01

    Full Text Available Fatigue crack initiation at particles is studied in hot rolled 2050-T8 and 7050-T7451 material, using 1 to 4 mm cross section specimens. Both size and aspect ratio of particles are observed to affect their probability of being damaged. In 2050-T8 material, the probability that a matrix crack initiate at a cracked particle increases with its size, and no effect of aspect ratio is observed. In 2050-T8 specimens, matrix cracks initiate at both precracked (Al, Cu, Fe, Mn particles and particles cracked during cycling. Initiation in 7050-T74 specimens occur on Mg2Si particles which may be cracked or debonded, and Al7Cu2Fe particles that are cracked during cyclic loading.

  10. New X-ray refractometry for nondestructive characterization of high performance composites; Charakterisierung von Hochleistungsverbundwerkstoffen mittels Roentgenrefraktion

    Energy Technology Data Exchange (ETDEWEB)

    Harbich, K W; Hentschel, M P [Bundesanstalt fuer Materialforschung und -pruefung, Berlin (Germany). Labor 6.22 ` ` Zerstoerungsfreie Charakterisierung von Materialstrukturen` `

    1994-12-01

    Facing the basic relevance of single fibre bonding for the mechanical properties of composites relating testing methods are requested. These have not yet been satisfactory. A new nondestructive method provides a fast and precise tool to determine the fraction of debonded fibres by refraction of X-rays at the interface of fibres in composites. The systematic analysis of thinwalled unidirectional tapes of carbon fibres in thermoplastics results in specific characteristics of different lots. These were successfully exploited for the improvement of the processing parameters. The new method is selective for fibre orientation. The detection of specific defects in composites of orthogonal fibre orientation is performed by X-ray refraction topography. First investigations reveal clearly the detectibility and identification of impact damages and paper inserts. (orig.)

  11. Shape and 'gap' effects on the behavior of variably confined concrete

    International Nuclear Information System (INIS)

    Harries, Kent A.; Carey, Shawn A.

    2003-01-01

    Factors affecting the behavior of variably confined concrete are presented. The effect of debonding the fiber-reinforced polymer (FRP) jacket to the concrete substrate and providing a gap between the concrete and confining jacket is investigated. A second parameter--the shape of the cross section--is also investigated. An experimental program involving the compression testing of standard cylinders and similarly sized square specimens having external FRP jackets providing passive confinement is presented. Factors affecting jacket efficiency and the appropriateness of factors accounting for specimen shape are determined experimentally and discussed. The provision of a gap affected the axial stress at which the confining jacket was engaged, resulting in a reduced maximum attainable concrete strength. The jacket efficiency was not affected by the provision of the gap. The shape of the specimens was observed to affect the level of confinement generated. Square specimens exhibit lower confinement levels than circular specimens having the same jacket

  12. Analysis of an Orthotropic Deck Stiffened with a Cement-Based Overlay

    DEFF Research Database (Denmark)

    Walter, Rasmus; Olesen, John Forbes; Stang, Henrik

    2007-01-01

    decks. A solution might be to enhance the stiffness of the traditional orthotropic bridge deck by using a cement-based overlay. In this paper, an orthotropic steel bridge deck stiffened with a cement-based overlay is analyzed. The analysis is based on nonlinear fracture mechanics, and utilizes......Over the past years, with increasing traffic volumes and higher wheel loads, fatigue damage in steel parts of typical orthotropic steel bridge decks has been experienced on heavily trafficked routes. A demand exists to find a durable system to increase the fatigue safety of orthotropic steel bridge...... the finite-element method. The stiffness of the steel deck reinforced with an overlay depends highly on the composite action. The composite action is closely related to cracking of the overlay and interfacial cracking between the overlay and underlying steel plate (debonding). As an example, a real size...

  13. An investigation of hot deformation response of particulate-reinforced magnesium + 9% titanium composite

    International Nuclear Information System (INIS)

    Raghunath, B.K.; Karthikeyan, R.; Ganesan, G.; Gupta, M.

    2008-01-01

    An experimental analysis was performed to predict flow curves, dynamic recrystallisation behaviour of AZ91magnesium/titanium metal matrix composite based on result from hot compression test. The compression tests were carried out in a temperature range of 300-500 o C and at a strain rate range of 0.001-1 s -1 and the flow curves were obtained. The processing map of the studied material was obtained by following the dynamic material model. Microstructural characterization studies conducted on the compressed composite samples using optical and scanning electron microscopy, revealed dynamic recrystallization, debonding of Ti Particles, particle breakage, and flow localization. The observations were performed in order to describe the behavior of the material under hot forming operation in terms of material damage and micro structural modification

  14. An investigation of hot deformation response of particulate-reinforced magnesium + 9% titanium composite

    Energy Technology Data Exchange (ETDEWEB)

    Raghunath, B.K. [Department of Manufacturing Engineering, Faculty of Engineering and Technology, Annamalai University, Chidambaram 608 002, Tamil Nadu (India); Karthikeyan, R. [Department of Manufacturing Engineering, Faculty of Engineering and Technology, Annamalai University, Chidambaram 608 002, Tamil Nadu (India)], E-mail: ramkalaikarthi@rediffmail.com; Ganesan, G. [Department of Manufacturing Engineering, Faculty of Engineering and Technology, Annamalai University, Chidambaram 608 002, Tamil Nadu (India); Gupta, M. [Department of Mechanical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260 (Singapore)

    2008-07-01

    An experimental analysis was performed to predict flow curves, dynamic recrystallisation behaviour of AZ91magnesium/titanium metal matrix composite based on result from hot compression test. The compression tests were carried out in a temperature range of 300-500 {sup o}C and at a strain rate range of 0.001-1 s{sup -1} and the flow curves were obtained. The processing map of the studied material was obtained by following the dynamic material model. Microstructural characterization studies conducted on the compressed composite samples using optical and scanning electron microscopy, revealed dynamic recrystallization, debonding of Ti Particles, particle breakage, and flow localization. The observations were performed in order to describe the behavior of the material under hot forming operation in terms of material damage and micro structural modification.

  15. Aesthetic and functional outcomes using a multiloop edgewise archwire for camouflage orthodontic treatment of a severe Class III open bite malocclusion.

    Science.gov (United States)

    Marañón-Vásquez, Guido Artemio; Soldevilla Galarza, Luciano Carlos; Tolentino Solis, Freddy Antonio; Wilson, Cliff; Romano, Fábio Lourenço

    2017-09-01

    Occasionally, orthodontists will be challenged to treat malocclusions and skeletal disharmonies, which by their complexity one might think that the only treatment alternative is the surgical-orthodontic approach. A male patient, aged 17 years old, was diagnosed with a skeletal Class III malocclusion, anterior open bite and negative overjet. An unpleasant profile was the patient's 'chief complaint' showing interest in facial aesthetics improvement. Nevertheless, the patient and his parents strongly preferred a non-surgical treatment approach. He was treated with a multiloop edgewise archwire to facilitate uprighting and distal en-masse movement of lower teeth, correct the Class III open bite malocclusion, change the inclination of the occlusal plane and obtain the consequent morphological-functional adaptation of the mandible. The Class III malocclusion was corrected and satisfactory changes in the patient's profile were obtained. Active treatment was completed in 2 years, and facial result remained stable at 2 years 6 months after debonding.

  16. A simpler, safer, higher performance cooling system arrangement for water cooled divertors

    International Nuclear Information System (INIS)

    Carelli, M.D.; Kothmann, R.E.; Green, L.; Zhan, N.J.; Stefani, F.; Roidt, R.M.

    1994-01-01

    A cooling system arrangement is presented which is specifically designed for high heat flux water cooled divertors. The motivation behind the proposed open-quotes unichannelclose quotes configuration is to provide maximum safety; this design eliminates flow instabilities liable to occur in parallel channel designs, it eliminates total blockage, it promotes cross flow to counteract the effects of partial blockage and/or local hot spots, and it is much more tolerant to the effects of debonding between the beryllium armor and the copper substrate. Added degrees of freedom allow optimization of the design, including the possibility of operating at very high heat transfer coefficients associated with nucleate boiling, while at the same time providing ample margin against departure from nucleate boiling. Projected pressure drop, pumping power, and maximum operating temperatures are lower than for conventional parallel channel designs

  17. Effect of fiber coatings on room and elevated temperature mechanical properties of Nicalon trademark fiber reinforced Blackglas trademark ceramic matrix composites (CMCs)

    International Nuclear Information System (INIS)

    Aly, E.I.; Freitag, D.W.; Littlefield, J.E.

    1993-01-01

    With the development of silicon organometallic preceramic polymers as precursors for producing oxidation resistant ceramic matrices, through the polymer pyrolysis route, the fabrication of lightweight, complex advanced aircraft and missile structures from fiber reinforced composites is increasingly becoming more feasible. Besides refinement of processing techniques, the potential for achieving this objective depends upon identifying and developing the proper debond barrier coating layer, between the fiber and the matrix, for optimization of strength, toughness, and durability properties. Blackglas trademark based CMC's reinforced with Nicalon trademark SiC fibers with different types of coatings were fabricated. Coating schemes evaluated include CVD applied single layer boron nitride (BN) composition, dual-layer coatings of BN/SiC, and triple-layer coatings of SiC BN/SiC. Results of tensile and flexural property tests, scanning electron microscopy (SEM) of fracture surfaces, and auger electron spectroscopy (AES) microanalysis of the fiber/matrix interface have been discussed

  18. Influence of different functionalization on mechanical and interface behavior of MWCNTs/NBR sealing composites

    Science.gov (United States)

    Li, Kun; Gu, Boqin

    2017-04-01

    Rubber sealants are key components in processing industries. Carbon nanotubes (CNTs), which are randomly dispersed in polymer, are able to generate exciting effects. Focusing on mechanical properties of composites and interface characteristic between the fillers and matrix, carrying out SEM, DMA and uniaxial tensile tests, the tensile strength of the composites with 4 phr (parts by weight per hundred parts of rubber) multiwalled carbon nanotubes (MWNTs) is obviously improved. MWNTs with different functionalization have different influence on the viscoelastic and mechanical properties of the composites. Results indicate that MWNTs-COOH are broken when composites fractured. While MWNTs, MWNTs-OH and MWNTs-NH2 are pulled out from the matrix because interface debonds under the tensile failure. The interfacial shear stress (IFSS) is about 4.7 MPa in composites. The glass transition temperature (T g) shifts higher temperatures compared to pure NBR (Acrylonitrile-butadiene Rubber). The presence of the nanotubes limite the movement of NBR macromolecules.

  19. Toughening of carbon fibre reinforced polymer composites with rubber nanoparticles for advanced industrial applications

    Directory of Open Access Journals (Sweden)

    N. G. Ozdemir

    2016-05-01

    Full Text Available This study investigates the effects of nano carboxylic acrylonitrile butadiene rubber (CNBR-NP and nano acrylonitrile butadiene rubber (NBR-NP on the interlaminar shear strength and fracture toughness of carbon fibre reinforced polymer composites (CFRP with dicyandiamide-cured epoxy matrix. The results show that nano-size dispersion of rubber significantly improved the Mode I delamination fracture toughness (GIC of the CFRP by 250% and its Mode II delamination fracture toughness (GIIC by 80% with the addition of 20 phr of CNBR-NP. For the NBR-NP system, the GIC and GIIC delamination fracture toughness of the CFRP were increased by 200 and 80% respectively with the addition of 20 phr (parts per hundred rubber of nano rubber to the matrix. Scanning electron microscopy (SEM images of the fracture surface revealed that the toughening was mainly achieved by debonding of the nano rubber, crack path deflection and fibre bridging.

  20. Stretchable Conductive Composites from Cu-Ag Nanowire Felt.

    Science.gov (United States)

    Catenacci, Matthew J; Reyes, Christopher; Cruz, Mutya A; Wiley, Benjamin J

    2018-04-24

    Materials that retain a high conductivity under strain are essential for wearable electronics. This article describes a conductive, stretchable composite consisting of a Cu-Ag core-shell nanowire felt infiltrated with a silicone elastomer. This composite exhibits a retention of conductivity under strain that is superior to any composite with a conductivity greater than 1000 S cm -1 . This work also shows how the mechanical properties, conductivity, and deformation mechanism of the composite changes as a function of the stiffness of the silicone matrix. The retention of conductivity under strain was found to decrease as the Young's modulus of the matrix increased. This was attributed to void formation as a result of debonding between the nanowire felt and the elastomer. The nanowire composite was also patterned to create serpentine circuits with a stretchability of 300%.

  1. Temperature dependence of bending strength for plasma sprayed zirconia coating; Plasuma yosha zirconia himaku no magetsuyosa no ondo izonsei

    Energy Technology Data Exchange (ETDEWEB)

    Arai, M.; Sakuma, T. [Central Research Inst. of Electric Power Industry, Tokyo (Japan)] Mizutani, T. [Tokyo Inst. of Tech. (Japan)] Kishimoto, K. [Tokyo Inst. of Tech. (Japan). Faculty of Engineering] Saito, M. [Toshiba Corp. (Japan). Heavy Apparatus Engineering Lab.

    1998-02-01

    Plasma sprayed zirconia applying to the thermal barrier coating in gas turbine has been developing for protecting the hot parts such as blades and nozzles from high-temperature enviroments. In this paper, four point bending tests under various temperature conditions are conducted on plasma sprayed zirconia and its mechanical properties are examined. Results show that the bending strength at room temperature for plasma sprayed zirconia is much lower than that of sintered zirconia and is decreased with the increase in temperature. However, Weibull modulus at each temperature is relatively large and the dispersion of bending strength is very small in comparison with that of sintered zirconia. It is also clarified by the SEM observations of fracture surface that many defects such as debonding and microcrack are responsible for the lower bending strength. 9 refs., 8 figs., 1 tab.

  2. Micromechanical failure in fiber-reinforced composites

    DEFF Research Database (Denmark)

    Ashouri Vajari, Danial

    Micromechanical failure mechanisms occurring in unidirectional fiber-reinforced composites are studied by means of the finite element method as well as experimental testing. This study highlights the effect of micro-scale features such as fiber/matrix interfacial debonding, matrix cracking...... and microvoids on the microscopic and macroscopic mechanical response of composite materials. To this end, first a numerical study is carried out to explore ways to stabilize interfacial crack growth under dominant Mode-I fracture using the cohesive zone model. Consequently, this study suggests a method...... composites. In the first approach, the J2 plasticity model is implemented to model the elasto-plastic behavior of the matrix while in the second strategy the modified Drucker-Prager plasticity model is utilized to account for brittle-like and pressure dependent behavior of an epoxy matrix. In addition...

  3. Long fiber polymer composite property calculation in injection molding simulation

    Science.gov (United States)

    Jin, Xiaoshi; Wang, Jin; Han, Sejin

    2013-05-01

    Long fiber filled polymer composite materials have attracted a great attention and usage in recent years. However, the injection and compression molded long fiber composite materials possess complex microstructures that include spatial variations in fiber orientation and length. This paper presents the recent implemented anisotropic rotary diffusion - reduced strain closure (ARD-RSC) model for predicting fiber orientation distribution[1] and a newly developed fiber breakage model[2] for predicting fiber length distribution in injection and compression molding simulation, and Eshelby-Mori-Tanaka model[3,4] with fiber-matrix de-bonding model[5] have been implemented to calculate the long fiber composite property distribution with predicted fiber orientation and fiber length distributions. A validation study on fiber orientation, fiber breakage and mechanical property distributions are given with injection molding process simulation.

  4. Homogenized rigid body and spring-mass (HRBSM) model for the pushover analysis of out-of-plane loaded unreinforced and FRP reinforced walls

    Science.gov (United States)

    Bertolesi, Elisa; Milani, Gabriele

    2017-07-01

    The present paper is devoted to the discussion of a series of unreinforced and FRP retrofitted panels analyzed adopting the Rigid Body and Spring-Mass (HRBSM) model developed by the authors. To this scope, a total of four out of plane loaded masonry walls tested up to failure are considered. At a structural level, the non-linear analyses are conducted replacing the homogenized orthotropic continuum with a rigid element and non-linear spring assemblage by means of which out of plane mechanisms are allowed. FRP retrofitting is modeled adopting two noded truss elements whose mechanical properties are selected in order to describe possible debonding phenomenon or tensile rupture of the strengthening. The outcome provided numerically are compared to the experimental results showing a satisfactory agreement in terms of global pressure-deflection curves and failure mechanisms.

  5. Flexural behaviour of RCC beams with externally bonded FRP

    Science.gov (United States)

    Vignesh, S. Arun; Sumathi, A.; Saravana Raja Mohan, K.

    2017-07-01

    The increasing use of carbon and glass fibre reinforced polymer (FRP) sheets for strengthening existing reinforced concrete beams has generated considerable interest in understanding the behavior of the FRP sheets when subjected to bending. The study on flexure includes various parameters like percentage of increase in strength of the member due to the externally bonded Fiber reinforced polymer, examining the crack patterns, reasons of debonding of the fibre from the structure, scaling, convenience of using the fibres, cost effectiveness etc. The present work aims to study experimentally about the reasons behind the failure due to flexure of an EB-FRP concrete beam by studying the various parameters. Deflection control may become as important as flexural strength for the design of FRPreinforced concrete structures. A numerical model is created using FEM software and the results are compared with that of the experiment.

  6. Effect of simultaneous ion irradiation on microstructural change of SiC/SiC composites at high temperature

    International Nuclear Information System (INIS)

    Taguchi, T.; Wakai, E.; Igawa, N.; Nogami, S.; Snead, L.L.; Hasegawa, A.; Jitsukawa, S.

    2002-01-01

    The effect of simultaneous triple ion irradiation of He, H and Si on microstructural evolution of two kinds of SiC/SiC composites (HNS composite (using Hi-Nicalon type S SiC fiber) and TSA composite (using Tyranno SA SiC fiber)) at 1000 deg. C has been investigated. The microstructure observations of SiC/SiC composites irradiated to 10 dpa were examined by transmission electron microscopy. He bubbles were hardly formed in matrix of TSA composite, but many helium bubbles and some cracks were observed at grain boundaries of matrix of HNS composite. He bubbles and cracks were not, on the other hand, observed in the both fiber fabrics of HNS and TSA composites. Debonding between fiber and carbon layer following irradiation region was not observed in the both composites. Under these irradiation conditions, TSA composite showed the better microstructural stability against ion beams irradiation than one of HNS composite

  7. Operational modal analysis and wavelet transformation for damage identification in wind turbine blades

    DEFF Research Database (Denmark)

    Ulriksen, Martin Dalgaard; Tcherniak, Dmitri; Kirkegaard, Poul Henning

    2014-01-01

    The presented study demonstrates an application of a previously proposed modal and wavelet analysis-based damage identification method to a wind turbine blade. A trailing edge debonding was introduced to a SSP 34m blade mounted on a test rig. Operational modal analysis (OMA) was conducted to obtain...... are captured in the CWT by significantly magnified transform coefficients, thus providing combined damage detection, localization, and size assessment. It was found that due to the nature of the proposed method, the value of the identification results highly depends on the number of employed measurement points....... Since only a limited number of measurement points were utilized in the experiments, valid damage identification can only be obtained when employing high-frequency modes....

  8. Using lamb waves tomonitor moisture absorption thermally fatigues composite laminates

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jae Sun; Cho, Youn Ho [School of Mechanical Engineering, Pusan National University, Busan (Korea, Republic of)

    2016-06-15

    Nondestructive evaluation for material health monitoring is important in aerospace industries. Composite laminates are exposed to heat cyclic loading and humid environment depending on flight conditions. Cyclic heat loading and moisture absorption may lead to material degradation such as matrix breaking, debonding, and delamination. In this paper, the moisture absorption ratio was investigated by measuring the Lamb wave velocity. The composite laminates were manufactured and subjected to different thermal aging cycles and moisture absorption. For various conditions of these cycles, not only changes in weight and also ultrasonic wave velocity were measured, and the Lamb wave velocity at various levels of moisture on a carbon-epoxy plate was investigated. Results from the experiment show a linear correlation between moisture absorption ratio and Lamb wave velocity at different thermal fatigue stages. The presented method can be applied as an alternative solution in the online monitoring of composite laminate moisture levels in commercial flights.

  9. Toughness amplification in copper/epoxy joints through pulsed laser micro-machined interface heterogeneities

    KAUST Repository

    Hernandez Diaz, Edwin

    2017-11-21

    This work addresses the mechanics of debonding along copper/epoxy joints featuring patterned interfaces. Engineered surface heterogeneities with enhanced adhesion properties are generated through pulsed laser irradiation. Peel tests are carried out to ascertain the effect of patterns shape and area fraction on the mechanical response. Experimental results are evaluated with the support of three-dimensional finite element simulations based on the use of cohesive surfaces. Results discussion is largely framed in terms of effective peel force and energy absorbed to sever the samples. It is shown that surface heterogeneities act as sites of potential crack pinning able to trigger crack initiation, propagation and arrest. Surface patterns ultimately enable a remarkable increase in the effective peel force and dissipated energy with respect to baseline homogeneous sanded interface.

  10. Durability properties for adhesively bonded structural aerospace applications

    International Nuclear Information System (INIS)

    Shaffer, D.K.; Davis, G.D.; McNamara, D.K.; Shah, T.K.; Desai, A.

    1992-01-01

    This paper reports on the importance of good bond durability of adhesively joined aerospace components which has been recognized for many years. Military and civilian aircraft are exposed to harsh environments in addition to severe thermal and stress cycles during their service lives. Moisture is responsible for the majority of bond failures in the field. The presence of surface contaminants (e.g., fluoride, silicones) and the non-neutral pH of poor rinse water are common causes of adhesion problems in production environments. Honeycomb panels, stringer skins, doubler plates and core cowl assemblies are bonded joint structures that are subject to environmental- or contaminant-induced debonding. The identification and characterization of the causes of such bond failures leads to improved production quality, yield and cost reduction

  11. A mechanical model for FRP-strengthened beams in bending

    Directory of Open Access Journals (Sweden)

    P. S. Valvo

    2012-10-01

    Full Text Available We analyse the problem of a simply supported beam, strengthened with a fibre-reinforced polymer (FRP strip bonded to its intrados and subjected to bending couples applied to its end sections. A mechanical model is proposed, whereby the beam and FRP strip are modelled according to classical beam theory, while the adhesive and its neighbouring layers are modelled as an interface having a piecewise linear constitutive law defined over three intervals (elastic response – softening response – debonding. The model is described by a set of differential equations with appropriate boundary conditions. An analytical solution to the problem is determined, including explicit expressions for the internal forces, displacements and interfacial stresses. The model predicts an overall non-linear mechanical response for the strengthened beam, ranging over several stages: from linearly elastic behaviour to damage, until the complete detachment of the FRP reinforcement.

  12. Thermomechanical response of a cross-ply titanium matrix composite subjected to a generic hypersonic flight profile

    International Nuclear Information System (INIS)

    Mirdamadi, M.; Johnson, W.S.

    1993-01-01

    Cross-ply laminate behavior of Ti-15V-3Cr-3AI-3Sn (Ti-15-3) matrix reinforced with continuous silicon-carbide fibers (SCS-6) subjected to a generic hypersonic flight profile was evaluated experimentally and analytically. Thermomechanical fatigue test techniques were developed to conduct a simulation of a generic hypersonic flight profile. A micromechanical analysis was used. The analysis predicts the stress-strain response of the laminate and of the constituents in each ply during thermal and mechanical cycling by using only constituent properties as input. The fiber was modeled as elastic with transverse orthotropic and temperature-dependent properties. The matrix was modeled using a thermoviscoplastic constitutive relation. The fiber transverse modulus was reduced in the analysis to simulate the fiber-matrix interface failure. Excellent correlation was found between measured and predicted laminate stress-strain response due to generic hypersonic flight profile when fiber debonding was modeled

  13. ZrB₂-CNTs Nanocomposites Fabricated by Spark Plasma Sintering.

    Science.gov (United States)

    Jin, Hua; Meng, Songhe; Xie, Weihua; Xu, Chenghai; Niu, Jiahong

    2016-11-29

    ZrB₂-based nanocomposites with and without carbon nanotubes (CNTs) as reinforcement were prepared at 1600 °C by spark plasma sintering. The effects of CNTs on the microstructure and mechanical properties of nano-ZrB₂ matrix composites were studied. The results indicated that adding CNTs can inhibit the abnormal grain growth of ZrB₂ grains and improve the fracture toughness of the composites. The toughness mechanisms were crack deflection, crack bridging, debonding, and pull-out of CNTs. The experimental results of the nanograined ZrB₂-CNTs composites were compared with those of the micro-grained ZrB₂-CNTs composites. Due to the small size and surface effects, the nanograined ZrB₂-CNTs composites exhibited stronger mechanical properties: the hardness, flexural strength and fracture toughness were 18.7 ± 0.2 GPa, 1016 ± 75 MPa, and 8.5 ± 0.4 MPa·m 1/2 , respectively.

  14. Defining Threshold Values of Encapsulant and Backsheet Adhesion for PV Module Reliability: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Bosco, Nicholas S [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Kurtz, Sarah [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Eafanti, Joshua [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Tracy, Jared [Stanford University; Dauskardt, Reinhold [Stanford University

    2017-08-28

    The width-tapered cantilever beam method is used to quantify the debond energy (adhesion) of encapsulant and backsheet structures of 27 modules collected from the field. The collected population of modules contains both those that have remained in-tact and those with instances of either or both encapsulant and backsheet delamination. From this survey, initial threshold values (an adhesion value above which a module should remain intact throughout its lifetime) for encapsulant and backsheet interfaces are proposed. For encapsulants this value is about 60 J/m2 and for backsheets about 20 J/m2. It is expected that these values will continue to be refined and evolve as the width-tapered cantilever beam method becomes adopted by the PV industry, and that they may aid in the future improvement of accelerated lifetime tests and the development of new, low-cost materials.

  15. Fracture Characterization of PVC Foam Core Sandwich Specimen Using the DCB-UBM Test Method

    DEFF Research Database (Denmark)

    Saseendran, Vishnu; Berggreen, Christian; Carlsson, Leif A.

    coupled with experimental validation is paramount to determine the fracture resistance of the face/core interface. In this paper, the test-rig exploiting the double cantilever beam with uneven bending moments (DCB-UBM) concept is used to determine the fracture toughness of PVC foam core sandwich......Face/core debond failure in sandwich composites is a critical failure mode. Lack of cohesion between face and core will lead to loss of structural integrity. The estimation of interface fracture toughness especially at the face/core interface is extremely challenging, provided the dissimilarity...... composites. The DCB-UBM test enables fracture testing over a large range of mode-mixities as expressed by a phase angle (ψ) which is a measure of the amount of shear loading at the crack tip. A desired phase angle may be achieved by changing the moment-ratio (MR = Md/Ms)....

  16. Dynamic surface deformation of silicone elastomers for management of marine biofouling: laboratory and field studies using pneumatic actuation.

    Science.gov (United States)

    Shivapooja, Phanindhar; Wang, Qiming; Szott, Lizzy M; Orihuela, Beatriz; Rittschof, Daniel; Zhao, Xuanhe; López, Gabriel P

    2015-01-01

    Many strategies have been developed to improve the fouling release (FR) performance of silicone coatings. However, biofilms inevitably build on these surfaces over time. Previous studies have shown that intentional deformation of silicone elastomers can be employed to detach biofouling species. In this study, inspired by the methods used in soft-robotic systems, controlled deformation of silicone elastomers via pneumatic actuation was employed to detach adherent biofilms. Using programmed surface deformation, it was possible to release > 90% of biofilm from surfaces in both laboratory and field environments. A higher substratum strain was required to remove biofilms accumulated in the field environment as compared with laboratory-grown biofilms. Further, the study indicated that substratum modulus influences the strain needed to de-bond biofilms. Surface deformation-based approaches have potential for use in the management of biofouling in a number of technological areas, including in niche applications where pneumatic actuation of surface deformation is feasible.

  17. Cohesive zone model of carbon nanotube-coated carbon fiber/polyester composites

    International Nuclear Information System (INIS)

    Agnihotri, Prabhat Kamal; Kar, Kamal K; Basu, Sumit

    2012-01-01

    It has been previously reported that the average properties of carbon nanotube-coated carbon fiber/polyester multiscale composites critically depend on the length and density of nanotubes on the fiber surface. In this paper the effect of nanotube length and density on the interfacial properties of the carbon nanotube-coated carbon fiber–polymer interface has been studied using shear lag and a cohesive zone model. The latter model incorporates frictional sliding after complete debonding between the fiber and matrix and has been developed to quantify the effect of nanotube coating on various interfacial characterizing parameters. Our numerical results indicate that fibers with an optimal coverage and length of nanotubes significantly increase the interfacial strength and friction between the fiber and polymer. However, they also embrittle the interface compared with bare fibers. (paper)

  18. Nanomorphology of graphene and CNT reinforced polymer and its effect on damage: Micromechanical numerical study

    DEFF Research Database (Denmark)

    Pontefisso, Alessandro; Mishnaevsky, Leon

    2016-01-01

    of nanocomposites with inclusions of arbitrary and complex shapes. The effect of curved, zigzagged, snakelike shapes of real carbon nanotubes, as well as re-stacking of graphene on the damage evolution was studied in the computational experiments based on the developed code. The potential of hybrid (carbon...... nanotubes and graphene) nanoscale reinforcement was studied with view on its effect of damage resistance. It was demonstrated that idealized, cylinder like models of carbon nanotubes in polymers lead to an underestimation of the stress concentration and damage likelihood in the nanocomposites. The main...... damage mechanisms in CNT reinforced polymers are debonding and pull-out/fiber bridging, while in graphene reinforced polymers the main role is played by crack deviation and stack splitting, with following micro-crack merging. The potential of hybrid (carbon nanotubes and graphene) nanoscale reinforcement...

  19. Fatigue Crack Growth Behavior of and Recognition of AE Signals from Composite Patch-Repaired Aluminum Panel

    International Nuclear Information System (INIS)

    Kim, Sung Jin; Kwon, Oh Yang; Jang, Yong Joon

    2007-01-01

    The fatigue crack growth behavior of a cracked and patch-repaired Ah2024-T3 panel has been monitored by acoustic emission(AE). The overall crack growth rate was reduced The crack propagation into the adjacent hole was also retarded by introducing the patch repair. AE signals due to crack growth after the patch repair and those due to debonding of the plate-patch interface were discriminated by using the principal component analysis. The former showed high center frequency and low amplitude, whereas the latter showed long rise tine, low frequency and high amplitude. This type of AE signal recognition method could be effective for the prediction of fatigue crack growth behavior in the patch-repaired structures with the aid of AE source location

  20. Erosion resistance and adhesion of composite metal/ceramic coatings produced by plasma spraying

    International Nuclear Information System (INIS)

    Ramm, D.A.J.; Hutchings, I.M.; Clyne, T.W.

    1993-01-01

    Ceramic coatings can exhibit greater erosion resistance than most metallic coatings. Such coatings are conveniently produced by thermal spraying. Unfortunately, thermally sprayed ceramic coatings often exhibit poor adhesion, partly as a consequence of the development of residual stresses during spraying and subsequent cooling. Composite coatings have been studied using aluminium/alumina deposits on steel substrates. The incorporation of ceramics within a ductile matrix has potential for sharply reducing the erosive wear at high erodent impact angles, whilst retaining the good erosion resistance of ceramics at low angles. It is shown that the proportion of metal and ceramic at the free surface can be specified so as to optimise the erosion resistance. Experiments have also been carried out on the resistance of the coatings to debonding during four-point bending of the coated substrate. Progress is being made towards the tailoring of composition profiles in graded coatings so as to optimise the combination of erosion resistance and adhesion. (orig.)

  1. In situ reacted rare-earth hexaaluminate interphases

    International Nuclear Information System (INIS)

    Cain, M.G.; Cain, R.L.; Lewis, M.H.

    1997-01-01

    A novel in situ reaction between a ceria-doped zirconia interphase coating on Saphikon fibers and an outer alumina coating has resulted in the formation of oriented hexaaluminate platelets which can act as a low fracture energy interface barrier for crack deflection in oxide-oxide ceramic-matrix composites (CMCs). The reaction proceeds only in reducing environments where the reduction of the cerium and zirconium ions to their 3+ valent state causes a destabilization phenomenon consistent with previously reported findings. The diffusion of the cerium from the zirconia into solid solution with the alumina can stabilize the layered hexaaluminate structure. Preferred orientational growth of the hexaaluminate parallel to the coating interface was observed which is the required orientation for enhanced debonding at the fiber/matrix interface in long-fiber-reinforced CMCs

  2. [Effects of different resin removal methods on shear bond strength of rebonded orthodontic brackets].

    Science.gov (United States)

    Wu, Hai-miao; Zhao, Bin-jiao; Chen, Dong

    2015-06-01

    To compare the shear bond strength (SBS) of rebonded orthodontic metal brackets with different resin removal methods. Forty extracted premolars were chosen as samples and divided into 4 experimental groups. The teeth were bonded with brackets. The brackets from 3 groups were debonded while adhesive remnants were removed from bracket bases by methods of grinding, sandblasting, and direct flaming, respectively and then rebonded. The SBS values of all rebonded brackets were determined after pH cycling experiment for 30 days. Some rebonded bracket bases were selected and observed under scanning electron microscope (SEM). The data was analyzed by one-way ANOVA test using SPSS 13.0 software package. Statistical analysis revealed a significant difference of SBS values among the 4 experimental groups (Pbrackets after resin removal by grinding and sandblasting have a similar SBS compared to the initial brackets adhesive.

  3. High toughness alumina/aluminate: The role of hetero-interfaces

    International Nuclear Information System (INIS)

    Brito, M.E.; Yasuoka, M.; Kanzaki, S.

    1996-01-01

    Silica doped alumina/aluminate materials present a combination of high strength and high toughness not achieved before in other alumina systems, except for transformation toughened alumina. The authors have associated the increase in toughness to crack bridging by anisotropically grown alumina grains with concurrent interfacial debonding of these grains. A HREM study of grain boundaries and hetero-interface structures in this material shows the absence of amorphous phases at grain boundaries. Local Auger electron analysis of fractured surfaces revealed the coexistence of Si and La at the grain facets exposed by the noticeable intergranular fracture mode of this material. It is concluded that a certain and important degree of boundaries weakness is related to both presence of Si at the interfaces and existence of alumina/aluminate hetero-interfaces

  4. Multi scale analysis by acoustic emission of damage mechanisms in natural fibre woven fabrics/epoxy composites.

    Directory of Open Access Journals (Sweden)

    Touchard F.

    2010-06-01

    Full Text Available This paper proposes to develop an experimental program to characterize the type and the development of damage in composite with complex microstructure. A multi-scale analysis by acoustic emission has been developed and applied to hemp fibre woven fabrics/epoxy composite. The experimental program consists of tensile tests performed on single yarn, neat epoxy resin and composite materials to identify their AE amplitude signatures. A statistical analysis of AE amplitude signals has been realised and correlated with microscopic observations. Results have enabled to identify three types of damage in composites and their associated AE amplitudes: matrix cracking, interfacial debonding and reinforcement damage and fracture. Tracking of these damage mechanisms in hemp/epoxy composites has been performed to show the process of damage development in natural fibre reinforced composites.

  5. Enhancement of the in-plane shear properties of carbon fiber composites containing carbon nanotube mats

    Science.gov (United States)

    Kim, Hansang

    2015-01-01

    The in-plane shear property of carbon fiber laminates is one of the most important structural features of aerospace and marine structures. Fiber-matrix debonding caused by in-plane shear loading is the major failure mode of carbon fiber composites because of the stress concentration at the interfaces. In this study, carbon nanotube mats (CNT mat) were incorporated in two different types of carbon fiber composites. For the case of woven fabric composites, mechanical interlocking between the CNTs and the carbon fibers increased resistance to shear failure. However, not much improvement was observed for the prepreg composites as a result of incorporation of the CNT mats. The reinforcement mechanism of the CNT mat layer was investigated by a fractographic study using scanning electron microscopy. In addition, the CNT mat was functionalized by three different methods and the effectiveness of the functionalization methods was determined and the most appropriate functionalization method for the CNT mat was air oxidation.

  6. Thermal shock problems of bonded structure for plasma facing components

    International Nuclear Information System (INIS)

    Shibui, M.; Kuroda, T.; Kubota, Y.

    1991-01-01

    Thermal shock tests have been performed on W(Re)/Cu and Mo/Cu duplex structures with a particular emphasis on two failure modes: failure on the heated surface and failure near the bonding interface. The results indicate that failure of the duplex structure largely depends on the constraint of thermal strain on the heated surface and on the ductility changes of armour materials. Rapid debonding of the bonding interface may be attributed to the yielding of armour materials. This leads to a residual bending deformation when the armour cools down. Arguments are also presented in this paper on two parameter characterization of the failure of armour materials and on stress distribution near the free edge of the bonding interface. (orig.)

  7. Deformation, Failure, and Fatigue Life of SiC/Ti-15-3 Laminates Accurately Predicted by MAC/GMC

    Science.gov (United States)

    Bednarcyk, Brett A.; Arnold, Steven M.

    2002-01-01

    NASA Glenn Research Center's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) (ref.1) has been extended to enable fully coupled macro-micro deformation, failure, and fatigue life predictions for advanced metal matrix, ceramic matrix, and polymer matrix composites. Because of the multiaxial nature of the code's underlying micromechanics model, GMC--which allows the incorporation of complex local inelastic constitutive models--MAC/GMC finds its most important application in metal matrix composites, like the SiC/Ti-15-3 composite examined here. Furthermore, since GMC predicts the microscale fields within each constituent of the composite material, submodels for local effects such as fiber breakage, interfacial debonding, and matrix fatigue damage can and have been built into MAC/GMC. The present application of MAC/GMC highlights the combination of these features, which has enabled the accurate modeling of the deformation, failure, and life of titanium matrix composites.

  8. An investigation of the compressive strength of Kevlar 49/epoxy composites

    Science.gov (United States)

    Kulkarni, S. V.; Rosen, B. W.; Rice, J. S.

    1975-01-01

    Tests were performed to evaluate the effect of a wide range of variables including matrix properties, interface properties, fiber prestressing, secondary reinforcement, and others on the ultimate compressive strength of Kevlar 49/epoxy composites. Scanning electron microscopy is used to assess the resulting failure surfaces. In addition, a theoretical study is conducted to determine the influence of fiber anisotropy and lack of perfect bond between fiber and matrix on the shear mode microbuckling. The experimental evaluation of the effect of various constituent and process characteristics on the behavior of these unidirectional composites in compression did not reveal any substantial increase in strength. However, theoretical evaluations indicate that the high degree of fiber anisotropy results in a significant drop in the predicted stress level for internal instability. Scanning electron microscope data analysis suggests that internal fiber failure and smooth surface debonding could be responsible for the measured low compressive strengths.

  9. Stress transfer of a Kevlar 49 fiber pullout test studied by micro-Raman spectroscopy.

    Science.gov (United States)

    Lei, Zhenkun; Wang, Quan; Qiu, Wei

    2013-06-01

    The interfacial stress transfer behavior of a Kevlar 49 aramid fiber-epoxy matrix was studied with fiber pullout tests, the fibers of which were stretched by a homemade microloading device. Raman spectra on the embedded fiber were recorded by micro-Raman spectroscopy, under different strain levels. Then, the fiber axial stress was obtained by the relationship between the stress and Raman shift of the aramid fiber. Experimental results revealed that the fiber axial stress increased significantly with the load. The shear stress concentration occurred at the fiber entry to the epoxy resin. Thus, interfacial friction stages exist in the debonded fiber segment, and the interfacial friction shear stress is constant within one stage. The experimental results are consistent with the theoretical model predictions.

  10. Study on Tensile Properties of Nanoreinforced Epoxy Polymer: Macroscopic Experiments and Nanoscale FEM Simulation Prediction

    Directory of Open Access Journals (Sweden)

    Zhenqing Wang

    2013-01-01

    Full Text Available The effect of nanosilica contents on mechanical properties of the epoxy matrix with some nanoparticle aggregations was studied in macroscopic experiments and nanoscale simulation, particularly with regard to the effective modulus and ultimate stress. Three analytical models were used to obtain the effective elastic modulus of nanoparticle-reinforced composites. Based on Monte-Carlo method, the special program for the automatic generation of 2D random distribution particles without overlapping was developed for nanocomposite modeling. Weight fractions of nanoparticles were converted to volume fractions, in order to coordinate the content unit in the simulation. In numerical analysis, the weak interface strengthening and toughening mechanism was adopted. Virtual crack closure technique (VCCT and extended finite element method (XFEM were used to simulate phenomena of nanoparticle debonding and matrix crack growth. Experimental and simulation results show a good agreement with each other. By way of simulation, the weak interface toughening and strengthening mechanism of nanocomposites is confirmed.

  11. THE STUDY ON THE DURABILITY OF SUBMERGED STRUCTURE DISPLACEMENT DUE TO CONCRETE FAILURE

    Directory of Open Access Journals (Sweden)

    M. Mohd

    2016-09-01

    Full Text Available Concrete structures that exposed to marine environments are subjected to multiple deterioration mechanisms. An overview of the existing technology for submerged concrete, pressure resistant, concrete structures which related such as cracks, debonds, and delamination are discussed. Basic knowledge related to drowning durability such as submerged concrete structures in the maritime environment are the durability of a concrete and the ability to resist to weathering, chemical attack, abrasion or other deterioration processes. The measuring techniques and instrumentation for geometrical monitoring of submerged structural displacements have traditionally been categorized into two groups according to the two main groups, namely as geodetic surveying and geotechnical structural measurements of local displacements. This paper aims to study the durability of submerged concrete displacement and harmful effects of submerged concrete structures.

  12. Transformation between divacancy defects induced by an energy pulse in graphene.

    Science.gov (United States)

    Xia, Jun; Liu, XiaoYi; Zhou, Wei; Wang, FengChao; Wu, HengAn

    2016-07-08

    The mutual transformations among the four typical divacancy defects induced by a high-energy pulse were studied via molecular dynamics simulation. Our study revealed all six possible mutual transformations and found that defects transformed by absorbing energy to overcome the energy barrier with bonding, debonding, and bond rotations. The reversibility of defect transformations was also investigated by potential energy analysis. The energy difference was found to greatly influence the transformation reversibility. The direct transformation path was irreversible if the energy difference was too large. We also studied the correlation between the transformation probability and the input energy. It was found that the transformation probability had a local maxima at an optimal input energy. The introduction of defects and their structural evolutions are important for tailoring the exceptional properties and thereby performances of graphene-based devices, such as nanoporous membranes for the filtration and desalination of water.

  13. Toughness enhancement of tungsten reinforced with short tungsten fibres

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Y. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Zhang, L.H. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); University of Science and Technology of China, Hefei 230026 (China); Fang, Q.F., E-mail: qffang@issp.ac.cn [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); University of Science and Technology of China, Hefei 230026 (China); Zhang, T.; Wang, X.P.; Hao, T.; Liu, C.S. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China)

    2017-04-06

    The feasibility and toughening efficiency of the short tungsten fibre reinforcement on tungsten were investigated in W{sub f}/W composites fabricated by powder metallurgy method of spark plasma sintering. Fibres in the composites presented a Z-free laminar structure. Partial recrystallization of fibre grains occurred but fibre crack or damage was not detected. Fracture energy of W{sub f}/W composites was estimated in tensile tests, and the results indicated great toughness improvement over pure tungsten in virtue of frictional pullout and plastic deformation of fibres, and matrix-fibres interfacial debonding since 873 K. The specimen with mass fraction of 10% and fibre diameter of 100 µm exhibits the largest elongation of 9±1.1% and the highest ultimate strength of 482±13 MPa at 873 K.

  14. Finite element modelling for mode-I fracture behaviour of CFRP

    Science.gov (United States)

    Chetan, H. C.; Kattimani, Subhaschandra; Murigendrappa, S. M.

    2018-04-01

    Debonding is a major failure mechanism in Carbon Fiber Reinforced Polymer (CFRP) due to presence of many adhesion joins, in between many layers. In the current study a finite element simulation is carried out using Virtual Crack Closure Technique (VCCT) and Cohesive Zone Modelling (CZM) using Abaqus as analysis tool. A comparative study is performed in to order analyze convergence of results from CZM and VCCT. It was noted that CZM results matched well with published literature. The results from VCCT were also in good comparison with experimental data of published literature, but were seen to be overestimated. Parametric study is performed to evaluate the variation of input parameters like initial stiffness, element size, peak stress and energy release rate `G'. From the numerical evaluation, it was noted that CZM simulation relies largely on element size and peak stress.

  15. Some Aspects of Formation of Cracks in FRC with Main Reinforcement

    DEFF Research Database (Denmark)

    Brincker, Rune; Simonsen, J.; Hansen, W.

    1997-01-01

    In this paper the response of fibre reinforced concrete (FRC) with main reinforcement in pure tension is considered. Test results are presented showing three distinct regimes: a regime og linear elasticity, a regime of yielding at approximately constant stress, and finally, a regime of strain...... hardening. a simple model is presented which takes into account the debonding between the reinforcement and the fiber reinforced matrix as well as the crack opening relation of the fiber reinforced matrix. The fracture process is described from the un-cracked state and formation of the first crack till......, and a more ductile contribution from the fiber bridging, a plastic regime will be present in the tensile response. The case of a parabolic crack opening relation defines a brittleness number that describes the transition from formation of unstable discrete cracks to smaller cracks controlled by the softening...

  16. Research of Effective Width of FRP U-shaped Hoop Reinforcement Properties of Concrete Beams by Shear

    Directory of Open Access Journals (Sweden)

    Li Baokun

    2015-01-01

    Full Text Available The paste fiber reinforced composite material (hereinafter referred to as FRP U-shaped hoop of reinforced concrete beams interfacial debonding is an important reinforcement technology research. For the effective width of the CFRP U-shaped hoop reinforcement, it is still a lack of in-depth research, only relying on the test research huge workload, this article (ANSYS and the numerical simulation in the whole process of the shear load release properties of finite element calculation software. According to the results of finite element analysis, the author studied the CFRP U-shaped hoop to increase the width of the shear capacity of reinforced concrete beams by the impact.

  17. Modeling and Measurement of Sustained Loading and Temperature-Dependent Deformation of Carbon Fiber-Reinforced Polymer Bonded to Concrete.

    Science.gov (United States)

    Jeong, Yoseok; Lee, Jaeha; Kim, WooSeok

    2015-01-29

    This paper aims at presenting the effects of short-term sustained load and temperature on time-dependent deformation of carbon fiber-reinforced polymer (CFRP) bonded to concrete and pull-off strength at room temperature after the sustained loading period. The approach involves experimental and numerical analysis. Single-lap shear specimens were used to evaluate temperature and short-term sustained loading effects on time-dependent behavior under sustained loading and debonding behavior under pull-off loading after a sustained loading period. The numerical model was parameterized with experiments on the concrete, FRP, and epoxy. Good correlation was seen between the numerical results and single-lap shear experiments. Sensitivity studies shed light on the influence of temperature, epoxy modulus, and epoxy thickness on the redistribution of interfacial shear stress during sustained loading. This investigation confirms the hypothesis that interfacial stress redistribution can occur due to sustained load and elevated temperature and its effect can be significant.

  18. Damage analysis of CF/AF hybrid fabric reinforced plastic laminated composites with scanned image microscopy

    Science.gov (United States)

    Miyasaka, Chiaki; Kasano, Hideaki; Shull, Peter J.

    2004-07-01

    The article presents an experimental study that has been conducted to evaluate the impact loading damage within hybrid fabric laminates-carbon and Aramid fibers. The experiments have been undertaken on a series of interply hybrid specimens with different preprags stacking sequences. Impact damage was created using an air-gun like impact device propelling spherical steel balls with diameters of 5.0mm and 10.0mm and having velocities of 113m/s and 40m/s respectively. The resulting specimen surface and internal damage (e.g., micro-cracking and debonding) was visualized nondestructively by a scanning acoustic microscope (SAM) while further interrogation of specific internal damage was visualized using a scanning electron microscope (SEM) on cross-sectioned panels.

  19. Prestressing Effects on the Performance of Concrete Beams with Near-surface-mounted Carbon-fiber-reinforced Polymer Bars

    Science.gov (United States)

    Hong, Sungnam; Park, Sun-Kyu

    2016-07-01

    The effects of various prestressing levels on the flexural behavior of concrete beams strengthened with prestressed near-surface-mounted (NSM) carbon-fiber-reinforced polymer (CFRP) bars were investigated in this study. Four-point flexural tests up to failure were performed using a total of six strengthened prestressed and nonprestressed concrete beams. The nonprestressed strengthened beam failed by premature debonding at the interface of concrete and the epoxy adhesive, but the prestressed one failed owing due to rupture of the CFRP bar. As the prestressing level of the CFRP bar increased, the cracking and yield loads of the prestressed beams increased, but its effect on their deflections was insignificant. The ultimate load was constant regardless of prestressing level, but the ultimate deflection was almost inversely proportional to the level.

  20. Rubber friction on road surfaces: Experiment and theory for low sliding speeds

    Energy Technology Data Exchange (ETDEWEB)

    Lorenz, B.; Persson, B. N. J. [PGI, FZ Jülich, 52425 Jülich (Germany); Oh, Y. R.; Nam, S. K.; Jeon, S. H. [Hankook Tire Co. LTD., 112 Gajeongbuk-ro, Yuseong-gu, Daejeon 305-725 (Korea, Republic of)

    2015-05-21

    We study rubber friction for tire tread compounds on asphalt road surfaces. The road surface topographies are measured using a stylus instrument and atomic force microscopy, and the surface roughness power spectra are calculated. The rubber viscoelastic modulus mastercurves are obtained from dynamic mechanical analysis measurements and the large-strain effective modulus is obtained from strain sweep data. The rubber friction is measured at different temperatures and sliding velocities, and is compared to the calculated data obtained using the Persson contact mechanics theory. We conclude that in addition to the viscoelastic deformations of the rubber surface by the road asperities, there is an important contribution to the rubber friction from shear processes in the area of contact. The analysis shows that the latter contribution may arise from rubber molecules (or patches of rubber) undergoing bonding-stretching-debonding cycles as discussed in a classic paper by Schallamach.

  1. Toughness amplification in copper/epoxy joints through pulsed laser micro-machined interface heterogeneities

    KAUST Repository

    Diaz, Edwin Hernandez; Alfano, Marco; Pulungan, Ditho Ardiansyah; Lubineau, Gilles

    2017-01-01

    This work addresses the mechanics of debonding along copper/epoxy joints featuring patterned interfaces. Engineered surface heterogeneities with enhanced adhesion properties are generated through pulsed laser irradiation. Peel tests are carried out to ascertain the effect of patterns shape and area fraction on the mechanical response. Experimental results are evaluated with the support of three-dimensional finite element simulations based on the use of cohesive surfaces. Results discussion is largely framed in terms of effective peel force and energy absorbed to sever the samples. It is shown that surface heterogeneities act as sites of potential crack pinning able to trigger crack initiation, propagation and arrest. Surface patterns ultimately enable a remarkable increase in the effective peel force and dissipated energy with respect to baseline homogeneous sanded interface.

  2. Creep behaviour of porous metal supports for solid oxide fuel cells

    DEFF Research Database (Denmark)

    Boccaccini, Dino; Frandsen, Henrik Lund; Sudireddy, Bhaskar Reddy

    2014-01-01

    The creep behaviour of porous ironechromium alloy used as solid oxide fuel cell support was investigated, and the creep parameters are compared with those of dense strips of similar composition under different testing conditions. The creep parameters were determined using a thermo......-mechanical analyser with applied stresses in the range from 1 to 15 MPa and temperatures between 650 and 800 _C. The GibsoneAshby and Mueller models developed for uniaxial creep of open-cell foams were used to analyse the results. The influence of scale formation on creep behaviour was assessed by comparing the creep...... data for the samples tested in reducing and oxidising atmospheres. The influence of preoxidation on creep behaviour was also investigated. In-situ oxidation during creep experiments increases the strain rate while pre-oxidation of samples reduces it. Debonding of scales at high stress regime plays...

  3. Investigation of displacement, strain and stress in single step transversely isotropic elastic bonded joint

    Science.gov (United States)

    Apu, Md. Jakaria; Islam, Md. Shahidul

    2016-07-01

    Bi-material joint is often used in many advanced materials and structures. Determination of the bonding strength at the interface is very difficult because of the presence of the stress singularity. In this paper, the displacement and stress fields of a transversely isotropic bi-material joint around an interface edge are determined. Autodesk Simulation Mechanical 2015 is used to carry out the numerical computations. Stress and displacement fields demonstrate that the values near the edge of joint where the stress singularity occurs are larger than that at the inner portion. From the numerical results, it is suggested that de-bonding of the interface may occur at the interface edge of the joint due to the higher stress concentration at the free edge.

  4. Microstructural evolution and wear behaviors of laser cladding Ti_2Ni/α(Ti) dual-phase coating reinforced by TiB and TiC

    International Nuclear Information System (INIS)

    Song, R.; Li, J.; Shao, J.Z.; Bai, L.L.; Chen, J.L.; Qu, C.C.

    2015-01-01

    Graphical abstract: - Highlights: • A TiC+TiB reinforced intermetallic matrix coating was fabricated by laser cladding. • The microstructural evolution of the reinforcements was analyzed. • A formula was established in term of wear loss, sliding time and applied load. • Wear behaviors were investigated by in situ continuing tests in different time intervals. • The transformation of wear mechanism at different applied loads was revealed. - Abstract: The Ti_2Ni/α(Ti) dual-phase coating reinforced by TiB and TiC was fabricated on the Ti6Al4V substrate by laser cladding. Phase constituents were confirmed by a theoretical prediction combined with X-ray diffraction (XRD) analyses. From the surface to the bottom of the coating, a regular evolution of the reinforcements’ microstructure, namely TiC_p+(TiB+TiC)_e, (TiB+TiC)_e and TiB_p+(TiB+TiC)_e (p and e were the abbreviations of primary and eutectic, respectively), was investigated by scanning electron microscopy (SEM). The coating possessed the higher microhardness than that of the substrate. An in situ dynamic method (in situ continuing tests at different time intervals) was designed to reveal wear behaviors at different wear stages. A quantitative calculation formula was established by a mathematic model to predict wear losses under different sliding time and applied loads in a definite precision. The wear mechanism was transformed from brittle debonding (at 10 N) to the joint action of brittle debonding and micro-cutting (at 20 N and 30 N) due to the microstructural evolution across the depth from the surface of the coating.

  5. Dentin-composite bond strength measurement using the Brazilian disk test.

    Science.gov (United States)

    Carrera, Carola A; Chen, Yung-Chung; Li, Yuping; Rudney, Joel; Aparicio, Conrado; Fok, Alex

    2016-09-01

    This study presents a variant of the Brazilian disk test (BDT) for assessing the bond strength between composite resins and dentin. Dentin-composite disks (ϕ 5mm×2mm) were prepared using either Z100 or Z250 (3M ESPE) in combination with one of three adhesives, Adper Easy Bond (EB), Adper Scotchbond Multi-Purpose (MP) and Adper Single Bond (SB), and tested under diametral compression. Acoustic emission (AE) and digital image correlation (DIC) were used to monitor debonding of the composite from the dentin ring. A finite element (FE) model was created to calculate the bond strengths using the failure loads. Fracture modes were examined by scanning electron microscopy (SEM). Most specimens fractured along the dentin-resin composite interface. DIC and AE confirmed interfacial debonding immediately before fracture of the dentin ring. Results showed that the mean bond strength with EB (14.9±1.9MPa) was significantly higher than with MP (13.2±2.4MPa) or SB (12.9±3.0MPa) (p0.05). Z100 (14.5±2.3MPa) showed higher bond strength than Z250 (12.7±2.5MPa) (pstrength between dentin and composite, with zero premature failure, reduced variability in the measurements, and consistent failure at the dentin-composite interface. The new test could help to predict the clinical performance of adhesive systems more effectively and consistently by reducing the coefficient of variation in the measured bond strength. Copyright © 2016 Elsevier Ltd. All rights reserved.

  6. Dentin-Composite Bond Strength Measurement Using the Brazilian Disk Test

    Science.gov (United States)

    Carrera, Carola A.; Chen, Yung-Chung; Li, Yuping; Rudney, Joel; Aparicio, Conrado; Fok, Alex

    2016-01-01

    Objectives This study presents a variant of the Brazilian disk test (BDT) for assessing the bond strength between composite resins and dentin. Methods Dentin-composite disks (φ 5 mm × 2 mm) were prepared using either Z100 or Z250 (3M ESPE) in combination with one of three adhesives, Adper Easy Bond (EB), Adper Scotchbond Multi-Purpose (MP) and Adper Single Bond (SB), and tested under diametral compression. Acoustic emission (AE) and digital image correlation (DIC) were used to monitor debonding of the composite from the dentin ring. A finite element (FE) model was created to calculate the bond strengths using the failure loads. Fracture modes were examined by scanning electron microscopy (SEM). Results Most specimens fractured along the dentin-resin composite interface. DIC and AE confirmed interfacial debonding immediately before fracture of the dentin ring. Results showed that the mean bond strength with EB (14.9±1.9 MPa) was significantly higher than with MP (13.2±2.4 MPa) or SB (12.9±3.0 MPa) (p0.05). Z100 (14.5±2.3 MPa) showed higher bond strength than Z250 (12.7±2.5 MPa) (padhesive failure mode. EB failed mostly at the dentin-adhesive interface, whereas MP at the composite-adhesive interface; specimens with SB failed at the composite-adhesive interface and cohesively in the adhesive. Conclusions The BDT variant showed to be a suitable alternative for measuring the bond strength between dentin and composite, with zero premature failure, reduced variability in the measurements, and consistent failure at the dentin-composite interface. PMID:27395367

  7. Effects of surface treatments on bond strength of dental Ti-20Cr and Ti-10Zr alloys to porcelain

    International Nuclear Information System (INIS)

    Lin, Hsi-Chen; Wu, Shih-Ching; Ho, Wen-Fu; Huang, Ling-Hsiu; Hsu, Hsueh-Chuan

    2010-01-01

    The purpose of this study was to investigate the effect of surface treatments, including sandblasting and grinding, on the bond strength between a low-fusing porcelain and c.p. Ti, Ti-20Cr and Ti-10Zr alloys. The surface treatments were divided into 2 groups. Grinding surface treatment was applied to the first group, which served as the control, and sandblasting was applied to the second group. After treatment, low-fusing porcelain (Titankeramik) was fired onto the surface of the specimens. A universal testing machine was used to perform a 3-point bending test. The metal-ceramic interfaces were subjected to scanning electron microscopic analysis. Of the sandblasted samples, the debonding test showed that Ti-20Cr alloy had the strongest (31.50 MPa) titanium-ceramic bond (p < 005), followed by c.p. Ti (29.4 MPa) and Ti-10Zr (24.3 MPa). Of the grinded samples, Ti-20Cr alloy showed 27.3 MPa titanium-ceramic bond (p < 005), followed by c.p. Ti (14.3 MPa) and Ti-10Zr (failure). The SEM micrographs of the metal surface after debonding showed residual porcelain retained on all samples. On the whole, sandblasting surface treatment appears to have had a more beneficial effect on the Ti-ceramic bond strength than grinding surface treatment. Furthermore, surface treatment of Ti-20Cr with either grinding or sandblasting resulted in adequate bond strength, which exceeded the lower limit value in the ISO 9693 standard (25 MPa).

  8. Transmission of Er:YAG laser through different dental ceramics.

    Science.gov (United States)

    Sari, Tugrul; Tuncel, Ilkin; Usumez, Aslihan; Gutknecht, Norbert

    2014-01-01

    The aim of this study was to determine the erbium-doped yttrium aluminum garnet (Er:YAG) laser transmission ratio through different dental ceramics with different thicknesses. Laser debonding procedure of adhesively luted all-ceramic restorations is based on the transmission of laser energy through the ceramic and the ablation of resin cement, because of the transmitted laser energy. Five different dental ceramics were evaluated in this study: sintered zirconium-oxide core ceramic, monolithic zirconium-oxide ceramic, feldspathic ceramic, leucite-reinforced glass ceramic, and lithium disilicate-reinforced glass ceramic. Two ceramic discs with different thicknesses (0.5 and 1 mm) were fabricated for each group. Ceramic discs were placed between the sensor membrane of the laser power meter and the tip of the contact handpiece of an Er:YAG laser device with the aid of a custom- made acrylic holder. The transmission ratio of Er:YAG laser energy (500 mJ, 2 Hz, 1 W, 1000 μs) through different ceramic discs was measured with the power meter. Ten measurements were made for each group and the results were analyzed with two way analysis of variance (ANOVA) and Tukey honestly significant difference (HSD) tests. The highest transmission ratio was determined for lithium disilicate-reinforced ceramic with 0.5 mm thickness (88%) and the lowest was determined for feldspathic ceramic with 1 mm thickness (44%). The differences among the different ceramics and between the different thicknesses were significant (pCeramic type and thickness should be taken into consideration to adjust the laser irradiation parameters during laser debonding of adhesively luted all-ceramic restorations.

  9. Resistance to bond degradation between dual-cure resin cements and pre-treated sintered CAD-CAM dental ceramics

    Science.gov (United States)

    Osorio, Raquel; Monticelli, Francesca; Osorio, Estrella; Toledano, Manuel

    2012-01-01

    Objective: To evaluate the bond stability of resin cements when luted to glass-reinforced alumina and zirconia CAD/CAM dental ceramics. Study design: Eighteen glass-infiltrated alumina and eighteen densely sintered zirconia blocks were randomly conditioned as follows: Group 1: No treatment; Group 2: Sandblasting (125 µm Al2O3-particles); and Group 3: Silica-coating (50 µm silica-modified Al2O3-particles). Composite samples were randomly bonded to the pre-treated ceramic surfaces using different resin cements: Subgroup 1: Clearfil Esthetic Cement (CEC); Subgroup 2: RelyX Unicem (RXU); and Subgroup 3: Calibra (CAL). After 24 h, bonded specimens were cut into 1 ± 0.1 mm2 sticks. One-half of the beams were tested for microtensile bond strength (MTBS). The remaining one-half was immersed in 10 % NaOCl aqueous solution (NaOClaq) for 5 h before testing. The fracture pattern and morphology of the debonded surfaces were assessed with a field emission gun scanning electron microscope (FEG-SEM). A multiple ANOVA was conducted to analyze the contributions of ceramic composition, surface treatment, resin cement type, and chemical challenging to MTBS. The Tukey test was run for multiple comparisons (p ceramic interfacial longevity depended on cement selection rather than on surface pre-treatments. The MDP-containing and the self-adhesive resin cements were both suitable for luting CAD/CAM ceramics. Despite both cements being prone to degradation, RXU luted to zirconia or untreated or sandblasted alumina showed the most stable interfaces. CAL experimented spontaneous debonding in all tested groups. Key words:CAD/CAM ceramic, alumina, zirconia, resin cement, surface pre-treatment, sandblasting, silica-coating, chemical aging, bond degradation, microtensile bond strength. PMID:22322517

  10. Adaptation of adhesive post and cores to dentin after in vitro occlusal loading: evaluation of post material influence.

    Science.gov (United States)

    Dietschi, Dider; Ardu, Stefano; Rossier-Gerber, Anne; Krejci, Ivo

    2006-12-01

    Fatigue resistance of post and cores is critical to the long term behavior of restored nonvital teeth. The purpose of this in vitro trial was to evaluate the influence of the post material's physical properties on the adaptation of adhesive post and core restorations after cyclic mechanical loading. Composite post and cores were made on endodontically treated deciduous bovine teeth using 3 anisotropic posts (made of carbon, quartz, or quartz-and-carbon fibers) and 3 isotropic posts (zirconium, stainless steel, titanium). Specimens were submitted to 3 successive loading phases--250,000 cycles at 50 N, 250,000 at 75 N, and 500,000 at 100 N--at a rate of 1.5 Hz. Restoration adaptation was evaluated under SEM, before and during loading (margins) and after test completion (margins and internal interfaces). Six additional samples were fabricated for the characterization of interface micromorphology using confocal microscopy. Mechanical loading increased the proportion of marginal gaps in all groups; carbon fiber posts presented the lowest final gap proportion (7.11%) compared to other stiffer metal-ceramic or softer fiber posts (11.0% to 19.1%). For internal adaptation, proportions of debonding between dentin and core or cement varied from 21.69% (carbon post) to 47.37% (stainless steel post). Debonding at the post-cement interface occurred only with isotropic materials. Confocal microscopy observation revealed that gaps were generally associated with an incomplete hybrid layer and reduced resin tags. Regardless of their rigidity, metal and ceramic isotropic posts proved less effective than fiber posts at stabilizing the post and core structure in the absence of the ferrule effect, due to the development of more interfacial defects with either composite or dentin.

  11. Compressive failure model for fiber composites by kink band initiation from obliquely aligned, shear-dislocated fiber breaks

    Energy Technology Data Exchange (ETDEWEB)

    Bai, J.; Phoenix, S.L. [Cornell University, Ithaca, NY (United States). Dept. of Theoretical and Applied Mechanics

    2005-04-01

    Predicting compressive failure of a unidirectional fibrous composite is a longstanding and challenging problem that we study from a new perspective. Motivated by previous modelling of tensile failure as well as experimental observations on compressive failures in single carbon fibers, we develop a new micromechanical model for the compressive failure process in unidirectional, planar composites. As the compressive load is increased, random fiber failures are assumed to occur due to statistically distributed flaws, analogous to what occurs in tension. These breaks are often shear-mode failures with slanted surfaces that induce shear dislocations, especially when they occur in small groups aligned obliquely. Our model includes interactions of dislocated and neighboring intact fibers through a system of fourth-order, differential equations governing transverse deformation, and also allows for local matrix plastic yielding and debonding from the fiber near and within the dislocation arrays. Using the Discrete Fourier Transform method, we find a 'building-block' analytical solution form, which naturally embodies local length scales of fiber microbuckling and instability. Based on the influence function, superposition approach, a computationally efficient scheme is developed to model the evolution of fiber and matrix stresses. Under increasing compressive strain the simulations show that matrix yielding and debonding crucially lead to large increases in bending strains in fibers next to small groups of obliquely aligned, dislocated breaks. From the paired locations of maximum fiber bending in flanking fibers, the triggering of an unstable kink band becomes realistic. The geometric features of the kink band, such as the fragment lengths and orientation angles, will depend on the fiber and matrix mechanical and geometric properties. In carbon fiber-polymer matrix systems our model predicts a much lower compressive failure stress than obtained from Rosen

  12. In vivo determination of tooth mobility after fixed orthodontic appliance therapy with a novel intraoral measurement device.

    Science.gov (United States)

    Konermann, Anna; Al-Malat, R; Skupin, J; Keilig, L; Dirk, C; Karanis, R; Bourauel, C; Jäger, A

    2017-05-01

    Valid measurement systems recording tooth mobility upon displacement within the subtle range of physiological strains are missing. Here, we introduce a novel in vivo measurement device and demonstrate a first clinical application by monitoring tooth mobility changes during retention after fixed multibracket appliance therapy. Tooth mobility was measured in vivo on 21 patients (11 female, 10 male; mean age 16.1 ± 3.1 years) by displacing the upper first incisor 0.2 mm lingually for 0.2, 0.5, 1, 2, 5, and 10 s with the novel intraoral device. Measurements were recorded directly after, as much as 2, 7, and 14 days and up to 6 months after appliance debonding. Device performance was precise and valid in clinical use. Data revealed significant interindividual varying tooth mobility, which was very high during the first 2 days after appliance removal. After 1 week, mobility values decreased, but were generally higher upon short loadings compared to long ones. After 3 months, tooth mobility was significantly lower than directly after debonding. Interestingly, males exhibited significantly less mobility than females. Our work is the first using an in vivo measurement device capable of performing and recording tooth displacements within this delicate range and in such precision. Furthermore, our findings elucidate tooth mobility changes after multibracket treatment, giving important information for retention periods. Establishment of this novel measurement device in clinical use is an important improvement when approaching the complexity of tooth mobility in vivo regarding different issues like orthodontics, periodontal disease, or bruxism.

  13. Kekuatan Lentur Komposit Polyester Berpenguat Serat Tapis Kelapa

    Directory of Open Access Journals (Sweden)

    I Made Astika

    2015-07-01

    Full Text Available Penelitian ini bertujuan untuk menyelidiki sifat mekanis yaitu kekuatan lentur dari kompositpolyester yang diperkuat dengan serat tapis kelapa. Di masa depan komposit ini dapatdigunakan untuk menggantikan kayu, bambu dan gipsun yang harganya mahal dan tidaktahan air. Komposit dibuat dengan memanfaatkan serat sabut kelapa dan matriks resinUnsaturated-Polyester (UPRs jenis Yucalac 157 BQTN, campuran 1% hardener jenis MEKPO(Methyl Ethyl Ketone Peroxide dan perendaman serat dalam larutan alkali KMnO4 0,5%.Metode produksi yang digunakan adalah press hand lay up dengan orientasi serat acak.Desain komposit dengan variasi fraksi volume serat 20, 25 dan 30% dan variasi panjang serat5, 10 dan 15 mm. Hasil penelitian menunjukkan bahwa semakin besar fraksi volume danpanjang serat dalam komposit maka kekuatan lentur semakin tinggi. Mode patahan yangteramati adalah patah getas, debonding, pullout dan crack deflection.Kata kunci: komposit, serat tapis kelapa, kekuatan lentur, mode patahan The purpose of this study is to investigate the mechanical properties i.e. flexural strength ofcomposites coconut filter fiber. In the future this material can be used to replace the wood,bamboo and gipsun which are high price and lower water resistance.The research material made with coconut filter fiber as reinforcement and matrix resinunsaturated polyester (UPRs type Yukalac BQTN 157, with 1% hardener types MEKPO(Methyl Ethyl Ketone Peroxide and fiber treatment by 0.5% KMnO4. Production methods arepress hand lay-up and the variations of fiber volume fraction are 20, 25 and 30% and fiberlength are 5, 10 and 15 mm. Testing of mechanical properties is flexural test (ASTM - D790The results of research show that the longer of fiber and the bigger of fiber volume fraction,the higher of flexural strength are obtained. The fracture mode are overload, debonding ,pullout and crack deflectionKeywords : composites, coconut filter fiber, flexural strength, fracture mode

  14. Four chemical methods of porcelain conditioning and their influence over bond strength and surface integrity

    Science.gov (United States)

    Stella, João Paulo Fragomeni; Oliveira, Andrea Becker; Nojima, Lincoln Issamu; Marquezan, Mariana

    2015-01-01

    OBJECTIVE: To assess four different chemical surface conditioning methods for ceramic material before bracket bonding, and their impact on shear bond strength and surface integrity at debonding. METHODS: Four experimental groups (n = 13) were set up according to the ceramic conditioning method: G1 = 37% phosphoric acid etching followed by silane application; G2 = 37% liquid phosphoric acid etching, no rinsing, followed by silane application; G3 = 10% hydrofluoric acid etching alone; and G4 = 10% hydrofluoric acid etching followed by silane application. After surface conditioning, metal brackets were bonded to porcelain by means of the Transbond XP system (3M Unitek). Samples were submitted to shear bond strength tests in a universal testing machine and the surfaces were later assessed with a microscope under 8 X magnification. ANOVA/Tukey tests were performed to establish the difference between groups (α= 5%). RESULTS: The highest shear bond strength values were found in groups G3 and G4 (22.01 ± 2.15 MPa and 22.83 ± 3.32 Mpa, respectively), followed by G1 (16.42 ± 3.61 MPa) and G2 (9.29 ± 1.95 MPa). As regards surface evaluation after bracket debonding, the use of liquid phosphoric acid followed by silane application (G2) produced the least damage to porcelain. When hydrofluoric acid and silane were applied, the risk of ceramic fracture increased. CONCLUSIONS: Acceptable levels of bond strength for clinical use were reached by all methods tested; however, liquid phosphoric acid etching followed by silane application (G2) resulted in the least damage to the ceramic surface. PMID:26352845

  15. Effectiveness of bovine-derived xenograft versus bioactive glass with periodontally accelerated osteogenic orthodontics in adults: a randomized, controlled clinical trial.

    Science.gov (United States)

    Bahammam, Maha A

    2016-11-30

    Periodontally accelerated osteogenic orthodontics (PAOO) combines periodontal therapy with orthodontic therapy, which minimises treatment time. This study compared the effectiveness of a bovine-derived xenograft with that of bioactive glass when combined with PAOO for the treatment of adult patients with moderate crowding of the teeth. In this prospective, single-masked clinical trial, 33 orthodontic patients (20 women, 13 men; mean age 21.2 ± 1.43 [18 - 27] years), were randomly allocated to one of three groups. Group 1 underwent a modified corticotomy technique on the labial side only, whereas group 2 was treated with the same technique combined with PAOO using a bovine-derived xenograft and group 3 was treated in the same way but combining PAOO with bioactive glass. The total treatment duration was recorded from the start of active orthodontic treatment, immediately after corticotomy, and at the time of debonding. Probing depth was evaluated clinically and bone density and root length were evaluated radiographically on the day of surgery (baseline, T1), post-treatment at debonding (T2), and 9 months post-treatment (T3). The duration of orthodontic treatment was markedly reduced to an average of 11.4 ± 0.14 weeks in all groups. All probing depths were orthodontic treatment and periodontal surgery is an effective treatment for adult patients that decreases the duration of active treatment and reduces the risk of root resorption. Use of a bovine-derived xenograft with modified corticotomy provided superior benefits in terms of increased bone density than did the use of bioactive glass. The study was retrospectively registered at ClinicalTrials.gov under Clinical Trial Registration Number: NCT02796911 .

  16. Main Clinical Outcomes of Feldspathic Porcelain and Glass-Ceramic Laminate Veneers: A Systematic Review and Meta-Analysis of Survival and Complication Rates.

    Science.gov (United States)

    Morimoto, Susana; Albanesi, Rafael Borges; Sesma, Newton; Agra, Carlos Martins; Braga, Mariana Minatel

    2016-01-01

    The aim of this study was to perform a systematic review and meta-analysis based on clinical trials that evaluated the main outcomes of glass-ceramic and feldspathic porcelain laminate veneers. A systematic search was carried out in Cochrane and PubMed databases. From the selected studies, the survival rates for porcelain and glass-ceramic veneers were extracted, as were complication rates of clinical outcomes: debonding, fracture/chipping, secondary caries, endodontic problems, severe marginal discoloration, and influence of incisal coverage and enamel/dentin preparation. The Cochran Q test and the I(2) statistic were used to evaluate heterogeneity. Out of the 899 articles initially identified, 13 were included for analysis. Metaregression analysis showed that the types of ceramics and follow-up periods had no influence on failure rate. The estimated overall cumulative survival rate was 89% (95% CI: 84% to 94%) in a median follow-up period of 9 years. The estimated survival for glass-ceramic was 94% (95% CI: 87% to 100%), and for feldspathic porcelain veneers, 87% (95% CI: 82% to 93%). The meta-analysis showed rates for the following events: debonding: 2% (95% CI: 1% to 4%); fracture/chipping: 4% (95% CI: 3% to 6%); secondary caries: 1% (95% CI: 0% to 3%); severe marginal discoloration: 2% (95% CI: 1% to 10%); endodontic problems: 2% (95% CI: 1% to 3%); and incisal coverage odds ratio: 1.25 (95% CI: 0.33 to 4.73). It was not possible to perform meta-analysis of the influence of enamel/dentin preparation on failure rates. Glass-ceramic and porcelain laminate veneers have high survival rates. Fracture/ chipping was the most frequent complication, providing evidence that ceramic veneers are a safe treatment option that preserve tooth structure.

  17. Microstructural evolution and wear behaviors of laser cladding Ti{sub 2}Ni/α(Ti) dual-phase coating reinforced by TiB and TiC

    Energy Technology Data Exchange (ETDEWEB)

    Song, R.; Li, J., E-mail: jacob_lijun@sina.com; Shao, J.Z.; Bai, L.L.; Chen, J.L.; Qu, C.C.

    2015-11-15

    Graphical abstract: - Highlights: • A TiC+TiB reinforced intermetallic matrix coating was fabricated by laser cladding. • The microstructural evolution of the reinforcements was analyzed. • A formula was established in term of wear loss, sliding time and applied load. • Wear behaviors were investigated by in situ continuing tests in different time intervals. • The transformation of wear mechanism at different applied loads was revealed. - Abstract: The Ti{sub 2}Ni/α(Ti) dual-phase coating reinforced by TiB and TiC was fabricated on the Ti6Al4V substrate by laser cladding. Phase constituents were confirmed by a theoretical prediction combined with X-ray diffraction (XRD) analyses. From the surface to the bottom of the coating, a regular evolution of the reinforcements’ microstructure, namely TiC{sub p}+(TiB+TiC){sub e}, (TiB+TiC){sub e} and TiB{sub p}+(TiB+TiC){sub e} (p and e were the abbreviations of primary and eutectic, respectively), was investigated by scanning electron microscopy (SEM). The coating possessed the higher microhardness than that of the substrate. An in situ dynamic method (in situ continuing tests at different time intervals) was designed to reveal wear behaviors at different wear stages. A quantitative calculation formula was established by a mathematic model to predict wear losses under different sliding time and applied loads in a definite precision. The wear mechanism was transformed from brittle debonding (at 10 N) to the joint action of brittle debonding and micro-cutting (at 20 N and 30 N) due to the microstructural evolution across the depth from the surface of the coating.

  18. Banded versus Single-sided bonded space maintainers: A Comparative Study

    Directory of Open Access Journals (Sweden)

    Sudhir Mittal

    2018-01-01

    Full Text Available Background: The present study is conducted to evaluate and compare the clinical performance of conventional band and loop space maintainer and fiber reinforced composite resin (FRCR space maintainers. Materials and Methods: A total of 45 extraction sites in the age group of 6–9 years having premature loss of primary molars or indicated for extraction were selected for the study. The patients were randomly divided into three groups as Group I, in which conventional band and loop space maintainer was given, Group II and Group III (FRCR, in which FRCR (everStick CandB and impregnated glass fibers (Interlig space maintainers were given, respectively. Patients were recalled at 3, 6, and 12-month interval for evaluation of all the three types of space maintainer. Results: Overall success rate of Group I was 86.7%, for Group II was 80%, and for Group III was 73.3% at the end of the study. Patient acceptability was significantly higher in Group II and Group III (FRCR as compared to Group I (Conventional band and loop. In Group I, cement loss and fracture of loop, whereas in Group II and Group III, debonding at enamel composite was the most common failure followed by debonding at fiber composite and fiber fracture. FRCR space maintainers were found to be cost-effective as compared to Group I. More linear changes and angular changes were recorded in Group I as compared to Group II and Group III but difference was not significant (P > 0.05. Conclusion: Only single (buccal surface application of FRCR space maintainers showed almost equal clinical efficacy compared to conventional band and loop space maintainer with significantly better patient acceptability, less cost, and time taken.

  19. Cladding of aluminum on AISI 304L stainless steel by cold roll bonding: Mechanism, microstructure, and mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Akramifard, H.R., E-mail: akrami.1367@ut.ac.ir [School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, P.O. Box 11155-4563, Tehran (Iran, Islamic Republic of); Mirzadeh, H., E-mail: hmirzadeh@ut.ac.ir [School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, P.O. Box 11155-4563, Tehran (Iran, Islamic Republic of); Advanced Metalforming and Thermomechanical Processing Laboratory, School of Metallurgy and Materials Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Parsa, M.H., E-mail: mhparsa@ut.ac.ir [School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, P.O. Box 11155-4563, Tehran (Iran, Islamic Republic of); Center of Excellence for High Performance Materials, School of Metallurgy and Materials Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Advanced Metalforming and Thermomechanical Processing Laboratory, School of Metallurgy and Materials Engineering, University of Tehran, Tehran (Iran, Islamic Republic of)

    2014-09-08

    The AA1050 aluminum alloy and AISI 304L stainless steel sheets were stacked together to fabricate Al/304L/Al clad sheet composites by the cold roll bonding process, which was performed at temperatures of ∼100 and 23 °C to produce austenitic and austenitic–martensitic microstructures in the AISI 304L counterpart, respectively. The peel test results showed that the threshold reduction required to make a suitable bond at room temperature is below 10%, which is significantly lower than the required reduction for cold roll bonding of Al sheets. The tearing of the Al sheet during the peel test signified that the bond strength of the roll bonded sheets by only 38% reduction has reached the strength of Al, which is a key advantage of the developed sheets. The extrusion of Al through the surface cracks and settling inside the 304L surface valleys due to strong affinity between Al and Fe was found to be the bonding mechanism. Subsequently, the interface and tensile behaviors of three-layered clad sheets after soaking at 200–600 °C for 1 h were investigated to characterize the effect of annealing treatment on the formation and thickening of intermetallic compound layer and the resultant mechanical properties. Field emission scanning electron microscopy, X-ray diffraction, and optical microscopy techniques revealed that an intermediate layer composed mainly of Al{sub 13}Fe{sub 4}, FeC and Al{sub 8}SiC{sub 7} forms during annealing at 500–600 °C. A significant drop in tensile stress–strain curves after the maximum point (UTS) was correlated to the interface debonding. It was found that the formation of intermediate layer by post heat treatment deteriorates the bond quality and encourages the debonding process. Moreover, the existence of strain-induced martensite in clad sheets was found to play a key role in the enhancement of tensile strength.

  20. Evaluation of bond strength and load deflection rate of multi-stranded fixed retainer wires: An In-Vitro Study

    Directory of Open Access Journals (Sweden)

    Renu Sarah Samson

    2018-01-01

    Full Text Available Background: Fixed orthodontic retainers must be well retained on the tooth surfaces, allow physiologic movement of teeth and exert minimal forces on the teeth to be retained. Previous studies analyzed the bond strength and amount of deflection caused due to the debonding force but not the magnitude of force needed for unit deformation. Aims: This study aims to evaluate and compare the bond strength and load deflection rate (LDR of three different fixed retainer wires. Materials and Methods: The wires were divided into three Groups: A – three-stranded twisted ligature wire, B – Bond-A-Braid (Reliance Orthodontics, and C – three-stranded twisted lingual retainer wire (3M Unitek. Twenty models were prepared for each group with a passive 15 mm long lingual retainer wire bonded to two lower incisors. An occlusogingival force was applied to the wire until it debonded. For LDR, three-point bending test was done at 0.5 mm deflection. These forces were measured using a Universal Instron Testing Machine. Statistical Analysis: Mean bond strength/LDR and pairwise comparisons were analyzed with one-way ANOVA and Tukey's honest significant difference post hoc test, respectively. Results: Group C exhibited the highest mean bond strength and LDR of 101.17N and 1.84N, respectively. The intergroup comparisons were all statistically significant. Conclusion: Compared to the other two wire types, Group C might be better retained on the teeth due to its higher bond strength. With its relatively higher LDR value, it may resist deformation from occlusal forces, thereby reducing inadvertent tooth movement and yet remain flexible enough to allow physiologic tooth movements.

  1. Shear Bond Strength of Orthodontic Brackets Bonded to Zirconium Crowns.

    Science.gov (United States)

    Mehmeti, Blerim; Azizi, Bleron; Kelmendi, Jeta; Iljazi-Shahiqi, Donika; Alar, Željko; Anić-Milošević, Sandra

    2017-06-01

    An increasing demand for esthetic restorations has resulted in an increased use of all-ceramic restorations, such as zirconium. However, one of the challenges the orthodontist must be willing to face is how to increase bond strength between the brackets and various ceramic restorations.Bond strength can beaffected bybracket type, by the material that bracketsaremade of, and their base surface design or retention mode. ​: A im: of this study was to perform a comparative analysis of the shear bond strength (SBS) of metallic and ceramic orthodontic brackets bonded to all-zirconium ceramic surfaces used for prosthetic restorations, and also to evaluate the fracture mode of these two types of orthodontic brackets. Twenty samples/semi-crowns of all-zirconium ceramic, on which orthodontic brackets were bonded, 10 metallic and 10 ceramic polycrystalline brackets, were prepared for this research. SBS has been testedby Universal Testing Machine, with a load applied using a knife edged rod moving at a fixed rate of 1 mm/min, until failure occurred. The force required to debond the brackets was recorded in Newton, then SBS was calculated to MPa. In addition, the samples were analyzed using a digital camera magnifier to determine Adhesive Remnant Index (ARI). Statistical data were processed using t-test, and the level of significance was set at α = 0.05. Higher shear bond strength values were observed in metallic brackets bonded to zirconium crowns compared tothoseof ceramic brackets, with a significant difference. During the test, two of the ceramic brackets were partially or totally damaged. Metallic brackets, compared to ceramic polycrystalline brackets, seemed tocreate stronger adhesion with all-zirconium surfaces due to their better retention mode. Also, ceramic brackets showed higher fragility during debonding.

  2. Effect of Er:YAG Laser and Sandblasting in Recycling of Ceramic Brackets.

    Science.gov (United States)

    Yassaei, Soghra; Aghili, Hossein; Hosseinzadeh Firouzabadi, Azadeh; Meshkani, Hamidreza

    2017-01-01

    Introduction: This study was performed to determine the shear bond strength of rebonded mechanically retentive ceramic brackets after recycling with Erbium-Doped Yttrium Aluminum Garnet (Er:YAG) laser or sandblasting. Methods: Twenty-eight debonded ceramic brackets plus 14 intact new ceramic brackets were used in this study. Debonded brackets were randomly divided into 2 groups of 14. One group was treated by Er:YAG laser and the other with sandblasting. All the specimens were randomly bonded to 42 intact human upper premolars. The shear bond strength of all specimens was determined with a universal testing machine at a crosshead speed of 0.5 mm/min until bond failure occurred. The recycled bracket base surfaces were observed under a scanning electron microscope (SEM). Analysis of variance (ANOVA) and Tukey tests were used to compare the shear bond strength of the 3 groups. Fisher exact test was used to evaluate the differences in adhesive remnant index (ARI) scores. Results: The highest bond strength belonged to brackets recycled by Sandblasting (16.83 MPa). There was no significant difference between the shear bond strength of laser and control groups. SEM photographs showed differences in 2 recycling methods. The laser recycled bracket appeared to have as well-cleaned base as the new bracket. Although the sandblasted bracket photographs showed no remnant adhesives, remarkable micro-roughening of the base of the bracket was apparent. Conclusion: According to the results of this study, both Er:YAG laser and sandblasting were efficient to mechanically recondition retentive ceramic brackets. Also, Er:YAG laser did not change the design of bracket base while removing the remnant adhesives which might encourage its application in clinical practice.

  3. Etching of enamel for direct bonding with a thulium fiber laser

    Science.gov (United States)

    Kabaş Sarp, Ayşe S.; Gülsoy, Murat

    2011-03-01

    Background: Laser etching of enamel for direct bonding can decrease the risk of surface enamel loss and demineralization which are the adverse effects of acid etching technique. However, in excess of +5.5°C can cause irreversible pulpal responses. In this study, a 1940- nm Thulium Fiber Laser in CW mode was used for laser etching. Aim: Determination of the suitable Laser parameters of enamel surface etching for direct bonding of ceramic brackets and keeping that intrapulpal temperature changes below the threshold value. Material and Method: Polycrystalline ceramic orthodontic brackets were bonded on bovine teeth by using 2 different kinds of etching techniques: Acid and Laser Etching. In addition to these 3 etched groups, there was also a group which was bonded without etching. Brackets were debonded with a material testing machine. Breaking time and the load at the breaking point were measured. Intrapulpal temperature changes were recorded by a K-type Thermocouple. For all laser groups, intrapulpal temperature rise was below the threshold value of 5.5°C. Results and Conclusion: Acid-etched group ( 11.73 MPa) significantly required more debonding force than 3- second- irradiated ( 5.03 MPa) and non-etched groups ( 3.4 MPa) but the results of acid etched group and 4- second- irradiated group (7.5 MPa) showed no significant difference. Moreover, 4- second irradiated group was over the minimum acceptable value for clinical use. Also, 3- second lasing caused a significant reduction in time according to acid-etch group. As a result, 1940- nm laser irradiation is a promising method for laser etching.

  4. Clinical acceptability of two self-etch adhesive resins for the bonding of orthodontic brackets to enamel.

    Science.gov (United States)

    Schnebel, Bradley; Mateer, Scott; Maganzini, Anthony Louis; Freeman, Katherine

    2012-12-01

    To determine whether two self-adhesive resin cements, Clearfil SA and RelyX, can be used to successfully bond orthodontic brackets to enamel. Seventy extracted premolars were custom mounted, cleaned and randomly divided into three groups. In group 1 (control), orthodontic brackets were bonded to 25 premolars using the Transbond Plus and Transbond XT two step adhesive systerm adhesive. In group 2, brackets were bonded to 25 premolars using Clearfil SA. In group 3, brackets were bonded to 20 premolars using RelyX. The brackets were debonded using a universal testing machine and shear bond strengths recorded. After debonding, each tooth was examined under 20× magnification to evaluate the residual adhesive remaining. An ANOVA with Duncan's Multiple Range Test was used to determine whether there were significant differences in shear bond strength between the groups. A Kruskal-Wallis Test and a Bonferroni multiple comparison procedure were used to compare the bond failure modes (adhesive remnant index scores) between the groups. The mean shear bond strengths for the brackets bonded using Clearfil SA and RelyX were 5·930±1·840 and 3·334±1·953 MPa, respectively. Both were significantly lower than that for the brackets bonded using Transbond (7·875±3·611 MPa). Both self-etch adhesive resin cement groups showed a greater incidence of bracket failure at the enamel/adhesive interface while the Transbond group showed a higher incidence at the bracket/adhesive interface. The shear bond strengths of the self-etch adhesive resin cements may be inadequate to successfully bond orthodontic brackets to enamel.

  5. Development of a novel bioactive glass for air-abrasion to selectively remove orthodontic adhesives.

    Science.gov (United States)

    Taha, Ayam A; Hill, Robert G; Fleming, Padhraig S; Patel, Mangala P

    2018-05-01

    To develop a novel, bioactive glass for removing residual orthodontic adhesive via air-abrasion, following bracket debonding, and to evaluate its effectiveness against a proprietary bioactive glass 45S5(Sylc™)-air-abrasion, and a slow-speed tungsten carbide (TC) bur. Three glasses were prepared and their bioactivity was proved. One novel glass (QMAT3) was selected due to its appropriate hardness, lower than that of enamel/45S5(Sylc™). Sixty extracted human premolars were randomly assigned to adhesive removal using: (a) QMAT3-air-abrasion, (b) 45S5(Sylc™)-air-abrasion, and (c) TC bur, which were further subdivided (n = 10) based on the adhesive used (Transbond XT™ or Fuji Ortho LC™). Enamel roughness was assessed using scanning electron microscopy (SEM) and non-contact profilometry before bracket bonding, after removing residual adhesive following bracket debonding and after polishing. QMAT3 formed apatite faster (6 h) than 45S5(Sylc™) (24 h) in Tris solution. QMAT3-air-abrasion gave the lowest enamel roughness (Ra) after removing the adhesives. SEM images showed a pitted, roughened enamel surface in the TC bur group and to a lesser extent with 45S5(Sylc™), while a virtually smooth surface without any damage was observed in the QMAT3-air-abrasion group. The time taken for adhesive removal with QMAT3 was comparable to 45S5(Sylc™) but was twice as long with the TC bur. QMAT3-air-abrasion is a promising technique for selective removal of adhesives without inducing tangible enamel damage. A novel bioactive glass has been developed as an alternative to the use of TC burs for orthodontic adhesive removal.

  6. Film processing characteristics of nano gold suitable for conductive application on flexible substrates

    International Nuclear Information System (INIS)

    Gupta, Ashish; Mandal, Saumen; Katiyar, Monica; Mohapatra, Yashowanta N.

    2012-01-01

    In spite of large number of studies and wide use of thiol encapsulated gold nanoparticles, the mechanism of their transformation to thin gold films for conductive applications is not as yet well understood. In order to understand and optimize the process of conversion of nanoparticle based ink for printing on plastic substrates, we synthesize and study thiolated Au nanoparticles, with average size of 2 nm, but with differing carbon chain length viz. butane (Au-C4), hexane (Au-C6) and octane (Au-C8). The link between the properties of Au nanoparticle and its transformation from nonconductive gold nanoparticle ink to conductive gold film is studied using a variety of techniques such as thermo gravimetric analysis (TGA), X-ray diffraction (XRD), atomic force microscopy, scanning electron microscopy and electrical conductivity measurements. A combined study of the shape of solution TGA and differential thermal analysis indicates occurrence of two distinct processes corresponding to disentanglement and debonding of thiol chains preceding the sintering of nanoparticles. The lowest sintering temperature is observed to be approximately 155 °C for chain length C4, and hence Au-C4 on polyethylene terephthalate substrates is studied in detail. Though XRD peaks of thick drop-cast films on polyethylene terephthalate substrate show increasing peak intensity with annealing temperature as expected, for spin coated thin films, in contrast, the peak intensity decreases with increase in annealing temperature. Electrical conductivity of the thin films is comparable to bulk gold after conversion, but decreases with increase in annealing temperature demonstrating the usefulness of insights obtained in the study for optimization of annealing schedules. - Highlights: ► Sintering of alkanethiol capped Au nanoparticles is chainlength dependent. ► Sintering temperature depends on thiol debonding. ► Butanethiol capped Au nanoparticles are the most suitable for flexible substrates.

  7. Interface effects on the micromechanical response of a transversely loaded single fiber SCS-6/Ti-6Al-4V composite

    International Nuclear Information System (INIS)

    Warrier, S.G.; Majumdar, B.S.; Gundel, D.B.; Miracle, D.B.

    1996-01-01

    The ability of a fiber-matrix interface to support a transverse load is typically evaluated in straight-sided composite specimens where a stress singularity exists at the free surface of the interface. This stress singularity is often the cause of crack initiation and debonding during transverse loading. In order to develop a fundamental understanding of the transverse behavior of the fiber-matrix interface, it is necessary to alter the crack initiation site from the free surface to an internal location. To achieve this objective, a cross-shaped specimen has been recently developed. In this study, based on the experimentally observed onset of nonlinearity in the stress-strain curve of these specimens and finite element analysis, the bond strength of the SCS-6/Ti-6Al-4V interface was determined to be 115 MPa. The micromechanical behavior of these specimens under transverse loading was examined by finite element analysis using this interface bond strength value and compared with experimental observations. Results demonstrate that the proposed geometry was successful in suppressing debonding at the surface and altering it to an internal event. The results from numerical analysis correlated well with the experimental stress-strain curve and several simple analytical models. In an attempt to identify the true bond strength and the interface failure criterion, the present study suggests that if failure initiates under tensile radial stresses, then the normal bond strength of the SCS-6/Ti-6Al-4V composites is about 115 MPa; under shear failure, the tangential shear strength of the interface is about 180 MPa

  8. Reliability Estimation for Single-unit Ceramic Crown Restorations

    Science.gov (United States)

    Lekesiz, H.

    2014-01-01

    The objective of this study was to evaluate the potential of a survival prediction method for the assessment of ceramic dental restorations. For this purpose, fast-fracture and fatigue reliabilities for 2 bilayer (metal ceramic alloy core veneered with fluorapatite leucite glass-ceramic, d.Sign/d.Sign-67, by Ivoclar; glass-infiltrated alumina core veneered with feldspathic porcelain, VM7/In-Ceram Alumina, by Vita) and 3 monolithic (leucite-reinforced glass-ceramic, Empress, and ProCAD, by Ivoclar; lithium-disilicate glass-ceramic, Empress 2, by Ivoclar) single posterior crown restorations were predicted, and fatigue predictions were compared with the long-term clinical data presented in the literature. Both perfectly bonded and completely debonded cases were analyzed for evaluation of the influence of the adhesive/restoration bonding quality on estimations. Material constants and stress distributions required for predictions were calculated from biaxial tests and finite element analysis, respectively. Based on the predictions, In-Ceram Alumina presents the best fast-fracture resistance, and ProCAD presents a comparable resistance for perfect bonding; however, ProCAD shows a significant reduction of resistance in case of complete debonding. Nevertheless, it is still better than Empress and comparable with Empress 2. In-Ceram Alumina and d.Sign have the highest long-term reliability, with almost 100% survivability even after 10 years. When compared with clinical failure rates reported in the literature, predictions show a promising match with clinical data, and this indicates the soundness of the settings used in the proposed predictions. PMID:25048249

  9. A Large-scale Finite Element Model on Micromechanical Damage and Failure of Carbon Fiber/Epoxy Composites Including Thermal Residual Stress

    Science.gov (United States)

    Liu, P. F.; Li, X. K.

    2018-06-01

    The purpose of this paper is to study micromechanical progressive failure properties of carbon fiber/epoxy composites with thermal residual stress by finite element analysis (FEA). Composite microstructures with hexagonal fiber distribution are used for the representative volume element (RVE), where an initial fiber breakage is assumed. Fiber breakage with random fiber strength is predicted using Monte Carlo simulation, progressive matrix damage is predicted by proposing a continuum damage mechanics model and interface failure is simulated using Xu and Needleman's cohesive model. Temperature dependent thermal expansion coefficients for epoxy matrix are used. FEA by developing numerical codes using ANSYS finite element software is divided into two steps: 1. Thermal residual stresses due to mismatch between fiber and matrix are calculated; 2. Longitudinal tensile load is further exerted on the RVE to perform progressive failure analysis of carbon fiber/epoxy composites. Numerical convergence is solved by introducing the viscous damping effect properly. The extended Mori-Tanaka method that considers interface debonding is used to get homogenized mechanical responses of composites. Three main results by FEA are obtained: 1. the real-time matrix cracking, fiber breakage and interface debonding with increasing tensile strain is simulated. 2. the stress concentration coefficients on neighbouring fibers near the initial broken fiber and the axial fiber stress distribution along the broken fiber are predicted, compared with the results using the global and local load-sharing models based on the shear-lag theory. 3. the tensile strength of composite by FEA is compared with those by the shear-lag theory and experiments. Finally, the tensile stress-strain curve of composites by FEA is applied to the progressive failure analysis of composite pressure vessel.

  10. Effects of silica coating and silane surface conditioning on the bond strength of rebonded metal and ceramic brackets

    Directory of Open Access Journals (Sweden)

    Saadet Atsü

    2011-06-01

    Full Text Available OBJECTIVE: The aim of this study was to evaluate the effects of tribochemical silica coating and silane surface conditioning on the bond strength of rebonded metal and ceramic brackets. MATERIAL AND METHODS: Twenty debonded metal and 20 debonded ceramic brackets were randomly assigned to receive one of the following surface treatments (n=10 for each group: (1 sandblasting (control; (2 tribochemical silica coating combined with silane. Brackets were rebonded to the enamel surface on the labial and lingual sides of premolars with a light-polymerized resin composite. All specimens were stored in distilled water for 1 week and then thermocycled (5,000 cycles between 5-55ºC. Shear bond strength values were measured using a universal testing machine. Student's t-test was used to compare the data (α=0.05. Failure mode was assessed using a stereomicroscope, and the treated and non-treated bracket surfaces were observed by scanning electron microscopy. RESULTS: Rebonded ceramic brackets treated with silica coating followed by silanization had significantly greater bond strength values (17.7±4.4 MPa than the sandblasting group (2.4±0.8 MPa, P<0.001. No significant difference was observed between the rebonded metal brackets treated with silica coating with silanization (15±3.9 MPa and the sandblasted brackets (13.6±3.9 MPa. Treated rebonded ceramic specimens primarily exhibited cohesive failure in resin and adhesive failure at the enamel-adhesive interface. CONCLUSIONS: In comparison to sandblasting, silica coating with aluminum trioxide particles followed by silanization resulted in higher bond strengths of rebonded ceramic brackets.

  11. Bond strengths of different orthodontic adhesives after enamel conditioning with the same self-etching primer.

    Science.gov (United States)

    Scougall-Vilchis, Rogelio J; Zárate-Díaz, Chrisel; Kusakabe, Shusuke; Yamamoto, Kohji

    2010-05-01

    To determine the shear bond strengths (SBS) of stainless steel brackets bonded with seven light-cured orthodontic adhesives after the enamel was conditioned with the same self-etching primer. A total of 140 extracted human molars were randomly divided into seven groups (N = 20). In all the groups, the enamel was conditioned with Transbond Plus SEP (TPSEP). Stainless steel brackets were bonded with the following orthodontic adhesives: Group I, Transbond XT; Group II, Blūgloo; Group III, BeautyOrtho Bond; Group IV, Enlight; Group V, Light Bond; Group VI, Transbond CC; Group VII, Xeno Ortho. The teeth were stored in distilled water at 37 degrees C for 24 hours and debonded with a universal testing machine. The modified adhesive remnant index (ARI) was also recorded. There were no significant differences in the SBS values among the groups: I (18.0 +/- 7.4 MPa); II (18.3 +/- 5.1 MPa); III (14.8 +/- 4.3 MPa); IV (18.3 +/- 7.0 MPa); V (16.4 +/- 4.3 MPa); VI (20.3 +/- 5.3 MPa); VII (15.9 +/- 6.4 MPa), but significant differences in ARI were found. The seven orthodontic adhesives evaluated in this study can be successfully used for bonding stainless steel brackets when the enamel is conditioned with TPSEP, however, the differences among some groups might influence the clinical bond strengths. In addition, the amount of residual adhesive remaining on the teeth after debonding differed among the adhesives. Further studies are required to better understand the differences in SBS and ARI.

  12. Effects of silane application on the shear bond strength of ceramic orthodontic brackets to enamel surface

    Directory of Open Access Journals (Sweden)

    Pinandi Sri Pudyani

    2016-12-01

    Full Text Available Background: Fixed orthodontic appliances with ceramic brackets are used frequently to fulfill the aesthetic demand of patient through orthodontic treatment. Ceramic brackets have some weaknesses such as bond strength and enamel surface damage. In high bond strength the risk of damage in enamel surfaces increases after debonding. Purpose: This study aimed to determine the effect of silane on base of bracket and adhesive to shear bond strength and enamel structure of ceramic bracket. Method: Sixteen extracted upper premolars were randomly divided into four groups based on silane or no silane on the bracket base and on the adhesive surface. Design of the base on ceramic bracket in this research was microcrystalline to manage the influence of mechanical interlocking. Samples were tested in shear mode on a universal testing machine after attachment. Following it, adhesive remnant index (ARI scores were used to assess bond failure site. Statistical analysis was performed using a two-way Anova and the Mann-Whitney test. A scanning electron microscope (SEM with a magnification of 2000x was used to observe enamel structure after debonding. Result: Shear bond strength was increased between group without silane and group with silane on the base of bracket (p<0,05. There was no significance different between group without silane and group with silane on adhesive (p<0,05. Conclusion: Application of silane on base of bracket increases shear bond strength, however, application of silane on adhesive site does not increase shear bond strength of ceramic bracket. Most bonding failure occurred at the enamel adhesive interface and damage occurred on enamel structure in group contains silane of ceramic bracket.

  13. Rate-dependent elastic hysteresis during the peeling of pressure sensitive adhesives.

    Science.gov (United States)

    Villey, Richard; Creton, Costantino; Cortet, Pierre-Philippe; Dalbe, Marie-Julie; Jet, Thomas; Saintyves, Baudouin; Santucci, Stéphane; Vanel, Loïc; Yarusso, David J; Ciccotti, Matteo

    2015-05-07

    The modelling of the adherence energy during peeling of Pressure Sensitive Adhesives (PSA) has received much attention since the 1950's, uncovering several factors that aim at explaining their high adherence on most substrates, such as the softness and strong viscoelastic behaviour of the adhesive, the low thickness of the adhesive layer and its confinement by a rigid backing. The more recent investigation of adhesives by probe-tack methods also revealed the importance of cavitation and stringing mechanisms during debonding, underlining the influence of large deformations and of the related non-linear response of the material, which also intervenes during peeling. Although a global modelling of the complex coupling of all these ingredients remains a formidable issue, we report here some key experiments and modelling arguments that should constitute an important step forward. We first measure a non-trivial dependence of the adherence energy on the loading geometry, namely through the influence of the peeling angle, which is found to be separable from the peeling velocity dependence. This is the first time to our knowledge that such adherence energy dependence on the peeling angle is systematically investigated and unambiguously demonstrated. Secondly, we reveal an independent strong influence of the large strain rheology of the adhesives on the adherence energy. We complete both measurements with a microscopic investigation of the debonding region. We discuss existing modellings in light of these measurements and of recent soft material mechanics arguments, to show that the adherence energy during peeling of PSA should not be associated to the propagation of an interfacial stress singularity. The relevant deformation mechanisms are actually located over the whole adhesive thickness, and the adherence energy during peeling of PSA should rather be associated to the energy loss by viscous friction and by rate-dependent elastic hysteresis.

  14. Influence of Photobiomodulation Therapy on Gingivitis Induced by Multi-Bracket Appliances: A Split-Mouth Randomized Controlled Trial.

    Science.gov (United States)

    Stein, Steffen; Schauseil, Michael; Hellak, Andreas; Korbmacher-Steiner, Heike; Braun, Andreas

    2018-05-18

    The objective of this split-mouth trial was to investigate the influence of photobiomodulation therapy (PBMT) on adjuvant treatment of gingivitis induced by multi-bracket appliances, after bracket debonding and professional tooth cleaning. Thirteen patients (mean age 16.15 years; standard deviation ±2.12 years) who had completed active orthodontic treatment with fixed orthodontic appliances in an orthodontic clinic were included on a randomized basis. At time point T0, after bracket debonding and professional tooth cleaning, the papilla bleeding index (PBI) and bleeding on probing (BOP) were assessed in the upper jaw by the blinded investigator (M.S.), who was not aware at any time of which quadrant received PBMT. The study was based on a patient-blinded split-mouth design. In each patient, PBMT was administered by a practitioner (S.S.) in one upper quadrant (wavelength: 660 nm; Power: 100 mW; Power density: 100 mW/cm 2 ; Energy density per application point = 2 J/cm 2 ; Energy per application point = 2 J; Total dose = 52 J/cm 2 ; Total energy = 52 J; Irradiation time: 26 × 20 sec), while the other upper quadrant received a simulated laser application with the laser system turned off. Randomized equal allocation of the sides was accomplished. The second PBI and BOP assessment followed 4-6 days after laser irradiation (T1) by M.S. No statistical differences were observed between the sides with regard to PBI and BOP values at T0 (p > 0.05). The PBI and BOP values decreased significantly between T0 and T1 on both sides (p appliances.

  15. MRI monitoring of autologous hyaline cartilage grafts in the knee joint: a follow-up study over 12 months; MRT-Monitoring autologer Chondrozytentransplantate im Kniegelenk: Eine Verlaufsstudie ueber 12 Monate

    Energy Technology Data Exchange (ETDEWEB)

    Mueller-Horvat, C.; Schick, F.; Claussen, C.D.; Groenewaeller, E. [Abt. fuer Radiologische Diagnostik, Eberhard-Karls-Univ. Tuebingen (Germany)

    2004-12-01

    Purpose: To evaluate the suitability of different MR sequences for monitoring the stage of maturation of hyaline cartilage grafts in the knee joint and the early detection of complications like hypertrophy. In addition, it was analyzed whether indirect MR arthrography can indicate debonding of the graft. Materials and Methods: MRI examinations were performed in 19 patients, aged 17-43 years, with autologous transplantation of a hyaline cartilage tissue graft after knee trauma. Examination dates were prior to transplantation to localize the defect, and 6 weeks, 3, 6 and 12 months after transplantation to control morphology and maturation of the autologous graft. Standard T2- and protondensity-weighted turbo spin echo (TSE) sequences and T1-weighted spin echo (SE) sequences were used, as well as gradient echo (GRE) sequences with and without magnetization transfer (MT) prepulses. In some cases, indirect MR arthrography was performed. Results: Cartilage defect and the hyaline cartilage graft could be detected in all 19 patients. Hypertrophy of the graft could be found early in 3 patients and debonding in 1 patient. For depicting the graft a short time after surgery. T2-weighted TSE-sequences showed the best results. Six and 12 months after transplantation, spoiled 3D-GRE-sequences like FLASH3D (fast low angle shot) showed reduced artifacts due to magnetic residues from the surgery. Difference images from GRE-sequences with and without MT pulse provided high contrast between cartilage and surrounding tissue. The quantification of the MT effect showed an assimilation of the graft to the original cartilage within 12 months. Indirect MR arthrography showed subchondral contrast medium even 12 months after transplantation in 3 patients. (orig.)

  16. Analysis of Particle-Dispersed Composites Accounting Stochastically for Interfacial Damage

    International Nuclear Information System (INIS)

    Huajian Chang; Michihiko Nakagaki

    2002-01-01

    More and more composite materials have been being utilized in nuclear facilities. While the external loading applied, the stress in composite is concentrated, which is harmful and may cause interfacial damage. The de-bonding and sliding at the interface between matrix and particles are the most common phenomena. In this paper, a statistically elastoplastic constitutive model for particle-dispersed composites is developed by accounting stochastically for both interfacial damage and localized plasticity. The effects of damaged interface on the strain field in composite are considered in two ways. First, the damaged interface between the matrix and the particles makes the strain field inside inclusions is different from that of the particles with perfectly bonded interface. Second, it contributes an additional strain, which is due to the displacement jump at the matrix-inclusion interface. This additional is defined as an integration of displacement jumps between the matrix and the particles over their interface. In present paper, the first part is considered by using a modified Eshelby's S-tensor. After deriving the local relative displacement distributions between matrix and inclusion at the interface, the second contribution of damaged interface to the average strain can be expressed in terms of the corresponding Eigen-strain or the uniform external loading, by introducing the damage-relevant tensors, which are transformation tensors and tends to zero if interfacial damage does not take place. Both the tangential and normal discontinuities at the interface are independently modeled. The model uses statistic scheme with distribution functions in the stress/strain space, so that the meso-local effects of plastic deformation, interfacial damage and their interactions are accounted for. In order to verify the feasibility and performance of the proposed constitutive model, numerical calculations are carried out. It is found that the damaged interface conditions of de-bonding

  17. Evaluation of metal-ceramic bond characteristics of three dental Co-Cr alloys prepared with different fabrication techniques.

    Science.gov (United States)

    Wang, Hongmei; Feng, Qing; Li, Ning; Xu, Sheng

    2016-12-01

    Limited information is available regarding the metal-ceramic bond strength of dental Co-Cr alloys fabricated by casting (CAST), computer numerical control (CNC) milling, and selective laser melting (SLM). The purpose of this in vitro study was to evaluate the metal-ceramic bond characteristics of 3 dental Co-Cr alloys fabricated by casting, computer numerical control milling, and selective laser melting techniques using the 3-point bend test (International Organization for Standardization [ISO] standard 9693). Forty-five specimens (25×3×0.5 mm) made of dental Co-Cr alloys were prepared by CAST, CNC milling, and SLM techniques. The morphology of the oxidation surface of metal specimens was evaluated by scanning electron microscopy (SEM). After porcelain application, the interfacial characterization was evaluated by SEM equipped with energy-dispersive spectrometry (EDS) analysis, and the metal-ceramic bond strength was assessed with the 3-point bend test. Failure type and elemental composition on the debonding interface were assessed by SEM/EDS. The bond strength was statistically analyzed by 1-way ANOVA and Tukey honest significant difference test (α=.05). The oxidation surfaces of the CAST, CNC, and SLM groups were different. They were porous in the CAST group but compact and irregular in the CNC and SLM groups. The metal-ceramic interfaces of the SLM and CNC groups showed excellent combination compared with those of the CAST group. The bond strength was 37.7 ±6.5 MPa for CAST, 43.3 ±9.2 MPa for CNC, and 46.8 ±5.1 MPa for the SLM group. Statistically significant differences were found among the 3 groups tested (P=.028). The debonding surfaces of all specimens exhibited cohesive failure mode. The oxidation surface morphologies and thicknesses of dental Co-Cr alloys are dependent on the different fabrication techniques used. The bond strength of all 3 groups exceed the minimum acceptable value of 25 MPa recommended by ISO 9693; hence, dental Co-Cr alloy

  18. PNNL Technical Support to The Implementation of EMTA and EMTA-NLA Models in Autodesk® Moldflow® Packages

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Ba Nghiep; Wang, Jin

    2012-12-01

    Under the Predictive Engineering effort, PNNL developed linear and nonlinear property prediction models for long-fiber thermoplastics (LFTs). These models were implemented in PNNL’s EMTA and EMTA-NLA codes. While EMTA is a standalone software for the computation of the composites thermoelastic properties, EMTA-NLA presents a series of nonlinear models implemented in ABAQUS® via user subroutines for structural analyses. In all these models, it is assumed that the fibers are linear elastic while the matrix material can exhibit a linear or typical nonlinear behavior depending on the loading prescribed to the composite. The key idea is to model the constitutive behavior of the matrix material and then to use an Eshelby-Mori-Tanaka approach (EMTA) combined with numerical techniques for fiber length and orientation distributions to determine the behavior of the as-formed composite. The basic property prediction models of EMTA and EMTA-NLA have been subject for implementation in the Autodesk® Moldflow® software packages. These models are the elastic stiffness model accounting for fiber length and orientation distributions, the fiber/matrix interface debonding model, and the elastic-plastic models. The PNNL elastic-plastic models for LFTs describes the composite nonlinear stress-strain response up to failure by an elastic-plastic formulation associated with either a micromechanical criterion to predict failure or a continuum damage mechanics formulation coupling damage to plasticity. All the models account for fiber length and orientation distributions as well as fiber/matrix debonding that can occur at any stage of loading. In an effort to transfer the technologies developed under the Predictive Engineering project to the American automotive and plastics industries, PNNL has obtained the approval of the DOE Office of Vehicle Technologies to provide Autodesk, Inc. with the technical support for the implementation of the basic property prediction models of EMTA and

  19. Effect of heat treatment on residual stress and wear behaviors of the TiNi/Ti2Ni based laser cladding composite coatings

    Science.gov (United States)

    Tao, Yang-Feng; Li, Jun; Lv, Ying-Hao; Hu, Lie-Feng

    2017-12-01

    The TiNi/Ti2Ni based composite coatings reinforced by TiC and TiB2 were prepared on Ti6Al4V at different circumstance temperatures (25 °C, 400 °C, 600 °C, and 800 °C) by laser cladding, then were preserved for 3 h. Macromorphologies and microstructures of the coatings were examined through an optical microscope (OM), an X-ray diffractometer (XRD), a scanning electron microscope (SEM), and an energy dispersive spectrometer (EDS). Residual stresses along the depth direction of the coatings were measured by the nanoindentation method, and wear behaviors of the coatings were also investigated using an ultra-functional wear testing machine. Results showed that the coatings were mainly composed of TiNi/Ti2Ni as the matrix and TiC/TiB2 as the reinforcement. A small amount of Cr2Ti was formed in the coatings prepared at 400 °C and 600 °C. Besides that, Ti3Al was also observed in the coating prepared at 800 °C. The tensile stress existed in the coatings prepared at 25 °C, 400 °C and 600 °C when the coating prepared at 800 °C was regarded as the stress-free reference. The average residual stress in the surface of coating prepared at 25 °C reached the largest value of about 2.79 GPa and presented a decreasing tendency with increasing the circumstance temperature (1.03 GPa at 400 °C, 0.52 GPa at 600 °C, and 0 GPa at 800 °C). It revealed that the rise in circumstance temperature contributed to the reduction in cracking susceptibility in the laser cladding coating. However, the wear volumes of the coatings were increased with increasing the circumstance temperature (0.1912 mm3 at 25 °C, 0.2828 mm3 at 400 °C, 0.3732 mm3 at 600 °C, and 0.6073 mm3 at 800 °C) due to the weakening in strain-hardening effect and the reduction in reinforcement density. The wear mechanism of the coatings was transformed from the single brittle-debonding into the combination of micro-cutting and brittle-debonding when the circumstance temperature was changed from room temperature to

  20. Veneered zirconia inlay-retained fixed dental prostheses: 10-Year results from a prospective clinical study.

    Science.gov (United States)

    Rathmann, Friederike; Bömicke, Wolfgang; Rammelsberg, Peter; Ohlmann, Brigitte

    2017-09-01

    The purpose of this study was to evaluate the 10-year clinical performance of zirconia-based inlay-retained fixed dental prostheses (IRFDP). For replacement of a molar in 27 patients, 30 IRFDP were luted by use of different cements, Panavia F (Kuraray Europe GmbH) or Multilink Automix (Ivoclar Vivadent GmbH), with use of inlay/inlay, inlay/full-crown, or inlay/partial-crown retainers for anchorage. Frameworks were milled from yttria-stabilized zirconia (IPS e.maxZirCAD; Ivoclar Vivadent GmbH) and fully veneered with pressable ceramic (IPS e.max ZirPress; Ivoclar Vivadent GmbH). Before luting, the IRFDP were silica-coated (Rocatec; 3M Espe) and silanized (Monobond S; Ivoclar Vivadent GmbH). Complications (for example, chipping or delamination of the veneering ceramic, debonding, secondary caries, endodontic treatment, and abutment tooth fracture) and failure were reported, by use of standardized report forms, 2 weeks, 6 months, and 1, 2, and 10 years after cementation. Statistical analysis included Kaplan-Meier survival and success (complication-free survival) and Cox regression analysis (α=0.05 for all). During the 10-year observation period, the complications most often observed were chipping of the veneer and debonding. Twenty-five restorations failed and one participant dropped out. Cumulative 10-year survival and success were 12.1% and 0%, respectively. The design of the retainer, use of a dental dam, choice of cement, and location in the dental arch had no statistically significant effect on the occurrence of complications. Use of fully veneered zirconia-based IRFDP with this technique cannot be recommended. A large incidence of complications and poor survival were observed for fully veneered zirconia-based IRFDP, revealing an urgent need for further design improvements for this type of restoration. This, again, emphasizes the need for testing of new restoration designs in clinical trials before implementation in general dental practice. Copyright © 2017

  1. Changes in root lengths of maxillary incisors during orthodontic retention period

    Directory of Open Access Journals (Sweden)

    Ravanmehr H

    2006-01-01

    Full Text Available Background and Aim: External apical root resorption is a common iatrogenic consequence of orthodontic treatment. Much controversy exists in the literature about changes in root lengths at post treatment periods. Although many practitioners believe that resorption becomes stable after active treatment, quantitative data are scarce. The purpose of this study was to determine quantitative changes in root lengths of maxillary incisors during fixed orthodontic post treatment period, and to assess if it is influenced by gender and factors related to active treatment. Materials and Methods: This was a case cross over study, performed on 80 patients (52 females and 28 males aged between 13 and 22 years. At debonding stage and beginning of retention phase of fixed orthodontic treatment, Hawley type retainer was fabricated for maxillary arch. Periapical radiographs of maxillary incisors using standard parallel technique were obtained immediately after debonding, and 3 and 7 months later. Crown and root lengths of maxillary incisors were measured using computer program. Changes in root lengths were calculated considering correction factors. Also associations between some factors and the change in root lengths during post treatment periods were assessed. These included gender, type of treatment plan (non extraction/extraction, technique (standard edgewise/straight-wire edgewise and duration of active treatment (less than 2 years/2 years and more. T-test and 4-way ANOVA were used for statistical analysis with P0.05 as the limit of significance. Results: No significant relation was found between apical root resorption of maxillary central incisors and time elapsed after treatment. Significant relation was observed between apical root resorption of maxillary lateral incisors and the length of post treatment period. No significant relation was found between root length changes of maxillary incisors during post treatment period and gender, type of treatment

  2. Mechanical performance of Hi-Nicalon/CVI-SiC composites with multilayer SiC/C interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Halverson, H.G.; Carter, R.H.; Curtin, W.A. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Engineering Science and Mechanics

    1997-12-01

    The mechanical properties and interfacial characteristics of new SiC/SiC ceramic composites, composed of Hi-Nicalon fibers in a CVI-SiC matrix and having a variety of multilayer SiC/C coatings between the fibers and the matrix, are studied in detail to elucidate the roles of the coatings and fibers. Axial tension tests and unload/reload hysteresis loop measurements are performed to determine mechanical performance. All materials exhibit the strong and tough behavior characteristic of good ceramic composites, with all multilayer variants performing quite similarly. SEM microscopy demonstrates that matrix cracks penetrate through the multilayers and debond at the fiber/inner-coating interface. Analysis of the hysteretic behavior leads to values for interfacial sliding resistance {tau} {approx} 11 ksi and interfacial toughness {Gamma}{sub i} {approx} 2 J/m{sup 2} that are nearly independent of multilayer structure, and are similar to values obtained for standard pyrolitic carbon interfaces. These results all indicate debonding at the fiber surface for all coating structures, which provides a common roughness, {tau}, and {Gamma}{sub i}. Analysis of fiber fracture mirrors provides an estimate of the in-situ strength of the fibers and demonstrates the high strength retention of the Hi-Nicalon fibers. The in-situ fiber strengths are combined with the measured pullout lengths to obtain an independent determination of {tau} = 8.5 ksi that agrees well with the value found from the hysteretic behavior. Predictions of composite strength using the derived fiber strengths agree well with the measured value although the predicted failure strain is too large. This study demonstrates that Hi-Nicalon fiber/CVI-SiC composites perform well for a wide range of multilayer interface structures and that the interfaces present relatively high values of {tau} and {Gamma}{sub i}, both of which are beneficial to strength and toughness. The small carbon layer thicknesses in these multilayer

  3. Forced reptation revealed by chain pull-out simulations.

    Science.gov (United States)

    Bulacu, Monica; van der Giessen, Erik

    2009-08-14

    We report computation results obtained from extensive molecular dynamics simulations of tensile disentanglement of connector chains placed at the interface between two polymer bulks. Each polymer chain (either belonging to the bulks or being a connector) is treated as a sequence of beads interconnected by springs, using a coarse-grained representation based on the Kremer-Grest model, extended to account for stiffness along the chain backbone. Forced reptation of the connectors was observed during their disentanglement from the bulk chains. The extracted chains are clearly seen following an imaginary "tube" inside the bulks as they are pulled out. The entropic and energetic responses to the external deformation are investigated by monitoring the connector conformation tensor and the modifications of the internal parameters (bonds, bending, and torsion angles along the connectors). The work needed to separate the two bulks is computed from the tensile force induced during debonding in the connector chains. The value of the work reached at total separation is considered as the debonding energy G. The most important parameters controlling G are the length (n) of the chains placed at the interface and their areal density. Our in silico experiments are performed at relatively low areal density and are disregarded if chain scission occurs during disentanglement. As predicted by the reptation theory, for this pure pull-out regime, the power exponent from the scaling G proportional, variant n(a) is a approximately 2, irrespective of chain stiffness. Small variations are found when the connectors form different number of stitches at the interface, or when their length is randomly distributed in between the two bulks. Our results show that the effects of the number of stitches and of the randomness of the block lengths have to be considered together, especially when comparing with experiments where they cannot be controlled rigorously. These results may be significant for

  4. Shear Bond Strength of Ceramic Brackets with Different Base Designs: Comparative In-vitro Study

    Science.gov (United States)

    Ansari, Mohd. Younus; Agarwal, Deepak K; Bhattacharya, Preeti; Ansar, Juhi; Bhandari, Ravi

    2016-01-01

    Introduction Knowledge about the Shear Bond Strength (SBS) of ceramic brackets with different base design is essential as it affects bond strength to enamel. Aim The aim of the present study was to evaluate and compare the effect of base designs of different ceramic brackets on SBS, and to determine the fracture site after debonding. Materials and Methods Four groups of ceramic brackets and one group of metal brackets with different base designs were used. Adhesive precoated base of Clarity Advanced (APC Flash-free) (Unitek/3M, Monrovia, California), microcrystalline base of Clarity Advanced (Unitek/3M, Monrovia, California), polymer mesh base of InVu (TP Orthodontics, Inc., La Porte, IN, United States), patented bead ball base of Inspire Ice (Ormco, Glendora, California), and a mechanical mesh base of Gemini Metal bracket (Unitek/3M, Monrovia, California). Ten brackets of each type were bonded to 50 maxillary premolars with Transbond XT (Unitek/3M). Samples were stored in distilled water at room temperature for 24 hours and subsequently tested in shear mode on a universal testing machine (Model 3382; Instron Corp., Canton, Massachusetts, USA) at a cross head speed of 1mm/minute with the help of a chisel. The debonded interface was recorded and analyzed to determine the predominant bond failure site under an optical microscope (Stereomicroscope) at 10X magnification. One way analysis of variance (ANOVA) was used to compare SBS. Tukey’s significant differences tests were used for post-hoc comparisons. The Adhesive Remnant Index (ARI) scores were compared by chi-square test. Results Mean SBS of microcrystalline base (27.26±1.73), was the highest followed by bead ball base (23.45±5.09), adhesive precoated base (20.13±5.20), polymer mesh base (17.54±1.91), and mechanical mesh base (17.50±2.41) the least. Comparing the frequency (%) of ARI Score among the groups, chi-square test showed significantly different ARI scores among the groups (χ2 = 34.07, pbrackets

  5. Assessment of bracket surface morphology and dimensional change

    Directory of Open Access Journals (Sweden)

    Pillai Devu Radhakrishnan

    2017-01-01

    Full Text Available Objective: The objective of this study was to compare the surface morphology and dimensional stability of the bracket slot at the onset of treatment and after 12 months of intraoral exposure. The study also compared the amount of calcium at the bracket base which indicates enamel loss among the three orthodontic brackets following debonding after 12 months of intraoral exposure. Materials and Methods: The sample consisted of 60 (0.022” MBT canine brackets. They were divided into three groups: self-ligating, ceramic bracket with metal slot, and stainless steel (SS brackets. The slot dimensions, micromorphologic characteristics of as-received and retrieved brackets were measured with a stereomicroscope and scanning electron microscope (SEM, respectively. The amount of calcium at the bracket base which indicates enamel damage was quantified using energy-dispersive X-ray spectrometry (EDX. Results: The results showed statistically significant alterations (P < 0.05 in the right vertical dimension, internal tie wing width (cervical, right and left depth of the slot (Kruskal–Wallis test. Multiple comparison using Mann–Whitney test showed that ceramic brackets underwent (P < 0.05 minimal alterations in the right vertical dimension, internal tie wing width (cervical, right and left depth of the slot (0.01 mm, −0.003 mm, 0.006 mm, −0.002 mm, respectively when compared with the changes seen in SS and self-ligating brackets. SEM analysis revealed an increase in the surface roughness of ceramic with metal slot brackets and self-ligating bracket showed the least irregularity. The presence of calcium was noted on all evaluated brackets under EDX, but ceramic with metal slot brackets showed a significantly greater amount of enamel loss (P = 0.001. Conclusion: Ceramic brackets were found to be dimensionally stable when compared to SS and self-ligating. Self-ligating bracket showed minimal surface irregularity. Ceramic with metal slot brackets showed a

  6. Dynamic tensile behavior of two-dimensional carbon fiber reinforced silicon carbide matrix composites

    International Nuclear Information System (INIS)

    Chen Xuan; Li Yulong

    2011-01-01

    Graphical abstract: The dynamic tensile behavior of 2D C/SiC composites was experimentally investigated by means of SHTB. Both the fracture surface and bundle fracture surfaces of composites were observed. The strain rate sensitivity of in-bundle interface was concluded as the dominant contributor to the strain rate sensitivity of the tensile strength. Highlights: → The tensile strength increases with strain rate. → The tensile failure strain remains independent of strain rate. → Macro-structural morphology reveals rough fracture surface under dynamic loading. → SEM morphology reveals integrated bundle pull-out under dynamic loading. → Strain rate sensitivity of in-bundle interface leads to that of the tensile strength. - Abstract: An investigation has been undertaken to determine the dynamic and quasi-static tensile behavior of two-dimensional carbon fiber reinforced silicon carbide matrix (2D-C/SiC) composites by means of the split Hopkinson tension bar and an electronic universal test machine respectively. The results indicate that the tensile strength of 2D C/SiC composites is increased at high strain rate. Furthermore, coated specimens show not only a 15% improvement in tensile strength but heightened strain rate sensitivity compared with uncoated ones. It is also shown that the tensile failure strain is strain rate insensitive and remains around 0.4%. Optical macrograph of failed specimens under dynamic loading revealed jagged fracture surfaces characterized by delamination and crack deviation, together with obvious fiber pull-out/splitting, in contrast with the smooth fracture surfaces under quasi-static loading. Scanning electron microscopy micrograph of fracture surface under dynamic loading clearly displayed integrated bundle pull-out which implies suppressed in-bundle debonding and enhanced in-bundle interfacial strengthening, in contrast with extensive in-bundle debonding under quasi-static loading. Thus we conclude that, with 2D C

  7. In vitro shear bond strength of Y-TZP ceramics to different core materials with the use of three primer/resin cement systems.

    Science.gov (United States)

    Al-Harbi, Fahad A; Ayad, Neveen M; Khan, Zahid A; Mahrous, Amr A; Morgano, Steven M

    2016-01-01

    Durability of the bond between different core materials and zirconia retainers is an important predictor of the success of a dental prosthesis. Nevertheless, because of its polycrystalline structure, zirconia cannot be etched and bonded to a conventional resin cement. The purpose of this in vitro study was to compare the effects of 3 metal primer/resin cement systems on the shear bond strength (SBS) of 3 core materials bonded to yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramic retainers. Zirconia ceramic (Cercon) disks (5×3 mm) were airborne-particle abraded, rinsed, and air-dried. Disk-shaped core specimens (7×7 mm) that were prepared of composite resin, Ni-Cr, and zirconia were bonded to the zirconia ceramic disks by using one of 3 metal primer/cement systems: (Z-Prime Plus/BisCem, Zirconia Primer/Multilink Automix, or Clearfil Ceramic Primer/Clearfil SA). SBS was tested in a universal testing machine. Stereomicroscopy was used to evaluate the failure mode of debonded specimens. Data were analyzed using 2-way ANOVA and post hoc analysis using the Scheffe procedure (α=.05). Clearfil SA/Clearfil Ceramic Primer system with an Ni-Cr core yielded the highest SBS value (19.03 MPa), whereas the lowest SBS value was obtained when Multilink Automix/Zirconia Primer system was used with the zirconia core group (4.09 MPa). Differences in mean SBS values among the cement/primer groups were statistically significant, except for Clearfil SA and BisCem with both composite resin and zirconia cores. Differences in mean SBS values among the core subgroups were not statistically significant, except for zirconia core with BisCem, Multilink, and Clearfil SA. The predominant failure mode was adhesive, except for Clearfil SA and BisCem luting agents with composite resin cores, which displayed cohesive failure, and Multilink Automix with a composite resin, core as well as Clearfil SA with Ni-Cr cores, where the debonded specimens of each group displayed a mixed

  8. Three-dimensional analysis of enamel surface alteration resulting from orthodontic clean-up -comparison of three different tools.

    Science.gov (United States)

    Janiszewska-Olszowska, Joanna; Tandecka, Katarzyna; Szatkiewicz, Tomasz; Stępień, Piotr; Sporniak-Tutak, Katarzyna; Grocholewicz, Katarzyna

    2015-11-18

    The present study aimed at 3D analysis of adhesive remnants and enamel loss following the debonding of orthodontic molar tubes and orthodontic clean-up to assess the effectiveness and safety of One-Step Finisher and Polisher and Adhesive Residue Remover in comparison to tungsten carbide bur. Thirty human molars were bonded with chemical-cure orthodontic adhesive (Unite, 3M, USA), stored 24 h in 0.9 % saline solution, debonded and cleaned using three methods (Three groups of ten): tungsten carbide bur (Dentaurum, Pforzheim, Germany), one-step finisher and polisher (One gloss, Shofu Dental, Kyoto, Japan) and Adhesive Residue Remover (Dentaurum, Pforzheim, Germany). Direct 3D scanning in blue-light technology to the nearest 2 μm was performed before etching and after adhesive removal. Adhesive remnant height and volume as well as enamel loss depth and volume were calculated. An index of effectiveness and safety was proposed and calculated for every tool; adhesive remnant volume and duplicated enamel lost volume were divided by a sum of multiplicands. Comparisons using parametric ANOVA or nonparametric ANOVA rank Kruskal-Wallis tests were used to compare between tools for adhesive remnant height and volume, enamel loss depth and volume as well as for the proposed index. No statistically significant differences in the volume (p = 0.35) or mean height (p = 0.24) of adhesive remnants were found (ANOVA rank Kruskal-Wallis test) between the groups of teeth cleaned using different tools. Mean volume of enamel loss was 2.159 mm(3) for tungsten carbide bur, 1.366 mm(3) for Shofu One Gloss and 0.659 mm(3) for Adhesive Residue Remover - (F = 2.816, p = 0.0078). A comparison of the proposed new index between tools revealed highly statistically significant differences (p = 0.0081), supporting the best value for Adhesive Residue Remover and the worst - for tungsten carbide bur. The evaluated tools were all characterized by similar effectiveness. The most

  9. Advances in telescope mirror cleaning

    Science.gov (United States)

    Blanken, Maarten F.; Chopping, Alan K.; Dee, Kevin M.

    2004-09-01

    Metrology and cleaning techniques for telescope mirrors are generally well established. CO2 cleaning and water washing are mainly used. Water washing has proven to be the best method of removing oil and water stains and restoring the aluminium to nearly fresh values. The risk of water getting to unwanted places such as electronics or other optics prevents this method from being employed more often. Recently the Isaac Newton Group introduced a new cleaning technique for their telescope mirrors, which reduces the risks discussed above. This technique uses water vapour instead of water to wash the mirror. The advantage of this method is that the amount of water needed is drastically reduced. In addition the pressure of the vapour will blow away any large dust particles on the mirror and the temperature shock between the vapour and the mirror will help to de-bond the dust particles. Adding a soapy solution will help to clean oil and watermarks of the mirror. This paper describes the vapour cleaning method, tests that have been done and the overall findings.

  10. Development of Fracture Toughness Evaluation Method for Composite Materials by Non-Destructive Testing Method

    International Nuclear Information System (INIS)

    Lee, Y. T.; Kim, K. S.

    1998-01-01

    Fracture process of continuous fiber reinforced composites is very complex because various fracture mechanisms such as matrix cracking, debonding, delamination and fiber breaking occur simultaneously during crack growth. If fibers cause crack bridging during crack growth, the stable crack growth and unstable crack growth appear repeatedly. Therefore, it is very difficult to exactly determine tile starting point of crack growth and the fracture toughness at the critical crack length in composites. In this research, fracture toughness test for CFRP was accomplished by using acoustic emission(AE) and recording of tile fracture process in real time by video-microscope. The starting point of crack growth, pop-in point and the point of unstable crack growth can be exactly determined. Each fracture mechanism can be classified by analyzing the fracture process through AE and video-microscope. The more reliable method is the fracture toughness measurement of composite materials was proposed by using the combination of R-curve method, AE and video microscope

  11. Intrinsic Osteoinductivity of Porous Titanium Scaffold for Bone Tissue Engineering

    Directory of Open Access Journals (Sweden)

    Maryam Tamaddon

    2017-01-01

    Full Text Available Large bone defects and nonunions are serious complications that are caused by extensive trauma or tumour. As traditional therapies fail to repair these critical-sized defects, tissue engineering scaffolds can be used to regenerate the damaged tissue. Highly porous titanium scaffolds, produced by selective laser sintering with mechanical properties in range of trabecular bone (compressive strength 35 MPa and modulus 73 MPa, can be used in these orthopaedic applications, if a stable mechanical fixation is provided. Hydroxyapatite coatings are generally considered essential and/or beneficial for bone formation; however, debonding of the coatings is one of the main concerns. We hypothesised that the titanium scaffolds have an intrinsic potential to induce bone formation without the need for a hydroxyapatite coating. In this paper, titanium scaffolds coated with hydroxyapatite using electrochemical method were fabricated and osteoinductivity of coated and noncoated scaffolds was compared in vitro. Alizarin Red quantification confirmed osteogenesis independent of coating. Bone formation and ingrowth into the titanium scaffolds were evaluated in sheep stifle joints. The examinations after 3 months revealed 70% bone ingrowth into the scaffold confirming its osteoinductive capacity. It is shown that the developed titanium scaffold has an intrinsic capacity for bone formation and is a suitable scaffold for bone tissue engineering.

  12. Direct observation of toughening mechanisms in carbon nanotube ceramic matrix composites

    International Nuclear Information System (INIS)

    Xia, Z.; Riester, L.; Curtin, W.A.; Li, H.; Sheldon, B.W.; Liang, J.; Chang, B.; Xu, J.M.

    2004-01-01

    The excellent mechanical properties of carbon nanotubes (CNTS) are driving research into the creation of new strong, tough nanocomposite systems. Here, the first evidence of toughening mechanisms operating in carbon-nanotube-reinforced ceramic composites is presented. A highly ordered array of parallel multiwall CNTs in an alumina matrix was fabricated. Nanoindentation introduced controlled cracks and the damage was examined by scanning electron microscopy. These nanocomposites exhibit the three hallmarks of toughening found in micron-scale fiber composites: crack deflection at the CNT/matrix interface; crack bridging by CNTs; and CNT pullout on the fracture surfaces. Interface debonding and sliding can thus occur in materials with microstructures approaching the atomic scale. Furthermore, for certain geometries a new mechanism of nanotube collapse in 'shear bands' occurs, rather than crack formation, suggesting that these materials can have multiaxial damage tolerance. The quantitative indentation data and computational models are used to determine the multiwall CNT axial Young's modulus as 200-570 GPa, depending on the nanotube geometry and quality. Three-dimensional FEM analysis indicates that matrix residual stresses on the order of 300 MPa are sustained in these materials without spontaneous cracking, suggesting that residual stress can be used to engineer enhanced performance. These nanoscale ceramic composites thus have potential for toughening and damage tolerance at submicron scales, and so are excellent candidates for wear-resistant coatings

  13. Effect of fatigue testing on the properties of Glass-Epoxy composites using the acoustic tool

    Directory of Open Access Journals (Sweden)

    Menail Younès

    2017-01-01

    Full Text Available This study presents the experimental results of the influence of mechanical fatigue on composite material. The plates of Glass fiber with SR 1500 epoxy resin with SD 2505 composite were realized by vacuum molding. Experimental tests were carried out on a standard hydraulic machine INSTRON 8516. The machine is interfaced with a dedicated computer for controlling and data acquisition. The fatigue tests were performed using sinusoidal type of waveform at a displacement control with frequency of 10 Hz. The evolution of Young’s modulus and strain based on fatigue gives us an idea about the resistance of the material. Degradation of mechanical properties was observed, and the results have showed that the Young’s modulus of plates undergo only minor changes. In fact, the residual stiffness and residual strength decrease when the cycle number of fatigue increase (100 to 50000 cycles, indicating that the studied composites have experienced some forms of mechanical damage.The mechanical tests were backed by Acoustic Emission Monitoring (AEM during the load cycle, in order to understand the nature of the failure process in the composites such as fiber breakage, matrix crazing, matrix debonding and delamination etc.

  14. Bond strength of compomers to dentin using acidic primers.

    Science.gov (United States)

    Tate, W H; You, C; Powers, J M

    1999-10-01

    To determine the in vitro bond strengths of seven compomer/bonding agent restorative systems to human dentin. Seven compomer/bonding agents were bonded to human dentin, stored in water at 37 degrees C for 24 hours, and debonded in tension. Bonding conditions were with and without phosphoric acid etching, with and without the use of combined primer/bonding agents, and under moist and wet bond interfaces. Without phosphoric acid etching, F2000/F2000 Compomer Primer/Adhesive and F2000/Single Bond Dental Adhesive System were less sensitive to dentin wetness. With moist dentin, bond strengths of Dyract/Prime & Bond 2.1, Dyract AP/Prime & Bond 2.1, Hytac/OSB light-curing, one-component bonding agent, F2000/Single Bond, and Freedom/STAE single component light-cured dentin/enamel adhesive system, were improved with phosphoric acid etching. Also, with moist dentin, the bond strength of F2000/F2000 Compomer Primer/Adhesive in the 3M Clicker dispensing system was higher without phosphoric acid etching, whereas bonds of Compoglass/Syntac Single-component were not affected by phosphoric acid etching. Bonding did not occur without primer/bonding agent, regardless of surface condition or use of phosphoric acid etching.

  15. A novel blister test to evaluate the interface strength between nickel coating and low carbon steel substrate

    International Nuclear Information System (INIS)

    Xiao, L.H.; Su, Xu Ping.; Wang, J.H.; Zhou, Y.C.

    2009-01-01

    A novel blister test theory model was developed based on the bending theory of beams for assessing the interface strength of the nickel coating/low carbon steel substrate material system. The strain energy of the debonded nickel coating was calculated analytically and by finite element analysis, respectively. The analytic solutions agree well with the FE calculation results. Some blister tests were carried out on the WII-5 Computer Controlled Material Mechanical Properties Testing Machine, using four nickel-coated specimens type-A, -B, -C and -D which were electrodeposited on low carbon steel substrate. Here, types A, B, C and D correspond to the nickel coating thickness of 5 μm, 10 μm, 15μm and 25μm, respectively. The interface strength, evaluated by this blister test method, is 196.86 J/m 2 and 269.40 J/m 2 for type-C and -D specimens, respectively. However the tests demonstrate that the type-A and -B specimens were cut through by the spindle and no delaminations between the coating and the substrate could be found

  16. Tensile toughness test and high temperature fracture analysis of thermal barrier coatings

    International Nuclear Information System (INIS)

    Qian, G.; Nakamura, T.; Berndt, C.C.; Leigh, S.H.

    1997-01-01

    In this paper, an effective fracture toughness test which uses interface fracture mechanics theory is introduced. This method is ideally suited for determining fracture resistance of multilayered thermal barrier coatings (TBCs) consisting of ceramic and bond layers and, unlike other fracture experiments, requires minimal set-up over a simple tensile adhesion test. Furthermore, while other test methods usually use edge cracked specimens, the present test models a crack embedded within the coatings, which is more consistent with actual TBCs where failure initiates from internal voids or defects. The results of combined computational and experimental analysis show that any defects located within the ceramic coating can significantly weaken a TBC, whereas the debonding resistances of the bond coating and its interfaces are found to be much higher. In a separate analysis, the authors have studied fracture behavior of TBCs subjected to thermal loading in a high temperature environment. The computed fracture parameters reveal that when the embedded crack size is on order of the coating thickness, the fracture driving force is comparable to the fracture resistance of the coating found in the toughness test. In addition, the major driving force for fracture derives from the thermal insulating effect across the crack faces rather than the mismatch in the coefficients of thermal expansion. The authors have also investigated the effects of functionally graded material (FGM) within TBCs and found its influences on the fracture parameters to be small. This result implies that the FGM may not contribute toward enhancing the fracture toughness of the TBCs considered here

  17. Room Temperature Mechanical Properties of A356 Alloy with Ni Additions from 0.5 Wt to 2 Wt %

    Directory of Open Access Journals (Sweden)

    Lucia Lattanzi

    2018-03-01

    Full Text Available In recent years, the influence of Ni on high-temperature mechanical properties of casting Al alloys has been extensively examined in the literature. In the present study, room temperature mechanical properties of an A356 alloy with Ni additions from 0.5 to 2 wt % were investigated. The role of Ni-based compounds and eutectic Si particles in reinforcing the Al matrix was studied with image analysis and was then related to tensile properties and microhardness. In the as-cast condition, the formation of the 3D network is not sufficient to determine an increase of mechanical properties of the alloys since fracture propagates by cleavage through eutectic Si particles and Ni aluminides or by the debonding of brittle phases from the aluminum matrix. After T6 heat treatment the increasing amount of Ni aluminides, due to further addition of Ni to the alloy, together with their brittle behavior, leads to a decrease of yield strength, ultimate tensile strength, and Vickers microhardness. Despite the fact that Ni addition up to 2 wt % hinders spheroidization of eutectic Si particles during T6 heat treatment, it also promotes the formation of a higher number of brittle Ni-based compounds that easily promote fracture propagation.

  18. Constitutive modelling of composite biopolymer networks.

    Science.gov (United States)

    Fallqvist, B; Kroon, M

    2016-04-21

    The mechanical behaviour of biopolymer networks is to a large extent determined at a microstructural level where the characteristics of individual filaments and the interactions between them determine the response at a macroscopic level. Phenomena such as viscoelasticity and strain-hardening followed by strain-softening are observed experimentally in these networks, often due to microstructural changes (such as filament sliding, rupture and cross-link debonding). Further, composite structures can also be formed with vastly different mechanical properties as compared to the individual networks. In this present paper, we present a constitutive model presented in a continuum framework aimed at capturing these effects. Special care is taken to formulate thermodynamically consistent evolution laws for dissipative effects. This model, incorporating possible anisotropic network properties, is based on a strain energy function, split into an isochoric and a volumetric part. Generalisation to three dimensions is performed by numerical integration over the unit sphere. Model predictions indicate that the constitutive model is well able to predict the elastic and viscoelastic response of biological networks, and to an extent also composite structures. Copyright © 2016 Elsevier Ltd. All rights reserved.

  19. Skeletal anteroposterior discrepancy and vertical type effects on lower incisor preoperative decompensation and postoperative compensation in skeletal Class III patients.

    Science.gov (United States)

    Ahn, Hyo-Won; Baek, Seung-Hak

    2011-01-01

    To determine the initial compensation, preoperative decompensation, and postoperative compensation of the lower incisors according to the skeletal anteroposterior discrepancy and vertical type in skeletal Class III patients. The samples consisted of 68 skeletal Class III patients treated with two-jaw surgery and orthodontic treatment. Lateral cephalograms were taken before preoperative orthodontic treatment (T0) and before surgery (T1) and after debonding (T2). According to skeletal anteroposterior discrepancy/vertical type (ANB, criteria  =  -4°; SN-GoMe, criteria  =  35°) at the T0 stage, the samples were allocated into group 1 (severe anteroposterior discrepancy/hypodivergent vertical type, N  =  17), group 2 (moderate anteroposterior discrepancy/hypodivergent vertical type, N  =  17), group 3 (severe anteroposterior discrepancy/hyperdivergent vertical type, N  =  17), or group 4 (moderate anteroposterior discrepancy/hyperdivergent vertical type, N  =  17). After measurement of variables, one-way analysis of variance with Duncan's multiple comparison test, crosstab analysis, and Pearson correlation analysis were performed. At T0, groups 3 and 2 exhibited the most and least compensated lower incisors. In group 2, good preoperative decompensation and considerable postoperative compensation resulted in different values for T0, T1, and T2 (IMPA, T0 lower incisors in Class III patients.

  20. Surface decoration of short-cut polyimide fibers with multi-walled carbon nanotubes and their application for reinforcement of lightweight PC/ABS composites

    Science.gov (United States)

    Zhang, Le; Han, Enlin; Wu, Yulun; Wang, Xiaodong; Wu, Dezhen

    2018-06-01

    The surface decoration of short-cut polyimide (PI) fibers with multi-walled carbon nanotubes (MWCNTs) was performed by fabricating a polydopamine (PDA) coating layer on the fiber surface and then immobilizing MWCNTs onto the coating layer via covalent bonding. This successful surface decoration was confirmed by scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared microscopy and static water contact angle. The application of the surface-decorated PI fibers as reinforcing fibers for reinforcement of polycarbonate (PC)/acrylonitrile-butadiene-styrene copolymer (ABS) alloy was investigated, which indicated that the MWCNTs-decorated PI fibers not only could effectively reinforce the PC/ABS alloy but also generated a significant lightweighting effect on the resulting composites. The maximum mechanical properties were achieved for the composites at a fiber content of 20 wt.% and a fiber length of 3 mm. This significant reinforcement effect is attributed to the enhancement of interaction bonding strength between the fibers and matrix as a result of the surface decoration of PI fibers with MWCNTs. The morphological investigation suggested that fiber rupture was the major energy dissipation mechanism in the tensile and impact failures, whereas fiber debonding and pullout were partly involved in the fracture energy dissipation. In addition, the presence of surface-decorated PI fibers slightly enhanced the thermal stability and load bearing capability of composites. This work can provide a type of high-performance lightweight composite material for automobile and aviation industries.

  1. Self-monitoring fiber reinforced polymer strengthening system for civil engineering infrastructures

    Science.gov (United States)

    Jiang, Guoliang; Dawood, Mina; Peters, Kara; Rizkalla, Sami

    2008-03-01

    Fiber reinforced polymer (FRP) materials are currently used for strengthening civil engineering infrastructures. The strengthening system is dependant on the bond characteristics of the FRP to the external surface of the structure to be effective in resisting the applied loads. This paper presents an innovative self-monitoring FRP strengthening system. The system consists of two components which can be embedded in FRP materials to monitor the global and local behavior of the strengthened structure respectively. The first component of the system is designed to evaluate the applied load acting on a structure based on elongation of the FRP layer along the entire span of the structure. Success of the global system has been demonstrated using a full-scale prestressed concrete bridge girder which was loaded up to failure. The test results indicate that this type of sensor can be used to accurately determine the load prior to failure within 15 percent of the measured value. The second sensor component consists of fiber Bragg grating sensors. The sensors were used to monitor the behavior of steel double-lap shear splices tested under tensile loading up to failure. The measurements were used to identify abnormal structural behavior such as epoxy cracking and FRP debonding. Test results were also compared to numerical values obtained from a three dimensional shear-lag model which was developed to predict the sensor response.

  2. Study of MA Effect on Yield Strength and Ductility of X80 Linepipe Steels Weld

    Science.gov (United States)

    Huda, Nazmul; Lazor, Robert; Gerlich, Adrian P.

    2017-09-01

    Multipass GMAW (Gas Metal Arc Welding) welding was used to join X80 linepipe materials using two weld metals of slightly different compositions. Welding wires with diameters of 0.984 and 0.909 mm were used while applying the same heat input in each pass. The slight difference in the wire diameters resulted in different HAZ microstructures. The microstructures in the doubly reheated HAZ of both welds were found to contain bainite-ferrite. However, etching also revealed a difference in martensite-austenite (MA) fraction in these reheated zones. The MA exhibited twice the hardness of ferrite when measured by nanoindentation. Tensile testing from the reheated zone of both welds revealed a difference in yield strength, tensile strength and elongation of the transverse weld specimens. In the reheated zone of weld A, (produced with a 0.984 mm wire) a higher fraction of MA was observed, which resulted in higher strength but lower elongation compared to weld B. The ductility of weld A was found severely impaired (to nearly half of weld B) due to formation of closely spaced voids around the MA, along with debonding of MA from the matrix, which occurs just above the yield stress.

  3. Weak interfaces for UV cure nanoimprint lithography

    Science.gov (United States)

    Houle, Frances; Fornof, Ann; Simonyi, Eva; Miller, Dolores; Truong, Hoa

    2008-03-01

    Nanoimprint lithography using a photocurable organic resist provides a means of patterning substrates with a spatial resolution in the few nm range. The usefulness of the technique is limited by defect generation during template removal, which involves fracture at the interface between the template and the newly cured polymer. Although it is critical to have the lowest possible interfacial fracture toughness (Gc less than 0.1 Jm-2) to avoid cohesive failure in the polymer, there is little understanding on how to achieve this using reacting low viscosity resist fluids. Studies of debonding of a series of free-radical cured polyhedral silsesquioxane crosslinker formulations containing selected reactive diluents from fluorosilane-coated quartz template materials will be described. At constant diluent fraction the storage modulus of cured resists follows trends in initial reaction rate, not diluent Tg. Adhesion is uncorrelated with both Tg and storage modulus. XPS studies of near-interface compositions indicate that component segregation within the resist fluid on contact with the template, prior to cure, plays a significant role in controlling the fracture process.

  4. The Retentive Strength of Cemented Zirconium Oxide Crowns after Dentin Pretreatment with Desensitizing Paste Containing 8% Arginine and Calcium Carbonate

    Science.gov (United States)

    Pilo, Raphael; Harel, Noga; Nissan, Joseph; Levartovsky, Shifra

    2016-01-01

    The effect of dentin pretreatment with Desensitizing Paste containing 8% arginine and calcium carbonate on the retention of zirconium oxide (Y-TZP) crowns was tested. Forty molar teeth were mounted and prepared using a standardized protocol. Y-TZP crowns were produced using computer-aided design and computer-aided manufacturing (CAD-CAM) technology. The 40 prepared teeth were either pretreated with Desensitizing Paste or not pretreated. After two weeks, each group was subdivided into two groups, cemented with either Resin Modified Glass Ionomer Cement (RMGIC) or Self Adhesive Resin Cement (SARC)). Prior to cementation, the surface areas of the prepared teeth were measured. After aging, the cemented crown-tooth assemblies were tested for retentive strength using a universal testing machine. The debonded surfaces of the teeth and crowns were examined microscopically at 10× magnification. Pretreating the dentin surfaces with Desensitizing Paste prior to cementation did not affect the retention of the Y-TZP crowns. The retentive values for RMGIC (3.04 ± 0.77 MPa) were significantly higher than those for SARC (2.28 ± 0.58 MPa). The predominant failure modes for the RMGIC and SARC were adhesive cement-dentin and adhesive cement-crown, respectively. An 8.0% arginine and calcium carbonate in-office desensitizing paste can be safely used to reduce post-cementation sensitivity without reducing the retentive strength of Y-TZP crowns. PMID:27023532

  5. Fifteen-year survival of anterior all-ceramic cantilever resin-bonded fixed dental prostheses.

    Science.gov (United States)

    Kern, Matthias

    2017-01-01

    The aim of this follow-up study was to report the long-term outcome of all-ceramic cantilever resin-bonded fixed dental prostheses (RBFDPs). In 16 patients (mean age of 33.3±17.5years) 22 RBFDPs made from a glass-infiltrated alumina ceramic (In-Ceram) were inserted with a phosphate monomer containing luting agent after air-abrasion of the retainer wings. The abutment preparation included a shallow groove on the cingulum and a small proximal box. The restorations replacing 16 maxillary and 6 mandibular incisors were followed over a mean observation time of 188.7 months. No restoration debonded. Two RBFDPs fractured and were lost 48 and 214 months after insertion, respectively. The 10-year and 15-year survival rates were both 95.4% and dropped to 81.8% after 18 years. Anterior all-ceramic cantilever RBFDPs exhibited an excellent clinical longevity. Copyright © 2016 Elsevier Ltd. All rights reserved.

  6. Scalable bonding of nanofibrous polytetrafluoroethylene (PTFE) membranes on microstructures

    Science.gov (United States)

    Mortazavi, Mehdi; Fazeli, Abdolreza; Moghaddam, Saeed

    2018-01-01

    Expanded polytetrafluoroethylene (ePTFE) nanofibrous membranes exhibit high porosity (80%-90%), high gas permeability, chemical inertness, and superhydrophobicity, which makes them a suitable choice in many demanding fields including industrial filtration, medical implants, bio-/nano- sensors/actuators and microanalysis (i.e. lab-on-a-chip). However, one of the major challenges that inhibit implementation of such membranes is their inability to bond to other materials due to their intrinsic low surface energy and chemical inertness. Prior attempts to improve adhesion of ePTFE membranes to other surfaces involved surface chemical treatments which have not been successful due to degradation of the mechanical integrity and the breakthrough pressure of the membrane. Here, we report a simple and scalable method of bonding ePTFE membranes to different surfaces via the introduction of an intermediate adhesive layer. While a variety of adhesives can be used with this technique, the highest bonding performance is obtained for adhesives that have moderate contact angles with the substrate and low contact angles with the membrane. A thin layer of an adhesive can be uniformly applied onto micro-patterned substrates with feature sizes down to 5 µm using a roll-coating process. Membrane-based microchannel and micropillar devices with burst pressures of up to 200 kPa have been successfully fabricated and tested. A thin layer of the membrane remains attached to the substrate after debonding, suggesting that mechanical interlocking through nanofiber engagement is the main mechanism of adhesion.

  7. Remarkable weakness against cleavage stress for YBCO-coated conductors and its effect on the YBCO coil performance

    International Nuclear Information System (INIS)

    Yanagisawa, Y.; Nakagome, H.; Takematsu, T.; Takao, T.; Sato, N.; Takahashi, M.; Maeda, H.

    2011-01-01

    Cleavage strength for YBCO-coated conductor is extremely low, typically 0.5 MPa. The remarkable weakness is due to cracks on the slit edge of the conductor. The cleavage stress appears on YBCO double pancake coils impregnated with epoxy. The cleavage stress should be avoided in the coil winding. Cleavage strength for an YBCO-coated conductor at 77 K was investigated with a model experiment. The nominal cleavage strength for an YBCO-coated conductor is extremely low, typically 0.5 MPa. This low nominal cleavage strength is due to stress concentration on a small part of the YBCO-coated conductor in cleavage fracture. Debonding by the cleavage stress occurs at the interface between the buffer layer and the Hastelloy substrate. The nominal cleavage strength for a slit edge of the conductor is 2.5-times lower than that for the original edge of the conductor; cracks and micro-peel existing over the slit edge reduce the cleavage strength for the slit edge. Cleavage stress and peel stress should be avoided in coil winding, as they easily delaminate the YBCO-coated conductor, resulting in substantial degradation of coil performance. These problems are especially important for epoxy impregnated YBCO-coated conductor coils. It appears that effect of cleavage stress and peel stress are mostly negligible for paraffin impregnated YBCO-coated conductor coils or dry wound YBCO-coated conductor coils.

  8. The research on x-ray nondestructive testing and image processing technology of explosive components

    International Nuclear Information System (INIS)

    Shi, C.; Zhai, X.; Liu, Z.; Lin, H.

    2004-01-01

    The explosive components will inevitably produce defects such as impurity, crack and degumming during production and storage, therefore the inside substance of the explosive components must be examined and the findings concerned must be identified and estimated in order to ensure the quality and service life of the explosive components. Firstly, some analyses are conducted on the usual X-ray NDT system theory, and the simulation explosive component is made with some pre-built defects such as debonding, cracks, blow holes, impurities, and non-uniform density. The image testing system most fit for the explosive components is established. Secondly, the ways of X-ray digital image processing are discussed; the obtained images are enhanced and restored through the self-accommodating build-up arithmetic and proper restoring methods. By means of the results of the overall comparison and analysis of the digital image processing technology, it is clearly indicated that it is feasible to use X-ray digital-imaging ways to carry out the NDT of explosive components and identify the inside defects. (author)

  9. Poly(dimethylsiloxane) / tetraethyl orthosilicate modified hydroxyapatite composites: mechanical properties and biocompatibility evaluation

    International Nuclear Information System (INIS)

    Bareiro, O.; Santos, L. A.

    2012-01-01

    A composite of poly(dimethylsiloxane)/hydroxyapatite (PDMS/HAp) has been developed and its mechanical properties and biocompatibility were assessed. The processing of the composite involved the surface modification of HAp with 5 or 10 %(wt/wt) tetraethyl orthosilicate (TEOS) solutions, followed by mixing in a two roll open mixer with the silicone. The energy dispersive spectroscopy (EDS) spectra indicated evidence of a silane layer in the HAp modified surface. In tensile property measurement, the PDMS/modified-HAp composite showed higher values of tensile strength (2.41 MPa) and lower elongation at break (73.44 %) than the PDMS/unmodified HAp composite, 2.26 MPa and 365.58 % respectively. In both cases, the composites showed higher values of tensile strength than the original silicone (1.97 MPa). Scanning electron microscopy (SEM) micrographs of the PDMS/unmodified-HAp composite exhibited debonding of the HAp particles from the elastomeric matrix at the fracture surface. On the other hand, HAp particles remained well attached to the matrix in the PDMS/modified-HAp composite. The presence of HAp improved the biocompatibility of the silicone. The soaking of the composites for 7 days in a simulated body fluid (SBF) formed a dense and homogeneous layer of HAp like crystals in the surface of the composites. The surface modification of HAp powders with TEOS solutions formed a strong interface PDMS/HAp, this enhanced the tensile strength of the composite. (author)

  10. The mechanical response of a PBX and binder: combining results across the strain-rate and frequency domains

    International Nuclear Information System (INIS)

    Drodge, D R; Williamson, D M; Palmer, S J P; Proud, W G; Govier, R K

    2010-01-01

    The mechanical response of a polymer bonded explosive (PBX) has been measured using a Split Hopkinson Pressure Bar at a strain-rate of 2000 s -1 , across a range of temperatures from 173 to 333 K, with the aim of observing its behaviour in the glassy regime. The yield stresses increased monotonically with decreasing temperature and no plateau was found. The failure mechanism was found to transition from shear-banding with crystal debonding fracture to brittle failure with some evidence of crystal fracture. Similar experiments were performed on samples of its nitrocellulose-based binder material, at a strain-rate of 3000 s -1 across a temperature range 173-273 K. The failure stresses of the binder approach that of the composite at temperatures near -70 0 C. The elastic moduli were estimated from post-equilibrium regions of the stress-strain curves, and compared with those obtained for the composite using 5 MHz ultrasonic sound-speed measurement, and powder dynamic mechanical analysis measurements and quasi-static behaviour reported in a previous paper. The moduli were plotted on a common frequency axis: a temperature shift was applied to collapse the curves, which agreed with the Cox-Merz rule.

  11. Comparative Investigation of Tungsten Fibre Nets Reinforced Tungsten Composite Fabricated by Three Different Methods

    Directory of Open Access Journals (Sweden)

    Linhui Zhang

    2017-07-01

    Full Text Available Tungsten fibre nets reinforced tungsten composites (Wf/W containing four net layers were fabricated by spark plasma sintering (SPS, hot pressing (HP and cold rolling after HP (HPCR, with the weight fraction of fibres being 17.4%, 10.5% and 10.5%, respectively. The relative density of the HPCRed samples is the highest (99.8% while that of the HPed composites is the lowest (95.1%. Optical and scanning electron microscopy and electron back scattering diffraction were exploited to characterize the microstructure, while tensile and hardness tests were used to evaluate the mechanical properties of the samples. It was found that partial recrystallization of fibres occurred after the sintering at 1800 °C. The SPSed and HPed Wf/W composites begin to exhibit plastic deformation at 600 °C with tensile strength (TS of 536 and 425 MPa and total elongation at break (TE of 11.6% and 23.0%, respectively, while the HPCRed Wf/W composites exhibit plastic deformation at around 400 °C. The TS and TE of the HPCRed Wf/W composites at 400 °C are 784 MPa and 8.4%, respectively. The enhanced mechanical performance of the Wf/W composites over the pure tungsten can be attributed to the necking, cracking, and debonding of the tungsten fibres.

  12. Water and saliva contamination effect on shear bond strength of brackets bonded with a moisture-tolerant light cure system.

    Science.gov (United States)

    Vicente, Ascensión; Mena, Ana; Ortiz, Antonio José; Bravo, Luis Alberto

    2009-01-01

    To evaluate the effects of water and saliva contamination on shear bond strength of brackets bonded with a moisture-tolerant light cure system. Brackets were bonded to 240 bovine lower incisors divided into 12 groups. Four bonding procedures were evaluated, including (1) TSEP/Transbond XT, (2) TMIP/ Transbond XT, (3) TSEP/Transbond PLUS, and (4) TMIP/Transbond PLUS, each under three different bonding conditions: without contamination, with water contamination, and with saliva contamination. Shear bond strength was measured with a universal testing machine. The adhesive remnant on the teeth was quantified with the use of image analyzing equipment. Without contamination, bond strengths for the four procedures were similar (P > .05). TSEP/Tranbond PLUS and TMIP/Transbond PLUS left significantly less adhesive on the teeth after debonding than TSEP/Transbond XT and TMIP/Transbond XT (P .017), although for TMIP/ Transbond XT, both variables showed significant reductions after contamination (P < .017). TSEP/Transbond PLUS, TMIP/Transbond PLUS, and TSEP/Transbond XT showed greater tolerance to wet conditions than was shown by TMIP/Transbond XT.

  13. Computer Code for Nanostructure Simulation

    Science.gov (United States)

    Filikhin, Igor; Vlahovic, Branislav

    2009-01-01

    Due to their small size, nanostructures can have stress and thermal gradients that are larger than any macroscopic analogue. These gradients can lead to specific regions that are susceptible to failure via processes such as plastic deformation by dislocation emission, chemical debonding, and interfacial alloying. A program has been developed that rigorously simulates and predicts optoelectronic properties of nanostructures of virtually any geometrical complexity and material composition. It can be used in simulations of energy level structure, wave functions, density of states of spatially configured phonon-coupled electrons, excitons in quantum dots, quantum rings, quantum ring complexes, and more. The code can be used to calculate stress distributions and thermal transport properties for a variety of nanostructures and interfaces, transport and scattering at nanoscale interfaces and surfaces under various stress states, and alloy compositional gradients. The code allows users to perform modeling of charge transport processes through quantum-dot (QD) arrays as functions of inter-dot distance, array order versus disorder, QD orientation, shape, size, and chemical composition for applications in photovoltaics and physical properties of QD-based biochemical sensors. The code can be used to study the hot exciton formation/relation dynamics in arrays of QDs of different shapes and sizes at different temperatures. It also can be used to understand the relation among the deposition parameters and inherent stresses, strain deformation, heat flow, and failure of nanostructures.

  14. Unified model to predict flexural shear behavior of externally bonded RC beams

    International Nuclear Information System (INIS)

    Colotti, V.; Spadea, G.; Swamy, R.N.

    2006-01-01

    Structural strengthening with externally bonded reinforcement is now recognized as a cost-effective, structurally sound and practically efficient method of rehabilitating deteriorating and damaged reinforced concrete beams. There is now an urgent need to develop a sound engineering basis which can predict the failure loads of all such strengthened beams in a reliable and consistent manner. Existing models to predict the behavior at ultimate of strengthened beams suffer from many limitations and weaknesses. This paper presents a unified global model, based on the Strut-and-Tie approach, to predict the failure loads of reinforced concrete beams strengthened for flexure and/or shear. This structural model is based on rational engineering principles, considers all the possible failure modes, and incorporates the load transfer mechanism bond to reflect the debonding phenomena which has a dominant influence on the failure process of plated beams. The model is validated against about 200 strengthened beam test reported in the literature and failing in flexure and/or shear, involving a large number of structural variables and steel, carbon and glass fiber reinforced polymer laminates as reinforcing medium. (author)

  15. Tensile properties of neutron irradiated solid HIP 316L(N). ITER Task T214, NET deliverable GB6 ECN-5

    International Nuclear Information System (INIS)

    Van Osch, E.V.; Tjoa, G.L.; Boskeljon, J.; Van Hoepen, J.

    1998-05-01

    The tensile properties of neutron irradiated Hot Isostatically Pressed (HIP) joints of type 316L(N) stainless steel (heat PM-130) have been measured. Cylindrical tensile test specimens of 4 mm diameter were irradiated in the High Flux Reactor (HFR) in Petten, The Netherlands, simulating the first wall conditions by a combination of high displacement damage with proportional amounts of helium. The solid HIP specimens were irradiated up to a target dose level of 5 dpa at a temperature of 550K. The damage levels realized range from 3.0 to 4.1 dpa, with helium contents up to 38 appm. Post irradiation testing temperatures ranged from 300 to 700K. The report contains the experimental conditions and summarises the results, which are given in terms of engineering stresses and strains and reduction of area. The main conclusions are that the unirradiated solid-HIP material is very soft, assumingly due to the relatively large grain size. Neutron irradiation induces both hardening and reduction of ductility, similar to the behaviour of 316L(N) plate. No failures related to debonding were observed for the tests of the unirradiated samples, however one of eight tested irradiated specimens fractured in the HIP joint, showing a flat fracture surface and a low reduction of area. 6 refs

  16. Lingual orthodontics for children and adolescents: improvement of the indirect bonding protocol

    Science.gov (United States)

    2013-01-01

    Introduction Demineralization of the dental enamel is a finding associated with fixed orthodontic treatment. When an indirect bonding procedure is used in children and adolescents the area beneath the bracket base may be affected. Aim To evaluate if the addition of an extra layer of a hydrophilic resin, to a conventional indirect bonding protocol, can reduce the incidence of demineralization beneath the bracket base. Methods 40 patients under 18 years of age were treated with completely customized lingual appliances. Two different bonding protocols were used either with or without the application of an additional layer of hydrophilic resin. Demineralization beneath the bracket base, after de-bonding, was evaluated by standardized intra-oral photographs. Results The addition of an extra layer of a hydrophilic resin helps to reduce the number of demineralized areas beneath the bracket bases significantly (three times less). The severity of the few remaining defects were minor and without any clinical consequence. Conclusion When bonding a completely customized lingual appliance in children and adolescents, an extra layer of a hydrophilic resin should be added to the teeth. PMID:24025345

  17. A Reference-Free and Non-Contact Method for Detecting and Imaging Damage in Adhesive-Bonded Structures Using Air-Coupled Ultrasonic Transducers

    Directory of Open Access Journals (Sweden)

    Timotius Yonathan Sunarsa

    2017-12-01

    Full Text Available Adhesive bonded structures have been widely used in aerospace, automobile, and marine industries. Due to the complex nature of the failure mechanisms of bonded structures, cost-effective and reliable damage detection is crucial for these industries. Most of the common damage detection methods are not adequately sensitive to the presence of weakened bonding. This paper presents an experimental and analytical method for the in-situ detection of damage in adhesive-bonded structures. The method is fully non-contact, using air-coupled ultrasonic transducers (ACT for ultrasonic wave generation and sensing. The uniqueness of the proposed method relies on accurate detection and localization of weakened bonding in complex adhesive bonded structures. The specimens tested in this study are parts of real-world structures with critical and complex damage types, provided by Hyundai Heavy Industries® and IKTS Fraunhofer®. Various transmitter and receiver configurations, including through transmission, pitch-catch scanning, and probe holder angles, were attempted, and the obtained results were analyzed. The method examines the time-of-flight of the ultrasonic waves over a target inspection area, and the spatial variation of the time-of-flight information was examined to visualize and locate damage. The proposed method works without relying on reference data obtained from the pristine condition of the target specimen. Aluminum bonded plates and triplex adhesive layers with debonding and weakened bonding were used to examine the effectiveness of the method.

  18. Development and Characterization of Embedded Sensory Particles Using Multi-Scale 3D Digital Image Correlation

    Science.gov (United States)

    Cornell, Stephen R.; Leser, William P.; Hochhalter, Jacob D.; Newman, John A.; Hartl, Darren J.

    2014-01-01

    A method for detecting fatigue cracks has been explored at NASA Langley Research Center. Microscopic NiTi shape memory alloy (sensory) particles were embedded in a 7050 aluminum alloy matrix to detect the presence of fatigue cracks. Cracks exhibit an elevated stress field near their tip inducing a martensitic phase transformation in nearby sensory particles. Detectable levels of acoustic energy are emitted upon particle phase transformation such that the existence and location of fatigue cracks can be detected. To test this concept, a fatigue crack was grown in a mode-I single-edge notch fatigue crack growth specimen containing sensory particles. As the crack approached the sensory particles, measurements of particle strain, matrix-particle debonding, and phase transformation behavior of the sensory particles were performed. Full-field deformation measurements were performed using a novel multi-scale optical 3D digital image correlation (DIC) system. This information will be used in a finite element-based study to determine optimal sensory material behavior and density.

  19. Influence of Interface Gap on the Stress Behaviour of Smart Single Lap Joints Under Time Harmonic Load

    Directory of Open Access Journals (Sweden)

    Ivanova Jordanka

    2017-06-01

    Full Text Available Adhesive joints are frequently used in different composite structures due to their improved mechanical performance and better understanding of the failure mechanics. The application of such structures can be seen in aerospace and high technology components. The authors developed and applied modified shear lag analysis to investigate the hygrothermalpiezoelectric response of a smart single lap joint at environmental conditions (with/without an interface gap along the overlap zone and under dynamic time harmonic mechanical and electric loads. The main key is the study of the appearance of possible delamination along the interface. As illustrative examples, the analytical closed form solution of the structure shear and the axial stresses response, as well as the interface debond length, including influence of mechanical, piezoelectric, thermal characteristics and frequencies is performed and discussed. All results are presented in figures. The comparison of the shear stress and electric fields for both cases of overlap zone (continuous or with a gap is also shown in figures and discussed.

  20. A parametric study of the dynamic failure of energetic composites

    Science.gov (United States)

    Tanasoiu, Bogdan; Koslowski, Marisol

    2017-09-01

    Heating by frictional sliding of cracks is often considered to be one of the most important causes of localized melting and ignition in solid explosives. Furthermore, recent high speed X-ray phase contrast experiments on energetic composites under dynamic compression [Parab et al., Appl. Phys. Lett. 109(13) (2016)] show that most fracture events appear inside the particles. Initial cracks develop in regions where particles are close, and widespread fragmentation is observed in the interior of the particles as the stress waves propagate through the sample. However, most simulations have focused on interface debonding of energetic composites and, in general, do not include fracture of the particles explicitly. A phase field damage approach is used to model the dynamic response of a system of cyclotetramethylene-tetranitramine particles embedded in a Sylgard matrix. The simulations show several damage mechanisms observed in the experiments. The effects of the energy release rate and the initial crack distribution on the energy dissipation due to fracture are studied. The numerical results confirm that initial cracks play an important role in the evolution of damage, energy dissipation and consequently, the formation of hot-spots.

  1. Spectral element modelling of wave propagation in isotropic and anisotropic shell-structures including different types of damage

    International Nuclear Information System (INIS)

    Schulte, R T; Fritzen, C-P; Moll, J

    2010-01-01

    During the last decades, guided waves have shown great potential for Structural Health Monitoring (SHM) applications. These waves can be excited and sensed by piezoelectric elements that can be permanently attached onto a structure offering online monitoring capability. However, the setup of wave based SHM systems for complex structures may be very difficult and time consuming. For that reason there is a growing demand for efficient simulation tools providing the opportunity to design wave based SHM systems in a virtual environment. As usually high frequency waves are used, the associated short wavelength leads to the necessity of a very dense mesh, which makes conventional finite elements not well suited for this purpose. Therefore in this contribution a flat shell spectral element approach is presented. By including electromechanical coupling a SHM system can be simulated entirely from actuator voltage to sensor voltage. Besides a comparison to measured data for anisotropic materials including delamination, a numerical example of a more complex, stiffened shell structure with debonding is presented.

  2. Hot Roll Bonding of Aluminum to Twin-Roll Cast (TRC) Magnesium and Its Subsequent Deformation Behavior

    Science.gov (United States)

    Saleh, H.; Schmidtchen, M.; Kawalla, R.

    2018-02-01

    In an experiment in which twin-roll cast AZ31 magnesium alloy and commercial purity aluminum (AA 1050) sheets were bonded by hot rolling as Al/Mg/Al laminate composites, it was found that increasing the preheating temperatures up to 400 °C enhances the bonding strength of composites. Further increases in the preheating temperatures accelerate the magnesium oxide growth and thus reduce the bonding strength. The influence of the reduction ratio on the bonding properties was also studied, whereby it was observed that increasing the rolling reduction led to an increase in the bonding strength. The experimental results show that the optimum bonding strength can be obtained at rolling temperatures of 375-400 °C with a 50-60% reduction in thickness. On the other hand, the subsequent deformation behavior of composite was assessed using plane strain compression and deep drawing tests. We demonstrate that the composites produced using the optimum roll bonding conditions exhibited sufficient bonding during subsequent deformation and did not reveal any debonding at the bonding interface.

  3. Effects of contamination by either blood or a hemostatic agent on the shear bond strength of orthodontic buttons

    Science.gov (United States)

    Alkis, Huseyin; Turkkahraman, Hakan

    2013-01-01

    Objective To evaluate the effects of contamination by either blood or a hemostatic agent on the shear bond strength (SBS) of orthodontic buttons. Methods We used 45 freshly extracted, non-carious, impacted third molars that were divided into 3 groups of 15. Each tooth was etched with 37% phosphoric acid gel for 30 s. Human blood or the blood stopper agent was applied to the tooth surface in groups I and II, respectively. Group III teeth were untreated (controls). Orthodontic buttons were bonded to the teeth using light-curing composite resin. After bonding, the SBS of the button was determined using a Universal testing machine. Any adhesive remaining after debonding was assessed and scored according to the modified adhesive remnant index (ARI). ANOVA with post-hoc Tukey's test was used to determine significant differences in SBS and Fisher's exact test, to determine significant differences in ARI scores among groups. Results ANOVA indicated a significant difference between groups (p Contamination of tooth surfaces with either blood or hemostatic agent significantly decreased the SBS of orthodontic buttons. When the contamination risk is high, it is recommended to use the blood stopper agent when bonding orthodontic buttons on impacted teeth. PMID:23671834

  4. Static coefficient of friction between stainless steel and PMMA used in cemented hip and knee implants.

    Science.gov (United States)

    Nuño, N; Groppetti, R; Senin, N

    2006-11-01

    Design of cemented hip and knee implants, oriented to improve the longevity of artificial joints, is largely based on numerical models. The static coefficient of friction between the implant and the bone cement is necessary to characterize the interface conditions in these models and must be accurately provided. The measurement of this coefficient using a repeatable and reproducible methodology for materials used in total hip arthroplasty is missing from the literature. A micro-topographic surface analysis characterized the surfaces of the specimens used in the experiments. The coefficient of friction between stainless steel and bone cement in dry and wet conditions using bovine serum was determined using a prototype computerized sliding friction tester. The effects of surface roughness (polished versus matt) and of contact pressure on the coefficient of friction have also been investigated. The serum influences little the coefficient of friction for the matt steel surface, where the mechanical interactions due to higher roughness are still the most relevant factor. However, for polished steel surfaces, the restraining effect of proteins plays a very relevant role in increasing the coefficient of friction. When the coefficient of friction is used in finite element analysis, it is used for the debonded stem-cement situation. It can thus be assumed that serum will propagate between the stem and the cement mantle. The authors believe that the use of a static coefficient of friction of 0.3-0.4, measured in the present study, is appropriate in finite element models.

  5. Role of loading direction on cyclic behaviour characteristics of AM30 extrusion and its fatigue damage modelling

    Energy Technology Data Exchange (ETDEWEB)

    Roostaei, Ali A., E-mail: aaroostaei@uwaterloo.ca; Jahed, Hamid, E-mail: hjahed@uwaterloo.ca

    2016-07-18

    Anisotropic fatigue and cyclic behaviour of AM30 Mg alloy extrusion is investigated by performing fully-reversed strain-controlled tension-compression cyclic tests at strain amplitudes between 0.3% and 2.3%, along extrusion (ED) and transverse (TD) directions. The shapes of half-life hysteresis loops suggest the predominance of slip and twinning/de-twinning mechanisms below and above the strain amplitude of 0.5%, respectively. The twinning/de-twinning occurrence is found to be more extensive during straining along ED, which results in higher asymmetry of hysteresis loops, and thereby, higher induced mean stress. This adversely affects the fatigue resistance and yields to less number of cycles before failure in ED. Optical microscopy and texture analysis are employed to validate the findings. In addition, fracture surfaces are studied by scanning electron microscopy to identify the sources of fatigue crack initiation. Persistent slip bands (PSBs) and twin lamellae interfaces are evidenced as crack initiation sites at low and high strain amplitudes, respectively. Cracks emanated from debonded inclusion interface are also observed. Lastly, estimated fatigue life by Smith-Watson-Topper (SWT) and Jahed-Varvani (JV) fatigue models are compared with experimental life obtained through this study as well as the ones reported in the literature. The JV energy model is proven to yield better life predictions.

  6. Asymmetric extractions in a patient with a hopeless maxillary central incisor, followed by treatment with mini-implant anchorage.

    Science.gov (United States)

    Jung, Min-Ho

    2018-05-01

    Premolar extraction is 1 option for treatment of patients with malocclusion and severe crowding or protrusion. When the patient has missing or hopeless teeth other than premolars, it is possible to consider removal of those teeth to use the space to decrease crowding. A 15-year-old girl sought treatment for severe crowding. She had already lost her maxillary right first premolar as a result of caries 1 year previously and had a hopeless maxillary right central incisor. Her mandibular left first molar still caused discomfort even after endodontic treatment. Extractions of the maxillary right central incisor and mandibular right first premolar and left first molar were chosen to resolve the occlusion problems. Orthodontic mini-implants were placed to translocate the maxillary left central incisor across the midpalatal suture to use the space in the maxillary right quadrant to relieve the crowding. Although a different extraction option was used in each quadrant, the final occlusion was acceptable. After debonding, porcelain crowns were placed on the anterior teeth to improve esthetics. The treatment result remained stable after 2 years of retention. Copyright © 2018 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.

  7. Transverse Tensile Properties of 3 Dimension-4 Directional Braided Cf/SiC Composite Based on Double-Scale Model

    Science.gov (United States)

    Niu, Xuming; Sun, Zhigang; Song, Yingdong

    2017-11-01

    In this thesis, a double-scale model for 3 Dimension-4 directional(3D-4d) braided C/SiC composites(CMCs) has been proposed to investigate mechanical properties of it. The double-scale model involves micro-scale which takes fiber/matrix/porosity in fibers tows into consideration and the unit cell scale which considers the 3D-4d braiding structure. Basing on the Micro-optical photographs of composite, we can build a parameterized finite element model that reflects structure of 3D-4d braided composites. The mechanical properties of fiber tows in transverse direction are studied by combining the crack band theory for matrix cracking and cohesive zone model for interface debonding. Transverse tensile process of 3D-4d CMCs can be simulated by introducing mechanical properties of fiber tows into finite element of 3D-4d braided CMCs. Quasi-static tensile tests of 3D-4d braided CMCs have been performed with PWS-100 test system. The predicted tensile stress-strain curve by the double scale model finds good agreement with the experimental results.

  8. Raman measurements of Kevlar-29 fiber pull-out test at different strain levels

    Science.gov (United States)

    Wang, Quan; Lei, Zhenkun; Kang, Yilan; Qiu, Wei

    2008-11-01

    This paper adopted Kevlar-29 fiber monofilament embedding technology to prepare fiber/ epoxy resin tensile specimen. The specimen was pulled on a homemade and portable mini-loading device. At the same time micro-Raman spectroscopy is introduced to detect the distributions of stress on the embedded fiber at different strain levels. The characteristic peak shift of the 1610 cm-1 in Raman band has a linear relationship with the strain or stress. The experimental results show that the fiber axial stress decreases gradually from the embedded fiber-start to the embedded fiber-end at the same strain level. At different strain levels, the fiber axial stress increases along with the applied load. It reveals that there is a larger fiber axial stress distribution under a larger strain level. And the stress transfer is realized gradually from the embedded fiber-start to the fiber-end. Stress concentration exists in the embedded fiber-end, which is a dangerous region for interfacial debonding easily.

  9. Sintering behavior, microstructure and properties of TiC-FeCr hard alloy

    Institute of Scientific and Technical Information of China (English)

    Farid Akhtar; Shiju Guo; Jawid Askari; Jianjun Tian

    2007-01-01

    TiC based cermets were produced with FeCr,as a binder,by conventional P/M (powder metallurgy) to near >97% of the theoretical density.Sintering temperature significantly affects the mechanical properties of the composite.The sintering temperature of>1360 ℃ caused severe chemical reaction between TiC particles and the binder phase.In the TiC-FeCr cermets,the mechanical properties did not vary linearly with the carbide content.Optimum mechanical properties were found in the composite containing 57wt%TiC reinforcement,when sintered at 1360 ℃ for 1 h.Use of carbon as an additive enhanced the mechanical properties of the composites.Cermets containing carbon as an additive with 49wt% TiC exhibited attractive mechanical properties.The microstructure of the developed composite contained less or no debonding,representing good wettability of the binder with TiC particles.Homogeneous distribution of the TiC particles ensured the presence of isotropic mechanical properties and homogeneous distribution of stresses in the composite.Preliminary experiments for evaluation of the oxidation resistance of FeCr bonded TiC cermets indicate that they are more resistant than WC-Co hardmetals.

  10. Development of integrated damage detection system for international America's Cup class yacht structures using a fiber optic distributed sensor

    Science.gov (United States)

    Akiyoshi, Shimada; Naruse, Hiroshi; Uzawa, Kyoshi; Murayama, Hideaki; Kageyama, Kazuro

    2000-06-01

    We constructed a new health monitoring system to detect damage using a fiber optic distributed sensor, namely a Brillouin optical time domain reflectometer (BOTDR), and installed it in International America's Cup Class (IACC) yachts, the Japanese entry in America's Cup 2000. IACC yachts are designed to be as fast as possible, so it is essential that they are lightweight and encounter minimum water resistance. Advanced composite sandwich structures, made with carbon fiber reinforced plastic (CFRP) skins and a honeycomb core, are used to achieve the lightweight structure. Yacht structure designs push the strength of the materials to their limit and so it is important to detect highly stressed or damaged regions that might cause a catastrophic fracture. The BOTDR measures changes in the Brillouin frequency shift caused by distributed strain along one optical fiber. We undertook two experiments: a pulling test and a four point bending test on a composite beam. The former showed that no slippage occurred between the optical fiber glass and its coating. The latter confirmed that a debonding between the skin and the core of 300 mm length could be found with the BOTDR. Next we examined the effectiveness with which this system can assess the structural integrity of IACC yachts. The results show that our system has the potential for use as a damage detection system for smart structures.

  11. Fatigue crack propagation in self-assembling nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Klingler, Andreas; Wetzel, Bernd [Institute for Composite Materials (IVW GmbH) Technical University of Kaiserslautern, 67633 Kaiserslautern (Germany)

    2016-05-18

    Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.

  12. In vitro evaluation of an alternative method to bond molar tubes

    Directory of Open Access Journals (Sweden)

    Célia Regina Maio Pinzan-Vercelino

    2011-02-01

    Full Text Available Despite the advances in bonding materials, many clinicians today still prefer to place bands on molar teeth. Molar bonding procedures need improvement to be widely accepted clinically. OBJECTIVE: The purpose of this study was to evaluate the shear bond strength when an additional adhesive layer was applied on the occlusal tooth/tube interface to provide reinforcement to molar tubes. MATERIAL AND METHODS: Sixty third molars were selected and allocated to the 3 groups: group 1 received a conventional direct bond followed by the application of an additional layer of adhesive on the occlusal tooth/tube interface, group 2 received a conventional direct bond, and group 3 received a conventional direct bond and an additional cure time of 10 s. The specimens were debonded in a universal testing machine. The results were analyzed statistically by ANOVA and Tukey's test (α=0.05. RESULTS: Group 1 had a significantly higher (p0.05. CONCLUSIONS: The present in vitro findings indicate that the application of an additional layer of adhesive on the tooth/tube interface increased the shear bond strength of the bonded molar tubes.

  13. Effect of autoclave induced low-temperature degradation on the adhesion energy between yttria-stabilized zirconia veneered with porcelain.

    Science.gov (United States)

    Li, Kai Chun; Waddell, J Neil; Prior, David J; Ting, Stephanie; Girvan, Liz; van Vuuren, Ludwig Jansen; Swain, Michael V

    2013-11-01

    To investigate the effect of autoclave induced low-temperature degradation on the adhesion energy between yttria-stabilized zirconia veneered with porcelain. The strain energy release rate using a four-point bending stable fracture test was evaluated for two different porcelains [leucite containing (VM9) and glass (Zirox) porcelain] veneered to zirconia. Prior to veneering the zirconia had been subjected to 0 (control), 1, 5, 10 and 20 autoclave cycles. The specimens were manufactured to a total bi-layer dimension of 30 mm × 8 mm × 3 mm. Subsequent scanning electron microscopy/energy dispersive spectrometry, electron backscatter diffraction and X-ray diffraction analysis were performed to identify the phase transformation and fracture behavior. The strain energy release rate for debonding of the VM9 specimens were significantly higher (pautoclave cycles lowered the strain energy release rate significantly (pautoclave cycles between 5 and 20. The monoclinic phase reverted back to tetragonal phase after undergoing conventional porcelain firing cycles. EBSD data showed significant changes of the grain size distribution between the control and autoclaved specimen (cycle 20). Increasing autoclave cycles only significantly decreased the adhesion of the VM9 layered specimens. In addition, a conventional porcelain firing schedule completely reverted the monoclinic phase back to tetragonal. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  14. Effect of Nanosilica Particle Size on the Water Permeability, Abrasion Resistance, Drying Shrinkage, and Repair Work Properties of Cement Mortar Containing Nano-SiO2

    Directory of Open Access Journals (Sweden)

    Sattawat Haruehansapong

    2017-01-01

    Full Text Available This work presents the effect of nanosilica particle sizes on durability properties and repair work properties of cement mortar containing nanosilica (NS. Three different NS particle sizes of 12, 20, and 40 nm were used and compared with those of cement mortar without NS and cement mortar with silica fume (SF. Interesting results were obtained in which the particle size of NS affected directly the abrasion resistance and water permeability. NS with particle size of 40 nm is the optimum size and gave the highest abrasion resistance and water permeability. For repair work properties, cement mortars containing NS (12 and 20 nm and SF experienced higher drying shrinkage than that of cement mortar without NS and then presented cracking behavior and debonding between the cement mortars and concrete substrate. Cement mortar containing 40 nm of NS gave the lowest drying shrinkage, the lowest crack number, and the highest adhesive strength. These results indicate that the particle size of NS affected not only the durability properties but also the repair work properties of cement mortar.

  15. Advanced Booster Composite Case/Polybenzimidazole Nitrile Butadiene Rubber Insulation Development

    Science.gov (United States)

    Gentz, Steve; Taylor, Robert; Nettles, Mindy

    2015-01-01

    The NASA Engineering and Safety Center (NESC) was requested to examine processing sensitivities (e.g., cure temperature control/variance, debonds, density variations) of polybenzimidazole nitrile butadiene rubber (PBI-NBR) insulation, case fiber, and resin systems and to evaluate nondestructive evaluation (NDE) and damage tolerance methods/models required to support human-rated composite motor cases. The proposed use of composite motor cases in Blocks IA and II was expected to increase performance capability through optimizing operating pressure and increasing propellant mass fraction. This assessment was to support the evaluation of risk reduction for large booster component development/fabrication, NDE of low mass-to-strength ratio material structures, and solid booster propellant formulation as requested in the Space Launch System NASA Research Announcement for Advanced Booster Engineering Demonstration and/or Risk Reduction. Composite case materials and high-energy propellants represent an enabling capability in the Agency's ability to provide affordable, high-performing advanced booster concepts. The NESC team was requested to provide an assessment of co- and multiple-cure processing of composite case and PBI-NBR insulation materials and evaluation of high-energy propellant formulations.

  16. Low temperature thermocompression bonding between aligned carbon nanotubes and metallized substrate

    Energy Technology Data Exchange (ETDEWEB)

    Chen, M X; Gan, Z Y; Liu, S [School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China); Song, X H, E-mail: chimish@163.com [Division of MOEMS, Wuhan National Lab for Optoelectronics, Wuhan 430074 (China)

    2011-08-26

    Vertically aligned carbon nanotube (VACNT) turf is proposed for use as an electrical and thermal contact material. For these applications, one route for circumventing the high temperatures required for VACNT growth using chemical vapor deposition (CVD) is used to grow firstly VACNTs on one substrate and then transfer them to other substrates. In this work, a nano thermocompression bonding technique between VACNTs and a metallized substrate is developed to allow dry mechanical transfer of the VACNTs. Unlike the diffusion bonding between two bulk materials, nano metal clusters have a high surface energy and the atoms are very active to form alloy with the contacted bulk metal material even at much lower temperatures, so nano thermocompression bonding can decrease the bonding temperature (150 deg. C) and pressure (1 MPa) and greatly shorten the bonding time from hours to 20 min. A debonding experiment shows that the bonding strength between VACNTs and the metallized layer is so high that a break is less likely to occur at the bonding interface.

  17. Joining of Tungsten Armor Using Functional Gradients

    International Nuclear Information System (INIS)

    John Scott O'Dell

    2006-01-01

    The joining of low thermal expansion armor materials such as tungsten to high thermal expansion heat sink materials has been a major problem in plasma facing component (PFC) development. Conventional planar bonding techniques have been unable to withstand the high thermal induced stresses resulting from fabrication and high heat flux testing. During this investigation, innovative functional gradient joints produced using vacuum plasma spray forming techniques have been developed for joining tungsten armor to copper alloy heat sinks. A model was developed to select the optimum gradient architecture. Based on the modeling effort, a 2mm copper rich gradient was selected. Vacuum plasma pray parameters and procedures were then developed to produce the functional gradient joint. Using these techniques, dual cooling channel, medium scale mockups (32mm wide x 400mm length) were produced with vacuum plasma spray formed tungsten armor. The thickness of the tungsten armor was up to 5mm thick. No evidence of debonding at the interface between the heat sink and the vacuum plasma sprayed material was observed.

  18. Superior toughness obtained via tuning the compatibility of poly(ethylene terephthalate)/poly(ethylene–octene) blends

    International Nuclear Information System (INIS)

    Su, Juan-juan; Peng, Fang; Gao, Xiang; Yang, Guang-hui; Fu, Qiang; Wang, Ke

    2014-01-01

    Highlights: • Develop a new elastomer-toughened plastic system based on PET. • Superior toughness was achieved by adding POE into PET. • The best toughness correlated with a moderate level of interfacial adhesion. • The mechanism of toughening was attributed to matrix shear yielding. - Abstract: As a partial of the systematic investigation of the preparation and characterization of poly(ethylene terephthalate) (PET) blending/compounding materials with excellent comprehensive mechanics in the authors’ group, this study deals with the compatibilization modification of PET/elastomer blends to obtain superior toughness. Poly(ethylene–octene) (POE) was employed as elastomer toughener, while maleic anhydride grafted POE (mPOE) was selected as compatibilizer. To highlight the effect of compatibility on toughening, the sum amount of elastomer component, POE and mPOE, was fixed at 20 wt%, but the mass ratio of mPOE/POE was changeable. It is interesting to find that an optimization of toughening can be attained at 3 wt% mPOE, at which the notched impact strength is about 15 folds for that of neat PET. The toughening behavior observed is due to a combination of good dispersion of elastomer phase particles and, particularly, appropriate interfacial adhesion condition. Microscopic fractured morphology reveals that a moderate level of interfacial adhesion is important for good dispersion of elastomer phase and debonding between PET matrix and elastomer particles, which initiate matrix shear yielding to dissipate more energy than other interfacial adhesion conditions

  19. Effect of Rebonding on the Bond Strength of Orthodontic Tubes: A Comparison of Light Cure Adhesive and Resin-Modified Glass Ionomer Cement In Vitro

    Directory of Open Access Journals (Sweden)

    Monika Aleksiejunaite

    2017-01-01

    Full Text Available The purpose of this study was to determine the impact of different enamel preparation procedures and compare light cure composite (LCC and resin-modified glass ionomer (RMGI on the bond strength of orthodontic metal tubes rebonded to the enamel. Twenty human molars were divided into two groups (n=10. Tubes were bonded using LCC (Transbond XT in group 1 and RMGI (Fuji Ortho LC in group 2. The tubes in each group were bonded following manufacturers’ instructions (experiment I and then debonded using testing machine. Then, the same brackets were sandblasted and rebonded twice. Before the first rebonding, the enamel was cleaned using carbide bur (experiment II and before second rebonding, it was cleaned using carbide bur and soda blasted (experiment III. Mann–Whitney and Wilcoxon signed-rank tests showed no significant difference between RMGI and LCC bond strengths in case of normal bonding and rebonding, when enamel was cleaned using carbide bur before rebonding. Enamel soda blasting before rebonding significantly increased RMGI tensile bond strength value compared to LLC (p<0.05. LCC and RMGI (especially RMGI provide sufficient bond strengths for rebonding of molar tubes, when residual adhesive from previous bonding is removed and enamel soda blasted.

  20. Effect of elevated temperature on the tensile strength of Napier/glass-epoxy hybrid reinforced composites

    Science.gov (United States)

    Ridzuan, M. J. M.; Majid, M. S. Abdul; Afendi, M.; Firdaus, A. Z. Ahmad; Azduwin, K.

    2017-11-01

    The effects of elevated temperature on the tensile strength of Napier/glass-epoxy hybrid reinforced composites and its morphology of fractured surfaces are discussed. Napier/glass-epoxy hybrid reinforced composites were fabricated by using vacuum infusion method by arranging Napier fibres in between sheets of woven glass fibres. Napier and glass fibres were laminated with estimated volume ratios were 24 and 6 vol. %, respectively. The epoxy resin was used as matrix estimated to 70 vol. %. Specimens were tested to failure under tension at a cross-head speed of 1 mm/min using Universal Testing Machine (Instron) with a load cell 100 kN at four different temperatures of RT, 40°C, 60°C and 80°C. The morphology of fractured surface of hybrid composites was investigated by field emission scanning electron microscopy. The result shows reduction in tensile strength at elevated temperatures. The increase in the temperature activates the process of diffusion, and generates critical stresses which cause the damage at first-ply or at the centre of the hybrid plate, as a result lower the tensile strength. The observation of FESEM images indicates that the fracture mode is of evolution of localized damage, from fibre/matrix debonding, matric cracking, delamination and fibre breakage.