Analysis of stress intensity factor in orthotropic bi-material mixed interface crack
赵文彬; 张雪霞; 崔小朝; 杨维阳
2014-01-01
Adopting the complex function approach, the paper studies the stress intensity factor in orthotropic bi-material interface cracks under mixed loads. With con-sideration of the boundary conditions, a new stress function is introduced to transform the problem of bi-material interface crack into a boundary value problem of partial dif-ferential equations. Two sets of non-homogeneous linear equations with 16 unknowns are constructed. By solving the equations, the expressions for the real bi-material elastic constantεt and the real stress singularity exponentsλt are obtained with the bi-material engineering parameters satisfying certain conditions. By the uniqueness theorem of limit, undetermined coeﬃcients are determined, and thus the bi-material stress intensity factor in mixed cracks is obtained. The bi-material stress intensity factor characterizes features of mixed cracks. When orthotropic bi-materials are of the same material, the degenerate solution to the stress intensity factor in mixed bi-material interface cracks is in complete agreement with the present classic conclusion. The relationship between the bi-material stress intensity factor and the ratio of bi-material shear modulus and the relationship be-tween the bi-material stress intensity factor and the ratio of bi-material Young’s modulus are given in the numerical analysis.
Case Study of Crack Initiation from Bi-material Notches
Klusák, Jan; Knésl, Zdeněk
2011-01-01
Roč. 452-453, - (2011), s. 449-452. ISSN 1013-9826. [Fracture and Damage Mechanics /9./. Nagasaki, 20.09.2010-22.09.2010] R&D Projects: GA ČR GAP108/10/2049; GA ČR GA101/08/0994 Institutional research plan: CEZ:AV0Z20410507 Keywords : Crack initiation * bi-material notch * fracture mechanics Subject RIV: JL - Materials Fatigue, Friction Mechanics
Stress intensity factors of eccentric cracks in bi-materials plate under mode I loading
Bi-material plates were generally used to joint electronic devices or mechanical components requiring dissimilar materials to be attached. During services, mechanical failure can be occurred due to the formation of cracks at the interfacial joint or away from the centre. Generally, linear elastic fracture mechanics approach is used to characterize these cracks based on stress intensity factors (SIF). Based on the literature survey, the SIFs for the central cracks were easily available. However, the SIFs for eccentric cracks were difficult to obtain. Therefore, this paper presented the SIFs for eccentric cracks subjected to mode I tension loading. Three important parameters were used such as relative crack depth, a/L, relative offset distance, b/L and elastic mismatch, E1/E2 or α. It was found that such parameters significantly affected the characteristic of SIFs and it was depend on the location of cracks
Characterizing and Modeling Brittle Bi-material Interfaces Subjected to Shear
Anyfantis, Konstantinos N.; Berggreen, Christian
2014-12-01
This work is based on the investigation, both experimentally and numerically, of the Mode II fracture process and bond strength of bondlines formed in co-cured composite/metal joints. To this end, GFRP-to-steel double strap joints were tested in tension, so that the bi-material interface was subjected to shear with debonding occurring under Mode II conditions. The study of the debonding process and thus failure of the joints was based both on stress and energy considerations. Analytical formulas were utilized for the derivation of the respective shear strength and fracture toughness measures which characterize the bi-material interface, by considering the joint's failure load, geometry and involved materials. The derived stress and toughness magnitudes were further utilized as the parameters of an extrinsic cohesive law, applied in connection with the modeling the bi-material interface in a finite element simulation environment. It was concluded that interfacial fracture in the considered joints was driven by the fracture toughness and not by strength considerations, and that LEFM is well suited to analyze the failure of the joint. Additionally, the double strap joint geometry was identified and utilized as a characterization test for measuring the Mode II fracture toughness of brittle bi-material interfaces.
Power-logarithmic stress singularities and the coefficient vectors for V-notched cracks in a bi-material are obtained by using complex potentials and the concept of repeated roots for general solutions. On several examples, it is shown that the results obtained using the complex potential approach are identical to those found by Bogy (1970) using the Mellin transform method, and to those found by Dempsey and Sinclair (1979, 1981) using the Airy stress function approach
Vellender, A; Movchan, A B
2011-01-01
We define a weight function in a bi-material strip containing a semi-infinite crack and an imperfect interface and analyse a problem of anti-plane shear. We then present an asymptotic algorithm which uses the weight function to evaluate the coefficients in asymptotics of solutions to problems of wave propagation in a thin bi-material strip containing a periodic array of cracks situated at the interface between two materials.
Crack propagation from bi-material notches – matched asymptotic procedure
Klusák, Jan; Profant, T.; Ševeček, O.; Kotoul, M.
488-489, - (2012), s. 416-419. ISSN 1013-9826. [International Conference on Fracture and Damage Mechanics - FDM 2011 /10./. Dubrovník, 19.09.2011-21.09.2011] R&D Projects: GA ČR GAP108/10/2049 Institutional research plan: CEZ:AV0Z20410507 Keywords : Orthotropic bi-material notch * two-state integral * matched asymptotic expansion Subject RIV: JL - Materials Fatigue, Friction Mechanics
Interface Mechanics of Bi-Material Beams and its Application: A Review%双材料梁界面力学及其应用:综述
乔丕忠; 刘庆辉
2016-01-01
A bi-material or bi-layer structure is increasingly used in various engineering applications,such as thin film coating,piezoelectric materials,composite laminates and sandwiches,adhesive joints,concrete structures strengthed by FRP,etc.However,interface fracture or interlaminar delamination is one of the most common failure modes in this type of layered structures.In general,damage mechanics (stress-based methods) is used to predict the initiation of delamination,followed by fracture mechanics which can be applied to describe the propagation of existing delamination/debond or crack.Thus,it is essential to predict the stresses in the adhesive layer of intact bi-material system and analyze the fracture and other related characteristics of bi-material structures with delamination.First,the models in the stress analysis of the adhesively bonded bi-material beams were summarized,thus laying the foundation for the delamination initiation prediction.Then,the basic approaches in the fracture mechanics analysis of bi-material beams were reviewed.Furthermore,the crack tip method in obtaining the fracture parameters were briefly introduced,with a focus on the effect of crack-tip deformation.Finally,the effects of interface delamination on other mechanical behaviors,e.g.,buckling and vibration,were introduced.%双材料结构在工程中得到了广泛应用,如薄膜涂层、压电材料、复合材料层合板和夹层板、粘结接头、FRP加固混凝土结构等;然而,这些结构的破坏通常是从界面及其附近开始的.通常利用损伤力学的方法(材料强度的方法)来预测裂纹的萌生,利用断裂力学的方法来预测裂纹的扩展;因此,开展双材料结构的界面应力分析和具分层双材料结构的断裂以及相关分析是至关重要的.首先介绍双材料梁粘结界面应力分析的基本模型,从而为预测裂纹的萌生提供了有力工具.然后综述双材料梁界面断裂力学分析的基本方法,并详细介
Klusák, Jan; Hrstka, M.; Profant, T.; Krepl, Ondřej; Ševeček, O.; Kotoul, M.
2014-01-01
Roč. 71, JUN (2014), s. 67-75. ISSN 0167-8442 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0068; GA ČR GA14-11234S Institutional support: RVO:68081723 Keywords : Bi-material notch * Crack initiation direction * Non-singular stress term * Generalized fracture mechanics * Path-independent integral Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.262, year: 2014
Interface cracks in piezoelectric materials
Govorukha, V.; Kamlah, M.; Loboda, V.; Lapusta, Y.
2016-02-01
Due to their intrinsic electromechanical coupling behavior, piezoelectric materials are widely used in sensors, actuators and other modern technologies. It is well known that piezoelectric ceramics are very brittle and susceptible to fracture. In many cases, fracture occurs at interfaces as debonding and cracks. This leads to an undesired degradation of electrical and mechanical performance. Because of the practical and fundamental importance of the problem, interface cracks in piezoelectric materials have been actively studied in the last few decades. This review provides a comprehensive survey of recent works on cracks situated at the interface of two materials, at least one of which has piezoelectric or piezoelectromagnetic properties. Different electric boundary conditions along the crack faces are discussed. The oscillating and contact zone models for in-plane straight interface cracks between two dissimilar piezoelectric materials or between piezoelectric and non-piezoelectric ones are reviewed. Different peculiarities related to the investigation of interface cracks in piezoelectric materials for the anti-plane case, for functionally graded and thermopiezoelectric materials are presented. Papers related to magnetoelectroelastic bimaterials, to steady state motion of interface cracks in piezoelectric bimaterials and to circular arc-cracks at the interface of piezoelectric materials are reviewed, and various methods used to address these problems are discussed. The review concludes with an outlook on future research directions.
ZHAO Ming-hao; LI Dong-xia; SHEN Ya-peng
2005-01-01
The integral-differential equations for three-dimensional planar interfacial cracks of arbitrary shape in transversely isotropic bimaterials were derived by virtue of the Somigliana identity and the fundamental solutions, in which the displacement discontinuities across the crack faces are the unknowns to be determined. The interface is parallel to both the planes of isotropy. The singular behaviors of displacement and stress near the crack border were analyzed and the stress singularity indexes were obtained by integral equation method. The stress intensity factors were expressed in terms of the displacement discontinuities. In the non-oscillatory case, the hyper-singular boundary integral-differential equations were reduced to hyper-singular boundary integral equations similar to those of homogeneously isotropie materials.
Characterizing and Modeling Brittle Bi-material Interfaces Subjected to Shear
Anyfantis, Konstantinos; Berggreen, Christian
2014-01-01
This work is based on the investigation, both experimentally and numerically, of the Mode II fracture process and bond strength of bondlines formed in co-cured composite/metal joints. To this end, GFRP-to-steel double strap joints were tested in tension, so that the bimaterial interface was...
Nonlinear finite element analysis of crack growth at the interface of rubber-like bimaterials
Yang, Xiaoxiang; Fu, Mingwang; Wang, Xiurong; Liu, Xiaoying
2011-10-01
This paper presents the characteristics of the crack growth at the interface of rubber-rubber and rubber-steel bimaterials under tensile deformation using the non-linear finite element method. By using the commercial finite element software ABAQUS, the J integral calculations are carried out for the initial interface crack in the interfaces in-between two Neo-Hookean materials, two Mooney-Rivlin materials, Neo-Hookean and Mooney-Rivlin rubbers, Neo-Hookean and Polynomial, Mooney-Rivlin and Polynomial, and the Mooney-Rivlin and steel bi-materials. The computational results of the maximum J integral direction around the crack tip illustrate the possible direction of crack growth initiation. Furthermore, it is found that the crack bends to the softer rubber material at a certain angle with the initial crack direction if the crack depth is relatively small. For the crack with a larger depth, the crack propagates to grow along the interface in-between the bimaterials.
In this study, criterions are proposed to describe crack initiation in the vicinity of an interface in brittle bi-materials. The purpose is to provide a guide for the elaboration of ceramic multi-layer structures being able to develop damage tolerance by promoting crack deflection along interfaces. Several cracking mechanisms are analyzed, like the competition between the deflection of a primary crack along the interface or its penetration in the second layer. This work is first completed in a general case and is then used to describe the crack deviation at the interface in ceramic matrix composites and nuclear fuels. In this last part, experimental tests are carried out to determine the material fracture properties needed to the deflection criteria. An optimization of the fuel coating can be proposed in order to increase its toughness. (author)
Acoustic emission assessment of interface cracking in thermal barrier coatings
Yang, Li; Zhong, Zhi-Chun; Zhou, Yi-Chun; Zhu, Wang; Zhang, Zhi-Biao; Cai, Can-Ying; Lu, Chun-Sheng
2016-04-01
In this paper, acoustic emission (AE) and digital image correlation methods were applied to monitor interface cracking in thermal barrier coatings under compression. The interface failure process can be identified via its AE features, including buckling, delamination incubation and spallation. According to the Fourier transformation of AE signals, there are four different failure modes: surface vertical cracks, opening and sliding interface cracks, and substrate deformation. The characteristic frequency of AE signals from surface vertical cracks is 0.21 MHz, whilst that of the two types of interface cracks are 0.43 and 0.29 MHz, respectively. The energy released of the two types of interface cracks are 0.43 and 0.29 MHz, respectively. Based on the energy released from cracking and the AE signals, a relationship is established between the interface crack length and AE parameters, which is in good agreement with experimental results.
Fracture mechanics parameters for cracks on a slightly undulating interface
Yang, Lin; Qu, Jianmin
1993-11-01
Typical bimaterial interfaces are nonplanar due to surface facets or roughness. Crack-tip stress fields of an interface crack must be influenced by nonplanarity of the interface. Consequently, interface toughness is affected. The crack-tip fields of a finite crack on an elastic/rigid interface with periodic undulation are studied. Particular emphasis is given to the fracture mechanics parameters, such as the stress intensity factors, crack-tip energy release rate, and crack-tip mode mixity. When the amplitude of interface undulation is very small relative to the crack length (which is the case for rough interfaces), asymptotic analysis is used to convert the nonplanarity effects into distributed dislocations located on the planar interface. Then, the resulting stress fields near the crack tip are obtained by using the Fourier integral transform method. It is found that the stress fields at the crack tip are strongly influenced by nonplanarity of the interface. Generally speaking, nonplanarity of the interface tends to shield the crack tip by reducing the crack-tip stress concentration.
Steady-state propagation of interface corner crack
Veluri, Badrinath; Jensen, Henrik Myhre
2013-01-01
Steady-state propagation of interface cracks close to three-dimensional corners has been analyzed. Attention was focused on modeling the shape of the interface crack front and calculating the critical stress for steady-state propagation of the crack. The crack propagation was investigated by...... estimating the fracture mechanics parameters that includes the strain energy release rate, crack front profiles and the three-dimensional mode-mixity along the interface crack front. A numerical approach was then applied for coupling the far field solutions based on the Finite Element Method to the near...... field (crack tip) solutions based on the J-integral. The adopted two-dimensional numerical approach for the calculation of fracture mechanical properties was compared with three-dimensional models for quarter-circular and straight sided crack front shapes. A quantitative approach was formulated based on...
Accelerated fatigue crack growth simulation in a bimaterial interface
Moslemian, Ramin; Karlsson, A.M.; Berggreen, Christian
2011-01-01
A method for accelerated simulation of fatigue crack growth in a bimaterial interface (e.g. in a face/core sandwich interface) is proposed. To simulate fatigue crack growth, a routine is incorporated in the commercial finite element program ANSYS and a method to accelerate the simulation is...
Poitou, B
2007-11-15
In this study, criterions are proposed to describe crack initiation in the vicinity of an interface in brittle bi-materials. The purpose is to provide a guide for the elaboration of ceramic multi-layer structures being able to develop damage tolerance by promoting crack deflection along interfaces. Several cracking mechanisms are analyzed, like the competition between the deflection of a primary crack along the interface or its penetration in the second layer. This work is first completed in a general case and is then used to describe the crack deviation at the interface in ceramic matrix composites and nuclear fuels. In this last part, experimental tests are carried out to determine the material fracture properties needed to the deflection criteria. An optimization of the fuel coating can be proposed in order to increase its toughness. (author)
Effect of anisotropic plasticity on mixed mode interface crack growth
Tvergaard, Viggo; Legarth, Brian Nyvang
2007-01-01
region analyzed. Crack growth resistance curves are calculated numerically, and based on these results the dependence of the steady-state fracture toughness on the near-tip mode mixity is determined. Different initial orientations of the principal axes relative to the interface are considered and it is......Crack growth along an interface between a solid with plastic anisotropy and an elastic substrate is modelled by representing the fracture process in terms of a traction–separation law specified on a crack plane. A phenomenological elastic–viscoplastic material model is applied, using one of two...
Fracture Mechanics Analyses for Interface Crack Problems - A Review
Krueger, Ronald; Shivakumar, Kunigal; Raju, Ivatury S.
2013-01-01
Recent developments in fracture mechanics analyses of the interfacial crack problem are reviewed. The intent of the review is to renew the awareness of the oscillatory singularity at the crack tip of a bimaterial interface and the problems that occur when calculating mode mixity using numerical methods such as the finite element method in conjunction with the virtual crack closure technique. Established approaches to overcome the nonconvergence issue of the individual mode strain energy release rates are reviewed. In the recent literature many attempts to overcome the nonconvergence issue have been developed. Among the many approaches found only a few methods hold the promise of providing practical solutions. These are the resin interlayer method, the method that chooses the crack tip element size greater than the oscillation zone, the crack tip element method that is based on plate theory and the crack surface displacement extrapolation method. Each of the methods is validated on a very limited set of simple interface crack problems. However, their utility for a wide range of interfacial crack problems is yet to be established.
Molecular modeling of cracks at interfaces in nanoceramic composites
Pavia, F.; Curtin, W. A.
2013-10-01
Toughness in Ceramic Matrix Composites (CMCs) is achieved if crack deflection can occur at the fiber/matrix interface, preventing crack penetration into the fiber and enabling energy-dissipating fiber pullout. To investigate toughening in nanoscale CMCs, direct atomistic models are used to study how matrix cracks behave as a function of the degree of interfacial bonding/sliding, as controlled by the density of C interstitial atoms, at the interface between carbon nanotubes (CNTs) and a diamond matrix. Under all interface conditions studied, incident matrix cracks do not penetrate into the nanotube. Under increased loading, weaker interfaces fail in shear while stronger interfaces do not fail and, instead, the CNT fails once the stress on the CNT reaches its tensile strength. An analytic shear lag model captures all of the micromechanical details as a function of loading and material parameters. Interface deflection versus fiber penetration is found to depend on the relative bond strengths of the interface and the CNT, with CNT failure occurring well below the prediction of the toughness-based continuum He-Hutchinson model. The shear lag model, in contrast, predicts the CNT failure point and shows that the nanoscale embrittlement transition occurs at an interface shear strength scaling as τs~ɛσ rather than τs~σ typically prevailing for micron scale composites, where ɛ and σ are the CNT failure strain and stress, respectively. Interface bonding also lowers the effective fracture strength in SWCNTs, due to formation of defects, but does not play a role in DWCNTs having interwall coupling, which are weaker than SWCNTs but less prone to damage in the outerwall.
Alexandrov, Sergei; Goldstein, Robert
2016-04-01
The main objective of the present paper is to compare, by means of a problem permitting a closed-form solution, qualitative behavior of solutions based on three models of strain hardening plasticity and two models of viscoplasticity. The elastic portion of the strain tensor is neglected. The study focuses on the solution behavior near frictional interfaces. The solution behavior essentially depends on the model chosen. Such features of the solutions as nonexistence and singularity are emphasized. The key constitutive parameter that divides all the models considered into two groups is the saturation stress. In particular, under certain conditions no solution satisfying the regime of sticking exists for the models that involve the saturation stress. Qualitative comparison with numerous experimental observations is made. It is concluded that models with a saturation stress, including the models considered in the present paper, may be capable of describing the generation of a narrow layer of severe plastic deformation in the vicinity of frictional interfaces.
A new node-pairs contact algorithm is proposed to deal with a composite material or bi-material interface crack face contact and friction problem (e.g., resistant coating and thermal barrier coatings) subjected to complicated load conditions. To decrease the calculation scale and calculation errors, the local Lagrange multipliers are solved only on a pair of contact nodes using the Jacobi iteration method, and the constraint modification of the tangential multipliers are required. After the calculation of the present node-pairs Lagrange multiplier, it is turned to next contact node-pairs until all node-pairs have finished. Compared with an ordinary contact algorithm, the new local node-pairs contact algorithm is allowed a more precise element on the contact face without the stiffness matrix singularity. The stress intensity factors (SIFs) and the contact region of an infinite plate central crack are calculated and show good agreement with those in the literature. The contact zone near the crack tip as well as its influence on singularity of stress fields are studied. Furthermore, the frictional contacts are also considered and found to have a significant influence on the SIFs. The normalized mode-II stress intensity factors KII for the friction coefficient decrease by 16% when f changes from 1 to 0
Nonlinear Scattering from Partially Closed Cracks and Imperfect Interfaces
This project has investigated the potential offered by nonlinear scattering phenomena to detect stress-corrosion, surface-breaking cracks, and regions of extended interfaces which are often invisible to conventional inspection methods because of their partial closure and/or the high background noise generated by the surrounding microstructure. The investigation has looked into the basic physics of the interaction between ultrasonic waves and rough surfaces in contact, since the latter offers a prototypical example of a mechanical system which is characterized by a dynamics similar to that of a partially closed crack. To this end, three fundamental mechanisms which may be activated by an inspecting ultrasonic wave have been considered. The first mechanism is described by the Hertz force law which governs the interaction between asperities in contact that are subjected to a normal load. The second mechanism considers the dynamics of two spherical asperities subjected to an oscillating tangential load. To this end, the model developed by Mindlin and Deresiewizc has been used. The third mechanism accounts for the effect of forces of adhesion, and can be described by a model developed by Greenwood and Johnson. The validity of this model is rather general and covers the extreme cases of very soft and very rigid contacts. This model aims at describing the effect of fluid layers with thickness of atomic size, which may be present within a crack. Statistical models accounting for the topography of the two rough surfaces in contact have been developed, and the macroscopic stiffness of the interface recovered. These results have been used to formulate effective boundary conditions to be enforced at the interface, and the reflection and transmission problem has been solved in a variety of situations of experimental significance. The main conclusion of this part of the project is that the second harmonic component is the dominant feature of the nonlinear response of an
WEIGHT FUNCTIONS FOR INTERFACE CRACKS IN DISSIMILAR ANISOTROPIC MATERIALS
MA Lifeng; CHEN Yiheng
2004-01-01
Bueckner's work conjugate integral customarily adopted for linear elastic materials is established for an interface crack in dissimilar anisotropic materials. The difficulties in separating Stroh's six complex arguments involved in the integral for the dissimilar materials are overcome and then the explicit function representations of the integral are given and studied in detail. It is found that the pseudo-orthogonal properties of the eigenfunction expansion form (EEF) for a crack presented previously in isotropic elastic cases, in isotopic bimaterial cases, and in orthotropic cases are also valid in the present dissimilar arbitrary anisotropic cases. The relation between Bueckner's work conjugate integral and the J-integral in these cases is obtained by introducing a complementary stressdisplacement state. Finally, some useful path-independent integrals and weight functions are proposed for calculating the crack tip parameters such as the stress intensity factors.
Zouhar, Michal; Hutař, Pavel; Náhlík, Luboš; Ševčík, Martin; Knésl, Zdeněk
2012-01-01
Roč. 19, 2/3 (2012), s. 155-164. ISSN 1802-1484 R&D Projects: GA ČR(CZ) GAP107/10/0361; GA ČR(CZ) GAP108/12/1560 Institutional support: RVO:68081723 Keywords : stability criterion * critical distance * bi-material interface Subject RIV: JL - Materials Fatigue, Friction Mechanics
Crack stability condition at the interface between two polymer materials
Zouhar, Michal; Hutař, Pavel; Náhlík, Luboš; Ševčík, Martin; Knésl, Zdeněk
Brno, Česká republika : Institute of Physics of Materials , Academy of Sciences of the Czech Republic, 2011 - (Náhlík, L.; Zouhar, M.; Ševčík, M.; Seitl, S.; Majer, Z.), s. 247-250 ISBN 978-80-87434-03-1. [ Applied Mechanics 2011. Velké Bílovice (CZ), 18.04.2011-20.04.2011] R&D Projects: GA ČR GA106/09/0279 Institutional research plan: CEZ:AV0Z20410507 Keywords : stability criterion * critical distance * bi-material * generalized stress intensity factor Subject RIV: JL - Materials Fatigue, Friction Mechanics
Analyses of crack growth along interface of patterned wafer-level Cu-Cu bonds
Tvergaard, Viggo; Hutchinson, John W.
2009-01-01
computational model provides the resistance curve of macroscopic crack driving force versus crack advance as dependent on the work of separation and strength of the interface as well as the pattern geometry and the parameters controlling the plasticity of the Cu films. Plasticity in the Cu films makes a major...... with lines of unbonded interface, all aligned parallel to the crack front. The interface toughness model employs a cohesive zone to represent separation of the interface and J(2) flow theory of plasticity to characterize the Cu films. Remote mode I loading is imposed on the elastic Si substrates. The...
Predictions of mixed mode interface crack growth using a cohesive zone model for ductile fracture
Tvergaard, Viggo
2004-01-01
here extended to cover non-symmetric mixed mode loading conditions for crack growth along an interface between dissimilar elastic-plastic solids. Crack growth resistance curves are calculated, and the dependence of the interface fracture toughness on the degree of mode mixity is studied. (C) 2003......Special interface elements that account for ductile failure by the nucleation and growth of voids to coalescence are used to analyse crack growth. In these elements the stress component tangential to the interface is accounted for, as determined by the requirement of compatibility with the...
Crack Growth along Interfaces in Porous Ceramic Layers
Sørensen, Bent F.; Horsewell, Andy
2001-01-01
Crack growth along porous ceramic layers was studied experimentally. Double cantilever beam sandwich specimens were loaded with pure bending moments to obtain stable crack growth. The experiments were conducted in an environmental scanning electron microscope enabling in situ observations of...
Interface debond crack growth in tension–tension cyclic loading of single fiber polymer composites
Pupurs, Andrejs; Goutianos, Stergios; Brøndsted, Povl;
2013-01-01
Fiber/matrix interface debond crack growth from a fiber break is defined as one of the key mechanisms of fatigue damage in unidirectional composites. Considering debond as an interface crack its growth in cyclic loading is analyzed utilizing a power law, where the debond growth rate is a power...... glass fiber/epoxy single fiber composites. Analytical method in the steady-state growth region and FEM for short debonds are combined for calculating the strain energy release rate of the growing debond crack. Interface failure parameters in fatigue are determined by fitting the modeling and...
In-situ observations on crack propagation along polymer/glass interfaces.
Vellinga, W.P; Timmerman, R.; van Tijum, R.; de Hosson, J.T.M.; Buchheit, TE; Minor, AM; Spolenak, R; Takashima, K
2005-01-01
The propagation of crack fronts along a PET-glass interface is illustrated. The experimental set-up consists of an Asymmetric Double Cantilever Beam in an optical microscope. Image processing techniques used to isolate the crack fronts are discussed in some detail. The fronts are found to propagate
Effect of T-stress on crack growth along an interface between ductile and elastic solids
Tvergaard, Viggo
2003-01-01
For crack growth along an interface joining an elastic-plastic solid to an elastic substrate the effect of a non-singular stress component in the crack growth direction in the elastic-plastic solid is investigated. Conditions of small scale yielding are assumed, and due to the mismatch of elastic...
Interface fatigue crack propagation in sandwich X-joints – Part I: Experiments
Moslemian, Ramin; Berggreen, Christian
2013-01-01
/core interface of the joints. Sandwich tear test specimens with a face/core debond representing a debonded sandwich X-joint were tested under cyclic loading. Fatigue tests were conducted on the sandwich tear test specimens with H45, H100 and H250 PVC cores and glass/polyester face sheets. The Digital Image...... interface. The interface crack eventually kinked into the face sheet, resulting in large-scale fiber bridging. Finally, mixed mode bending tests were conducted to measure crack growth rates of the face/core interface at mode-mixity phase angles similar to those calculated for the sandwich tear test...
LIU Diankui; LIN Hong
2004-01-01
An analytical method is developed for scattering of SH-waves and dynamic stress concentration by an interacting interface crack and a circular cavity near bimaterial interface. A suitable Green's function is contructed, which is the fundamental solution of the displacement field for an elastic half space with a circular cavity impacted by an out-plane harmonic line source loading at the horizontal surface. First, the bimaterial media is divided into two parts along the horizontal interface, one is an elastic half space with a circular cavity and the other is a complete half space.Then the problem is solved according to the procedure of combination and by the Green's function method. The horizontal surfaces of the two half spaces are loaded with undetermined anti-plane forces in order to satisfy continuity conditions at the linking section, or with some forces to recover cracks by means of crack-division technique. A series of Fredholm integral equations of first kind for determining the unknown forces can be set up through continuity conditions as expressed in terms of the Green's function. Moreover, some expressions are given in this paper, such as dynamic stress intensity factor (DSIF) at the tip of the interface crack and dynamic stress concentration factor (DSCF) around the circular cavity edge. Numerical examples are provided to show the influences of the wave numbers,the geometrical location of the interface crack and the circular cavity, and parameter combinations of different media upon DSIF and DSCF.
Effect of residual stresses on interface crack growth by void expansion mechanism
Tvergaard, Viggo
Crack growth along an interface between two adjacent elastic-plastic materials in a layered solid is analysed, using special interface elements to represent the fracture process ahead of the crack-tip. These interface elements account for ductile failure by the nucleation and growth of voids to...... coalescence. In these elements the stress components normal to the interface and the shear stresses are given by equilibrium with the surrounding material, and the stress component tangential to the interface is determined by the requirement of compatibility with the surrounding material in the tangential...... direction. It is assumed that the layers are sufficiently thick, so that the plastic regions around the crack-tip are much smaller than the thickness of the nearest layers. The analyses focus on the effect of initial residual stresses in the layered material, or on T-stress components induced during loading...
P.O. Judt
2015-10-01
Full Text Available In many engineering applications special requirements are directed to a material's fracture behavior and the prediction of crack paths. Especially if the material exhibits anisotropic elastic properties or fracture toughnesses, e.g. in textured or composite materials, the simulation of crack paths is challenging. Here, the application of path independent interaction integrals (I-integrals, J-, L- and M-integrals is beneficial for an accurate crack tip loading analysis. Numerical tools for the calculation of loading quantities using these path-invariant integrals are implemented into the commercial finite element (FE-code ABAQUS. Global approaches of the integrals are convenient considering crack tips approaching other crack faces, internal boundaries or material interfaces. Curved crack faces require special treatment with respect to integration contours. Numerical crack paths are predicted based on FE calculations of the boundary value problem in connection with an intelligent adaptive re-meshing algorithm. Considering fracture toughness anisotropy and accounting for inelastic effects due to small plastic zones in the crack tip region, the numerically predicted crack paths of different types of specimens with material interfaces and internal boundaries are compared to subcritically grown paths obtained from experiments.
Klusák J.
2009-12-01
Full Text Available The study of bi-material notches becomes a topical problem as they can model efficiently geometrical or material discontinuities. When assessing crack initiation conditions in the bi-material notches, the generalized stress intensity factors H have to be calculated. Contrary to the determination of the K-factor for a crack in an isotropic homogeneous medium, for the ascertainment of the H-factor there is no procedure incorporated in the calculation systems. The calculation of these fracture parameters requires experience. Direct methods of estimation of H-factors need choosing usually length parameter entering into calculation. On the other hand the method combining the application of the reciprocal theorem (Ψ-integral and FEM does not require entering any length parameter and is capable to extract the near-tip information directly from the far-field deformation.
Study of Composite Interface Fracture and Crack Growth Monitoring Using Carbon Nanotubes
Bily, Mollie A.; Kwon, Young W.; Pollak, Randall D.
2010-08-01
Interface fracture of woven fabric composite layers was studied using Mode II fracture testing. Both carbon fiber and E-glass fiber composites were used with a vinyl ester resin. First, the single-step cured (i.e., co-cured) composite interface strength was compared to that of the two-step cured interface as used in the scarf joint technique. The results showed that the two-step cured interface was as strong as the co-cured interface. Carbon nanotubes were then applied to the composite interface using two-step curing, and then followed by Mode II fracture testing. The results indicated a significant improvement of the interface fracture toughness due to the dispersed carbon nanotube layer for both carbon fiber and E-glass fiber composites. The carbon nanotube layer was then evaluated as a means to monitor crack growth along the interface. Because carbon nanotubes have very high electrical conductivity, the electrical resistance was measured through the interface as a crack grew, thus disrupting the carbon nanotube network and increasing the resistance. The results showed a linear relationship between crack length and interface resistance for the carbon fiber composites, and allowed initial detection of failure in the E-glass fiber composites. This study demonstrated that the application of carbon nanotubes along a critical composite interface not only improves fracture properties but can also be used to detect and monitor interfacial damage.
Analysis of a permeable interface crack in elastic dielectric/piezoelectric bimaterials
Qun Li; Yiheng Chen
2007-01-01
A permeable interface crack between elastic dielectric material and piezoelectric material is studied based on the extended Stroh's formalism. Motivated by strong engi-neering demands to design new composite materials, the authors perform numerical analysis of interface crack tip sin-gularities and the crack tip energy release rates for 35 types of dissimilar bimaterials, respectively, which are constructed by five kinds of elastic dielectric materials: Epoxy, Poly-mer, A1203, SiC, and Si3N4 and seven kinds of practical piezoelectric ceramics: PZT-4, BaTiO3, PZT-5H, PZT-6B,PZT-7A, P-7, and PZT-PIC 151, respectively. The elastic dielectric material with much smaller permittivity than com-mercial piezoelectric ceramics is treated as a special trans-versely isotropic piezoelectric material with extremely small piezoelectricity. The present investigation shows that the structure of the singular field near the permeable interface crack tip consists of three singularities: r-1/2±iε and r-1/2,which is quite different from that in the impermeable inter-face crack. It can be concluded that different far field load-ing cases have significant influence on the near-tip fracture behaviors of the permeable interface crack. Based on the present theoretical treatment and numerical analysis, the elec-tric field induced crack growth is well explained, which pro-vides a better understanding of the failure mechanism induced from interface crack growth in elastic dielectric/piezoelectric bimaterials.
Numerical investigation of the stress field near a crack normal to ceramic.metal interface
Ceramic.metal interfaces are often present in composite materials. The presence of cracks has a major impact on the reliability of advanced materials, such as fiber or particle reinforced ceramic composites, ceramic interfaces and laminated ceramics. The understanding of the failure mechanisms is very important, as is as the estimation of fracture parameters at the tip of the crack approaching an interface and crack propagation path. A cracked sandwich plate loaded with axial uniform normal stress was numerically investigated using plane strain Finite Element Analysis. The numerical results for the singularity orders were compared with the analytical solution. The influences of the material combination and crack length on the radial and circumferential stresses and displacement distributions were investigated. The Stress Intensity Factors were determined based on numerical results using a displacement extrapolation method. The results for the non-dimensional stress intensity factors show that at lower crack lengths the influence of material mismatch is lower, but this influence increases with increasing crack length
Khatun, Tajkera; Dutta, Tapati; Tarafdar, Sujata
2015-08-01
We study the crack patterns developed on desiccating films of suspensions of three different clays-bentonite, halloysite nanoclay and laponite on a glass substrate. Varying the thickness of the layer, h gives the following new and interesting results: i) We can identify a critical thickness h c for bentonite and halloysite, above which isolated cracks join each other to form a fully connected network. ii) A topological analysis involving the Euler number is shown to be useful for characterising the patterns. iii) We find, further, that the total vertical surface area of the clay A v, which has opened up due to cracking, and the total area of the glass substrate A s, exposed by the hierarchical sequence of cracks are constant, independent of the layer thickness for a certain range of h. These results are shown to be consistent with a simple energy conservation argument, neglecting dissipative losses. Finally we show that if the crack pattern is viewed at successively finer resolution, the total cumulative area of cracks visible at a certain resolution scales with the layer thickness. PMID:26248703
Thermal sensitivity analysis of curved bi-material microcantilevers
Thermal sensitivity of bi-material microcantilevers plays a crucial role in temperature sensors and thermal actuators. Thermal loading experiments on bi-material microcantilevers show the dependence of thermal sensitivity on microcantilever curvature and width which is not addressed by currently used analytical models. In this work, a new thermal sensitivity model for curved bi-material microcantilevers is presented which correlates such dependence to the increase of microcantilever flexural rigidity caused by transverse curvature. The new model is validated against the results of thermal loading experiments carried out on gold-polysilicon and SU-8/silicon nitride bi-material microcantilevers with different widths and initial curvatures. (paper)
Interface crack growth for anisotropic plasticity with non-normality effects
Tvergaard, Viggo; Legarth, Brian Nyvang
2007-01-01
an oscillating stress singularity, and with conditions of small scale yielding this solution is applied as boundary conditions on the outer edge of the region analyzed. Crack growth resistance curves are calculated numerically, and the effect of the near-tip mode mixity on the steady-state fracture......A plasticity model with a non-normality plastic flow rule is used to analyze crack growth along an interface between a solid with plastic anisotropy and an elastic substrate. The fracture process is represented in terms of a traction-separation law specified on the crack plane. A phenomenological...
Prediction of crack propagation in layered ceramics with strong interfaces
Náhlík, Luboš; Šestáková, L.; Hutař, Pavel; Bermejo, R.
2010-01-01
Roč. 77, č. 11 (2010), s. 2192-2199. ISSN 0013-7944 R&D Projects: GA AV ČR(CZ) KJB200410803; GA ČR GA101/09/1821 Institutional research plan: CEZ:AV0Z20410507 Keywords : Ceramic laminate * Crack propagation direction * Residual stress * Flaw tolerant ceramics * Optimal design Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.571, year: 2010
Barthel E.
2010-06-01
Full Text Available Adhesion of thin film multilayers deposited on glass is a crucial issue for many industrial applications. Thus, it becomes of great interest to measure and also to increase the adhesion. Many mechanisms of toughening a brittle solid can be found in literature; but few of them can be applied to thin film layer. By introducing a heterogeneous interfacial toughness field, it should be possible to increase adhesion. This toughness modification would be the consequence of the existence of a pinning regime due to a local change of the toughness. To experimentally validate this new approach of adhesion modification, we investigate the crack front pinning by performing cleavage tests on multilayer coated samples with a heterogeneous interfacial toughness. We have tested different patterns of pinning region. The crack front morphology was nicely described in the framework of the perturbative approach initially developed by Gao and Rice and allowed us to determine the local value of the energy release rate (~adhesion.
Lu, M. C.; Erdogan, F.
1980-01-01
The basic crack problem which is essential for the study of subcritical crack propagation and fracture of layered structural materials is considered. Because of the apparent analytical difficulties, the problem is idealized as one of plane strain or plane stress. An additional simplifying assumption is made by restricting the formulation of the problem to crack geometries and loading conditions which have a plane of symmetry perpendicular to the interface. The general problem is formulated in terms of a coupled system of four integral equations. For each relevant crack configuration of practical interest, the singular behavior of the solution near and at the ends and points of intersection of the cracks is investigated and the related characteristic equations are obtained. The edge crack terminating at and crossing the interface, the T-shaped crack consisting of a broken layer and a delamination crack, the cross-shaped crack which consists of a delamination crack intersecting a crack which is perpendicular to the interface, and a delamination crack initiating from a stress-free boundary of the bonded layers are some of the practical crack geometries considered.
Interface crack between a compressible elastomer and a rigid substrate with finite slippage
Lengyel, Tamran H.; Qi, Yuan; Schiavone, Peter; Long, Rong
2016-05-01
We study the deformation of a crack between a soft elastomer and a rigid substrate with finite interfacial slippage. It is assumed that slippage occurs when the interfacial shear traction exceeds a threshold. This leads to a slip zone ahead of the crack tip where the shear traction is assumed to be equal to the constant threshold. We perform asymptotic analysis and determine closed-form solutions describing the near-tip crack opening displacement and the corresponding stress distributions. These solutions are consistent with numerical results based on finite element analysis. Our results reveal that slippage can significantly affect the deformation and stress fields near the tip of the interface crack. Specifically, depending on the direction of slippage, the crack opening profile may appear more blunted or sharpened than the parabola arising from for the case of zero interfacial shear traction or free slippage. The detailed crack opening profile is determined by the constant shear traction in the slip zone. More importantly, we find that the normal stress perpendicular to the interface can increase or decrease when slippage occurs, depending on the direction of slippage and the shear traction in the slip zone.
Analysis of Interface Properties of Hybrid Pre-stressed Strengthening RC Beams with Crack
zhihong, Xie; Peiyan, Huang; Yongchang, Guo; Jun, Deng; Genquan, Zhong
2010-05-01
A finite element (FE) analysis model of interface layer is established for the pre-stressed CFS-GFS hybrid strengthened beams. An elastic solution for the interfacial stress in the adhesive layer of the retrofitted beams is developed as well. The analytical results were compared with the FE results of interfacial stresses in the beams with different thickness of the adhesive and the fibre sheet. Different heights of Cracks in the interfacial layer of the concrete beam are considered in FE Model. Analysis results show the strengthening pattern is of excellent interface performance and the strength of the fiber sheet can be effectively utilized. The results also indicate the shear and normal stresses in the interfacial layer of the concrete beam release at the locations of the cracks and reach the maximal value before the concrete cracked. The shear and normal stresses in the adhesive layer increase abruptly, and the cracks in the adhesive layer then appear. The axial stresses of hybrid fiber sheet near the cracks decrease locally at the sites of the concrete cracks.
Analysis of Interface Properties of Hybrid Pre-stressed Strengthening RC Beams with Crack
A finite element (FE) analysis model of interface layer is established for the pre-stressed CFS-GFS hybrid strengthened beams. An elastic solution for the interfacial stress in the adhesive layer of the retrofitted beams is developed as well. The analytical results were compared with the FE results of interfacial stresses in the beams with different thickness of the adhesive and the fibre sheet. Different heights of Cracks in the interfacial layer of the concrete beam are considered in FE Model. Analysis results show the strengthening pattern is of excellent interface performance and the strength of the fiber sheet can be effectively utilized. The results also indicate the shear and normal stresses in the interfacial layer of the concrete beam release at the locations of the cracks and reach the maximal value before the concrete cracked. The shear and normal stresses in the adhesive layer increase abruptly, and the cracks in the adhesive layer then appear. The axial stresses of hybrid fiber sheet near the cracks decrease locally at the sites of the concrete cracks.
Estimation of stepwise crack propagation in ceramic laminates with strong interfaces
K. Štegnerová
2015-10-01
Full Text Available During the last years many researchers put so much effort to design layered structures combining different materials in order to improve low fracture toughness and mechanical reliability of the ceramics. It has been proven, that an effective way is to create layered ceramics with strongly bonded interfaces. After the cooling process from the sintering temperature, due to the different coefficients of thermal expansion of individual constituents of the composite, significant internal residual stresses are developed within the layers. These stresses can change the crack behaviour. This results to the higher value of so-called apparent fracture toughness, i.e. higher resistance of the ceramic laminate to the crack propagation. The contribution deals with a description of the specific crack behaviour in the layered alumina-zirconia ceramic laminate. The main aim is to clarify crack behaviour in the compressive layer and provide computational tools for estimation of crack behaviour in the field of strong residual stresses. The crack propagation was investigated on the basis of linear elastic fracture mechanics. Fracture parameters were computed numerically and by author’s routines. Finite element models were developed in order to obtain a stress distribution in the laminate containing a crack and to simulate crack propagation. The sharp change of the crack propagation direction was estimated using Sih’s criterion based on the strain energy density factor. Estimated crack behaviour is qualitatively in a good agreement with experimental observations. Presented approach contributes to the better understanding of the toughening mechanism of ceramic laminates and can be advantageously used for design of new layered ceramic composites and for better prediction of their failure.
On the path of a crack near a graded interface under large scale yielding
Rashid, M. M.; Tvergaard, Viggo
2003-01-01
The trajectory of a crack lying parallel to a thin graded layer between two plastically dissimilar materials is studied using the exclusion region (ER) theory of fracture. The ER theory is a theoretical framework for surface separation within which a broad range of fracture phenomenologies can be...... represented. In the present study, the direction of crack advance is determined by maximizing the resolved normal-opening force on the near-tip region, whereas separation itself is governed by the intensity of plastic deformation near the tip. A computational study was undertaken using the ER theory. The...... special-purpose finite element analysis platform accommodates arbitrary-and a priori unknown-crack trajectories. The model problem considered herein involves two plastically dissimilar, but elastically identical, materials joined by a thin, graded interface layer. The initial crack lies parallel to the...
Oscillatory Singularity Behaviors Near Interface Crack Tip for Mode II of Orthotropic Bimaterial
Xiaomei Yang
2013-01-01
Full Text Available The fracture behaviors near the interface crack tip for mode II of orthotropic bimaterial are discussed. The oscillatory singularity fields are researched. The stress functions are chosen which contain twelve undetermined coefficients and an unknown singularity exponent. Based on the boundary conditions and linear independence, the system of twelve nonhomogeneous linear equations is derived. According to the condition for the system of nonhomogeneous linear equations which has a solution, the singularity exponent is determined. Total coefficients are found by means of successive elimination of the unknowns. The theoretical formulae of stress intensity factors and analytic solutions of stress field near the interface crack tip are obtained. The crack tip field is shown by figures.
Analysis of mixed-mode fracture in concrete using interface elements and a cohesive crack model
Víctor O García-Álvarez; Ravindra Gettu; Ignacio Carol
2012-02-01
The paper presents a model, based on nonlinear fracture mechanics, for analysing crack propagation in quasi-brittle materials, such as concrete. The work is limited to two-dimensions, and therefore, the fracture modes of interest are mode I (pure tension) and mode II (pure shear). The constitutive model has been implemented in the context of the ﬁnite element method using interface elements. The fracture is simulated through a discrete crack represented by the interface with a cohesive crack stress-separation relation derived from the model, which is based on a fracture criterion, together with a ﬂow rule and a softening law. The model is used for simulating results from an experimental study on beams with centric and eccentric notches of high and normal strength concretes, and explaining other test results available in the literature.
Effect of fiber-matrix interface structure on crack stability of boron-aluminium
Experimental investigation into the effect produced by matrix-fiber interface structure in monodirected boron-aluminium samples on resistance to the propagation of the central crack perpendicular to the reinforcement direction, is conducted. Effect of interphase linking density structural parameter θ on the change of fracture toughness indices is evaluated
Abdi's numerical method(ref. 13) for representing a stress singularity by shifting the mid-side nodes of isoparametric elements is reviewed. A simple technique to obtain the optimal position of the mid-side nodes in quadratic isoparametric finite element is presented. From this technique we can directly obtain the position of the side-nodes adjacent to the crack tip. It is also observed that the present technique provides good accuracy for the expression of the opening displacement and the determination of the mid-side nodes for more wide range of material properties than that obtained by Abdi. And the finite element method is applied to determine stress intensity factors for pressurized crack perpendicular to and terminating at the interface of two bonded dissimilar materials. A proper definition for stress intensity factors of a crack perpendicular to bimaterial interface is provided. It is based upon a near-tip displacement solutions on the crack surface for interface crak between two dissimilar materials. Numerical testing is carried out with the eight-node and six-node elements. The results obtained are compared with the previous solutions. (Author)
Oscillatory Singularity Behaviors Near Interface Crack Tip for Mode II of Orthotropic Bimaterial
Junlin Li; Xuexia Zhang; Weiyang Yang; Xiaomei Yang
2013-01-01
The fracture behaviors near the interface crack tip for mode II of orthotropic bimaterial are discussed. The oscillatory singularity fields are researched. The stress functions are chosen which contain twelve undetermined coefficients and an unknown singularity exponent. Based on the boundary conditions and linear independence, the system of twelve nonhomogeneous linear equations is derived. According to the condition for the system of nonhomogeneous linear equations which has a solution, the...
Crack propagation in the vicinity of the interface between two elastic materials
Náhlík, Luboš; Šestáková, Lucie; Hutař, Pavel
Algérie: The Algerian Association for the Technology Transfer , 2008, s. 1-11. ISBN N. [Damage and Fracture Mechanics. Algérie (DZ), 01.06.2008-05.06.2008] R&D Projects: GA AV ČR(CZ) KJB200410803; GA ČR GP106/06/P239 Institutional research plan: CEZ:AV0Z20410507 Keywords : bimaterial interface * crack propagation direction * layered composites Subject RIV: JL - Materials Fatigue, Friction Mechanics
Crack propagation in the vicinity of the interface between two elastic materials
Náhlík, Luboš; Šestáková, Lucie; Hutař, Pavel
Milton Keynes : Springer Science + Business Media, 2009 - (Boukharouba, T.; Elboujdaini, M.; Pluvinage, G.), s. 255-263 ISBN 978-90-481-2668-2 R&D Projects: GA AV ČR(CZ) KJB200410803; GA ČR GP106/06/P239 Institutional research plan: CEZ:AV0Z20410507 Keywords : bimaterial interface * crack propagation direction * layered composites Subject RIV: JL - Materials Fatigue, Friction Mechanics
Initiation of interface crack at free edge between thin films with weak stress singularity
Delamination tests using sandwich type specimens are conducted for eight combinations of materials: thin films formed on silicon substrates which are relatively popular in micro-electronic industry, to develop a method for quantitative evaluation and comparison of crack initiation strength at the free edge. The difficulty stems from the difference of stress singularity, K ij/r λ (K ij: stress intensity, r: distance from free edge and λ: order of stress singularity), where λ is depending on the combination of materials. Thus, the critical K ij has different dimensions, MPa m λ, in each interface. Using the experimentally observed delamination load, the stress distribution along the interface is analyzed by boundary element method. Since the orders of stress singularity, λ, in the materials are less than 0.07 (weak singularity), the stress field near the interface edge is almost constant in atomic (nanometer) level. Then, the critical strength for the interface cracking is quantitatively represented by the concentrated stress near the edge. The effects of the several factors such as species of thin films, oxidized interlayers and deposition processes of thin films on the interface strength are evaluated on the basis of this critical stress as well
Mantič, V; Blázquez, A; Graciani, E; París, F
2013-01-01
The crack onset and propagation at the fibre-matrix interface in a composite under tensile/compressive remote biaxial transverse loads is studied by a new linear elastic - (perfectly) brittle interface model. In this model the interface is represented by a continuous distribution of springs which simulates the presence of a thin elastic layer. The constitutive law for the continuous distribution of normal and tangential of initially linear elastic springs takes into account possible frictionless elastic contact between fibre and matrix once a portion of the interface is broken. A brittle failure criterion is employed for the distribution of springs, which enables the study of crack onset and propagation. This interface failure criterion takes into account the variation of the interface fracture toughness with the fracture mode mixity. The main advantages of the present interface model are its simplicity, robustness and its computational efficiency when the so-called sequentially linear analysis is applied. Mo...
Fatigue crack growth simulations of interfacial cracks in bi-layered FGMs using XFEM
Bhattacharya, S.; Singh, I. V.; Mishra, B. K.; Bui, T. Q.
2013-10-01
An investigation of fatigue crack growth of interfacial cracks in bi-layered materials using the extended finite element method is presented. The bi-material consists of two layers of dissimilar materials. The bottom layer is made of aluminium alloy while the upper one is made of functionally graded material (FGM). The FGM layer consists of 100 % aluminium alloy on the left side and 100 % ceramic (alumina) on the right side. The gradation in material property of the FGM layer is assumed to be exponential from the alloy side to the ceramic side. The domain based interaction integral approach is extended to obtain the stress intensity factors for an interfacial crack under thermo-mechanical load. The edge and centre cracks are taken at the interface of bi-layered material. The fatigue life of the interface crack plate is obtained using the Paris law of fatigue crack growth under cyclic mode-I, mixed-mode and thermal loads. This study reveals that the crack propagates into the FGM layer under all types of loads.
Interface fatigue crack propagation in sandwich X-joints – Part II: Finite element modeling
Moslemian, Ramin; Berggreen, Christian
2013-01-01
The aim of the second and final part of this study is to simulate fatigue crack growth in the tested Sandwich Tear Test specimens, described in Part I, using the finite element method. To accelerate the simulation, a cycle jump method is utilized and implemented in the finite element routine. The...... proposed method is based on conducting finite element analysis for a set of cycles to establish a trend line, extrapolating the trend line spanning many cycles, and use the extrapolated state as initial state for additional finite element simulations. The measured da/dN relations of the face/core interface...
This paper firstly presents net-section limit moments for circumferential through-wall and part-through surface cracks at the interface between elbows and attached straight pipes under in-plane bending. Closed-form solutions are proposed based on fitting results from small strain FE limit analyses using elastic-perfectly plastic materials. Net-section limit moments for circumferential cracks at the interface between elbows and attached straight pipes are found to be close to those for cracks in the centre of elbows, implying that the location of the circumferential crack within an elbow has a minimal effect on the net-section limit moment. Accordingly it is also found that the assumption that the crack locates in a straight pipe could significantly overestimate the net-section limit load (and thus maximum load-carrying capacity) of the cracked component. Based on the proposed net-section limit moment, a method to estimate elastic-plastic J based on the reference stress approach is proposed for circumferential cracks at the interface between elbows and attached straight pipes under in-plane bending.
Influence of Re on the propagation of a Ni/Ni3 Al interface crack by molecular dynamics simulation
The influence of Re on the propagation of a (0 1 0)[1 0 1] crack in the Ni/Ni3Al interface, including crack propagation velocity, crack-tip shape, and dislocation emission, is investigated using a molecular dynamics method with a Ni–Al–Re embedded-atom-method potential. The propagation velocity of the crack noticeably decreases at 5 K when 3 or 6 at% Re atoms are added into the Ni matrix. At 1033 K, the crack tip becomes blunter and emission of dislocations becomes easier with Re addition, owing to the larger bond strength between Re and Ni atoms. Furthermore, we calculate the unstable stacking energy (γus), surface energy (γs), and adhesion work (Wad) of the interface. When Re atoms are randomly doped into a Ni matrix, γs/γus increases correspondingly. This means that Re addition decreases brittleness and improves ductility. The calculation also shows that γus is not affected by Re–Ni atomic interaction, and that Re–Re atomic interaction has some effect on γus. In addition, Wad increases with Re addition, and a small increase in Wad results in a larger decrease in crack velocity. This indicates that Re–Ni atomic interaction restrains crack propagation velocity at low temperature. (paper)
Junru, Yang; Chuanjuan, Song; Minglan, Wang; Yeukan, Zhang; Jing, Sun [College of Mechanical and Electronic Engineering, Shandong University of Science and Technology, Qingdao (China)
2016-01-15
The interface crack propagation problem in the cermet cladding material structure was studied. A comparative propagation property parameter (CP) suitable to judge the propagation direction of the interface crack in the cermet cladding material structure was proposed. The interface crack propagation criterion was established. Theoretical models of the CPs for the crack normal to and dwelling on the interface deflecting separately into the clad, the interface and the substrate were built, and the relations between the CPs and the load action angle, the clad thickness ratio and the load were investigated with an example. The research results show that, under the research conditions, the interface crack will more easily propagate into the clad layer than into the substrate.
The interface crack propagation problem in the cermet cladding material structure was studied. A comparative propagation property parameter (CP) suitable to judge the propagation direction of the interface crack in the cermet cladding material structure was proposed. The interface crack propagation criterion was established. Theoretical models of the CPs for the crack normal to and dwelling on the interface deflecting separately into the clad, the interface and the substrate were built, and the relations between the CPs and the load action angle, the clad thickness ratio and the load were investigated with an example. The research results show that, under the research conditions, the interface crack will more easily propagate into the clad layer than into the substrate
Shin, Jeong Woo [Korea Aerospace Research Institute, Daejeon (Korea, Republic of); Lee, Young Shin [Chungnam National University, Daejeon (Korea, Republic of)
2011-10-15
The dynamic propagation of an interface crack between two functionally graded material (FGM) layers under anti-plane shear is analyzed using the integral transform method. The properties of the FGM layers vary continuously along their thicknesses. The properties of the two FGM layers vary and the two layers are connected weak-discontinuously. A constant velocity Yoffe-type moving crack is considered. The Fourier transform is used to reduce the problem to a dual integral equation, which is then expressed to a Fredholm integral equation of the second kind. Numerical values on the dynamic energy release rate (DERR) are presented for the FGM to show the effect of the gradient of material properties, crack moving velocity, and thickness of FGM layers. The following are helpful to increase resistance to interface crack propagation in FGMs: a) increasing the gradient of material properties, b) an increase of shear modulus and density from the interface to the upper and lower free surface, and c) increasing the thickness of the FGM layer. The DERR increases or decreases with increase of the crack moving velocity.
The dynamic propagation of an interface crack between two functionally graded material (FGM) layers under anti-plane shear is analyzed using the integral transform method. The properties of the FGM layers vary continuously along their thicknesses. The properties of the two FGM layers vary and the two layers are connected weak-discontinuously. A constant velocity Yoffe-type moving crack is considered. The Fourier transform is used to reduce the problem to a dual integral equation, which is then expressed to a Fredholm integral equation of the second kind. Numerical values on the dynamic energy release rate (DERR) are presented for the FGM to show the effect of the gradient of material properties, crack moving velocity, and thickness of FGM layers. The following are helpful to increase resistance to interface crack propagation in FGMs: a) increasing the gradient of material properties, b) an increase of shear modulus and density from the interface to the upper and lower free surface, and c) increasing the thickness of the FGM layer. The DERR increases or decreases with increase of the crack moving velocity
Particle- and crack-size dependency of lithium-ion battery materials LiFePO4
Michael A. Stamps
2016-02-01
Full Text Available Lithium-ion batteries have become a widely-used commodity for satisfying the world’s mobile power needs. However, the mechanical degradation of lithium-ion batteries initiated by micro cracks is considered to be a bottleneck for advancing the current technology. This study utilizes a finite element method-based virtual crack closure technique to obtain particle- and crack-size-dependent estimates of mixed-mode energy release rates and stress intensity factors. Interfacial cracks in orthotropic bi-materials are considered in the current study, whereas the crack extension along the interface is assumed. The results show that energy release rate, stress intensity factor, and the propensity of crack extension are particle- and crack-size- dependent. In particular, our results show that for smaller plate-like LiFePO4 particles (100 nm × 45 nm, a crack has lesser tendency to extend if crack-to-particle size is less than 0.2, and for 200 nm × 90 nm particles, similar results are obtained for crack-to-particle sizes of less than 0.15. However, for larger particles (500 nm × 225 nm, it requires an almost flawless particle to have no crack extension. Therefore, the current study provides insight into the fracture mechanics of LiFePO4 and the associated crack-to-particle size dependency to prevent crack extensions.
Among integrity assessment method based on a fracture mechanics concept for piping system, a limit load method is one of the important way to predict a maximum load carrying capacity in the materials with high ductility in the sense that it is used to either assess directly structural integrity of pipe based on fully plastic fracture mechanics or calculate elasticplastic fracture mechanics parameters based on reference stress concept. In nuclear power plants, piping system often involves elbows welded to straight pipe. Since welded regions are vulnerable to cracking, it is important to predict an accurate limit load for pipes with a crack in the interface between elbows and attached pipes. However, although extensive works have been made for developing limit analysis methods for cracked pipes, they were mainly for straight pipes. Recently, limit moment solutions for elbow that is attached to straight pipe with a circumferential through-wall crack(TWC) in the interface were proposed, whereas limit pressure for this geometry is not suggested yet. In this context, plastic limit pressures of circumferential TWCs between elbow and straight pipe were calculated in the present study considering geometric parameters such as an elbow curvature, a pipe size and a crack length. In the present study, the FE plastic limit analyses for circumferential TWC in the interface between elbow and pipe under internal pressure were conducted based on elastic perfectly plastic assumption. Based on the present FE results, it is found that plastic limit pressures of straight pipes with circumferential TWC are not appropriate for predicting plastic limit pressures of circumferential TWC in the interface between elbow and pipe for shorter crack length
Jang, Yoon-Young; Han, Tae-Song; Huh, Nam-Su [Seoul National Univ., Seoul (Korea, Republic of); Jeong, Jae-Uk [Sungkyunkwan Univ., Suwon (Korea, Republic of)
2014-10-15
Among integrity assessment method based on a fracture mechanics concept for piping system, a limit load method is one of the important way to predict a maximum load carrying capacity in the materials with high ductility in the sense that it is used to either assess directly structural integrity of pipe based on fully plastic fracture mechanics or calculate elasticplastic fracture mechanics parameters based on reference stress concept. In nuclear power plants, piping system often involves elbows welded to straight pipe. Since welded regions are vulnerable to cracking, it is important to predict an accurate limit load for pipes with a crack in the interface between elbows and attached pipes. However, although extensive works have been made for developing limit analysis methods for cracked pipes, they were mainly for straight pipes. Recently, limit moment solutions for elbow that is attached to straight pipe with a circumferential through-wall crack(TWC) in the interface were proposed, whereas limit pressure for this geometry is not suggested yet. In this context, plastic limit pressures of circumferential TWCs between elbow and straight pipe were calculated in the present study considering geometric parameters such as an elbow curvature, a pipe size and a crack length. In the present study, the FE plastic limit analyses for circumferential TWC in the interface between elbow and pipe under internal pressure were conducted based on elastic perfectly plastic assumption. Based on the present FE results, it is found that plastic limit pressures of straight pipes with circumferential TWC are not appropriate for predicting plastic limit pressures of circumferential TWC in the interface between elbow and pipe for shorter crack length.
In-situ observation of crack propagation at the interface in SiC and W joining by HVEM
SiC/SiC composites are candidate materials for fusion applications due to their potential to retain strength and exhibit tough behavior at elevated temperatures. The irradiation stability of monolithic beta-SiC has been well studied and the mechanical property evaluation of SiC/SiC composites has been started under the standard test method of Continuous Fiber reinforced Ceramic Composites (CFCC's). It is important to know the initiation, coalescence and growth of crack in SiC/SiC composites. However there are no good tests for measuring the crack propagation at fracture of SiC/SiC composites than before. After mechanical testing, microstructure analysis of fracture region in SiC/SiC composites by Focused Ion Beam (FIB) was done, though the artifact during TEM specimen preparation would be introduced sometime. Recently we successfully developed a piezo driven nano indenting equipment for observation of crack propagation in SiC/SiC under the irradiation by High Voltage Electron Microscope (HVEM). Preliminary result of in-situ observation of shear crack propagation at the interface between SiC fiber and SiC matrix by HVEM shows a good agreement with the result of out situ experiment by using the cross section TEM specimen at the shear fracture interface between SiC fiber and SiC matrix prepared by FIB after the fiber pushing out testing by the nano indenter. The shear crack initiated and propagated at the interface between SiC matrix and carbon coated layer on the SiC fiber. (authors)
Z.J.YANG; A.J.DEEKS
2008-01-01
A frequency-domain approach based on the semi-analytical scaled boundary finite element method(SBFEM) was developed to calculate dynamic stress intensity factors(DSIFs) at bimaterial interface cracks subjected to transient loading.Be-cause the stress solutions of the SBFEM in the frequency domain are analytical in the radial direction,and the complex stress singularity at the bimaterial interface crack tip is explicitly represented in the stress solutions,the mixed-mode DSIFs were calculated directly by definition.The complex frequency-response functions of DSIFs were then used by the fast Fourier transform(FFT) and the inverse FFT to calculate time histories of DSIFs.A benchmark example was modelled.Good re-sults were obtained by modelling the example with a small number of degrees of freedom due to the semi-analytical nature of the SBFEM.
Z.J.YANG; A.J.DEEKS
2008-01-01
A frequency-domain approach based on the semi-analytical scaled boundary finite element method (SBFEM) was developed to calculate dynamic stress intensity factors (DSIFs) at bimaterial interface cracks subjected to transient loading. Be-cause the stress solutions of the SBFEM in the frequency domain are analytical in the radial direction, and the complex stress singularity at the bimaterial interface crack tip is explicitly represented in the stress solutions, the mixed-mode DSIFs were calculated directly by definition. The complex frequency-response functions of DSIFs were then used by the fast Fourier transform (FFT) and the inverse FFT to calculate time histories of DSIFs. A benchmark example was modelled. Good re-sults were obtained by modelling the example with a small number of degrees of freedom due to the semi-analytical nature of the SBFEM.
Zemlyanova, A. Y.
2013-03-08
A problem of an interface crack between two semi-planes made out of different materials under an action of an in-plane loading of general tensile-shear type is treated in a semi-analytical manner with the help of Dirichlet-to-Neumann mappings. The boundaries of the crack and the interface between semi-planes are subjected to a curvature-dependent surface tension. The resulting system of six singular integro-differential equations is reduced to the system of three Fredholm equations. It is shown that the introduction of the curvature-dependent surface tension eliminates both classical integrable power singularity of the order 1/2 and an oscillating singularity present in a classical linear elasticity solutions. The numerical results are obtained by solving the original system of singular integro-differential equations by approximating unknown functions with Taylor polynomials. © 2013 The Author.
Estimation of stepwise crack propagation in ceramic laminates with strong interfaces
Náhlík, Luboš; Štegnerová, Kateřina; Hutař, Pavel
2015-01-01
Roč. 9, č. 34 (2015), s. 116-124. ISSN 1971-8993. [International Conference on Crack Paths /5./. Ferrara, 16.09.2015-18.09.2015] R&D Projects: GA ČR(CZ) GA15-09347S Institutional support: RVO:68081723 Keywords : Ceramic laminates * Crack behaviour * Residual stresses * Strain energy density factor * Crack propagation direction Subject RIV: JL - Materials Fatigue, Friction Mechanics http://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.34.12
Bartolome, J.F.; Beltran, J.I.; Gutierrez-Gonzalez, C.F.; Pecharroman, C.; Munoz, M.C. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), C/Sor Juana Ines de la Cruz 3, 28049 Madrid (Spain); Moya, J.S. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), C/Sor Juana Ines de la Cruz 3, 28049 Madrid (Spain)], E-mail: jsmoya@icmm.csic.es
2008-08-15
Yttria-stabilized zirconia strengthened with lamellar flaky-shape Nb metal particles was obtained by hot-pressing at 1500 deg. C for 1 h. The ZrO{sub 2}-Nb interface has been studied by atomistic, first-principles calculations and by high-resolution transmission electron microscopy. The influence of the ceramic-metal interface on the crack growth resistance has been investigated. Crack growth is shown to occur with a rising resistance, governed by intact metal ligaments in the crack wake. Crack extension occurs by a combination of plastic deformation on the metal particles and interface debonding. The connection between the interface adhesion and this microstructural toughening mechanism has been evaluated.
Numerical simulations of material mismatch and ductile crack growth
Oestby, Erling
2002-07-01
Both the global geometry and inhomogeneities in material properties will influence the fracture behaviour of structures in presence of cracks. In this thesis numerical simulations have been used to investigate how some aspects of both these issues affect the conditions at the crack-tip. The thesis is organised in an introduction chapter, summarising the major findings and conclusions, a review chapter, presenting the main aspects of the developments in the field of fracture mechanics, and three research papers. Paper I considers the effect of mismatch in hardening exponent on the local near-tip stress field for stationary interface cracks in bi-materials under small scale yielding conditions. It is demonstrated that the stress level in the weaker material increases compared to what is found in the homogeneous material for the same globally applied load level, with the effect being of increasing importance as the crack-tip is approached. Although a coupling between the radial and angular dependence of the stress fields exists, the evolving stress field can still be normalised with the applied J. The effect on the increase in stress level can closely be characterised by the difference in hardening exponent, {delta}n, termed the hardening mismatch, and is more or less independent of the absolute level of hardening in the two materials. Paper II and Ill deal with the effects of geometry, specimen size, hardening level and yield stress mismatch in relation to ductile crack growth. The ductile crack growth is simulated through use of the Gurson model. In Paper H the effect of specimen size on the crack growth resistance is investigated for deep cracked bend and shallow cracked tensile specimens. At small amounts of crack growth the effect of specimen size on the crack growth resistance is small, but a more significant effect is found for larger amounts of crack growth. The crack growth resistance decreases in smaller specimens loaded in tension, whereas the opposite is
Lei Jun
2015-01-01
Full Text Available To determine fracture parameters of interfacial cracks in transverse isotropic magnetoelectroelastic composites, a displacement extrapolation formula was derived. The matrix-form formula can be applicable for both material components with arbitrary poling directions. The corresponding explicit expression of this formula was obtained for each poling direction normal to the crack plane. This displacement extrapolation formula is only related to the boundary quantities of the extended crack opening displacements across crack faces, which is convenient for numerical applications, especially for BEM. Meantime, an alternative extrapolation formula based on the path-independent J-integral and displacement ratios was presented which may be more adaptable for any domain-based numerical techniques like FEM. A numerical example was presented to show the correctness of these formulae.
In PWR the primary coolant circuit is coated with 23 CN 20-10 and intermediary alloys are used for welds between main components (pressure vessel, steam generators, pressurizers) made of low alloy steels and stainless steel pipes. After description of the chemical and structural particularities of the bonding zone and evidencing of the interface sensitivity to H2 induced cracking, the paper presents the implementation of the tensile shearing test: preparation, procedure, evaluation, results achieved. The prominent role of the stress relief treatment is highlighted
van der Waals force-induced crack healing in dry rough interfaces
Soylemez, Emrecan; de Boer, Maarten P.
2016-02-01
Spontaneous crack healing due to van der Waals forces is an important phenomenon in diverse areas such as precision assembly, locomotion, soft robotics, and micro- and nanomachines. For rough surfaces that can be described as a collection of asperities, parallel plate models are used to gain insight into the adhesion values. A single adhesion value is then found for a given surface description. However, experiments reveal a range of values. Here, implementing a simple beam model to gain physical insight, we show that an important contribution to the range can be due to the placement of asperities relative to the crack tip. For example, tall asperities far from the crack tip resist crack healing if they contact the substrate, but promote healing if not in contact with it. Due to this effect, the beam model predicts a range of values that is significant compared with the observed experiment variation. Furthermore, as the crack approaches mechanical equilibrium, the resisting action tends to dominate over the healing action, and the beam model predicts a lower adhesion value than the parallel plate model. These effects will be greatest in the case where the elasticity (Tabor) parameter is small.
Theoretical investigation of nonlinear ultrasonic wave modulation spectroscopy at crack interface
Kober, Jan; Převorovský, Zdeněk
2014-01-01
Roč. 61, January (2014), s. 10-15. ISSN 0963-8695 Institutional support: RVO:61388998 Keywords : ultrasonic testing * nonlinear wave modulation spectroscopy * classical nonlinearity * hysteretic nonlinearity * crack characterization Subject RIV: BI - Acoustics Impact factor: 2.225, year: 2014 http://www.sciencedirect.com/science/article/pii/S0963869513001175
Kvasha, Oleg V.; Boström, Anders; Glushkova, Natalia V.; Glushkov, Evgeny V.
2011-08-01
The propagation of in-plane (P-SV) waves in a symmetrically three-layered thick plate with a periodic array of interface cracks is investigated. The exact dispersion relation is derived based on an integral equation approach and Floquet's theorem. The interface cracks can be a model for interface damage, but a much simpler model is a recently developed spring boundary condition. This boundary condition is used for the thick plate and also in the derivation of plate equations with the help of power series expansions in the thickness coordinate. For low frequencies (cracks small compared to the wavelength) the three approaches give more or less coinciding dispersion curves, and this is a confirmation that the spring boundary condition is a reasonable approximation at low frequencies.
Basic modes of crack propagation through the interface in polymer layered structure
Zouhar, Michal; Hutař, Pavel; Náhlík, Luboš; Knésl, Zdeněk
488-489, č. 1 (2012), s. 162-165. ISSN 1013-9826. [International Conference on Fracture and Damage Mechanics - FDM 2011 /10./. Dubrovník, 19.09.2011-21.09.2011] R&D Projects: GA ČR GD106/09/H035; GA ČR GA106/09/0279 Institutional support: RVO:68081723 Keywords : fracture mechanics * slow crack growth * multilayer polymer pipe Subject RIV: JL - Materials Fatigue, Friction Mechanics
A New Approximate Fracture Mechanics Analysis Methodology for Composites with a Crack or Hole
Tsai, H. C.; Arocho, A.
1990-01-01
A new approximate theory which links the inherent flaw concept with the theory of crack tip stress singularities at a bi-material interface was developed. Three assumptions were made: (1) the existence of inherent flaw (i.e., damage zone) at the tip of the crack, (2) a fracture of the filamentary composites initiates at a crack lying in the matrix material at the interface of the matrix/filament, and (3) the laminate fails whenever the principal load-carrying laminae fails. This third assumption implies that for a laminate consisting of 0 degree plies, cracks into matrix perpendicular to the 0 degree filaments are the triggering mechanism for the final failure. Based on this theory, a parameter bar K sub Q which is similar to the stress intensity factor for isotropic materials but with a different dimension was defined. Utilizing existing test data, it was found that bar K sub Q can be treated as a material constant. Based on this finding a fracture mechanics analysis methodology was developed. The analytical results are correlated well with test results. This new approximate theory can apply to both brittle and metal matrix composite laminates with crack or hole.
Analysis of bonded anisotropic wedges with interface crack under anti-plane shear loading
M.GHADIRI; A.R.SHAHANI
2014-01-01
The antiplane stress analysis of two anisotropic finite wedges with arbitrary radii and apex angles that are bonded together along a common edge is investigated. The wedge radial boundaries can be subjected to displacement-displacement boundary condi-tions, and the circular boundary of the wedge is free from any traction. The new finite complex transforms are employed to solve the problem. These finite complex transforms have complex analogies to both kinds of standard finite Mellin transforms. The traction free condition on the crack faces is expressed as a singular integral equation by using the exact analytical method. The explicit terms for the strength of singularity are extracted, showing the dependence of the order of the stress singularity on the wedge angle, material constants, and boundary conditions. A numerical method is used for solving the resul-tant singular integral equations. The displacement boundary condition may be a general term of the Taylor series expansion for the displacement prescribed on the radial edge of the wedge. Thus, the analysis of every kind of displacement boundary conditions can be obtained by the achieved results from the foregoing general displacement boundary condition. The obtained stress intensity factors (SIFs) at the crack tips are plotted and compared with those obtained by the finite element analysis (FEA).
Isochromatics and caustics around the tips of interface cracks observed by digital image processing
Photoelasticity and the caustic method are two useful optical techniques for the investigation of mixed-mode crack problems and other stress concentration problems in the vicinity of holes and bores as well as for the evaluation of contact problems. The geometry of the caustics is proportional to the stress field gradient and therefore the caustic contour can be taken as a quantity for experimental measurements. In this paper, an overview about the numerical simulation and experimental modelling of cracks arising in plane disk-like models of two-phase composite structures will be given. Shadow optical and photoelastic data were collected from digitally sharpened isochromatic fringe patterns and caustics by using a digital image analysis system. By utilizing digital image processing and computergraphics techniques, a set of menu-driven software is developed for interactively implemented caustics and fringes processing. Stress intensity factors were also obtained by a special shadow optical-grid-method and the multi-point method of caustics and isochromatics, respectively. (orig.)
Effect of plasticity on cleavage crack growth resistance at an interface
Tvergaard, Viggo
1999-01-01
The mixed mode toughness of an interface joining an elastic-plastic metal to a solid which does not yield plastically is studied numerically for cases where fracture occurs by atomic separation. Thus, the length scale of the fracture process is typically much smaller than the dislocation spacing ...
In order to assess the harmfulness of detected defects in some nuclear power plants, EDF Group is led to develop advanced simulation tools. Among the targeted mechanisms are 3D non-planar quasi-static crack propagation, but also dynamic transients during unstable phases. In the present thesis, quasi-brittle crack growth is simulated based on the combination of the XFEM and cohesive zone models. These are inserted over large potential crack surfaces, so that the cohesive law will naturally separate adherent and de-bonding zones, resulting in an implicit update of the crack front, which makes the originality of the approach. This requires a robust insertion of non-smooth interface laws in the XFEM, which is achieved in quasi-statics with the use of XFEM-suited multiplier spaces in a consistent formulation, block-wise diagonal interface operators and an augmented Lagrangian formalism to write the cohesive law. Based on this concept and a novel directional criterion appealing to cohesive integrals, a propagation procedure over non-planar crack paths is proposed and compared with literature benchmarks. As for dynamics, an initially perfectly adherent cohesive law is implicitly treated within an explicit time-stepping scheme, resulting in an analytical determination of interface tractions if appropriate discrete spaces are used. Implementation is validated on a tapered DCB test. Extension to quadratic elements is then investigated. For stress-free cracks, it was found that a subdivision into quadratic sub-cells is needed for optimality. Theory expects enriched quadrature to be necessary for distorted sub-cells, but this could not be observed in practice. For adherent interfaces, a novel discrete multiplier space was proposed which has both numerical stability and produces quadratic convergence if used along with quadratic sub-cells. (author)
Improvement of adhesion performance of mortar-repair interface with inducing crack path into repair
A. Satoh
2015-10-01
Full Text Available The most important performance for repair materials is adhesion to the substrate. The authors experimentally find out that high modulus fine aggregates in repair material enhance strength of it as well as the strength of the interface repaired with it, compared to the ordinary repair without fine aggregates. This paper elaborates the mechanisms for that with fractographic observation and FEM analysis based on the results of experiment. Also the authors discuss the ways for enhancing the strength and ductility of the repaired mortar
Green's functions of one-dimensional quasicrystal bi-material with piezoelectric effect
Zhang, Liangliang; Wu, Di; Xu, Wenshuai; Yang, Lianzhi; Ricoeur, Andreas; Wang, Zhibin; Gao, Yang
2016-09-01
Based on the Stroh formalism of one-dimensional quasicrystals with piezoelectric effect, the problems of an infinite plane composed of two different quasicrystal half-planes are taken into account. The solutions of the internal and interfacial Green's functions of quasicrystal bi-material are obtained. Moreover, numerical examples are analyzed for a quasicrystal bi-material subjected to line forces or line dislocations, showing the contour maps of the coupled fields. The impacts of changing material constants on the coupled field components are investigated.
Vliv bi-materiálového rozhraní na hodnoty lomově mechanických parametrů K a T
Seitl, Stanislav
Plzeň : Škoda výzkum s.r.o., 2004 - (Mentl, V.), s. 70-76 [Únava a lomová mechanika 2004. Žinkovy (CZ), 20.04.2004-22.04.2004] R&D Projects: GA ČR GP101/04/P001 Institutional research plan: CEZ:AV0Z2041904 Keywords : T-stress, two-parameter, fracture mechanics, bi-material interface Subject RIV: JL - Materials Fatigue, Friction Mechanics
Klusák, Jan; Profant, T.; Kotoul, M.
2009-01-01
Roč. 3, č. 2 (2009), s. 297-304. ISSN 1802-680X R&D Projects: GA ČR GA101/08/0994 Institutional research plan: CEZ:AV0Z20410507 Keywords : Generalized stress intensity factor * Fracture mechanics * Bi-material notch * Generalized singular stress concentrator Subject RIV: JL - Materials Fatigue, Friction Mechanics
Transverse cracking of layered structures: evaluation of fatigue crack propagation
Náhlík, Luboš; Hutař, Pavel; Knésl, Zdeněk
2008-01-01
Roč. 567-568, - (2008), s. 221-224. ISSN 0255-5476. [MSMF /5./. Brno, 27.06.2007-29.06.2007] R&D Projects: GA ČR GP106/06/P239; GA ČR(CZ) GA101/05/0320 Institutional research plan: CEZ:AV0Z20410507 Keywords : layered composites * bi-material interface * effective stress intensity factor Subject RIV: JL - Materials Fatigue, Friction Mechanics
Crack growth kinetics across weld interface between Alloy 182 and LAS (Low Alloy Steel) and that between Alloy 182 and Metals to simulate weld dilution zone was investigated by CBB (Creviced Bent Beam) test. The main objective of this study is to investigate dynamic influence for a crack initiated in Alloy 182 to propagate into LAS. Specimens were subjected to CBB tests for 2000 h each in simulated BWR water with 8 ppm of dissolved oxygen. Mechanics conditions were described by equivalent stress intensity factor KJ values which are J values from elasto-plastic analysis. In small-sized specimens of 2 mm in thickness, cracks which initiated in Alloy 182 propagated into Metal21-4 (20%Ni, 4%Cr), while they did not into Metal21-5 (10%Ni, 2%Cr). In moderate-sized specimens of 10 mm in thickness, cracks did advance into Metals and LAS under KJ values more than 80 MPa·m1/2. (author)
Micro-devices with a bi-material-cantilever (BMC) commonly suffer initial curvature due to the mismatch of residual stress. Traditional corrective methods to reduce the residual stress mismatch generally involve the development of different material deposition recipes. In this paper, a new method for reducing residual stress mismatch in a BMC is proposed based on various previously developed deposition recipes. An initial material film is deposited using two or more developed deposition recipes. This first film is designed to introduce a stepped stress gradient, which is then balanced by overlapping a second material film on the first and using appropriate deposition recipes to form a nearly stress-balanced structure. A theoretical model is proposed based on both the moment balance principle and total equal strain at the interface of two adjacent layers. Experimental results and analytical models suggest that the proposed method is effective in producing multi-layer micro cantilevers that display balanced residual stresses. The method provides a generic solution to the problem of mismatched initial stresses which universally exists in micro-electro-mechanical systems (MEMS) devices based on a BMC. Moreover, the method can be incorporated into a MEMS design automation package for efficient design of various multiple material layer devices from MEMS material library and developed deposition recipes. (paper)
Conwell, Matthew; McKinley, Ian; Shi, Xiaoyang
2012-01-01
An extremely sensitive temperature measurement MEMS device is developed based on the principle of structural deflection in a bi-material cantilever caused by a difference in thermal expansion coefficients. A dual-beam asymmetrical geometry is used to produce a torsional response from the device. An analytical model is developed to predict the performance and optimize the free parameters of the device. In this work, it is performed to analyze the flexural and torsional eigenfrequencies as well as confirm the theoretical predictions of DC and AC response. Lastly, a procedure is developed to allow fabrication of the device using equipment available in the Columbia University clean room.
Klusák, Jan; Profant, T.; Kotoul, M.
Plzeň: University of West Bohemia, 2009 - (Adámek, V.; Zajíček, M.). s. 1-2 ISBN 978-80-7043-824-4. [Computational Mechanics 2009. 09.11.2009-11.11.2009, Nečtiny] R&D Projects: GA ČR GA101/08/0994 Institutional research plan: CEZ:AV0Z20410507 Keywords : Stress intensity factor * bi-material notch * generalized fracture mechanics Subject RIV: JL - Materials Fatigue, Friction Mechanics
A study of bi-material notches under a combined loading mode
Kopp, Dalibor; Klusák, Jan
Brno : Ústav fyziky materiálů, AV ČR, v.v.i, 2011 - (Náhlík, L.; Zouhar, M.; Ševčík, M.; Seitl, S.; Majer, Z.), s. 107-110 ISBN 978-80-87434-03-1. [ Applied Mechanics 2011. Velké Bílovice (CZ), 18.04.2011-20.04.2011] R&D Projects: GA ČR GAP108/10/2049 Institutional research plan: CEZ:AV0Z20410507 Keywords : Generalized linear elastic fracture mechanics * bi-material notch * Combined loading * stability criterion Subject RIV: JL - Materials Fatigue, Friction Mechanics
谢建和; 黄培彦; 郭永昌; 刘锋
2011-01-01
The propagation behavior of interface fatigue crack in reinforced concrete（RC） beam strengthened with prestressed fiber reinforced polymer（FRP） was studied.The mechanical analysis model was established for the interface crack tip in the strengthened beam under three-point bending.The theoretical derivation of stress intensity factor（SIF） for the interface crack was presented base on the mechanical model,and the effect of the prestress level on SIF was discussed.Combined with the experiments on interface fatigue crack propagation rate,a semi-empirical formula was developed for the propagation rate of interface crack in such strengthened beams.Results showed that the propagation of the interfacial fatigue crack has three stages： rapid propagation,steady propagation and instability propagation.The interface crack propagation rate was described in the form of Paris formula before the instability propagation.SIF of the initial crack at mid-span interface reached the maximum and then decreased with the interface crack length.In elastic range of the reinforcing steel bar,the strengthened beam with prestress had large SIF compared with the strengthened beam without prestress.%以预应力纤维增强复合材料（FRP）片材加固钢筋混凝土（RC）梁为研究对象,探讨了该类加固梁中FRP与混凝土之间界面疲劳裂纹的扩展规律。基于界面裂纹尖端的力学分析模型,理论推导了三点弯曲加固梁的界面裂纹应力强度因子（SIF）的计算公式,分析了FRP预应力水平对SIF的影响,并结合加固梁的界面裂纹扩展实验,提出了该类加固梁界面疲劳裂纹扩展速率的半经验公式。研究结果表明：加固梁的界面疲劳裂纹扩展可分为裂纹快速扩展、稳定扩展及失稳扩展3个阶段;在加固梁失稳破坏之前,界面疲劳裂纹的扩展速率可以Paris公式的形式表
Dynamics of pre-strained bi-material elastic systems linearized three-dimensional approach
Akbarov, Surkay D
2015-01-01
This book deals with dynamics of pre-stressed or pre-strained bi-material elastic systems consisting of stack of pre-stressed layers, stack of pre-stressed layers and pre-stressed half space (or half plane), stack of pre-stressed layers as well as absolute rigid foundation, pre-stressed compound solid and hollow cylinders and pre-stressed sandwich hollow cylinders. The problems considered in the book relate to the dynamics of a moving and oscillating moving load, forced vibration caused by linearly located or point located time-harmonic forces acting to the foregoing systems. Moreover, a considerable part of the book relate to the problems regarding the near surface, torsional and axisymmetric longitudinal waves propagation and dispersion in the noted above bi-material elastic systems. The book carries out the investigations within the framework of the piecewise homogeneous body model with the use of the Three-Dimensional Linearized Theory of Elastic Waves in Initially Stressed Bodies.
Sensitivity alteration of fiber Bragg grating sensors with additive micro-scale bi-material coatings
Zhang, Xixi; Alemohammad, Hamidreza; Toyserkani, Ehsan
2013-02-01
This paper describes a combined fabrication method for creating a bi-material micro-scale coating on fiber Bragg grating (FBG) optical sensors using laser-assisted maskless microdeposition (LAMM) and electroless nickel plating. This bi-material coating alters the sensitivity of the sensor where it also acts as a protective layer. LAMM is used to coat bare FBGs with a 1-2 µm thick conductive silver layer followed by the electroless nickel plating process to increase layer thickness to a desired level ranging from 1 to 80 µm. To identify an optimum coating thickness and predict its effect on the sensor's sensitivity to force and temperature, an optomechanical model is developed in this study. According to the model if the thickness of the Ni layer is 30-50 µm, maximum temperature sensitivity is achieved. Our analytical and experimental results suggest that the temperature sensitivity of the coated FBG with 1 µm Ag and 33 µm Ni is almost doubled compared to a bare FBG with sensitivity of 0.011 ± 0.001 nm °C-1. In contrast, the force sensitivity is decreased; however, this sensitivity reduction is less than the values reported in the literature.
Sensitivity alteration of fiber Bragg grating sensors with additive micro-scale bi-material coatings
This paper describes a combined fabrication method for creating a bi-material micro-scale coating on fiber Bragg grating (FBG) optical sensors using laser-assisted maskless microdeposition (LAMM) and electroless nickel plating. This bi-material coating alters the sensitivity of the sensor where it also acts as a protective layer. LAMM is used to coat bare FBGs with a 1–2 µm thick conductive silver layer followed by the electroless nickel plating process to increase layer thickness to a desired level ranging from 1 to 80 µm. To identify an optimum coating thickness and predict its effect on the sensor's sensitivity to force and temperature, an optomechanical model is developed in this study. According to the model if the thickness of the Ni layer is 30–50 µm, maximum temperature sensitivity is achieved. Our analytical and experimental results suggest that the temperature sensitivity of the coated FBG with 1 µm Ag and 33 µm Ni is almost doubled compared to a bare FBG with sensitivity of 0.011 ± 0.001 nm °C−1. In contrast, the force sensitivity is decreased; however, this sensitivity reduction is less than the values reported in the literature. (paper)
Streza, M.; Hodisan, I.; Prejmerean, C.; Boue, C.; Tessier, Gilles
2015-03-01
The evaluation of a dental restoration in a non-invasive way is of paramount importance in clinical practice. The aim of this study was to assess the minimum detectable open crack at the cavity-restorative material interface by the lock-in thermography technique, at laser intensities which are safe for living teeth. For the analysis of the interface, 18 box-type class V standardized cavities were prepared on the facial and oral surfaces of each tooth, with coronal margins in enamel and apical margins in dentine. The preparations were restored with the Giomer Beautifil (Shofu) in combination with three different adhesive systems. Three specimens were randomly selected from each experimental group and each slice has been analysed by visible, infrared (IR), and scanning electron microscopy (SEM). Lock-in thermography showed the most promising results in detecting both marginal and internal defects. The proposed procedure leads to a diagnosis of micro-leakages having openings of 1 µm, which is close to the diffraction limit of the IR camera. Clinical use of a thermographic camera in assessing the marginal integrity of a restoration becomes possible. The method overcomes some drawbacks of standard SEM or dye penetration testing. The results support the use of an IR camera in dentistry, for the diagnosis of micro-gaps at bio-interfaces.
Falzon, Brian G.; Hawkins, Stephen C; Huynh, Chi P.; Radjef, Racim; Brown, Callum
2013-01-01
A novel approach for introducing aligned multi-walled carbon nanotubes (MWCNTs) in a carbon-fibre composite pre-impregnated (prepreg) laminate, to improve the through-thickness fracture toughness, is presented. Carbon nanotube (CNT) 'forests' were grown on a silicon substrate with a thermal oxide layer, using a chemical vapour deposition (CVD) process. The forests were then transferred to a pre-cured laminate interface, using a combination of pressure and heat, while maintaining through-thick...
Zouhar, Michal; Hutař, Pavel; Náhlík, Luboš; Knésl, Zdeněk
2011-01-01
Roč. 47, č. 2 (2011), s. 203-210. ISSN 0191-5665 R&D Projects: GA ČR GC101/09/J027; GA ČR GD106/09/H035; GA ČR GA106/09/0279 Institutional research plan: CEZ:AV0Z20410507 Keywords : multilayer plastic pipes * bimaterial interface * stability criteria * critical stress * time-depended material properties Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 0.409, year: 2011
In order to clarify the behaviour and mechanism of the hydrogen embrittlement in SUS304ULC/Ta/Zr explosive bonded joint, the hydrogen embrittlement cracking at Ta/Zr bond interface was characterised. Cracks occurred in the Zr substrate along the wavy interface of the hydrogen-charged Ta/Zr joint. The cracking susceptibility increased drastically when the potential of specimen during hydrogen-charging was reduced below the redox potential of hydrogen, γ-ZrH and δ-ZrH were precipitated in the hydrogen-charged Zr and the precipitated γ-ZrH possessed a (0002)α-Zr parallel (11-bar1)γ-ZrH, [21-bar1-bar0]α-Zr parallel [110]γ-ZrH crystallographic relationship. An in-situ observation of the hydrogen embrittlement cracking with SEM and TEM revealed that cracks were initiated in zirconium hydrides and propagated preferentially along zirconium hydrides. These results suggested that the hydrogen embrittlement mechanism of the Zr base metal was caused by the precipitation of zirconium hydrides and the brittle fracture of them. (author)
Estimation of range and dose distribution for bi-material targets in heavy-ion irradiation
In order to evaluate the field irradiated with incident ions and the deposited dose distribution in a patient body, we have proposed to use the positron emitters produced through projectile fragmentation reactions of stable heavy ions. In the previous, years, we established the method to estimate the range of incident ions and the dose distribution in uniform targets by using the MLE method. In this year, we performed irradiation experiments for bi-material targets consisting of PMMA, lung equivalent material, water, etc. with 12C of 290 MeV/u and 16O of 350 MeV/u. The annihilation events from the positron emitters produced by 12C and 16O ions were detected with a positron camera for 500 s just after the irradiation. Then the range was determined in each target by applying the MLE method. Consequently, for all the targets, the evaluated ranges agreed with those calculated from the depth-dose distributions measured with an ionization chamber within an accuracy of 3.0 mm. (author)
... Our Faculty Our Staff Rheumatology Specialty Centers Knuckle Cracking Q & A September 10, 2007 By Arthritis Center ... immediately. Question: Are there any side effects to cracking knuckles? There is no evidence that cracking knuckles ...
Research on an AlSiNx bi-material thermal-mechanical uncooled infrared FPA pixel
Zhang, Xia; Zhang, Da-cheng
2011-08-01
AlSiNx bi-material thermal strain structure is used in uncooled optic readout infrared focal plane array (UOR IR FPA) pixel based on Micro-Electro-Mechanical Systems (MEMS) technology. In this paper, the problems that the AlSiNxstructure prevents FPA pixel scaling down and fill factor improving, and the Au reflection layer of the pixel leads to larger readout light energy loss are analyzed. The feasibility of AlSiNx instead of AlSiNx in the UOR IR FPA fabrication is researched in detail. The theoretical analyzing and simulation results demonstrate that, with optimized thicknesses and their matching designing of SiNx and Al, the thermal-mechanical response of AlSiNx bi-material structure is improved to 1.8 times and the intensity of optic readout signal is improved to about 2 times compared with AuSiNAlSiNx one.
D. Sujan
2010-01-01
Full Text Available Problem statement: The thermal mismatch induced interfacial stresses are one of the major reliability issues in electronic packaging and composite materials. Consequently an understanding of the nature of the interfacial stresses under different temperature conditions is essential in order to eliminate or reduce the risk of structural and functional failure. Approach: In this analysis, a model was proposed for the shearing and peeling stresses occurring at the interface of two bonded dissimilar materials with the effect of different uniform temperatures in the layers. The model was then upgraded by accounting thickness wise linear temperature gradients in the layers using two temperature drop ratios. The upgraded models were then compared with the existing uniform temperature model. The proposed model can be seen as a more generalized form to predict interfacial stresses at different temperature conditions that may occur in the layers. Results: The results were presented for an electronic bi-material package consisting of die and die-attach. Conclusion: The numerical simulation is in a good matching agreement with analytical results.
Singular and non-singular stress terms for the failure assessment of bi-material notches
Krepl, Ondřej; Klusák, Jan; Profant, T.
Brno : Ústav fyziky materiálů AV ČR, v. v. i., 2015 - (Dlouhý, A.; Kunz, L.). s. 386-386 ISBN 978-80-87434-07-9. [ICSMA-17 International Conference on the Strength of Materials /17./. 09.08.2015-14.08.2015, Brno] Institutional support: RVO:68081723 Keywords : Generalized fracture mechanics * Singular stress concentrators * Crack initiation Subject RIV: JL - Materials Fatigue, Friction Mechanics
Hydrogen embrittlement cracking behaviours of SUS304/Ta/Zr explosive bonded joint during underwater polishing were investigated. Hydrogen embrittlement cracks occurred in the Zr substrate adjacent to the Ta/Zr bond interface during underwater polishing. The open circuit potential of Zr during underwater polishing was drastically reduced immediately after mechanical polishing (within a fraction of a second). The hydrogen yields of Zr-Ta alloys and cold-worked Zr during underwater polishing were estimated from the corrosion current determined by the Tafel extrapolation method. The hydrogen yield increased with a decrease in the Ta content of Zr-Ta alloy, and with an increase in the degree of working (rolling reduction) of Zr. It was deduced that the mechanical grinding in water removing the passive oxide film on the Zr substrate led to the hydrogen absorption into the Zr substrate and the precipitation of zirconium hydrides. Accordingly, hydrogen embrittlement cracks occurred in the deformation layer of Zr around the Ta/Zr bond interface due to the tensile residual stress in the explosive bonded joint. (author)
B. Barišić
2008-10-01
Full Text Available The goal of the paper is to present an outline of different modeling approach at determining of backward extrusion force on AlCu5PbBi material and to compare them with experimental obtained results. Stochastic modeling in the paper is based on the statistic processing of central composite experimental design i.e. in this investigations central composite circumscribed (CCC design. The numerical modeling is based on the finite element method (FEM using ABAQUS 6.4.1. Explicit software.
Bi-material notches under various normal-shear loading modes
Klusák, Jan; Kopp, Dalibor; Profant, T.
Zurich : Trans Tech Publications, 2014 - (Milazzo, A.; Aliabadi, M.), s. 361-364 ISBN 978-3-03785-830-1. ISSN 1013-9826. - (Key Engineering Materials. 577-578). [FDM 2013 - International Conference on Fracture and Damage Mechanics /12./. Sardinia (IT), 17.09.2013-19.09.2013] R&D Projects: GA ČR(CZ) GAP104/11/0833 Institutional support: RVO:68081723 Keywords : general singular stress concentrator * crack initiation * Combined loading mode Subject RIV: JL - Materials Fatigue, Friction Mechanics
Zhang, Xia; Jiao, Bin-bin; Chen, Da-peng; Ye, Tian-chun
2009-07-01
Bi-material cantilever is an important basic structure in MEMS device. Most of the materials with thermal property fit for bi-material are not adhering together steadily. An adhesive layer in between is needed. In this paper, based on the thermal stress and combined deformation in Mechanics of Materials, a model related to the physics properties, structure dimension, and the tilt angle caused by thermal stress is set up. A research of how to select the materials and how to determinate the thickness and other size of a bi-material cantilever is carry out by this model, further more, an optic read out IR image chip pixel is designed that shows this model is simple and practical.
Observation of Intralaminar Cracking in the Edge Crack Torsion Specimen
Czabaj, Michael W.; Ratcliffe, James G.; Davidson, Barry D.
2013-01-01
The edge crack torsion (ECT) test is evaluated to determine its suitability for measuring fracture toughness associated with mode III delamination growth onset. A series of ECT specimens with preimplanted inserts with different lengths is tested and examined using nondestructive and destructive techniques. Ultrasonic inspection of all tested specimens reveals that delamination growth occurs at one interface ply beneath the intended midplane interface. Sectioning and optical microscopy suggest that the observed delamination growth results from coalescence of angled intralaminar matrix cracks that form and extend across the midplane plies. The relative orientation of these cracks is approximately 45 deg with respect to the midplane, suggesting their formation is caused by resolved principal tensile stresses arising due to the global mode-III shear loading. Examination of ECT specimens tested to loads below the level corresponding to delamination growth onset reveals that initiation of intralaminar cracking approximately coincides with the onset of nonlinearity in the specimen's force-displacement response. The existence of intralaminar cracking prior to delamination growth onset and the resulting delamination extension at an unintended interface render the ECT test, in its current form, unsuitable for characterization of mode III delamination growth onset. The broader implications of the mechanisms observed in this study are also discussed with respect to the current understanding of shear-driven delamination in tape-laminate composites.
Máša, Bohuslav; Náhlík, Luboš; Hutař, Pavel
Brno: Brno University of Technology. Institute of Solid Mechanics, Mechatronics and Biomechanics, 2014 - (Fuis, V.), s. 392-395 ISBN 978-80-214-4871-1. ISSN 1805-8248. [Engineering Mechanics 2014 /20./. Svratka (CZ), 12.05.2014-15.05.2014] R&D Projects: GA MŠk(CZ) EE2.3.30.0063 Institutional support: RVO:68081723 Keywords : Stress singularity exponent * Residual stress * Singular stress concentrator * Material interface * Ceramic composites Subject RIV: JI - Composite Materials
BWR pipe crack remedies evaluation
This paper presents results on: (a) the influence of simulated BWR environments on the stress-corrosion-cracking (SCC) susceptibility of types 304, 316 NG, and 347 stainless steel (SS), (b) fracture-mechanics crack growth rate measurements on these materials and weld overlay specimens in different environments, and (c) residual stress measurements and metallographic evaluations of conventional pipe weldments treated by a mechanical-stress-improvement process (MSIP) as well as those produced by a narrow-gap welding procedure. Crack initiation studies on types 304 and 316 NG SS under crevice and non-crevice conditions in 2890C water containing 0.25 ppm dissolved oxygen with low sulfate concentrations indicate that SCC initiates at low strains (3%) in the nuclear grade material. Crack growth measurements on fracture-mechanics-type specimens, under low-frequency cyclic loading, show that the type 316 NG steel cracks at a somewhat lower rate (≅ 40%) than sensitized type 304 SS in an impurity environment with 0.25 ppm dissolved oxygen; however, the latter material stops cracking when sulfate is removed from the water. Crack growth in both materials ceases under simulated hydrogen-water chemistry conditions (6 ppb oxygen) even with 100 ppb sulfate present in the water. An unexpected results was obtained in the test on a weld overlay specimen in the impurity environment, viz., the crack grew to the overlay interface at a nominal rate, branched at 900 in both directions, and then grew at a high rate (parallel to the nominal applied load). Residual stress measurements on MSIP-treated weldments and those produced by a narrow-gap welding procedure indicate that these techniques produce compressive stresses over most of the inner surface near the weld and heat-affected zones. (orig.)
Profant, T.; Klusák, Jan; Ševeček, O.; Kotoul, M.; Hrstka, M.; Marcián, P.
Zurich : Trans Tech Publications, 2014 - (Šandera, P.), s. 745-748 ISBN 978-3-03785-934-6. ISSN 1013-9826. - (Key Engineering Materials. 592-593). [MSMF 7 - International Conference on Materials Structure & Micromechanics of Fracture /7./. Brno (CZ), 01.07.2013-03.07.2013] Institutional support: RVO:68081723 Keywords : Orthotropic bi-material notch * two-state integral * non-singular stress terms * T-stress * matched asymptotic expansion Subject RIV: JL - Materials Fatigue, Friction Mechanics http://www.scientific.net/KEM.592-593.745
Perturbation of Mode III interfacial cracks
Piccolroaz, A.; Mishuris, G.; Movchan, A. B.
2010-01-01
We consider the perturbation problem of a Mode III interfacial crack. The perturbation is of geometrical type and can be both perturbation of the crack faces and perturbation of the interface, which can deviate from the initial straight line configuration. Asymptotic formulae are derived for the first-order perturbation of the stress intensity factor. It is shown that, due to the unsymmetrical nature of the problem, the Mode III skew-symmetric weight function derived in Piccolroaz et al. (200...
邵卓平; 吴贻军; 王福利
2012-01-01
Bamboo is a kind of biologic composite material strengthened by fibers that distribute asymmetrically, and the property of toughness depends on the property of component material as well as the characteristic of meso-structure. The study showed that the whole process of bamboo transverse bending fracture includes the cracking of parenchyma tissue, the layering of interface, the fracture of bamboo fiber bundle and the pull-out of bamboo fiber bundle and other various damage patterns. Different organization structures contribute different toughness to the evolution of damage for different energy wastage. In order to find out the main structure factors that lead to the excellent toughness property, the meso-mechanics method was applied to study the energy absorbing mechanism of parenchyma tissue crack pattern and interface layering pattern during process of bamboo transverse bending fracture. Then the strain energy release rate analysis equation of the two patterns above was obtained and the critical strain energy release rate analysis equation of the bamboo specimens with crack perpendicular to grain loaded with bending load and the transverse crack transforming to initial crack along grain.%采用细观力学方法,研究竹材在横弯断裂过程中基本组织开裂与界面脱粘这2种损伤模式的能量吸收机制,并推导得到这2种损伤模式的应变能释放率解析式,以及含垂直纹理裂纹的竹试件在承受弯曲载荷时、横向裂纹转向顺纹启裂时的临界应变能释放率解析式.
Hutař, Pavel; Náhlík, Luboš; Šestáková, Lucie; Ševčík, Martin; Knésl, Zdeněk; Nezbedová, E.
2010-01-01
Roč. 92, č. 5 (2010), s. 1120-1125. ISSN 0263-8223 R&D Projects: GA ČR GA106/09/0279 Institutional research plan: CEZ:AV0Z20410507 Keywords : Protective layers * Multi-layer pipes damage * Fracture mechanics * Bi-material interface * Generalized stress intensity factor Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.028, year: 2010
Crack growth rate under cyclic bending in the explosively welded steel/titanium bimetals
Highlights: ► The results of the tests on fatigue crack growth in a steel/titanium composite under oscillatory bending. ► Hardness of both joined materials in all their section is higher than hardness of the materials before cladding. ► The main crack propagated in the direction parallel to the loading action and they did not include secondary cracks. ► When the crack growth was being passed along the interface line, decrease of the crack growth rate took place. -- Abstract: The paper presents the results of the tests on fatigue crack growth in a steel/titanium composite under oscillatory bending. Two kinds of specimens of rectangular cross sections were tested. In the tested specimens, the ratio of heights of basic and overlaid materials was h1:h2 = 2.5:1 and 1:1. In the specimens, the fatigue crack growth was parallel to the applied loading and its direction changed at the interface line. Next, the crack growth along the interface line or the crack growth passing through the interface line were observed. When the crack growth passed along the interface line, decrease of the crack growth rate took place. The specimens have the uniform crack growth at both sides of lateral surfaces. At the composite fractures in the steel and titanium, transcrystalline cracks are dominating.
Determination of fatigue cracking direction in composite laminates
DAI Yao; HAO Gui-xiang; LI Yong-dong; HE Jia-wen; CUI Jian-guo; LI Nian; FU Yong-hui; SUN Jun
2005-01-01
The interface plays the central role in the failure analysis of composite laminates, therefore, the interface material properties are taken as the independent parameters. A simple, universal and practicable criterion, i.e. a ratio criterion of strain energy release rate, is proposed to determine the growing direction of a fatigue crack in the composite laminates. The method of arbitrary lines, which is very effective to solve the problems with high gradient feature, is used to analyze the experimental results at the key moments when a crack kinks, turns into the interface,or bifurcates. An approximate method of computing the energy release rate is given. The fatigue fracture tests of composite laminates are carried out, and the numerical predictions of crack growing directions agree well with the experimental results. It is concluded that the methods suggested in this paper are effective to obtain the cracking history and the growing path of a fatigue crack in composite laminates.
Stress corrosion cracking and vibration corrosion cracking
Under certain conditions of stress practically all metallic materials are subject to such cracking corrosion processes. They are much feared because as a rule they are not recognized until the damage - leakage of a container, fracture of a component part-occurs. They may belong to the category of either stress corrosion cracking or vibration corrosion cracking, depending on the different mechanisms of the damage process. As the denominations indicate, one constitutes the interaction between local corrosion attack and mainly static tensile stress (load stress and/or non-load stress) and the other a combination of varying mechanical stress over time and corrosion. Hydrogen-induced cracking is a special form of stress corrosion cracking characterized by trapping of atomic hydrogen in material and subsequent cracking owing to the interaction with mechanical stress. (orig./HP)
Influence of cracks on rebar corrosion in carbonated concretes
This paper presents an experimental program allowing the determination of the effect of pre-cracks and their orientations on both initiation and propagation of reinforcement steel corrosion due to carbonation in different environmental conditions, in order to propose an operational model allowing the evaluation of the kinetic of corrosion of the reinforcement steel in cooling towers of nuclear power plants. The cracking mode that generates cracks which are representative of those appearing on the cooling towers is a three-point bending test performed on prismatic samples of 7*7*28 cm3 size with 6 mm steel bars. The length of damaged steel / concrete interface, which appears following a three-point bending test, is then quantified. This length could be determining in the initiation and the propagation of corrosion. Results show that this length is dependent on the residual crack opening and that the length of damaged interface in its lower part is larger than that on the upper part due to the Top Bar effect. After cracking, the samples will be exposed to carbon dioxide to ensure carbonation of the steel bar localized at the bottom of the crack and the concrete/steel interface, damaged by the load applied during the three-point bending test. After carbonation of the interface, samples will be submitted to corrosion in different environmental conditions whose effect on the kinetics of corrosion will be determined. The work done so far permits the definition of the cracking protocol (three points bending) that allows obtaining cracks which are representative of those existing on cooling towers. Moreover, the length of steel/concrete damaged interface with respect to crack opening is quantified. It was found that this length is proportional to the crack opening. In addition, it was shown that the Top Bar effect increases the damaged interface length at the lower part of steel bars
Gear Crack Propagation Investigation
1995-01-01
Reduced weight is a major design goal in aircraft power transmissions. Some gear designs incorporate thin rims to help meet this goal. Thin rims, however, may lead to bending fatigue cracks. These cracks may propagate through a gear tooth or into the gear rim. A crack that propagates through a tooth would probably not be catastrophic, and ample warning of a failure could be possible. On the other hand, a crack that propagates through the rim would be catastrophic. Such cracks could lead to disengagement of a rotor or propeller from an engine, loss of an aircraft, and fatalities. To help create and validate tools for the gear designer, the NASA Lewis Research Center performed in-house analytical and experimental studies to investigate the effect of rim thickness on gear-tooth crack propagation. Our goal was to determine whether cracks grew through gear teeth (benign failure mode) or through gear rims (catastrophic failure mode) for various rim thicknesses. In addition, we investigated the effect of rim thickness on crack propagation life. A finite-element-based computer program simulated gear-tooth crack propagation. The analysis used principles of linear elastic fracture mechanics, and quarter-point, triangular elements were used at the crack tip to represent the stress singularity. The program had an automated crack propagation option in which cracks were grown numerically via an automated remeshing scheme. Crack-tip stress-intensity factors were estimated to determine crack-propagation direction. Also, various fatigue crack growth models were used to estimate crack-propagation life. Experiments were performed in Lewis' Spur Gear Fatigue Rig to validate predicted crack propagation results. Gears with various backup ratios were tested to validate crack-path predictions. Also, test gears were installed with special crack-propagation gages in the tooth fillet region to measure bending-fatigue crack growth. From both predictions and tests, gears with backup ratios
Mode III effects on interface delamination
Tvergaard, Viggo; Hutchinson, J.W.
2008-01-01
For crack growth along an interface between dissimilar materials the effect of combined modes I, II and III at the crack-tip is investigated. First, in order to highlight situations where crack growth is affected by a mode III contribution, examples of material configurations are discussed where...... mode III has an effect. Subsequently, the focus is on crack growth along an interface between an elastic-plastic solid and an elastic substrate. The analyses are carried out for conditions of small-scale yielding, with the fracture process at the interface represented by a cohesive zone model. Due to...... the mismatch of elastic properties across the interface the corresponding elastic solution has an oscillating stress singularity, and this solution is applied as boundary conditions on the outer edge of the region analyzed. For several combinations of modes I, II and III crack growth resistance curves...
Crack propagation behavior of TiN coatings by laser thermal shock experiments
Highlights: ► The crack propagation behavior of TiN coating after laser thermal shock experiment was observed by using FIB and TEM. ► Intercolumnar cracks between TiN columnar grains were predominant cracking mode after laser thermal shock. ► Cracks were propagated from the coating surface to the substrate at low laser pulse energy and cracks were originated at coating-substrate interface at high laser pulse energy. ► The cracks from the interface spread out transversely through the weak region of the columnar grains by repetitive laser shock. - Abstract: The crack propagation behavior of TiN coatings, deposited onto 304 stainless steel substrates by arc ion plating technique, related to a laser thermal shock experiment has been investigated using focused ion beam (FIB) and transmission electron microscopy (TEM). The ablated regions of TiN coatings by laser ablation system have been investigated under various conditions of pulse energies and number of laser pulses. The intercolumnar cracks were predominant cracking mode following laser thermal shock tests and the cracks initiated at coating surface and propagated in a direction perpendicular to the substrate under low loads conditions. Over and above those cracks, the cracks originated from coating-substrate interface began to appear with increasing laser pulse energy. The cracks from the interface also spread out transversely through the weak region of the columnar grains by repetitive laser shock.
Modeling Delamination of Interfacial Corner Cracks in Multilayered Structures
Veluri, Badrinath (Badri); Jensen, Henrik Myhre
Multilayered electronic components, typically of heterogeneous materials, delaminate under thermal and mechanical loading. A phenomenological model focused on modeling the shape of such interface cracks close to corners in layered interconnect structures for calculating the critical stress for st...
François, Marc Louis Maurice
2009-01-01
Due to their microstructure, quasi brittle materials present rough cracks. Under sliding of the crack lips, this roughness involves in one hand induced opening and in the other hand some apparent plasticity which is due to the interlocking of the crack lips combined with Coulomb's friction. The proposed model is written under the irreversible thermodynamics framework. Micromechanics uses the Del Piero and Owen's structured deformation theory. Opening of the crack depends upon the crack shape and the relative sliding of the crack lips. The thermodynamic force associated to the sliding has the mechanical meaning of the force acting in order to make the crack slide. Yield surface is defined as a limitation of this force with respect to the Coulomb's friction and the Barenblatt cohesion. The crack orientation is defined as the one for which the criterion is reached for the lowest stress level. A decreasing cohesion, respect to sliding is supposed. Tension and compression reference cases are envisaged.
The possible causes of cold cracking can be relatively clearly defined according to today's state of knowledge. By knowing these causes, it is possible to control the risk of cold cracking to the greatest extent; with the knowledge of the position and dimensions of these cracks, as well as the time of their occurence together with an optimization of the testing technique, the detection control of the cracking freedom can be almost considered as solved. (orig.)
A tubing weld cracking (TWC) test was developed for applications involving advanced austenitic alloys (such as modified 800H and 310HCbN). Compared to the Finger hot cracking test, the TWC test shows an enhanced ability to evaluate the crack sensitivity of tubing materials. The TWC test can evaluate the cracking tendency of base as well as filter materials. Thus, it is a useful tool for tubing suppliers, filler metal producers and fabricators
Interaction between Interfacial Collinear Griffith Cracks in Composite Media under Thermal Loading
Mishra, P. K.; Das, S.
2016-05-01
This article deals with the interactions between a central crack and a pair of outer cracks situated at the interface of orthotropic elastic half planes under thermo-mechanical loading. The mixed boundary value problem has been reduced to a pair of singular integral equations which has been solved numerically using Jacobi polynomial method. The interaction effects have been obtained in terms of stress magnification factors depending on the crack spacing and crack length. The phenomena of crack shielding and crack amplification have been depicted through graphs for different particular cases.
Matrix fatigue crack development in a notched continuous fiber SCS-6/Ti-15-3 composite
Hillberry, B. M.; Johnson, W. S.
1990-01-01
In this study the extensive matrix fatigue cracking that has been observed in notched SCS-6/Ti-15-3 composites is investigated. Away from the notch a uniform spacing of the fatigue cracks develops. Closer to the notch, fiber-matrix debonding which occurs increases the crack spacing. Crack spacing and debond length determined from shear-lag cylinder models compare favorably with experimental observations. Scanning electron microscope (SEM) fractography showed that the principal fatigue crack initiation occurred around the zero degree fibers. Interface failure in the 90 degree plies does not lead to the development of the primary fatigue cracking.
Matrix Crack Detection by an Embedded Polarimetric Sensor
无
2006-01-01
Polarimetric optical fibre sensors have been embedded within the 0° ply and close to the 0/90 interface of transparent cross-ply GFRP coupons. The laminate ply cracks may initiate and propagate across the coupon when the coupons were subjected to an increasing quasi-static load in a servo-hydraulic testing machine.Crack accumulation have been monitored using a long gauge-length extensometer. The response of the strain signal, the optical signal and the load signal to cracks at different positions in the coupon in relation to the extensometer and optical sensor positions have been acquired and compared by means of video images of the crack growth. The relationship between crack growth and sensor response was demonstrated. The displacement induced by a new transverse crack has been predicted and compared with experimental data.
Modified Dugdale cracks and Fictitious cracks
Nielsen, Lauge Fuglsang
1998-01-01
A number of theories are presented in the literature on crack mechanics by which the strength of damaged materials can be predicted. Among these are theories based on the well-known Dugdale model of a crack prevented from spreading by self-created constant cohesive flow stressed acting in local a......-critical loads. Such information, which cannot be obtained experimentally, are needed in viscoelastic lifetime analysis.Finally, the question is considered whether or not fracture properties experimentally determined are real (genuine) material properties.......A number of theories are presented in the literature on crack mechanics by which the strength of damaged materials can be predicted. Among these are theories based on the well-known Dugdale model of a crack prevented from spreading by self-created constant cohesive flow stressed acting in local...... (displacement) respectively of material considered. The practical applicability of the two models is limited such that predicted strength sigma_CR must be less than sigma_L/3, which corresponds to an assumption that fictitious cracks are much smaller than real crack lengths considered. The reason for this...
Interface Fracture in Adhesively Bonded Shell Structures
Jensen, Henrik Myhre
2007-01-01
Two methods for the prediction of crack propagation through the interface of adhesively bonded shells are discussed. One is based on a fracture mechanics approach; the other is based on a cohesive zone approach. Attention is focussed on predicting the shape of the crack front and the critical...
Creep Behavior and Durability of Cracked CMC
Bhatt, R. T.; Fox, Dennis; Smith, Craig
2015-01-01
To understand failure mechanisms and durability of cracked Ceramic matrix composites (CMCs), Melt Infiltration (MI) SiCSiC composites with Sylramic-iBN fibers and full Chemical vapour infiltration SiCSiC composites with Sylramic-ion bombarded BN (iBN) and Hi-Nicalon -S fibers were pre-cracked between 150 to 200 megapascal and then creep and Sustained Peak Low Cycle Fatigue (SPLCF) tested at 13150 C at stress levels from 35 to 103 megapascal for up to 200 hours under furnace and burner rig conditions. In addition creep testing was also conducted on pre-cracked full Chemical vapour infiltration SiCSiC composites at 14500 C between 35 and 103 megapascal for up to 200 hours under furnace conditions. If the specimens survived the 200 hour durability tests, then they were tensile tested at room temperature to determine their residual tensile properties. The failed specimens were examined by Scanning electron microscope (SEM) to determine the failure modes and mechanisms. The influence of crack healing matrix, fiber types, crack density, testing modes and interface oxidation on durability of cracked Ceramic matrix composites (CMCs) will be discussed.
Application of a cycle jump technique for acceleration of fatigue crack growth simulation
Moslemian, Ramin; Karlsson, A.M.; Berggreen, Christian
2010-01-01
A method for accelerated simulation of fatigue crack growth in a bimaterial interface is proposed. To simulate fatigue crack growth in a bimaterial interface a routine is developed in the commercial finite element code ANSYS and a method to accelerate the simulation is implemented. The proposed...... method is based on conducting finite element analysis for a set of cycles to establish a trend line, extrapolating the trend line spanning many cycles, and use the extrapolated state as initial state for additional FE simulations. The inputs of the developed method are the crack growth rate vs. energy...... release rate diagrams for different mode-mixities. Once these diagrams for a specific interface are available, fatigue crack growth in any structure with the same interface can be simulated. Using the developed method, fatigue crack growth in the interface of a sandwich beam is simulated. Results of the...
A penny-shaped crack in a filament-reinforced matrix. I - The filament model. II - The crack problem
Erdogan, F.; Pacella, A. H.
1974-01-01
The study deals with the elastostatic problem of a penny-shaped crack in an elastic matrix which is reinforced by filaments or fibers perpendicular to the plane of the crack. An elastic filament model is first developed, followed by consideration of the application of the model to the penny-shaped crack problem in which the filaments of finite length are asymmetrically distributed around the crack. Since the primary interest is in the application of the results to studies relating to the fracture of fiber or filament-reinforced composites and reinforced concrete, the main emphasis of the study is on the evaluation of the stress intensity factor along the periphery of the crack, the stresses in the filaments or fibers, and the interface shear between the matrix and the filaments or fibers. Using the filament model developed, the elastostatic interaction problem between a penny-shaped crack and a slender inclusion or filament in an elastic matrix is formulated.
Pevnost v ohybu a hydrolytická stabilita FRC/PFC dentálního bi-materiálu
Dombková, Julie
2010-01-01
Tato bakalářská práce se zabývá pevností v ohybu FRC/PFC dentálních bi-materiálů a do jaké míry jsou schopny odolávat hydrolytické degradaci. Vzorky ve tvaru trámečku byly zatěžovány ve tříbodém ohybu. Pevnost a modul pružnosti byly měřeny za použití univerzálního testovacího stroje Zwick Z0100. Skenovací elektronový mikroskop (SEM) byl použit pro pozorování porušených míst. Ze získaných výsledků vyplývá, že mechanické vlastnosti jsou ovlivněny kvalitou smáčení vláknového kompozitu, prostorov...
Assessment of the stability of a surface crack in laminates
Hutař, Pavel; Ševčík, Martin; Náhlík, Luboš; Zouhar, Michal; Knésl, Zdeněk
2014-01-01
Roč. 50, č. 1 (2014), s. 9-16. ISSN 0191-5665 R&D Projects: GA ČR(CZ) GAP108/12/1560 Institutional support: RVO:68081723 Keywords : periodically layered composite * interface crack * generalized stress intensity factor * fracture mechanics of interface Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 0.473, year: 2014
A nonlinear interface model applied to masonry structures
Lebon, Frédéric; Raffa, Maria Letizia; Rizzoni, Raffaella
2015-12-01
In this paper, a new imperfect interface model is presented. The model includes finite strains, micro-cracks and smooth roughness. The model is consistently derived by coupling a homogenization approach for micro-cracked media and arguments of asymptotic analysis. The model is applied to brick/mortar interfaces. Numerical results are presented.
Elevated temperature crack growth
Kim, K. S.; Vanstone, R. H.
1992-01-01
The purpose of this program was to extend the work performed in the base program (CR 182247) into the regime of time-dependent crack growth under isothermal and thermal mechanical fatigue (TMF) loading, where creep deformation also influences the crack growth behavior. The investigation was performed in a two-year, six-task, combined experimental and analytical program. The path-independent integrals for application to time-dependent crack growth were critically reviewed. The crack growth was simulated using a finite element method. The path-independent integrals were computed from the results of finite-element analyses. The ability of these integrals to correlate experimental crack growth data were evaluated under various loading and temperature conditions. The results indicate that some of these integrals are viable parameters for crack growth prediction at elevated temperatures.
Eliminating cracking during drying
Jin, Qiu; Tan, Peng; Schofield, Andrew B.; Xu, Lei
2013-01-01
When colloidal suspensions dry, stresses build up and cracks often occur - a phenomenon undesirable for important industries such as paint and ceramics. We demonstrate an effective method which can completely eliminate cracking during drying: by adding emulsion droplets into colloidal suspensions, we can systematically decrease the amount of cracking, and eliminate it completely above a critical droplet concentration. Since the emulsion droplets eventually also evaporate, our technique achiev...
Crack identification in elasticity
Crack and defect, e.g. hole, identification in elasticity, is formulated as an output optimization problem, where predictions of a suitably parametrized mechanical model are compared with measured data. For the mechanical part the elastostatic analysis is done by the boundary element method, including hypersingular boundary elements for the cracks. In addition, unilateral contact effects along the crack boundaries, i.e., the possibility of partially closed cracks, are considered. Unilateral crack identification has been studied. The numerical solution of the (ill-posed) inverse problem usually requires the use of specialized algorithms and techniques. Among others, we consider neural networks, filter-driven optimization and genetic algorithms. It seems that classical optimization works only in connection with sensitivity analysis for the accurate calculation of the first derivatives for classical cracks and for unilateral cracks). A short review of recent contributions in this area together with the numerical results of our on-going investigation will be presented in the conference. The effect of unilateral contact on the crack identification will be examined. Multiple-crack and multipleload identification problems will be considered. The effectiveness of various solution algorithms will be discussed. Promising directions of further research in this area will be pointed out. Refs. 7 (author)
Growth of inclined fatigue cracks using the biaxial CJP model
G. Laboviciute
2015-07-01
Full Text Available The CJP model of crack tip stresses is a modified version of the Williams crack tip stress field which takes account of simplified stress distributions that arise from the presence of a zone of plastic deformation associated with the crack flanks and crack tip, and that act on the elastic field responsible for driving crack growth. The elastic stress field responsible for crack growth is therefore controlled by the applied loading and by the induced boundary stresses at the interface with the plastic zone. This meso-scale model of crack tip stresses leads to a modified set of crack tip stress intensity factors that include the resultant influence of plastic wake-induced crack tip shielding, and which therefore have the potential to help resolve some longstanding controversies associated with plasticity-induced closure. A full-field approach has now been developed for stress using photoelasticity and also for displacement using digital image correlation. This paper considers the characterisation of crack growth rate data with the biaxial CJP model, using compact tension specimens that contain inclined cracks at the notch tip with initial angles of 30°, 45° and 60° to the horizontal axis. Significant experimental difficulties are experienced in growing cracks in a biaxial field under uniaxial tensile loading, as the natural tendency of the crack is to turn so that it becomes perpendicular to the maximum principal stress direction. However, crack angle is not an issue in the CJP model which calculates the stress field parallel with, and perpendicular to, the crack plane. These stress components can be rotated into directions comparable with the usual KI and KII directions and used to calculate stress intensity parameters that should be directly comparable with the standard stress intensity formulations. Another difficulty arises, however, in finding published expressions for KI and KII for CT specimens with curved or kinked cracks. The CJP model
Structural Considerations on Fatigue Cracks
Cornel Bit
2015-07-01
Full Text Available This paper has been focused on the modern theoretical and experimental investigations on fatigue of metals which are now largely concentrated on three important areas: fatigue crack nucleation, short crack growth and long crack propagation. The main differences concerning the short cracks and long cracks mechanical investigation analysis have been presented.
Structural Considerations on Fatigue Cracks
Cornel Bit
2015-01-01
This paper has been focused on the modern theoretical and experimental investigations on fatigue of metals which are now largely concentrated on three important areas: fatigue crack nucleation, short crack growth and long crack propagation. The main differences concerning the short cracks and long cracks mechanical investigation analysis have been presented.
Perturbation of Mode III interfacial cracks
Piccolroaz, A; Movchan, A B
2010-01-01
We consider the perturbation problem of a Mode III interfacial crack. The perturbation is of geometrical type and can be both perturbation of the crack faces and perturbation of the interface, which can deviate from the initial straight line configuration. Asymptotic formulae are derived for the first-order perturbation of the stress intensity factor. It is shown that, due to the unsymmetrical nature of the problem, the Mode III skew-symmetric weight function derived in Piccolroaz et al. (2009) is essential for the derivation of the correct asymptotic formulae. To illustrate the method, we present the numerical results for different geometrical perturbations of a half-plane interfacial crack in an infinite bimaterial structure. Discussion on the extension of the method to finite bodies is also presented.
Some dynamic crack growth problems are investigated, from basic academic tests to actual industrial situations, using analytical or numerical methods. The purpose of this paper is to describe the successive fast crack growth and arrest, driven by a discontinuity in fracture toughness. The main purpose of this article is the description of both crack growth and arrest, with the same governing equations for a wide range of examples. The initial problem is the peel test of a thin film bonded to a flat rigid surface. The film is divided in two zones of different bonding properties. This entails a fast de-bonding process, followed by an arrest. The problem is analytically solved, with the combined use of the characteristics method and the Griffith criterion. Then, a bi-material Double Cantilever Beam (DCB) is considered, the materials concerned having different surface energies. This test involves a dynamic crack growth, which is numerically handled with Cohesive Zone Models (CZM). These models are derived from general energy concepts of the fracture process. Comparative predictions with dynamic and static analyses are discussed for these two problems. Finally, a real survey of a Pressure Water Reactor vessel shell, affected by an edge crack and submitted to an inner pressure loading, is carried out with CZM. Two situations are investigated. First, the initial flaw is assumed to propagate in a homogeneous base steel of constant toughness. Secondly, a small elastic zone of low toughness is embedded in the base metal along the crack path. We will focus on the possible crack jump and arrest in these two configurations, depending on whether the base metal exhibits elastic or plastic behavior, and on the relative toughness of the small zone with respect to the surrounding material. (authors)
The regulatory issues associated with cracking of boiling water reactor (BWR) internals is being addressed by the Nuclear Regulatory Commission (NRC) staff and is the subject of a voluntary industry initiative. The lessons learned from this effort will be applied to pressurized water reactor (PWR) internals cracking issues
Chudnovsky, A.
1984-01-01
A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.
Analysis of diffusive mass transport in a cracked buffer
In the disposal vault design for the Canadian Nuclear Fuel Waste Management Program, cylindrical containers of used nuclear fuel would be placed in vertical boreholes in rock and surrounded with a bentonite-based buffer material. The buffer is expected to absorb and/or retard radionuclides leaching from the fuel after the containers fail. There is some evidence, however, that the buffer may be susceptible to cracking. In this report we investigate numerically the consequences of cracking on uranium diffusion through the buffer. The derivation of the mass-transport equations and the numerical solution method are presented for the solubility-limited diffusion of uranium in a cracked buffer system for both swept-away and semi-impermeable boundary conditions at the rock-buffer interface. The results indicate that for swept-away boundary conditions the total uranium flux through the cracked buffer system is, as expected, greater than through the uncracked buffer. The effect of the cracks is strongly dependent on the ratio D/Deff, where D and Deff are the pore-water and the effective buffer diffusion coefficient, respectively. However, although a decrease in Deff enhances the effect of cracks on the total cumulative flux (relative to the uncracked buffer), it also decreases the total cumulative flux through the cracked buffer system (relative to a cracked buffer with a larger Deff value). Finally, for semi-impermeable boundary conditions, the effect of cracks on the total radionuclide flux is relatively small
Crack path simulation for cylindrical contact under fretting conditions
R.A. Cardoso
2016-02-01
Full Text Available In this work different strategies to estimate crack path for cylindrical contacts under fretting conditions are carried out. The main goal is to propose and to evaluate methodologies not only to estimate the direction of crack initiation but also the subsequent propagation in its earlier stages, where the stress field is multiaxial, non-proportional and decays very fast due to the proximity with the contact interface. Such complex conditions pose a substantial challenge to the modelling of crack path. The numerical simulations are provided by a 2D Finite Element Analysis taking into account interactions between the crack faces. The results show that, under fretting conditions, models based on the critical plane method are not effective to estimate the crack initiation orientation, while models based on a so called “critical direction” applied along a critical distance provide better results. Regarding the subsequent crack propagation orientation, it was possible to see that stress intensity factor based models where one considers an infinitesimal virtual crack emerging from an original preexistent crack are powerful mechanisms of crack orientation estimation.
Larsen, James M.; Allison, John E.
This book contains chapters on fracture mechanics parameters for small fatigue cracks, monitoring small-crack growth by the replication method, measurement of small cracks by photomicroscopy (experiments and analysis), and experimental mechanics of microcracks. Other topics discussed are the real-time measurement of small-crack-opening behavior using an interferometric strain/displacement gage; direct current electrical potential measurement of the growth of small cracks; an ultrasonic method for the measurement of the size and opening behavior of small fatigue cracks; and the simulation of short crack and other low closure loading conditions, utilizing constant K(max) Delta-K-decreasing fatigue crack growth procedures.
Li Ming Zhou
2016-01-01
Full Text Available Based on the finite element software ABAQUS and graded element method, we developed a dummy node fracture element, wrote the user subroutines UMAT and UEL, and solved the energy release rate component of functionally graded material (FGM plates with cracks. An interface element tailored for the virtual crack closure technique (VCCT was applied. Fixed cracks and moving cracks under dynamic loads were simulated. The results were compared to other VCCT-based analyses. With the implementation of a crack speed function within the element, it can be easily expanded to the cases of varying crack velocities, without convergence difficulty for all cases. Neither singular element nor collapsed element was required. Therefore, due to its simplicity, the VCCT interface element is a potential tool for engineers to conduct dynamic fracture analysis in conjunction with commercial finite element analysis codes.
Fuel pellets undergo thermally induced cracking during normal reactor operation. Some fuel performance codes have included models that address the effects of fuel cracking on fuel rod thermal and mechanical behavior. However, models that rely too heavily on continuum mechanics formulations (annular gaps and solid cylindrical pellets) characteristically do not adequately predict cladding axial elongations. Calculations of bamboo ridging generally require many assumptions concerning fuel geometry, and some of the methods used are too complex and expensive to employ on a routine basis. Some of these difficulties originate from a lack of definition of suitable parameters which describe the cracked fuel medium. The methodology is being improved by models that describe cracked fuel behavior utilizing parameters with stronger physical foundations instead of classical continuum formulations. This paper presents a modelling concept and a set of measurable parameters that have been shown to improve the prediction of the mechanical behavior of cracked fuel/cladding systems without added computational expense. The transition from classical annular gap/cylindrical pellet models to modified bulk properties and further to local behavior for cracked fuel systems is discussed. The results of laboratory experiments to verify these modelling parameters are shown. Data are also presented from laboratory experiments on unirradiated and irradiated rods which show that fuel rod mechanical response depends on fuel fragment size. The impact of these data on cracked fuel behavior and failure modelling is also discussed. (author)
Zhao, Zenghui; Lv, Xianzhou; Wang, Weiming; Tan, Yunliang
2016-01-01
Considering the structure effect of tunnel stability in western mining of China, three typical kinds of numerical model were respectively built as follows based on the strain softening constitutive model and linear elastic-perfectly plastic model for soft rock and interface: R-M, R-C(s)-M and R-C(w)-M. Calculation results revealed that the stress-strain relation and failure characteristics of the three models vary between each other. The combination model without interface or with a strong interface presented continuous failure, while weak interface exhibited 'cut off' effect. Thus, conceptual models of bi-material model and bi-body model were established. Then numerical experiments of tri-axial compression were carried out for the two models. The relationships between stress evolution, failure zone and deformation rate fluctuations as well as the displacement of interface were detailed analyzed. Results show that two breakaway points of deformation rate actually demonstrate the starting and penetration of the main rupture, respectively. It is distinguishable due to the large fluctuation. The bi-material model shows general continuous failure while bi-body model shows 'V' type shear zone in weak body and failure in strong body near the interface due to the interface effect. With the increasing of confining pressure, the 'cut off' effect of weak interface is not obvious. These conclusions lay the theoretical foundation for further development of constitutive model for soft rock-coal combination body. PMID:27066329
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.
THE EFFECT OF AN ELASTIC TRIANGULAR INCLUSION ON A CRACK
焦贵德; 王银邦
2003-01-01
The interaction between an elastic triangular inclusion and a crack is investigated. The problem is formulated using the boundary integral equations for traction boundary value problems derived by Chau and Wang as basic equations. By using the continuity condition of traction and displacement on interface as supplement equations, a set of equations for solving the interaction problem between an inclusion and a crack are obtained, which are solved by asing a new boundary element method. The results in terms of stress intensity factors (SIFs) are calculated for a variety of crack-inclusion arrangements and the elastic constants of the matrix and the inclusion. The results are valuable for studying new composite materials.
Cracks in Polymer Spherulites: Phenomenological Mechanisms in Correlation with Ring Bands
Eamor M. Woo
2016-09-01
Full Text Available This article reviews possible mechanisms of various crack forms and their likely correlations with interior crystal lamellae and discontinuous interfaces in spherulites. Complex yet periodically repetitive patterns of cracks in spherulites are beyond attributions via differences in thermal expansion coefficients, which would cause random and irregular cracks in the contract direction only. Cracks in brittle polymers such as poly(l-lactic acid (PLLA, or poly(4-hydroxyl butyrate (PHB, or more ductile polymers such as poly(trimethylene terephthalate (PTT are examined and illustrated, although for focus and demonstration, more discussions are spent on PLLA. The cracks can take many shapes that bear extremely striking similarity to the ring-band or lamellar patterns in the same spherulites. Crack patterns may differ significantly between the ring-banded and ringless spherulites, suggesting that the cracks may be partially shaped and governed by interfaces of lamellae and how the lamellar crystals assemble themselves in spherulites. Similarly, with some exceptions, most of the cracks patterns in PHB or PTT are also highly guided by the lamellar assembly in either ring-banded spherulites or ringless spherulites. Some exceptions of cracks in spherulites deviating from the apparent crystal birefringence patterns do exist; nevertheless, discontinuous interfaces in the initial lamellae neat the nuclei center might be hidden by top crystal over-layers of the spherulites, which might govern crack propagation.
Wiseman, Peter
1977-01-01
Presents a discussion of the manufacture of ethylene by thermal cracking of hydrocarbon feedstocks that is useful for introducing the subject of industrial chemistry into a chemistry curriculum. (MLH)
Thoft-Christensen, Palle
Modelling of corrosion cracking of reinforced concrete structures is complicated as a great number of uncertain factors are involved. To get a reliable modelling a physical and mechanical understanding of the process behind corrosion in needed.......Modelling of corrosion cracking of reinforced concrete structures is complicated as a great number of uncertain factors are involved. To get a reliable modelling a physical and mechanical understanding of the process behind corrosion in needed....
2009-01-01
A kinetic interface for orientation detection in a video training system is disclosed. The interface includes a balance platform instrumented with inertial motion sensors. The interface engages a participant's sense of balance in training exercises.......A kinetic interface for orientation detection in a video training system is disclosed. The interface includes a balance platform instrumented with inertial motion sensors. The interface engages a participant's sense of balance in training exercises....
Material size effects on crack growth along patterned wafer-level Cu–Cu bonds
Tvergaard, Viggo; Niordson, Christian Frithiof; Hutchinson, John W.
2013-01-01
together. Crack growth along the bond interface is here studied numerically using finite element analyses. The experiments have shown that plasticity in the Cu films makes a major contribution to the macroscopic interface toughness. To account for the size dependence of the plastic flow a strain gradient...... plasticity model is applied here for the metal. A cohesive zone model is applied to represent the crack growth along the bond between the two Cu films. This cohesive zone model incorporates the effect of higher order stresses in the continuum, such that the higher order tractions on the crack faces decay to...... zero values when the crack separation process takes place.The analyses focus on a pattern of Cu lines orthogonal to the crack growth direction, and the analyses are carried out for plane strain conditions with the assumption of small scale yielding under remote mode I loading. When crack growth over a...
Crack growth and rupture characteristics of stress corrosion cracks
The contribution describes rupture-mechanical studies on stress-corrosion cracks which occurred at components during use. The tests are complemented by test specimens with stress-corrosion cracks which were induced in the laboratory. The tests show that the stress-corrosion cracks of the tested higher-tensile heat-treatable steels have an intercrystalline crack development, crack branchings and multiple cracks with differing linear and depth expansions. With the same external stress and fracture toughness, the load on stress-corrosion cracks must be at least 1.4 times higher in order to initiate the fracture. The critical crack sizes are at least two times bigger than the result of a fracture-mechanical evaluation based on clean and unbranched cracks. (orig./RHM)
FATIGUE CRACK INITIATION AND PROPAGATION OF A TiNi SHAPE MEMORY ALLOY
Gloanec, Anne-Lise; Cerrachio, Priscillia; Reynier, Bertrand; Van Herpen, Alain; Riberty, Patrice
2010-01-01
Fatigue crack initiation and propagation stages of a TiNi shape memory alloy are examined thanks to a low cycle fatigue interrupted test. Submitted to fatigue cyclic loading, the response of the alloy presents a classical pseudoelastic response. Two potential initiation crack areas are highlighted: at the phase interfaces or at the grain boundaries. Then, propagation results from the coalescence of many microscopic cracks. These two stages are detectable at the last 20% of the total fatigue l...
Kumar, Deepak; Roy, Rene; Kweon, Jin-Hwe; Choi, Jin-ho
2015-10-01
Sub-laminate damage in the form of matrix cracking and delamination was simulated by using interface cohesive elements in the finite element (FE) software ABAQUS. Interface cohesive elements were inserted parallel to the fiber orientation in the transverse ply with equal spacing (matrix cracking) and between the interfaces (delamination). Matrix cracking initiation in the cohesive elements was based on stress traction separation laws and propagated under mixed-mode loading. We expanded the work of Shi et al. (Appl. Compos. Mater. 21, 57-70 2014) to include delamination and simulated additional [45/-45/0/90]s and [02/90n]s {n = 1,2,3} CFRP laminates and a [0/903]s GFRP laminate. Delamination damage was quantified numerically in terms of damage dissipative energy. We observed that transverse matrix cracks can propagate to the ply interface and initiate delamination. We also observed for [0/90n/0] laminates that as the number of 90° ply increases past n = 2, the crack density decreases. The predicted crack density evolution compared well with experimental results and the equivalent constraint model (ECM) theory. Empirical relationships were established between crack density and applied stress by linear curve fitting. The reduction of laminate elastic modulus due to cracking was also computed numerically and it is in accordance with reported experimental measurements.
Pease, Bradley Justin; Geiker, Mette Rica; Stang, Henrik; Weiss, Jason
2006-01-01
Reinforced concrete structures are known to crack due to restrained shrinkage, temperature gradients, application of load, and expansive reactions. Cracks provide paths for rapid ingress of moisture, chlorides, and other aggressive substances, which may affect the long-term durability of the...... structure. For example, concrete cracks located at the reinforcing steel may contribute to a rapid corrosion initiation and propagation. Previous research has shown that cracked reinforced concrete under static flexural loading may have an increased ingress of chloride ions along the reinforcement/concrete...... interface. The aim of this paper is to provide a detailed description of the development of cracks in reinforced concrete under flexural load. Cracking at both realistic service load levels (1.0-1.8 times estimated cracking load) and unrealistically high service load levels (> 0.5 times beam capacity) has...
Modified time reversal imaging of a closed crack based on nonlinear scattering
Blanloeuil, Philippe; Rose, L. R. Francis; Guinto, Jed A.; Veidt, Martin; Wang, Chun H.
2016-04-01
A recent variant of time reversal imaging is used to detect and characterize a closed crack based on both the fundamental and the second harmonic components of the scattered waves in the presence of Contact Acoustic Nonlinearity at the crack interface. A Finite Element model, which includes unilateral contact with Coulomb friction to account for contact between the crack faces, is used to compute the scattered field resulting from the interaction between incident longitudinal plane waves and the crack. The knowledge of the scattering for multiple incident angles constitutes the input for the imaging algorithm. Good reconstruction of the crack is obtained from both harmonic sources, and second harmonic based images also enables one to identify the location of the second harmonic sources along the crack. This first imaging based on the second harmonic also offers potential baseline free detection of closed cracks.
Effects of multiple cracks on the forced response of centrifugal impellers
Wang, Shuai; Zi, Yanyang; Wan, Zhiguo; Li, Bing; He, Zhengjia
2015-08-01
The effects of multiple cracks on the forced response of centrifugal impellers are investigated using a finite-element based component mode synthesis method (CMS) in this paper. The main objective is to gain some insights into the response characteristics of multiple cracked impellers and to explore efficient methods for identifying the cracks. First, in order to generate an efficient model for the nonlinear vibration analysis, a novel hybrid interface CMS method is proposed and used to conduct reduced-order modeling for the cracked impeller. Then, a method for multiple cracks modeling is developed to account for the crack breathing effects. Finally, numerical results are presented using a representative impeller with double cracks. The shifts of natural frequencies and the nonlinear forced response due to multiple cracks are of interest. Lengths and relative positions of the cracks are also considered. The results show that the natural frequencies and forced response become complexly depending on the lengths and relative positions of cracks, and the response amplitudes of blades periodically fluctuate versus blade number when an impeller suffers from cracks or mistuning. A potential method for identifying the lengths and relative positions of multiple cracks are also discussed in this paper.
Although it is possible to simulate the ground blast from a single explosive shot with a simple computer algorithm and appropriate constants, the most commonly used modelling methods do not account for major changes in geology or shot energy because mechanical features such as tectonic stresses, fault structure, microcracking, brittle-ductile transition, and water content are not represented in significant detail. An alternative approach for modelling called Statistical Crack Mechanics is presented in this paper. This method, developed in the seventies as a part of the oil shale program, accounts for crack opening, shear, growth, and coalescence. Numerous photographs and micrographs show that shocked materials tend to involve arrays of planar cracks. The approach described here provides a way to account for microstructure and give a representation of the physical behavior of a material at the microscopic level that can account for phenomena such as permeability, fragmentation, shear banding, and hot-spot formation in explosives
Crack propagation in Hastelloy X
The fatigue and creep crack growth rates of Hastelloy X were examined both in air and impure helium. Creep crack growth rate is higher in air and impure helium at 6500C. Initial creep crack growth from the original sharp fatigue crack is by an intergranular mode of fracture. As the cracking accelerates at higher stress intensities, growth is by a mixed mode of both intergranular and transgranular fracture. Fatigue crack growth rate increases with increasing temperature and decreasing frequency for the range of stress intensities reported in the literature and is lower in impure helium than in air
Over the last several years, the Heavy Section Steel Technology (HSST) Program has conducted several fracture mechanics experiments on large specimens that produced crack-arrest fracture-toughness values above 220 MPa·√m, which is the limit imposed by the ASME Code and the limit included in the Issues on Pressurized Thermal Shock studies. It is therefore appropriate and timely to investigate the influence that these high crack-arrest data have on the integrity assessment of nuclear Reactor Pressure Vessels (RPVs). A review of the evolution of the Pressurized Thermal Shock (PTS) issue and current methods of analysis provides insight into the motivation for the HSST Program performing the large-specimen fracture mechanics experiments. During the early 1970s, it was recognized that RPVs could be subjected to severe thermal shock as the result of a large-break loss-of-coolant accident (LBLOCA). Analyses performed at that time indicated that thermal shock alone would not result in failure (through-wall cracking) of the vessel. However, a combination of pressure and a less severe thermal shock, the result of some postulated transients, could result in vessel failure. In March 1978, such a transient occurred at the Rancho Seco nuclear power plant. As a result of these events, parametric PTS studies were undertaken. Because of the apparent need for and the existence of high-temperature crack-arrest capability, the NRC HSST Program and others began to investigate the effect of higher crack-arrest values on the probability of failure and to determine if these values actually exist for prototypical RPV materials. This report describes the results of HSST Program large-specimen crack-arrest testing
A consistent partly cracked XFEM element for cohesive crack growth
Asferg, Jesper L.; Poulsen, Peter Noe; Nielsen, Leif Otto
2007-01-01
Present extended finite element method (XFEM) elements for cohesive crack growth may often not be able to model equal stresses on both sides of the discontinuity when acting as a crack-tip element. The authors have developed a new partly cracked XFEM element for cohesive crack growth with extra...... was used to solve the non-linear equations. The performance of the element is illustrated by modelling fracture mechanical benchmark tests. Investigations were carried out on the performance of the element for different crack lengths within one element. The results are compared with previously...... enrichments to the cracked elements. The extra enrichments are element side local and were developed by superposition of the standard nodal shape functions for the element and standard nodal shape functions for a sub-triangle of the cracked element. With the extra enrichments, the crack-tip element becomes...
Crack evolution in bulk metallic glasses
In the present study, the mechanisms underlying plastic deformation of a Ni-based bulk metallic glass (BMG) are explored. Based on the microstructural investigations, a model is proposed how fracture emerges in BMGs. After deformation, the glass is macroscopically more fragile indicating a decrease in the viscosity within the shear bands due to shear softening. These fluctuations of viscosity and therefore Poisson ratio between the deformed and undeformed regions appear to be the initiation sites for nanometer-scale cracks, which are aligned parallel to the applied force. Coalescence of voids is believed to form these small cracks, which eventually interconnect along the interface between the sheared and unsheared regions to form a detrimental defect resulting in fracture.
Diagnostics - Crack Detection '87
The Proceedings of the International Symposium Diagnostics -Crack Detection '87 which was held from June 23 to 26 1987 in Sala (CSSR) contains 5 papers falling under the INIS Subject Scope. The said papers mainly deal with the problems of in-service diagnostics of pumps and steam turbines of nuclear power plants with WWER reactors, as well as crack detection of materials and welded joints of equipment and the control of the water regimen of the primary circuit of such power plants. (Z.M.)
Crack Propagation in Honeycomb Cellular Materials: A Computational Approach
Marco Paggi
2012-02-01
Full Text Available Computational models based on the finite element method and linear or nonlinear fracture mechanics are herein proposed to study the mechanical response of functionally designed cellular components. It is demonstrated that, via a suitable tailoring of the properties of interfaces present in the meso- and micro-structures, the tensile strength can be substantially increased as compared to that of a standard polycrystalline material. Moreover, numerical examples regarding the structural response of these components when subjected to loading conditions typical of cutting operations are provided. As a general trend, the occurrence of tortuous crack paths is highly favorable: stable crack propagation can be achieved in case of critical crack growth, whereas an increased fatigue life can be obtained for a sub-critical crack propagation.
Lokhandwala, Kaaeid A.; Baker, Richard W.
2001-01-01
Processes and apparatus for providing improved catalytic cracking, specifically improved recovery of olefins, LPG or hydrogen from catalytic crackers. The improvement is achieved by passing part of the wet gas stream across membranes selective in favor of light hydrocarbons over hydrogen.
The participants of the conference heard 36 papers of which 13 were incorporated in INIS. The incorporated papers deal with the quality control of the equipment of nuclear power plants, with technical specifications and possibilities of diverse crack detection devices, as well as with personnel training for nondestructive materials testing. (E.S.)
Laitinen, Amy
2012-01-01
The basic currency of higher education--the credit hour--represents the root of many problems plaguing America's higher education system: the practice of measuring time rather than learning. "Cracking the Credit Hour" traces the history of this time-based unit, from the days of Andrew Carnegie to recent federal efforts to define a credit hour. If…
Tailoring Sandwich Face/Core Interfaces for Improved Damage Tolerance
Lundsgaard-Larsen, Christian; Berggreen, Christian; Carlsson, Leif A.
2010-01-01
beam specimen loaded by uneven bending moments (DCB-UBM) allows for accurate measurements of the J integral as the crack propagates under large scale fibre bridging. By altering the mode-mixity of the loading, the crack path changes and deflects from the interface into the adjacent face or core. The...
The inverse, crack identification problem in elasticity can be formulated as an output error minimization problem which, nevertheless, can not be solved without difficulties by classical numerical optimization. A review of all these previous results, where we used neural networks, filter-driven optimization and genetic algorithms is presented and in a companion lecture during this conference. The use of neural networks for the solution of the inverse problem makes possible the on-line solution of the problem. In fact, one usually approximates the inverse mapping (measurements versus crack quantities). Most of the effort is spent for the learning of this relation, while a sufficiently trained neural network provides predictions with, practically, zero computational cost. Potential applications include on-line, in-flight health monitoring systems with applications in civil and mechanical engineering and production control. In this paper we present new developments in the design of specialized neural networks for the solution of the crack identification problem. Emphasis is posed on the effective use of the learning data, which are produced by the boundary element method. Several technical data will be discussed. They include thoughts about the effective choice of the neural network architecture, the number of training examples and of the learning algorithms will be provided, together with the results of our recent numerical investigation. A detailed application for one or more elliptical cracks using static analysis results with the use of back-propagation trained neural networks will be provided. The general methodology follows our previously published results. By using more refined algorithms for the numerical solution of the neural network learning problem, which are based on the MERLIN optimization system developed in the department of the second author, we are able to solve complicated tasks. First results based on dynamic investigations (wave propagation driven
Crack Cocaine and Infectious Tuberculosis
Story, A.; Bothamley, G.; Hayward, A.
2008-01-01
We hypothesize that crack cocaine is independently associated with smear-positive tuberculosis (TB). In a case-control study of TB in London, 19 (86%) of 22 crack cocaine users with pulmonary TB were smear positive compared with 302 (36%) of 833 non-drug users. Respiratory damage caused by crack cocaine may predispose drug users to infectivity.
Crack patterns over uneven substrates.
Nandakishore, Pawan; Goehring, Lucas
2016-02-28
Cracks in thin layers are influenced by what lies beneath them. From buried craters to crocodile skin, crack patterns are found over an enormous range of length scales. Regardless of absolute size, their substrates can dramatically influence how cracks form, guiding them in some cases, or shielding regions from them in others. Here we investigate how a substrate's shape affects the appearance of cracks above it, by preparing mud cracks over sinusoidally varying surfaces. We find that as the thickness of the cracking layer increases, the observed crack patterns change from wavy to ladder-like to isotropic. Two order parameters are introduced to measure the relative alignment of these crack networks, and, along with Fourier methods, are used to characterise the transitions between crack pattern types. Finally, we explain these results with a model, based on the Griffith criteria of fracture, that identifies the conditions for which straight or wavy cracks will be seen, and predicts how well-ordered the cracks will be. Our metrics and results can be applied to any situation where connected networks of cracks are expected, or found. PMID:26762761
Modified Dugdale crack models - some easy crack relations
Nielsen, Lauge Fuglsang
1997-01-01
The Dugdale crack model is widely used in materials science to predict strength of defective (cracked) materials. A stable Dugdale crack in an elasto-plastic material is prevented from spreading by uniformly distributed cohesive stresses acting in narrow areas at the crack tips. These stresses are......_Ldelta_CR where sigma_L is strength, and at the same time constant flow stress, of the uncracked material while delta_CR is flow limit (displacement).Obviously predictions by the Dugdale model are most reliable for materials with stress-strain relations where flow can actually be described (or well approximated......) by a constant flow stress (sigma_L). A number of materials, however, do not at all exhibit this kind of flow. Such materials are considered in this paper by Modified Dugdale crack models which apply for any cohesive stress distribution in crack front areas. Formally modified Dugdale crack models...
A penny-shaped crack in a filament reinforced matrix. 1: The filament model
Erdogan, F.; Pacella, A. H.
1973-01-01
The electrostatic problem of a penny-shaped crack in an elastic matrix which reinforced by filaments or fibers perpendicular to the plane of the crack was studied. The elastic filament model was developed for application to evaluation studies of the stress intensity factor along the periphery of the crack, the stresses in the filaments or fibers, and the interface shear between the matrix and the filaments or fibers. The requirements expected of the model are a sufficiently accurate representation of the filament and applicability to the interaction problems involving a cracked elastic continuum with multi-filament reinforcements. The technique for developing the model and numerical examples of it are shown.
Reduced-order modeling for mistuned centrifugal impellers with crack damages
Wang, Shuai; Zi, Yanyang; Li, Bing; Zhang, Chunlin; He, Zhengjia
2014-12-01
An efficient method for nonlinear vibration analysis of mistuned centrifugal impellers with crack damages is presented. The main objective is to investigate the effects of mistuning and cracks on the vibration features of centrifugal impellers and to explore effective techniques for crack detection. Firstly, in order to reduce the input information needed for component mode synthesis (CMS), the whole model of an impeller is obtained by rotation transformation based on the finite element model of a sector model. Then, a hybrid-interface method of CMS is employed to generate a reduced-order model (ROM) for the cracked impeller. The degrees of freedom on the crack surfaces are retained in the ROM to simulate the crack breathing effects. A novel approach for computing the inversion of large sparse matrix is proposed to save memory space during model order reduction by partitioning the matrix into many smaller blocks. Moreover, to investigate the effects of mistuning and cracks on the resonant frequencies, the bilinear frequency approximation is used to estimate the resonant frequencies of the mistuned impeller with a crack. Additionally, statistical analysis is performed using the Monte Carlo simulation to study the statistical characteristics of the resonant frequencies versus crack length at different mistuning levels. The results show that the most significant effect of mistuning and cracks on the vibration response is the shift and split of the two resonant frequencies with the same nodal diameters. Finally, potential quantitative indicators for detection of crack of centrifugal impellers are discussed.
Ravn, Anders P.; Staunstrup, Jørgen
1994-01-01
This paper proposes a model for specifying interfaces between concurrently executing modules of a computing system. The model does not prescribe a particular type of communication protocol and is aimed at describing interfaces between both software and hardware modules or a combination of the two....... The model describes both functional and timing properties of an interface...
Multiscale modeling of crack initiation and propagation at the nanoscale
Shiari, Behrouz; Miller, Ronald E.
2016-03-01
Fracture occurs on multiple interacting length scales; atoms separate on the atomic scale while plasticity develops on the microscale. A dynamic multiscale approach (CADD: coupled atomistics and discrete dislocations) is employed to investigate an edge-cracked specimen of single-crystal nickel, Ni, (brittle failure) and aluminum, Al, (ductile failure) subjected to mode-I loading. The dynamic model couples continuum finite elements to a fully atomistic region, with key advantages such as the ability to accommodate discrete dislocations in the continuum region and an algorithm for automatically detecting dislocations as they move from the atomistic region to the continuum region and then correctly "converting" the atomistic dislocations into discrete dislocations, or vice-versa. An ad hoc computational technique is also applied to dissipate localized waves formed during crack advance in the atomistic zone, whereby an embedded damping zone at the atomistic/continuum interface effectively eliminates the spurious reflection of high-frequency phonons, while allowing low-frequency phonons to pass into the continuum region. The simulations accurately capture the essential physics of the crack propagation in a Ni specimen at different temperatures, including the formation of nano-voids and the sudden acceleration of the crack tip to a velocity close to the material Rayleigh wave speed. The nanoscale brittle fracture happens through the crack growth in the form of nano-void nucleation, growth and coalescence ahead of the crack tip, and as such resembles fracture at the microscale. When the crack tip behaves in a ductile manner, the crack does not advance rapidly after the pre-opening process but is blunted by dislocation generation from its tip. The effect of temperature on crack speed is found to be perceptible in both ductile and brittle specimens.
Highlights: → A nanostructured and layered steel exhibits high strength and large ductility. → The excellent combination originates from a multiple interlaminar cracking. → The initiation and propagation of cracks are controlled by three aspects. → The cracks are deflected by interface and arrested by compressive residual stress. → Finally, the cracks are blunted by the graded grain size distribution. - Abstract: A layered and nanostructured (LN) 304 SS sheet was produced by combination of surface mechanical attrition treatment (SMAT) with warm co-rolling. The microstructure of LN sheet is characterized by a periodic distribution of nanocrystalline layers and micron-grained layers with a graded transition of grain size. Tensile test results show that exceptional properties of high yield strength and large elongation to fracture are achieved. A multiple interlaminar cracking was observed by scanning electron microscopy, which is induced by repeated crack initiation and propagation. The toughening mechanisms of the LN sheet are proposed to be controlling the crack propagation path by several strategies. The main cracks initiating at interface defects are arrested by large compressive residual stress, deflected by weak interface bonding and blunted by the graded grain size distribution.
Chen, A.Y. [School of Material Science and Engineering, University of Shanghai for Science and Technology, 200093 (China); Department of Mechanical Engineering, The Hong Kong Polytechnic University (Hong Kong); Li, D.F. [Department of Mechanical Engineering, Hong Kong Polytechnic University (Hong Kong); Zhang, J.B. [Baosteel Technology Centre, Shanghai 201900 (China); Liu, F.; Liu, X.R. [School of Material Science and Engineering, University of Shanghai for Science and Technology, 200093 (China); Lu, J., E-mail: jianlu@cityu.edu.hk [Department of Manufacturing Engineering and Engineering Management, City University of Hong Kong (Hong Kong)
2011-11-15
Highlights: {yields} A nanostructured and layered steel exhibits high strength and large ductility. {yields} The excellent combination originates from a multiple interlaminar cracking. {yields} The initiation and propagation of cracks are controlled by three aspects. {yields} The cracks are deflected by interface and arrested by compressive residual stress. {yields} Finally, the cracks are blunted by the graded grain size distribution. - Abstract: A layered and nanostructured (LN) 304 SS sheet was produced by combination of surface mechanical attrition treatment (SMAT) with warm co-rolling. The microstructure of LN sheet is characterized by a periodic distribution of nanocrystalline layers and micron-grained layers with a graded transition of grain size. Tensile test results show that exceptional properties of high yield strength and large elongation to fracture are achieved. A multiple interlaminar cracking was observed by scanning electron microscopy, which is induced by repeated crack initiation and propagation. The toughening mechanisms of the LN sheet are proposed to be controlling the crack propagation path by several strategies. The main cracks initiating at interface defects are arrested by large compressive residual stress, deflected by weak interface bonding and blunted by the graded grain size distribution.
The leaks through steam-generator cracks are the subject of a research carried out in cooperation between EDF and UCL. A software called ECREVISSE to predict the mass flow rate has been developed and has been successfully validated. The purpose of the paper is to present the mathematical model used in ECREVISSE as well as some comparison between the results and the presently available data. The model takes into account the persistence of some metastable liquid in the crack and the special flow pattern which appears in such particular geometry. Although the model involves the use of several correlations (friction, heat transfer), no adjustment of parameters against the data has been needed, neither in the single-phase part of the flow, or in the two-phase part. (authors). 8 figs., 1 tab., 20 refs
Delayed hydride cracking: alternative pre-cracking method
The internal components of nuclear reactors built-in Zr alloys are prone to a failure mechanism known as Delayed Hydride Cracking (DHC). This situation has triggered numerous scientific studies in order to measure the crack propagation velocity and the threshold stress intensity factor associated to DHC. Tests are carried out on fatigued pre-crack samples to ensure similar test conditions and comparable results. Due to difficulties in implementing the fatigue pre-crack method it would be desirable to replace it with a pre-crack produced by the same process of DHC, for which is necessary to demonstrate equivalence of this two methods. In this work tests on samples extracted from two Zr-2.5 Nb tubes were conducted. Some of the samples were heat treated to obtain a range in their metallurgical properties as well as different DHC velocities. A comparison between velocities measured in test samples pre-cracked by fatigue and RDIH is done, demonstrating that the pre-cracking method does not affect the measured velocity value. In addition, the incubation (tinc), which is the time between the application of the load and the first signal of crack propagation, in samples pre-cracked by RDIH, was measured. It was found that these times are sufficiently short, even in the worst cases (lower speed) and similar to the ones of fatigued pre-cracked samples. (author)
Subcritical crack growth in marble
Nara, Yoshitaka; Nishida, Yuki; Toshinori, Ii; Harui, Tomoki; Tanaka, Mayu; Kashiwaya, Koki
2016-04-01
It is essential to study time-dependent deformation and fracturing in various rock materials to prevent natural hazards related to the failure of a rock mass. In addition, information of time-dependent fracturing is essential to ensure the long-term stability of a rock mass surrounding various structures. Subcritical crack growth is one of the main causes of time-dependent fracturing in rock. It is known that subcritical crack growth is influenced by not only stress but also surrounding environment. Studies of subcritical crack growth have been widely conducted for silicate rocks such as igneous rocks and sandstones. By contrast, information of subcritical crack growth in carbonate rocks is not enough. Specifically, influence of surrounding environment on subcritical crack growth in carbonate rock should be clarified to ensure the long-term stability of a rock mass. In this study, subcritical crack growth in marble was investigated. Especially, the influence of the temperature, relative humidity and water on subcritical crack growth in marble is investigated. As rock samples, marbles obtained in Skopje-City in Macedonia and Carrara-City in Italy were used. To measure subcritical crack growth, we used the load relaxation method of the double-torsion (DT) test. All measurements by DT test were conducted under controlled temperature and relative humidity. For both marbles, it was shown that the crack velocity in marble in air increased with increasing relative humidity at a constant temperature. Additionally, the crack velocity in water was much higher than that in air. It was also found that the crack velocity increased with increasing temperature. It is considered that temperature and water have significant influences on subcritical crack growth in marble. For Carrara marble in air, it was recognized that the value of subcritical crack growth index became low when the crack velocity was higher than 10-4 m/s. This is similar to Region II of subcritical crack growth
Crack interaction with microstructure
Sharvan Kumar
2007-09-01
Full Text Available Designing microstructure for damage tolerance requires a detailed understanding of how an advancing crack interacts with the microstructure (and sometimes modifies it locally at multiple length scales. Advances in experimental techniques, such as the availability of well-controlled straining stages for optical and electron microscopes, the focused ion beam, electron backscattered diffraction, and nanoindentation, enable probing at these length scales in real time and through interrupted tests. Simultaneously, increasing computational power coupled with new computational methods, such as finite element analysis (FEA incorporating cohesive elements at the continuum level, discrete dislocation methodology at the mesoscopic level, and coupled atomistic/continuum methods that transitions atomic level information to the mesoscopic level, have made it possible to begin addressing these complex problems. By reviewing crack growth in a variety of multiphase alloys including steels, titanium aluminides, Mo alloys, and nanocrystalline metals, we demonstrate various aspects of crack interaction with microstructure, and how these problems are being addressed through experiments and computations.
Simulating UT measurements from bolthole cracks
Grandin, Robert; Gray, Tim; Roberts, Ron
2016-02-01
Analytical computer models of UT measurements are becoming more prominent in evaluating NDE methods - a process known as Model Assisted Probability of Detection, or MAPOD. As inspection requirements become more stringent, the respective models become more complex. An important application for aerospace structures involves inspection for cracks near boltholes in plate and layered structures. This paper describes a project to develop and validate analytical models for bolthole crack inspection, as well as to implement and demonstrate those models within an integrated graphical interface which can be used to simulate these inspections. The work involves a combination of approximate, paraxial, bulk-wave models as well as more rigorous, analytical models that include both bulk and surface/plate modes. The simpler models have greater flexibility and efficiency for handling complex geometry, while the more exact models are useful for benchmarking and assessing the accuracy of the paraxial versions. Model results will be presented for bolthole cracks in single layered components. Extensions of the models to multiple layers and to more complex geometries and materials will also be discussed.
Crack bridging in stress corrosion cracking of duplex stainless steels
Wedge open loaded (WOL) specimens of age hardened Zeron 100 duplex stainless steel were tested in 3.5 wt % NaCl solution with cathodic polarizes applied at-900m V/SCE to investigate stress corrosion cracking mechanism in duplex stainless steel. The interaction between microstructure and mechanism of stress corrosion cracking was studied. Fracture mechanism was studied by using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The material was found cracked by ferrite cleavage, austenite tearing and austenite dissolution by environment. The ferrite cleavage took place along [100] planes and [112] twin habit planes. The austenite grains appear to act as crack bridging and crack arrester and failed by tearing and stress corrosion cracking. (author)
CRACKS IN ROADWAY COVERING: METHODS FOR IMPROVEMENMT OF CRACK RESISTANCE
I. I. Leonovich
2014-11-01
Full Text Available Crack formation is presently considered as an actual problem in the global practice. The paper provides various approaches pertaining to improvement of asphalt-concrete composition with the purpose to prevent formation of temperature and fatigue cracks and develop design and technology measures for avoidance of reflection cracking in asphalt-concrete strengthening layers. However there is no comprehensive solution of the problem that combines a material science and affirmative approaches. Existing technology for crack sealing in roadway covering is rather efficient at the stage of its operation and makes it possible to eliminate cracks depending on their nature and opening width but there is no efficient diagnostic and control system for preventing cracks with opening width up to1 mmwith the purpose to exclude their further development.
Effect of secondary cracks on hydrogen embrittlement of bainitic steels
Highlights: ► HE was reduced and secondary cracks were increased with Al addition. ► HE was increased and secondary cracks were reduced after H-charged. ► Due to hydrogen, the dislocation emission and motion were enhanced. - Abstract: Hydrogen embrittlement and secondary cracks of bainitic steels were studied by means of the slow strain rate test (SSRT), in situ tension in transmission electron microscopy (TEM) analysis and scanning electron microscopy (SEM). The results showed that the microstructure of the bainitic steels became finer, the phase interfaces as irreversible hydrogen traps significantly were increased, the nano-scale carbides were precipitated from retained austenite, and hydrogen embrittlement was decreased greatly with Al addition. Lots of secondary cracks were formed with Al addition. The stress concentration was relaxed and the hydrogen embrittlement was reduced significantly because of the presence of secondary cracks. Due to hydrogen, the dislocation emission and motion were enhanced and the formation of secondary cracks was reduced.
Analysis of steady-state ductile crack growth
Niordson, Christian
1999-01-01
The fracture strength under quasi-static steady-state crack growth in an elastic-plastic material joined by a laser weld is analyzed. Laser welding gives high mismatch between the yield stress within the weld and the yield stress in the base material. This is due to the fast termic cycle, which the...... fracture zone. Both models predict that in general a thinner laser weld gives higher interface strength. Furthermore, both fracture criteria show, that the preferred path of the crack is close outside the weld material; a phenomenon also observed in experiments....
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2001-01-01
A special designed experiment was conducted for observing cr ack initiation and growth in P/M Rene95 superalloy under tension-tensi on loading by self-made SEM in-situ fatigue loading stag. Several alum ina inclusion particles exposed at the specimen surface were observed carefully. During fatigue test inclusions led to cracks initiation. Th e cracks can be formed by two mechanisms. Generally, the cracks nuclea ted at the interface between inclusion and matrix. Sometimes, cracks w ere also formed inside the inclusion. As the increase of cycles, some cracks at the interface between inclusion and matrix broadened and pro pagated along the direction about 45€?to the loading axis. On the oth er hand, the cracks inside the inclusion propagated in the inclusion a nd towards matrix.
Asperities, Crack Front Waves and Crack Self Healing
Rajak, Pankaj; Kalia, Rajiv; Nakano, Aiichiro; Vashishta, Priya
We have performed petascale simulations to study nanomaterial systems capable of sensing and repairing damage in high temperature/high pressure operating conditions. The system we have studied is a ceramic nanocomposite consisting of silicon carbide/silicon dioxide core/shell nanoparticles embedded in alumina. We observe that the interaction of the crack with core/shell asperities gives rise to crack-front waves. We also study crack healing by diffusion of silica into the crack as a function of nanoparticle size and inter-particle distance. Our results are well supported by experimental observations.
On the Crack Bifurcation and Fanning of Crack Growth Data
Forman, Royce G.; Zanganeh, Mohammad
2015-01-01
Crack growth data obtained from ASTM load shedding method for different R values show some fanning especially for aluminum alloys. It is believed by the authors and it has been shown before that the observed fanning is due to the crack bifurcation occurs in the near threshold region which is a function of intrinsic properties of the alloy. Therefore, validity of the ASTM load shedding test procedure and results is confirmed. However, this position has been argued by some experimentalists who believe the fanning is an artifact of the test procedure and thus the obtained results are invalid. It has been shown that using a special test procedure such as using compressively pre-cracked specimens will eliminate the fanning effect. Since not using the fanned data fit can result in a significantly lower calculated cyclic life, design of a component, particularly for rotorcraft and propeller systems will considerably be impacted and therefore this study is of paramount importance. In this effort both test procedures i.e. ASTM load shedding and the proposed compressive pre-cracking have been used to study the fatigue crack growth behavior of compact tension specimens made of aluminum alloy 2524-T3. Fatigue crack growth paths have been closely observed using SEM machines to investigate the effects of compression pre-cracking on the crack bifurcation behavior. The results of this study will shed a light on resolving the existing argument by better understanding of near threshold fatigue crack growth behavior.
Highlights: • We examine PWSCC cracks of Alloy 600 through microscopic equipment. • Oxygen diffuses into the grain boundaries from the external primary water. • Cr oxides are precipitated on the crack tips and the attacked grain boundaries. • The oxide structure inside a crack consists of double (inner and outer) layers. • The penetrated oxygen strongly affects the PWSCC behaviors of Alloy 600. -- Abstract: Stress corrosion cracks in Alloy 600 compact tension specimens tested at 325 °C in a simulated primary water environment of a pressurized water reactor were analyzed using microscopic equipment. Oxygen diffused into the grain boundaries just ahead of the crack tips from the external primary water. As a result of oxygen penetration, Cr oxides were precipitated on the crack tips and the attacked grain boundaries. The oxide layer in the crack interior was revealed to consist of double (inner and outer) layers. Cr oxides were found in the inner layer, with NiO and (Ni,Cr) spinels in the outer layer. Cr depletion (or Ni enrichment) zones were created in the attacked grain boundary, the crack tip, and the interface between the crack and matrix, which means that the formation of Cr oxides was due to the Cr diffusion from the surrounding matrix. The oxygen penetration and resultant metallurgical changes around the crack tip are believed to be significant factors affecting the PWSCC initiation and growth behaviors of Alloy 600
Fatigue crack growth in SiC particulates reinforced Al matrix graded composite
The SiC/Al graded composite was fabricated by powder metallurgy processing and its fatigue crack growth behavior was studied. The volume percentage of SiC particulates was distributed from 5 to 30% layer by layer on the cross section. Since the aluminium was dissolved together, there was no evident interface between the two layers with different volume fraction of SiC particulates. Fatigue crack growth was in direction of from 5 to 30% SiC layers under sinusoidal wave-form. The retardation of fatigue crack growth was found when crack propagated from low volume fraction of SiC to high volume fraction of SiC. The crack deflection and branching between two layers were observed, which decreased crack growth rates. In view of crack tip driving force, the plasticity mismatch between the layers shielded crack tip driving force, i.e. decreased the effective J-integral at the tip of the crack as the plastic zone of the crack tip spread from the weaker material into the stronger material
Optimization of stochastic database cracking
Bhardwaj, Meenesh
2013-01-01
Variant Stochastic cracking is a significantly more resilient approach to adaptive indexing. It showed [1]that Stochastic cracking uses each query as a hint on how to reorganize data, but not blindly so; it gains resilience and avoids performance bottlenecks by deliberately applying certain arbitrary choices in its decision making. Therefore bring, adaptive indexing forward to a mature formulation that confers the workload-robustness that previous approaches lacked. Original cracking relies o...
2014-01-01
While cracking a code might seem like something few of us would encounter in our daily lives, it is actually far more prevalent than we may realize. Anyone who has had personal information taken because of a hacked email account can understand the need for cryptography and the importance of encryption-essentially the need to code information to keep it safe. This detailed volume examines the logic and science behind various ciphers, their real world uses, how codes can be broken, and the use of technology in this oft-overlooked field.
This document contains articles, expertises, comments on the problem of cracks as well as indications to other assumed lacks of safety in French and also German pressure water reactors. One chapter deals with the former Framatome safety engineer Etemad. Towards the end, there is also a chronological listing of regional events as well as articles from the supra-regional press. Now and then, selected remarks made by politicians are given which indicate an insufficient level of information in the responsible persons and which make clear that faults in the control instances can make existing reactor unsafeties even worse. (orig./HP)
Comprehensive Structural Integrity is a reference work which covers all activities involved in the assurance of structural integrity. It provides engineers and scientists with an unparalleled depth of knowledge in the disciplines involved. The new online Volume 11 is dedicated to the mechanical characteristics of materials. This paper contains the chapter 11.03 and is structured as follows: General aspects of SCC testing; Non-precracked specimens; Precracked specimens - the fracture mechanics approach to SCC; Crack growth measurement; Limitations of the LEFM approach to SCC; The use of SCC data; Guide to selection of mechanical scc test method
Some practical crack path examples
Les P. Pook
2007-07-01
Full Text Available It is well known that many engineering structures and components, as well as consumer items, contain cracks or crack-like flaws. It is widely recognised that crack growth must be considered both in designand in the analysis of failures. The complete solution of a crack growth problem includes determination of the crack path. Macroscopic aspects of crack paths have been of industrial interest for a very long time.At the present state of the art the factors controlling the path taken by a crack are not completely understood.Eight brief case studies are presented. These are taken from the author’s professional and personal experience of macroscopic crack paths over many years. They have been chosen to illustrate various aspects of crack paths. One example is in a component from a major structure, three examples are in laboratory specimens, and four are in nuisance failures. Such nuisance failures cause, in total, a great deal of inconvenience and expensive, but do not normally receive much publicity.
A study on fatigue crack propagation considering crack tip plasticity
Fatigue crack propagation of materials considering crack tip plasticity was studied. For this, fatigue tests were performed with compact tension (CT) specimens of Inconel 690, Inconel 600, Inconel 718 and Type 304 stainless steel at room temperature. Fatigue test on Inconel 600 was performed to be used as a reference data of Inconel 690. Inconel 718 specimen, which has very high yield strength, was selected to simulate different plasticity at the crack tip in comparison with 304 stainless steel. The effect of specimen thickness on fatigue crack propagation was studied with 304 stainless steel of 3mm-, 6mm- and 25mm-thick specimens. Inconel 690 has been proposed as a substitute material for Inconel 600 in pressurized water reactor (PWR) steam generator tube application. This alloy was developed to improve the stress corrosion cracking resistance of Inconel 600. Now, it is known that Inconel 690 has better intergranular stress corrosion cracking (IGSCC) property than Inconel 600. But, more data of Inconel 690 about mechanical properties are needed in steam generator design. To investigate the effects of heat treatment on yield strength and fatigue crack propagation of Inconel 690, tensile tests and fatigue tests were performed on heat-treated specimen. From the test results, it is believed that chromium carbide precipitates at the grain boundaries reduce fatigue crack growth rate (FCGR) of Inconel 690 by crack tip blunting as far as the fatigue cracking is intergranular fracture mode. To investigate the effect of residual stress on fatigue crack propagation, residual stresses were introduced by induction-heat treatment. And, the distribution of residual stresses was measured with 3mm-thick 304 stainless steel by X-ray diffraction (XRD) measurement. From the tests, it was found that FCGR was increased in tensile residual stress region and decreased in compressive region. From the fatigue tests on 304 stainless steel, it was found that FCGR of thick specimen was faster
Effect of Crack Opening on Penetrant Crack Detectability
Weaver, Devin
2009-01-01
Results: From the testing we were able to determine all the cracks within the test range were detectable or better with developer. Many of the indications after development lost their linearity and gave circular indications. Our tests were performed in a laboratory and our procedure would be difficult in an industrial setting. Conclusions: The "V" did not significantly affect our ability to detect the POD cracks with fluorescent penetrant. Conduct same experiment with more cracks. The 0.025 and 0.050 POD specimens are clean and documented with the SEM. Conduct water-wash fluorescent penetrant test at EAFB. The poppet cracks are tighter than the POD specimen cracks. Flight FCV poppets: 0.01 mils (0.3 microns) Langley fatigue cracked poppets: 0.02 mils (0.5 microns) POD specimen (post 5 mils): 0.05 mils (1.4 microns) We could not detect cracks in Langley fatigue-cracked poppets with fluorescent penetrant. Investigate inability of penetrant to wet the poppet surface.
Modelling of ultrasonic nondestructive testing of cracks in claddings
Nondestructive testing with ultrasound is a standard procedure in the nuclear power industry. To develop and qualify the methods extensive experimental work with test blocks is usually required. This can be very time-consuming and costly and it also requires a good physical intuition of the situation. A reliable mathematical model of the testing situation can, therefore, be very valuable and cost-effective as it can reduce experimental work significantly. A good mathematical model enhances the physical intuition and is very useful for parametric studies, as a pedagogical tool, and for the qualification of procedures and personnel. The present project has been concerned with the modelling of defects in claddings. A cladding is a layer of material that is put on for corrosion protection, in the nuclear power industry this layer is often an austenitic steel that is welded onto the surface. The cladding is usually anisotropic and to some degree it is most likely also inhomogeneous, particularly in that the direction of the anisotropy is varying. This degree of inhomogeneity is unknown but probably not very pronounced so for modelling purposes it may be a valid assumption to take the cladding to be homogeneous. However, another important complicating factor with claddings is that the interface between the cladding and the base material is often corrugated. This corrugation can have large effects on the transmission of ultrasound through the interface and can thus greatly affect the detectability of defects in the cladding. In the present project the only type of defect that is considered is a planar crack that is situated inside the cladding. The investigations are, furthermore, limited to two dimensions, and the crack is then only a straight line. The crack can be arbitrarily oriented and situated, but it must not intersect the interface to the base material. The crack can be surface-breaking, and this is often the case of most practical interest, but it should then be
Replica-Based Crack Inspection
Newman, John A.; Willard, Scott A.; Smith, Stephen W.; Piascik, Robert S.
2008-01-01
Surface replication has been proposed as a method for crack detection in space shuttle main engine flowliner slots. The results of a feasibility study show that examination of surface replicas with a scanning electron microscope can result in the detection of cracks as small as 0.005 inch, and surface flaws as small as 0.001 inch, for the flowliner material.
Experiences on IGSCC crack manufacturing
Veron, P. [Equipos Nucleares, S.A., Maliano (Spain)
1997-02-01
The author presents his experience in manufacturing IGSCC realistic defects, mainly in INCONEL 600 MA Steam Generator Tubes. From that experience he extracts some knowledge about this cracking (influence of chemistry in the environment, stress state, crack growth rate, and occurrence in laboratory condition of break before leak).
Highlights: → FIB 3D sectioning has been used for the analysis of cracking in zirconium oxides. → We observe a gradual production of cracks, not a sudden burst of crack nucleation at transition. → The location of cracks near the metal/oxide interface is closely linked to the interface geometry. → Cracks are not generated as a result of the kinetic transition, but may instead play a role in encouraging the transition. → The process by which cracks become connected to the oxidising environment may be critical controlling the corrosion rate. - Abstract: Using FIB sectioning and reconstruction techniques we have performed a quantitative analysis on the microstructure of cracks and the topography of the metal-oxide interface in oxides formed on ZIRLOTM alloys in high-temperature water. The most significant observation is the continuous production of cracks both before and after the transition in kinetics, not a sudden burst of crack nucleation at transition as assumed in the literature. By concluding that cracks are not generated as a result of the transition and are not the primary cause, we suggest that a process by which cracks within the scale become connected to the oxidising environment through interconnected nanoporosity may be critical in controlling the overall rate of oxidation.
Vears, R E
2014-01-01
Microprocessor Interfacing provides the coverage of the Business and Technician Education Council level NIII unit in Microprocessor Interfacing (syllabus U86/335). Composed of seven chapters, the book explains the foundation in microprocessor interfacing techniques in hardware and software that can be used for problem identification and solving. The book focuses on the 6502, Z80, and 6800/02 microprocessor families. The technique starts with signal conditioning, filtering, and cleaning before the signal can be processed. The signal conversion, from analog to digital or vice versa, is expl
Modified maximum tangential stress criterion for fracture behavior of zirconia/veneer interfaces.
Mirsayar, M M; Park, P
2016-06-01
The veneering porcelain sintered on zirconia is widely used in dental prostheses, but repeated mechanical loadings may cause a fracture such as edge chipping or delamination. In order to predict the crack initiation angle and fracture toughness of zirconia/veneer bi-layered components subjected to mixed mode loadings, the accuracy of a new and traditional fracture criteria are investigated. A modified maximum tangential stress criterion considering the effect of T-stress and critical distance theory is introduced, and compared to three traditional fracture criteria. Comparisons to the recently published fracture test data show that the traditional fracture criteria are not able to properly predict the fracture initiation conditions in zirconia/veneer bi-material joints. The modified maximum tangential stress criterion provides more accurate predictions of the experimental results than the traditional fracture criteria. PMID:26807673
BOUNDARY ELEMENT ANALYSIS OF INTERACTION BETWEEN AN ELASTIC RECTANGULAR INCLUSION AND A CRACK
王银邦
2004-01-01
The interaction between an elastic rectangular inclusion and a kinked crack in an infinite elastic body was considered by using boundary element method. The new complex boundary integral equations were derived. By introducing a complex unknown function H(t)related to the interface displacement density and traction and applying integration by parts,the traction continuous condition was satisfied automatically. Only one complex boundary integral equation was obtained on interface and involves only singularity of order l/ r. To verify the validity and effectiveness of the present boundary element method, some typical examples were calculated. The obtained results show that the crack stress intensity factors decrease as the shear modulus of inclusion increases. Thus, the crack propagation is easier near a softer inclusion and the harder inclusion is helpful for crack arrest.
Integral identities for a semi-infinite interfacial crack in anisotropic elastic bimaterials
Morini, L; Mishuris, G; Radi, E
2012-01-01
The focus of the article is on analysis of a semi-infinite crack at the interface between two dissimilar anisotropic elastic materials, loaded by a general asymmetrical system of forces acting on the crack faces. Recently derived symmetric and skew-symmetric weight functions matrices are introduced for both plane strain and antiplane shear cracks, and used together with the fundamental reciprocal identity (Betti formula) in order to formulate the elastic fracture problem in terms of singular integral equations relating the applied loading and the resulting crack opening. The proposed compact formulation can be used to solve many problems in linear elastic fracture mechanics (for example various classic crack problems in homogeneous and heterogeneous media). This formulation is also fundamental in many multiphysics applications, where the elastic problem is coupled with other concurrent physical phenomena.
Effect of PCC Joint Skew on Reflective Cracking in HMA Overlays
Ghauch, By Ziad G
2011-01-01
Reflective cracking is a relatively premature distress that occurs in HMA materials overlaying cracked and jointed underlying pavements. The high concentration of stresses and strains in the vicinity of the discontinuity of the old pavement causes the cracks to reflect into the newly placed HMA overlay. While it is a common practice to use skewed transverse joints in rigid pavements to improve the latter's performance, the impact of such a practice on the cracking of a potential HMA overlay has not been examined so far. In this context, this study investigates the effect of using skewed transverse joints in rigid pavements on reflective cracking development in the HMA overlay. Advanced three-dimensional Finite Element models including viscoelastic material properties for the HMA overlay, 3D beam modeling of dowel bars, non-uniform tire-pavement contact stresses, friction interfaces, and infinite boundary elements were constructed for both normal and skewed transverse joints using ABAQUS v-6.11. The potential ...
Crack propagation tests of HIPed DSCu/SS joints for plasma facing components
Aluminum oxide dispersion strengthened copper (DSCu), used as the heat sink, and AISI 316L(N) type stainless steel (SS), used for cooling pipes, were metallurgically joined to be used as first wall of plasma facing components. Hot isostatic pressing (HIP) was proposed as the joining fabrication technique in the first-wall/blanket components. In this study, fracture toughness and fatigue crack growth rate tests were carried out for the fracture strength evaluation of HIPed joints. Permissible crack lengths during fabrication of first-wall components were evaluated from the results of the fracture toughness tests. In crack growth rate tests, the crack prepared in the DSCu propagated, turned at the HIPed interface, and propagated along it. Therefore, it was found that the crack provided in the DSCu heat sink did not propagate through the SS cooling pipe
The Cracking of Irradiated Uranium
Structural features other than fission-product gas bubbles seen in unrestrained, unalloyed uranium irradiated in the alpha range to burn-ups of up to 0.7% of all atoms are described. The main features are: (1) Brittle grain-boundary cracks in which the grains appear to have parted without plastic deformation. These cracks are associated with thermal cycling and high maximum temperatures (~600°C). (2) Transgranular cracks, which are comparatively rare. It is suggested that they may be related to the pseudo-cleavage or ''twin parting'' observed in unirradiated uranium by Cahn. (3) Grain boundary ''creep voids'' believed to arise from the coalescence of vacancies under tensile stress. The voids may form a path for crack propagation or may themselves coalesce to form cracks. Apart from the direct effects of these features in increasing the volume and changing the thermal conductivity and mechanical properties of the uranium, a mechanism is discussed by which cracks may accumulate fission-product gas and cause further volume increases. The possible effects of structural variations in the uranium and of restraint during irradiation on the incidence of cracking and void formation are considered. (author)
Fatigue crack growth in a unidirectional SCS-6/Ti-15-3 composite
Kantzos, Peter; Telesman, Jack; Ghosn, Louis
1989-01-01
An investigation was conducted to characterize and model the fatigue crack growth (FCG) behavior of a SCS-6/Ti-15-3 metal matrix composite. Part of the study was conducted using a fatigue loading stage mounted inside a scanning electron microscope (SEM). This unique facility allowed high magnification viewing of the composite fatigue processes and measurement of the near crack tip displacements. The unidirectional composite was tested in the (0)8 (i.e., longitudinal) and (90)8 (i.e., transverse) orientations. For comparison purposes unreinforced matrix material produced by the identical process as the reinforced material was also tested. The results of the study reveal that the fatigue crack growth behavior of the composite is a function of specimen geometry, fiber orientation and the interaction of local stress fields with the highly anisotropic composite. In the case of (0)8 oriented single edge notch (SEN) specimens and (90)8 oriented compact tension (CT) specimens, the crack growth was normal to the loading direction. However, for the (0)8 CT specimens the crack grew mostly parallel to the loading and the fiber direction. The unusual fatigue behavior of the (0)8 CT specimens was attributed to the specimen geometry and the associated high tensile bending stresses perpendicular to the fiber direction. These stresses resulted in preferential cracking in the weak interface region perpendicular to the fiber direction. The interface region, and in particular the carbon coating surrounding the fiber proved to be the composites weakest link. In the (0)8 SEN the crack growth was confined to the matrix leaving behind unbroken fibers which bridged the cracked surfaces. As the crack grew longer, more fibers bridged the crack resulting in a progressive decrease in the crack growth rates and eventual crack arrest. The actual near crack tip displacement measurements were used in a proposed formulation for a bridging-corrected effective crack driving force, delta K(sub eff
Probabilistic Analysis of Crack Width
J. Marková
2000-01-01
Full Text Available Probabilistic analysis of crack width of a reinforced concrete element is based on the formulas accepted in Eurocode 2 and European Model Code 90. Obtained values of reliability index b seem to be satisfactory for the reinforced concrete slab that fulfils requirements for the crack width specified in Eurocode 2. However, the reliability of the slab seems to be insufficient when the European Model Code 90 is considered; reliability index is less than recommended value 1.5 for serviceability limit states indicated in Eurocode 1. Analysis of sensitivity factors of basic variables enables to find out variables significantly affecting the total crack width.
Perturbation analysis of Mode III interfacial cracks advancing in a dilute heterogeneous material
Piccolroaz, Andrea; Movchan, Alexander; Movchan, Natasha
2011-01-01
The paper addresses the problem of a Mode III interfacial crack advancing quasi-statically in a heterogeneous composite material, that is a two-phase material containing elastic inclusions, both soft and stiff, and defects, such as microcracks, rigid line inclusions and voids. It is assumed that the bonding between dissimilar elastic materials is weak so that the interface is a preferential path for the crack. The perturbation analysis is made possible by means of the fundamental solutions (symmetric and skew-symmetric weight functions) derived in Piccolroaz et al. (2009). We derive the dipole matrices of the defects in question and use the corresponding dipole fields to evaluate effective tractions along the crack faces and interface to describe the interaction between the main interfacial crack and the defects. For a stable propagation of the crack, the perturbation of the stress intensity factor induced by the defects is then balanced by the elongation of the crack along the interface, thus giving an expli...
Crack propagation under the stainless steel cladding of nuclear reactor vessels is monitored by ultrasonic testing. This work study signal processing to improve detection and sizing of defects. Two possibilities are examined: processing of each individual signal and simultaneous processing of all the signals giving a B-SCAN image. The bibliographic study of time-frequency methods shows that they are not suitable for pulses. Then decomposition in instantaneous frequency and envelope is used. Effect of interference of 2 close echoes on instantaneous frequency is studies. The deconvolution of B-SCAN images is obtained by the transducer field. A point-by-point deconvolution method, less noise sensitive, is developed. B-SCAN images are processed in 2 phases: interface signal processing and deconvolution. These calculations improve image accuracy and dynamics. Water-stell interface and ferritic-austenitic interface are separated. Echoes of crack top are visualized and crack-hole differentiation is improved
Crack propagation studies and bond coat properties in thermal barrier coatings under bending
A K Ray; N Roy; K M Godiwalla
2001-04-01
Ceramic based thermal barrier coatings (TBC) are currently considered as a candidate material for advanced stationary gas turbine components. Crack propagation studies under bending are described that were performed on plasma sprayed ZrO2, bonded by MCrAlY layer to Ni base superalloy. The crack propagation behaviour of the coatings at room temperature in as received and oxidized conditions revealed a linear growth of the cracks on the coating till the yield point of the super alloy was reached. High threshold load at the interface between the ceramic layer and the bond coat was required to propagate the crack further into the bond coat. Once the threshold load was surpassed the crack propagated into the brittle bond coat without an appreciable increase in the load. At temperatures of 800°C the crack propagated only in the TBC (ceramic layer), as the ductile bond coat offered an attractive sink for the stress relaxation. Effects of bond coat oxidation on crack propagation in the interface region have been examined and are discussed.
Frequency Domain Structural Synthesis Applied to Quasi-Static Crack Growth Modeling
Young W. Kwon
2009-01-01
Full Text Available Quasi-static crack growth in a composite beam was modeled using the structural synthesis technique along with a finite element model. The considered crack was an interface crack in the shear mode (i.e. mode II, which occurs frequently in the scarf joint of composite structures. The analysis model was a composite beam with an edge crack at the midplane of the beam subjected to a three-point bending load. In the finite element model, beam finite elements with translational degrees of freedom only were used to model the crack conveniently. Then, frequency domain structural synthesis (substructure coupling was applied to reduce the computational time associated with a repeated finite element calculation with crack growth. The quasi-static interface crack growth in a composite beam was predicted using the developed computational technique, and its result was compared to experimental data. The computational and experimental results agree well. In addition, the substructure-based synthesis technique showed the significantly improved computational efficiency when compared to the conventional full analysis.
Bachlechner; Omeltchenko; Nakano; Kalia; Vashishta; Ebbsjo; Madhukar
2000-01-10
Mechanical behavior of the Si(111)/Si(3)N4(0001) interface is studied using million atom molecular dynamics simulations. At a critical value of applied strain parallel to the interface, a crack forms on the silicon nitride surface and moves toward the interface. The crack does not propagate into the silicon substrate; instead, dislocations are emitted when the crack reaches the interface. The dislocation loop propagates in the (1; 1;1) plane of the silicon substrate with a speed of 500 (+/-100) m/s. Time evolution of the dislocation emission and nature of defects is studied. PMID:11015901
Mechanical behavior of the Si(111)/Si3N4 (0001) interface is studied using million atom molecular dynamics simulations. At a critical value of applied strain parallel to the interface, a crack forms on the silicon nitride surface and moves toward the interface. The crack does not propagate into the silicon substrate; instead, dislocations are emitted when the crack reaches the interface. The dislocation loop propagates in the (1 11) plane of the silicon substrate with a speed of 500 (±100) m/s . Time evolution of the dislocation emission and nature of defects is studied. (c) 2000 The American Physical Society
Highlights: • We discuss interfacial superconductivity, a field boosted by the discovery of the superconducting interface between LaAlO. • This system allows the electric field control and the on/off switching of the superconducting state. • We compare superconductivity at the interface and in bulk doped SrTiO. • We discuss the role of the interfacially induced Rashba type spin–orbit. • We briefly discuss superconductivity in cuprates, in electrical double layer transistor field effect experiments. • Recent observations of a high Tc in a monolayer of FeSe deposited on SrTiO3 are presented. - Abstract: Low dimensional superconducting systems have been the subject of numerous studies for many years. In this article, we focus our attention on interfacial superconductivity, a field that has been boosted by the discovery of superconductivity at the interface between the two band insulators LaAlO3 and SrTiO3. We explore the properties of this amazing system that allows the electric field control and on/off switching of superconductivity. We discuss the similarities and differences between bulk doped SrTiO3 and the interface system and the possible role of the interfacially induced Rashba type spin–orbit. We also, more briefly, discuss interface superconductivity in cuprates, in electrical double layer transistor field effect experiments, and the recent observation of a high Tc in a monolayer of FeSe deposited on SrTiO3
Crack Tip Parameters for Growing Cracks in Linear Viscoelastic Materials
Brincker, Rune
In this paper the problem of describing the asymptotic fields around a slowly growing crack in a linearly viscoelastic material is considered. It is shown that for plane mixed mode problems the asymptotic fields must be described by 6 parameters: 2 stress intensity factors and 4 deformation inten...... value problem, and a displacement boundary value problem. The results show that the stress intensity factors and the displacement intensity factors do not depend explicitly upon the velocity of the crack tip.......In this paper the problem of describing the asymptotic fields around a slowly growing crack in a linearly viscoelastic material is considered. It is shown that for plane mixed mode problems the asymptotic fields must be described by 6 parameters: 2 stress intensity factors and 4 deformation...... intensity factors. In the special case of a constant Poisson ratio only 2 deformation intensity factors are needed. Closed form solutions are given both for a slowly growing crack and for a crack that is suddenly arrested at a point at the crack extension path. Two examples are studied; a stress boundary...
Iqbal, AKM Asif; Arai, Yoshio
2016-02-01
The fatigue crack propagation behaviour of a cast hybrid metal matrix composite (MMC) was investigated and compared with the crack propagation behaviour of MMC with Al2O3 and Al alloy in this article. Three dimensional (3D) surface analysis is carried out to analyze the crack propagation mechanism. All three materials clearly show near threshold and stable crack growth regions, but the rapid crack growth region is not clearly understood. The crack propagation resistance is found higher in hybrid MMC than that of MMC with Al2O3 whisker and the Al alloy in the low ΔK region. The crack propagation in the hybrid MMC in the near-threshold region is directed by the debonding of reinforcement-matrix followed by void nucleation in the Al alloy matrix. Besides, the crack propagation in the stable- or midcrack-growth region is controlled by the debonding of particle-matrix and whisker-matrix interface caused by the cycle-by-cycle crack growth along the interface. The transgranular fracture of the reinforcement and void formation are also observed. Due to presence of large volume of inclusions and the microstructural inhomogeneity, the area of striation formation is reduced in the hybrid MMC, caused the unstable fracture.
Caustic stress corrosion cracking
Liquid Metal Fast Breeder Reactors (LMFBRs) use sodium as a coolant for transfer of heat from the core to the steam generators. Maintenance and examination of the system require removal of sodium from components of the system. One process for removal reacts the sodium with water vapor and removes the residual sodium hydroxide from the components by rinsing with liquid water. This process exposes components such as pumps, heat exchangers, valves, and fuel-handling machines to contact with aqueous NaOH solutions in various concentrations over a range of temperatures and times. Since stress can be present in these components, as generated by fabrication, structural loads, deformation in service, and possible wedging action by corrosion products, conditions are potentially available for the mechanism of caustic stress corrosion cracking (CSCC). Since LMFBR components are fabricated from Types 304 and 316 stainless steels which have been found to be susceptible to CSCC, it was therefore considered necessary to establish the threshold of CSCC so that the components could be processed under conditions avoiding CSCC. The materials used in the testing program included heats of Types 304 and 316 stainless steel, Inconel 600 and 718, hardfacing deposits of Stellite 6 and 156, and three special wear-resistant, carbide-type materials. The analysis of these materials is tabulated
The conversion of residual fuel oil to usable middle distillates was discussed. The residue conversion processing paths are usually based on separation, carbon rejection, or hydrogen addition principles. Super Oil Cracking (SOC) uses a slurry catalyst system in a new, tubular reactor to achieve high levels of hydrothermal conversion. SOC can upgrade a variety of heavy, high metals residue feedstocks with high yields of middle distillates. The SOC products can also be further treated into feedstocks for FCC or hydrocracking. The SOC process can be incorporated easily into a refinery to obtain incremental residue conversion directly. It can also be integrated with other residue processes, acting as a demetallization and decarbonization step which results in enhanced overall conversion. The relative rate of coke formation and its handling are distinguishing characteristics between residue upgrading technologies. The SOC process operates at higher temperatures that other residue hydrocracking processes resulting in higher rates of thermal decomposition, thus preventing coke formation. SOC process can operate as a stand-alone upgrader or can be integrated with other bottoms processing steps to extend the refiner's range of options for increasing bottoms conversion.3 tabs., 14 figs
Peridynamic model for fatigue cracking.
Silling, Stewart A.; Abe Askari (Boeing)
2014-10-01
The peridynamic theory is an extension of traditional solid mechanics in which the field equations can be applied on discontinuities, such as growing cracks. This paper proposes a bond damage model within peridynamics to treat the nucleation and growth of cracks due to cyclic loading. Bond damage occurs according to the evolution of a variable called the %22remaining life%22 of each bond that changes over time according to the cyclic strain in the bond. It is shown that the model reproduces the main features of S-N data for typical materials and also reproduces the Paris law for fatigue crack growth. Extensions of the model account for the effects of loading spectrum, fatigue limit, and variable load ratio. A three-dimensional example illustrates the nucleation and growth of a helical fatigue crack in the torsion of an aluminum alloy rod.
Wang, Jiandong; Li, Liqun; Tao, Wang
2016-08-01
It is generally believed that cracks in metal matrix composites (MMC) parts manufacturing are crucial to the reliable material properties, especially for the reinforcement particles with high volume fraction. In this paper, WC particles (WCp) reinforced Fe-based metal matrix composites (WCp/Fe) were manufactured by laser melting deposition (LMD) technology to investigate the characteristics of cracks formation. The section morphology of composites were analyzed by optical microscope (OM), and microstructure of WCp, matrix and interface were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), in order to study the crack initiation and propagation behavior under different laser process conditions. The temperature of materials during the laser melting deposition was detected by the infrared thermometer. The results showed that the cracks often appeared after five layers laser deposition in this experiment. The cracks crossed through WC particles rather than the interface, so the strength of interface obtained by the LMD was relatively large. When the thermal stress induced by high temperature gradient during LMD and the coefficient of thermal expansion mismatch between WC and matrix was larger than yield strength of WC, the cracks would initiate inside WC particle. Cracks mostly propagated along the eutectic phases whose brittleness was very large. The obtained thin interface was beneficial to transmitting the stress from particle to matrix. The influence of volume fraction of particles, laser power and scanning speed on cracks were investigated. This paper investigated the influence of WC particles size on cracks systematically, and the smallest size of cracked WC in different laser processing parameters was also researched.
Batman-cracks. Observations and numerical simulations
Selvadurai, A. P. S.; Busschen, A. Ten; Ernst, L. J.
1991-05-01
To ensure mechanical strength of fiber reinforced plastics (FRP), good adhesion between fibers and the matrix is considered to be an essential requirement. An efficient test of fiber-matrix interface characterization is the fragmentation test which provides information about the interface slip mechanism. This test consists of the longitudinal loading of a single fiber which is embedded in a matrix specimen. At critical loads the fiber experiences fragmentation. This fragmentation will terminate depending upon the shear-slip strength of the fiber-matrix adhesion, which is inversely proportional to average fragment lengths. Depending upon interface strength characteristics either bond or slip matrix fracture can occur at the onset of fiber fracture. Certain particular features of matrix fracture are observed at the locations of fiber fracture in situations where there is sufficient interface bond strength. These refer to the development of fractures with a complex surface topography. The experimental procedure involved in the fragmentation tests is discussed and the boundary element technique to examine the development of multiple matrix fractures at the fiber fracture locations is examined. The mechanics of matrix fracture is examined. When bond integrity is maintained, a fiber fracture results in a matrix fracture. The matrix fracture topography in a fragmentation test is complex; however, simplified conoidal fracture patterns can be used to investigate the crack extension phenomena. Via a mixed-mode fracture criterion, the generation of a conoidal fracture pattern in the matrix is investigated. The numerical results compare favorably with observed experimental data derived from tests conducted on fragmentation test specimens consisting of a single glass fiber which is embedded in a polyester matrix.
Tidwell, Jenifer
2010-01-01
Despite all of the UI toolkits available today, it's still not easy to design good application interfaces. This bestselling book is one of the few reliable sources to help you navigate through the maze of design options. By capturing UI best practices and reusable ideas as design patterns, Designing Interfaces provides solutions to common design problems that you can tailor to the situation at hand. This updated edition includes patterns for mobile apps and social media, as well as web applications and desktop software. Each pattern contains full-color examples and practical design advice th
21 CFR 137.190 - Cracked wheat.
2010-04-01
... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Cracked wheat. 137.190 Section 137.190 Food and... Related Products § 137.190 Cracked wheat. Cracked wheat is the food prepared by so cracking or cutting into angular fragments cleaned wheat other than durum wheat and red durum wheat that, when tested...
Effect of crack opening on UT response
Virkkunen, I.; Kemppainen, M. [Trueflaw OY, Espoo (Finland); Pitkaenen, J. [Posiva, Olkiluoto (Finland)
2006-07-01
Crack opening is one of the key parameters affecting the UT response of the crack. Tight cracks with small opening tend to be more difficult to detect and characterize than cracks that have wider opening. In particular, the opening of crack tip has marked effect on the crack tip diffraction signal often used for crack sizing. Service-induced cracks found exhibit wide variety of different openings. The opening is affected by the service loads and crack growth mechanism. In general, cracks grown by high loads tend to have wider opening than cracks produced by small loads. Furthermore, residual stresses may alter the opening. In order to simulate the wide variety of openings of the service-induced cracks, a novel method for producing artificial flaws with controlled opening is presented. A set of similar realistic flaws was produced by controlled thermal fatigue loading. The as-produced ''baseline'' UT response of these cracks was recorded with phased array technique using shear waves. Some of the flaws were then subjected to different loading sequences to manipulate their opening. The UT response of the modified cracks was then recorded and compared to that of the baseline response. The crack tip signals were measured also with longitudinal waves before cutting the specimen. Finally, the sample was carefully sectioned to reveal the opening of the produced flaws and the effect of crack opening to the UT response is analyzed. (orig.)
Kinking conditions for running cracks
Andrianopoulos, N.; Kourkoulis, S.
1994-01-01
The problem of the abrupt change of the direction of a crack, propagating with high velocity, is studied in the present work. The study is based on a unified approach of the directional instability phenomena, which accompany running cracks. According to this approach, the running tip is simulated by a prebranched configuration, consisted of two microcracks of arbitrary lengths and orientations. The final macroscopically observed result depends both on these, a priori unknown, relative lengths...
Wide plate crack arrest testing
To predict the behavior of a nuclear pressure vessel undergoing pressurized thermal shock, certain information on dynamic crack propagation and arrest is required. The purpose of the work described is to provide such data on wide plates fracturing at temperatures up to the upper shelf region. Four tests have been completed on the 26 MN Universal Testing Machine at NBS. The specimens are to be fractured in a thermal gradient that, in the most extreme case, might extend from -1000C to 2000 across the 1 meter specimen width. This is done so that the crack will initiate in a cold, brittle region and arrest in a hot, tough region. An important part of this study is data acquisition from the numerous strain gages, thermocouples, timing wires, crack mouth opening displacement gages, and acoustic emission transducers that are mounted on the specimen. Each test has been different with respect to conditions of testing, specimen configuration, and instrumentation used. The progressive changes in test procedure represent attempts to obtain the desired crack run and arrest behavior and to improve upon the quality of the data collected. In particular, efforts were made to initiate crack propagation at lower stress intensity factors. Also, strain gage combinations and locations were optimized to better deduce the crack position as a function of time. Another result of great interest that can be deduced from these tests is the initiation of fracture toughness and the arrest toughness