Buckling of Bucket Foundations
DEFF Research Database (Denmark)
Madsen, Søren; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo
2012-01-01
In this paper, the risk of structural buckling during installation of large-diameter bucket foundations is addressed using numerical methods. Imperfect geometries are introduced based on the pre-buckling mode shapes from a linear Eigenvalue buckling analysis. Various imperfect geometries are intr......In this paper, the risk of structural buckling during installation of large-diameter bucket foundations is addressed using numerical methods. Imperfect geometries are introduced based on the pre-buckling mode shapes from a linear Eigenvalue buckling analysis. Various imperfect geometries...
Shama, Mohamed
2013-01-01
Buckling of Ship Structures presents a comprehensive analysis of the buckling problem of ship structural members. A full analysis of the various types of loadings and stresses imposed on ship plating and primary and secondary structural members is given. The main causes and consequences of the buckling mode of failure of ship structure and the methods commonly used to control buckling failure are clarified. This book contains the main equations required to determine the critical buckling stresses for both ship plating and the primary and secondary stiffening structural members. The critical buckling stresses are given for ship plating subjected to the induced various types of loadings and having the most common boundary conditions encountered in ship structures. The text bridges the gap existing in most books covering the subject of buckling of ship structures in the classical analytical format, by putting the emphasis on the practical methods required to ensure safety against buckling of ship structur...
Buckled membranes for microstructures
Popescu, D.O.; Lammerink, Theodorus S.J.; Elwenspoek, Michael Curt
1994-01-01
Based on energy variation methods we calculated the deflection of membranes under the combined load of an external pressure and an internal lateral stress. A lateral load gives rise to buckling once a critical load is exceeded. The combination of transversal loads and lateral loads changes the
Buckling failures in insect exoskeletons.
Parle, Eoin; Herbaj, Simona; Sheils, Fiona; Larmon, Hannah; Taylor, David
2015-12-17
Thin walled tubes are often used for load-bearing structures, in nature and in engineering, because they offer good resistance to bending and torsion at relatively low weight. However, when loaded in bending they are prone to failure by buckling. It is difficult to predict the loading conditions which cause buckling, especially for tubes whose cross sections are not simple shapes. Insights into buckling prevention might be gained by studying this phenomenon in the exoskeletons of insects and other arthropods. We investigated the leg segments (tibiae) of five different insects: the locust (Schistocerca gergaria), American cockroach (Periplaneta americana), death's head cockroach (Blaberus discoidalis), stick insect (Parapachymorpha zomproi) and bumblebee (Bombus terrestris audax). These were tested to failure in cantilever bending and modelled using finite element analysis (FEA). The tibiae of the locust and the cockroaches were found to be approximately circular in shape. Their buckling loads were well predicted by linear elastic FEA, and also by one of the analytical solutions available in the literature for elastic buckling. The legs of the stick insect are also circular in cross section but have several prominent longitudinal ridges. We hypothesised that these ridges might protect the legs against buckling but we found that this was not the case: the loads necessary for elastic buckling were not reached in practice because yield occurred in the material, causing plastic buckling. The legs of bees have a non-circular cross section due to a pollen-carrying feature (the corbicula). We found that this did not significantly affect their resistance to buckling. Our results imply that buckling is the dominant failure mode in the tibia of insects; it likely to be a significant consideration for other arthropods and any organisms with stiff exoskeletons. The interactions displayed here between material properties and cross sectional geometry may provide insights for the
Energy Technology Data Exchange (ETDEWEB)
Yang, Dian; Whitesides, George M.
2017-12-26
A soft actuator is described, including: a rotation center having a center of mass; a plurality of bucklable, elastic structural components each comprising a wall defining an axis along its longest dimension, the wall connected to the rotation center in a way that the axis is offset from the center of mass in a predetermined direction; and a plurality of cells each disposed between two adjacent bucklable, elastic structural components and configured for connection with a fluid inflation or deflation source; wherein upon the deflation of the cell, the bucklable, elastic structural components are configured to buckle in the predetermined direction. A soft actuating device including a plurality of the soft actuators and methods of actuation using the soft actuator or soft actuating device disclosed herein are also described.
Scleral buckling with hydrogel implant
Directory of Open Access Journals (Sweden)
Das Taraprasad
1991-01-01
Full Text Available The hydrogel implant for scleral buckling, first developed in 1980, is said to combine the advantages of both solid silicone rubber and silicone sponges. But it is still not widely used. Our clinical experience with the hydrogel implant used in 23 cases of rhegmatogenous retinal detachment is described. It was used both as exoplant and implant. Anatomical success was achieved in 91% of the cases. There was no infection, erosion, migration of extrusion of the buckle. The advantages are that it is soft, elastic, nontoxic, and nonpyogenic; it is devoid of infection and postoperatively it swells up, for additional heightening of the buckle. This new material appears to combine the advantages of both silicone sponge and solid silicon rubber thereby providing an ideal buckling material.
Dynamic Delamination Buckling In Composite Laminates
Grady, Joseph E.; Chamis, Christos C.; Aiello, Robert A.
1989-01-01
Procedure for mathematical modeling of dynamic delamination buckling and propagation of delamination, with plate bending elements and multipoint constraints, developed and incorporated into finite-element computer program. Predicts time at which delamination buckling occurs, shape of dynamic-buckling mode, and strain-energy-release rate due to extension of delamination crack. Method extended to handle such other defects as transply and edge cracks.
Shear buckling analysis of a hat-stiffened panel
Ko, William L.; Jackson, Raymond H.
1994-01-01
A buckling analysis was performed on a hat-stiffened panel subjected to shear loading. Both local buckling and global buckling were analyzed. The global shear buckling load was found to be several times higher than the local shear buckling load. The classical shear buckling theory for a flat plate was found to be useful in predicting the local shear buckling load of the hat-stiffened panel, and the predicted local shear buckling loads thus obtained compare favorably with the results of finite element analysis.
Buckling and Post-buckling Performance of Advanced Composite Stiffened Panel Under Compression
Directory of Open Access Journals (Sweden)
ZHANG Haoyu
2016-08-01
Full Text Available The axial compressive experiment was conducted on the domestic advanced composite stiffened panel, and its buckling and post-buckling performance was analyzed by monitoring strain and out-of-plane displacement of typical positions. The initial buckling load and buckling mode of panels were calculated by engineering methods to direct the follow-up axial compressive experiment. The experimental results show that the buckling patterns are mainly local buckling of panels between stiffeners, the second buckling of few positions of panels and cylindrical buckling of all 4 stiffeners successively; after local buckling of panels, part of load bearded by panels before is transferred to stiffeners and then stiffeners become the main bearing part; after fracture failure of stiffeners, the specimen is destroyed rapidly; the average value of failure load is 482.67 kN, which is 2.37 times of 204 kN of the average value of buckling load; the composite stiffened panel can bear more load after buckling.
STABILITY MATRICES FOR LATERAL BUCKLING ANALYSIS
African Journals Online (AJOL)
ES OBE
functional to investigate the lateral buckling behaviour of a class of beams comprising bi- symmetric sections. While retaining the coupled modes of displacements at ... programmed either in basic or FORTRAN and with efficient programming, a saving in computer time can be made. 1.0 INTRODUCTION. Lateral buckling of ...
Buckling driven debonding in sandwich columns
DEFF Research Database (Denmark)
Østergaard, Rasmus Christian
2008-01-01
results from two mechanisms: (a) interaction of local debond buckling and global buckling and (b) the development of a damaged zone at the debond crack tip. Based on the pronounced imperfection sensitivity, the author predicts that an experimental measurement of the strength of sandwich structures may...... exhibit a large scatter caused by geometrical variations between test specimens. (C) 2007 Elsevier Ltd. All rights reserved....
Liquid buckling in a practical situation
Ghosh, Sumana; Das, Gargi; Das, Prasanta Kumar
2016-08-01
Buckling of an oil filament is observed during the core annular flow of high viscous oil and water, when it encountered a sudden expansion in its flow path. Suitable mathematical equations have been suggested to predict the distance of initiation of buckling from the plane of area change and other characteristics of the deformed oil core. It is proposed that the initiation of buckling depends on the balance of inertial and viscous forces. The model predicts that as the oil flow rate increases, the fluid jet has to travel a larger distance from the plane of area change to initiate buckling. Frequency and radius of the buckled oil filament are also predicted from the model.
Macro stress mapping on thin film buckling
Energy Technology Data Exchange (ETDEWEB)
Goudeau, P.; Villain, P.; Renault, P.-O.; Tamura, N.; Celestre, R.S.; Padmore, H.A.
2002-11-06
Thin films deposited by Physical Vapour Deposition techniques on substrates generally exhibit large residual stresses which may be responsible of thin film buckling in the case of compressive stresses. Since the 80's, a lot of theoretical work has been done to develop mechanical models but only a few experimental work has been done on this subject to support these theoretical approaches and nothing concerning local stress measurement mainly because of the small dimension of the buckling (few 10th mm). This paper deals with the application of micro beam X-ray diffraction available on synchrotron radiation sources for stress mapping analysis of gold thin film buckling.
Buckling optimisation of sandwich cylindrical panels
Abouhamzeh, M.; Sadighi, M.
2016-06-01
In this paper, the buckling load optimisation is performed on sandwich cylindrical panels. A finite element program is developed in MATLAB to solve the governing differential equations of the global buckling of the structure. In order to find the optimal solution, the genetic algorithm Toolbox in MATLAB is implemented. Verifications are made for both the buckling finite element code and also the results from the genetic algorithm by comparisons to the results available in literature. Sandwich cylindrical panels are optimised for the buckling strength with isotropic or orthotropic cores with different boundary conditions. Results are presented in terms of stacking sequence of fibers in the face sheets and core to face sheet thickness ratio.
Scleral buckle infection with Alcaligenes xylosoxidans
Directory of Open Access Journals (Sweden)
Chih-Kang Hsu
2014-01-01
Full Text Available We describe a rare case of extraocular inflammation secondary to scleral buckle infection with Alcaligenes xylosoxidans. A 60-year-old female with a history of retinal detachment repair with open-book technique of scleral buckling presented with purulent discharge and irritation in the right eye that had begun 4 weeks earlier and had been treated ineffectively at another hospital. Conjunctival erosion with exposure of the scleral buckle was noted. The scleral buckle was removed and cultured. The explanted material grew gram-negative rod later identified as A. xylosoxidans. On the basis of the susceptibility test results, the patient was treated by subconjunctival injection and fortified topical ceftazidime. After 4 weeks of treatment, the infection resolved.
Buckling and Post-Buckling Behaviors of a Variable Stiffness Composite Laminated Wing Box Structure
Wang, Peiyan; Huang, Xinting; Wang, Zhongnan; Geng, Xiaoliang; Wang, Yuansheng
2017-10-01
The buckling and post-buckling behaviors of variable stiffness composite laminates (VSCL) with curvilinear fibers were investigated and compared with constant stiffness composite laminates (CSCL) with straight fibers. A VSCL box structure was evaluated under a pure bending moment. The results of the comparative test showed that the critical buckling load of the VSCL box was approximately 3% higher than that of the CSCL box. However, the post-buckling load-bearing capacity was similar due to the layup angle and the immature status of the material processing technology. The properties of the VSCL and CSCL boxes under a pure bending moment were simulated using the Hashin criterion and cohesive interface elements. The simulation results are consistent with the experimental results in stiffness, critical buckling load and failure modes but not in post-buckling load capacity. The results of the experiment, the simulation and laminated plate theory show that VSCL greatly improves the critical buckling load but has little influence on the post-buckling load-bearing capacity.
Stochastic estimation of microactuator buckling
Energy Technology Data Exchange (ETDEWEB)
Bahrami, Mohsen; Tayefeh, Mohsen [Department of Mechanical Engineering, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of)
2006-04-01
In order to make a robust design of microsystems, it is important to analyze the electrical, thermal and mechanical fields including the actual input parameters. These microdevices, which typically are made of brittle materials such as polysilicon, show wide scatter (stochastic behavior) in properties as well as substantial uncertainty in the shape and geometry because of manufacturing processes. These behaviors necessitate either costly and time-consuming trial-and-error designs or, more efficiently, the development of a probabilistic design methodology for MEMS. Computer aided MEMS simulations regarding performance, power consumption, and reliability is an important design task due to high prototyping costs. Since microbeams have a wide range of applications in MEMS actuation mechanisms, analysis of the thermomechanical behavior of these actuators is very important. In the present work, assessing meaningful uncertainties involved in thermally driven microbeams, the stochastic finite element model (SFEM) is developed and implemented. The analysis shows a large deviation in buckling temperature and thermal stresses for reasonable probability density functions of characteristic parameters. Although computationally significantly more expensive than deterministic electromechanical simulation, the work illustrates the requirement of stochastic modeling for true estimation of microsystems' performance.
Functional buckling behavior of silicone rubber shells for biomedical use.
van der Houwen, E B; Kuiper, L H; Burgerhof, J G M; van der Laan, B F A M; Verkerke, G J
2013-12-01
The use of soft elastic biomaterials in medical devices enables substantial function integration. The consequent increased simplification in design can improve reliability at a lower cost in comparison to traditional (hard) biomaterials. Functional bi-stable buckling is one of the many new mechanisms made possible by soft materials. The buckling behavior of shells, however, is typically described from a structural failure point of view: the collapse of arches or rupture of steam vessels, for example. There is little or no literature about the functional elastic buckling of small-sized silicone rubber shells, and it is unknown whether or not theory can predict their behavior. Is functional buckling possible within the scale, material and pressure normally associated with physiological applications? An automatic speech valve is used as an example application. Silicone rubber spherical shells (diameter 30mm) with hinged and double-hinged boundaries were subjected to air pressure loading. Twelve different geometrical configurations were tested for buckling and reverse buckling pressures. Data were compared with the theory. Buckling pressure increases linearly with shell thickness and shell height. Reverse buckling shows these same relations, with pressures always below normal buckling pressure. Secondary hinges change normal/reverse buckling pressure ratios and promote symmetrical buckling. All tested configurations buckled within or closely around physiological pressures. Functional bi-stable buckling of silicone rubber shells is possible with adjustable properties in the physiological pressure range. Results can be predicted using the proposed relations and equations. Copyright © 2013 Elsevier Ltd. All rights reserved.
The cutting of metals via plastic buckling.
Udupa, Anirudh; Viswanathan, Koushik; Ho, Yeung; Chandrasekar, Srinivasan
2017-06-01
The cutting of metals has long been described as occurring by laminar plastic flow. Here we show that for metals with large strain-hardening capacity, laminar flow mode is unstable and cutting instead occurs by plastic buckling of a thin surface layer. High speed in situ imaging confirms that the buckling results in a small bump on the surface which then evolves into a fold of large amplitude by rotation and stretching. The repeated occurrence of buckling and folding manifests itself at the mesoscopic scale as a new flow mode with significant vortex-like components-sinuous flow. The buckling model is validated by phenomenological observations of flow at the continuum level and microstructural characteristics of grain deformation and measurements of the folding. In addition to predicting the conditions for surface buckling, the model suggests various geometric flow control strategies that can be effectively implemented to promote laminar flow, and suppress sinuous flow in cutting, with implications for industrial manufacturing processes. The observations impinge on the foundations of metal cutting by pointing to the key role of stability of laminar flow in determining the mechanism of material removal, and the need to re-examine long-held notions of large strain deformation at surfaces.
Assessment of chandelier-assisted scleral buckling surgery
Directory of Open Access Journals (Sweden)
Mohsen A Abou Shousha
2015-01-01
Using 25 G chandelier endoillumination, surgical microscope, and wide-angle noncontact viewing system of PPV in scleral buckling surgery is easier and more convenient than the original buckling procedure using an indirect ophthalmoscope.
Analyses of Phase III Dynamic Buckling Tests. Final Report
1990-02-01
Thermal buckling of railroad tracks in the lateral plane is an important problem in the design and maintenance of continuous welded rail (CWR) tracks. The problem is manifested through derailments which are attributable to track buckling, indicating ...
Stability Matrices for Lateral Buckling Analysis of Beams | Jiki ...
African Journals Online (AJOL)
-symmetric sections has been proposed. The formulation employs a coupled lateral buckling functional to investigate the lateral buckling behaviour of a class of beams comprising bi-symmetric sections. While retaining the coupled modes of ...
Local buckling failure analysis of high-strength pipelines
National Research Council Canada - National Science Library
Yan Li Jian Shua Zhong-Li Jin Ya-Tong Zhao Kui Xu
2017-01-01
... combined with internal pressure. Finite element analysis was built according to previous data to study local buckling behavior of pressurized and unpressurized pipes under bending conditions and their differences in local buckling failure modes...
Enhanced piezoelectric wind energy harvesting based on a buckled beam
Zhang, Jiantao; Zhang, Jia; Shu, Chang; Fang, Zhou
2017-05-01
In order to improve the wind energy conversion efficiency, this study entails a concept utilizing the buckling behavior of a buckled beam to induce large amplitude oscillations in a PVDF beam harvester. Specifically, when the buckled beam subjected to the buckling load is in an unstable condition, the wind load can trigger the drastic vibration of the PVDF beam harvester. Experimental results demonstrate that the output performances of the proposed harvester are improved dramatically compared with a traditional cantilever beam harvester.
21 CFR 886.3300 - Absorbable implant (scleral buckling method).
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Absorbable implant (scleral buckling method). 886... SERVICES (CONTINUED) MEDICAL DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3300 Absorbable implant (scleral buckling method). (a) Identification. An absorbable implant (scleral buckling method) is a device...
Vibration and Buckling of Web Plate of the Plate Girder
高橋, 和雄; 呉, 明強; 中澤, 聡志; 筑紫, 宏之
1998-01-01
The vibration and buckling of the web of the plate girder are studied in this paper. The small deflection theory of the thin plate is used. The finite strip method is employed to solve vibration and buckling of the plate girder. Natural frequenies of buckling properties are shown for various plate girder bridges.
Thermal post-buckling of slender composite and FGM columns ...
Indian Academy of Sciences (India)
A simple and novel finite element (FE) formulation is proposed to study the thermal post-buckling of composite and FGM columns with axially immovable ends and operating in severe thermal environment. A linear eigenvalue analysis gives the critical buckling temperature but practically the buckled columns canwithstand ...
Repeated buckling of composite shear panels
Singer, Josef; Weller, Tanchum
1990-01-01
Failures in service of aerospace structures and research at the Technion Aircraft Structures Laboratory have revealed that repeatedly buckled stiffened shear panels might be susceptible to premature fatigue failures. Extensive experimental and analytical studies have been performed at Technion on repeated buckling, far in excess of initial buckling, for both metal and composite shear panels with focus on the influence of the surrounding structure. The core of the experimental investigation consisted of repeated buckling and postbuckling tests on Wagner beams in a three-point loading system under realistic test conditions. The effects of varying sizes of stiffeners, of the magnitude of initial buckling loads, of the panel aspect ratio and of the cyclic shearing force, V sub cyc, were studied. The cyclic to critical shear buckling ratios, (V sub cyc/V sub cr) were on the high side, as needed for efficient panel design, yet all within possible flight envelopes. The experiments were supplemented by analytical and numerical analyses. For the metal shear panels the test and numerical results were synthesized into prediction formulas, which relate the life of the metal shear panels to two cyclic load parameters. The composite shear panels studied were hybrid beams with graphite/epoxy webs bonded to aluminum alloy frames. The test results demonstrated that composite panels were less fatigue sensitive than comparable metal ones, and that repeated buckling, even when causing extensive damage, did not reduce the residual strength by more than 20 percent. All the composite panels sustained the specified fatigue life of 250,000 cycles. The effect of local unstiffened holes on the durability of repeatedly buckled shear panels was studied for one series of the metal panels. Tests on 2024 T3 aluminum panels with relatively small unstiffened holes in the center of the panels demonstrated premature fatigue failure, compared to panels without holes. Preliminary tests on two graphite
Membrane Buckling Induced by Curved Filaments
Lenz, Martin; Crow, Daniel J. G.; Joanny, Jean-François
2009-07-01
We present a novel buckling instability relevant to membrane budding in eukaryotic cells. In this mechanism, curved filaments bind to a lipid bilayer without changing its intrinsic curvature. As more and more filaments adsorb, newly added ones are more and more strained, which destabilizes the flat membrane. We perform a linear stability analysis of filament-dressed membranes and find that the buckling threshold is within reasonable in vivo parameter values. We account for the formation of long tubes previously observed in cells and in purified systems. We study strongly deformed dressed membranes and their bifurcation diagram numerically. Our mechanism could be validated by a simple experiment.
Scleral Buckle Infection With Pseudallescheria boydii.
Law, Janice C; Breazzano, Mark P; Eliott, Dean
2017-08-01
Pseudallescheria boydii is a ubiquitous fungus that infects soft tissues and is known to cause ocular disease, including keratitis and endophthalmitis, in rare cases. In immunocompromised hosts, P. boydii can disseminate to or from the eye and other organs with lethal consequences. Postoperative P. boydii infections have, in rare cases, complicated several types of ocular surgeries in immunocompetent patients, but never for a scleral buckle. The authors present the first case of an infected scleral buckle from P. boydii. [Ophthalmic Surg Lasers Imaging Retina. 2017;48:676-678.]. Copyright 2017, SLACK Incorporated.
Fundamental concepts in the suppression of delamination buckling by stitching
Cox, B. N.
1992-01-01
Elementary results are presented for the buckling of stitched, laminated composites containing delamination cracks. The stitching fibers are assumed to provide continuous, linear restoring tractions opposing the deflection of the delaminated layer adjacent to the crack. It is shown that there exists a characteristic length a(0) for buckling: if the length, 2a, of the delamination crack exceeds 2a(0), then, when buckling occurs, it will consist of waves of period 2a(0) and will usually not span the whole delamination. Simple expressions are derived for the critical buckling load and the minimum stitching density required to suppress buckling of the delaminated layer.
Buckling Instability of Self-Assembled Colloidal Columns
Swan, James W.; Vasquez, Paula A.; Furst, Eric M.
2014-09-01
Suspended, slender self-assembled domains of magnetically responsive colloids are observed to buckle in microgravity. Upon cessation of the magnetic field that drives their assembly, these columns expand axially and buckle laterally. This phenomenon resembles the buckling of long beams due to thermal expansion; however, linear stability analysis predicts that the colloidal columns are inherently susceptible to buckling because they are freely suspended in a Newtonian fluid. The dominant buckling wavelength increases linearly with column thickness and is quantitatively described using an elastohydrodynamic model and the suspension thermodynamic equation of state.
Critical Buckling Load on Large Spherical Shells
DEFF Research Database (Denmark)
Wedellsborg, B. W.
1962-01-01
Approximate evaluation for watertanks, hortonspheres, vapor containers, containment vessels for nuclear reactors, and so forth, has been computed, taking into account out-of-roundness and local flattened areas; graphs have been plotted giving critical buckling load as function of maximum radial...
Dynamic Pulse Buckling--Theory and Experiment
1983-02-01
these effects, we analyzed" the shells of Figure 3.30 with the numerical code SABOR /DRASTIC 6. In the numerical analysis, responses in modes n - 20...times, before strain-rate reversal or significant transfer of hoop energy to buckling, the results from the simple theory and from SABOR /DRASTIC 6 are
Computational modelling of buckling of woven fabrics
CSIR Research Space (South Africa)
Anandjiwala, RD
2006-02-01
Full Text Available The fabric buckling model proposed by Grosberg and Swani has been modified by incorporating Huang’s bilinear bending rule. The proposed model is an extension of the present model and also covers the special cases. The numerical results appear...
Elastic buckling strength of corroded steel plates
Indian Academy of Sciences (India)
Elastic buckling assessment of a corroded plate with irregular surfaces is evaluated only on the basis of numerical analysis with FEM. A computer code in Fortran 90 is developed to generate irregular surfaces based on the mean and standard deviation of thickness diminution. By using shell elements with variable thickness ...
Elastic buckling strength of corroded steel plates
Indian Academy of Sciences (India)
Corrosion makes structures more vulnerable to buckling and yielding failures. It is common practice to assume a uniform thickness reduction for general corrosion. To estimate the remaining strength of corroded structures, typically a much higher level of accuracy is required, since the actual corroded structures have ...
On the buckling of an elastic holey column
Johnson, C. G.; Jain, U.; Hazel, A. L.; Pihler-Puzović, D.; Mullin, T.
2017-11-01
We report the results of a numerical and theoretical study of buckling in elastic columns containing a line of holes. Buckling is a common failure mode of elastic columns under compression, found over scales ranging from metres in buildings and aircraft to tens of nanometers in DNA. This failure usually occurs through lateral buckling, described for slender columns by Euler's theory. When the column is perforated with a regular line of holes, a new buckling mode arises, in which adjacent holes collapse in orthogonal directions. In this paper, we firstly elucidate how this alternate hole buckling mode coexists and interacts with classical Euler buckling modes, using finite-element numerical calculations with bifurcation tracking. We show how the preferred buckling mode is selected by the geometry, and discuss the roles of localized (hole-scale) and global (column-scale) buckling. Secondly, we develop a novel predictive model for the buckling of columns perforated with large holes. This model is derived without arbitrary fitting parameters, and quantitatively predicts the critical strain for buckling. We extend the model to sheets perforated with a regular array of circular holes and use it to provide quantitative predictions of their buckling.
The Eulerian buckling test for orthodontic wires.
De Santis, R; Dolci, F; Laino, A; Martina, R; Ambrosio, L; Nicolais, L
2008-04-01
Orthodontic treatment is mainly dependent on the loads developed by metal wires. The load developed by a buckled orthodontic wire is of great concern for molar distalization and cannot be simply derived from mechanical properties measured through classical tests (i.e. tensile, torsion, and bending). A novel testing method, based on the Eulerian approach of a simple supported beam, has been developed in order to measure the load due to buckling of orthodontic wires. Elastic titanium molybdenum alloy (TMA; SDS Ormco) and superelastic Nitinol (3M Unitek) and copper nickel-titanium (NiTi; SDS Ormco) wires, each having a rectangular cross section of 0.016 x 0.022 square inches (0.41 x 0.56 mm(2)), were used. The wires were activated and deactivated by loading and unloading. In order to analyse thermo-mechanical properties in buckling, mechanical tests were assisted by calorimetric measurements through differential scanning calorimetry (DSC). Statistical analysis to determine differences between the samples was undertaken using two-way analysis of variance (ANOVA) and Tukey's post hoc test, and one-way ANOVA to assess differences between the tested wires under similar conditions and different materials. The results suggest that the load due to buckling depends on material composition, wire length, the amount of activation, temperature, and deformation rate. The results can be considered as the lower bound for the loads experienced by teeth as far as a buckled wire is concerned. At a temperature higher than the austenite finish transition temperature, superelastic wires were strongly dependent on temperature and deformation rate. The effect due to an increase of deformation rate was similar to that of a decrease of temperature. Load variations due to temperature of a superelastic wire with a length of 20 mm were estimated to be approximately 4 g/degrees C. The high performance of an applied superelastic wire may be related to the high dynamics of the load in relation to
Photothermally reprogrammable buckling of nanocomposite gel sheets.
Hauser, Adam W; Evans, Arthur A; Na, Jun-Hee; Hayward, Ryan C
2015-04-27
Patterning deformation within the plane of thin elastic sheets represents a powerful tool for the definition of complex and stimuli-responsive 3D buckled shapes. Previous experimental methods, however, have focused on sheets that access a limited number of shapes pre-programmed into the sheet, restricting the degree of dynamic control. Here, we demonstrate on-demand reconfigurable buckling of poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM) hydrogel network films containing gold nanoparticles (AuNPs) by patterned photothermal deswelling. Predictable, easily controllable, and reversible transformations from a single flat gel sheet to numerous different three-dimensional forms are shown. Importantly, the response time is limited by poroelastic mass transport, rather than photochemical switching kinetics, enabling reconfiguration of shape on timescales of several seconds, with further increases in speed possible by reducing film thickness. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Linear and nonlinear buckling analysis of a locally stretched plate
Energy Technology Data Exchange (ETDEWEB)
Kilardj, Madina; Ikhenzzen, Ghania [University of Sciences and Technology Houari Boumediene (U.S.T.H.B), Bab Ezzouar, Algiers (Algeria); Merssager, Tanguy; Kanit, Toufik [Laboratoire de Mecanique de Lille Universite Lille 1, Cite ScientifiqueVilleneuve d' Ascq cedex (France)
2016-08-15
Uniformly stretched thin plates do not buckle unless they are in special boundary conditions. However, buckling commonly occurs around discontinuities, such as cracks, cuts, narrow slits, holes, and different openings, of such plates. This study aims to show that buckling can also occur in thin plates that contain no defect or singularity when the stretching is local. This specific stability problem is analyzed with the finite element method. A brief literature review on stretched plates is presented. Linear and nonlinear buckling stress analyses are conducted for a partially stretched rectangular plate, and various load cases are considered to investigate the influence of the partial loading expanse on the critical tensile buckling load. Results are summarized in iso-stress areas, tables and graphs. Local stretching on one end of the plate induces buckling in the thin plate even without geometrical imperfection.
Buckling of Carbon Nanotubes: A State of the Art Review
Shima, Hiroyuki
2011-01-01
The nonlinear mechanical response of carbon nanotubes, referred to as their “buckling" behavior, is a major topic in the nanotube research community. Buckling means a deformation process in which a large strain beyond a threshold causes an abrupt change in the strain energy vs. deformation profile. Thus far, much effort has been devoted to analysis of the buckling of nanotubes under various loading conditions: compression, bending, torsion, and their certain combinations. Such extensive studies have been motivated by (i) the structural resilience of nanotubes against buckling and (ii) the substantial influence of buckling on their physical properties. In this contribution, I review the dramatic progress in nanotube buckling research during the past few years. PMID:28817032
Circumferential buckling instability of a growing cylindrical tube
Moulton, D.E.
2011-03-01
A cylindrical elastic tube under uniform radial external pressure will buckle circumferentially to a non-circular cross-section at a critical pressure. The buckling represents an instability of the inner or outer edge of the tube. This is a common phenomenon in biological tissues, where it is referred to as mucosal folding. Here, we investigate this buckling instability in a growing elastic tube. A change in thickness due to growth can have a dramatic impact on circumferential buckling, both in the critical pressure and the buckling pattern. We consider both single- and bi-layer tubes and multiple boundary conditions. We highlight the competition between geometric effects, i.e. the change in tube dimensions, and mechanical effects, i.e. the effect of residual stress, due to differential growth. This competition can lead to non-intuitive results, such as a tube growing to be thinner and yet buckle at a higher pressure. © 2011 Elsevier Ltd. All rights reserved.
CHAOTIC VIBRATION OF BUCKLED BEAMS AND PLATES
Directory of Open Access Journals (Sweden)
Daniela BARAN
2009-12-01
Full Text Available The great developing of numerical analysis of the dynamic systems emphasizes the existence of astrong dependence of the initial conditions, described in the phase plane by attractors with acomplicated geometrical structure. The Lyapunov exponents are used to determine if there is a realstrong dependence on the initial conditions: there is at least a positive exponent if the system has achaotic evolution and all the Lyapunov exponents are negative if the system has not such anevolution. Determining the largest Lyapunov exponent , which is easier to calculate, is sufficient todraw such conclusions. In this paper we shall use the greatest Lyapunov exponent to study twowell-known problems who leads to chaotic motions: the problem of the buckled beam and the panelflutter problem. In the problem of the buckled beam we verify the results obtained with theMelnikov theorem with the maximum Lyapunov exponent [1]. The flutter of a buckled plate is alsoa problem characterized by strong dependence of the initial conditions, existence of attractors withcomplicated structure existence of periodic unstable motions with very long periods (sometimesinfinite periods.
How child-resistant are stroller belt buckles?
Ridenour, M V
1997-04-01
70 children, between the ages of 24 and 36 months, participated in the assessment of three different styles of stroller seat buckles representing difficulties for children to disconnect the buckle mechanism in the restraint system. None could prevent all the children from opening the restraint system. One was much easier for children to open than the other two styles. Stroller-restraint buckles provide false security to parents who use strollers, as there are no published standards regarding the use of children's stroller seat-belt buckles as a safety device.
Uncertainty modelling of critical column buckling for reinforced ...
Indian Academy of Sciences (India)
Buckling is a critical issue for structural stability in structural design. In most of the buckling analyses, applied loads, structural and material properties are considered certain. However, in reality, these parameters are uncertain. Therefore, a prognostic solution is necessary and uncertainties have to be considered. Fuzzy logic ...
On the buckling of an elastic rotating beam
DEFF Research Database (Denmark)
Furta, Stanislaw D.; Kliem, Wolfhard; Pommer, Christian
1997-01-01
A nonlinear model is developed, which describes the buckling phenomena of an elastic beam clamped to the interior of a rotating wheel. We use a power series method to obtain an approximate expression of the buckling equation and compare this with previous results in the literature. The linearized...
On the static buckling of an externally pressurized finite circular ...
African Journals Online (AJOL)
The static buckling behaviour of an imperfect finite cylindrical shell, stressed by either a lateral or hydrostatic pressure, is here investigated by assuming that the imperfection can be regarded as the first term in the Fourier sine series expansion .The buckling modes are assumed to be in the shape of the imperfection which is ...
Thermal post-buckling of slender composite and FGM columns ...
Indian Academy of Sciences (India)
G Venkateswara Rao
Abstract. A simple and novel finite element (FE) formulation is proposed to study the thermal post-buckling ... rise from the initial stress free temperature when subjected .... (GPa) n=0.5 n=1 n=2 n=5 n=10. Figure 3. Variation of Young's Modulus across thickness of. FGM beam. Thermal post-buckling of slender composite. 871 ...
A multiple buckling curve formulation for design of aluminium alloy ...
African Journals Online (AJOL)
The paper refers to the overall stability design of aluminium structural elements. Buckling curves for members subjected to compression and members subjected to bending are dealt with. The formulation is based on probabilistic considerations of two random events, namely the elastic buckling of a perfect member and the ...
Bending energy of buckled edge dislocations
Kupferman, Raz
2017-12-01
The study of elastic membranes carrying topological defects has a longstanding history, going back at least to the 1950s. When allowed to buckle in three-dimensional space, membranes with defects can totally relieve their in-plane strain, remaining with a bending energy, whose rigidity modulus is small compared to the stretching modulus. In this paper we study membranes with a single edge dislocation. We prove that the minimum bending energy associated with strain-free configurations diverges logarithmically with the size of the system.
Buckling and vibration of circular cylindrical shells containing hot liquid
Ganesan, N.; Pradeep, V.
2005-11-01
Cylindrical shell filled with hot liquid is analyzed for buckling and vibration behavior using semi-analytical finite element method. A parametric study is conducted on a 316L stainless-steel cylinder filled with hot liquid. The temperature distribution in shell domain is obtained by using axisymmetric eight-node ring finite elements, capable of taking axial variation of temperature into account. Three-node ring elements are used for buckling and vibration analysis, formulated using semi-analytical finite element method. Thermal stress resultants and moment resultants in the shell are estimated and static buckling analysis is carried out to find the buckling temperature of the container for different levels of filling of liquid and for two different boundary conditions. Free vibration analysis carried out by considering initial stress effect and added mass effect due to hot liquid. Two different geometries are considered to study the effect of geometry on buckling temperature.
Buckling of a thin rod under cylindrical constraint
Miller, Jay; Su, Tianxiang; Wicks, Nathan; Pabon, Jahir; Bertoldi, Katia; Reis, Pedro
2013-03-01
We investigate the buckling and post-buckling behavior of a thin elastic rod, under cylindrical constraint, with distributed loading. Our precision model experiments consist of injecting a custom-fabricated rod into a transparent glass pipe. Under imposed velocity (leading to frictional axial loading), a portion of the initially straight rod first buckles into a sinusoidal mode and eventually undergoes a secondary instability into a helical configuration. The buckling and post-buckling behavior is found to be highly dependent on the system's geometry, namely the injected rod length and the aspect ratio of the rod to pipe diameter, as well as material parameters. We quantify the critical loads for this sequence of instabilities, contrast our results with numerical experiments and rationalize the observed behavior through scaling arguments.
Experimental study on dynamic buckling phenomena for supercavitating underwater vehicle
Directory of Open Access Journals (Sweden)
Minho Chung
2012-09-01
Full Text Available Dynamic buckling, also known as parametric resonance, is one of the dynamic instability phenomena which may lead to catastrophic failure of structures. It occurs when compressive dynamic loading is applied to the structures. Therefore it is essential to establish a reliable procedure to test and evaluate the dynamic buckling behaviors of structures, especially when the structure is designed to be utilized in compressive dynamic loading environment, such as supercavitating underwater vehicle. In the line of thought, a dynamic buckling test system is designed in this work. Using the test system, dynamic buckling tests including beam, plate, and stiffened plate are carried out, and the dynamic buckling characteristics of considered structures are investigated experimentally as well as theoretically and numerically.
Endoilluminator-assisted scleral buckling: Our results
Directory of Open Access Journals (Sweden)
Varun Gogia
2014-01-01
Full Text Available Aims: The aim was to evaluate the long-term surgical outcomes of endoillumination assisted scleral buckling (EASB in primary rhegmatogenous retinal detachment (RRD. Methods: Twenty-five eyes of 25 patients with primary RRD and proliferative vitreoretinopathy ≤C2 where any preoperative break could not be localised, were included. All patients underwent 25 gauge endoilluminator assisted rhegma localisation. Successful break determination was followed by cryopexy and standard scleral buckling under surgical microscope. Anatomical and functional outcomes were evaluated at the end of 2 years. Results: At least one intraoperative break could be localized in 23 of 25 (92% eyes. Median age of these patients was 46 years (range: 17-72. Thirteen eyes (56.52% were phakic, 8 (34.78% were pseudophakic and 2 (8.6% were aphakic. Anatomical success (attachment of retina was achieved in 22 (95.63% of 23 eyes with EASB. All eyes remained attached at the end of 2 years. Significant improvement in mean visual acuity (VA was achieved at the end of follow-up (1.09 ± 0.46 log of the minimum angle of resolution [logMAR] compared with preoperative VA (1.77 ± 0.28 logMAR (P < 0.001. Conclusion: EASB can be considered an effective alternative to vitreoretinal surgery in simple retinal detachment cases with the added advantage of enhanced microscopic magnification and wide field illumination.
Elastic Buckling Behaviour of General Multi-Layered Graphene Sheets
Directory of Open Access Journals (Sweden)
Rong Ming Lin
2015-04-01
Full Text Available Elastic buckling behaviour of multi-layered graphene sheets is rigorously investigated. Van der Waals forces are modelled, to a first order approximation, as linear physical springs which connect the nodes between the layers. Critical buckling loads and their associated modes are established and analyzed under different boundary conditions, aspect ratios and compressive loading ratios in the case of graphene sheets compressed in two perpendicular directions. Various practically possible loading configurations are examined and their effect on buckling characteristics is assessed. To model more accurately the buckling behaviour of multi-layered graphene sheets, a physically more representative and realistic mixed boundary support concept is proposed and applied. For the fundamental buckling mode under mixed boundary support, the layers with different boundary supports deform similarly but non-identically, leading to resultant van der Waals bonding forces between the layers which in turn affect critical buckling load. Results are compared with existing known solutions to illustrate the excellent numerical accuracy of the proposed modelling approach. The buckling characteristics of graphene sheets presented in this paper form a comprehensive and wholesome study which can be used as potential structural design guideline when graphene sheets are employed for nano-scale sensing and actuation applications such as nano-electro-mechanical systems.
A generalized interpretation of buckling experiments for thermal neutrons
Energy Technology Data Exchange (ETDEWEB)
Woznicka, Urszula E-mail: urszula.woznicka@ifj.edu.pl; Drozdowicz, Krzysztof; Dabrowska, Joanna
2000-12-11
The buckling experiment is a well-known pulsed measurement method used to determine the thermal neutron diffusion parameters of a medium. In the classic form of the method, a dependence between the geometric buckling B{sup 2} (in cm{sup -2}) and the thermal neutron time decay constant {lambda} (in s{sup -1}) are involved. In the present paper, dimensionless values for the decay constant and for the buckling are introduced. This unification offers a method to generalize the description of the buckling experiment and makes it possible to compare experiments made for different media. The application of this procedure is exemplified on results for polyethylene of two different densities (from a Monte-Carlo-simulated experiment) and for Plexiglas (from a real laboratory experiment). The conclusion is that the buckling experiment is relatively easy for interpretation in the dimensionless buckling range which does not exceed 0.2. It corresponds, for example, to the geometric buckling B{sup 2}=1.1 cm{sup -2} for polyethylene of density 0.57 g cm{sup -3} or to B{sup 2}=3.0 cm{sup -2} for polyethylene of density 0.95 g cm{sup -3}.
Pseudo-nonlinear dynamic analysis of buckled pipes
Gültekin Sınır, B.
2013-02-01
In this study, the post-divergence behavior of fluid-conveying pipes supported at both ends is investigated using the nonlinear equations of motion. The governing equation exhibits a cubic nonlinearity arising from mid-plane stretching. Exact solutions for post-buckling configurations of pipes with fixed-fixed, fixed-hinged, and hinged-hinged boundary conditions are investigated. The pipe is stable at its original static equilibrium position until the flow velocity becomes high enough to cause a supercritical pitchfork bifurcation, and the pipe loses stability by static divergence. In the supercritical fluid velocity regime, the equilibrium configuration becomes unstable and bifurcates into multiple equilibrium positions. To investigate the vibrations that occur in the vicinity of a buckled equilibrium position, the pseudo-nonlinear vibration problem around the first buckled configuration is solved precisely using a new solution procedure. By solving the resulting eigenvalue problem, the natural frequencies and the associated mode shapes of the pipe are calculated. The dynamic stability of the post-buckling configurations obtained in this manner is investigated. The first buckled shape is a stable equilibrium position for all boundary conditions. The buckled configurations beyond the first buckling mode are unstable equilibrium positions. The natural frequencies of the lowest vibration modes around each of the first two buckled configurations are presented. Effects of the system parameters on pipe behavior as well as the possibility of a subcritical pitchfork bifurcation are also investigated. The results show that many internal resonances might be activated among the vibration modes around the same or different buckled configurations.
Buckling localization in a cylindrical panel under axial compression
DEFF Research Database (Denmark)
Tvergaard, Viggo; Needleman, A.
2000-01-01
Localization of an initially periodic buckling pattern is investigated for an axially compressed elastic-plastic cylindrical panel of the type occurring between axial stiffeners on cylindrical shells. The phenomenon of buckling localization and its analogy with plastic flow localization in tensile...... test specimens is discussed in general. For the cylindrical panel, it is shown that buckling localization develops shortly after a maximum load has been attained, and this occurs for a purely elastic panel as well as for elastic-plastic panels. In a case where localization occurs after a load maximum...
Buckling Response of Thick Functionally Graded Plates
Directory of Open Access Journals (Sweden)
BOUAZZA MOKHTAR
2014-11-01
Full Text Available In this paper, the buckling of a functionally graded plate is studied by using first order shear deformation theory (FSDT. The material properties of the plate are assumed to be graded continuously in the direction of thickness. The variation of the material properties follows a simple power-law distribution in terms of the volume fractions of constituents. The von Karman strains are used to construct the equilibrium equations of the plates subjected to two types of thermal loading, linear temperature rise and gradient through the thickness are considered. The governing equations are reduced to linear differential equation with boundary conditions yielding a simple solution procedure. In addition, the effects of temperature field, volume fraction distributions, and system geometric parameters are investigated. The results are compared with the results of the no shear deformation theory (classic plate theory, CPT.
Biomechanical effect of segmental scleral buckling surgery.
Wang, Fang; Lee, Heow Pueh; Lu, Chun
2007-02-01
The current paper studies the mechanical effect of segmental buckling surgery for treatment of retinal detachment using the finite element (FE) method. The effects of different eye sizes, intraocular pressures, and silicon sponge size and locations are examined. Indicative study on the visual optics from the emmetropia to the myopia by the surgery is also carried out. Ophthalmologists may have an advanced understanding of the possible surgical outcomes from the current study in order to plan better patient-specific surgical procedure. The solid tissues in the 3D FE model are modeled by eight-node hexagonal solid elements using a Lagrangian mesh. The inner vitreous and aqueous liquids are modeled by a Eulerian mesh. The eye tissues are treated as hyperelastic solids, and the liquids are represented with linear polynomial equations of state. The segmental scleral buckling procedure induces stress concentrations in the suture region, which may lead to bleeding. A smaller eye sustains relatively higher stress, thus has a greater chance to bleed. Smaller silicon implant leads to much higher stress, and the effect of the relative posterior and anterior positions of the silicon sponge is inconsistent. The surgery causes or aggravates myopia due to the average corneal curvature increase, although the optical length of the eye is reduced at high indentations. Exceptions are eyes with very large or small intraocular pressure at moderate indentation. Eyes with small intraocular pressure may sustain more severe refractive error by the surgery. Astigmatism may be caused or aggravated by the irregular deformation of the cornea and the deflection of the crystalline lens.
Measurement of impact-induced delamination buckling in composite laminates
Grady, J. E.; Depaola, K. J.
1987-01-01
High-velocity impact tests were performed on graphite/epoxy laminates with embedded delaminations. High-speed photography of the transversely impacted laminates shows that dynamic local buckling of the sublaminate region formed by the delamination can cause a mode-I-dominated propagation of that delamination. Simultaneous recordings of the dynamic strain histories at several locations in the buckled sublaminate region are used to measure the laminate and sublaminate responses to the impact loading. Flexural motion resulting from transverse impact is shown to reduce local buckling of the sublaminate. This buckling causes a progressive separation of the delaminated surfaces and subsequent extension of the delamination in a mode-I dominated fashion.
Track buckling prevention : theory, safety concepts, and applications
2013-03-31
This report is a part of the John A. Volpe National Transportation Systems Centers Track Stability Research Program for the Federal Railroad Administration on thermal buckling of continuous welded rail (CWR) track and its prevention. Presented in ...
Concept for the layout against buckling of cooling tower shells
Energy Technology Data Exchange (ETDEWEB)
Mungan, I.
1981-10-01
Hypotheses and considerations governing the buckling design of cooling tower shells are presented. The theoretical and experimental investigations themselves have already been published in various research reports. A list of publications is presented.
Buckling and failure characteristics of graphite-polyimide shear panels
Shuart, M. J.; Hagaman, J. A.
1983-01-01
The buckling and failure characteristics of unstiffened, blade stiffened, and hat stiffened graphite-polyimide shear panels are described. The picture frame shear test is used to obtain shear stress-strain data at room temperature and at 316 deg C. The experimental results are compared with a linear buckling analysis, and the specimen failure modes are described. The effect of the 316 deg C test temperature on panel behavior are discussed.
BUCKLING OF ANISOTROPIC PLATES BY THE RITZ METHOD
Yshii, Lucas Nobumichi; Santana, Rafael Christovão; Monteiro, Francisco Alex Correia; Neto, Eliseu Lucena
2017-01-01
The Ritz method is used in the buckling analysis of anisotropic plates under several combinations of in-plane loads and boundary conditions. Ritz bases are generated from modi ed Legendre polynomials, and the plate rigidities are carefully chosen to provide thermodynamically admissible materials. The accuracy of the proposed approach is assessed by means of several examples solved by nite element models.Keywords: Ritz method, Anisotropic plates, Buckling analysis
Buckling Instability Behavior of Steel Bridge under Fire Hazard
Ying Wang; Muyu Liu
2016-01-01
Failure of buckling instability will most likely occur before the displacement reaches the allowable value of the code when a tanker burns under the steel bridge. This research focuses on critical buckling stress of bridge under fire hazard and a thermal analysis model of a steel bridge is established by FDS (Fire Dynamics Simulator). Thermal parameters of the steel are determined by the polynomial fitting method. Temperature field and elastic modulus of the bridge changing with time are calc...
Delayed Buckling and Guided Folding of Inhomogeneous Capsules
Datta, Sujit; Kim, Shin-Hyun; Paulose, Jayson; Abbaspourrad, Alireza; Nelson, David R.; Weitz, David A
2012-01-01
Colloidal capsules can sustain an external osmotic pressure; however, for a sufficiently large pressure, they will ultimately buckle. This process can be strongly influenced by structural inhomogeneities in the capsule shells. We explore how the time delay before the onset of buckling decreases as the shells are made more inhomogeneous; this behavior can be quantitatively understood by coupling shell theory with Darcy’s law. In addition, we show that the shell inhomogeneity can dramatically c...
Buckling Instability Behavior of Steel Bridge under Fire Hazard
Directory of Open Access Journals (Sweden)
Ying Wang
2016-01-01
Full Text Available Failure of buckling instability will most likely occur before the displacement reaches the allowable value of the code when a tanker burns under the steel bridge. This research focuses on critical buckling stress of bridge under fire hazard and a thermal analysis model of a steel bridge is established by FDS (Fire Dynamics Simulator. Thermal parameters of the steel are determined by the polynomial fitting method. Temperature field and elastic modulus of the bridge changing with time are calculated by determining the heat release rate function of tanker. Critical buckling stress of the bridge web and bottom floor changing with time is calculated according to steel floor buckling theory. Finite element software ANSYS is used to verify the result. Results show that when a tanker is burning for 17 minutes, critical buckling stress of steel web will be reduced to τcrl,lw(T = 19.1 MPa and σcrl,lw(T = 38.8 MPa, which is less than the web stress (τ = 19.6 MPa, σ = 39.8 MPa caused by dead and live load. So steel web will be the first to show shear flexural bending buckling failure. Displacement in the midspan will reach 35.4 mm at this time, which was less than the allowable displacement (50 mm set by standard. The best rescue time of the bridge under fire hazard is within 15 minutes.
Thermal buckling comparative analysis using Different FE (Finite Element) tools
Energy Technology Data Exchange (ETDEWEB)
Banasiak, Waldemar; Labouriau, Pedro [INTECSEA do Brasil, Rio de Janeiro, RJ (Brazil); Burnett, Christopher [INTECSEA UK, Surrey (United Kingdom); Falepin, Hendrik [Fugro Engineers SA/NV, Brussels (Belgium)
2009-12-19
High operational temperature and pressure in offshore pipelines may lead to unexpected lateral movements, sometimes call lateral buckling, which can have serious consequences for the integrity of the pipeline. The phenomenon of lateral buckling in offshore pipelines needs to be analysed in the design phase using FEM. The analysis should take into account many parameters, including operational temperature and pressure, fluid characteristic, seabed profile, soil parameters, coatings of the pipe, free spans etc. The buckling initiation force is sensitive to small changes of any initial geometric out-of-straightness, thus the modeling of the as-laid state of the pipeline is an important part of the design process. Recently some dedicated finite elements programs have been created making modeling of the offshore environment more convenient that has been the case with the use of general purpose finite element software. The present paper aims to compare thermal buckling analysis of sub sea pipeline performed using different finite elements tools, i.e. general purpose programs (ANSYS, ABAQUS) and dedicated software (SAGE Profile 3D) for a single pipeline resting on an the seabed. The analyses considered the pipeline resting on a flat seabed with a small levels of out-of straightness initiating the lateral buckling. The results show the quite good agreement of results of buckling in elastic range and in the conclusions next comparative analyses with sensitivity cases are recommended. (author)
Isomerization dynamics of a buckled nanobeam.
Collins, Peter; Ezra, Gregory S; Wiggins, Stephen
2012-11-01
We analyze the dynamics of a model of a nanobeam under compression. The model is a two-mode truncation of the Euler-Bernoulli beam equation subject to compressive stress applied at both ends. We consider parameter regimes where the first mode is unstable and the second mode can be either stable or unstable, and the remaining modes (neglected) are always stable. Material parameters used correspond to a silicon nanobeam. The two-mode model Hamiltonian is the sum of a (diagonal) kinetic energy term and a potential energy term. The form of the potential energy function suggests an analogy with isomerization reactions in chemistry, where "isomerization" here corresponds to a transition between two stable beam configurations. We therefore study the dynamics of the buckled beam using the conceptual framework established for the theory of isomerization reactions. When the second mode is stable the potential energy surface has an index one saddle, and when the second mode is unstable the potential energy surface has an index two saddle and two index one saddles. Symmetry of the system allows us to readily construct a phase space dividing surface between the two "isomers" (buckled states); we rigorously prove that, in a specific energy range, it is a normally hyperbolic invariant manifold. The energy range is sufficiently wide that we can treat the effects of the index one and index two saddles on the isomerization dynamics in a unified fashion. We have computed reactive fluxes, mean gap times, and reactant phase space volumes for three stress values at several different energies. In all cases the phase space volume swept out by isomerizing trajectories is considerably less than the reactant density of states, proving that the dynamics is highly nonergodic. The associated gap time distributions consist of one or more "pulses" of trajectories. Computation of the reactive flux correlation function shows no sign of a plateau region; rather, the flux exhibits oscillatory decay
Interaction of hydraulic and buckling mechanisms in blowout fractures.
Nagasao, Tomohisa; Miyamoto, Junpei; Jiang, Hua; Tamaki, Tamotsu; Kaneko, Tsuyoshi
2010-04-01
The etiology of blowout fractures is generally attributed to 2 mechanisms--increase in the pressure of the orbital contents (the hydraulic mechanism) and direct transmission of impacts on the orbital walls (the buckling mechanism). The present study aims to elucidate whether or not an interaction exists between these 2 mechanisms. We performed a simulation experiment using 10 Computer-Aided-Design skull models. We applied destructive energy to the orbits of the 10 models in 3 different ways. First, to simulate pure hydraulic mechanism, energy was applied solely on the internal walls of the orbit. Second, to simulate pure buckling mechanism, energy was applied solely on the inferior rim of the orbit. Third, to simulate the combined effect of the hydraulic and buckling mechanisms, energy was applied both on the internal wall of the orbit and inferior rim of the orbit. After applying the energy, we calculated the areas of the regions where fracture occurred in the models. Thereafter, we compared the areas among the 3 energy application patterns. When the hydraulic and buckling mechanisms work simultaneously, fracture occurs on wider areas of the orbital walls than when each of these mechanisms works separately. The hydraulic and buckling mechanisms interact, enhancing each other's effect. This information should be taken into consideration when we examine patients in whom blowout fracture is suspected.
Investigations on Buckling Behaviour of Laminated Curved Composite Stiffened Panels
Kumar, N. Jeevan; Babu, P. Ramesh; Pandu, Ratnakar
2014-04-01
In Industrial applications structural efficiency is primary concern, this brings about the need of strong and lightweight materials. Due to their high specific strength, fibre reinforced polymers find wide application in these areas. Panels made of composite materials are widely used in aerospace structures, automobile, civil, marine and biomedical industries because of their good mechanical properties, impact resistance, excellent damage tolerance and also low fabrication cost. In this Paper, buckling and post-buckling analysis was performed on composite stiffened panel to obtain the critical load and modes of failures, with different parameters like ply-orientation, different composite materials, and stiffeners and by changing the number of stiffeners was derived. To analyze the post buckling behaviour of composite stiffened panels the nonlinear finite element analysis is employed and substantial investigations are undertaken using finite element (FE) model. Effect of critical parameters on buckling behaviour is studied and parametric studies were conducted with analytical tool to understand the structural behaviour in the post buckling range.
Spherical shells buckling to the sound of music
Lee, Anna; Marthelot, Joel; Reis, Pedro
We study how the critical buckling load of spherical elastic shells can be modified by a fluctuating external pressure field. In our experiments, we employ thin elastomeric shells of nearly uniform thickness fabricated by the coating of a hemispherical mold with a polymer solution, which upon curing yields elastic structures. A shell is submerged in a water bath and loaded quasi-statically until buckling occurs by reducing its inner volume with a syringe pump. Simultaneously, a plunger connected to an electromagnetic shaker is placed above the shell and driven sinusoidally to create a fluctuating external pressure field that can excite dynamic vibration modes of the shell. These dynamic modes induce effective compressive stresses, in addition to those from the inner pressure loading, which can modify the critical conditions for the onset of buckling. We systematically quantify how the frequency and amplitude of the external driving affects the buckling strength of our shells. In specific regions of the parameter space, we find that pressure fluctuations can result in large reductions of the critical buckling pressure. This is analogous to the classic knock-down effect in shells due to intrinsic geometric imperfections, albeit now in a way that can be controlled externally.
Critical thickness ratio for buckled and wrinkled fruits and vegetables
Dai, Hui-Hui; Liu, Yang
2014-11-01
This work aims at establishing the geometrical constraint for buckled and wrinkled shapes by modeling a fruit/vegetable with exocarp and sarcocarp as a hyperelastic layer-substrate structure subjected to uniaxial compression. A careful analysis on the derived bifurcation condition leads to the finding of a critical thickness ratio which separates the buckling and wrinkling modes, and remarkably, which is independent of the material stiffnesses. More specifically, it is found that if the thickness ratio is smaller than this critical value a fruit/vegetable should be in a buckled shape (under a sufficient stress); if a fruit/vegetable is in a wrinkled shape the thickness ratio is always larger than this critical value. To verify the theoretical prediction, we consider four types of buckled fruits/vegetables and four types of wrinkled fruits/vegetables with three samples in each type. The geometrical parameters for the 24 samples are measured and it is found that indeed all the data fall into the theoretically predicted buckling or wrinkling domains.
Fine Belt-Buckles of Walrus Ivory – also Made in Greenland
DEFF Research Database (Denmark)
Roesdahl, Else
2015-01-01
On the production of decorative artefacts in Norse Greenland - and new finds of walrus ivory belt buckles......On the production of decorative artefacts in Norse Greenland - and new finds of walrus ivory belt buckles...
Research on the Numerical Simulation of Sleeper in the Pipeline Global Buckling Controlling Practice
Directory of Open Access Journals (Sweden)
Liu Wen-Bin
2017-01-01
Full Text Available This paper analyzed the lateral buckling of pipelines located in Western Africa with ABAQUS software. The application of sleepers in practice is explored to guide the pipeline buckling controlling design.
Vibrations of post-buckled rods: The singular inextensible limit
Neukirch, Sébastien
2012-01-01
The small-amplitude in-plane vibrations of an elastic rod clamped at both extremities are studied. The rod is modeled as an extensible, shearable, planar Kirchhoff elastic rod under large displacements and rotations, and the vibration frequencies are computed both analytically and numerically as a function of the loading. Of particular interest is the variation of mode frequencies as the load is increased through the buckling threshold. While for some modes there are no qualitative changes in the mode frequencies, other frequencies experience rapid variations after the buckling threshold, the thinner the rod, the more abrupt the variations. Eventually, a mismatch for half of the frequencies at buckling arises between the zero thickness limit of the extensible model and the inextensible model. © 2011 Elsevier Ltd. All rights reserved.
Effect of corrosion on the buckling capacity of tubular members
Øyasæter, F. H.; Aeran, A.; Siriwardane, S. C.; Mikkelsen, O.
2017-12-01
Offshore installations are subjected to harsh marine environment and often have damages from corrosion. Several experimental and numerical studies were performed in the past to estimate buckling capacity of corroded tubular members. However, these studies were either based on limited experimental tests or numerical analyses of few cases resulting in semi-empirical relations. Also, there are no guidelines and recommendations in the currently available design standards. To fulfil this research gap, a new formula is proposed to estimate the residual strength of tubular members considering corrosion and initial geometrical imperfections. The proposed formula is verified with results from finite element analyses performed on several members and for varying corrosion patch parameters. The members are selected to represent the most relevant Eurocode buckling curve for tubular members. It is concluded that corrosion reduces the buckling capacity significantly and the proposed formula can be easily applied by practicing engineers without performing detailed numerical analyses.
Buckling of a fiber bundle embedded in epoxy
Hahn, H. T.; Sohi, M. M.
1986-01-01
Buckling of a fiber bundle embedded in epoxy resin was studied to gain insight into compressive failure mechanisms in unidirectional composites. The fibers used were E-glass, T300 graphite, T700 graphite, and P75 graphite. These fibers were combined with two different resins: Epon 815/V140 and Epon 828/Z. In both resins the failure mode of the bundle was found to be microbuckling of fibers for the first three types of fibers; however, the high-modulus P75 fibers failed in shear without any sign of microbuckling. The strains at which microbuckling occurred were higher than the compressive failure strains of the corresponding unidirectional composites. In the soft resin, Epon 815/V140, fibers buckled at lower strains than in the stiff resin, Epon 828/Z. The buckling strains and the segment lengths followed the trends predicted for a single filament embedded in an infinite matrix.
Design of laminated plates for maximum buckling load
Shin, Yung S.; Haftka, Raphael T.; Watson, Layne T.; Plaut, Raymond H.
1989-01-01
The buckling load of laminated plates having midplane symmetry is maximized for a given total thickness. The thicknesses of the layers are taken as the design variables. Buckling analysis is carried out using the finite element method. The optimality equations are solved by a homotopy method which permits tracing optima as a function of total thickness. It is shown that for any design with a given stacking sequence of ply orientations, there exists a design associated with any other stacking sequence which possesses the same bending stiffness matrix and same total thickness. Hence, from the optimum design for a given stacking sequence, one can directly determine the optimum design for any rearrangement of the ply orientations, and the optimum buckling load is independent of the stacking sequence.
Surface effect on the buckling of piezoelectric nanofilms
Zhang, Jin; Wang, Chengyuan; Adhikari, Sondipon
2012-07-01
A sandwich-plate model is developed to account for the effect of surface layers on the buckling of piezoelectric nanofilms (PNFs) due to an electrical voltage. The physical mechanisms of the surface effects are investigated and the contributions to the resultant effect are evaluated for surface piezoelectricity, surface stress and surface elasticity. It is found that the surface effect originates primarily from the residual surface stresses and enhanced piezoelectric coefficient due to the surface piezoelectricity. Its influence on the critical buckling voltage of a PNF depends sensitively on the thickness, the length-to-thickness ratio and the nature of residual surface stress. In addition, the intrinsic buckling may occur for a thin PNF where the relatively strong residual surface compression is achieved.
Buckling of Fiber Reinforced Composite Plates with Nanofiber Reinforced Matrices
Chamis, Christos C.; Murthy, Pappu L. N.
2010-01-01
Anisotropic composite plates were evaluated with nanofiber reinforced matrices (NFRM). The nanofiber reinforcement volumes ratio in the matrix was 0.01. The plate dimensions were 20 by 10 by 1.0 in. (508 by 254 by 25.4 mm). Seven different loading condition cases were evaluated: three for uniaxial loading, three for pairs of combined loading, and one with three combined loadings. The anisotropy arose from the unidirectional plates having been at 30 from the structural axis. The anisotropy had a full 6 by 6 rigidities matrix which were satisfied and solved by a Galerkin buckling algorithm. The buckling results showed that the NFRM plates buckled at about twice those with conventional matrix.
Bifurcations in the optimal elastic foundation for a buckling column
Energy Technology Data Exchange (ETDEWEB)
Rayneau-Kirkhope, Daniel, E-mail: ppxdr@nottingham.ac.u [School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD (United Kingdom); Farr, Robert [Unilever R and D, Olivier van Noortlaan 120, AT3133, Vlaardingen (Netherlands); London Institute for Mathematical Sciences, 22 South Audley Street, Mayfair, London (United Kingdom); Ding, K. [Department of Physics, Fudan University, Shanghai, 200433 (China); Mao, Yong [School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD (United Kingdom)
2010-12-01
We investigate the buckling under compression of a slender beam with a distributed lateral elastic support, for which there is an associated cost. For a given cost, we study the optimal choice of support to protect against Euler buckling. We show that with only weak lateral support, the optimum distribution is a delta-function at the centre of the beam. When more support is allowed, we find numerically that the optimal distribution undergoes a series of bifurcations. We obtain analytical expressions for the buckling load around the first bifurcation point and corresponding expansions for the optimal position of support. Our theoretical predictions, including the critical exponent of the bifurcation, are confirmed by computer simulations.
Locally Corroded Stiffener Effect on Shear Buckling Behaviors of Web Panel in the Plate Girder
Directory of Open Access Journals (Sweden)
Jungwon Huh
2015-01-01
Full Text Available The shear buckling failure and strength of a web panel stiffened by stiffeners with corrosion damage were examined according to the degree of corrosion of the stiffeners, using the finite element analysis method. For this purpose, a plate girder with a four-panel web girder stiffened by vertical and longitudinal stiffeners was selected, and its deformable behaviors and the principal stress distribution of the web panel at the shear buckling strength of the web were compared after their post-shear buckling behaviors, as well as their out-of-plane displacement, to evaluate the effect of the stiffener in the web panel on the shear buckling failure. Their critical shear buckling load and shear buckling strength were also examined. The FE analyses showed that their typical shear buckling failures were affected by the structural relationship between the web panel and each stiffener in the plate girder, to resist shear buckling of the web panel. Their critical shear buckling loads decreased from 82% to 59%, and their shear buckling strength decreased from 88% to 76%, due to the effect of corrosion of the stiffeners on their shear buckling behavior. Thus, especially in cases with over 40% corrosion damage of the vertical stiffener, they can have lower shear buckling strength than their design level.
Nucleation of Multiple Buckled Structures in Intertwined DNA Double Helices
Brahmachari, Sumitabha; Gunn, Kathryn H.; Giuntoli, Rebecca D.; Mondragón, Alfonso; Marko, John F.
2017-11-01
We study the statistical-mechanical properties of intertwined double-helical DNAs (DNA braids). In magnetic tweezers experiments, we find that torsionally stressed stretched braids supercoil via an abrupt buckling transition, which is associated with the nucleation of a braid end loop, and that the buckled braid is characterized by a proliferation of multiple domains. Differences between the mechanics of DNA braids and supercoiled single DNAs can be understood as an effect of the increased bulkiness in the structure of the former. The experimental results are in accord with the predictions of a statistical-mechanical model.
Electromechanical stability of buckled thin metal films on elastomer
Energy Technology Data Exchange (ETDEWEB)
Kim, Donyoung; Hwang, Hyun-Sik; Khang, Dahl-Young, E-mail: dykhang@yonsei.ac.kr
2011-06-01
Oxidizable metals such as Al are found to become highly resistive when exposed to air in buckled state, > 10x resistance increase compared to that in flat configuration. On the other hand, noble metal and oxide conductor films, such as Au and indium tin oxide show negligible resistance increase. The enhanced oxidation of grain boundaries that are exposed to air when buckled is found to be responsible for the observed electromechanical stability. Simple yet effective method, i.e., thin capping layer of noble metal, to prevent the oxidation of non-noble metal is proposed and experimentally verified.
Experimental and Numerical Study of Buckling of Vacuum Chambers for Fast-Cycling Synchrotrons
DEFF Research Database (Denmark)
Bräuner, Lars Erik
The optimal functioning of the long span thin walled elliptical cross section shells used as vacuum chambers for fast-cycling synchrotrons is provided by their buckling capacity. Also it is often necessary to design inter-stiffener panels of elliptical shells used as vacuum chambers to resist any...... pressure. Buckling analysis for shells is further complicated by the observation that geometric imperfections have an important influence on the buckling mode as well as on the buckling load-carrying capacity. Buckling loads are, in general, considerably lower than the lowest critical loads predicted from...
Effect of Topological Defects on Buckling Behavior of Single-walled Carbon Nanotube
Directory of Open Access Journals (Sweden)
Wang Guoxiu
2011-01-01
Full Text Available Abstract Molecular dynamic simulation method has been employed to consider the critical buckling force, pressure, and strain of pristine and defected single-walled carbon nanotube (SWCNT under axial compression. Effects of length, radius, chirality, Stone–Wales (SW defect, and single vacancy (SV defect on buckling behavior of SWCNTs have been studied. Obtained results indicate that axial stability of SWCNT reduces significantly due to topological defects. Critical buckling strain is more susceptible to defects than critical buckling force. Both SW and SV defects decrease the buckling mode of SWCNT. Comparative approach of this study leads to more reliable design of nanostructures.
Studies of the Buckling of Composite Plates in Compression
DEFF Research Database (Denmark)
Hayman, B.; Berggreen, Christian; Lundsgaard-Larsen, Christian
2011-01-01
As part of the Network of Excellence on Marine Structures (MARSTRUCT), a series of studies has been carried out into the buckling of glass-fibre-reinforced polymer plates with in-plane compression loading. The studies have included fabrication and testing of square, laminated panels with various...
Studies of the buckling of composite plates in compression
DEFF Research Database (Denmark)
Hayman, B.; Berggreen, Christian; Lundsgaard-Larsen, Christian
2009-01-01
As part of the MARSTRUCT Network of Excellence on Marine Structures, a series of studies has been carried out into the buckling of glass fibre reinforced polymer plates with in-plane compression loading. The studies have included fabrication and testing of square, laminated panels with various...
An embeddable optical strain gauge based on a buckled beam
Du, Yang; Chen, Yizheng; Zhu, Chen; Zhuang, Yiyang; Huang, Jie
2017-11-01
We report, for the first time, a low cost, compact, and novel mechanically designed extrinsic Fabry-Perot interferometer (EFPI)-based optical fiber sensor with a strain amplification mechanism for strain measurement. The fundamental design principle includes a buckled beam with a coated gold layer, mounted on two grips. A Fabry-Perot cavity is produced between the buckled beam and the endface of a single mode fiber (SMF). A ceramic ferrule is applied for supporting and orienting the SMF. The principal sensor elements are packaged and protected by two designed metal shells. The midpoint of the buckled beam will experience a deflection vertically when the beam is subjected to a horizontally/axially compressive displacement. It has been found that the vertical deflection of the beam at midpoint can be 6-17 times larger than the horizontal/axial displacement, which forms the basis of a strain amplification mechanism. The user-configurable buckling beam geometry-based strain amplification mechanism enables the strain sensor to achieve a wide range of strain measurement sensitivities. The designed EFPI was used to monitor shrinkage of a square brick of mortar. The strain was measured during the drying/curing stage. We envision that it could be a good strain sensor to be embedded in civil materials/structures under a harsh environment for a prolonged period of time.
Functional buckling behavior of silicone rubber shells for biomedical use
van der Houwen, E B; Kuiper, L H; Burgerhof, J G M; van der Laan, B F A M; Verkerke, G J
2013-01-01
BACKGROUND: The use of soft elastic biomaterials in medical devices enables substantial function integration. The consequent increased simplification in design can improve reliability at a lower cost in comparison to traditional (hard) biomaterials. Functional bi-stable buckling is one of the many
Buckling analysis of rectangular composite plates with rectangular ...
Indian Academy of Sciences (India)
Logo of the Indian Academy of Sciences ... A numerical study is carried out using finite element method, to examine the effects of square and rectangular cutout on the buckling behavior of a sixteen ply quasi-isotropic graphite/epoxy symmetrically laminated rectangular composite plate [ 0 ∘ / + 45 ∘ / − 45 ∘ / 90 ∘ ] 2 s ...
Uncertainty modelling of critical column buckling for reinforced ...
Indian Academy of Sciences (India)
gates the material uncertainties on column design and proposes an uncertainty model for critical column buckling reinforced concrete buildings. Fuzzy logic algorithm was employed in the study. Lower and upper bounds of elastic modulus representing mate- rial properties were defined to take uncertainties into account.
Buckling-driven Delamination in Layered Spherical Shells
DEFF Research Database (Denmark)
Sørensen, Kim Dalsten; Jensen, Henrik Myhre
2008-01-01
An analysis of buckling-driven delamination of a thin film on a spherical substrate has been carried out. The effects of the substrate having a double curvature compared to previous studies of delamination on cylindrical substrates turn out to be non-trivial: In addition to the effect of the shap...
Ground state instabilities of protein shells are eliminated by buckling.
Singh, Amit R; Perotti, Luigi E; Bruinsma, Robijn F; Rudnick, Joseph; Klug, William S
2017-11-15
We propose a hybrid discrete-continuum model to study the ground state of protein shells. The model allows for shape transformation of the shell and buckling transitions as well as the competition between states with different symmetries that characterize discrete particle models with radial pair potentials. Our main results are as follows. For large Föppl-von Kármán (FvK) numbers the shells have stable isometric ground states. As the FvK number is reduced, shells undergo a buckling transition resembling that of thin-shell elasticity theory. When the width of the pair potential is reduced below a critical value, then buckling coincides with the onset of structural instability triggered by over-stretched pair potentials. Chiral shells are found to be more prone to structural instability than achiral shells. It is argued that the well-width appropriate for protein shells lies below the structural instability threshold. This means that the self-assembly of protein shells with a well-defined, stable structure is possible only if the bending energy of the shell is sufficiently low so that the FvK number of the assembled shell is above the buckling threshold.
Buckling analysis of partially corroded steel plates with irregular ...
Indian Academy of Sciences (India)
Corrosion is a long-term, inevitable process, lessens the thickness and load carrying capacity of structures. Old steel structures are more vulnerable to buckling, yielding and fracture due to corrosion. In lieu of a detailed analysis, average thickness assumption is employed for general type of corrosion. However, the ...
Parametric study on buckling behaviour of thin stainless steel ...
African Journals Online (AJOL)
It is well known that thin cylindrical shell structures have wide applications as one of the important structural elements in many engineering fields and its load carrying capacity is decided by its buckling strength which in turn predominantly depends on geometrical imperfections present in it. Geometrical imperfections can be ...
On the dynamic buckling of stochastically imperfect finite cylindrical ...
African Journals Online (AJOL)
The dynamic buckling load of stochastically imperfect finite right circular cylindrical shells subjected to step loading is determined by means of regular perturbation procedures .The imperfection is assumed to be a Gaussian random function of position and consequently is homogeneous. The result obtained is implicit in the ...
Buckling analysis and small scale effect of biaxially compressed ...
Indian Academy of Sciences (India)
Duan & Wang (2007) reported bending analysis of circular graphene sheets based on non-local elasticity theory. Some research works have been reported on the thermal effect on buckling of nanotubes (Ghorbanpour Arani et al. 2011), vibration of nanotubes (Ghorbanpour Arani et al 2010), multilayered graphene sheets.
Uncertain Buckling Load and Reliability of Columns with Uncertain Properties
DEFF Research Database (Denmark)
Köylüoglu, H. U.; Nielsen, Søren R. K.; Cakmak, A. S.
Continuous and finite element methods are utilized to determine the buckling load of columns with material and geometrical uncertainties considering deterministic, stochastic and interval models for the bending rigidity of columns. When the bending rigidity field is assumed to be deterministic...
Dynamic Buckling Test Analyses of a High Degree CWR Track
1991-02-01
Thermal buckling of railroad tracks in the lateral plane is an important problem in the design and maintenance of continuous welded rail (CWR) tracks. The work reported here is part of a major investigation carried out by the John A. Volpe National T...
Orbital cellulitis following silicone-sponge scleral buckles
Directory of Open Access Journals (Sweden)
Nemet AY
2013-10-01
Full Text Available Arie Y Nemet, Joseph R Ferencz, Ori Segal, Amit Meshi Department of Ophthalmology, Meir Medical Center, Kfar Saba, Israel Background: Acute or chronic infection of the scleral explant is rare. We report seven cases of scleral explant infections that caused orbital cellulitis. Materials and methods: This was a retrospective chart review of oculoplastics at oculoplastics and vitreo-retinal units in a secondary referral hospital. All subjects had orbital cellulitis secondary to scleral buckle in the range of January 1990 to March 2010. Demographics, imaging studies, and pathology specimens were reviewed. Results: A total of 841 silicone-sponge scleral buckle implants for rhegmatogenous retinal detachment were performed. Forty were extracted (4.75%; annual rate of 1.9 cases. Seven (0.83% had orbital cellulitis. The mean time from implantation to presentation was 5.7 years. There was bacterial growth in all specimens, with Staphylococcus aureus in four. Conclusions: Patients who are operated on with silicone-sponge scleral buckling for rhegmatogenous retinal detachment sometimes require removal of the implant because of infection. However, the infection rate is low. Patients should be followed in the long term for possible complications. Keywords: scleral explant infection, scleral buckle, orbital cellulitis, rhegmatogenous retinal detachment
Local buckling of aluminium and steel plates with multiple holes
Scheperboer, I.C.; Efthymiou, E.; Maljaars, J.
2016-01-01
This paper considers local buckling of perforated square aluminium plates. Plates of various slenderness with simply supported edges and subjected to uniaxial compression are studied using the finite element method. Different perforation patterns are investigated, from a single circular hole to 25
On the dynamic buckling of lightly damped cylindrical shells ...
African Journals Online (AJOL)
The dynamic buckling load of finite imperfect, lightly but viscously damped cylindrical shells subjected to a periodic load, is determined using the technique of multiple scaling (two-timing) regular perturbation analysis. The geometric imperfection, assumed deterministic, are also assumed small and are expanded in a double ...
On the dynamic buckling of a weakly damped nonlinear elastic ...
African Journals Online (AJOL)
In this paper we determine the dynamic buckling load of a strictly nonlinear but weakly damped elastic oscillatory model structure subjected to small perturbations The loading history is explicitly time dependent and varies slowly with time over a natural period of oscillation of the structure. A multiple timing regular ...
Scleral buckling biomaterials and implants for retinal detachment surgery.
Baino, Francesco
2010-11-01
Scleral buckling is a widely used surgical procedure that aims at repairing retinal detachments. Many materials and procedural techniques have been variously proposed and tested in an attempt to find the best combination for providing optimal results to the patient. This review highlights the evolution of scleral buckling implants and chronicles the main advances that have been made in such a context. Specifically, the limitations of the materials and implants fallen in disuse, as well as the advantages of currently adopted devices are critically examined and discussed. Future directions for the research are considered, underlining in particular the great potential carried by the development of accurate mathematical models for describing the postoperative evolution of buckled eye. These analytical models, supported by a comprehensive data set provided by advanced techniques of medical investigations, may become useful tools for helping surgeons to choose, and to design if necessary, the best buckling material and configuration to be used in each specific clinical case. Copyright © 2010 IPEM. Published by Elsevier Ltd. All rights reserved.
Elastic buckling analysis of corroded stiffened plates with irregular ...
Indian Academy of Sciences (India)
Numerical simulation is used to study the influence of corrosion damage in stiffened plates focusing on elastic buckling strength. Three-dimensional specta are used to simulate geometries of corroded surfaces and finite element method is employed for computing Euler stress of stiffened plates. The influence of corrosion ...
Post-buckling analysis of composite beams: A simple intuitive ...
Indian Academy of Sciences (India)
Emam S A and Nayfeh A H 2010 Corrigendum to post-buckling and free vibrations of composite beams. Composite Struct. 92: 2608. Gunda J B, Gupta R K, Ranga Janardhan G and Venkateswara Rao G 2011 Large amplitude vibration analysis of composite beams: simple closed-form solutions. Composite Struct. 93(2): ...
Buckled graphene: A model study based on density functional theory
Khan, M. A.; Mukaddam, M. A.; Schwingenschlögl, U.
2010-09-01
We make use of ab initio calculations within density functional theory to investigate the influence of buckling on the electronic structure of single layer graphene. Our systematic study addresses a wide range of bond length and bond angle variations in order to obtain insights into the energy scale associated with the formation of ripples in a graphene sheet.
Buckling analysis of partially corroded steel plates with irregular ...
Indian Academy of Sciences (India)
For the structural safety assessment of corroded structures, load carrying capacity reduction should .... Elastic buckling assessment of corroded plates with irregular surfaces is only on the basis of numerical analysis with ... Ahmad Rahbar-Ranji. Eigenvalue analyses are performed using computer code ANSYS (version 5.6).
Coupled buckling design of steel laced columns | Uziak | Botswana ...
African Journals Online (AJOL)
A new design method developed by the authors that gives an opportunity to account for the interaction of different modes of buckling is presented. Eurocode 3 model is used as the reference model. In the reference model, an equivalent geometric imperfection comprising of an initial bow being equal to the length divided by ...
Buckling of Thin Films in Nano-Scale
Directory of Open Access Journals (Sweden)
Li L.A.
2010-06-01
Full Text Available Investigation of thin film buckling is important for life prediction of MEMS device which are damaged mainly by the delamination and buckling of thin films. In this paper the mechanical and thermal properties of compressed thin film titanium films with 150 nm thickness deposited on an organic glass substrate under mechanical and thermal loads were measured and characterized. In order to simulate the thin films which subjected to compound loads and the buckle modes the external uniaxial compression and thermal loading were subjected to the specimen by the symmetric loading device and the electrical film in this experiment. The temperature of the thin film deposited on substrate was measured using thermoelectric couple. The range of temperature accords with the temperature range of the MEMS. It is found that the size and number of the delamination and buckling of the film are depended upon the pre-fixed mechanical loading and thermal temperature. The thermal transient conduction and thermal stability of the film and substrate was studied with finite element method.
Experimental investigations on buckling of cylindrical shells under ...
Indian Academy of Sciences (India)
This paper presents experimental studies on buckling of cylindrical shell models under axial and transverse shear loads. Tests are carried out using an experimental facility specially designed, fabricated and installed, with provision for in-situ measurement of the initial geometric imperfections. The shell models are made by ...
Combined compressive and shear buckling analysis of hypersonic aircraft sandwich panels
Ko, William L.; Jackson, Raymond H.
1992-01-01
The combined-load (compression and shear) buckling equations were established for orthotropic sandwich panels by using the Rayleigh-Ritz method to minimize the panel total potential energy. The resulting combined-load buckling equations were used to generate buckling interaction curves for super-plastically-formed/diffusion-bonded titanium truss-core sandwich panels and titanium honeycomb-core sandwich panels having the same specific weight. The relative combined-load buckling strengths of these two types of sandwich panels are compared with consideration of their sandwich orientations. For square and nearly square panels of both types, the combined load always induces symmetric buckling. As the panel aspect ratios increase, antisymmetric buckling will show up when the loading is shear-dominated combined loading. The square panel (either type) has the highest combined buckling strength, but the combined load buckling strength drops sharply as the panel aspect ratio increases. For square panels, the truss-core sandwich panel has higher compression-dominated load buckling strength. However, for shear dominated loading, the square honeycomb-core sandwich panel has higher shear-dominated combined load buckling strength.
Combined compressive and shear buckling analysis of hypersonic aircraft structural sandwich panels
Ko, William L.; Jackson, Raymond H.
1991-01-01
The combined-load (compression and shear) buckling equations were established for orthotropic sandwich panels by using the Rayleigh-Ritz method to minimize the panel total potential energy. The resulting combined-load buckling equations were used to generate buckling interaction curves for super-plastically-formed/diffusion-bonded titanium truss-core sandwich panels and titanium honeycomb-core sandwich panels having the same specific weight. The relative combined-load buckling strengths of these two types of sandwich panels are compared with consideration of their sandwich orientations. For square and nearly square panels of both types, the combined load always induces symmetric buckling. As the panel aspect ratios increase, antisymmetric buckling will show up when the loading is shear-dominated combined loading. The square panel (either type) has the highest combined buckling strength, but the combined load buckling strength drops sharply as the panel aspect ratio increases. For square panels, the truss-core sandwich panel has higher compression-dominated combined load buckling strength. However, for shear dominated loading, the square honeycomb-core sandwich panel has higher shear-dominated combined load buckling strength.
An impact test system design and its applications to dynamic buckling of a spacer grid assembly
Energy Technology Data Exchange (ETDEWEB)
Liu, Sheng, E-mail: liusheng_05@126.com; Fan, Chenguang; Yang, Yiren
2016-11-15
This study is aimed at investigating the dynamic buckling load, dynamic stiffness, damping and buckling characteristics of the spacer grid assembly (SGA). A pendulum impact test system is designed to experiment the buckling of SGAs. Three criterions are discussed and compared to determine the buckling loads of SGAs: B-R criterion, energy criterion and extreme value criterion. Two approaches are applied to calculate the dynamic stiffness of SGAs: One method is natural period method based on the hypothesis of harmonic motion of the pendulum whose period is approximated because of the passivation and tailing of the impact force time history; and the other is energy method based on the conservation of mechanical energy. The equivalent viscous damping is defined as the resultant cause of dissipation and is obtained by the energy principle. The impact force time history loses its approximate symmetry after buckling occurs. The impact force and displacement reach their maxima almost at the same time at pre-buckling states but not post-buckling states. Vertical straps in SGA are found to be transversely shared by horizontal straps at the buckling position. The buckling of SGA results from the lack of strength of complete structure; and the strength of material has no effects on the buckling.
Using the Hypergeometric Model to analyze the buckling of drillstrings in curved boreholes
Energy Technology Data Exchange (ETDEWEB)
Sampaio, J.H.B. Jr. [PETROBRAS, Rio de Janeiro (Brazil); Eustes, A.W. III [Colorado School of Mines, Golden, CO (United States). Petroleum Engineering Dept.
1998-12-31
Current methodologies for analytically determining the onset of buckling of drillstrings within curved boreholes are limited. In this paper, the Hypergeometric Model is shown to be an effective model to determine drillstring buckling within curved boreholes. With the Hypergeometric Model, the analysis of drillstring buckling results in curves expressing the local buckling force versus the angle of inclination. The local buckling force alone, however, does not contain all the information required for a practical analysis. From the local buckling force curve, the positional buckling force is derived. The positional buckling force considers the distributed weight of the drillstring and the friction between the drillstring and the borehole wall. From this curve, the point of minimum resistance to buckling of the drillstring is determined. Using the local and positional buckling force curves, experimental results and simulations are presented. When multiple configurations exist (for example tapered drillstrings, tapered boreholes, multi-curved boreholes, or any combination of these), the analysis procedure uses superposition of two or more single configuration curves and a graphical algorithm. The Hypergeometric Model permits the optimization of the position of the crossing points (cross-over positioning, casing-shoe positioning, and change of curvature) to achieve extended reach with less risk and cost. The procedure for this model and examples are presented in this paper.
Glassy Spin Dynamics in Geometrically Frustrated Buckled Colloidal Crystals
Directory of Open Access Journals (Sweden)
Di Zhou
2017-05-01
Full Text Available Geometrical frustration arises when the lattice geometry prevents local interaction energies from minimizing simultaneously. Whether and how geometrically frustrated spins or charges in clean crystals exhibit glassy dynamics remain elusive due to the lack of measurements on microscopic dynamics. Here, we employ buckled monolayer colloidal crystals to mimic frustrated antiferromagnetic Ising spins on triangular lattices and measure single-spin dynamics using video microscopy. Both attractive and repulsive colloidal crystals buckled into zigzag stripes with glassy dynamics at low effective temperatures in experiment and simulation. The simple local spin configurations enable uncovering correlations among structure, dynamics, and soft vibrational modes. Machine learning analysis further reveals facilitated dynamics to be an important mechanism of structural relaxation. Moreover, our simulation reveals a similar structure and dynamics in lattice Coulomb liquids. Hence, spin-lattice coupling and long-range interaction can similarly lift degeneracy, induce a rugged landscape, and, thus, produce glassy dynamics.
Reversible patterning of spherical shells through constrained buckling
Marthelot, J.; Brun, P.-T.; Jiménez, F. López; Reis, P. M.
2017-07-01
Recent advances in active soft structures envision the large deformations resulting from mechanical instabilities as routes for functional shape morphing. Numerous such examples exist for filamentary and plate systems. However, examples with double-curved shells are rarer, with progress hampered by challenges in fabrication and the complexities involved in analyzing their underlying geometrical nonlinearities. We show that on-demand patterning of hemispherical shells can be achieved through constrained buckling. Their postbuckling response is stabilized by an inner rigid mandrel. Through a combination of experiments, simulations, and scaling analyses, our investigation focuses on the nucleation and evolution of the buckling patterns into a reticulated network of sharp ridges. The geometry of the system, namely, the shell radius and the gap between the shell and the mandrel, is found to be the primary ingredient to set the surface morphology. This prominence of geometry suggests a robust, scalable, and tunable mechanism for reversible shape morphing of elastic shells.
BUCKLING OF A COLUMN WITH TEMPERATURE DEPENDENT MATERIAL PROPERTIES
Directory of Open Access Journals (Sweden)
Ömer SOYKASAP
2001-01-01
Full Text Available Buckling of a column with temperature dependent material properties is investigated. Euler-Bernoulli theory of thin beams is used to derive the element matrices by means of the minimum potential energy principle. Temperature dependency of material properties is taken into account in the formulation. The column is divided into finite elements with the axial degrees of freedom defined at the outer fiber of the column. Column elements have simpler derivations and compact element matrices than those of classical beam-bending element. Some illustrative examples are presented to show the convergence of numerical results obtained by the use of new elements. The results are compared with those of the classical beam-bending element and analytical solution. The new element converges to the analytical results as powerful as the classical beam-bending element. The temperature effects on the buckling loads of the column with temperature dependent material properties are also examined.
Buckled graphene: A model study based on density functional theory
Khan, Yasser
2010-09-01
We make use of ab initio calculations within density functional theory to investigate the influence of buckling on the electronic structure of single layer graphene. Our systematic study addresses a wide range of bond length and bond angle variations in order to obtain insights into the energy scale associated with the formation of ripples in a graphene sheet. © 2010 Elsevier B.V. All rights reserved.
Buckling analyses of composite laminated panels with delamination
Albiol de Andrés, David
2009-01-01
Buckling response of composite laminated panels with an arti cial delamination was numerically investigated. Implementation of the nite-element models required a previous study on the simulation of fracture mechanisms under general mixed-mode loading conditions with the use of cohesive elements. To pursue this aim, a methodology based on numerical analyses and parametric studies of the DCB (Double Cantilever Beam) and ENF (End Notched Flexure) tests on AS4/PEEK laminates was developed....
Outpatient- and inpatient-based buckling surgery: a comparative study
Directory of Open Access Journals (Sweden)
Lee JC
2014-04-01
Full Text Available Jin Cheol Lee,* Yu Cheol Kim*Department of Ophthalmology, Keimyung University School of Medicine, Dongsan Medical Center, Daegu, Korea *Both authors contributed equally to this workPurpose: To evaluate the clinical outcomes of ambulatory buckling surgery, comparing outpatient- with inpatient-based surgery.Methods: The authors performed a retrospective study of 80 consecutive cases of rhegmato genous retinal detachment from January 2009 to December 2011 treated by scleral buckling surgery. Two groups of patients were defined according to inpatient (group 1 or outpatient (group 2 surgery, and a comparison of several parameters between these two groups was performed.Results: Of the 80 subjects in this study, the average age of group 1 (50 patients was 49.7 years, and that of group 2 (30 patients was 47.5 years. There were no statistically significant differences in the average logarithm of the minimum angle of resolution-visual acuity, the condition of the lens, or the presence of retinal lattice degeneration prior to the surgery between the groups. There were no statistically significant differences in the patterns of tear or retinal detachment or in surgical procedure between the groups. Comparing the best-corrected visual acuity after 6 months with that prior to the surgery, the changes in group 1 and group 2 were 0.26 and 0.31, respectively. The functional success rates of group 1 and group 2 after 6 months were 90% and 93%, respectively, and the anatomical success rates of group 1 and group 2 after 6 months were 94% and 96%, respectively, but these were also statistically insignificant.Conclusion: Hospitalization is not essential for buckling surgery in uncomplicated rhegmatogenous retinal detachment surgery.Keywords: ambulatory, scleral buckling, rhegmatogenous retinal detachment
Energy harvesting from controlled buckling of piezoelectric beams
Ansari, M. H.; Karami, M. Amin
2015-11-01
A piezoelectric vibration energy harvester is presented that can generate electricity from the weight of passing cars or crowds. The energy harvester consists of a piezoelectric beam, which buckles when the device is stepped on. The energy harvester can have a horizontal or vertical configuration. In the vertical (direct) configuration, the piezoelectric beam is vertical and directly sustains the weight of the vehicles or people. In the horizontal (indirect) configuration, the vertical weight is transferred to a horizontal axial force through a scissor-like mechanism. Buckling of the beam results in significant stresses and, thus, large power production. However, if the beam’s buckling is not controlled, the beam will fracture. To prevent this, the axial deformation is constrained to limit the deformations of the beam. In this paper, the energy harvester is analytically modeled. The considered piezoelectric beam is a general non-uniform beam. The natural frequencies, mode shapes, and the critical buckling force corresponding to each mode shape are calculated. The electro-mechanical coupling and the geometric nonlinearities are included in the model. The design criteria for the device are discussed. It is demonstrated that a device, realized with commonly used piezoelectric patches, can generate tens of milliwatts of power from passing car traffic. The proposed device could also be implemented in the sidewalks or integrated in shoe soles for energy generation. One of the key features of the device is its frequency up-conversion characteristics. The piezoelectric beam undergoes free vibrations each time the weight is applied to or removed from the energy harvester. The frequency of the free vibrations is orders of magnitude larger than the frequency of the load. The device is, thus, both efficient and insensitive to the frequency of the force excitations.
Scleral buckling for retinal detachment in patients with retinoblastoma
Energy Technology Data Exchange (ETDEWEB)
Buzney, S.M.; Pruett, R.C.; Regan, C.D.; Walton, D.S.; Smith, T.R.
1984-10-15
Three children (two girls and one boy) with bilateral retinoblastoma each developed a presumed rhegmatogenous retinal detachment in one eye. All three eyes had previously received radiation and cryotherapy. In each case the retinal detachment responded promptly to conventional surgical methods via scleral buckling in the area of treated retinoblastoma and presumed retinal break. All three eyes have retained useful vision for follow-up periods of 3.5 to 12 years.
Why Buckling Stellar Bars Weaken in Disk Galaxies
Martinez-Valpuesta, Inma; Shlosman, Isaac
2004-01-01
Young stellar bars in disk galaxies experience a vertical buckling instability which terminates their growth and thickens them, resulting in a characteristic peanut/boxy shape when viewed edge on. Using N-body simulations of galactic disks embedded in live halos, we have analyzed the bar structure throughout this instability and found that the outer third of the bar dissolves completely while the inner part (within the vertical inner Lindblad resonance) becomes less oval. The bar acquires the...
Concrete Cover Influence on Inelastic Buckling of Longitudinal Reinforcing Bars
Korentz, Jacek; Kucharczyk, Anna
2017-10-01
The paper presents the results of numerical analyses of post yielding behaviour of compressed reinforcing bars, taking into account the impact of concrete cover on static equilibrium path. Concrete cover was modelled as a transverse ties with characteristics like for the tensioned concrete. The calculations were performed for various parameters of concrete cover and bar slenderness, with the use commercial system Abaqus/CAE. The results of analysis showed that the concrete cover has a significant impact on inelastic buckling of reinforcing bars.
Mechanics of nanowire/nanotube in-surface buckling on elastomeric substrates
Xiao, J.; Ryu, S. Y.; Huang, Y.; Hwang, K.-C.; Paik, U.; Rogers, J. A.
2010-02-01
A continuum mechanics theory is established for the in-surface buckling of one-dimensional nanomaterials on compliant substrates, such as silicon nanowires on elastomeric substrates observed in experiments. Simple analytical expressions are obtained for the buckling wavelength, amplitude and critical buckling strain in terms of the bending and tension stiffness of the nanomaterial and the substrate elastic properties. The analysis is applied to silicon nanowires, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanotube bundles. For silicon nanowires, the measured buckling wavelength gives Young's modulus to be 140 GPa, which agrees well with the prior experimental studies. It is shown that the energy for in-surface buckling is lower than that for normal (out-of-surface) buckling, and is therefore energetically favorable.
Snap-Through Buckling Problem of Spherical Shell Structure
Directory of Open Access Journals (Sweden)
Sumirin Sumirin
2014-12-01
Full Text Available This paper presents results of a numerical study on the nonlinear behavior of shells undergoing snap-through instability. This research investigates the problem of snap-through buckling of spherical shells applying nonlinear finite element analysis utilizing ANSYS Program. The shell structure was modeled by axisymmetric thin shell of finite elements. Shells undergoing snap-through buckling meet with significant geometric change of their physical configuration, i.e. enduring large deflections during their deformation process. Therefore snap-through buckling of shells basically is a nonlinear problem. Nonlinear numerical operations need to be applied in their analysis. The problem was solved by a scheme of incremental iterative procedures applying Newton-Raphson method in combination with the known line search as well as the arc- length methods. The effects of thickness and depth variation of the shell is taken care of by considering their geometrical parameter l. The results of this study reveal that spherical shell structures subjected to pressure loading experience snap-through instability for values of l≥2.15. A form of ‘turn-back’ of the load-displacement curve took place at load levels prior to the achievement of the critical point. This phenomenon was observed for values of l=5.0 to l=7.0.
Investigation of adatom adsorption on single layer buckled germanium selenide
Energy Technology Data Exchange (ETDEWEB)
Arkın, H., E-mail: holgar@eng.ankara.edu.tr [Department of Physics Engineering, Ankara University, Ankara (Turkey); Aktürk, E., E-mail: ethem.akturk@adu.edu.tr [Department of Physics, Adnan Menderes University, 09100 Aydın (Turkey); Nanotechnology Application and Research Center, Adnan Menderes University, 09100 Aydın (Turkey)
2016-12-30
Highlights: • Buckled GeSe (b-GeSe) has a stable honeycomb structure. • b-GeSe is a semiconductor with a indirect band gap of 2.29 eV. • In low coverage, b-GeSe attains half metallicity through the adsorption of Si, Ge, P and Br. - Abstract: A recent study of Hu et al. [1] predicted that 2D single layer of asymmetric washboard germanium selenide is found to be stable and display semiconducting properties. Motivating from this study, we have shown that another phase, which is 2D buckled honeycomb germanium selenide, is also stable. This phase exhibits semiconducting behavior with a band gap of 2.29 eV. Furthermore, on the basis of the first principles, spin-polarized density functional calculations, we investigate the effect of selected adatoms adsorption on the b-GeSe single layer. The adatoms Se, Ge, S, Si, C, Br and P are chemisorbed with significant binding energy where this effects modify the electronic structure of the single layer buckled GeSe locally by tuning the band gap. Net integer magnetic moment can be achieved and b-GeSe attains half metallicity through the adsorption of Si, Ge, P and Br.
Snap-buckling in asymmetrically constrained elastic strips
Sano, Tomohiko G.; Wada, Hirofumi
2018-01-01
When a flat elastic strip is compressed along its axis, it is bent in one of two possible directions via spontaneous symmetry breaking, forming a cylindrical arc. This is a phenomenon well known as Euler buckling. When this cylindrical section is pushed in the other direction, the bending direction can suddenly reverse. This instability is called "snap-through buckling" and is one of the elementary shape transitions in a prestressed thin structure. Combining experiments and theory, we study snap-buckling of an elastic strip with one end hinged and the other end clamped. These asymmetric boundary constraints break the intrinsic symmetry of the strip, generating mechanical behaviors, including largely hysteretic but reproducible force responses and switchlike discontinuous shape changes. We establish the set of exact analytical solutions to fully explain all our major experimental and numerical findings. Asymmetric boundary conditions arise naturally in diverse situations when a thin object is in contact with a solid surface at one end. The introduction of asymmetry through boundary conditions yields new insight into complex and programmable functionalities in material and industrial design.
Current research on shear buckling and thermal loads with PASCO - Panel analysis and sizing code
Stroud, W. J.; Greene, W. H.; Anderson, M. S.
1984-01-01
The stiffened composite structural panel analysis and sizing code designated 'PASCO' encompasses both the generality required for the exploitation of composite materials' design flexibility and an accurate buckling analysis for the detection of complex buckling modes. PASCO can accordingly design for buckling, frequency, material strength, and panel stiffness requirements. Attention is given to an additional thermal loading design capability. Design studies illustrate the importance of the multiple load condition capability when thermal loads are present.
A Review of the Theory and Methods for Determining Dynamic Pulse Buckling of Cylindrical Shells
1989-09-01
allowed t lie shells to buckle, deform plastica iv and damip owi to a fiital deformed shape. The permanent peak deformations for a range of imnpulse...8217nonlinear dynamic buckling analysis is frequently beyond the current state of the art ’. Lindberg and Kennedy [26], investigate plastic flow buckling theory...The shadd regions of Figure B.1 art 71 regions of instability. The effect of damping on the system is to shift the regions of instability away from the
COMPPAP - COMPOSITE PLATE BUCKLING ANALYSIS PROGRAM (UNIX VERSION)
Smith, J. P.
1994-01-01
The Composite Plate Buckling Analysis Program (COMPPAP) was written to help engineers determine buckling loads of orthotropic (or isotropic) irregularly shaped plates without requiring hand calculations from design curves or extensive finite element modeling. COMPPAP is a one element finite element program that utilizes high-order displacement functions. The high order of the displacement functions enables the user to produce results more accurate than traditional h-finite elements. This program uses these high-order displacement functions to perform a plane stress analysis of a general plate followed by a buckling calculation based on the stresses found in the plane stress solution. The current version assumes a flat plate (constant thickness) subject to a constant edge load (normal or shear) on one or more edges. COMPPAP uses the power method to find the eigenvalues of the buckling problem. The power method provides an efficient solution when only one eigenvalue is desired. Once the eigenvalue is found, the eigenvector, which corresponds to the plate buckling mode shape, results as a by-product. A positive feature of the power method is that the dominant eigenvalue is the first found, which is this case is the plate buckling load. The reported eigenvalue expresses a load factor to induce plate buckling. COMPPAP is written in ANSI FORTRAN 77. Two machine versions are available from COSMIC: a PC version (MSC-22428), which is for IBM PC 386 series and higher computers and compatibles running MS-DOS; and a UNIX version (MSC-22286). The distribution medium for both machine versions includes source code for both single and double precision versions of COMPPAP. The PC version includes source code which has been optimized for implementation within DOS memory constraints as well as sample executables for both the single and double precision versions of COMPPAP. The double precision versions of COMPPAP have been successfully implemented on an IBM PC 386 compatible running
Local Cooling during Welding : Prediction and Control of Residual Stresses and Buckling Distortion
Van der Aa, E.M.
2007-01-01
One of the major problems during welding of thin plate structures is the occurrence of buckling distortion. This type of distortion is caused by the formation of compressive welding stresses; when these stresses exceed a certain critical stress level, the structure will buckle. Most methods for
a model for the determination of the critical buckling load of self ...
African Journals Online (AJOL)
HP
Most tall columns under axial load fail by buckling. Considering the widespread use of this type of structure and the critical role it plays in service delivery, its failure will result in possible loss of lives and property and disruption of services. It is therefore necessary to evolve alternative methods of determination of the buckling ...
Ultimate Strength of a Ship’s Hull Girder in Plastic and Buckling Modes.
1980-06-01
drawn for deep - web -frame plate panels, of low slenderness ratio, simple supported and edges kept straight. It should be noted, however, that the range...H.-G., "Notes on the Buckling and Post-buckling Behaviour of Deep Web Frames," J. Marine Tech., July 1972. V. 62 [34] Timoshenko, S., "Stability of
Computation Analysis of Buckling Loads of Thin-Walled Members with Open Sections
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Lihua Huang
2016-01-01
Full Text Available The computational methods for solving buckling loads of thin-walled members with open sections are not unique when different concerns are emphasized. In this paper, the buckling loads of thin-walled members in linear-elastic, geometrically nonlinear-elastic, and nonlinear-inelastic behaviors are investigated from the views of mathematical formulation, experiment, and numerical solution. The differential equations and their solutions of linear-elastic and geometrically nonlinear-elastic buckling of thin-walled members with various constraints are derived. Taking structural angle as an example, numerical analysis of elastic and inelastic buckling is carried out via ANSYS. Elastic analyses for linearized buckling and nonlinear buckling are realized using finite elements of beam and shell and are compared with the theoretical results. The effect of modeling of constraints on numerical results is studied when shell element is applied. The factors that influence the inelastic buckling load in numerical solution, such as modeling of constraint, loading pattern, adding rib, scale factor of initial defect, and yield strength of material, are studied. The noteworthy problems and their solutions in numerically buckling analysis of thin-walled member with open section are pointed out.
A global FE. Local analytical approach to modelling failure in localized buckles caused by crash
Dekker, R.; Walters, C.L.
2016-01-01
Localized buckles can occur in crashes when compressive stresses are dominant. However, due to their local appearance, they might be overlooked by a finite element analysis, meaning that local failure due to buckling will not be predicted. This could, for example, be catastrophic in the case of the
Micro-wrinkling and delamination-induced buckling of stretchable electronic structures
Energy Technology Data Exchange (ETDEWEB)
Oyewole, O. K. [Department of Theoretical and Applied Physics, African University of Science and Technology, Km 10, Airport Road, Galadimawa, Abuja, Federal Capital Territory (Nigeria); Department of Materials Science and Engineering, Kwara State University, Malete, P.M.B 1530, Ilorin, Kwara State (Nigeria); Yu, D. [Department of Mechanical and Aerospace Engineering, Princeton University, Olden Street, Princeton, New Jersey 08544 (United States); Princeton Institute of Science and Technology of Materials, Princeton University, 70 Prospect Street, Princeton, New Jersey 08544 (United States); Du, J. [Department of Mechanical and Aerospace Engineering, Princeton University, Olden Street, Princeton, New Jersey 08544 (United States); Princeton Institute of Science and Technology of Materials, Princeton University, 70 Prospect Street, Princeton, New Jersey 08544 (United States); Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, 137 Reber Building, University Park, Pennsylvania (United States); Asare, J.; Fashina, A. [Department of Theoretical and Applied Physics, African University of Science and Technology, Km 10, Airport Road, Galadimawa, Abuja, Federal Capital Territory (Nigeria); Oyewole, D. O. [Department of Materials Science and Engineering, African University of Science and Technology, Km 10, Airport Road, Galadimawa, Abuja, Federal Capital Territory (Nigeria); Physics Advanced Laboratory, Sheda Science and Technology Complex, P.M.B 186, Garki, Abuja, Federal Capital Territory (Nigeria); Anye, V. C. [Department of Materials Science and Engineering, African University of Science and Technology, Km 10, Airport Road, Galadimawa, Abuja, Federal Capital Territory (Nigeria); Zebaze Kana, M. G. [Department of Materials Science and Engineering, Kwara State University, Malete, P.M.B 1530, Ilorin, Kwara State (Nigeria); Physics Advanced Laboratory, Sheda Science and Technology Complex, P.M.B 186, Garki, Abuja, Federal Capital Territory (Nigeria); and others
2015-06-21
This paper presents the results of experimental and theoretical/computational micro-wrinkles and buckling on the surfaces of stretchable poly-dimethylsiloxane (PDMS) coated with nano-scale Gold (Au) layers. The wrinkles and buckles are formed by the unloading of pre-stretched PDMS/Au structure after the evaporation of nano-scale Au layers. They are then characterized using atomic force microscopy and scanning electron microscopy. The critical stresses required for wrinkling and buckling are analyzed using analytical models. The possible interfacial cracking that can occur along with film buckling is also studied using finite element simulations of the interfacial crack growth. The implications of the results are discussed for potential applications of micro-wrinkles and micro-buckles in stretchable electronic structures and biomedical devices.
Active buckling control of smart plate as diaphragm with PZT5 sensor/actuator patches
Viliani, N. S.; Pourrostami, H.; Mostafavi, S. M.; Hashemizadeh, F.; Safian, M. R.; Hashemi, M.
2014-12-01
In current study, buckling analyses of smart plate is presented. The various types of piezoelectric materials are under investigation for petrochemical industry and other applications. The PZT sensor output is used to determine the input to the PZT actuator using the feedback control algorithm for buckling control of FG plate. This study investigated the governing differential equations of motion of smart plate which includes FG plate as the membrane and PZT5 patches as actuator and sensor. The Fourier series method adopted to obtain the solution for the equation of motion. Also the effects of feedback gain and FGM volume fraction exponent on the critical buckling load for PZT-5A are studied. The potential application of current study can be found in optimal design of sensor's diaphragm. The variation of critical buckling load vs. feedback gain indicates that by increasing the feedback gain, the buckling load increases.
Buckling of a stiff thin film on an elastic graded compliant substrate.
Chen, Zhou; Chen, Weiqiu; Song, Jizhou
2017-12-01
The buckling of a stiff film on a compliant substrate has attracted much attention due to its wide applications such as thin-film metrology, surface patterning and stretchable electronics. An analytical model is established for the buckling of a stiff thin film on a semi-infinite elastic graded compliant substrate subjected to in-plane compression. The critical compressive strain and buckling wavelength for the sinusoidal mode are obtained analytically for the case with the substrate modulus decaying exponentially. The rigorous finite element analysis (FEA) is performed to validate the analytical model and investigate the postbuckling behaviour of the system. The critical buckling strain for the period-doubling mode is obtained numerically. The influences of various material parameters on the results are investigated. These results are helpful to provide physical insights on the buckling of elastic graded substrate-supported thin film.
Buckling and Vibration of Fiber Reinforced Composite Plates With Nanofiber Reinforced Matrices
Chamis, Christos C.; Murthy, Pappu L. N.
2011-01-01
Anisotropic composite plates were evaluated with nanofiber reinforced matrices (NFRM). The nanofiber reinforcement volumes ratio in the matrix was 0.01. The plate dimensions were 20 by 10 by 1.0 in. (508 by 254 by 25.4 mm). Seven different loading condition cases were evaluated for buckling: three for uniaxial loading, three for pairs of combined loading, and one with three combined loadings. The anisotropy arose from the unidirectional plates having been at 30 from the structural axis. The anisotropy had a full 6 by 6 rigidities matrix which were satisfied and solved by a Galerkin buckling algorithm. For vibration the same conditions were used with the applied cods about a small fraction of the buckling loads. The buckling and vibration results showed that the NFRM plates buckled at about twice those with conventional matrix.
Energy Technology Data Exchange (ETDEWEB)
Cho, Hee Keun [Andong National University, Andong (Korea, Republic of); Rowlands, Robert E. [University of Wisconsin-Madison, Madison (United States)
2015-09-15
To maximize buckling loads of composite laminates, optimization is carried out using a Genetic algorithm (GA) in conjunction with finite element analysis. A perforated laminated composite plate is used for buckling analysis. The geometry is discretized into solid three dimensional twenty node isoparametric layered composite elements developed for this study. Fiber orientations of each element and individual plies are controlled independently by the genetic algorithm, which is especially advantageous for complex problems including many design variables. This approach for composite buckling produces more enhanced results than conventional methods, such as changing the stacking sequence of various rectilinear orthotropic plies with different fiber orientations, different ply thicknesses or different local fiber densities. Additionally, it can be used in diverse areas from sensitive local buckling to global stability of structures. The genetic algorithm, finite element analysis and eigen buckling analysis are numerically combined into a composite optimization code, COMBO20. The successful performance of the proposed approach is demonstrated with an example.
Research on Annular Frictional Pressure Loss of Hydraulic-Fracturing in Buckling Coiled Tubing
Liu, Bin; Cai, Meng; Li, Junliang; Xu, Yongquan; Wang, Peng
2018-01-01
Compared with conventional hydraulic fracturing, coiled tubing (CT) annular delivery sand fracturing technology is a new method to enhance the recovery ratio of low permeability reservoir. Friction pressure loss through CT has been a concern in fracturing. The small diameter of CT limits the cross-sectional area open to flow, therefore, to meet large discharge capacity, annular delivery sand technology has been gradually developed in oilfield. Friction pressure is useful for determining the required pump horsepower and fracturing construction design programs. Coiled tubing can buckle when the axial compressive load acting on the tubing is greater than critical buckling load, then the geometry shape of annular will change. Annular friction pressure loss elevates dramatically with increasing of discharge capacity, especially eccentricity and CT buckling. Despite the frequency occurrence of CT buckling in oilfield operations, traditionally annular flow frictional pressure loss considered concentric and eccentric annuli, not discussing the effects of for discharge capacity and sand ratio varying degree of CT buckling. The measured data shows that the factors mentioned above cannot be ignored in the prediction of annular pressure loss. It is necessary to carry out analysis of annulus flow pressure drop loss in coiled tubing annular with the methods of theoretical analysis and numerical simulation. Coiled tubing buckling has great influence on pressure loss of fracturing fluid. Therefore, the correlations have been developed for turbulent flow of Newtonian fluids and Two-phase flow (sand-liquid), and that improve the friction pressure loss estimation in coiled tubing operations involving a considerable level of buckling. Quartz sand evidently increases pressure loss in buckling annular, rising as high as 40%-60% more than fresh water. Meanwhile, annulus flow wetted perimeter increases with decreasing helical buckling pitch of coiled tubing, therefore, the annulus flow
Buckling of Single-Crystal Silicon Nanolines under Indentation
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Min K. Kang
2008-01-01
Full Text Available Atomic force microscope-(AFM- based indentation tests were performed to examine mechanical properties of parallel single-crystal silicon nanolines (SiNLs of sub-100-nm line width, fabricated by a process combining electron-beam lithography and anisotropic wet etching. The SiNLs have straight and nearly atomically flat sidewalls, and the cross section is almost perfectly rectangular with uniform width and height along the longitudinal direction. The measured load-displacement curves from the indentation tests show an instability with large displacement bursts at a critical load ranging from 480 μN to 700 μN. This phenomenon is attributed to a transition of the buckling mode of the SiNLs under indentation. Using a set of finite element models with postbuckling analyses, we analyze the indentation-induced buckling modes and investigate the effects of tip location, contact friction, and substrate deformation on the critical load of mode transition. The results demonstrate a unique approach for the study of nanomaterials and patterned nanostructures via a combination of experiments and modeling.
Effects of state recovery on creep buckling under variable loading
Robinson, D. N.; Arnold, S. M.
1986-04-01
Structural alloys embody internal mechanisms that allow recovery of state with varying stress and elevated temperature, i.e., they can return to a softer state following periods of hardening. Such material behavior is known to strongly influence structural response under some important thermomechanical loadings, for example, that involving thermal ratchetting. The influence of dynamic and thermal recovery on the creep buckling of a column under variable loading is investigated. The column is taken as the idealized (Shanley) sandwich column. The constitutive model, unlike the commonly employed Norton creep model, incorporates a representation of both dynamic and thermal (state) recovery. The material parameters of the constitutive model are chosen to characterize Narloy Z, a representative copper alloy used in thrust nozzle liners of reusable rocket engines. Variable loading histories include rapid cyclic unloading/reloading sequences and intermittent reductions of load for extended periods of time; these are superimposed on a constant load. The calculated results show that state recovery significantly affects creep buckling under variable loading. Structural alloys embody internal mechanisms that allow recovery of state with varying stress and time.
Crown sealing and buckling instability during water entry of spheres
Marston, J. O.
2016-04-05
We present new observations from an experimental investigation of the classical problem of the crown splash and sealing phenomena observed during the impact of spheres onto quiescent liquid pools. In the experiments, a 6 m tall vacuum chamber was used to provide the required ambient conditions from atmospheric pressure down to of an atmosphere, whilst high-speed videography was exploited to focus primarily on the above-surface crown formation and ensuing dynamics, paying particular attention to the moments just prior to the surface seal. In doing so, we have observed a buckling-type azimuthal instability of the crown. This instability is characterised by vertical striations along the crown, between which thin films form that are more susceptible to the air flow and thus are drawn into the closing cavity, where they atomize to form a fine spray within the cavity. To elucidate to the primary mechanisms and forces at play, we varied the sphere diameter, liquid properties and ambient pressure. Furthermore, a comparison between the entry of room-temperature spheres, where the contact line pins around the equator, and Leidenfrost spheres (i.e. an immersed superheated sphere encompassed by a vapour layer), where there is no contact line, indicates that the buckling instability appears in all crown sealing events, but is intensified by the presence of a pinned contact line. © 2016 Cambridge University Press.
Film stresses and electrode buckling in organic solar cells
Brand, Vitali
2012-08-01
We investigate the film stresses that develop in the polymer films and metal electrodes of poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction (BHJ) organic solar cells. A compressive biaxial stress of ∼-36 MPa was measured in PEDOT:PSS while a tensile stress of ∼6 MPa was measured in the BHJ layer. We then analyze the effect of electrode deposition rate on the film stresses in the Al electrode. Compressive stresses of ∼-100 to -145 MPa in the Al electrode lead to a buckling instability resulting in undulating electrode surface topography. The BHJ layer was found to have the lowest cohesion (∼1.5-1.8 J/m 2) among the layers of the solar cell and dependent on the Al electrode deposition rate. The cohesive failure path in the BHJ layer exhibited the same periodicity and orientation of the Al electrode buckling topography. We discuss the implications of the film stresses on damage processes during device fabrication and operation. © 2012 Elsevier B.V. All rights reserved.
Buckling instability of a thin-layer rectilinear Couette flow
Slim, Anja; Mahadevan, L
2011-01-01
We analyse the buckling stability of a thin, viscous sheet when subject to simple shear, providing conditions for the onset of the dominant out-of-plane modes using two models: (i) an asymptotic theory for the dynamics of a viscous plate and (ii) the full Stokes equations. In either case, the plate is stabilised by a combination of viscous resistance, surface tension and buoyancy relative to an underlying denser fluid. In the limit of vanishing thickness, plates buckle at a shear rate $\\gamma/(\\mu d)$ independent of buoyancy, where 2d is the plate thickness, $\\gamma$ is the average surface tension between the upper and lower surfaces and $\\mu$ is the fluid viscosity. For thicker plates stabilised by an equal surface tension at the upper and lower surfaces, at and above onset, the most unstable mode has moderate wavelength, is stationary in the frame of the centre-line, spans the width of the plate with crests and troughs aligned at approximately $45^\\circ$ to the walls and closely resembles elastic shear mode...
Torsional Buckling and Writhing Dynamics of Elastic Cables and DNA
Energy Technology Data Exchange (ETDEWEB)
Goyal, S; Perkins, N C; Lee, C L
2003-02-14
Marine cables under low tension and torsion on the sea floor can undergo a dynamic buckling process during which torsional strain energy is converted to bending strain energy. The resulting three-dimensional cable geometries can be highly contorted and include loops and tangles. Similar geometries are known to exist for supercoiled DNA and these also arise from the conversion of torsional strain energy to bending strain energy or, kinematically, a conversion of twist to writhe. A dynamic form of Kirchhoff rod theory is presented herein that captures these nonlinear dynamic processes. The resulting theory is discretized using the generalized-method for finite differencing in both space and time. The important kinematics of cross-section rotation are described using an incremental rotation ''vector'' as opposed to traditional Euler angles or Euler parameters. Numerical solutions are presented for an example system of a cable subjected to increasing twist at one end. The solutions show the dynamic evolution of the cable from an initially straight element, through a buckled element in the approximate form of a helix, and through the dynamic collapse of this helix through a looped form.
Anatomical and Visual Outcomes of Three Different Scleral Buckling Techniques
Directory of Open Access Journals (Sweden)
Touka Banaee
2009-04-01
Full Text Available
PURPOSE: To compare the anatomical and visual outcomes of three different scleral buckling techniques and to explore the effect of cryotherapy and subretinal fluid drainage (SRFD on outcomes of surgery. METHODS: This retrospective study was performed on 111 eyes of 109 patients undergoing scleral buckling for rhegmatogenous retinal detachments (RRDs by a single surgeon. Pre-, intra- and postoperative data were retrieved from hospital records. RESULTS: Buckles were radial in 27 (24.3%, circumferential (segmental in 16 (14.4% and encircling in 68 (61.3% eyes. Anatomical and visual results were comparable with all three buckling techniques. Application of cryotherapy, the spot number, and SRFD did not affect anatomical and visual results. The only preoperative factor associated with poorer anatomical results was the presence of multiple retinal breaks (P=0.006. The following preoperative factors affected visual outcomes on univariate analysis: extent of retinal detachment (r=0.417, P=0.011 and relative afferent pupillary defect (r=0.423, P=0.02. Preoperative macular status (attached vs detached also had a significant effect on visual outcomes (P < 0.001. Based on multivariate analysis however, only preoperative macular status was significantly correlated with visual results (P=0.022. Silicone sponges placed for non
Directory of Open Access Journals (Sweden)
Kołakowski Zbigniew
2016-06-01
Full Text Available A review of papers that investigate the static and dynamic coupled buckling and post-buckling behaviour of thin-walled structures is carried out. The problem of static coupled buckling is sufficiently well-recognized. The analysis of dynamic interactive buckling is limited in practice to columns, single plates and shells. The applications of finite element method (FEM or/and analytical-numerical method (ANM to solve interaction buckling problems are on-going. In Poland, the team of scientists from the Department of Strength of Materials, Lodz University of Technology and co-workers developed the analytical-numerical method. This method allows to determine static buckling stresses, natural frequencies, coefficients of the equation describing the post-buckling equilibrium path and dynamic response of the plate structure subjected to compression load and/or bending moment. Using the dynamic buckling criteria, it is possible to determine the dynamic critical load. They presented a lot of interesting results for problems of the static and dynamic coupled buckling of thin-walled plate structures with complex shapes of cross-sections, including an interaction of component plates. The most important advantage of presented analytical-numerical method is that it enables to describe all buckling modes and the post-buckling behaviours of thin-walled columns made of different materials. Thin isotropic, orthotropic or laminate structures were considered.
Dynamic delamination buckling in composite laminates under impact loading: Computational simulation
Grady, Joseph E.; Chamis, Christos C.; Aiello, Robert A.
1987-01-01
A unique dynamic delamination buckling and delamination propagation analysis capability has been developed and incorporated into a finite element computer program. This capability consists of the following: (1) a modification of the direct time integration solution sequence which provides a new analysis algorithm that can be used to predict delamination buckling in a laminate subjected to dynamic loading, and (2) a new method of modeling the composite laminate using plate bending elements and multipoint constraints. This computer program is used to predict both impact induced buckling in composite laminates with initial delaminations and the strain energy release rate due to extension of the delamination. It is shown that delaminations near the outer surface of a laminate are susceptible to local buckling and buckling-induced delamination propagation when the laminate is subjected to transverse impact loading. The capability now exists to predict the time at which the onset of dynamic delamination buckling occurs, the dynamic buckling mode shape, and the dynamic delamination strain energy release rate.
Dynamic delamination buckling in composite laminates under impact loading - Computational simulation
Grady, Joseph E.; Chamis, Christos C.; Aiello, Robert A.
1989-01-01
A unique dynamic delamination buckling and delamination propagation analysis capability has been developed and incorporated into a finite element computer program. This capability consists of the following: (1) a modification of the direct time integration solution sequence which provides a new analysis algorithm that can be used to predict delamination buckling in a laminate subjected to dynamic loading, and (2) a new method of modeling the composite laminate using plate bending elements and multipoint constraints. This computer program is used to predict both impact induced buckling in composite laminates with initial delaminations and the strain energy release rate due to extension of the delamination. It is shown that delaminations near the outer surface of a laminate are susceptible to local buckling and buckling-induced delamination propagation when the laminate is subjected to transverse impact loading. The capability now exists to predict the time at which the onset of dynamic delamination buckling occurs, the dynamic buckling mode shape, and the dynamic delamination strain energy release rate.
Overall Buckling and Wringkling of Debonded Sandwich Beams: Finite Element and Experimental Results
Directory of Open Access Journals (Sweden)
Bambang K. Hadi
2006-05-01
Full Text Available Overall buckling and wrinkling of debonded sandwich beams under compressive loads were analyzed by both finite element and experimental methods. In the finite element method, a quarter and a half models of the specimens were analyzed. It shows that a quarter model is not adequate to analyze buckling of debonded sandwich beams, since it will disregard overall buckling mode that may occur in sandwich beams having compressive loads. At least a half model should be used to analyze buckling of sandwich beams. A finite element program UNA was used extensively to analyze the buckling loads. Experimental buckling of sandwich beams was carried out using a compression testing machine. Two LVDTs were used to measure deflections of the specimen during experimental loading. The loads were measured using load cells available in the machine. Specimens having core thickness of 45 and 75 mm were tested to represent overall and wrinkling modes respectively. The delamination lengths were 20, 60 and 80 mm, which represent 10, 30 and 40% of the beam length. The results show that the differences between experimental and finite element methods were less than 10%. Both overall buckling and wrinkling modes were shown in these specimens.
Monitoring the buckling threshold of drying colloidal droplets using water-ethanol mixtures.
Marty, G; Tsapis, N
2008-10-01
We visualize the drying of droplets of colloids suspended in a mixture of two miscible solvents, namely water and ethanol. After a period of isotropic shrinkage, droplets suddenly buckle like elastic shells. For a fixed colloid solid fraction, the buckling threshold evolves as a function of ethanol content, due to changes of the solvent mixture physical properties, such as viscosity and evaporation rate. A simplified model predicting the qualitative behavior of the buckling threshold as a function of the initial ethanol mass fraction has been developed that fits well experimental results.
Directory of Open Access Journals (Sweden)
Zoltán Juhász
2015-01-01
Full Text Available We analyse the buckling process of composite plates with through-the-width delamination and straight crack front applying uniaxial compression. We are focusing on the mixed mode buckling case, where the non-uniform distribution of the in-plane forces controls the occurence of the buckling of the delaminated layers. For the analysis, semi-discrete finite elements will be derived based on the Lèvy-type method. The method of harmonic balance is used for taking into account the force distribution that is generally non uniform in-plane.
Methods to Analyze Flexural Buckling of the Consequent Slabbed Rock Slope under Top Loading
Hongyan Liu; Guihe Wang; Feng Huang
2016-01-01
The consequent slabbed rock slope is prone to flexural buckling failure under its self-weight and top loading. However, nearly none of the existing studies consider the effect of the top loading on the slope flexural critical buckling height (CBH). Therefore, on the basis of Euler’s Method and the flexural buckling failure mode of the consequent slabbed rock slope, the calculation method of the CBH of the vertical slabbed rock slope under the self-weight is firstly proposed, and then it is ex...
Mehralian, Fahimeh; Tadi Beni, Yaghoub
2017-11-04
Molecular dynamics simulations are conducted to investigate the buckling characteristics of functionalized carbon nanotubes (f-CNTs) under axial compression at various temperatures. The influences of functionalization, content of functional groups, chirality and diameter, as well as temperature on buckling response of pristine and functionalized CNTs are investigated. It is found that the buckling capacity of CNTs deteriorates drastically by functionalization, though the increase in the content of functional groups slightly enhances their stability. Besides, the results show that temperature considerably contributes to the stability of nanotubes but interestingly it has the most pronounced impact on pristine CNTs than functionalized ones, as defective CNTs.
Analysis of the LOFT Modular Drag Disc Turbine Transducer (MDTT) spring for compressive buckling
Energy Technology Data Exchange (ETDEWEB)
Mosby, W.R.
1978-08-04
The LOFT Modular Drag Disc Turbine Transducer (MDTT) springs (for range 2, rhoV/sup 2/ = 4900 lbm/ft-sec/sup 2/) were analyzed to determine the static rhoV/sup 2/ load needed to cause a buckling failure. The static load needed to cause elastic buckling was found to be equivalent to a rhoV/sup 2/ value of 431,000 lbm/ft-sec/sup 2/ according to classical buckling theory, but could be as low as rhoV/sup 2/ = 100,000 lbm/ft-sec/sup 2/ due to uncertain end fixity and other spring imperfections.
Conditions for Symmetries in the Buckle Patterns of Laminated-Composite Plates
Nemeth, Michael P.
2012-01-01
Conditions for the existence of certain symmetries to exist in the buckle patterns of symmetrically laminated composite plates are presented. The plates considered have a general planform with cutouts, variable thickness and stiffnesses, and general support and loading conditions. The symmetry analysis is based on enforcing invariance of the corresponding eigenvalue problem for a group of coordinate transformations associated with buckle patterns commonly exhibited by symmetrically laminated plates. The buckle-pattern symmetries examined include a central point of inversion symmetry, one plane of reflective symmetry, and two planes of reflective symmetry.
Electrostatics-Driven Hierarchical Buckling of Charged Flexible Ribbons.
Yao, Zhenwei; Olvera de la Cruz, Monica
2016-04-08
We investigate the rich morphologies of an electrically charged flexible ribbon, which is a prototype for many beltlike structures in biology and nanomaterials. Long-range electrostatic repulsion is found to govern the hierarchical buckling of the ribbon from its initially flat shape to its undulated and out-of-plane twisted conformations. In this process, the screening length is the key controlling parameter, suggesting that a convenient way to manipulate the ribbon morphology is simply to change the salt concentration. We find that these shapes originate from the geometric effect of the electrostatic interaction, which fundamentally changes the metric over the ribbon surface. We also identify the basic modes by which the ribbon reshapes itself in order to lower the energy. The geometric effect of the physical interaction revealed in this Letter has implications for the shape design of extensive ribbonlike materials in nano- and biomaterials.
Buckling Behavior of Cold-Formed Studs with Thermal Perforations
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Garifullin Marsel
2016-01-01
Full Text Available Studies have shown that the optimal structural scheme for low-rise buildings that meets all regulatory requirements is a frame system. In this connection, thin-walled cold-formed steel (CFS profiles seem to be the best material for constructing light steel framed (LSF walls. The framework of LSF walls is usually constructed from CFS C-shaped profiles. To increase the thermal effectiveness of a wall, CFS profiles usually have thermal perforations and thus are called thermoprofiles. However, these openings have a negative impact on bearing capacity of profiles and require accurate evaluation. In this article a relatively new reticular-stretched thermoprofile with diamond-shaped openings is considered. The article deals with the buckling analysis of perforated CFS C-sections subjected to compression.
Middendorf, Jill M; Shortkroff, Sonya; Dugopolski, Caroline; Kennedy, Stephen; Siemiatkoski, Joseph; Bartell, Lena R; Cohen, Itai; Bonassar, Lawrence J
2017-09-14
Many studies have measured the global compressive properties of tissue engineered (TE) cartilage grown on porous scaffolds. Such scaffolds are known to exhibit strain softening due to local buckling under loading. As matrix is deposited onto these scaffolds, the global compressive properties increase. However the relationship between the amount and distribution of matrix in the scaffold and local buckling is unknown. To address this knowledge gap, we studied how local strain and construct buckling in human TE constructs changes over culture times and GAG content. Confocal elastography techniques and digital image correlation (DIC) were used to measure and record buckling modes and local strains. Receiver operating characteristic (ROC) curves were used to quantify construct buckling. The results from the ROC analysis were placed into Kaplan-Meier survival function curves to establish the probability that any point in a construct buckled. These analysis techniques revealed the presence of buckling at early time points, but bending at later time points. An inverse correlation was observed between the probability of buckling and the total GAG content of each construct. This data suggests that increased GAG content prevents the onset of construct buckling and improves the microscale compressive tissue properties. This increase in GAG deposition leads to enhanced global compressive properties by prevention of microscale buckling. Copyright © 2017 Elsevier Ltd. All rights reserved.
Ko, William L.; Jackson, Raymond H.
1993-01-01
Combined inplane compressive and shear buckling analysis was conducted on flat rectangular sandwich panels using the Raleigh-Ritz minimum energy method with a consideration of transverse shear effect of the sandwich core. The sandwich panels were fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that slightly slender (along unidirectional compressive loading axis) rectangular sandwich panels have the most desirable stiffness-to-weight ratios for aerospace structural applications; the degradation of buckling strength of sandwich panels with rising temperature is faster in shear than in compression; and the fiber orientation of the face sheets for optimum combined-load buckling strength of sandwich panels is a strong function of both loading condition and panel aspect ratio. Under the same specific weight and panel aspect ratio, a sandwich panel with metal matrix composite face sheets has much higher buckling strength than one having monolithic face sheets.
Detailed modelling of delamination buckling of thin films under global tension.
Toth, F; Rammerstorfer, F G; Cordill, M J; Fischer, F D
2013-04-01
Tensile specimens of metal films on compliant substrates are widely used for determining interfacial properties. These properties are identified by the comparison of experimentally observed delamination buckling and a mathematical model which contains the interface properties as parameters. The current two-dimensional models for delamination buckling are not able to capture the complex stress and deformation states arising in the considered uniaxial tension test in a satisfying way. Therefore, three-dimensional models are developed in a multi-scale approach. It is shown that, for the considered uniaxial tension test, the buckling and associated delamination process are initiated and driven by interfacial shear in addition to compressive stresses in the film. The proposed model is able to reproduce all important experimentally observed phenomena, like cracking stress of the film, film strip curvature and formation of triangular buckles. Combined with experimental data, the developed computational model is found to be effective in determining interface strength properties.
Effects of Shell-Buckling Knockdown Factors in Large Cylindrical Shells
Hrinda, Glenn A.
2012-01-01
Shell-buckling knockdown factors (SBKF) have been used in large cylindrical shell structures to account for uncertainty in buckling loads. As the diameter of the cylinder increases, achieving the manufacturing tolerances becomes increasingly more difficult. Knockdown factors account for manufacturing imperfections in the shell geometry by decreasing the allowable buckling load of the cylinder. In this paper, large-diameter (33 ft) cylinders are investigated by using various SBKF's. An investigation that is based on finite-element analysis (FEA) is used to develop design sensitivity relationships. Different manufacturing imperfections are modeled into a perfect cylinder to investigate the effects of these imperfections on buckling. The analysis results may be applicable to large- diameter rockets, cylindrical tower structures, bulk storage tanks, and silos.
Finite element based investigation of buckling and vibration behaviour of thin walled box beams
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Ramkumar K.
2013-12-01
Full Text Available Thin-walled box type conventional and composite structures are having wide applications for building the structural system which are used in advanced ships, aerospace, civil, construction equipment and etc. Often these structures are subjected to vibration and buckling due to the environmental effect such as mechanical, thermal, electrical, magnetic, and acoustic or a combination of these. Also dampingmaterial and structural stiffness plays an important role for the improvement of vibration, noise control, fatigue and bulking resistance of these structures. So it is important to know the dynamic and buckling characteristics of these structures. Pre-stress in a structure affects the stiffness, which modifies the dynamic and stability characteristics of the structure. So it is also important to know the influence of pre-stress on the vibration and buckling character. In this paper, buckling and dynamic characteristics of the thin-walled box type structures are analyzed using finite element software ANSYS.
De'nan, Fatimah; Hassan, Md Hadli Abu; Rahim, Mohd Asri Ab
2017-10-01
This paper presents a study on the ultimate load behaviour of corrugated girder webs under shear loading following nonlinear finite element analysis. Sensitivity analyses conducted herein are numbers of corrugation wave, elements density, initial imperfection and material nonlinearities. This paper aimed to investigate the influence of this sensitivity to the ultimate shear load, buckling and post-buckling behaviours of the corrugated web girder under shear loading condition. Two web thicknesses have been considered in the study, while flanges were designed to be strong enough to ensure the shear governed. The corrugated profiled geometry remained constant for all models. The ultimate shear loads were reported and compared with the existing theoretical design. Based on the numerical results, this sensitivity analysis does not have a major effect on ultimate shear load and post-buckling behaviours. However, when the girder is controlled by elastic buckling, the shear resistance is higher compared to the sear calculated according to the existing theoretical design.
Axial buckling scrutiny of doubly orthogonal slender nanotubes via nonlocal continuum theory
Energy Technology Data Exchange (ETDEWEB)
Kiani, Keivan [K.N. Toosi University of Technolog, Tehran (Iran, Islamic Republic of)
2015-10-15
Using nonlocal Euler-Bernoulli beam theory, buckling behavior of elastically embedded Doubly orthogonal single-walled carbon nanotubes (DOSWCNTs) is studied. The nonlocal governing equations are obtained. In fact, these are coupled fourth-order integroordinary differential equations which are very difficult to be solved explicitly. As an alternative solution, Galerkin approach in conjunction with assumed mode method is employed, and the axial compressive buckling load of the nanosystem is evaluated. For DOSWCNTs with simply supported tubes, the influences of the slenderness ratio, aspect ratio, intertube free space, small-scale parameter, and properties of the surrounding elastic matrix on the axial buckling load of the nanosystem are addressed. The proposed model could be considered as a pivotal step towards better understanding the buckling behavior of more complex nanosystems such as doubly orthogonal membranes or even jungles of carbon nanotubes.
Application of Nonlocal Elasticity Shell Model for Axial Buckling of Single-Walled Carbon Nanotubes
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Farzad Khademolhosseini
2009-10-01
Full Text Available Recently, nano devices have been developed which use Carbon Nanotubes (CNTs as structural elements. To define the range of applicability of CNTs in such devices, it is important to investigate failure modes such as the axial buckling limit. Classical continuum models are inaccurate as they are unable to account for the size-effects in such devices. In this work, a modified nonlocal continuum shell model for the axial buckling of CNTs is proposed and compared with a nonlocal model for torsional buckling. This is done through modifying classical continuum models by incorporating basic concepts from nonlocal elasticity. Furthermore, molecular dynamics (MD simulations are performed on a range of nanotubes with different diameters. Compared to classical models, the modified nonlocal models provide a much better fit to MD simulation results. Using MD simulation results for axial buckling, values of the nonlocal constant and shell thickness are calculated.
On modelling of lateral buckling failure in flexible pipe tensile armour layers
DEFF Research Database (Denmark)
Østergaard, Niels Højen; Lyckegaard, Anders; Andreasen, Jens H.
2012-01-01
In the present paper, a mathematical model which is capable of representing the physics of lateral buckling failure in the tensile armour layers of flexible pipes is introduced. Flexible pipes are unbounded composite steel–polymer structures, which are known to be prone to lateral wire buckling...... when exposed to repeated bending cycles and longitudinal compression, which mainly occurs during pipe laying in ultra-deep waters. On the basis of multiple single wire analyses, the mechanical behaviour of both layers of tensile armour wires can be determined. Since failure in one layer destabilises...... the torsional equilibrium which is usually maintained between the layers, lateral wire buckling is often associated with a severe pipe twist. This behaviour is discussed and modelled. Results are compared to a pipe model, in which failure is assumed not to cause twist. The buckling modes of the tensile armour...
Sasaoka, Ryu; Azegami, Hideyuki; Murachi, Shunji; Kitoh, Junzoh; Ishida, Yoshito; Kawakami, Noriaki; Makino, Mitsunori; Matsuyama, Yukihiro
A hypothesis that idiopathic scoliosis is a buckling phenomenon of the fourth or sixth mode, which is the second or third lateral bending mode, induced by the growth of vertebral bodies was presented in a previous paper by the authors using numerical simulations with a finite-element model of the spine. This paper presents experimental proof of the buckling phenomenon using mechanical spine models constructed with the geometrical data of the finite-element model used in a previous work. Using three spine mechanical models with different materials at intervertebral joints, the change in the natural vibration eigenvalue of the second lateral bending mode with the growth of vertebral bodies was measured by experimental modal analysis. From the result, it was observed that natural vibration eigenvalue decreased with the growth of vertebral bodies. Since the increase in primary factor inducing the buckling phenomenon decreases natural vibration eigenvalue, the obtained result confirms the buckling hypothesis.
Alternative Shape of Suction Caisson to Reduce Risk of Buckling under high Pressure
DEFF Research Database (Denmark)
Madsen, Søren; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo
2013-01-01
Using large suction caissons for offshore wind turbines is an upcoming technology also referred to as bucket foundations. During operation the bucket foundation is loaded by a large overturning moment from the wind turbine and the wave loads. However, during installation the bucket is loaded...... by uniform external pressure and vertical forces. The bucket foundation does not require heavy installation equipment, but since it is constructed as a thin steel shell structure, instability, in the form of buckling, becomes a crucial issue during installation. Typically, the bucket foundation is a large...... cylindrical monopod foundation made of steel. In this paper, an alternative design/shape of the suction caisson, having a smaller risk of buckling under high pressure is presented. The risk of structural buckling is addressed using numerical methods to determine the buckling pressures of the re-designed...
On modelling of lateral buckling failure in flexible pipe tensile armour layers
DEFF Research Database (Denmark)
Østergaard, Niels Højen; Lyckegaard, Anders; Andreasen, Jens H.
2012-01-01
the torsional equilibrium which is usually maintained between the layers, lateral wire buckling is often associated with a severe pipe twist. This behaviour is discussed and modelled. Results are compared to a pipe model, in which failure is assumed not to cause twist. The buckling modes of the tensile armour......In the present paper, a mathematical model which is capable of representing the physics of lateral buckling failure in the tensile armour layers of flexible pipes is introduced. Flexible pipes are unbounded composite steel–polymer structures, which are known to be prone to lateral wire buckling...... when exposed to repeated bending cycles and longitudinal compression, which mainly occurs during pipe laying in ultra-deep waters. On the basis of multiple single wire analyses, the mechanical behaviour of both layers of tensile armour wires can be determined. Since failure in one layer destabilises...
How Does A Porous Shell Collapse? Delayed Buckling And Guided Folding Of Inhomogeneous Capsules
Datta, Sujit S.; Kim, Shin-Hyun; Paulose, Jayson; Abbaspourrad, Alireza; Nelson, David R.; Weitz, David A
2012-01-01
Colloidal capsules can sustain an external osmotic pressure; however, for a sufficiently large pressure, they will ultimately buckle. This process can be strongly influenced by structural inhomogeneities in the capsule shells. We explore how the time delay before the onset of buckling decreases as the shells are made more inhomogeneous; this behavior can be quantitatively understood by coupling shell theory with Darcy's law. In addition, we show that the shell inhomogeneity can dramatically c...
Effect of Geometrical Imperfection on Buckling Failure of ITER VVPSS Tank
Jha, Saroj Kumar; Gupta, Girish Kumar; Pandey, Manish Kumar; Bhattacharya, Avik; Jogi, Gaurav; Bhardwaj, Anil Kumar
2017-04-01
The ‘Vacuum Vessel Pressure Suppression System’ (VVPSS) is part of ITER machine, which is designed to protect the ITER Vacuum Vessel and its connected systems, from an over-pressure situation. It is comprised of a partially evacuated tank of stainless steel approximately 46 m long and 6 m in diameter and thickness 30 mm. It is to hold approximately 675 tonnes of water at room temperature to condense the steam resulting from the adverse water leakage into the Vacuum Vessel chamber. For any vacuum vessel, geometrical imperfection has significant effect on buckling failure and structural integrity. Major geometrical imperfection in VVPSS tank depends on form tolerances. To study the effect of geometrical imperfection on buckling failure of VVPSS tank, finite element analysis (FEA) has been performed in line with ASME section VIII division 2 part 5 [1], ‘design by analysis method’. Linear buckling analysis has been performed to get the buckled shape and displacement. Geometrical imperfection due to form tolerance is incorporated in FEA model of VVPSS tank by scaling the resulted buckled shape by a factor ‘60’. This buckled shape model is used as input geometry for plastic collapse and buckling failure assessment. Plastic collapse and buckling failure of VVPSS tank has been assessed by using the elastic-plastic analysis method. This analysis has been performed for different values of form tolerance. The results of analysis show that displacement and load proportionality factor (LPF) vary inversely with form tolerance. For higher values of form tolerance LPF reduces significantly with high values of displacement.
The Combinations of Thermal and Load Stresses for the Onset of Permanent Buckling in Plates
Zender, George W; Pride, Richard A
1957-01-01
A simple and practical method for evaluating the onset of permanent buckling in plates in the presence of combined thermal and compressive load stresses is outlined. A particular application of the method shows reasonable agreement with tests of 17-7 PH stainless-steel square tubes. The results indicate that the compressive load stress which the plate can support at the onset of permanent buckling is substantially reduced as the temperature difference of the plate and adjoining members increases.
Housner, J. M.; Stein, M.
1975-01-01
A computer program is presented which was developed for the combined compression and shear of stiffened variable thickness orthotropic composite panels on discrete springs: boundary conditions are general and include elastic boundary restraints. Buckling solutions are obtained by using a newly developed trigonometric finite difference procedure which improves the solution convergence rate over conventional finite difference methods. The classical general shear buckling results which exist only for simply supported panels over a limited range of orthotropic properties, were extended to the complete range of these properties for simply supported panels and, in addition, to the complete range of orthotropic properties for clamped panels. The program was also applied to parametric studies which examine the effect of filament orientation upon the buckling of graphite-epoxy panels. These studies included an examination of the filament orientations which yield maximum shear or compressive buckling strength for panels having all four edges simply supported or clamped over a wide range of aspect ratios. Panels with such orientations had higher buckling loads than comparable, equal weight, thin skinned aluminum panels. Also included among the parameter studies were examinations of combined axial compression and shear buckling and examinations of panels with rotational elastic edge restraints.
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Caiqi Zhao
2016-06-01
Full Text Available To solve the problem of critical buckling in the structural analysis and design of the new long-span hollow core roof architecture proposed in this paper (referred to as a “honeycomb panel structural system” (HSSS, lateral compression tests and finite element analyses were employed in this study to examine the lateral compressive buckling performance of this new type of honeycomb panel with different length-to-thickness ratios. The results led to two main conclusions: (1 Under the experimental conditions that were used, honeycomb panels with the same planar dimensions but different thicknesses had the same compressive stiffness immediately before buckling, while the lateral compressive buckling load-bearing capacity initially increased rapidly with an increasing honeycomb core thickness and then approached the same limiting value; (2 The compressive stiffnesses of test pieces with the same thickness but different lengths were different, while the maximum lateral compressive buckling loads were very similar. Overall instability failure is prone to occur in long and flexible honeycomb panels. In addition, the errors between the lateral compressive buckling loads from the experiment and the finite element simulations are within 6%, which demonstrates the effectiveness of the nonlinear finite element analysis and provides a theoretical basis for future analysis and design for this new type of spatial structure.
Buckling of imperfect, anisotropic, ring-stiffened cylinders under combined loads
Ley, Robert P.; Johnson, Eric R.; Guerdal, Zafer
1994-01-01
The objective of this study is to develop an anlysis to predict buckling loads of ring-stiffened anisotropic cylinders subject to axial compression, torsion, and internal pressure. This structure is modeled as a branched shell. A nonlinear axisymmetric prebuckling equilibrium state is assumed which is amenable to an exact solution within each branch. Axisymmetric geometric imperfections are included. Buckling displacements are represented by a Fourier series in the circumferential coordination and the finite-element method in the axial coordinate. Application of the Trefftz criterion to the second variation of the total potential energy leads to a nonlinear eigenvalue problem for the buckling load and mode. Results are presented for both unstiffened and ring-stiffened cylinders in the form of buckling interaction diagrams. Imperfections can cause an unexpected buckling mode in the ring web which would not occur for the perfect structure, and pressurization diminishes the benefit of adding rings to the unstiffened shell to increase the buckling load. The implementation of the analysis methodology into a structural sizing algorithm is discussed.
Buckling Design and Imperfection Sensitivity of Sandwich Composite Launch-Vehicle Shell Structures
Schultz, Marc R.; Sleight, David W.; Myers, David E.; Waters, W. Allen, Jr.; Chunchu, Prasad B.; Lovejoy, Andrew W.; Hilburger, Mark W.
2016-01-01
Composite materials are increasingly being considered and used for launch-vehicle structures. For shell structures, such as interstages, skirts, and shrouds, honeycomb-core sandwich composites are often selected for their structural efficiency. Therefore, it is becoming increasingly important to understand the structural response, including buckling, of sandwich composite shell structures. Additionally, small geometric imperfections can significantly influence the buckling response, including considerably reducing the buckling load, of shell structures. Thus, both the response of the theoretically perfect structure and the buckling imperfection sensitivity must be considered during the design of such structures. To address the latter, empirically derived design factors, called buckling knockdown factors (KDFs), were developed by NASA in the 1960s to account for this buckling imperfection sensitivity during design. However, most of the test-article designs used in the development of these recommendations are not relevant to modern launch-vehicle constructions and material systems, and in particular, no composite test articles were considered. Herein, a two-part study on composite sandwich shells to (1) examine the relationship between the buckling knockdown factor and the areal mass of optimized designs, and (2) to interrogate the imperfection sensitivity of those optimized designs is presented. Four structures from recent NASA launch-vehicle development activities are considered. First, designs optimized for both strength and stability were generated for each of these structures using design optimization software and a range of buckling knockdown factors; it was found that the designed areal masses varied by between 6.1% and 19.6% over knockdown factors ranging from 0.6 to 0.9. Next, the buckling imperfection sensitivity of the optimized designs is explored using nonlinear finite-element analysis and the as-measured shape of a large-scale composite cylindrical
Imperfection sensitivity of pressured buckling of biopolymer spherical shells.
Zhang, Lei; Ru, C Q
2016-06-01
Imperfection sensitivity is essential for mechanical behavior of biopolymer shells [such as ultrasound contrast agents (UCAs) and spherical viruses] characterized by high geometric heterogeneity. In this work, an imperfection sensitivity analysis is conducted based on a refined shell model recently developed for spherical biopolymer shells of high structural heterogeneity and thickness nonuniformity. The influence of related parameters (including the ratio of radius to average shell thickness, the ratio of transverse shear modulus to in-plane shear modulus, and the ratio of effective bending thickness to average shell thickness) on imperfection sensitivity is examined for pressured buckling. Our results show that the ratio of effective bending thickness to average shell thickness has a major effect on the imperfection sensitivity, while the effect of the ratio of transverse shear modulus to in-plane shear modulus is usually negligible. For example, with physically realistic parameters for typical imperfect spherical biopolymer shells, the present model predicts that actual maximum external pressure could be reduced to as low as 60% of that of a perfect UCA spherical shell or 55%-65% of that of a perfect spherical virus shell, respectively. The moderate imperfection sensitivity of spherical biopolymer shells with physically realistic imperfection is largely attributed to the fact that biopolymer shells are relatively thicker (defined by smaller radius-to-thickness ratio) and therefore practically realistic imperfection amplitude normalized by thickness is very small as compared to that of classical elastic thin shells which have much larger radius-to-thickness ratio.
Buckling and vibration analysis of laminated panels using VICONOPT
Kennedy, David; Williams, Fred W.; Anderson, Melvin S.
1994-01-01
The analysis aspects of the 23,000-line FORTRAN program VIPASA with constraints and optimization (VICONOPT) are described. Overall stiffness matrices assembled from the earlier exact vibration and instability of plate assemblies including shear and anisotropy (VIPASA) flat plate stiffnesses are optionally coupled by Langrangian multipliers to find critical buckling loads, or natural frequencies of undamped vibration, of prismatic assemblies of anisotropic flat plates with arbitrarily located point supports or simple transverse supporting frames. The longitudunal continuity of typical wing and fuselage panels is closely approximated because the solutions are for the infinitely long structure obtained by repeating a bay and its supports longitudinally. Any longitudinally invariant in-plane plate stresses are permitted, and very rapid solutions are guaranteed by numerous refinements, including multilevel substructuring and a method for repetitive cross sections that is exact for regular polygons used to represent cylinders. Modal displacements and stresses in or between plies of laminated plates are calculated and plotted, with values being recovered at all nodes of substructures. Comparison with usual approximate finite-element methods confirms that, for comparably converged solutions, VICONOPT is typically between 100 and 10(exp 4) times faster.
Scleral Buckling for Rhegmatogenous Retinal Detachment Associated with Pars Planitis.
Kim, Yong-Kyu; Yoon, Wontae; Ahn, Jae Kyoun; Park, Sung Pyo
2016-01-01
Purpose. To evaluate the surgical outcome of scleral buckling (SB) in rhegmatogenous retinal detachment (RRD) patients associated with pars planitis. Methods. Retrospective review of RRD patients (32 eyes of pars planitis RRD and 180 eyes of primary RRD) who underwent SB. We compared primary and final anatomical success rates and visual outcomes between two groups. Results. Primary and final anatomical success were achieved in 25 (78.1%) and 31 (96.8%) eyes in the pars planitis RRD group and in 167 eyes (92.7%) and 176 eyes (97.7%) in primary RRD group, respectively. Both groups showed significant visual improvement (p Pars planitis RRD group was associated with higher rate of postoperative proliferative vitreoretinopathy (PVR) development (12.5% versus 2.8%, p = 0.031). Pars planitis and high myopia were significant preoperative risk factors and pseudophakia was borderline risk for primary anatomical failure after adjusting for various clinical factors. Conclusions. Pars planitis associated RRD showed inferior primary anatomical outcome after SB due to postoperative PVR development. However, final anatomical and visual outcomes were favorable. RRD cases associated with pars planitis, high myopia, and pseudophakia might benefit from different surgical approaches, such as combined vitrectomy and SB.
Buckling of Flat Thin Plates under Combined Loading
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Ion DIMA
2015-03-01
Full Text Available This article aims to provide a quick methodology to determine the critical values of the forces applied to the central plane of a flat isotropic plate at which a change to the stable configuration of equilibrium occurs. Considering the variety of shapes, boundary conditions and loading combinations, the article does not intend to make an exhaustive presentation of the plate buckling. As an alternative, there will be presented only the most used configurations such as: rectangular flat thin plates, boundary conditions with simply supported (hinged or clamped (fixed edges, combined loadings with single compression or single shear or combination between them, compression and shear, with or without transverse loading, encountered at wings and control surfaces shell of fin and rudder or stabilizer and elevator. The reserve factor and the critical stresses will be calculated using comparatively two methods, namely the methodology proposed by the present article and ASSIST 6.6.2.0 – AIRBUS France software, a dedicated software to local calculations, for a simply supported plate under combined loading, compression on the both sides and shear.
Thermal Behavior of Cylindrical Buckling Restrained Braces at Elevated Temperatures
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Elnaz Talebi
2014-01-01
Full Text Available The primary focus of this investigation was to analyze sequentially coupled nonlinear thermal stress, using a three-dimensional model. It was meant to shed light on the behavior of Buckling Restraint Brace (BRB elements with circular cross section, at elevated temperature. Such bracing systems were comprised of a cylindrical steel core encased in a strong concrete-filled steel hollow casing. A debonding agent was rubbed on the core’s surface to avoid shear stress transition to the restraining system. The numerical model was verified by the analytical solutions developed by the other researchers. Performance of BRB system under seismic loading at ambient temperature has been well documented. However, its performance in case of fire has yet to be explored. This study showed that the failure of brace may be attributed to material strength reduction and high compressive forces, both due to temperature rise. Furthermore, limiting temperatures in the linear behavior of steel casing and concrete in BRB element for both numerical and analytical simulations were about 196°C and 225°C, respectively. Finally it is concluded that the performance of BRB at elevated temperatures was the same as that seen at room temperature; that is, the steel core yields prior to the restraining system.
Helical instability in film blowing process: Analogy to buckling instability
Lee, Joo Sung; Kwon, Ilyoung; Jung, Hyun Wook; Hyun, Jae Chun
2017-12-01
The film blowing process is one of the most important polymer processing operations, widely used for producing bi-axially oriented film products in a single-step process. Among the instabilities observed in this film blowing process, i.e., draw resonance and helical motion occurring on the inflated film bubble, the helical instability is a unique phenomenon portraying the snake-like undulation motion of the bubble, having the period on the order of few seconds. This helical instability in the film blowing process is commonly found at the process conditions of a high blow-up ratio with too low a freezeline position and/or too high extrusion temperature. In this study, employing an analogy to the buckling instability for falling viscous threads, the compressive force caused by the pressure difference between inside and outside of the film bubble is introduced into the simulation model along with the scaling law derived from the force balance between viscous force and centripetal force of the film bubble. The simulation using this model reveals a close agreement with the experimental results of the film blowing process of polyethylene polymers such as low density polyethylene and linear low density polyethylene.
Scleral Buckling for Rhegmatogenous Retinal Detachment Associated with Pars Planitis
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Yong-Kyu Kim
2016-01-01
Full Text Available Purpose. To evaluate the surgical outcome of scleral buckling (SB in rhegmatogenous retinal detachment (RRD patients associated with pars planitis. Methods. Retrospective review of RRD patients (32 eyes of pars planitis RRD and 180 eyes of primary RRD who underwent SB. We compared primary and final anatomical success rates and visual outcomes between two groups. Results. Primary and final anatomical success were achieved in 25 (78.1% and 31 (96.8% eyes in the pars planitis RRD group and in 167 eyes (92.7% and 176 eyes (97.7% in primary RRD group, respectively. Both groups showed significant visual improvement (p<0.001 and there were no significant differences in final visual acuity. Pars planitis RRD group was associated with higher rate of postoperative proliferative vitreoretinopathy (PVR development (12.5% versus 2.8%, p=0.031. Pars planitis and high myopia were significant preoperative risk factors and pseudophakia was borderline risk for primary anatomical failure after adjusting for various clinical factors. Conclusions. Pars planitis associated RRD showed inferior primary anatomical outcome after SB due to postoperative PVR development. However, final anatomical and visual outcomes were favorable. RRD cases associated with pars planitis, high myopia, and pseudophakia might benefit from different surgical approaches, such as combined vitrectomy and SB.
The buckling instability of aggregating red blood cells.
Flormann, Daniel; Aouane, Othmane; Kaestner, Lars; Ruloff, Christian; Misbah, Chaouqi; Podgorski, Thomas; Wagner, Christian
2017-08-11
Plasma proteins such as fibrinogen induce the aggregation of red blood cells (RBC) into rouleaux, which are responsible for the pronounced shear thinning behavior of blood, control the erythrocyte sedimentation rate (ESR) - a common hematological test - and are involved in many situations of physiological relevance such as structuration of blood in the microcirculation or clot formation in pathological situations. Confocal microscopy is used to characterize the shape of RBCs within rouleaux at equilibrium as a function of macromolecular concentration, revealing the diversity of contact zone morphology. Three different configurations that have only been partly predicted before are identified, namely parachute, male-female and sigmoid shapes, and quantitatively recovered by numerical simulations. A detailed experimental and theoretical analysis of clusters of two cells shows that the deformation increases nonlinearly with the interaction energy. Models indicate a forward bifurcation in which the contacting membrane undergoes a buckling instability from a flat to a deformed contact zone at a critical value of the interaction energy. These results are not only relevant for the understanding of the morphology and stability of RBC aggregates, but also for a whole class of interacting soft deformable objects such as vesicles, capsules or cells in tissues.
Buckling instabilities in patterned, poly(N-isopropylacrylamide) microgels
Toomey, Ryan; Dupont, Samuel; Cates, Ryan
2010-03-01
Stimuli-sensitive hydrogels facilitate reconfigurable microstructures with response integrated at the material level. Response is engendered by a competing mechanism: the elasticity of the network counterbalances expansion by the solvent. If the strength of expansion can be controlled by an environmental cue, the hydrogel can be adjusted in situ. The equilibrium state occurs when the osmotic stress exerted by the solvent in the gel equals the osmotic pressure of the solvent outside the gel. For a free structure, the equilibrium state corresponds to homogenous swelling. If a free surface of the gel is mechanically constrained, however, the dimensions available for the relief of the osmotic stress are reduced, resulting in non-uniform or inhomogeneous swelling. In this study, we demonstrate how mechanical constraints impose differential gel swelling, leading to complex three-dimensional structures that arise from two-dimensional poly(N-isopropylacrylamide) microstructures. Depending on the initial geometry of the constrained gel, three general modes of swelling-induced deformation can be observed: lateral differential swelling, bulk sinusoidal buckling, and surface wrinkling. Through confocal microscopy and 3D image rendering, the mechanics of swelling has been evaluated and compared to linear elastic theory.
Britt, V. O.
1993-01-01
An approximate analysis for buckling of biaxial- and shear-loaded anisotropic panels with centrally located elliptical cutouts is presented in the present paper. The analysis is composed of two parts, a prebuckling analysis and a buckling analysis. The prebuckling solution is determined using Lekhnitskii's complex variable equations of plane elastostatics combined with a Laurent series approximation and a boundary collocation method. The buckling solution is obtained using the principle of minimum potential energy. A by-product of the minimum potential energy equation is an integral equation which is solved using Gaussian quadrature. Comparisons with documented experimental results and finite element analyses indicate that the approximate analysis accurately predicts the buckling loads of square biaxial- and shear-loaded panels having elliptical cutouts with major axes up to sixty percent of the panel width. Results of a parametric study are presented for shear- and compression-loaded rectangular anisotropic panels with elliptical cutouts. The effects of panel aspect ratio, cutout shape, cutout size, cutout orientation, laminate anisotropy, and combined loading on the buckling load are examined.
Design criteria for bi-stable behavior in a buckled multi-layered MEMS bridge
Michael, Aron; Kwok, Chee Yee
2006-10-01
In this paper, the bi-stability of a buckled multi-layered micro-bridge with elastically constrained boundary conditions is studied theoretically and experimentally. The residual moment due to non-symmetric distribution of residual stress in the layers of the micro-bridge is taken into consideration. The buckled shape model, which characterizes the initial buckled deflection, is employed in this study. A systematic method of designing bi-stable buckled micro-bridges has been developed and applied to multi-layered structures. The method is tested against ANSYS simulation and shown to be in excellent agreement. Two multi-layer micro-bridges have been fabricated: (i) 2.5 µm thick low stress SiO2/1 µm thick high compressive stress SiO2/2 µm thick SCS Si; (ii) 1 µm thick high compressive stress SiO2/2 µm thick SCS Si. The fabricated bridges are tested for bi-stability by thermal actuation and the results agree well with the analysis. The intrinsic bi-stable nature of a buckled micro-bridge can only be guaranteed as long as the residual moment is within a certain threshold value.
What happens between pure hydraulic and buckling mechanisms of blowout fractures?
Nagasao, Tomohisa; Miyamoto, Junpei; Shimizu, Yusuke; Jiang, Hua; Nakajima, Tatsuo
2010-06-01
The present study aims to evaluate how the ratio of the hydraulic and buckling mechanisms affects blowout fracture patterns, when these two mechanisms work simultaneously. Three-dimensional computer-aided-design (CAD)models were generated simulating ten skulls. To simulate impact, 1.2J was applied on the orbital region of these models in four patterns. Pattern 1: All the energy works to cause the hydraulic effect. Pattern 2: Two-thirds of the energy works to cause the hydraulic effect; one-third of the energy works to cause the buckling effect. Pattern 3: One-third of the energy works to cause the hydraulic effect; two-thirds of the energy works to cause the buckling effect. Pattern 4: The entire energy quantum works to cause the buckling effect. Using the finite element method, the regions where fractures were theoretically expected to occur were calculated and were compared between the four patterns. More fracture damage occurred for Pattern 1 than Pattern 2, and for Pattern 3 than for Pattern 4. The hydraulic and buckling mechanisms interact with one another. When these two mechanisms are combined, the orbital walls tend to develop serious fractures. Copyright (c) 2009 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.
Variational Principles for Buckling of Microtubules Modeled as Nonlocal Orthotropic Shells
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Sarp Adali
2014-01-01
Full Text Available A variational principle for microtubules subject to a buckling load is derived by semi-inverse method. The microtubule is modeled as an orthotropic shell with the constitutive equations based on nonlocal elastic theory and the effect of filament network taken into account as an elastic surrounding. Microtubules can carry large compressive forces by virtue of the mechanical coupling between the microtubules and the surrounding elastic filament network. The equations governing the buckling of the microtubule are given by a system of three partial differential equations. The problem studied in the present work involves the derivation of the variational formulation for microtubule buckling. The Rayleigh quotient for the buckling load as well as the natural and geometric boundary conditions of the problem is obtained from this variational formulation. It is observed that the boundary conditions are coupled as a result of nonlocal formulation. It is noted that the analytic solution of the buckling problem for microtubules is usually a difficult task. The variational formulation of the problem provides the basis for a number of approximate and numerical methods of solutions and furthermore variational principles can provide physical insight into the problem.
Thermal buckling of double-layered graphene system in humid environment
Sobhy, Mohammed; Zenkour, Ashraf M.
2018-01-01
In this paper, the effect of humidity conditions on thermal buckling analysis of graphene system contained two layers under different boundary conditions is investigated. The two-variable shear deformation plate theory is employed with the nonlocal continuum theory to deduce the governing stability equations. These equations are solved analytically to obtain the thermal buckling of the nanoplate system with simply supported, clamped and free boundary conditions. The present system of double-layered graphene sheets is composed from two sheets of graphene joined together by an elastic medium and hedged by two-parameter foundations. The external foundations are modeled as Winkler–Pasternak model. Two characteristic types of thermal buckling are considered: synchronous and asynchronous modes of buckling. The temperature rise and moisture concentration are assumed as a fixed, linear or nonlinear function of z (along the thickness direction). For the validation of the formulations, the present results are compared with those published in the references. Furthermore, the influences of the nonlocal parameter, humidity and other parameters on thermal buckling of double-layered graphene system are all discussed.
Heard, W. L., Jr.; Anderson, M. S.; Slysh, P.
1976-01-01
An engineering procedure is presented for calculating the compressive buckling strength of isogrid cylinders using shell of revolution techniques and accounting for loading beyond the material proportional limit and/or local buckling of the skin prior to general buckling. A general nondimensional chart is presented which can be used in conjunction with formulas based on simple deformation plasticity theory to calculate postbuckling stiffnesses of the skin. The stiffening grid system is treated as an equivalent isotropic grid layer. Stiffnesses are determined for this grid layer, when loaded beyond the proportional limit, by the same plasticity theory used for the skin and a nonlinear stress-strain curve constructed from simple isogrid-handbook formulas and standard-reference-manual stress-strain curves for the material involved. Comparison of prebuckling strains and buckling results obtained by this procedure with data from a large isogrid-cylinder test is excellent with the calculated buckling load no more than 4 percent greater than the test value.
Non-linear buffeting response analysis of long-span suspension bridges with central buckle
Wang, Hao; Li, Aiqun; Zhao, Gengwen; Li, Jian
2010-06-01
The rigid central buckle employed in the Runyang Suspension Bridge (RSB) was the first time it was used in a suspension bridge in China. By using a spectral representation method and FFT technique combined with measured data, a 3D fluctuating wind field considering the tower wind effect is simulated. A novel FE model for buffeting analysis is then presented, in which a specific user-defined Matrix27 element in ANSYS is employed to simulate the aeroelastic forces and its stiffness or damping matrices are parameterized by wind velocity and vibration frequency. A nonlinear time history analysis is carried out to study the influence of the rigid central buckle on the wind-induced buffeting response of a long-span suspension bridge. The results can be used as a reference for wind resistance design of long-span suspension bridges with a rigid central buckle in the future.
Micro-buckling of periodically layered composites in regions of stress concentration
DEFF Research Database (Denmark)
Poulios, Konstantinos; Niordson, Christian Frithiof
2016-01-01
-buckling related failure in regions of stress concentrations. A series of parametric studies show the effect of non-uniform stress distributions due to bending loads and the presence of geometrical features such as notches and holes on the initiation of micro-buckling. The contribution of the bending stiffness...... of the reinforcing layers on the resistance against micro-buckling introduces a dependence on the layer thickness, resulting in size-scale dependent strength limits. Therefore, both the shape and dimensions of the considered geometrical features and the layering thickness of the micro-structure are varied as part...... of the parametric studies. Moreover, the impact of imperfections in the composite micro-structure on the strength of the considered specimens is investigated....
DEFF Research Database (Denmark)
Sönmez, Ümit; Tutum, Cem Celal
2008-01-01
In this work, a new compliant bistable mechanism design is introduced. The combined use of pseudo-rigid-body model (PRBM) and the Elastica buckling theory is presented for the first time to analyze the new design. This mechanism consists of the large deflecting straight beams, buckling beams......, and a slider. The kinematic analysis of this new mechanism is studied, using nonlinear Elastica buckling beam theory, the PRBM of a large deflecting cantilever beam, the vector loop closure equations, and numerically solving nonlinear algebraic equations. A design method of the bistable mechanism...... in microdimensions is investigated by changing the relative stiffness of the flexible beams. The actuation force versus displacement characteristics of several cases is explored and the full simulation results of one of the cases are presented. This paper demonstrates the united application of the PRBM...
Local buckling of thin-walled channel member flange made of aluminum alloy
Szymczak, Czesław; Kujawa, Marcin
2017-03-01
The paper deals with local stability of the thin-walled compressed flange of channel columns and beams made of aluminum alloy. The aim of paper is to find critical stress of local buckling of the flange member taking into account the web-flange interaction in linear and nonlinear elastic range of the member material. The governing differential equation of the problem is derived with aid of the principle of stationary total potential energy. The equation solution leads to the critical buckling stress and assessment of the number of half-waves in linear elastic range of the member material. Taking into account these results the analytical formula of the critical buckling stress in nonlinear elastic range is established using the tangent modulus theory and the Ramberg-Osgood stress-strain relationship. Finally the analytical results for simply supported members are compared with the FEM solutions and good agreement is observed.
Ur Rahim, Mohammad Reyaz; Akhtar, S.; Bharti, P. K.
2017-08-01
The performance of buckling load of tubular structures under quasi-static axial loading is quite appreciable, numerous tubes of various cross-section have been extensively investigated and corrugated sections have been designed to further improve the performance. In this paper, a carefully designed set of key performance indicators (KPIs) is utilized to assess and compare the buckling load of circular and corrugated tubes. A series of diagrams related to KPIs with various parameters of tubes are presented to demonstrate the influence of sectional configuration on the performance of tubes as well as the effect of the material on the potential of the same. The work is inestimable to engineering designs and applications, and further studies on the buckling load of other configurations.
Directory of Open Access Journals (Sweden)
Ur Rahim Mohammad Reyaz
2017-08-01
Full Text Available The performance of buckling load of tubular structures under quasi-static axial loading is quite appreciable, numerous tubes of various cross-section have been extensively investigated and corrugated sections have been designed to further improve the performance. In this paper, a carefully designed set of key performance indicators (KPIs is utilized to assess and compare the buckling load of circular and corrugated tubes. A series of diagrams related to KPIs with various parameters of tubes are presented to demonstrate the influence of sectional configuration on the performance of tubes as well as the effect of the material on the potential of the same. The work is inestimable to engineering designs and applications, and further studies on the buckling load of other configurations.
Effect of flurbiprofen sodium on pupillary dilatation during scleral buckling surgery
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Roysarkar T
1994-01-01
Full Text Available Maintenance of pupillary dilatation is necessary for success of scleral buckling procedures. The efficacy of 0.03% flurbiprofen in preventing intraoperative miosis was evaluated by a prospective randomized, double-masked controlled trial of 60 patients. Thirty patients received 0.03% flurbiprofen 6 times at 15 minute intervals 90 minutes preoperatively in addition to the routine dilation regimen. The treated group had a mean pupillary decrease of 1.88 mm and the control group had a decrease of 1.57 mm (p > 0.05. Flurbiprofen did not affect the pupillary size at any step of the surgery. Factors such as age of the patient, lens status, number of cryo applications, duration of surgery, and the size and extent of buckle were assessed. The use of flurbiprofen did not affect the mean pupillary change for any of these groups. Preoperative use of flurbiprofen does not significantly decrease intraoperative miosis during scleral buckling procedures
European column buckling curves and finite element modelling including high strength steels
DEFF Research Database (Denmark)
Jönsson, Jeppe; Stan, Tudor-Cristian
2017-01-01
Eurocode allows for finite element modelling of plated steel structures, however the information in the code on how to perform the analysis or what assumptions to make is quite sparse. The present paper investigates the deterministic modelling of flexural column buckling using plane shell elements...... in advanced non-linear finite element analysis (GMNIA) with the goal of being able to reestablish the European buckling curves. A short comprehensive historical review is given on the development of the European buckling curves and the related assumptions made with respect to deterministic modelling of column...... deterministic analysis can be performed based on given magnitudes of characteristic yield stress, material stress–strain relationship, and given characteristic values for imperfections and residual stresses. The magnitude of imperfections and residual stresses are discussed as well as how the use of equivalent...
Implementation of Fiber Optic Sensing System on Sandwich Composite Cylinder Buckling Test
Pena, Francisco; Richards, W. Lance; Parker, Allen R.; Piazza, Anthony; Schultz, Marc R.; Rudd, Michelle T.; Gardner, Nathaniel W.; Hilburger, Mark W.
2018-01-01
The National Aeronautics and Space Administration (NASA) Engineering and Safety Center Shell Buckling Knockdown Factor Project is a multicenter project tasked with developing new analysis-based shell buckling design guidelines and design factors (i.e., knockdown factors) through high-fidelity buckling simulations and advanced test technologies. To validate these new buckling knockdown factors for future launch vehicles, the Shell Buckling Knockdown Factor Project is carrying out structural testing on a series of large-scale metallic and composite cylindrical shells at the NASA Marshall Space Flight Center (Marshall Space Flight Center, Alabama). A fiber optic sensor system was used to measure strain on a large-scale sandwich composite cylinder that was tested under multiple axial compressive loads up to more than 850,000 lb, and equivalent bending loads over 22 million in-lb. During the structural testing of the composite cylinder, strain data were collected from optical cables containing distributed fiber Bragg gratings using a custom fiber optic sensor system interrogator developed at the NASA Armstrong Flight Research Center. A total of 16 fiber-optic strands, each containing nearly 1,000 fiber Bragg gratings, measuring strain, were installed on the inner and outer cylinder surfaces to monitor the test article global structural response through high-density real-time and post test strain measurements. The distributed sensing system provided evidence of local epoxy failure at the attachment-ring-to-barrel interface that would not have been detected with conventional instrumentation. Results from the fiber optic sensor system were used to further refine and validate structural models for buckling of the large-scale composite structures. This paper discusses the techniques employed for real-time structural monitoring of the composite cylinder for structural load introduction and distributed bending-strain measurements over a large section of the cylinder by
Dehghani, Alireza; Razmjoo, Hassan; Fazel, Farhad; Karami, Mehdi; Etesampour, Akbar; Ghanbari, Heshmatolah; Kianersi, Farzan; Akhlaghi, Mohammadreza; Fesharaki, Hamid
2013-03-01
We aimed to compare peak systolic velocity of central retinal artery (PSV.CRA) and peak systolic velocity of ophthalmic artery (PSV.OA) between patients with retinal detachment who were treated with segmental scleral bucking and scleral buckling with encircling procedure. This study was a descriptive-analytic cross sectional study that was performed in Isfahan university referral centers since April 2010 to April 2011. Of the patients who have undergone scleral buckling surgery, 20 patients belonging to two groups were randomly selected to enroll in the study. Study groups were, patients who have undergone segmental scleral buckling and the other group were patients who have undergone scleral buckling with encircling procedure. Patients were invited to perform color Doppler imaging. PSV-RA and PSV-OA were measured and documented in both operated and unoperated eyes. All of the Doppler's performed at least three months after ophthalmic surgery. We found significant decrease in PSV.CRA among patients in both groups. In patients who had undergone scleral buckling with encircling procedure PSV.CRA was 11.03 ± 3.04 (cm/sec) and 14.83 ± 4.80 in operated and unoperated eye respectively (P = 0.03). In other hand, who treated with segmental scleral buckling these parameters were 11.02 ± 2.48 and 14.45 ± 4.69 (P = 0.03). PSV.OA did not change significantly in each method. The difference between mean PSV.CRA and PSV.OA in operated eye between two study groups was not significant. PSV.CRA reduced significantly in both surgery methods and PSV.OA changes was not significant. However, the mean PSV.CRA and PSV.OA changes did not show statistically significant difference between surgery methods.
Directory of Open Access Journals (Sweden)
Vali Parvaneh
2011-01-01
Full Text Available The effects of boundary conditions and defects on the buckling behavior of SWCNTs are investigated using a structural mechanics model. Due to the application of carbon nanotubes in different fields such as NEMS, where they are subjected to different loading and boundary conditions, an investigation of buckling behavior of nanotubes with different boundary conditions is necessary. Critical buckling loads and the effects of vacancy and Stone-Wales defects were studied for zigzag and armchair nanotubes with various boundary conditions and aspect ratios (length/diameter. The comparison of our results with those of the buckling of shells with cutouts indicates that vacancy defects in carbon nanotubes can most likely be modeled as cutouts of the shells. Finally, a hybrid vacancy defect and Stone-Wales defect are also developed, and their effect on the critical buckling loads is studied.
Dislocation dynamics and the viscoplastic buckling of dendritic web type silicon ribbon
Tsai, C. T.; Dillon, O. W., Jr.; De Angelis, R. J.
1987-01-01
The effect of dendrites (reinforced edges) on the residual stresses, dislocation densities and buckling behavior during growth of web type silicon ribbon is studied. A viscoplastic material response function (Haasen-Sumino model) is used to calculate the stresses and the disloction density at each point in the silicon ribbon. In addition, the role of dendrites on the viscoplastic buckling behavior of the ribbon is investigated. The critical thicknesses, the corresponding deflection shapes and lateral deflection speeds are calculated. These results are then compared with similar data obtained for flat plates.
On Compliance and Buckling Objective Functions in Topology Optimization of Snap-Through Problems
DEFF Research Database (Denmark)
Lindgaard, Esben; Dahl, Jonas
2013-01-01
This paper deals with topology optimization of static geometrically nonlinear structures experiencing snap-through behaviour. Different compliance and buckling criterion functions are studied and applied for topology optimization of a point loaded curved beam problem with the aim of maximizing...... the snap-through buckling load. The response of the optimized structures obtained using the considered objective functions are evaluated and compared. Due to the intrinsic nonlinear nature of the problem, the load level at which the objective function is evaluated has a tremendous effect on the resulting...
A fiber optic buckle transducer for measurement of in vitro tendon strain
Roriz, Paulo; Ramos, António; Marques, Manuel B.; Simões, José A.; Frazão, Orlando
2015-09-01
The purpose of the present study is to present a prototype of a fiber optic based buckle transducer suitable for measuring strain caused by stretching of a tendon. The device has an E-shape and its central arm is instrumented with a fiber Bragg grating (FBG) sensor. The tendon adjusts to the E-form in a fashion that when it is stretched the central arm bends causing a shift of the Bragg's wavelength (λB) that is proportional to the amount of strain. This prototype is presented as an alternative to conventional strain gauge (SG) buckle transducers.
BUCKLING BEHAVIOUR OF SINGLE-WALLED CARBON NANOTUBES UNDER AXIAL LOADING
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Grzegorz Litak
2017-03-01
Full Text Available We investigate a single walled Carbon Nanotube under an axially directed compressive line loading applied at both of its edges. The expected buckling behavior we study by application of a molecular computation approach. We formulate a global potential and search for its minimum to obtain the equilibrium configuration. Using besides the main parameter, which is the value of the loading, as second parameter the diameter of the tube, we are able to define the critical value of the diameter, for which we obtain the coincident case of local shell buckling.
Improvement of risk estimate on wind turbine tower buckled by hurricane
Li, Jingwei
2013-01-01
Wind is one of the important reasonable resources. However, wind turbine towers are sure to be threatened by hurricanes. In this paper, method to estimate the number of wind turbine towers that would be buckled by hurricanes is discussed. Monte Carlo simulations show that our method is much better than the previous one. Since in our method, the probability density function of the buckling probability of a single turbine tower in a single hurricane is obtained accurately but not from one approximated expression. The result in this paper may be useful to the design and maintenance of wind farms.
Hydrogen-Induced Buckling of Pd Films Deposited on Various Substrates
Vlček, Marián
2015-07-01
A Pd-H system is a model system suitable for studying interactions of hydrogen with metals. In the present work, we studied hydrogen-induced buckling of thin Pd films deposited on various substrates with different bonding strengths (sapphire, glimmer) and also the effect of deposition temperature. Lattice expansion and phase transitions were investigated by X-ray diffraction of synchrotron radiation. The influence of the substrate and microstructure of the film on the buckling process and phase transformation to palladium hydride are discussed.
DEFF Research Database (Denmark)
Lindgaard, Esben; Lund, Erik
2012-01-01
This paper presents a novel FEM-based approach for fiber angle optimal design of laminated composite structures exhibiting complicated nonlinear buckling behavior, thus enabling design of lighter and more cost-effective structures. The approach accounts for the geometrically nonlinear behavior...... of the structure by utilizing path tracing response analysis up until the buckling point. The method simultaneously includes loss of stability due to bifurcation and limiting behavior and thereby avoids problems related to mode or stability type switching during optimization. The optimization formulation...
Energy Technology Data Exchange (ETDEWEB)
MACKEY TC; JOHNSON KI; DEIBLER JE; PILLI SP; RINKER MW; KARRI NK
2007-02-14
This report documents a detailed buckling evaluation of the primary tanks in the Hanford double-shell waste tanks (DSTs), which is part of a comprehensive structural review for the Double-Shell Tank Integrity Project. This work also provides information on tank integrity that specifically responds to concerns raised by the Office of Environment, Safety, and Health (ES&H) Oversight (EH-22) during a review of work performed on the double-shell tank farms and the operation of the aging waste facility (AWF) primary tank ventilation system. The current buckling review focuses on the following tasks: (1) Evaluate the potential for progressive I-bolt failure and the appropriateness of the safety factors that were used for evaluating local and global buckling. The analysis will specifically answer the following questions: (a) Can the EH-22 scenario develop if the vacuum is limited to -6.6-inch water gage (w.g.) by a relief valve? (b) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario can develop? (c) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario cannot develop? (2) Develop influence functions to estimate the axial stresses in the primary tanks for all reasonable combinations of tank loads, based on detailed finite element analysis. The analysis must account for the variation in design details and operating conditions between the different DSTs. The analysis must also address the imperfection sensitivity of the primary tank to buckling. (3) Perform a detailed buckling analysis to determine the maximum allowable differential pressure for each of the DST primary tanks at the current specified limits on waste temperature, height, and specific gravity. Based on the I-bolt loads analysis and the small deformations that are predicted at the unfactored limits on vacuum and axial loads, it is very unlikely that the EH-22 scenario (i.e., progressive I-bolt failure leading to global
Buckling instabilities of nanoscale polymer films and colloidal particle layers
Gurmessa, Bekele Jemama
remarkable. Finally, through an integrated experimental methods and theoretical modeling, the response of discrete colloidal layers to mechanical deformations have been exploited. The buckling profiles measured experimentally demonstrate a great insight that the continuum model may not be able to predict the response of discrete systems. Theoretically, a granular model was constructed and structural stability analysis was investigated to predict the experimental observations. The overall agreement of the experiment and the modeling was good.
Buckling strength of tapered bridge girders under combined shear and bending
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Metwally Abu-Hamd
2016-08-01
Full Text Available This paper represents the finite element results for the local buckling of tapered plate girders subjected to combine pure bending and shear stresses. An idealized model is developed representing the loading of the tapered panel that generates uniform normal stresses due to flexure, or uniform and constant shear stresses in the case of shear. Eigen-value analysis was performed for several tapered web plate girders that have different geometric parameters. A parametric study is made to reduce the FE model size showing the effect of decreasing the tapered panel adjacent straight panels, maintaining the same result accuracy as a complete girder model. The combined buckling capacity of bending and shear is determined by applying all possible load pattern combinations, together with different interaction ratios. An analysis study is presented to investigate the effect of the tapering angle on the combined bending–shear capacity of the girder. The study also includes the effect of the flange and web slenderness on the local buckling of the girder. Considering residual stresses as part of the loading stresses, the analysis procedure is repeated for some cases, and the effect of combining of the residual stresses together with the external loads is found. Empirical approximate formulae are given to estimate the combined flexure–shear buckling resistance of the tapered girder safely.
Mean value first order second moment analysis of buckling of axially ...
African Journals Online (AJOL)
user
These imperfect models are analysed using ANSYS non-linear FE buckling analysis including both geometrical and material ... symmetric I- cross section in compression and bending. Warren .... where, the matrix Φ* is the pseudo-inverse of the matrix Φ. The pseudo-inverse is calculated using the following equation based.
Nonlocal modeling and buckling features of cracked nanobeams with von Karman nonlinearity
Akbarzadeh Khorshidi, Majid; Shaat, Mohamed; Abdelkefi, Abdessattar; Shariati, Mahmoud
2017-01-01
Buckling and postbuckling behaviors of cracked nanobeams made of single-crystalline nanomaterials are investigated. The nonlocal elasticity theory is used to model the nonlocal interatomic effects on the beam's performance accounting for the beam's axial stretching via von Karman nonlinear theory. The crack is then represented as torsional spring where the crack severity factor is derived accounting for the nonlocal features of the beam. By converting the beam into an equivalent infinite long plate with an edge crack subjected to a tensile stress at the far field, the crack energy release rate, intensity factor, and severity factor are derived according to the nonlocal elasticity theory. An analytical solution for the buckling and the postbuckling responses of cracked nonlocal nanobeams accounting for the beam axial stretching according to von Karman nonlinear theory of kinematics is derived. The impacts of the nonlocal parameter on the critical buckling loads and the static nonlinear postbuckling responses of cracked nonlocal nanobeams are studied. The results indicate that the buckling and postbuckling behaviors of cracked nanobeams are strongly affected by the crack location, crack depth, nonlocal parameter, and length-to-thickness ratio.
Energy Technology Data Exchange (ETDEWEB)
Zhou, L; Zhu, B E; Pan, Z Y; Wang, Y X; Zhu, J [Institute of Modern Physics, Fudan University, Shanghai 200433 (China)
2007-07-11
The effect of encapsulation of C60 fullerenes upon the buckling strength of hosting carbon nanotubes (CNTs) has been investigated, using molecular dynamics (MD) simulations. The simulation results show that encapsulating C60 fullerenes into some CNTs with diameters larger than that of the (10, 10) CNT, in particular the (14, 14) and (18, 18) CNTs, significantly reduces the buckling strength, in contrast to the conventional wisdom that fillings increase the mechanical strength of hollow structures. The simulations have also confirmed the previous findings that filling a (10, 10) CNT with C60 increases the buckling strength. Our detailed analysis reveals that the interaction between the C60 fullerenes and the hosting (10, 10) CNT is cylindrically symmetric, while the presence of a zigzag array of C60 inside the (14, 14) CNT breaks the cylindrical symmetry and so does the presence of the three arrays of C60 inside the (18, 18) CNT. The induced asymmetries cause one peak for the C60-(14, 14) system and three peaks for the C60-(18, 18) system in the corresponding force distribution along the circumferential direction. The force concentration leads to observed reduction in the buckling strength. The reduction is more severe for C60-(14, 14) than for C60-(18, 18), because the force distribution of the former system is more asymmetric.
Buckling of Hybrid Composite Carbon/Epoxy/Aluminum Plates with Cutouts
Directory of Open Access Journals (Sweden)
B. Achour
2018-02-01
Full Text Available Structural instability becomes an important concern in the composite plate safe and reliable design. In this research, a resistance analysis is carried out on plates made of hybrid composite material with and without elliptical cutouts using the finite element method. The carbon/epoxy/aluminum laminated plates are arranged in the following ordered manner [Al/(θ/-θ/Al]. The hybrid plate resistance to buckling submitted to uniaxial compression is highlighted. Results indicate that given a structural geometry, boundary and loading condition and stacking sequence, the buckling resistance of such plates is strongly influenced by the ply orientation, the anisotropy ratio, and the cutout presence, position and size. The critical load reduction is found to decrease linearly with the decrease of the geometric ratio a/b. When b=8a, the reduction factor N* increased from 1.8% to 7% when φ=90ο and φ=0ο respectively regardless of the ply orientation. Maximum reduction of the buckling critical load is important when the elliptical cutout is located in the middle of the plate. Regardless of the declination of the elliptical cutout, maximum reduction of the critical buckling stress is obtained when the ratio E2/E1=1.
Interaction between cracking, delamination and buckling in brittle elastic thin films
Vellinga, W. P.; Van den Bosch, M.; Geers, M. G. D.
2008-01-01
A discrete lattice based model for the interaction of cracking, delamination and buckling of brittle elastic coatings is presented. The model is unique in its simultaneous incorporation of the coating and of disorder in the interface and material properties, leading to realistic 3D bending (and
Adhesive in the buckling failure of corrugated fiberboard : a finite element investigation
Adeeb A. Rahman; Said M. Abubakr
1998-01-01
This research study proposed to include the glue material in a finite element model that represents the actual geometry and material properties of a corrugated fiberboard. The model is a detailed representation of the different components of the structure (adhesive, linerboard, medium) to perform buckling analysis of corrugated structures under compressive loads. The...
Nonlinear buckling of woven fabrics, part I: elastic and non-elastic cases
CSIR Research Space (South Africa)
Anandjiwala, RD
2005-01-01
Full Text Available In this paper the fabric buckling model proposed by Grosberg and Swani has been modified by incorporating Huang’s bending rule. The proposed model is an extension of the present model and also covers the special cases. The numerical results appear...
Lock and key colloids through polymerization-induced buckling of monodisperse silicon oil droplets
Sacanna, S.; Irvine, W.T.M.; Rossi, L.; Pine, D.J.
2011-01-01
We have developed a new simple method to fabricate bulk amounts of colloidal spheres with well defined cavities from monodisperse emulsions. Herein, we describe the formation mechanism of ‘‘reactive’’ silicon oil droplets that deform to reproducible shapes via a polymerization-induced buckling
a model for the determination of the critical buckling load of self ...
African Journals Online (AJOL)
HP
supporting lattice towers. This paper therefore proposes a simple model for the determination of the critical buckling load of self- supporting lattice towers. The proposed model idealizes the lattice tower as an equivalent solid beam- column whose cross-sectional-dimensions are the unknowns to be determined.
Evaluation of Kentucky's "Buckle Up Kentucky : It's the Law & It's Enforced" 2007 campaign.
2007-08-01
The objective of this report was to document the results of the "Buckle Up Kentucky: It's the Law & It's Enforced" 2007 campaign in Kentucky. Data were also taken to document the change in usage after enactment of the primary enforcement law. The cam...
Evaluation of Kentucky's "Buckle Up Kentucky : It's the Law & It's Enforced" 2004 campaign.
2004-07-01
The objective of this report was to document the results of the "Buckle Up Kentucky: It's the Law & It's Enforced" 2004 campaign in Kentucky. Data were also taken to document the change in usage after enactment of the primary enforcement law. The cam...
Evaluation of Kentucky's "Buckle Up Kentucky : It's the Law & It's Enforced" 2005 campaign.
2005-07-01
The objective of this report was to document the results of the "Buckle Up Kentucky: It's the Law & It's Enforced" 2005 campaign in Kentucky. Data were also taken to document the change in usage after enactment of the primary enforcement law. The cam...
Evaluation of Kentucky's "Buckle Up Kentucky : It's the Law & It's Enforced" campaign.
2003-08-01
The objective of this report was to document the results of the "Buckle Up Kentucky: It's the Law & It's Enforced" campaign in Kentucky. Data were also taken to document the change in usage after enactment of the primary enforcement law. The campaign...
Evaluation of Kentucky's "Buckle Up Kentucky : It's the Law & It's Enforced" 2006 campaign.
2006-07-01
The objective of this report was to document the results of the "Buckle Up Kentucky: It's the Law & It's Enforced" 2006 campaign in Kentucky. Data were also taken to document the change in usage after enactment of the primary enforcement law. The cam...
Local analytical sensitivity analysis for design of continua with optimized 3D buckling behavior
DEFF Research Database (Denmark)
Pedersen, Niels Leergaard; Pedersen, Pauli
2017-01-01
The localized analytical sensitivity for eigenfrequency is extended to the non-linear problem of 3D continuum buckling analysis. Implemented in a finite element approach the inherent complexity of mode switching and multiple eigenvalues is found not to be a practical problem. The number...
Post-Buckling Analysis of Curved Honeycomb Sandwich Panels Containing Interfacial Disbonds
Pineda, Evan J.; Bednarcyk, Brett A.; Krivanek, Thomas K.
2016-01-01
A numerical study on the effect of facesheet-core disbonds on the post-buckling response of curved honeycomb sandwich panels is presented herein. This work was conducted as part of the development of a damage tolerance plan for the next-generation Space Launch System heavy lift launch vehicle payload fairing. As such, the study utilized full-scale fairing barrel segments as the structure of interest. The panels were composed of carbon fiber reinforced polymer facesheets and aluminum honeycomb core. The panels were analyzed numerically using the finite element method incorporating geometric nonlinearity. In a predetermined circular region, facesheet and core nodes were detached to simulate a disbond, between the outer mold line facesheet and honeycomb core, induced via low-speed impact. Surface-to-surface contact in the disbonded region was invoked to prevent interpenetration of the facesheet and core elements and obtain realistic stresses in the core. The diameter of this disbonded region was varied and the effect of the size of the disbond on the post-buckling response was observed. Significant changes in the slope of the edge load-deflection response were used to determine the onset of global buckling and corresponding buckling load. Finally, several studies were conducted to determine the sensitivity of the numerical predictions to refinement in the finite element mesh.
Numerical Buckling Analysis of Large Suction Caissons for Wind Turbines on Deep Water
DEFF Research Database (Denmark)
Madsen, Søren; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo
2013-01-01
the suction caisson is loaded by external pressure (internal suction) due to evacuation of water inside the bucket and vertical forces due to gravity. The risk of structural buckling during installation of large-diameter suction caissons is addressed using numerical methods. Initial imperfect geometries...
The effect of delaminations on local buckling in wind turbine blades
DEFF Research Database (Denmark)
Haselbach, Philipp Ulrich; Bitsche, Robert; Branner, Kim
2015-01-01
was setup in Abaqus and cohesive elements were chosen for modelling delamination growth. For initial delaminations with a width of 30–50% of the cap width the study showed that delamination close to the surface started to grow in load ranges of normal operation conditions and led to local buckling modes...
Buckling of coped steel beams and steel beams with partial endplates
Maljaars, J.; Stark, J.W.B.; Steenbergen, H.M.G.M.
2004-01-01
Copes and partial endplates influence the resistance to lateral buckling of a steel beam. In order to quantify this influence, numerical research has been carried out with validated models. Full-scale laboratory tests carried out for the validation of the numerical models are described in the Annex
Mehralian, Fahimeh; Tadi Beni, Yaghoub; Karimi Zeverdejani, Mehran
2017-09-01
The present paper is concerned with the applicability of nonlocal strain gradient theory for axial buckling analysis of nanotubes. The first order shear deformation theory with the von Kármán geometrical nonlinearity is utilized to establish theoretical formulations. The governing equations and boundary conditions are derived using the minimum potential energy principle. As main purpose of this study, the small length scale parameters are calibrated for the axial buckling problem of carbon nanotubes (CNTs) using molecular dynamics (MDs) simulations. Further the influences of different geometrical and material parameters, such as length and thickness ratio as well as small length scale parameters on the buckling response of nanotubes are studied. It is indicated that the effect of small length scale parameters on the critical buckling load becomes more prominent by increasing thickness and decreasing length ratio. Moreover, the calibrated small length scale parameters presented herein would be useful for the purpose of applying the nonlocal strain gradient theory for the analysis of nanotubes. The calibrated nonlocal strain gradient theory presented herein should be useful for researchers who are using the nonlocal strain gradient shell theories for analysis of micro/nanotubes.
Free vibration of thermally loaded panels including initial imperfections and post-buckling effects
Murphy, K. D.; Virgin, L. N.; Rizzi, S. A.
1994-01-01
A combined theoretical and experimental approach is developed to consider the small amplitude free vibration characteristics of fully clamped panels under the influence of uniform heating. Included in this study are the effects of higher modes, in-plane boundary elasticity, initial imperfections, and post-buckling. Comparisons between theory and experiment reveal excellent agreement.
Exploiting Additive Manufacturing Infill in Topology Optimization for Improved Buckling Load
Directory of Open Access Journals (Sweden)
Anders Clausen
2016-06-01
Full Text Available Additive manufacturing (AM permits the fabrication of functionally optimized components with high geometrical complexity. The opportunity of using porous infill as an integrated part of the manufacturing process is an example of a unique AM feature. Automated design methods are still incapable of fully exploiting this design freedom. In this work, we show how the so-called coating approach to topology optimization provides a means for designing infill-based components that possess a strongly improved buckling load and, as a result, improved structural stability. The suggested approach thereby addresses an important inadequacy of the standard minimum compliance topology optimization approach, in which buckling is rarely accounted for; rather, a satisfactory buckling load is usually assured through a post-processing step that may lead to sub-optimal components. The present work compares the standard and coating approaches to topology optimization for the MBB beam benchmark case. The optimized structures are additively manufactured using a filamentary technique. This experimental study validates the numerical model used in the coating approach. Depending on the properties of the infill material, the buckling load may be more than four times higher than that of solid structures optimized under the same conditions.
Buckling Analysis of Bucket Foundations for Wind Turbines in Deep Water
DEFF Research Database (Denmark)
Madsen, Søren; Andersen, Lars; Ibsen, Lars Bo
2011-01-01
Using large suction caissons for offshore wind turbines is an upcoming technology also referred to as bucket foundations. The bucket foundation does not require heavy installation equipment, but since it is constructed as a thin steel shell structure, instability, in form of buckling, becomes...
A global FE-local analytical approach to modelling failure in localised buckles caused by crash
Dekker, R.; Walters, C.L.
2016-01-01
Localised buckles can occur in crasheswhen compressive stresses are dominant. However, due to their local appearance, they might be overlooked by a finite element analysis, meaning that local failure due to bucklingwill not be predicted. This could, for example, be catastrophic in the case of the
Błażejewski, Paweł; Marcinowski, Jakub
2017-06-01
Existing provisions leading to the assessment of the buckling resistance of pressurised spherical shells were published in the European Design Recommendations (EDR) [1]. This book comprises rules which refer to the stability of steel shells of different shapes. In the first step of the general procedure they require calculation of two reference quantities: the elastic critical buckling reference pRcr and the plastic reference resistance pRpl. These quantities should be determined in the linear buckling analysis (LBA) and in the materially nonlinear analysis (MNA) respectively. Only in the case of spherical shells the existing procedure has exceptional character. It is based on the geometrically nonlinear analysis (GNA) and on the geometrically and materially nonlinear analysis (GMNA), respectively. From this reason, in this particular case there was a need to change the existing approach. The new procedure was presented in the work of Błażejewski & Marcinowski in 2016 (comp. [2]). All steps of the procedure leading to the assessment of buckling resistance of pressurized steel, spherical shells were presented in this work. The elaborated procedure is consistent with provisions of Eurocode EN1993-1-6 (comp. [3]) and with recommendations inserted in Europeans Design Recommendations [1]. The proposed capacity curves were compared with existing proposal published in [1] for three different fabrication quality classes predicted in [3]. In this work also comparisons of author's proposals with experimental results obtained by other authors were presented.
Buckling tests of sandwich cylindrical shells with and without cut-outs
Bisagni, C.; Davidson, B.D.; Czabaj, M.W.; Ratcliffe, J.G.
2016-01-01
The results of buckling tests performed during the project DESICOS funded by the European Commission in the FP7 Programme are here presented. The tested structures are sandwich cylindrical shells that consist of reduced models of a component of the Ariane 5 launcher: the Dual Launch System. In
On the dynamic buckling of a lightly damped elastic cubic model ...
African Journals Online (AJOL)
In this paper, we employ a generalization of Lindsted-Poincare technique to determine the dynamic buckling load of a lightly and viscously damped elastic cubic model structure modulated by a sinusoidally slowly varying dynamic load. The imperfect elastic cubic (nonlinear) structure is itself a generalization of most elastic ...
Asymptotic solution on the dynamic buckling of a column stressed by ...
African Journals Online (AJOL)
This paper analysis the dynamic stability of a dynamically oscillatory system with slowly varying time dependent parameters. It utilizes the concept of multiple times scaling in an asymptotic evaluation of the dynamic buckling load of the imperfect elastic structure under investigation. Unlike most similar investigations to date ...
Local buckling of aluminium structures exposed to fire. Part 1: Tests
Maljaars, J.; Soetens, F.
2009-01-01
This paper describes an experimental investigation into local buckling of compressed aluminium alloy sections at elevated temperatures. Stress-strain relationships are derived based on uniaxial tensile tests. A special test set-up with a furnace is developed to test slender square hollow sections
Buckling Design Studies of Inverted, Oblate Bulkheads for a Propellant Tank
Smeltzer, Stanley S., III; Bowman, Lynn M.
2002-01-01
An investigation of the deformation and buckling characteristics of a composite, oblate bulkhead that has an inverted geometry and is subjected to pressure-only loading is presented for three bulkhead geometries and thicknesses. The effects of a stiffening support ring at the bulkhead to cylinder interface are also evaluated. Buckling analyses conducted using the axisymmetric shell code BOSOR4 are discussed for several bulkhead configurations. These results are analytically verified using results from the Structural Analysis of General Shells (STAGS) code for a selected bulkhead configuration. The buckling characterization of an inverted, oblate bulkhead requires careful attention as small changes in bulkhead parameters can have a significant effect on the critical buckling load. Comparison of BOSOR4 and STAGS results provided a very good correlation between the two analysis methods. In addition, the analysis code BOSOR4 was found to be an efficient sizing tool that is useful during the preliminary design stage of a practical shell structure. Together, these two aspects should give the design engineer confidence in sizing these stability critical structures. Additional characterization is warranted, especially for a composite tank structure, since only one bulkhead configuration was examined closely.
FEM simulations of lateral torsional buckling experiments on channel sections loaded in bending
Snijder, H.H.; Bijlaard, F.S.K.; Steenbergen, H.M.G.M.
2002-01-01
The lateral torsional buckling behaviour of hot rolled channel sections subjected to bending is studied in an overall project. The final objective of this project is to develop a design method. This paper concentrates on the validation of the FEM model against the experiments. For channel sections
Directory of Open Access Journals (Sweden)
Shrivastava Sachin
2015-01-01
Full Text Available A redesign of canard control-surface of an advanced all-metallic fighter aircraft was carried out by using carbon fibre composite (CFC for ribs and panels. In this study ply-orientations of CFC structure are optimized using a Genetic-Algorithm (GA with an objective function to have minimum failure index (FI according to Tsai-Wu failure criterion. The redesigned CFC structure was sufficiently strong to withstand aerodynamic loads from stress and deflection points of view. Now, in the present work CFC canard structure has been studied for its buckling strength in comparison to existing metallic design. In this study, the existing metallic design was found to be weak in buckling. Upon a detailed investigation, it was revealed that there are reported failures in the vicinity of zones where initial buckling modes are excited as predicted by the finite element based buckling analysis. In view of buckling failures, the redesigned CFC structure is sufficiently reinforced with stringers at specific locations. After providing reinforcements against buckling, the twist and the camber variations of the airfoil are checked and compared with existing structure data. Finally, the modal analysis has been carried out to compare the variation in excitation frequency due to material change. The CFC structure thus redesigned is safe from buckling and aerodynamic aspects as well.
Lateral-Torsional Buckling Instability Caused by Individuals Walking on Wood Composite I-Joists
Villasenor Aguilar, Jose Maria
Recent research has shown that a significant number of the falls from elevation occur when laborers are working on unfinished structures. Workers walking on wood I-joists on roofs and floors are prone to fall hazards. Wood I-joists have been replacing dimension lumber for many floor systems and a substantial number of roof systems in light-frame construction. Wood I-joists are designed to resist axial stresses on the flanges and shear stresses on the web while minimizing material used. However, wood I-joists have poor resistance to applied lateral and torsional loads and are susceptible to lateral-torsional buckling instability. Workers walking on unbraced or partially braced wood I-joists can induce axial and lateral forces as well as twist. Experimental testing demonstrated that workers cause lateral-torsional buckling instability in wood I-joists. However, no research was found related to the lateral-torsional buckling instability induced by individuals walking on the wood I-joists. Furthermore, no research was found considering the effects of the supported end conditions and partial bracing in the lateral-torsional buckling instability of wood I-joists. The goal of this research was to derive mathematical models to predict the dynamic lateral-torsional buckling instability of wood composite I-joists loaded by individuals walking considering different supported end conditions and bracing system configurations. The dynamic lateral-torsional buckling instability was analyzed by linearly combining the static lateral-torsional buckling instability with the lateral bending motion of the wood Ijoists. Mathematical models were derived to calculate the static critical loads for the simply supported end condition and four wood I-joist hanger supported end conditions. Additionally, mathematical models were derived to calculate the dynamic maximum lateral displacements and positions of the individual walking on the wood Ijoists for the same five different supported end
Skoczen, Blazej
1998-01-01
Mechanical stability of pressurized expansion bellows and tube-bellows-tube interconnects is considered.Effect of shear deformation on buckling pressure of bellows is shown y using Engesser's model. A generalized equivalent column concept is developed in order to study the effect of relaxation of support conditions on stability of interconnects containing expansion bellows. Two general modes of buckling are discussed: column instability of well-supported bellows (I) and buckling of tube-bellows--tube interconnect if the support-bellows distances are large enough (II). A dramatic drop of critical pressure in the transition region from mode I to mode II is shown.
DEFF Research Database (Denmark)
Bhushan, Karihaloo; Stang, Henrik
2008-01-01
This paper is concerned with development of a simple procedure to assess the threat posed by interlaminar matrix delaminations to the integrity of composite laminates when they are situated in a compressive stress field. Depending upon the size of the delamination, its location below the surface...... and on the level of the applied stress, it may or may not buckle away from the rest of the laminate. If it buckles, the post-buckling response will depend upon the applied compressive stress level, the thickness of the delaminated ply and the interlaminar critical energy release rate of the composite material...... for the mode mixity present at the delamination front. The pre- and post-buckling response is examined in its simplest form and guidelines provided for assessing whether or not a delamination detected during quality control or inspection poses a threat to the safe operation of the composite laminate....
National Research Council Canada - National Science Library
Chen, P
2000-01-01
...., both high temperatures (and temperatures gradients) and a transverse acoustic loading. Of particular interest in this study are situations in which the plate is buckled by the thermal effects and experiences frequent snap-throughs, i.e...
Directory of Open Access Journals (Sweden)
Spela Stunf
2011-01-01
Full Text Available Pre-existing scleral pathology is an important risk factor for globe rupture during scleral buckling procedures. We report here, the surgical management of an unexpected scleral pathology found at the scleral buckling procedure in a retinal detachment patient. A 77-year-old white female with retinal detachment underwent a scleral buckling procedure. The surgery was converted into a scleral graft procedure, as extreme scleral thinning was found intraoperatively. An alcohol-preserved donor sclera graft was used. The second surgery for definitive retinal alignment was performed two weeks later. The presented case of an unexpected scleral pathology in a retinal detachment patient was managed with a combination of scleral grafting and pars plana vitrectomy, without any major complications. The anatomical outcome was excellent and the scleral rupture was prevented; the visual outcome was satisfactory. A conversion of the scleral buckling procedure into a scleral graft procedure has proved to be safe and effective for unexpected scleral pathology.
Gates, Thomas S.; Odegard, Gregory M.; Nemeth, Michael P.; Frankland, Sarah-Jane V.
2004-01-01
A multi-scale analysis of the structural stability of a carbon nanotube-polymer composite material is developed. The influence of intrinsic molecular structure, such as nanotube length, volume fraction, orientation and chemical functionalization, is investigated by assessing the relative change in critical, in-plane buckling loads. The analysis method relies on elastic properties predicted using the hierarchical, constitutive equations developed from the equivalent-continuum modeling technique applied to the buckling analysis of an orthotropic plate. The results indicate that for the specific composite materials considered in this study, a composite with randomly orientated carbon nanotubes consistently provides the highest values of critical buckling load and that for low volume fraction composites, the non-functionalized nanotube material provides an increase in critical buckling stability with respect to the functionalized system.
Barrett, R.; McMurtry, R.; Vos, R.; Tiso, P.; De Breuker, R.
2005-01-01
This paper describes a new class of flight control actuators using Post-Buckled Precompressed (PBP) piezoelectric elements. These actuators are designed to produce significantly higher deflection and force levels than conventional piezoelectric actuator elements. Classical laminate plate theory
DEFF Research Database (Denmark)
Henrichsen, Søren Randrup; Lindgaard, Esben; Lund, Erik
2015-01-01
Robust buckling optimal design of laminated composite structures is conducted in this work. Optimal designs are obtained by considering geometric imperfections in the optimization procedure. Discrete Material Optimization is applied to obtain optimal laminate designs. The optimal geometric...
Energy Technology Data Exchange (ETDEWEB)
Liu, J.C. [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); Zhang, Y.Q., E-mail: cyqzhang@zju.edu.cn [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); State Key Laboratory of Mechanical Structural Strength and Vibration, Xi' an Jiaotong University, Xi' an 710049 (China); Fan, L.F. [College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100084 (China)
2017-04-11
The general equation for transverse vibration of double-viscoelastic-FGM-nanoplate system with viscoelastic Pasternak medium in between and each nanoplate subjected to in-plane edge loads is formulated on the basis of the Eringen's nonlocal elastic theory and the Kelvin model. The factors of the structural damping, medium damping, small size effect, loading ratio, and Winkler modulus and shear modulus of the medium are incorporated in the formulation. Based on the Navier's method, the analytical solutions for vibrational frequency and buckling load of the system with simply supported boundary conditions are obtained. The influences of these factors on vibrational frequency and buckling load of the system are discussed. It is demonstrated that the vibrational frequency of the system for the out-of-phase vibration is dependent upon the structural damping, small size effect and viscoelastic Pasternak medium, whereas the vibrational frequency for the in-phase vibration is independent of the viscoelastic Pasternak medium. While the buckling load of the system for the in-phase buckling case has nothing to do with the viscoelastic Pasternak medium, the buckling load for the out-of-phase case is related to the small size effect, loading ratio and Pasternak medium. - Highlights: • Vibration of double-viscoelastic-FGM-nanoplate system under in-plane edge loads is investigated. • Biaxial buckling of the system with simply supported boundary conditions is analyzed. • Explicit expression for the vibrational frequency and buckling load is obtained. • Impacts of viscoelastic Pasternak medium on vibrational frequency and buckling load are discussed. • Influences of structural damping, small size effect and loading ratio are also considered.
Directory of Open Access Journals (Sweden)
A. Farajpour
Full Text Available Carbon nanotubes are a new class of microtubule-stabilizing agents since they interact with protein microtubules in living cells, interfering with cell division and inducing apoptosis. In the present work, a modified beam model is developed to investigate the effect of carbon nanotubes on the buckling of microtubule bundles in living cell. A realistic interaction model is employed using recent experimental data on the carbon nanotube-stabilized microtubules. Small scale and surface effects are taken into account applying the nonlocal strain gradient theory and surface elasticity theory. Pasternak model is used to describe the normal and shearing effects of enclosing filament matrix on the buckling behavior of the system. An exact solution is obtained for the buckling growth rates of the mixed bundle in viscoelastic surrounding cytoplasm. The present results are compared with those reported in the open literature for single microtubules and an excellent agreement is found. Finally, the effects of different parameters such as the size, chirality, position and surface energy of carbon nanotubes on the buckling growth rates of microtubule bundles are studied. It is found that the buckling growth rate may increase or decrease by adding carbon nanotubes, depending on the diameter and chirality of carbon nanotubes. Keywords: Microtubules, Carbon nanotubes, Buckling, Size effects
An energy harvesting solution based on the post-buckling response of non-prismatic slender beams
Jiao, Pengcheng; Borchani, Wassim; Hasni, Hassene; Alavi, Amir H.; Lajnef, Nizar
2017-04-01
Systems based on post-buckled structural elements have been extensively used in many applications such as actuation, remote sensing and energy harvesting thanks to their efficiency enhancement. The post-buckling snap- through behavior of bilaterally constrained beams has been used to create an efficient energy harvesting mechanism under quasi-static excitations. The conversion mechanism has been used to transform low-rate and low-frequency excitations into high-rate motions. Electric energy can be generated from such high-rate motions using piezoelectric transducers. However, lack of control over the post-buckling behavior severely limits the mechanism's efficiency. This study aims to maximize the levels of the harvestable power by controlling the location of the snapping point along the beam at different buckling transitions. Since the snap-through location cannot be controlled by tuning the geometry properties of a uniform cross-section beam, non-uniform cross sections are examined. An energy-based theoretical model is herein developed to predict the post-buckling response of non-uniform cross-section beams. The total potential energy is minimized under constraints that represent the physical confinement of the beam between the lateral boundaries. Experimentally validated results show that changing the shape and geometry dimensions of non- uniform cross-section beams allows for the accurate control of the snap-through location at different buckling transitions. A 78.59% increase in harvested energy levels is achieved by optimizing the beam's shape.
Jiao, Pengcheng; Borchani, Wassim; Hasni, Hassene; Lajnef, Nizar
2017-08-01
Thanks to their efficiency enhancement systems based on post-buckled structural elements have been extensively used in many applications such as actuation, remote sensing and energy harvesting. The post-buckling snap-through behavior of bilaterally constrained beams has been exploited to create sensing or energy harvesting mechanisms for quasi-static applications. The conversion mechanism has been used to transform low-rate and low-frequency excitations into high-rate motions. Electric energy has been generated from such high-rate motions using piezoelectric transducers. However, lack of control over the post-buckling behavior severely limits the mechanism’s efficiency. This study aims to maximize the levels of harvestable power by controlling the location of snap-throughs along the beam at different buckling transitions. Since the snap-through location cannot be controlled by tuning the geometric properties of a uniform beam, non-uniform cross-sections are examined. An energy-based theoretical model is herein developed to predict the post-buckling response of non-prismatic beams. The total potential energy is minimized under constraints that represent the physical confinement of the beam between the lateral boundaries. The experimentally validated results show that changing the shape and geometric dimensions of non-uniform beams allows for the accurate controlling of the snap-through location at different buckling transitions. A 78.59% improvement in harvested energy levels has been achieved by optimization of beam shape.
Optical measurement on dynamic buckling behavior of stiffened composite panels under in-plane shear
Lei, Zhenkun; Bai, Ruixiang; Tao, Wang; Wei, Xiao; Leng, Ruijiao
2016-12-01
The buckling behavior and failure mode of a composite panel stiffened by I-shaped stringers under in-plane shear is studied using digital fringe projection profilometry. The basic principles of the dynamic phase-shifting technique, multi-frequency phase-unwrapping technique and inverse-phase technique for nonlinear error compensation are introduced. Multi-frequency fringe projection profilometry was used to monitor and measure the change in the morphology of a discontinuous surface of the stiffened composite panel during in-plane shearing. Meanwhile, the strain history of multiple points on the skin was obtained using strain rosettes. The buckling mode and deflection of the panel at different moments were analyzed and compared with those obtained using the finite element method. The experimental results validated the FEM analysis.
Evaporation-Induced Buckling and Fission of Microscale Droplet Interface Bilayers
Energy Technology Data Exchange (ETDEWEB)
Boreyko, Jonathan B [ORNL; Mruetusatorn, Prachya [ORNL; Sarles, Stephen A [ORNL; Retterer, Scott T [ORNL; Collier, Pat [ORNL
2013-01-01
Droplet interface bilayers (DIBs) are a robust platform for studying synthetic cellular membranes; however, to date no DIBs have been produced at cellular length scales. Here, we create microscale droplet interface bilayers ( DIBs) at the interface between aqueous femtoliter-volume droplets within an oil-filled microfluidic channel. The uniquely large area-to-volume ratio of the droplets results in strong evaporation effects, causing the system to transition through three distinct regimes. First, the two adjacent droplets shrink into the shape of a single spherical droplet, where an augmented lipid bilayer partitions two hemi-spherical volumes. In the second regime, the combined effects of the shrinking monolayers and growing bilayer force the confined bilayer to buckle to conserve its mass. Finally, at a bending moment corresponding to a critical shear stress, the buckling bilayer fissions a vesicle to regulate its shape and stress. The DIBs produced here enable evaporation-induced bilayer dynamics reminiscent of endo- and exocytosis in cells.
Origin of buckling phenomenon during drying of micrometer-sized colloidal droplets.
Bahadur, J; Sen, D; Mazumder, S; Bhattacharya, S; Frielinghaus, H; Goerigk, G
2011-07-05
The origin of the buckling of micrometer-sized colloidal droplets during evaporation-induced self-assembly (EISA) has been elucidated using electron microscopy and small-angle neutron scattering. Doughnut-like assembled grains with varying aspect ratios are formed during EISA at different physicochemical conditions. It has been revealed that this phenomenon is better explained by an existing hypothesis based on the formation of a viscoelastic shell of nanoparticles during drying than by other existing hypotheses based on the inertial instability of the initial droplets and hydrodynamic instability due to thermocapillary forces. This conclusion was further supported by the arrest of buckling through modification of the colloidal interaction in the initial dispersion. © 2011 American Chemical Society
Na, Kyung-Su; Kim, Ji-Hwan
2008-02-01
The volume fraction optimization of Functionally Graded Material (FGM) composite plate is investigated for stress reduction and thermo-mechanical buckling. Material properties are assumed to be temperature dependent and varied continuously in the thickness direction. The 3-D finite element is adopted using an 18-node solid element to analyze the plate model more accurately for the variation of material properties and temperature field in the thickness direction. Tensile and compressive stress ratios of the structure under mechanical load are evaluated for stress analysis. Temperature at each node is obtained by solving the steady-state heat transfer problem in the thermo-mechanical buckling analysis, and Newton-Raphson method is used for nonlinear analysis. Tensile stress ratios, compressive stress ratios and critical temperatures are analyzed for various thickness ratios and volume fraction distributions in the numerical study. Finally, the optimal design of FGM composite plate is investigated by considering the stress and the critical temperature.
Snap-through buckling of initially curved microbeam subject to an electrostatic force.
Chen, X; Meguid, S A
2015-05-08
In this paper, the snap-through buckling of an initially curved microbeam subject to an electrostatic force, accounting for fringing field effect, is investigated. The general governing equations of the curved microbeam are developed using Euler-Bernoulli beam theory and used to develop a new criterion for the snap-through buckling of that beam. The size effect of the microbeam is accounted for using the modified couple stress theory, and intermolecular effects, such as van der Waals and Casimir forces, are also included in our snap-through formulations. The snap-through governing equations are solved using Galerkin decomposition of the deflection. The results of our work enable us to carefully characterize the snap-through behaviour of the initially curved microbeam. They further reveal the significant effect of the beam size, and to a much lesser extent, the effect of fringing field and intermolecular forces, upon the snap-through criterion for the curved beam.
Effect of boundary conditions on piezoelectric buckled beams for vibrational noise harvesting
Cottone, F.; Mattarelli, M.; Vocca, H.; Gammaitoni, L.
2015-11-01
Nonlinear bistable systems have proven to be advantageous for energy harvesting of random and real ambient vibrations. One simple way of implementing a bistable transducer is setting a piezoelectric beam in a post-buckled configuration by axial compression. Besides, hinged or clamped-clamped type of boundary conditions correspond to two different post-buckled shape functions. Here we study, through theoretical analysis and numerical simulations, the efficiency of a hinged and clamped-clamped piezoelectric bridge under band-limited random noise with progressive axial load. Clamped configuration results to harvest 26% more power than hinged around an optimal axial load of 0.05%, while, in the intra-well trapped situation, above 0.1%, the two configurations present no substantial difference. Nevertheless, simulations confirm the advantage of exploiting inter-well oscillations in bistable regime.
A Simplified Analysis of the Post-buckling Behavior of a Compressed Reinforcing Bar
Directory of Open Access Journals (Sweden)
P. Kabele
2004-01-01
Full Text Available Recently, a computational methodology based on a sequential multiscale approach, which facilitates numerical simulation of an R/C building demolition has been developed. In this type of analysis, it is necessary to capture the behavior of compressed reinforcement bars until complete rupture, which occurs due to extensive bending in the post-buckling regime. To this end, a simplified analytical model of the post-buckling behavior of a compressed bar is proposed. The simplification consists namely in considering rigid-plastic material behavior, neglecting axial contraction of the central line, and approximating the shape of the deformed central line in the plastic hinges by a circular arch. Consequently, the axial loading force, bar end displacement, and extreme strain can be expressed in relatively simple closed forms. The results obtained with the proposed model show very close agreement with those obtained by a detailed and realistic finite element analysis, which justifies the use of the simplifying assumptions.
EXACT SOLUTION FOR TEMPERATURE-DEPENDENT BUCKLING ANALYSIS OF FG-CNT-REINFORCED MINDLIN PLATES
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Seyed Mohammad Mousavi
2016-03-01
Full Text Available This research deals with the buckling analysis of nanocomposite polymeric temperature-dependent plates reinforced by single-walled carbon nanotubes (SWCNTs. For the carbon-nanotube reinforced composite (CNTRC plate, uniform distribution (UD and three types of functionally graded (FG distribution patterns of SWCNT reinforcements are assumed. The material properties of FG-CNTRC plate are graded in the thickness direction and estimated based on the rule of mixture. The CNTRC is located in a elastic medium which is simulated with temperature-dependent Pasternak medium. Based on orthotropic Mindlin plate theory, the governing equations are derived using Hamilton’s principle and solved by Navier method. The influences of the volume fractions of carbon nanotubes, elastic medium, temperature and distribution type of CNTs are considered on the buckling of the plate. Results indicate that CNT distribution close to top and bottom are more efficient than those distributed nearby the mid-plane for increasing the stiffness of plates.
Reliability of engineering methods of assessment the critical buckling load of steel beams
Rzeszut, Katarzyna; Folta, Wiktor; Garstecki, Andrzej
2018-01-01
In this paper the reliability assessment of buckling resistance of steel beam is presented. A number of parameters such as: the boundary conditions, the section height to width ratio, the thickness and the span are considered. The examples are solved using FEM procedures and formulas proposed in the literature and standards. In the case of the numerical models the following parameters are investigated: support conditions, mesh size, load conditions, steel grade. The numerical results are compared with approximate solutions calculated according to the standard formulas. It was observed that for high slenderness section the deformation of the cross-section had to be described by the following modes: longitudinal and transverse displacement, warping, rotation and distortion of the cross section shape. In this case we face interactive buckling problem. Unfortunately, neither the EN Standards nor the subject literature give close-form formulas to solve these problems. For this reason the reliability of the critical bending moment calculations is discussed.
Nemeth, Michael P.
2014-01-01
Nonlinear and bifurcation buckling equations for elastic, stiffened, geometrically perfect, right-circular cylindrical, anisotropic shells subjected to combined loads are presented that are based on Sanders' shell theory. Based on these equations, a three-parameter approximate Rayleigh-Ritz solution and a classical solution to the buckling problem are presented for cylinders with simply supported edges. Extensive comparisons of results obtained from these solutions with published results are also presented for a wide range of cylinder constructions. These comparisons include laminated-composite cylinders with a wide variety of shell-wall orthotropies and anisotropies. Numerous results are also given that show the discrepancies between the results obtained by using Donnell's equations and variants of Sanders' equations. For some cases, nondimensional parameters are identified and "master" curves are presented that facilitate the concise representation of results.
Cherniaev, Aleksandr; Komarov, Valeriy
2015-10-01
Composite drive shafts are extensively used in automotive and aeronautical applications due to lightweight combined with exceptional strength and stiffness. Complexity of the drive shaft design problem associated with the need to determine rational values for multiple parameters characterizing composite material (fiber orientation angles, stacking sequence and ply thicknesses), as well as with the fact that multiple conflicting design constraints should be considered simultaneously. In this paper we approach this problem considering carbon/epoxy drive shaft design as a multistep optimization process. It includes the following steps: 1) determination of fiber orientation angles and laminate stacking sequence based on analysis of loading conditions and analytical expressions predicting buckling load and minimal natural frequency of idealized drive shaft; 2) finding rational ply thicknesses using formal optimization procedure utilizing response surface approximations and gradient-based optimization algorithm; and 3) verification analysis of the optimized configuration with the use of nonlinear buckling analysis to ensure satisfaction of stability constraint.
Bifurcation analysis and phase diagram of a spin-string model with buckled states
Ruiz-Garcia, M.; Bonilla, L. L.; Prados, A.
2017-12-01
We analyze a one-dimensional spin-string model, in which string oscillators are linearly coupled to their two nearest neighbors and to Ising spins representing internal degrees of freedom. String-spin coupling induces a long-range ferromagnetic interaction among spins that competes with a spin-spin antiferromagnetic coupling. As a consequence, the complex phase diagram of the system exhibits different flat rippled and buckled states, with first or second order transition lines between states. This complexity translates to the two-dimensional version of the model, whose numerical solution has been recently used to explain qualitatively the rippled to buckled transition observed in scanning tunneling microscopy experiments with suspended graphene sheets. Here we describe in detail the phase diagram of the simpler one-dimensional model and phase stability using bifurcation theory. This gives additional insight into the physical mechanisms underlying the different phases and the behavior observed in experiments.
Gao, Li; Zhang, Yihui; Zhang, Hui; Doshay, Sage; Xie, Xu; Luo, Hongying; Shah, Deesha; Shi, Yan; Xu, Siyi; Fang, Hui; Fan, Jonathan A; Nordlander, Peter; Huang, Yonggang; Rogers, John A
2015-06-23
Large-scale, dense arrays of plasmonic nanodisks on low-modulus, high-elongation elastomeric substrates represent a class of tunable optical systems, with reversible ability to shift key optical resonances over a range of nearly 600 nm at near-infrared wavelengths. At the most extreme levels of mechanical deformation (strains >100%), nonlinear buckling processes transform initially planar arrays into three-dimensional configurations, in which the nanodisks rotate out of the plane to form linear arrays with "wavy" geometries. Analytical, finite-element, and finite-difference time-domain models capture not only the physics of these buckling processes, including all of the observed modes, but also the quantitative effects of these deformations on the plasmonic responses. The results have relevance to mechanically tunable optical systems, particularly to soft optical sensors that integrate on or in the human body.
How tall can gelatin towers be? An introduction to elasticity and buckling
Taberlet, Nicolas; Ferrand, Jérémy; Camus, Élise; Lachaud, Léa; Plihon, Nicolas
2017-12-01
The stability of elastic towers is studied through simple hands-on experiments. Using gelatin-based stackable bricks, one can investigate the maximum height a simple structure can reach before collapsing. We show through experiments and by using the classical linear elastic theory that the main limitation to the height of such towers is the buckling of the elastic structures under their own weight. Moreover, the design and architecture of the towers can be optimized to greatly improve their resistance to self-buckling. To this aim, the maximum height of hollow and tapered towers is investigated. The experimental and theoretical developments presented in this paper can help students grasp the fundamental concepts in elasticity and mechanical stability.
Secondary Glaucoma Associated with Encircling Scleral Buckle Migration into the Cornea
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Şengül Özdek
2016-01-01
Full Text Available Transmuscular migration of the encircling band through rectus muscles and straddling of the cornea has only been reported in a few cases previously in the literature. This rare condition has never been associated with glaucoma. In this report, we aimed to describe a unique case with transmuscular migration of encircling buckle as a probable cause of glaucoma. A 17-year-old female presented with transmuscular migration of buckle and high intraocular pressure (IOP. Limbal/corneal migration of the silicone band was thought to be the main reason for the IOP rise; therefore, scleral band removal was performed. One month after removal, the patient was free of glaucoma medications and IOP was within normal limits. The retina remained attached during all postoperative visits. Transmuscular migration of the encircling band through rectus muscles and straddling of the cornea may act as a trigger for glaucoma.
Research development of buckling and ultimate strength of hull plate and stiffened panel
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CHEN Yanting
2017-01-01
Full Text Available Buckling and ultimate strength of hull plate and stiffened panel are important contents in the de-sign of ship structures,have achieved plenteous results in recent years. The research development of buck-ling and ultimate strength of steel hull plate and stiffened panel in the past decade at home and abroad is re-viewed for the convenience of carrying out studies and researches. The case of static loading is emphatical-ly described,the cyclic loading and dynamic loading are also introduced. A systematical overview is pre-sented for intact structures and damaged structures under single load or combined loads,in accordance with four kinds of research methods,which are experiment,numerical computation method,analytical method and comprehensive approach. The superiority and inferiority of each research method are assessed. Significant achievements are summarized,and six further problems are identified for the future study.
Kala, Zdeněk
2013-10-01
The paper deals with the statistical analysis of resistance of a hot-rolled steel IPE beam under major axis bending. The lateral-torsional buckling stability problem of imperfect beam is described. The influence of bending moments and warping torsion on the ultimate limit state of the IPE beam with random imperfections is analyzed. The resistance is calculated by means of the close form solution. The initial geometrical imperfections of the beam are considered as the formatively identical to the first eigen mode of buckling. Changes of mean values of the resistance, of mean values of internal bending moments, of the variance of resistance and of the variance of internal bending moments were studied in dependence on the beam non-dimensional slenderness. The values of non-dimensional slenderness for which the statistical characteristics of internal moments associated with random resistance are maximal were determined.
Free vibrations and buckling analysis of laminated plates by oscillatory radial basis functions
Neves, A. M. A.; Ferreira, A. J. M.
2015-12-01
In this paper the free vibrations and buckling analysis of laminated plates is performed using a global meshless method. A refined version of Kant's theorie which accounts for transverse normal stress and through-the-thickness deformation is used. The innovation is the use of oscillatory radial basis functions. Numerical examples are performed and results are presented and compared to available references. Such functions proved to be an alternative to the tradicional nonoscillatory radial basis functions.
Cohen, Gerald A.; Haftka, Raphael T.
1989-01-01
Buckling load sensitivity calculations in the shell-of-revolution program FASOR are discussed. This development is based on Koiter's initial postbuckling theory, which has been generalized to include the effect of stiffness changes, as well as geometric imperfections. The implementation in FASOR is valid for anisotropic, as well as orthotropic, shells. Examples are presented for cylindrical panels under axial compression, complete cylindrical shells in torsion, and antisymmetric angle-ply cylindrical panels under edge shear.
[Giant retinal tears treated with lens sparing, bimanual 23 g vitrectomy without scleral buckle].
Quezada-Ruiz, Carlos; Cano-Hidalgo, Rene Alfredo
2014-01-01
A giant retinal tear is defined as a full thickness break in the neurosensory retina that extends circumferentially for 3 or more clock hours around the retina in the presence of a posterior vitreous detachment. It is one of the more complex surgical scenarios that a retina surgeon can face. There is no consensus on the ideal surgical technique; however, the "traditional" approach has been to perform a combined procedure including lensectomy, scleral buckle and vitrectomy. To report the outcome over 2 years of five patients with giant retinal tears managed with lens sparing, bimanual 23-gauge vitrectomy without scleral buckle. Retrospective analysis of patients with giant retinal tears managed with lens sparing, bimanual 23-gauge vitrectomy without scleral buckle. Included in the analysis were age, lens status, etiology and size of the tear, pre- and postoperative visual acuity, anatomic success, tamponade used, laser or criopexy where recorded. Three patients had high myopia, one secondary to blunt trauma and one with Wagner-Stickler syndrome were included in the analysis. The size of the tear varied from 120-280°. Anatomic success was achieved in all patients. One patient developed proliferative vitreoretinopathy and was re-operated and the retina remained attached. In this group of selected patients, lens-sparing bimanual 23-gauge vitrectomy without scleral buckle seems a safe and effective option in the management of retinal detachment associated with giant retinal tears. Further prospective and comparative studies are warranted to establish the role of this technique in the treatment of patients with this complex pathology.
Vibration and Buckling Analysis of Moderately Thick Plates using Natural Element Method
Mohammad Etemadi; Fakhri Etemadi; Tayeb Pourreza
2015-01-01
Using natural element method (NEM), the buckling and the free vibration behaviors of moderate thick plates is studied here. The basis of NEM is natural neighbors and Voronoi cells concepts. The shape functions of nodes located in the domain is equal to the proportion of common natural neighbors area divided by area that related by each Voronoi cells. First step in analyzing the moderate thick plates is identification boundaries. This is done by nodes scattering on problem do...
Extrusion of hydrogel exoplant into upper eyelid 16 years after a scleral buckle procedure
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Chirag P Shah
2011-01-01
Full Text Available Sixteen years after scleral buckle surgery with a hydrogel episcleral exoplant, a 43-year-old woman presented with progressive binocular diplopia, ptosis, and an expanding mass in her upper eyelid. She underwent surgical removal of the hydrogel exoplant through an anterior approach. The exoplant proved to be friable, fragmented, and encapsulated in a fibrous tissue; the exoplant was removed in its entirety. Postoperatively, the eyelid mass resolved, while her diplopia and ptosis improved slightly.
Thermal Buckling and Free Vibration Analysis of Heated Functionally Graded Material Beams
Khalane Sanjay Anandrao; R. K. Gupta; P. Ramachandran; G. V. Rao
2013-01-01
The effect of temperature dependency of material properties on thermal buckling and free vibration of functionally graded material (FGM) beams is studied. The FGM beam is assumed to be at a uniform through thickness temperature, above the ambient temperature. Finite element system of equations based on the first order shear deformation theory is developed. FGM beam with axially immovable ends having the classical boundary conditions is analysed. An exhaustive set of numerical results, in term...
A model of laminar-turbulent transition based on viscous stream buckling
Kulish, Vladimir; Skote, Martin; Horak, Vladimir
2012-11-01
The model of viscous streams' buckling is used to determine values of the local Reynolds numbers, for which transition to turbulence begins. These values are then used to estimate the global critical Reynolds numbers. The method discussed in this work has been used to determine the critical values of the Reynolds number in some well-known flows, e. g. flow over a flat plate, circular pipe flow and free jets. The values thus found agree well with the known critical Re.
Vortex-induced buckling of a viscous drop impacting a pool
Li, Erqiang
2017-07-20
We study the intricate buckling patterns which can form when a viscous drop impacts a much lower viscosity miscible pool. The drop enters the pool by its impact inertia, flattens, and sinks by its own weight while stretching into a hemispheric bowl. Upward motion along the outer bottom surface of this bowl produces a vortical boundary layer which separates along its top and rolls up into a vortex ring. The vorticity is therefore produced in a fundamentally different way than for a drop impacting a pool of the same liquid. The vortex ring subsequently advects into the bowl, thereby stretching the drop liquid into ever thinner sheets, reaching the micron level. The rotating motion around the vortex pulls in folds to form multiple windings of double-walled toroidal viscous sheets. The axisymmetric velocity field thereby stretches the drop liquid into progressively finer sheets, which are susceptible to both axial and azimuthal compression-induced buckling. The azimuthal buckling of the sheets tends to occur on the inner side of the vortex ring, while their folds can be stretched and straightened on the outside edge. We characterize the total stretching from high-speed video imaging and use particle image velocimetry to track the formation and evolution of the vortex ring. The total interfacial area between the drop and the pool liquid can grow over 40-fold during the first 50 ms after impact. Increasing pool viscosity shows entrapment of a large bubble on top of the drop, while lowering the drop viscosity produces intricate buckled shapes, appearing at the earliest stage and being promoted by the crater motions. We also present an image collage of the most intriguing and convoluted structures observed. Finally, a simple point-vortex model reproduces some features from the experiments and shows variable stretching along the wrapping sheets.
Vortex-induced buckling of a viscous drop impacting a pool
Li, Er Qiang; Beilharz, Daniel; Thoroddsen, Sigurdur T.
2017-07-01
We study the intricate buckling patterns which can form when a viscous drop impacts a much lower viscosity miscible pool. The drop enters the pool by its impact inertia, flattens, and sinks by its own weight while stretching into a hemispheric bowl. Upward motion along the outer bottom surface of this bowl produces a vortical boundary layer which separates along its top and rolls up into a vortex ring. The vorticity is therefore produced in a fundamentally different way than for a drop impacting a pool of the same liquid. The vortex ring subsequently advects into the bowl, thereby stretching the drop liquid into ever thinner sheets, reaching the micron level. The rotating motion around the vortex pulls in folds to form multiple windings of double-walled toroidal viscous sheets. The axisymmetric velocity field thereby stretches the drop liquid into progressively finer sheets, which are susceptible to both axial and azimuthal compression-induced buckling. The azimuthal buckling of the sheets tends to occur on the inner side of the vortex ring, while their folds can be stretched and straightened on the outside edge. We characterize the total stretching from high-speed video imaging and use particle image velocimetry to track the formation and evolution of the vortex ring. The total interfacial area between the drop and the pool liquid can grow over 40-fold during the first 50 ms after impact. Increasing pool viscosity shows entrapment of a large bubble on top of the drop, while lowering the drop viscosity produces intricate buckled shapes, appearing at the earliest stage and being promoted by the crater motions. We also present an image collage of the most intriguing and convoluted structures observed. Finally, a simple point-vortex model reproduces some features from the experiments and shows variable stretching along the wrapping sheets.
FEM Modelling of Lateral-Torsional Buckling Using Shell and Solid Elements
DEFF Research Database (Denmark)
Valeš, Jan; Stan, Tudor-Cristian
2017-01-01
The paper describes two methods of FEM modelling of I-section beams loaded by bending moments. Series of random realizations with initial imperfections following the first eigenmode of lateral-torsional buckling were created. Two independent FEM software products were used for analyses of resista...... of resistance. At the end the difference and correlation between the results as well as advantages and disadvantages of both methods are discussed....
A comparative computational study of the electronic properties of planar and buckled silicene
Behera, Harihar; Mukhopadhyay, Gautam
2012-01-01
Using full potential density functional calculations within local density approximation (LDA), we report our investigation of the structural electronic properties of silicene (the graphene analogue of silicon), the strips of which has been synthesized recently on Ag(110) and Ag(100) surfaces. An assumed planar and an optimized buckled two dimensional (2D) hexagonal structures have been considered for comparisons of their electronic properties. Planar silicene shows a gapless band structure an...
Directory of Open Access Journals (Sweden)
Daniel da Rocha Lucena
2009-04-01
Full Text Available If the ocular media are clear, indirect binocular ophthalmoscopy allows retinal detachment and retinal tear identification and treatment under direct visualization. However, if opacities are present preventing direct fundus examination, ultrasonography becomes the most important tool for evaluating the posterior segment. In addition, ultrasonography can be useful in retinal tear treatment by guiding cryotherapy. In this article we describe a rhegmatogenous retinal detachment treatment technique applied to a patient with corneal opacity. Cryopexy and circumferential and radial buckle positioning were guided by ultrasonography, resulting in retinal attachment during the 6-month follow-up period.Quando os meios oculares são transparentes, oftalmoscopia binocular indireta permite a identificação de descolamento de retina e roturas, bem como seu tratamento sob visibilização direta. Porém, em olhos que apresentam opacidades de meios impedindo o exame oftalmoscópico, a ultrassonografia constitui o exame mais importante do segmento posterior do olho. Além disso, o tratamento de roturas retinianas também pode ser auxiliado pelo uso desse equipamento, orientando a crioterapia. Neste trabalho será apresentada técnica de tratamento de descolamento de retina regmatogênico, no qual a criopexia e o posicionamento dos "buckles" episclerais circunferencial e radial foram guiados pelo ultrassom em paciente com leucoma corneano. O tratamento resultou em aplicação retiniana durante o seguimento em seis meses.
Buckling analysis of stiff thin films suspended on a substrate with tripod surface relief structure
Yu, Qingmin; Chen, Furong; Li, Ming; Cheng, Huanyu
2017-09-01
A wavy configuration is a simple yet powerful structural design strategy, which has been widely used in flexible and stretchable electronics. A buckled structure created from a prestretch-contact-release process represents an early effort. Substrates with engineered surface relief structures (e.g., rectangular islands or tripod structure) have enabled stretchability to the devices without sacrificing their electric performance (e.g., high areal coverage for LEDs/photovoltaics/batteries/supercapacitors). In particular, the substrate with a tripod surface relief structure allows wrinkled devices to be suspended on a soft tripod substrate. This minimizes the contact area between devices and the deformed substrate, which contributes to a significantly reduced interfacial stress/strain. To uncover the underlying mechanism of such a design, we exploit the energy method to analytically investigate the buckling and postbuckling behaviors of stiff films suspended on a stretchable polymeric substrate with a tripod surface relief structure. Validated by finite element analysis, the predications from such an analytical study elucidate the deformed profile and maximum strain in the buckled and postbuckled stiff thin device films, providing a useful toolkit for future experimental designs.
Shape optimization of spacer grids / development of a FE model their buckling analysis
Energy Technology Data Exchange (ETDEWEB)
Kwak, B. M.; Im, S. Y.; Chang, J. H.; Jang, I. G.; Choi, K. H. [Korea Advanced Institute of Science and Technology, Taejon (Korea)
2000-04-01
An optimal design method is adopted for spacer grids. For contact analysis, a typical cell out of repeated pattern in the assembly is modeled. A commercial code, ABAQUS, is used for detailed analysis of frictional contact. For the optimization, design variables are taken from geometric parameters and several objectives are considered. The optimized shapes and resulting performances are discussed and shown satisfactory. This method is illustrated as a good design tool for structures that has complex behavior due to friction and wear. In this study considered is the buckling of spacer grids in the nuclear fuel assembly, which are required to have a sufficient strength against an accident like earthquake. Special attention is given to the modeling of the spot-welding and the constraints between the unit spacers assembled together : it is found that a proper treatment of the constraints is critical for accurate assessment of the buckling behavior including strain localization at the point of spot welding. The buckling strength of the 17 x 17 spacer grid, which is difficult to analyze due to a large number of degrees of freedom, is obtained from analysis for the smaller models 3 x 3, 5 x 5, 7 x 7 and 9 x 9 spacer grids. 9 refs., 36 figs., 8 tabs. (Author)
Directory of Open Access Journals (Sweden)
Mahdi Izadi
2015-06-01
Full Text Available Vulnerable buildings and their rehabilitation are important problems for earthquake regions. In recent decades the goal of building rehabilitation and strengthening has gained different rehabilitation systems. However, most of these strengthening techniques disturb the occupants, who must vacate the building during renovation. Several retrofitting techniques such as addition masonry infill wall, application of buckling restrained braces and local modification of components has been studied in order to improve the overall seismic performance of such buildings. In response to many of the practical issues and economic considerations, engineers use often convergent unbuckling steel bracing frames as the lateral load resisting system during an earthquake.This kind of bracings increases the hardness and strength of concrete structures.The aim of the present study is the evaluation and comparison of seismic performance and retrofitting of an existing 7-storeys concrete structure with buckling restrained bracings and shear walls by nonlinear static procedure (NSP and accordance with cod-361. The results show that the buckling restrained bracing, decreased drift to acceptable levels and Structure behaves on the life safety of performance level.
Lai, Changliang; Wang, Junbiao; Liu, Chuang
2014-10-01
Six typical composite grid cylindrical shells are constructed by superimposing three basic types of ribs. Then buckling behavior and structural efficiency of these shells are analyzed under axial compression, pure bending, torsion and transverse bending by finite element (FE) models. The FE models are created by a parametrical FE modeling approach that defines FE models with original natural twisted geometry and orients cross-sections of beam elements exactly. And the approach is parameterized and coded by Patran Command Language (PCL). The demonstrations of FE modeling indicate the program enables efficient generation of FE models and facilitates parametric studies and design of grid shells. Using the program, the effects of helical angles on the buckling behavior of six typical grid cylindrical shells are determined. The results of these studies indicate that the triangle grid and rotated triangle grid cylindrical shell are more efficient than others under axial compression and pure bending, whereas under torsion and transverse bending, the hexagon grid cylindrical shell is most efficient. Additionally, buckling mode shapes are compared and provide an understanding of composite grid cylindrical shells that is useful in preliminary design of such structures.
The fluid mechanics of scleral buckling surgery for the repair of retinal detachment.
Foster, William Joseph; Dowla, Nadia; Joshi, Saurabh Y; Nikolaou, Michael
2010-01-01
Scleral buckling is a common surgical technique used to treat retinal detachments that involves suturing a radial or circumferential silicone element on the sclera. Although this procedure has been performed since the 1960s, and there is a reasonable experimental model of retinal detachment, there is still debate as to how this surgery facilitates the re-attachment of the retina. Finite element calculations using the COMSOL Multiphysics system are utilized to explain the influence of the scleral buckle on the flow of sub-retinal fluid in a physical model of retinal detachment. We found that, by coupling fluid mechanics with structural mechanics, laminar fluid flow and the Bernoulli effect are necessary for a physically consistent explanation of retinal reattachment. Improved fluid outflow and retinal reattachment are found with low fluid viscosity and rapid eye movements. A simulation of saccadic eye movements was more effective in removing sub-retinal fluid than slower, reading speed, eye movements in removing subretinal fluid. The results of our simulations allow us to explain the physical principles behind scleral buckling surgery and provide insight that can be utilized clinically. In particular, we find that rapid eye movements facilitate more rapid retinal reattachment. This is contradictory to the conventional wisdom of attempting to minimize eye movements.
Methods to Analyze Flexural Buckling of the Consequent Slabbed Rock Slope under Top Loading
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Hongyan Liu
2016-01-01
Full Text Available The consequent slabbed rock slope is prone to flexural buckling failure under its self-weight and top loading. However, nearly none of the existing studies consider the effect of the top loading on the slope flexural critical buckling height (CBH. Therefore, on the basis of Euler’s Method and the flexural buckling failure mode of the consequent slabbed rock slope, the calculation method of the CBH of the vertical slabbed rock slope under the self-weight is firstly proposed, and then it is extended to that of the consequent slabbed rock slope. The effect of slope dip angle, friction angle, and cohesion between the neighboring rock slabs and rock elastic modulus on the slope CBH is discussed. Secondly, the calculation method of the CBH of the consequent slabbed rock slope under its self-weight and top loading is proposed according to the superposition principle. Finally, on the basis of the hypothesis that the rock mechanical behavior obeys the statistical damage model, the effect of the rock mechanical parameters n and ε0 on the slope CBH is studied. The results show that the rock strength has much effect on the slope CBH. If the rock is supposed to be a linear elastic body without failure in Euler’s Method, the result from it is the maximum of the slope CBH.
Buckling of Nonprismatic Column on Varying Elastic Foundation with Arbitrary Boundary Conditions
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Ahmad A. Ghadban
2017-01-01
Full Text Available Buckling of nonprismatic single columns with arbitrary boundary conditions resting on a nonuniform elastic foundation may be considered as the most generalized treatment of the subject. The buckling differential equation for such columns is extremely difficult to solve analytically. Thus, the authors propose a numerical approach by discretizing the column into a finite number of segments. Each segment has constants E (modulus of elasticity, I (moment of inertia, and β (subgrade stiffness. Next, an exact analytical solution is derived for each prismatic segment resting on uniform elastic foundation. These segments are then assembled in a matrix from which the critical buckling load is obtained. The derived formulation accounts for different end boundary conditions. Validation is performed by benchmarking the present results against analytical solutions found in the literature, showing excellent agreement. After validation, more examples are solved to illustrate the power and flexibility of the proposed method. Overall, the proposed method provides reasonable results, and the examples solved demonstrate the versatility of the developed approach and some of its many possible applications.
Upgrading the seismic capacity of existing RC buildings using buckling restrained braces
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Hamdy Abou-Elfath
2017-06-01
Full Text Available Many existing RC buildings do not meet the lateral strength requirements of current seismic codes and are vulnerable to significant damage or collapse in the event of future earthquakes. In the past few decades, buckling-restrained braces have become increasingly popular as a lateral force resisting system because of their capability of improving the strength, the stiffness and the energy absorbing capacity of structures. This study evaluates the seismic upgrading of a 6-story RC-building using single diagonal buckling restrained braces. Seismic evaluation in this study has been carried out by static pushover analysis and time history earthquake analysis. Ten ground motions with different PGA levels are used in the analysis. The mean plus one standard deviation values of the roof-drift ratio, the maximum story drift ratio, the brace ductility factors and the member strain responses are used as the basis for the seismic performance evaluations. The results obtained in this study indicate that strengthening of RC buildings with buckling restrained braces is an efficient technique as it significantly increases the PGA capacity of the RC buildings. The results also indicate the increase in the PGA capacity of the RC building with the increase in the amount of the braces.
Adhesion-governed buckling of thin-film electronics on soft tissues
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Bo Wang
2016-01-01
Full Text Available Stretchable/flexible electronics has attracted great interest and attention due to its potentially broad applications in bio-compatible systems. One class of these ultra-thin electronic systems has found promising and important utilities in bio-integrated monitoring and therapeutic devices. These devices can conform to the surfaces of soft bio-tissues such as the epidermis, the epicardium, and the brain to provide portable healthcare functionalities. Upon contractions of the soft tissues, the electronics undergoes compression and buckles into various modes, depending on the stiffness of the tissue and the strength of the interfacial adhesion. These buckling modes result in different kinds of interfacial delamination and shapes of the deformed electronics, which are very important to the proper functioning of the bio-electronic devices. In this paper, detailed buckling mechanics of these thin-film electronics on elastomeric substrates is studied. The analytical results, validated by experiments, provide a very convenient tool for predicting peak strain in the electronics and the intactness of the interface under various conditions.
Flow-induced buckling of flexible shells with non-zero Gaussian curvatures and thin spots.
Chang, Gary Han; Modarres-Sadeghi, Yahya
2017-03-29
We study the influence of one or multiple thin spots on the flow-induced instabilities of flexible shells of revolution with non-zero Gaussian curvatures. The shell's equation of motion is described by a thin doubly-curved shell theory and is coupled with perturbed flow pressure, calculated based on an inviscid flow model. We show that for shells with positive Gaussian curvatures conveying fluid, the existence of a thin spot results in a localized flow-induced buckling response of the shell in the neighborhood of the thin spot, and significantly reduces the critical flow velocity for buckling instability. For shells with negative Gaussian curvatures, the buckling response is extended along the shell's characteristic lines and the critical flow velocity is only slightly reduced. We also show that the length scale of the localized deformation generated by a thin spot is proportional to the shell's global thickness when the stiffness of the thin spot is negligible compared with the stiffness of the rest of the shell. When two thin spots exist at a distance, their influences are independent from each other for shells with positive Gaussian curvatures, but large-scale deformations can be created due to multiple thin spots on shells with negative curvatures, depending on the thin spots' relative position.
High-Fidelity Buckling Analysis of Composite Cylinders Using the STAGS Finite Element Code
Hilburger, Mark W.
2014-01-01
Results from previous shell buckling studies are presented that illustrate some of the unique and powerful capabilities in the STAGS finite element analysis code that have made it an indispensable tool in structures research at NASA over the past few decades. In particular, prototypical results from the development and validation of high-fidelity buckling simulations are presented for several unstiffened thin-walled compression-loaded graphite-epoxy cylindrical shells along with a discussion on the specific methods and user-defined subroutines in STAGS that are used to carry out the high-fidelity simulations. These simulations accurately account for the effects of geometric shell-wall imperfections, shell-wall thickness variations, local shell-wall ply-gaps associated with the fabrication process, shell-end geometric imperfections, nonuniform applied end loads, and elastic boundary conditions. The analysis procedure uses a combination of nonlinear quasi-static and transient dynamic solution algorithms to predict the prebuckling and unstable collapse response characteristics of the cylinders. Finally, the use of high-fidelity models in the development of analysis-based shell-buckling knockdown (design) factors is demonstrated.
Deflection and Buckling behaviour of simply supported nanocomposite beams under FSDT approach
Pramod kumar, P.; Subbarao, V. V.; Sarath Chandra, S.; Malathi, B.
2017-08-01
Due to their high strength-to-weight ratio, carbon nanotube (CNT) reinforced polymer composites are being considered as one of the most promising nanocomposites which can improve the performance when used in structural applications. The deflection and buckling behavior are the most important parameters needs to be considered in the design of structural members like beams, plates and shells. In the present paper the elastic constants of CNT reinforced polymer composites has been evaluated by using Mori-Tanaka micromechanics approach. Knowing the elastic properties of CNT reinforced polymer composites, an analytical study is being conducted to investigate the deflection and buckling behaviour of nanocomposites beams for different CNT volume fractions at different boundary conditions using first order shear deformation theory. The effect of stacking sequence and CNT radius on the deflection and buckling of beam is also been presented. This study is being conducted primarily with an intension to examine the stiffening effect of CNTs when used in polymer composites as reinforcement.
A piezoelectric energy harvester for broadband rotational excitation using buckled beam
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Zhengqiu Xie
2018-01-01
Full Text Available This paper proposes a rotational energy harvester using a piezoelectric bistable buckled beam to harvest low-speed rotational energy. The proposed harvester consists of a piezoelectric buckled beam with a center magnet, and a rotary magnet pair with opposite magnetic poles mounted on a revolving host. The magnetic plucking is used to harvest the angular kinetic energy of the host. The nonlinear snap-through mechanism is utilized to improve the vibration displacement and output voltage of the piezoelectric layer over a wide rotation frequency range. Theoretical simulation and experimental results show that the proposed energy harvester can yield a stable average output power ranging between 6.91-48.01 μW over a rotation frequency range of 1-14 Hz across a resistance load of 110 kΩ. Furthermore, dual attraction magnets were employed to overcome the suppression phenomenon at higher frequencies, which yields a broadband and flat frequency response over 6-14 Hz with the output power reaching 42.19-65.44 μW, demonstrating the great potential of the bistable buckled beam for wideband rotation motion energy harvesting.
On a compressed elastic-plastic column optimized for post-buckling behaviour
Bielski, Jan; Bochenek, Bogdan
2008-12-01
A model of a column is proposed in order to analyse the post-buckling behaviour of a structural element in the elastic-plastic deformation range. The ideal two point I-section applied here simplifies the deformation analysis, that is, the problem of development of plastic zones in a section is eliminated, but still gives the possibility for qualitative analysis and optimization of the post-critical equilibrium paths. The coefficients of linear or parabolic variability of thickness of the flanges and their distance (web width) are accepted as model parameters and hence could be used for design variables in the optimization procedure. Moreover, the stiffness of an additional elastic support of the free end of the beam is also included as a parameter or design variable. A material model is employed with non-linear asymptotic isotropic hardening without the Bauschinger effect. Change of the tangent modulus is continuous and smooth during the transition from the elastic to plastic deformation range. The main goal of the analysis is to determine the values of the design variables for which the post-critical equilibrium paths are stable at least in the specified range of a generalized displacement. The constraints for the constant volume of the flanges and web material are applied. The inequality constraints are imposed on the flange thickness and web width. Various formulations of the optimization problem are proposed for all types of non-linear behaviour, including elastic or plastic buckling and elastic or elastic-plastic post-buckling deformation.
Prakash, T.; Sundararajan, N.; Ganapathi, M.
2007-01-01
Here, the dynamic thermal buckling behavior of functionally graded spherical caps is studied considering geometric nonlinearity based on von Karman's assumptions. The formulation is based on first-order shear deformation theory and it includes the in-plane and rotary inertia effects. The material properties are graded in the thickness direction according to the power-law distribution in terms of volume fractions of the material constituents. The effective material properties are evaluated using homogenization method. The governing equations obtained using finite element approach are solved employing the Newmark's integration technique coupled with a modified Newton-Raphson iteration scheme. The pressure load corresponding to a sudden jump in the maximum average displacement in the time history of the shell structure is taken as the dynamic buckling load. The present model is validated against the available isotropic case. A detailed numerical study is carried out to highlight the influences of shell geometries, power law index of functional graded material and boundary conditions on the dynamic buckling load of shallow spherical shells.
Stam, Samantha; Gardel, Margaret
Viscoelastic networks of biopolymers coordinate the motion of intracellular objects during transport. These networks have nonlinear mechanical properties due to events such as filament buckling or breaking of cross-links. The influence of such nonlinear properties on the time and length scales of transport is not understood. Here, we use in vitro networks of actin and the motor protein myosin II to clarify how intracellular forces regulate active diffusion. We observe two transitions in the mean-squared displacement of cross-linked actin with increasing motor concentration. The first is a sharp transition from initially subdiffusive to diffusive-like motion that requires filament buckling but does not cause net contraction of the network. Further increase of the motor density produces a second transition to network rupture and ballistic actin transport. This corresponds with an increase in the correlation of motion and thus may be caused when forces propagate far enough for global motion. We conclude that filament buckling and overall network contraction require different amounts of force and produce distinct transport properties. These nonlinear transitions may act as mechanical switches that can be turned on to produce observed motion within cells.
Rad, Maryam Alsadat; Tijjani, Auwal Shehu; Ahmad, Mohd Ridzuan; Auwal, Shehu Muhammad
2016-12-23
This paper proposes a new technique for real-time single cell stiffness measurement using lead zirconate titanate (PZT)-integrated buckling nanoneedles. The PZT and the buckling part of the nanoneedle have been modelled and validated using the ABAQUS software. The two parts are integrated together to function as a single unit. After calibration, the stiffness, Young's modulus, Poisson's ratio and sensitivity of the PZT-integrated buckling nanoneedle have been determined to be 0.7100 N·m(-1), 123.4700 GPa, 0.3000 and 0.0693 V·m·N(-1), respectively. Three Saccharomyces cerevisiae cells have been modelled and validated based on compression tests. The average global stiffness and Young's modulus of the cells are determined to be 10.8867 ± 0.0094 N·m(-1) and 110.7033 ± 0.0081 MPa, respectively. The nanoneedle and the cell have been assembled to measure the local stiffness of the single Saccharomyces cerevisiae cells The local stiffness, Young's modulus and PZT output voltage of the three different size Saccharomyces cerevisiae have been determined at different environmental conditions. We investigated that, at low temperature the stiffness value is low to adapt to the change in the environmental condition. As a result, Saccharomyces cerevisiae becomes vulnerable to viral and bacterial attacks. Therefore, the proposed technique will serve as a quick and accurate process to diagnose diseases at early stage in a cell for effective treatment.
Ultra-stretchable conductors based on buckled super-aligned carbon nanotube films.
Yu, Yang; Luo, Shu; Sun, Li; Wu, Yang; Jiang, Kaili; Li, Qunqing; Wang, Jiaping; Fan, Shoushan
2015-06-14
Ultra-stretchable conductors are fabricated by coating super-aligned carbon nanotube (SACNT) films on pre-strained polydimethylsiloxane (PDMS) substrates and forming buckled SACNT structures on PDMS after release of the pre-strain. The parallel SACNT/PDMS conductors demonstrate excellent stability with normalized resistance changes of only 4.1% under an applied strain as high as 200%. The SACNT/PDMS conductors prepared with cross-stacked SACNT films show even lower resistance variation. The parallel SACNT/PDMS conductors exhibit high durability with a resistance increase of less than 5% after 10,000 cycles at 150% strain. In situ microscopic observations demonstrate that the buckled SACNT structures are straightened during the stretching process with reversible morphology evolution and thus the continuous SACNT conductive network can be protected from fracture. Due to the excellent electrical and mechanical properties of SACNT films and the formation of the buckled structure, SACNT/PDMS films exhibit high stretchability and durability, possessing great potential for use as ultra-stretchable conductors for wearable electronics, sensors, and energy storage devices.
Buckling Analysis of Functionally Graded Material Plates Using Higher Order Shear Deformation Theory
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B. Sidda Reddy
2013-01-01
Full Text Available The prime aim of the present study is to present analytical formulations and solutions for the buckling analysis of simply supported functionally graded plates (FGPs using higher order shear deformation theory (HSDT without enforcing zero transverse shear stresses on the top and bottom surfaces of the plate. It does not require shear correction factors and transverse shear stresses vary parabolically across the thickness. Material properties of the plate are assumed to vary in the thickness direction according to a power law distribution in terms of the volume fractions of the constituents. The equations of motion and boundary conditions are derived using the principle of virtual work. Solutions are obtained for FGPs in closed-form using Navier’s technique. Comparison studies are performed to verify the validity of the present results from which it can be concluded that the proposed theory is accurate and efficient in predicting the buckling behavior of functionally graded plates. The effect of side-to-thickness ratio, aspect ratio, modulus ratio, the volume fraction exponent, and the loading conditions on the critical buckling load of FGPs is also investigated and discussed.
Scleral buckling for retinal detachment in Ibadan, Sub-Saharan Africa: anatomical and visual outcome
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Oluleye TS
2013-05-01
Full Text Available TS Oluleye, OA Ibrahim, BA OlusanyaRetina and Vitreous Unit, Department of Ophthalmology, University College Hospital, Ibadan, NigeriaBackground: Scleral buckle surgery is not a commonly performed surgical procedure in Sub-Saharan Africa due to a paucity of trained vitreo retinal surgeons. The aim of the study was to review sclera buckle procedures with a view to evaluating the anatomical and visual outcomes.Methods: Case records of patients that had scleral buckle surgery at the Retina Unit of the University College Hospital, Ibadan, Nigeria, between 2007 and 2010 were reviewed. Information retrieved included patients' demographics, duration of symptoms, and presenting vision. Other information included site of retinal break, extent of retinal detachment, involvement of the fellow eye, and macular involvement. Postoperative retina reattachment and postoperative visual acuity were also recorded. Proportions and percentages were used to analyze data.Results: Forty five eyes of 42 patients were studied with a male to female ratio of 1.6:1. The mean age was 47.7 years (±17.6 years. The median duration before presentation was 3 months (range: 5 days – 156 months. Subtotal retinal detachment was found in 35 eyes (77.8% while total retinal detachment occurred in ten eyes (22.2%. Thirty four eyes (75.6% had "macular off" detachments. At 6 weeks, there was an improvement in visual acuity in 23 eyes (51.1%, while visual acuity remained the same in nine eyes (20% and was worse in 13 eyes (28.9%. Anatomical attachment was seen in 43 eyes (95.6% on the operation table, in 40 eyes (90.9% at first day postoperatively and in 32 eyes (86.5% at 6 weeks after surgery.Conclusion: Outcome of sclera buckle surgery for rhegmatogenous retinal detachment may be improved in developing countries of Sub Sahara Africa if adequate awareness is created to educate the populace on early presentation.Keywords: retinal detachment, scleral buckle surgery, anatomical and visual
Zobel, Isabelle; Erfani, Tahereh; Bennell, Kim L; Makovey, Joanna; Metcalf, Ben; Chen, Jian Sheng; March, Lyn; Zhang, Yuqing; Eckstein, Felix; Hunter, David J
2016-06-24
Knee osteoarthritis (OA) is one of the most frequent causes of limited mobility and diminished quality of life. Pain is the main symptom that drives individuals with knee OA to seek medical care and a recognized antecedent to disability and eventually joint replacement. Evidence shows that patients with symptomatic OA experience fluctuations in pain severity. Mechanical insults to the knee such as injury and buckling may contribute to pain exacerbation. Our objective was to examine whether knee injury and buckling (giving way) are triggers for exacerbation of pain in persons with symptomatic knee OA. We conducted a case-crossover study, a novel methodology in which participants with symptomatic radiographic knee OA who have had knee pain exacerbations were used as their own control (self-matched design), with all data collected via the Internet. Participants were asked to log-on to the study website and complete an online questionnaire at baseline and then at regular 10-day intervals for 3 months (control periods)-a total of 10 questionnaires. They were also instructed to go to the website and complete pain exacerbation questionnaires when they experienced an isolated incident of knee pain exacerbation (case periods). A pain exacerbation "case" period was defined as an increase of ≥2 compared to baseline. At each contact the pain exacerbation was designated a case period, and at all other regular 10-day contacts (control periods) participants were asked about knee injuries during the previous 7 days and knee buckling during the previous 2 days. The relationship of knee injury and buckling to the risk of pain exacerbation was examined using conditional logistic regression models. The analysis included 157 participants (66% women, mean age: 62 years, mean BMI: 29.5 kg/m(2)). Sustaining a knee injury was associated with experiencing a pain exacerbation (odds ratio [OR] 10.2, 95% CI 5.4, 19.3) compared with no injury. Knee buckling was associated with experiencing a
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Murayama, Y.; Suda, K.; Ichinomiya, T.; Shinbo, H. [Kajima Corp., Tokyo (Japan)
1994-10-31
For RC (reinforced concrete) columns such as towers of long-span cable-stayed bridges or high-rise piers, there is desired development of an analytical method including a method of arranging reinforcing bars for increasing their ductility against strong earthquake motion. For this, it is necessary to investigate their characteristics after their being rendered to maximum load and their final states, and hence there must be newly investigated the properties of a plastic hinge formed on the bottom of the column, particularly determination of the buckling point of reinforcing bars and a hysteresis model after the buckling. In this study, there is developed a direct method of measuring the stress of reinforcing bars embedded in a model specimen which is conventionally difficult to be measured, and there is investigated the stress-strain hysteresis of the bars before and after the buckling thereof. The principle of the method of measuring the stress is such that only a local minimum portion of objective reinforcing bars is rendered to rf quenching, and a distortion gauge is sticked to the center of the quenching. This is based upon a fact that that portion keeps a linear relationship between the stress and the strain even if a host material is yielded. On the basis of an experimental result, a mechanism of buckling of these bars is clarified and a buckling model of the reinforcing bars at the plastic hinge. 6 refs., 15 figs., 2 tabs.
Liu, P. F.; Zheng, J. Y.
2013-12-01
Multiple delamination causes severe degradation of the stiffness and strength of composites. Interactions between multiple delamination, and buckling and postbuckling under compressive loads add the complexity of mechanical properties of composites. In this paper, the buckling, postbuckling and through-the-width multiple delamination of symmetric and unsymmetric composite laminates are studied using 3D FEA, and the virtual crack closure technique with two delamination failure criteria: B-K law and power law is used to predict the delamination growth and to calculate the mixed-mode energy release rate. The compressive load-strain curves, load-central deflection curves and multiple delamination process for eight composite specimens with different initial delamination sizes and their distributions as well as two angle-ply configurations 04//(± θ)6//04 ( θ = 0° and 45°, and "//" denotes the delaminated interface) are comparatively studied. From numerical results, the unsymmetry decreases the local buckling load and initial delamination load, but does not affect the global buckling load compared with the symmetric laminates. Besides, the unsymmetry affects the unstable delamination and buckling behaviors of composite laminates largely when the initial multiple delamination sizes are relatively small.
Gursel Ozkurt, Zeynep; Demirci, Hakan
2017-01-01
To evaluate the use of subtenon amikacin injection for the treatment of Nocardia asteroides orbital cellulitis in a patient with a history of scleral buckle surgery. Case report. A 79-year-old diabetic woman presented with an 8-month history of diplopia, discharge, and swelling around her left eye. She had a scleral buckle surgery in this eye about 15 years ago. Examination of the left eye showed a visual acuity of 20/80, swollen and ptotic upper eyelid, chemotic conjunctiva, and limited extraocular motility. Magnetic resonance imaging showed an abscess under the scleral buckle. The scleral buckle was removed, and the abscess under the scleral buckle was drained. N. asteroides grew on the culture. Despite 4 months of the systemic trimethoprim/sulfamethoxazole and the topical fortified amikacin therapy, her infection worsened. After 5 monthly subtenon amikacin injections, the infection regressed dramatically, and her vision improved to 20/70. She used the systemic trimethoprim/sulfamethoxazole for 10 more months. After a 1-year follow-up, her external examination was normal, except for the left upper eyelid ptosis. Subtenon amikacin injection can be added to the regimen for N. asteroides orbital cellulitis, of which surgical drainage, systemic and topical antibiotic therapies are not enough to control infection.
Hagihara, Seiya; Miyazaki, Noriyuki
1998-05-01
Cylindrical shells are utilized as structural elements of nuclear power plants, heat exchangers or pressure vessels, which are operated under elevated temperature. Creep buckling is one of the failure modes of structures at elevated temperature. In some experiments conducted by other authors, axially compressive cylindrical shells with a large ratio of radius to thickness were observed to buckle with circumferential waves. It is observed that the circumferential waves occur due to bifurcation buckling. But, the critical time and the minimum loading for bifurcation buckling obtained from calculations of finite element analyses are not in very good agreement with those of the experiments. One of the reasons for the disagreement is considered to be that the creep constitutive equations employed in many previous analyses represent the steady creep. The creep phenomena usually have primary creep period, steady creep one and tertiary creep one. A creep strain - time relation through the three periods can be simulated by using a constitutive equation based on creep damage mechanics. In the present analysis, we analyzed the bifurcation creep buckling of circular cylindrical shells subjected to axial compression by the use of the finite element method taking account of the creep damage mechanics proposeol by of Kachanov-Rabotonov.
Ajori, S.; Haghighi, S.; Ansari, R.
2017-12-01
The buckling analysis of functionalized carbon nanotubes (CNTs) is of great importance for the better understanding of mechanical behavior of nanocomposites. The buckling behavior of carbene-functionalized CNTs (cfCNTs) under physical adsorption of polymer chains (cfCNTs/polymers) is studied in this paper by the classical molecular dynamics (MD) simulations. In this regard, to investigate the interactions between non-covalent polymer chains and cfCNTs, two different non-covalent functional groups, i.e. polycarbonate (PC) and polypropylene (PP), are selected. The findings are compared with those of pure CNTs under the physical adsorption of polymer chains (pCNTs/polymers). The obtained results show that at a given weight percentage of non-covalent functional groups, the gyration radius of cfCNTs/polymers is higher than that of pCNTs/polymers. Furthermore, an increase in the critical buckling force of cfCNTs/polymers is dependent on the type of non-covalent polymer chains. For cfCNTs/PC and cfCNTs/PP, the critical buckling force is respectively lower and higher than that of pCNTs/polymers for the similar weight percentage of non-covalent functional groups. In addition, it is found that the critical buckling strain of cfCNTs/polymers is smaller than that of pCNTs/polymers for the same weight percentage of non-covalent polymer chains.
Wang, S. B.; Fang, Y. Z.; Jia, H. K.; Li, L. A.; Wang, Z. Y.; Zhang, S. J.
2010-11-01
Thin films are used increasingly in technological applications involving microelectromechanical systems, optical reflectors, filters, dielectric stacks, and lithographic resists. However, although the mechanical properties of these submicrometer-thick films are paramount for their effective utilization, many issues remain unresolved to date on the measurement of such properties in thin-film systems. In this paper, an electromechanical device is designed to study the mechanical properties and stability of thin films using two piezoelectric translators. The buckling propagation of thin compressed titanium films deposited on organic glass substrates is investigated utilizing an optical microscope. The rigid-body displacement of the observation field, which is caused by external uniaxial compressive loading, is calculated by the digital image correlation method. Edge detection and filter are carried out to obtain binary images in which the edges of the buckle are obvious, and false noise is eliminated. Therefore, a series of binary images obtained under different loads contains the information on buckling propagation. Further, rigid-body displacement could be compensated for digitally, and the propagation of buckles could be singled out. The experimental results confirm the theoretical proposition that "subcritical" defects can be used to indicate the rigid-body displacement of a substrate. The same method can be used to investigate other problems associated with film buckling.
Ye, Hong-Ling; Wang, Wei-Wei; Chen, Ning; Sui, Yun-Kang
2017-10-01
The purpose of the present work is to study the buckling problem with plate/shell topology optimization of orthotropic material. A model of buckling topology optimization is established based on the independent, continuous, and mapping method, which considers structural mass as objective and buckling critical loads as constraints. Firstly, composite exponential function (CEF) and power function (PF) as filter functions are introduced to recognize the element mass, the element stiffness matrix, and the element geometric stiffness matrix. The filter functions of the orthotropic material stiffness are deduced. Then these filter functions are put into buckling topology optimization of a differential equation to analyze the design sensitivity. Furthermore, the buckling constraints are approximately expressed as explicit functions with respect to the design variables based on the first-order Taylor expansion. The objective function is standardized based on the second-order Taylor expansion. Therefore, the optimization model is translated into a quadratic program. Finally, the dual sequence quadratic programming (DSQP) algorithm and the global convergence method of moving asymptotes algorithm with two different filter functions (CEF and PF) are applied to solve the optimal model. Three numerical results show that DSQP&CEF has the best performance in the view of structural mass and discretion.
The conflicting role of buckled structure in phonon transport of 2D group-IV and group-V materials.
Peng, Bo; Zhang, Dequan; Zhang, Hao; Shao, Hezhu; Ni, Gang; Zhu, Yongyuan; Zhu, Heyuan
2017-06-08
Controlling heat transport through material design is one important step toward thermal management in 2D materials. To control heat transport, a comprehensive understanding of how structure influences heat transport is required. It has been argued that a buckled structure is able to suppress heat transport by increasing the flexural phonon scattering. Using a first principles approach, we calculate the lattice thermal conductivity of 2D mono-elemental materials with a buckled structure. Somewhat counterintuitively, we find that although 2D group-V materials have a larger mass and higher buckling height than their group-IV counterparts, the calculated κ of blue phosphorene (106.6 W mK(-1)) is nearly four times higher than that of silicene (28.3 W mK(-1)), while arsenene (37.8 W mK(-1)) is more than fifteen times higher than germanene (2.4 W mK(-1)). We report for the first time that a buckled structure has three conflicting effects: (i) increasing the Debye temperature by increasing the overlap of the pz orbitals, (ii) suppressing the acoustic-optical scattering by forming an acoustic-optical gap, and (iii) increasing the flexural phonon scattering. The former two, corresponding to the harmonic phonon part, tend to enhance κ, while the last one, corresponding to the anharmonic part, suppresses it. This relationship between the buckled structure and phonon behaviour provides insight into how to control heat transport in 2D materials.
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Maryam Alsadat Rad
2016-12-01
Full Text Available This paper proposes a new technique for real-time single cell stiffness measurement using lead zirconate titanate (PZT-integrated buckling nanoneedles. The PZT and the buckling part of the nanoneedle have been modelled and validated using the ABAQUS software. The two parts are integrated together to function as a single unit. After calibration, the stiffness, Young’s modulus, Poisson’s ratio and sensitivity of the PZT-integrated buckling nanoneedle have been determined to be 0.7100 N·m−1, 123.4700 GPa, 0.3000 and 0.0693 V·m·N−1, respectively. Three Saccharomyces cerevisiae cells have been modelled and validated based on compression tests. The average global stiffness and Young’s modulus of the cells are determined to be 10.8867 ± 0.0094 N·m−1 and 110.7033 ± 0.0081 MPa, respectively. The nanoneedle and the cell have been assembled to measure the local stiffness of the single Saccharomyces cerevisiae cells The local stiffness, Young’s modulus and PZT output voltage of the three different size Saccharomyces cerevisiae have been determined at different environmental conditions. We investigated that, at low temperature the stiffness value is low to adapt to the change in the environmental condition. As a result, Saccharomyces cerevisiae becomes vulnerable to viral and bacterial attacks. Therefore, the proposed technique will serve as a quick and accurate process to diagnose diseases at early stage in a cell for effective treatment.
Liao, Ming-Liang
2017-11-01
This study used molecular dynamics simulations to investigate buckling behaviors of cantilevered open-tip carbon nanocones (CNCs) subjected to transverse loading. Some interesting findings were attained in the study. The critical angles of the CNCs were observed to decrease with increases in the temperature, cone length, top diameter, and apex angle of the CNCs. While the critical loads of the CNCs were found to decrease with increasing temperature and cone length, they were noted to increase with enlargement of the top diameter and apex angle. The observed temperature effects were more evident as the cone length increased. In addition, each of the studied CNCs exhibited a near-bottom-indented buckling morphology at the examined temperatures, which is quite different from a top-center-indented buckling morphology of an open-tip CNC under pure bending. Accordingly, these results may provide beneficial information to the designs of ultra-sensitive mass detectors using CNCs.
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Tan Li
2017-01-01
Full Text Available This paper is devoted to develop a new 8-node higher-order hybrid stress element (QH8 for free vibration and buckling analysis based on the Mindlin/Reissner plate theory. In particular, a simple explicit expression of a refine method with an adjustable constant is introduced to improve the accuracy of the analysis. A combined mass matrix for natural frequency analysis and a combined geometric stiffness matrix for buckling analysis are obtained using the refined method. It is noted that numerical examples are presented to show the validity and efficiency of the present element for free vibration and buckling analysis of plates. Furthermore, satisfactory accuracy for thin and moderately thick plates is obtained and it is free from shear locking for thin plate analysis and can pass the nonzero shear stress patch test.
Noor, Ahmed K.; Burton, W. S.
1992-01-01
Analytic three-dimensional elasticity solutions are developed for the free vibration and buckling of thermally stressed rectangular multilayered angle-ply anisotropic plates which are assumed to have an antisymmetric lamination with respect to the middle plane. Sensitivity derivatives are evaluated and used to investigate the sensitivity of the vibration and buckling responses to variations in the different lamination and material parameters of the plate. A Duhamel-Neumann-type constitutive model is used, and the material properties are assumed to be independent of temperature. Numerical results are presented, showing the effects of variations in the material characteristics and fiber orientation of different layers, as well as the effect of initial thermal deformation on the vibrational and buckling responses of the plate.
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Alexandre Achille Grandinetti
2013-04-01
Full Text Available PURPOSE: To evaluate the changes in corneal topography after 20-gauge pars plana vitrectomy associated with scleral buckling for the repair of rhegmatogenous retinal detachment. METHODS: Twenty-five eyes of 25 patients with rhegmatogenous retinal detachment were included in this study. 20-gauge pars plana vitrectomy associated with scleral buckling was performed in all patients. The corneal topography of each was measured before surgery and one week, one month, and three months after surgery by computer-assisted videokeratoscopy. RESULTS: A statistically significant central corneal steepening (average, 0,9 D , p<0,001 was noted one week after surgery. The total corneal astigmatism had a significant increase in the first postoperative month (p=0,007. All these topographic changes persisted for the first month but returned to preoperative values three months after the surgery. CONCLUSION: Pars plana vitrectomy with scleral buckling was found to induce transient changes in corneal topography.
Current research on shear buckling and thermal loads with PASCO: Panel Analysis and Sizing Code
Stroud, W. J.; Greene, W. H.; Anderson, M. S.
1981-01-01
The PASCO computer program to obtain the detailed dimensions of optimum stiffened composite structural panels is described. Design requirements in terms of inequality constraints can be placed on buckling loads or vibration frequencies, lamina stresses and strains, and overall panel stiffness for each of many load conditions. General panel cross sections can be treated. An analysis procedure involving a smeared orthotropic solution was investigated. The conservatism in the VIPASA solution and the danger in a smeared orthotropic solution is explored. PASCO's capability to design for thermal loadings is also described. It is emphasized that design studies illustrate the importance of the multiple load condition capability when thermal loads are present.
Dynamic analysis of a buckled asymmetric piezoelectric beam for energy harvesting
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Van Blarigan, Louis, E-mail: louis01@umail.ucsb.edu; Moehlis, Jeff [Department of Mechanical Engineering, University of California, Santa Barbara, California 93106 (United States)
2016-03-15
A model of a buckled beam energy harvester is analyzed to determine the phenomena behind the transition between high and low power output levels. It is shown that the presence of a chaotic attractor is a sufficient condition to predict high power output, though there are relatively small areas where high output is achieved without a chaotic attractor. The chaotic attractor appears as a product of a period doubling cascade or a boundary crisis. Bifurcation diagrams provide insight into the development of the chaotic region as the input power level is varied, as well as the intermixed periodic windows.
A Semi-rigorous Approach for Interaction Between Local and Global Buckling in Steel Structures
DEFF Research Database (Denmark)
Virdi, Kuldeep
With an increasing trend towards the use of higher strength materials, members in steel structures become more slender. The cross-sectional plate elements of such members also become slender, triggering possible interaction between local buckling of the flange and web elements and the overall...... the rigorous analysis of such columns is carried out using numerical techniques such as the finite difference method, rapid solutions are obtained for an otherwise very complex problem. The paper includes a parametric study aimed at examining the design of stiffened plate elements such as those used in box-girders....
Buckling And Postbuckling Of An Imperfect Plate Subjected To The Shear Load
Directory of Open Access Journals (Sweden)
Psotný Martin
2015-12-01
Full Text Available The stability analysis of an imperfect plate subjected to the shear load is presented. To solve this problem, a specialized computer program based on FEM has been created. The nonlinear finite element method equations are derived from the variational principle of minimum of total potential energy. To obtain the nonlinear equilibrium paths, the Newton-Raphson iteration algorithm is used. Corresponding levels of the total potential energy are defined. Special attention is paid to the influence of imperfections on the post-critical buckling mode. Obtained results are compared with those gained using ANSYS system.
Anderson, Melvin S.; Kennedy, David
1993-01-01
The problem considered is the development of the necessary plate stiffnesses for use in the general purpose program VICONOPT for buckling and vibration of composite plate assemblies. The required stiffnesses include the effects of transverse shear deformation and are for sinusoidal response along the plate length as required in VICONOPT. The method is based on the exact solution of the plate differential equations for a composite laminate having fully populated A, B, and D stiffness matrices which leads to an ordinary differential equation of tenth order.
Buckling of Actin-Coated Membranes under Application of a Local Force
Energy Technology Data Exchange (ETDEWEB)
Helfer, E.; Harlepp, S.; Bourdieu, L.; Robert, J.; MacKintosh, F. C.; Chatenay, D.
2001-08-20
The mechanical properties of composite membranes obtained by self-assembly of actin filaments with giant fluid vesicles are studied by micromanipulation with optical tweezers. These complexes exhibit typical mechanical features of a solid shell, including a finite in-plane shear elastic modulus ({approx}10{sup -6} N /m). A buckling instability is observed when a localized force of the order of 0.5pN is applied perpendicular to the membrane plane. Although predicted for polymerized vesicles, this is the first evidence of such an instability.
Post-buckling capacity of bi-axially loaded rectangular steel plates
DEFF Research Database (Denmark)
Jönsson, Jeppe; Bondum, T. H.
2012-01-01
Results from a detailed numerical investigation of the post-buckling behaviour of rectangular simply supported steel plates subjected to biaxial in-plane loading are presented. The Steel plates are loaded through forced edge displacements. The effects of initial imperfections, aspect ratio, plate...... for biaxial stress. It is of great interest that short wave imperfections of a lower magnitude compared to conventionally used imperfections are seen to lower the capacity of the bi-axially loaded plates. The topic is of major concern in the flange plates of long span bridges with multi box girder...
Buckling of elastomer sheets under non-uniform electro-actuation.
Bense, Hadrien; Trejo, Miguel; Reyssat, Etienne; Bico, José; Roman, Benoît
2017-04-12
Dielectric elastomer sheets undergo in-plane expansion when stimulated by a transverse electric field. We study experimentally how dielectric plates subjected to a non-uniform voltage distribution undergo buckling instabilities. Two different configurations involving circular plates are investigated: plates freely floating on a bath of water, and plates clamped on a frame. We describe theoretically the out-of-plane deformation of the plates within the framework of weakly non-linear plate equations. This study constitutes a first step of a route to control the 3D activation of dielectric elastomers.
Stroud, W. J.; Greene, W. H.; Anderson, M. S.
1984-01-01
Buckling analyses used in PASCO are summarized with emphasis placed on the shear buckling analyses. The PASCO buckling analyses include the basic VIPASA analysis, which is essentially exact for longitudinal and transverse loads, and a smeared stiffener solution, which treats a stiffened panel as an orthotropic plate. Buckling results are then presented for seven stiffened panels loaded by combinations of longitudinal compression and shear. The buckling results were obtained with the PASCO, EAL, and STAGS computer programs. The EAL and STAGS solutions were obtained with a fine finite element mesh and are very accurate. These finite element solutions together with the PASCO results for pure longitudinal compression provide benchmark calculations to evaluate other analysis procedures.
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Magnucka-Blandzi, Ewa [Institute of Mathematics, Poznan University of Technology (Poland)
2016-06-08
The study is devoted to stability of simply supported beam under axial compression. The beam is subjected to an axial load located at any point along the axis of the beam. The buckling problem has been desribed and solved mathematically. Critical loads have been calculated. In the particular case, the Euler’s buckling load is obtained. Explicit solutions are given. The values of critical loads are collected in tables and shown in figure. The relation between the point of the load application and the critical load is presented.
Khdeir, A. A.; Librescu, L.
1988-01-01
A previously developed higher-order plate theory and a technique based on the state space concept are used to investigate free vibration and buckling problems of rectangular cross-ply laminated plates. Unified results are presented for the case of arbitrary boundary conditions on two opposite edges. Good agreement is obtained with previous data for simply supported edge conditions. It is pointed out that classical laminated plate theory tends to overpredict both eigenfrequencies and buckling loads, leading to an increase of the degree of orthotropicity of individual layers and of the thickness ratio of the plate.
Ridl, Romy; Bell, David; Villeneuve, Marlene
2017-04-01
Toe buckling deformation is a temporal product of induced stresses concentrated at the base of a slope. Prolonged induced stresses may lead to yielding of an anisotropic rock mass, either through rheological creep deformation (flexural toe buckling) or brittle failure (hinge buckling). Progressive deformation can lead to the breakout at the buckled toe and ultimately result in deep seated displacements on a mountain range scale, referred to as deep seated gravitational slope deformation (DSGSD). DSGSD can have a considerable impact on civil infrastructure and should be well understood for hazard identification, to inform civil engineering design and for resource management purposes. Toe buckling deformation was identified beneath the basal sliding zone of three large (≥50 Mm3) landslides in the Cromwell Gorge, New Zealand. This area was subjected to extensive geotechnical investigations for the Clyde Hydropower Scheme. During these investigations seventeen major landslides were identified in the Cromwell Gorge and subsequently stabilised. The data from the landslide stabilisation project, including 26.7 km of boreholes and 9 km of tunnels, for the three landslides exhibiting toe buckling was made available for this study. This comprehensive database has enabled comparison and validation of numerical simulations carried out for the Cromwell Gorge. The application of numerical modelling has demonstrated that toe buckling within the Cromwell Gorge is a result of the combination of induced stresses acting on an anisotropic schistose rock mass. The induced stresses comprise: i) topographically-induced gravitational stresses parallel to the slope, associated with the evolution of the Cromwell Gorge from a relatively low relief surface to present day topography (1400 m deep valley), and ii) active far-field tectonic stresses associated with the obliquely convergent stress regime of the Australian-Pacific continent plate boundary. Finite Element Method (FEM) numerical
Noor, Ahmed K.; Kim, Yong H.
1995-01-01
The results of a detailed study of the buckling and postbuckling responses of composite panels with central circular cutouts are presented. The panels are subjected to combined edge shear and temperature change. The panels are discretized by using a two-field degenerate solid element with each of the displacement components having a linear variation throughout the thickness of the panel. The fundamental unknowns consist of the average mechanical strains through the thickness and the displacement components. The effects of geometric nonlinearities and laminated anisotropic material behavior are included. The stability boundary, postbuckling response and the hierarchical sensitivity coefficients are evaluated. The hierarchical sensitivity coefficients measure the sensitivity of the buckling and postbuckling responses to variations in the panel stiffnesses, and the material properties of both the individual layers and the constituents (fibers and matrix). Numerical results are presented for composite panels with central circular cutouts subjected to combined edge shear and temperature change, showing the effects of variations in the hole diameter, laminate stacking sequence and fiber orientation, on the stability boundary and postbuckling response and their sensitivity to changes in the various panel parameters.
A numerical study on shear buckling capacity of Z-section steel purlin with opening
De'nan, Fatimah; Keong, Choong Kok; Hashim, Nor Salwani; Yuting, Ng
2017-10-01
Cold-formed Z-section steel purlin is one of the most commonly available steel purlin worldwide. A numerical study on Z-section steel purlin with opening under shear loading was carried out. Six (6) variables such as opening size, opening shape, section type, opening distance, opening position and opening arrangement were identified and tested to investigate their effect on shear capacity of Z-section steel purlin. Results indicated that the presence of web opening did not improve the shear behaviour of Z-section steel purlin. However, non-negligible improvement in terms of volume reduction was observed. Each 0.1D (where D is the section height) enlargement of opening size caused an approximate 10% drop in shear buckling capacity (SBC) while volume reduction (VR) increased exponentially. Diamond shape performed up to 55% better in SBC compared to circular shape opening but circular shape opening performed up to 24% better in VR. Sections with smaller section height had higher SBC compared to sections with bigger section height. Nevertheless, sections with bigger section height had higher VR. No significant difference in terms of shear buckling capacity was observed when opening distance was manipulated. Opening position had no effect on SBC and VR. Opening arrangement had no significant effect on SBC and VR. An optimal section of Z100-19 with 0.3D to 0.5D diamond shaped opening and an opening distance of 100mm centre to centre depending on design engineer's specification is proposed.
Ductility demands on buckling-restrained braced frames under earthquake loading
Fahnestock, Larry A.; Sause, Richard; Ricles, James M.; Lu, Le-Wu
2003-12-01
Accurate estimates of ductility demands on buckling-restrained braced frames (BRBFs) are crucial to performance-based design of BRBFs. An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS Center, Lehigh University to prepare for an upcoming experimental program. The analysis program DRAIN-2DX was used to model a one-bay, four-story prototype BRBF including material and geometric nonlinearities. The buckling-restrained brace (BRB) model incorporates both isotropic and kinematic hardening. Nonlinear static pushover and time-history analyses were performed on the prototype BRBF. Performance objectives for the BRBs were defined and used to evaluate the time-history analysis results. Particular emphasis was placed on global ductility demands and ductility demands on the BRBs. These demands were compared with anticipated ductility capacities. The analysis results, along with results from similar previous studies, are used to evaluate the BRBF design provisions that have been recommended for codification in the United States. The results show that BRB maximum ductility demands can be as high as 20 to 25. These demands significantly exceed those anticipated by the BRBF recommended provisions. Results from the static pushover and time-history analyses are used to demonstrate why the ductility demands exceed those anticipated by the recommended provisions. The BRB qualification testing protocol contained in the BRBF recommended provisions is shown to be inadequate because it requires only a maximum ductility demand of at most 7.5. Modifications to the testing protocol are recommended.
Stability of twisted rods, helices and buckling solutions in three dimensions
Majumdar, Apala
2014-11-03
© 2014 IOP Publishing Ltd & London Mathematical Society. We study stability problems for equilibria of a naturally straight, inextensible, unshearable Kirchhoff rod allowed to deform in three dimensions (3D), subject to terminal loads. We investigate the stability of the twisted, straight state in 3D for three different boundary-value problems, cast in terms of Dirichlet and Neumann boundary conditions for the Euler angles, with and without isoperimetric constraints. In all cases, we obtain explicit stability estimates in terms of the twist, external load and elastic constants and in the Dirichlet case, we compute bifurcation diagrams for the Euler angles as a function of the external load. In the same vein, we obtain explicit stability estimates for a family of prototypical helical equilibria in 3D and demonstrate that they are stable for a range of tensile and compressive forces. We propose a numerical L2-gradient flow model to study the stability and dynamical evolution (in viscous model situations) of Kirchhoff rod equilibria. In Nizette and Goriely 1999 J. Math. Phys. 40 2830-66, the authors construct a family of localized buckling solutions. We apply our L2-gradient flow model to these localized buckling solutions, demonstrate that they are unstable, study their evolution and the simulations demonstrate rich spatio oral patterns that strongly depend on the boundary conditions and imposed isoperimetric constraints.
Buckling, driven by constrained phase separation, of toroid-shaped hydrogels
Dimitriyev, Michael S.; Chang, Ya-Wen; Souslov, Anton; Fernandez-Nieves, Alberto; Goldbart, Paul M.
We investigate the buckling process observed in connection with the temperature-induced shrinking of an elastic toroid composed of hydrogel. Hydrogels are polymeric network media that become swollen when mixed with water, provided the temperature is low enough. As the temperature is increased beyond a certain point, such gels undergo a first-order de-swelling transition to a de-mixed state, in which the network segregates from the water, resulting in a shrunken phase. It is known that the rapid heating of swollen hydrogels beyond the de-swelling transition results in the formation of a shrunken-phase boundary region, or shell. This shell hinders the expulsion of fluid associated with the equilibration of the sample interior, and gives rise to a prolonged period of coexistence between shrunken and swollen domains in the interior of the sample. In contrast with the spherical case, toroidal samples have been observed to undergo a constrained phase separation that is accompanied by a global buckling (or ``Pringling'') deformation of the sample shape. We present a model of hydrogel toroid Pringling in which such deformations are driven by this phase separation process.
Mallick, Rajnish; Ganguli, Ranjan; Kumar, Ravi
2017-05-01
The optimized design of a smart post-buckled beam actuator (PBA) is performed in this study. A smart material based piezoceramic stack actuator is used as a prime-mover to drive the buckled beam actuator. Piezoceramic actuators are high force, small displacement devices; they possess high energy density and have high bandwidth. In this study, bench top experiments are conducted to investigate the angular tip deflections due to the PBA. A new design of a linear-to-linear motion amplification device (LX-4) is developed to circumvent the small displacement handicap of piezoceramic stack actuators. LX-4 enhances the piezoceramic actuator mechanical leverage by a factor of four. The PBA model is based on dynamic elastic stability and is analyzed using the Mathieu-Hill equation. A formal optimization is carried out using a newly developed meta-heuristic nature inspired algorithm, named as the bat algorithm (BA). The BA utilizes the echolocation capability of bats. An optimized PBA in conjunction with LX-4 generates end rotations of the order of 15° at the output end. The optimized PBA design incurs less weight and induces large end rotations, which will be useful in development of various mechanical and aerospace devices, such as helicopter trailing edge flaps, micro and nano aerial vehicles and other robotic systems.
Program Fidelity Measures Associated With an Effective Child Restraint Program: Buckle-Up Safely
Keay, Lisa; Simpson, Judy M.; Brown, Julie; Bilston, Lynne E.; Fegan, Maureen; Cosgrove, Louise; Stevenson, Mark; Ivers, Rebecca Q.
2015-01-01
Objectives. We sought to identify the program fidelity factors associated with successful implementation of the Buckle-Up Safely program, targeting correct use of age-appropriate child car restraints. Methods. In 2010, we conducted a cluster randomized controlled trial of 830 families with children attending preschools and long day care centers in South West Sydney, New South Wales, Australia. Families received the Buckle-Up Safely program in the intervention arm of the study (13 services). Independent observers assessed the type of restraint and whether it was used correctly. Results. This detailed process evaluation showed that the multifaceted program was implemented with high fidelity. Program protocols were adhered to and messaging was consistently delivered. Results from multilevel and logistic regression analyses show that age-appropriate restraint use was associated with attendance at a parent information session hosted at the center (adjusted odd ratio [AOR] = 3.66; 95% confidence interval [CI] = 1.61, 8.29) and adversely affected by the child being aged 2 to 3 years (AOR = 0.14; 95% CI = 0.07, 0.30) or being from a family with more than 2 children (AOR = 0.34; 95% CI = 0.17, 0.67). Conclusions. Findings highlight the importance of parents receiving hands-on education regarding the proper use of age-appropriate child restraints. PMID:25602901
Energy Technology Data Exchange (ETDEWEB)
Farajpour, A., E-mail: ariobarzan.oderj@gmail.com; Rastgoo, A.; Mohammadi, M.
2017-03-15
Piezoelectric nanomaterials such as zinc oxide (ZnO) are of low toxicity and have many biomedical applications including optical imaging, drug delivery, biosensing and harvesting biomechanical energy using hybrid nanogenerators. In this paper, the vibration, buckling and smart control of microtubules (MTs) embedded in an elastic medium in thermal environment using a piezoelectric nanoshell (PNS) are investigated. The MT and PNS are considered to be coupled by a filament network. The PNS is subjected to thermal loads and an external electric voltage which operates to control the mechanical behavior of the MT. Using the nonlocal continuum mechanics, the governing differential equations are derived. An exact solution is presented for simply supported boundary conditions. The differential quadrature method is also used to solve the governing equations for other boundary conditions. A detailed parametric study is conducted to investigate the effects of the elastic constants of surrounding medium and internal filament matrix, scale coefficient, electric voltage, the radius-to-thickness ratio of PNSs and temperature change on the smart control of MTs. It is found that the applied electric voltage can be used as an effective controlling parameter for the vibration and buckling of MTs.
Self-healing monovacancy in low-buckled silicene studied by first-principles calculations
Li, Rui; Han, Yang; Hu, Ting; Dong, Jinming; Kawazoe, Y.
2014-07-01
A new type of monovacancy (MV), MV-1, with a planelike sp3 hybridization at its defect core has been found in two-dimensional (2D) low-buckled silicene by using the first-principles study, which has never been found to exist stably in the 2D single-layer nanostructures, including other previously studied graphene, h-BN sheets, and single-layer MoS2. In addition, other two possible monovacancies (MV-2 and MV-3) with higher energies have also been found to exist in 2D low-buckled silicene. More importantly, it is found that the new type MV-1 is the most stable ground structure among the three possible MVs. And the high-energy MV-3 is unstable, easily decaying into MV-1, but metastable MV-2 could coexist with MV-1 at low temperatures less than 10 K. The diffusion coefficient of MV-1 is calculated to be 2.3×10-5cm2/s, much higher than that of the MV in graphene. Finally, electronic structures of the defective silicene with MV-1 and MV-2 are calculated, showing both of them are metallic.
Cumulative Ductility and Hysteretic Behavior of Small Buckling-Restrained Braces
Directory of Open Access Journals (Sweden)
Hidajat Sugihardjo
2017-01-01
Full Text Available Cumulative ductility is defined as a ratio of total energy to elastic energy which is dissipated by an element of the structural system during cyclic loading. An element of the structural system is categorized hysteretic if the cumulative ductility factor fulfills certain criteria. This study investigated both analytically and experimentally Small Buckling-Restrained Braces (SBRBs. The core of bracings was modeled using Menegotto-Pinto and bilinear functions. The restrained bracing members were in the shape of square hollow steel section. They were made of the assembly of two L-shaped steel sections. From the experimental study on four SBRB specimens, it was proven that the proposed SBRBs have performed relatively stable hysteretic curves up to two percent of strain and the cumulative ductility factor of 199–450. This value is sufficient for the Buckling-Restrained Brace (BRB elements as elastoplastic structural components. The comparisons of the hysteretic behaviors resulted by SBRB specimens using the Menegotto-Pinto functions and experiments exhibited good agreements, while the amount of energy dissipated by the SBRB specimens using the bilinear model agreed well with the experimental results. Based on the behavior of the experimental hysteretic, implementing the proposed SBRBs as components in ductile truss system is recommended.
Buckling of thin viscous sheets with inhomogenous viscosity under extensional flows
Srinivasan, Siddarth; Wei, Zhiyan; Mahadevan, L.
2016-11-01
We investigate the dynamics, shape and stability of a thin viscous sheet subjected to an extensional flow under an imposed non-uniform temperature field. Using finite element simulations, we first solve for the stretching flow to determine the pre-buckling sheet thickness and in-plane flow velocities. Next, we use this solution as the base state and solve the linearized partial differential equation governing the out-of-plane deformation of the mid-surface as a function of two dimensionless operating parameters: the normalized stretching ratio α and a dimensionless width of the heating zone β. We show the sheet can become unstable via a buckling instability driven by the development of localized compressive stresses, and determine the global shape and growth rates of the most unstable mode. The growth rate is shown to exhibit a transition from stationary to oscillatory modes in region upstream of the heating zone. Finally, we investigate the effect of surface tension and present an operating diagram that indicates regions of the parameter space that minimizes or entirely suppresses the instability while achieving desired outlet sheet thickness. Therefore, our work is directly relevant to various industrial processes including the glass redraw & float-glass method.
Growth-induced axial buckling of a slender elastic filament embedded in an isotropic elastic matrix
O'Keeffe, Stephen G.
2013-11-01
We investigate the problem of an axially loaded, isotropic, slender cylinder embedded in a soft, isotropic, outer elastic matrix. The cylinder undergoes uniform axial growth, whilst both the cylinder and the surrounding elastic matrix are confined between two rigid plates, so that this growth results in axial compression of the cylinder. We use two different modelling approaches to estimate the critical axial growth (that is, the amount of axial growth the cylinder is able to sustain before it buckles) and buckling wavelength of the cylinder. The first approach treats the filament and surrounding matrix as a single 3-dimensional elastic body undergoing large deformations, whilst the second approach treats the filament as a planar, elastic rod embedded in an infinite elastic foundation. By comparing the results of these two approaches, we obtain an estimate of the foundation modulus parameter, which characterises the strength of the foundation, in terms of the geometric and material properties of the system. © 2013 Elsevier Ltd. All rights reserved.
Subscale and Full-Scale Testing of Buckling-Critical Launch Vehicle Shell Structures
Hilburger, Mark W.; Haynie, Waddy T.; Lovejoy, Andrew E.; Roberts, Michael G.; Norris, Jeffery P.; Waters, W. Allen; Herring, Helen M.
2012-01-01
New analysis-based shell buckling design factors (aka knockdown factors), along with associated design and analysis technologies, are being developed by NASA for the design of launch vehicle structures. Preliminary design studies indicate that implementation of these new knockdown factors can enable significant reductions in mass and mass-growth in these vehicles and can help mitigate some of NASA s launch vehicle development and performance risks by reducing the reliance on testing, providing high-fidelity estimates of structural performance, reliability, robustness, and enable increased payload capability. However, in order to validate any new analysis-based design data or methods, a series of carefully designed and executed structural tests are required at both the subscale and full-scale level. This paper describes recent buckling test efforts at NASA on two different orthogrid-stiffened metallic cylindrical shell test articles. One of the test articles was an 8-ft-diameter orthogrid-stiffened cylinder and was subjected to an axial compression load. The second test article was a 27.5-ft-diameter Space Shuttle External Tank-derived cylinder and was subjected to combined internal pressure and axial compression.
Vibration and Buckling Analysis of Moderately Thick Plates using Natural Element Method
Directory of Open Access Journals (Sweden)
Mohammad Etemadi
2015-07-01
Full Text Available Using natural element method (NEM, the buckling and the free vibration behaviors of moderate thick plates is studied here. The basis of NEM is natural neighbors and Voronoi cells concepts. The shape functions of nodes located in the domain is equal to the proportion of common natural neighbors area divided by area that related by each Voronoi cells. First step in analyzing the moderate thick plates is identification boundaries. This is done by nodes scattering on problem domain. Mindlin/Reissner theory is used to express the equations of moderate thick plate. First and second order shape functions obtained from natural element method are used to discretize differential equations. Using numerical integration on whole discrete equations of domain, stiffness, geometry and mass matrices of plate are obtained. Buckling loads and vibration modes are expressed by substituting these matrices in plate equations of motions. Arbitrary shapes of plate are selected for solution. Comparing the results of the current approach with those obtained by other numerical analytical methods, it is shown that natural element method can solve problems with complex areas accurately.
Flow sensing by buckling monitoring of electrothermally actuated double-clamped micro beams
Energy Technology Data Exchange (ETDEWEB)
Kessler, Y.; Krylov, S.; Liberzon, A. [School of Mechanical Engineering, Tel Aviv University, Tel Aviv 69978 (Israel)
2016-08-22
We report on a flow sensing approach based on deflection monitoring of a micro beam buckled by the compressive thermal stress due to electrothermal Joule's heating. The air stream, convectively cooling the device, affects both the critical buckling values of the electric current and the postbuckling deflections of the structure. After calibration, the flow velocity can be obtained from the deflection measurements. The quasi-static responses of 1000 μm and 2000 μm long, 10 μm wide, and 30 μm high single crystal silicon beams were consistent with the prediction of the model, which couples thermoelectric, thermofluidic, and structural domains. The deflection sensitivity of up to 1.5 μm/(m/s) and the critical current sensitivity of up to 0.43 mA/(m/s) were registered in the experiments. Our model and experimental results demonstrate the feasibility of the sensing approach and further suggest that simple, robust, and potentially downscalable beam-type devices may have use in flow velocity and wall shear stress sensors.
A simplified lumped model for the optimization of post-buckled beam architecture wideband generator
Liu, Weiqun; Formosa, Fabien; Badel, Adrien; Hu, Guangdi
2017-11-01
Buckled beams structures are a classical kind of bistable energy harvesters which attract more and more interests because of their capability to scavenge energy over a large frequency band in comparison with linear generator. The usual modeling approach uses the Galerkin mode discretization method with relatively high complexity, while the simplification with a single-mode solution lacks accuracy. It stems on the optimization of the energy potential features to finally define the physical and geometrical parameters. Therefore, in this paper, a simple lumped model is proposed with explicit relationship between the potential shape and parameters to allow efficient design of bistable beams based generator. The accuracy of the approximation model is studied with the effectiveness of application analyzed. Moreover, an important fact, that the bending stiffness has little influence on the potential shape with low buckling level and the sectional area determined, is found. This feature extends the applicable range of the model by utilizing the design of high moment of inertia. Numerical investigations demonstrate that the proposed model is a simple and reliable tool for design. An optimization example of using the proposed model is demonstrated with satisfactory performance.
Jahangiri, Mehdi
2017-09-01
A hypothesis is proposed in this work to account for the geometry of individual vertically aligned carbon nanotubes (VACNTs) that not only justifies the directionality of their growth, but also explains the origin of the waviness frequently reported for these nanotube forests. Such waviness has fundamental effects on the transport/conduction properties of VACNTs, either through or along them, regarding phenomena such as mass, stress, heat and electricity. Despite the general opinion about randomness of carbon nanotubes (CNTs) tortuosity, we demonstrate here that rules of helical buckling of tubular strings is applicable to VACNTs, based on which a regular 3D helical geometry is proposed for VACNTs, with a 2D sine wave shape side-profile. In this framework, gradual increase of the total free surface energy by growth of CNTs ensues their partial cohesion, driven by van der Waals interactions, to reduce the excess surface energy. On the other hand, their cohesion is accompanied by their deformation and loss of straightness, which in turn, translates to buildup of an elastic strain energy in the system. The balance of the two energies along with the spatial constraints on each CNT at its contact points with neighboring CNTs, is manifested in its helical buckling, that is systematically influenced by nanostructural characteristics of VACNTs, such as their diameter, wall thickness and inter-CNT spacing.
Size-dependent vibrations of post-buckled functionally graded Mindlin rectangular microplates
Directory of Open Access Journals (Sweden)
R. Ansari
Full Text Available In this paper, the free vibration behavior of post-buckled functionally graded (FG Mindlin rectangular microplates are described based on the modified couple stress theory (MCST. This theory enables the consideration of the size-effect through introducing material length scale parameters. The FG microplates made of a mixture of metal and ceramic are considered whose volume fraction of components is expressed by a power law function. By means of Hamilton's principle, the nonlinear governing equations and associated boundary conditions are derived for FG micro-plates in the postbuckling domain. The governing equations and boundary conditions are then discretized by using the generalized differential quadrature (GDQ method before solving numerically by the pseudo-arclength continuation technique. In the solution procedure, the postbuckling problem of microplates is investigated first. Afterwards, the free vibration of microplates around the buckled configuration is discussed. The effects of dimensionless length scale parameter, material gradient index and aspect ratio on the on the postbuckling path and frequency of FG microplates subject to arbitrary edge supports are thoroughly discussed.
GoPro HERO 4 Black recording of scleral buckle placement during retinal detachment repair.
Ho, Vincent Y; Shah, Vaishali G; Yates, David M; Shah, Gaurav K
2017-08-01
GoPro and Google Glass technology have previously been used to record procedures in ophthalmology and other medical fields. In this manuscript, GoPro's latest HERO 4 Black edition camera (GoPro Inc, San Mateo, Calif.) will be used to record the placement of a scleral buckle during retinal detachment surgery. GoPro HERO 4 Black edition camera, which records 4K-quality video with a resolution of 3840 (pixels) x 2160 (lines), was mounted on a head strap to record placement of a scleral buckle for a retinal detachment. Excellent video quality was achieved with the 4K SuperView setting. Bluetooth connection with an Apple iPad (Apple Inc, Cupertino, Calif.) provided live streaming and use of the GoPro App. Zoom, horizontal/vertical alignment, exposure, and contrast adjustments were made with postproduction editing on GoPro Studio software. Video recording with the GoPro HERO 4 Black edition camera is an excellent way to document extraocular procedures to improve medical education, self-training, or medicolegal documentation. Copyright © 2017 Canadian Ophthalmological Society. Published by Elsevier Inc. All rights reserved.
Design, Analysis, and On-Sun Evaluation of Reflective Strips Under Controlled Buckling
Jaworske, Donald A.; Sechkar, Edward A.; Colozza, Anthony J.
2014-01-01
Solar concentrators are envisioned for use in a variety of space-based applications, including applications involving in situ resource utilization. Identifying solar concentrators that minimize mass and cost are of great interest, especially since launch cost is driven in part by the mass of the payload. Concentrators must also be able to survive the wide temperature excursions on the lunar surface. Identifying smart structures which compensate for changes in concentrator geometry brought about by temperature extremes are of interest. Some applications may benefit from the ability to change the concentrators focal pattern at will. This paper addresses a method of designing a single reflective strip to produce a desired focal pattern through the use of controlled buckling. Small variations in the cross section over the length of the reflective strip influence the distribution of light in the focal region. A finite element method of analysis is utilized here which calculates the curve produced for a given strip cross section and axial load. Varying axial force and strip cross section over the length of the reflective strip provide a means of optimizing ray convergence in the focal region. Careful selection of a tapered cross section yields a reflective strip that approximates a parabola. An array of reflective strips under controlled buckling produces a light weight concentrator and adjustments in the compression of individual strips provide a means of compensating for temperature excursions or changing the focal pattern at will.
Directory of Open Access Journals (Sweden)
R. A. Jafari-Talookolaei
2011-01-01
Full Text Available The aim of this paper is to present analytical and exact expressions for the frequency and buckling of large amplitude vibration of the symmetrical laminated composite beam (LCB with simple and clamped end conditions. The equations of motion are derived by using Hamilton's principle. The influences of axial force, Poisson effect, shear deformation, and rotary inertia are taken into account in the formulation. First, the geometric nonlinearity based on the von Karman's assumptions is incorporated in the formulation while retaining the linear behavior for the material. Then, the displacement fields used for the analysis are coupled using the equilibrium equations of the composite beam. Substituting this coupled displacement fields in the potential and kinetic energies and using harmonic balance method, we obtain the ordinary differential equation in time domain. Finally, applying first order of homotopy analysis method (HAM, we get the closed form solutions for the natural frequency and deflection of the LCB. A detailed numerical study is carried out to highlight the influences of amplitude of vibration, shear deformation and rotary inertia, slenderness ratios, and layup in the case of laminates on the natural frequency and buckling load.
Farajpour, A.; Rastgoo, A.; Mohammadi, M.
2017-03-01
Piezoelectric nanomaterials such as zinc oxide (ZnO) are of low toxicity and have many biomedical applications including optical imaging, drug delivery, biosensing and harvesting biomechanical energy using hybrid nanogenerators. In this paper, the vibration, buckling and smart control of microtubules (MTs) embedded in an elastic medium in thermal environment using a piezoelectric nanoshell (PNS) are investigated. The MT and PNS are considered to be coupled by a filament network. The PNS is subjected to thermal loads and an external electric voltage which operates to control the mechanical behavior of the MT. Using the nonlocal continuum mechanics, the governing differential equations are derived. An exact solution is presented for simply supported boundary conditions. The differential quadrature method is also used to solve the governing equations for other boundary conditions. A detailed parametric study is conducted to investigate the effects of the elastic constants of surrounding medium and internal filament matrix, scale coefficient, electric voltage, the radius-to-thickness ratio of PNSs and temperature change on the smart control of MTs. It is found that the applied electric voltage can be used as an effective controlling parameter for the vibration and buckling of MTs.
Yan, Zheng; Zhang, Fan; Wang, Jiechen; Liu, Fei; Guo, Xuelin; Nan, Kewang; Lin, Qing; Gao, Mingye; Xiao, Dongqing; Shi, Yan; Qiu, Yitao; Luan, Haiwen; Kim, Jung Hwan; Wang, Yiqi; Luo, Hongying; Han, Mengdi; Huang, Yonggang; Zhang, Yihui; Rogers, John A
2016-04-25
Origami is a topic of rapidly growing interest in both the scientific and engineering research communities due to its promising potential in a broad range of applications. Previous assembly approaches of origami structures at the micro/nanoscale are constrained by the applicable classes of materials, topologies and/or capability of control over the transformation. Here, we introduce an approach that exploits controlled mechanical buckling for autonomic origami assembly of 3D structures across material classes from soft polymers to brittle inorganic semiconductors, and length scales from nanometers to centimeters. This approach relies on a spatial variation of thickness in the initial 2D structures as an effective strategy to produce engineered folding creases during the compressive buckling process. The elastic nature of the assembly scheme enables active, deterministic control over intermediate states in the 2D to 3D transformation in a continuous and reversible manner. Demonstrations include a broad set of 3D structures formed through unidirectional, bidirectional, and even hierarchical folding, with examples ranging from half cylindrical columns and fish scales, to cubic boxes, pyramids, starfish, paper fans, skew tooth structures, and to amusing system-level examples of soccer balls, model houses, cars, and multi-floor textured buildings.
Scleral buckle is good option for treatment of uncomplicated retinal detachment
Directory of Open Access Journals (Sweden)
Iuuki Takasaka
2012-12-01
Full Text Available OBJETIVE: To describe the reattachment rate and visual acuity results of patients with uncomplicated rhegmatogenous retinal detachment who underwent segmental scleral buckle surgery. METHODS: Prospective case series of 100 patients with visual loss or symptoms (floaters and photopsia of less than 30 days' duration scheduled for surgery. No patient had a retinal break greater than 30°, a retinal detachment larger than 2 quadrants or proliferative vitreoretinopathy. RESULTS: The 1-week, 1-month, and 6-month anatomical success rates were 93%, 100%, and 100%, respectively. Seven patients underwent one additional retinal detachment surgery (pars plan vitrectomy after primary failure at 1-week follow-up. The preoperative, 1-month, and 6-month best correct visual acuity were 20/100, 20/80, and 20/50, respectively. The postoperative complications were: eyelid edema in 10% of the patients, transient ocular hypertension in 5%, macular pucker in 3%, transient diplopia in 3%, and hyphema (<0.5mm in 1%. CONCLUSION: In patients with uncomplicated retinal detachment, segmental scleral buckle showed a very good anatomical and functional success, with a few number of major complications.
Jahangiri, Mehdi
2017-09-15
A hypothesis is proposed in this work to account for the geometry of individual vertically aligned carbon nanotubes (VACNTs) that not only justifies the directionality of their growth, but also explains the origin of the waviness frequently reported for these nanotube forests. Such waviness has fundamental effects on the transport/conduction properties of VACNTs, either through or along them, regarding phenomena such as mass, stress, heat and electricity. Despite the general opinion about randomness of carbon nanotubes (CNTs) tortuosity, we demonstrate here that rules of helical buckling of tubular strings is applicable to VACNTs, based on which a regular 3D helical geometry is proposed for VACNTs, with a 2D sine wave shape side-profile. In this framework, gradual increase of the total free surface energy by growth of CNTs ensues their partial cohesion, driven by van der Waals interactions, to reduce the excess surface energy. On the other hand, their cohesion is accompanied by their deformation and loss of straightness, which in turn, translates to buildup of an elastic strain energy in the system. The balance of the two energies along with the spatial constraints on each CNT at its contact points with neighboring CNTs, is manifested in its helical buckling, that is systematically influenced by nanostructural characteristics of VACNTs, such as their diameter, wall thickness and inter-CNT spacing.
Stein, M.; Housner, J. D.
1978-01-01
A numerical analysis developed for the buckling of rectangular orthotropic layered panels under combined shear and compression is described. This analysis uses a central finite difference procedure based on trigonometric functions instead of using the conventional finite differences which are based on polynomial functions. Inasmuch as the buckle mode shape is usually trigonometric in nature, the analysis using trigonometric finite differences can be made to exhibit a much faster convergence rate than that using conventional differences. Also, the trigonometric finite difference procedure leads to difference equations having the same form as conventional finite differences; thereby allowing available conventional finite difference formulations to be converted readily to trigonometric form. For two-dimensional problems, the procedure introduces two numerical parameters into the analysis. Engineering approaches for the selection of these parameters are presented and the analysis procedure is demonstrated by application to several isotropic and orthotropic panel buckling problems. Among these problems is the shear buckling of stiffened isotropic and filamentary composite panels in which the stiffener is broken. Results indicate that a break may degrade the effect of the stiffener to the extent that the panel will not carry much more load than if the stiffener were absent.
Directory of Open Access Journals (Sweden)
Clinton Sibuea
2017-01-01
Full Text Available Pipa bawah laut merupakan suatu teknologi transportasi yang digunakan untuk mengangkut produk hidrokarbon. Industri minyak dan gas telah membuktikan bahwa penggunakan pipa bawah laut merupakan cara yang paling ekonomis untuk memindahkan fluida dalam skala besar. Pada penelitian ini, dilakukan analisis on-bottom stability dan local buckling pada pipa bawah laut dari platform ULA menuju platform UW milik PT.PHE ONWJ. Analisis on-bottom stability bertujuan untuk mengetahui apakah pipa bawah laut stabil secara vertikal dan lateral di dasar laut pada saat terkena beban hidrodinamis. Analisis local buckling bertujuan untuk menentukan panjang maksimum free span yang diijinkan agar pipa tidak mengalami buckling. Besar gaya horizontal pada kondisi instalasi dan operasi masing-masing adalah 405 N/m dan 1119 N/m. Besar gaya vertikal pada kondisi instalasi dan operasi masing-masing adalah 138 N/m dan 1058 N/m. Besar gaya tahanan tanah pada kondisi instalasi dan operasi masing-masing adalah 111 N/m dan 121 N/m. Hasil analisis absolute lateral static menunjukkan pipa bawah laut tidak stabil secara lateral pada kondisi instalasi dan operasi karena berat terendam aktual lebih kecil dari berat terendam minimum yang harus dipenuhi agar stabil. Hasil analisis generalized parameter menunjukkan pipa bawah laut tidak stabil secara lateral pada kondisi operasi, namun stabil secara lateral pada kondisi instalasi. Panjang free span pipa bawah laut maksimum yang diijinkan agar tidak terjadi local buckling adalah 50 m.
Dose, A
1941-01-01
The present report describes a device for ascertaining the bending and buckling effect in stress measurements on shell structures accessible from one side only. Beginning with a discussion of the relationship between flexural strain and certain parameters, the respective errors of the test method for great or variable skin curvature within the test range are analyzed and illustrated by specimen example.
Pineda, Evan J.; Myers, David E.; Bednarcyk, Brett A.; Krivanek, Thomas M.
2015-01-01
A numerical study on the effect of facesheet-core disbonds on the post-buckling response of curved honeycomb sandwich panels is presented herein. This work was conducted as part of the development of a damage tolerance approach for the next-generation Space Launch System heavy lift vehicle payload fairing. As such, the study utilized full-scale fairing barrel segments as the structure of interest. The panels were composed of carbon fiber reinforced polymer facesheets and aluminum honeycomb core. The panels were analyzed numerically using the finite element method. Facesheet and core nodes in a predetermined circular region were detached to simulate a disbond induced via low-speed impact between the outer mold line facesheet and honeycomb core. Surface-to-surface contact in the disbonded region was invoked to prevent interpenetration of the facesheet and core elements. The diameter of this disbonded region was varied and the effect of the size of the disbond on the post-buckling response was observed. A significant change in the slope of the edge load-deflection response was used to determine the onset of global buckling and corresponding buckling load.
Riddick, J. C.; Gates, T. S.; Frankland, S.-J. V.
2005-01-01
A multi-scale method to predict the stiffness and stability properties of carbon nanotube-reinforced laminates has been developed. This method is used in the prediction of the buckling behavior of laminated carbon nanotube-polyethylene composites formed by stacking layers of carbon nanotube-reinforced polymer with the nanotube alignment axes of each layer oriented in different directions. Linking of intrinsic, nanoscale-material definitions to finite scale-structural properties is achieved via a hierarchical approach in which the elastic properties of the reinforced layers are predicted by an equivalent continuum modeling technique. Solutions for infinitely long symmetrically laminated nanotube-reinforced laminates with simply-supported or clamped edges subjected to axial compression and shear loadings are presented. The study focuses on the influence of nanotube volume fraction, length, orientation, and functionalization on finite-scale laminate response. Results indicate that for the selected laminate configurations considered in this study, angle-ply laminates composed of aligned, non-functionalized carbon nanotube-reinforced lamina exhibit the greatest buckling resistance with 1% nanotube volume fraction of 450 nm uniformly-distributed carbon nanotubes. In addition, hybrid laminates were considered by varying either the volume fraction or nanotube length through-the-thickness of a quasi-isotropic laminate. The ratio of buckling load-to-nanotube weight percent for the hybrid laminates considered indicate the potential for increasing the buckling efficiency of nanotube-reinforced laminates by optimizing nanotube size and proportion with respect to laminate configuration.
Patil, Mayuri Suresh
Plates or members containing plate elements have been used in the offshore, aerospace and construction industry. Cutouts are often located to lighten the weight of the structure, but these cutouts reduce the ultimate strength of the plate. A number of studies have taken place for determining the buckling strength of a perforated plated but few discuss the effect of material strain hardening on the buckling strength of a perforated plate. Buckling strength is often considered as an important criterial to determine the serviceable limit of the perforated plate in the offshore structure. The aim of the present study is to investigate the effect of material strain hardening on the strength characteristic of a perforated plate under uniaxial loading. This load at some point could lead to a possibility of instability. A square plate with perforation is considered here. The plate is considered to be simply supported at all four edges and has been kept straight. The perforation is located at the center of the plate. A number of ANSYS static nonlinear analysis are undertaken with different strain hardening material properties for AL7075. The Ramberg-Osgood method is used to determine the stress-strain curve for different strain hardening values. The plate thickness and the cutout size of the perforation are varied to determine the effect on the strength. The study covers the behavior of the system in the elastic buckling and the elastic-plastic region.
Computer Simulation of the E.C.C.S. Buckling Curve using a Monte-Carlo Method
Strating, J.; Vos, H.
1973-01-01
The application of a Monte-Carlo simulation procedure to obtain the distribution function of the maximum load of a hinged column with imperfections is discussed. Buckling tests carried out by the E.C.C.S. on IPE 160 sections have been simulated. Information concerning the column variables is
Liu, Li; Geng, Bin; Sayed, Sayed Mir; Lin, Bao-Ping; Keller, Patrick; Zhang, Xue-Qin; Sun, Ying; Yang, Hong
2017-02-02
In this communication, we describe a two-stage temperature-varied photopatterning protocol to synthesize a series of single-layer dual-phase liquid crystalline elastomer films, which have the capabilities to perform versatile three-dimensional motions, such as bending, accordion-folding, wrinkling, curling, and buckling, under thermal stimulus.
DEFF Research Database (Denmark)
Gaiotti, Marco; Rizzo, Cesare M.; Branner, Kim
2014-01-01
This paper describes the experimental and numerical studies carried out on delaminated fiberglass epoxy resin laminates made-up by different fabrication methods, namely by vacuum infusion and prepreg. While the tested specimens were originally intended for the assessment of buckling behavior...
Stroud, W. J.; Greene, W. H.; Anderson, M. S.
1981-01-01
The shear buckling analyses used in PASCO are summarized. The PASCO analyses include the basic VIPASA analysis, which is essentially exact for longitudinal and transverse loads, and a smeared orthotropic solution which was added to alleviate a shortcoming in the VIPASA analysis. Buckling results are presented for six stiffened panels loaded by combinations of longitudinal compression and shear. The buckling results were obtained with the PASCO, EAL, and STAGS computer programs. The EAL and STAGS solutions were obtained with a fine finite element mesh and provide calculations for the entire range of combinations of longitudinal compression and shear loadings.
Mortada, Hassan A.
2013-01-01
The purpose would be to describe and evaluate a novel technique of episcleral macular buckling in postvitrectomy recurrent macular hole retinal detachment in highly myopic eyes. A 7mm silicone sponge strengthened with a U-shaped 0.5mm orthodontics stainless steel wire fed along its length and hand-bent to produce L-shaped buckle of appropriate shape and length, is used. The episcleral macular buckling has performed on 15 highly myopic eyes (axial length > 30mm) with recurrent macular hole ret...
Liu, Z F; Fang, S; Moura, F A; Ding, J N; Jiang, N; Di, J; Zhang, M; Lepró, X; Galvão, D S; Haines, C S; Yuan, N Y; Yin, S G; Lee, D W; Wang, R; Wang, H Y; Lv, W; Dong, C; Zhang, R C; Chen, M J; Yin, Q; Chong, Y T; Zhang, R; Wang, X; Lima, M D; Ovalle-Robles, R; Qian, D; Lu, H; Baughman, R H
2015-07-24
Superelastic conducting fibers with improved properties and functionalities are needed for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%) sheath-core conducting fibers created by wrapping carbon nanotube sheets oriented in the fiber direction on stretched rubber fiber cores. The resulting structure exhibited distinct short- and long-period sheath buckling that occurred reversibly out of phase in the axial and belt directions, enabling a resistance change of less than 5% for a 1000% stretch. By including other rubber and carbon nanotube sheath layers, we demonstrated strain sensors generating an 860% capacitance change and electrically powered torsional muscles operating reversibly by a coupled tension-to-torsion actuation mechanism. Using theory, we quantitatively explain the complementary effects of an increase in muscle length and a large positive Poisson's ratio on torsional actuation and electronic properties. Copyright © 2015, American Association for the Advancement of Science.
Impact buckling of thin bars in the elastic range hinged at both ends
Koning, Carel; Taub, Josef
1934-01-01
Following the development of the well-known differential equations of the problem and their resolution for failure in tension, the bending (transverse) oscillations of an originally not quite straight bar hinged at both ends and subjected to a constant longitudinal force (shock load) are analyzed. To this end the course of the bar form is expanded in a sinusoidal series, after which the investigation is carried through separately for the fundamental oscillation and the (n-1)the higher oscillations. The analysis of the fundamental oscillation distinguishes three cases: shock load lower, equal to, or higher than the Eulerian load. The investigation leads to functions which are proportional to the maximum stresses in time and space due to the shock stresses in buckling.
The magneto-elastica: from self-buckling to self-assembly
Vella, D.
2013-12-04
Spherical neodymium-iron-boron magnets are permanent magnets that can be assembled into a variety of structures owing to their high magnetic strength. A one-dimensional chain of these magnets responds to mechanical loadings in a manner reminiscent of an elastic rod. We investigate the macroscopic mechanical properties of assemblies of ferromagnetic spheres by considering chains, rings and chiral cylinders of magnets. Based on energy estimates and simple experiments, we introduce an effective magnetic bending stiffness for a chain of magnets and show that, used in conjunction with classic results for elastic rods, it provides excellent estimates for the buckling and vibration dynamics of magnetic chains. We then use this estimate to understand the dynamic self-assembly of a cylinder from an initially straight chain of magnets.
Fishlock, S. J.; O'Shea, S. J.; McBride, J. W.; Chong, H. M. H.; Pu, S. H.
2017-09-01
The simulation, fabrication and characterisation of nanographite MEMS resonators is reported in this paper. The deposition of nanographite is achieved using plasma-enhanced chemical vapour deposition directly onto numerous substrates such as commercial silicon wafers. As a result, many of the reliability issues of devices based on transferred graphene are avoided. The fabrication of the resonators is presented along with a simple undercutting method to overcome buckling, by changing the effective stress of the structure from ~436 MPa compressive, to ~13 MPa tensile. The characterisation of the resonators using electrostatic actuation and laser Doppler vibrometry is reported, demonstrating resonator frequencies from 5-640 kHz and quality factor above 1819 in vacuum obtained.
Dynamic buckling analysis of delaminated composite plates using semi-analytical finite strip method
Ovesy, H. R.; Totounferoush, A.; Ghannadpour, S. A. M.
2015-05-01
The delamination phenomena can become of paramount importance when the design of the composite plates is concerned. In the current study, the effect of through-the-width delamination on dynamic buckling behavior of a composite plate is studied by implementing semi-analytical finite strip method. In this method, the energy and work integrations are computed analytically due to the implementation of trigonometric functions. Moreover, the method can lead to converged results with comparatively small number of degrees of freedom. These features have made the method quite efficient. To account for delamination effects, displacement field is enriched by adding appropriate terms. Also, the penetration of the delamination surfaces is prevented by incorporating an appropriate contact scheme into the time response analysis. Some selected results are validated against those available in the literature.
Distortional buckling modes of semi-discretized thin-walled columns
DEFF Research Database (Denmark)
Andreassen, Michael Joachim; Jönsson, Jeppe
2012-01-01
stress equations for simply supported columns with constrained transverse displacements at the end sections and a constant axial initial stress. Based on the known boundary conditions the reduced order differential equations are solved by using the trigonometric solution functions and solving the related......This paper presents distorting buckling solutions for semi-discretized thin-walled columns using the coupled differential equations of a generalized beam theory (GBT). In two related papers recently published by the authors a novel semi-discretization approach to GBT has been presented. The cross...... section is discretized and analytical solutions are sought for the variation along the beam. With this new approach the general GBT equations for identification of a full set of deformation modes corresponding to both homogeneous and non-homogenous equations are formulated and solved. Thereby giving...
Buckle, ruck and tuck: A proposed new model for the response of graphite to neutron irradiation
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Heggie, M.I., E-mail: m.i.heggie@sussex.ac.uk [Chemistry Subject Group, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QJ (United Kingdom); Suarez-Martinez, I. [Nanochemistry Research Institute, Department of Chemistry, Curtin University of Technology, GPO Box U1987, Perth 6845, Western Australia (Australia); Davidson, C.; Haffenden, G. [Chemistry Subject Group, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QJ (United Kingdom)
2011-06-30
The default theory of radiation damage in graphite invokes Frenkel pair formation as the principal cause of physical property changes. We set out its inadequacies and present two new mechanisms that contribute to a better account for changes in dimension and stored energy. Damage depends on the substrate temperature, undergoing a change at approximately 250 deg. C. Below this temperature particle radiation imparts a permanent, nano-buckling to the layers. Above it, layers fold, forming what we describe as a ruck and tuck defect. We present first principles and molecular mechanics calculations of energies and structures to support these claims. Necessarily we extend the dislocation theory of layered materials. We cite good experimental evidence for these features from the literature on radiation damage in graphite.
Akbarov, Surkay
2013-01-01
This book investigates stability loss and buckling delamination problems of the viscoelastic composite materials and structural members made from these materials within the framework of the Three-Dimensional Linearized Theory of Stability (TDLTS). The investigation of stability loss problems is based on the study of an evolution of the initial infinitesimal imperfection in the structure of the material or of the structural members with time (for viscoelastic composites) or with external compressing forces (for elastic composites). This study is made within the scope of the Three-Dimensional Geometrically Non-Linear Theory of the Deformable Solid Body Mechanics. The solution to the corresponding boundary-value problems is presented in the series form in a small parameter which characterizes the degree of the initial imperfection. The boundary form perturbation technique is employed and nonlinear problems for the domains bounded by noncanonical surfaces are reduced to the same nonlinear problem for the correspo...
Ruiz-De-Gopegui, E; Ascaso, F J; Del Buey, M A; Cristóbal, J A
2011-11-01
To investigate the effects of encircling scleral buckle (SB) on corneal biomechanical properties of the cornea and its morphological parameters. We prospectively examined twelve eyes diagnosed with vitreous haemorrhage undergoing pars plana vitrectomy (PPV), and fifteen eyes undergoing combined PPV and scleral buckle (PPV/SB) for repair of rhegmatogenous retinal detachment (RRD). Corneal biomechanical properties, including corneal hysteresis (CH) and corneal resistance factor (CRF), were measured with an Ocular Response Analyser (ORA) before and 1-month postoperatively. The ORA also determined the values of intraocular pressure (IOPg) and corneal compensated IOP (IOPcc). Finally, four morphological parameters of the cornea were measured with the Orbscan II topographer (Orbtek, Inc.): mean corneal power, thinnest corneal point (μm), and anterior chamber depth (ACD). CH decreased significantly from 10.2+/-1.7mmHg to 7.6+/-1.1mmHg after PPV/SB (p=0.003), but not after PPV alone (9.8+/-3.2mmHg vs 11.6+/-2.7mmHg, P=.465). CRF did not change significantly after surgery in both groups. IOPg and IOPcc increased significantly in the PPV/SB group (P=.019 and P=.010, respectively) but not in PPV group (P=.715 and P=.273, respectively). Unlike the PPV group, values were significantly higher than IOPg values before (P=.001) and after surgery (P=.003) in the PPV/SB group IOPcc. Neither the PPV/SB group nor the PPV group showed any significant changes in the corneal morphological parameters after surgery (P>.05). SB surgery leads to a change in the corneal biomechanical properties without altering corneal morphological parameters. It may cause an underestimation error in IOP measurement. PPV may be a less invasive surgical approach for the repair of noncomplex RRD than PPV/SB. Copyright Â© 2010 Sociedad Española de Oftalmología. Published by Elsevier Espana. All rights reserved.
Flambage vertical des conduites en souillées Vertical Buckling of Buried Pipes
Directory of Open Access Journals (Sweden)
Bournazel C.
2006-11-01
Full Text Available Si l'apparition d'un flambage vertical des conduites rigides enfouies dans une tranchée est un phénomène assez rare, il peut ne pas en être de même pour des conduites flexibles dont les propriétés mécaniques sont de nature différente. Une étude théorique et expérimentale, ayant pour but de proposer une méthode analytique de calcul de l'apparition du flambage et de son évolution sous l'effet de la pression interne, a été réalisée. II apparaît que les conduites flexibles actuelles sont très sensibles à ce phénomène et qu'il serait nécessaire, pour l'éliminer à coup sûr, de réexaminer la structure des flexibles ou d'imaginer des artifices dans la procédure d'ensouillage Whereas the appearance of vertical buckling in rigid pipes buried in a trench is a relatively rare phenomenon, the same cannot be said for flexible pipes which have mechanical properties of a different nature. A theoretical and experimental study has been made with the aim of proposing an analytical method for computing the appearance of buckling and its evolution under the effect of outside pressure. Current flexible pipes appear to be very sensitive to this phenomenon, and to be certain of eliminating it the structure of flexible pipes should be reexamined or stratagems in the burying procedure should be devised.
Lai, Frank H P; Lo, Ernie C F; Chan, Vesta C K; Brelen, Mårten; Lo, Wai Ling; Young, Alvin L
2016-04-01
The purpose of the study is to evaluate the surgical outcomes of combined pars plana vitrectomy-scleral buckle (PPV-SB) versus pars plana vitrectomy (PPV) for rhegmatogenous retinal detachment complicated with proliferative vitreoretinopathy (PVR). One thousand one hundred and seventy four patients with rhegmatogenous retinal detachment surgery between January 2002 and December 2013 were retrospectively reviewed. Patients with grade C PVR treated with either combined PPV-SB or PPV alone were included in the study. Study outcomes included single surgery anatomic success rate and postoperative visual outcome at 12 months postoperatively. Seventy-seven patients with grade C PVR were identified for analysis. At the end of 12-month follow-up, 80.5 % eyes (33/41) in the PPV-SB group and 58.3 % eyes (21/36) in the PPV group achieved single surgery anatomical success. In a multiple logistic regression model, none of the baseline variables (age, gender, macula status, grade of PVR, extent of detachment, presence of vitreous hemorrhage, lens status, status of high myopia) nor types of retinal detachment surgery (use of scleral buckle, barrier endolaser, 360 degree endolaser, cryopexy, retinectomy, tamponade agent, phacoemulsification) had significant effect on single surgery anatomical success. The post-treatment mean logMAR visual acuity of the PPV-SB group was 1.58 ± 0.58 and the PPV group was 1.57 ± 0.61. There was no significant difference in the postoperative visual acuity between the two groups (P = 0.849). For patients with grade C PVR, PPV-SB did not demonstrate a superiority over PPV alone in achieving single surgery anatomical success.
Vibration of mechanically-assembled 3D microstructures formed by compressive buckling
Wang, Heling; Ning, Xin; Li, Haibo; Luan, Haiwen; Xue, Yeguang; Yu, Xinge; Fan, Zhichao; Li, Luming; Rogers, John A.; Zhang, Yihui; Huang, Yonggang
2018-03-01
Micro-electromechanical systems (MEMS) that rely on structural vibrations have many important applications, ranging from oscillators and actuators, to energy harvesters and vehicles for measurement of mechanical properties. Conventional MEMS, however, mostly utilize two-dimensional (2D) vibrational modes, thereby imposing certain limitations that are not present in 3D designs (e.g., multi-directional energy harvesting). 3D vibrational micro-platforms assembled through the techniques of controlled compressive buckling are promising because of their complex 3D architectures and the ability to tune their vibrational behavior (e.g., natural frequencies and modes) by reversibly changing their dimensions by deforming their soft, elastomeric substrates. A clear understanding of such strain-dependent vibration behavior is essential for their practical applications. Here, we present a study on the linear and nonlinear vibration of such 3D mesostructures through analytical modeling, finite element analysis (FEA) and experiment. An analytical solution is obtained for the vibration mode and linear natural frequency of a buckled ribbon, indicating a mode change as the static deflection amplitude increases. The model also yields a scaling law for linear natural frequency that can be extended to general, complex 3D geometries, as validated by FEA and experiment. In the regime of nonlinear vibration, FEA suggests that an increase of amplitude of external loading represents an effective means to enhance the bandwidth. The results also uncover a reduced nonlinearity of vibration as the static deflection amplitude of the 3D structures increases. The developed analytical model can be used in the development of new 3D vibrational micro-platforms, for example, to enable simultaneous measurement of diverse mechanical properties (density, modulus, viscosity etc.) of thin films and biomaterials.
Ozdek, S; Lonneville, Y; Onol, M; Gurelik, G; Hasanreisoglu, B
2003-10-01
To assess the effect of retinal detachment (RD) on retinal nerve fiber layer (RNFL) thickness by using a scanning laser polarimeter (NFA-GDx) after successful scleral buckling surgery for the treatment of rhegmatogenous RD. Consecutive patients who had successful scleral buckling surgery in one eye were assessed for RNFL thickness by using NFA-GDx prospectively. Fellow healthy eyes of the patients formed the control group. Eyes with RD surgery were compared with the control group with respect to three variables (superior average, inferior average, and average thickness) of NFA-GDx by using two-sampled t-test. Additionally, a possible effect of duration of RD on RNFL thickness was assessed with a correlation test. The study group consisted of 16 patients with a mean age of 49.8 years. The mean duration of RD was 28 days. Although the retardation values in operated eyes were less than that of the control eyes, the difference was not statistically significant (p > 0.05). However, these three values were seen to increase with increased duration of detachment and this correlation was statistically significant (R > 0.5, p < 0.03). RD seemed to cause minimal or no change in RNFL thickness as determined by GDx variables. The positive correlation between RNFL thickness and duration of RD, however, may be because of the proliferated Muller cells in eyes with RD, which may be responsible for some of the retardation measurements, which may be even more prominent in longstanding RD cases. This needs to be supported by further studies in larger patient groups with longer duration of RD and with histopathologic studies.
The role of multilayers in preventing the premature buckling of the pulmonary surfactant.
Al-Saiedy, Mustafa; Tarokh, Ali; Nelson, Sultan; Hossini, Kiavash; Green, Francis; Ling, Chang-Chun; Prenner, Elmar J; Amrein, Matthias
2017-08-01
The pulmonary surfactant is a protein-lipid mixture that spreads into a film at the air-lung interface. The highly-compacted molecules of the film keep the interface from shrinking under the influence of otherwise high surface tension and thus prevent atelectasis. We have previously shown that for the film to withstand a high film pressure without collapsing it needs to assume a specific architecture of a molecular monolayer with islands of stacks of molecular multilayers scattered over the area. Surface activity was assessed in a captive bubble surfactometer (CBS) and the role of cholesterol and oxidation on surfactant function examined. The surfactant film was conceptualized as a plate under pressure. Finite element analysis was used to evaluate the role of the multilayer stacks in preventing buckling of the plate during compression. The model of film topography was constructed from atomic force microscope (AFM) scans of surfactant films and known physical properties of dipalmitoylphosphatidylcholine (DPPC), a major constituent of surfactant, using ANSYS structural-analysis software. We report that multilayer structures increase film stability. In simulation studies, the critical load required to induce surfactant film buckling increased about two-fold in the presence of multilayers. Our in vitro surfactant studies showed that surface topography varied between functional and dysfunctional films. However, the critical factor for film stability was the anchoring of the multilayers. Furthermore, the anchoring of multilayers and mechanical stability of the film was dependent on the presence of hydrophobic surfactant protein-C. The current study expands our understanding of the mechanism of surfactant inactivation in disease. Copyright © 2017 Elsevier B.V. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
MACKEY TC; JOHNSON KI; DEIBLER JE; PILLI SP; RINKER MW; KARRI NK
2009-01-14
This report documents a detailed buckling evaluation of the primary tanks in the Hanford double-shell waste tanks (DSTs), which is part of a comprehensive structural review for the Double-Shell Tank Integrity Project. This work also provides information on tank integrity that specifically responds to concerns raised by the Office of Environment, Safety, and Health (ES&H) Oversight (EH-22) during a review of work performed on the double-shell tank farms and the operation of the aging waste facility (AWF) primary tank ventilation system. The current buckling review focuses on the following tasks: (1) Evaluate the potential for progressive anchor bolt failure and the appropriateness of the safety factors that were used for evaluating local and global buckling. The analysis will specifically answer the following questions: (a) Can the EH-22 scenario develop if the vacuum is limited to -6.6-inch water gage (w.g.) by a relief valve? (b) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario can develop? (c) What is the appropriate factor of safety required to protect against buckling if the EH-22 scenario cannot develop? (2) Develop influence functions to estimate the axial stresses in the primary tanks for all reasonable combinations of tank loads based on detailed finite element analysis. The analysis must account for the variation in design details and operating conditions between the different DSTs. The analysis must also address the imperfection sensitivity of the primary tank to buckling. (3) Perform a detailed buckling analysis to determine the maximum allowable differential pressure for each of the DST primary tanks at the current specified limits on waste temperature, height, and specific gravity. Based on the concrete anchor bolt loads analysis and the small deformations that are predicted at the unfactored limits on vacuum and axial loads, it is very unlikely that the EH-22 scenario (i.e., progressive anchor bolt
National Research Council Canada - National Science Library
Jumpei YASUNAGA; Choongmo KOO; Yasushi UEMATSU
2012-01-01
Two series of wind tunnel experiments and a finite element analysis are carried out to investigate the buckling behavior of thin cylindrical shell structures, such as open-topped oil-storage tanks...
Librescu, L.; Souza, M. A.
1993-01-01
The static post-buckling of simply-supported flat panels exposed to a stationary nonuniform temperature field and subjected to a system of subcritical in-plane compressive edge loads is investigated. The study is performed within a refined theory of composite laminated plates incorporating the effect of transverse shear and the geometric nonlinearities. The influence played by a number of effects, among them transverse shear deformation, initial geometric imperfections, the character of the in-plane boundary conditions and thickness ratio are studied and a series of conclusions are outlined. The influence played by the complete temperature field (i.e., the uniform through thickness and thickness-wise gradient) as compared to the one induced by only the uniform one, is discussed and the peculiarities of the resulting post-buckling behaviors are enlightened.
Neukirch, Sébastien
2014-02-01
In-plane vibrations of an elastic rod clamped at both extremities are studied. The rod is modeled as an extensible planar Kirchhoff elastic rod under large displacements and rotations. Equilibrium configurations and vibrations around these configurations are computed analytically in the incipient post-buckling regime. Of particular interest is the variation of the first mode frequency as the load is increased through the buckling threshold. The loading type is found to have a crucial importance as the first mode frequency is shown to behave singularly in the zero thickness limit in the case of prescribed axial displacement, whereas a regular behavior is found in the case of prescribed axial load. © 2013 Elsevier Ltd.
Directory of Open Access Journals (Sweden)
Chonghui Shao
2016-01-01
Full Text Available The flutter and thermal buckling behavior of laminated composite panels embedded with shape memory alloy (SMA wires are studied in this research. The classical plate theory and nonlinear von-Karman strain-displacement relation are employed to investigate the aeroelastic behavior of the smart laminated panel. The thermodynamic behaviors of SMA wires are simulated based on one-dimensional Brinson SMA model. The aerodynamic pressure on the panel is described by the nonlinear piston theory. Nonlinear governing partial differential equations of motion are derived for the panel via the Hamilton principle. The effects of ply angle of the composite panel, SMA layer location and orientation, SMA wires temperature, volume fraction and prestrain on the buckling, flutter boundary, and amplitude of limit cycle oscillation of the panel are analyzed in detail.
Pre-Test Analysis Predictions for the Shell Buckling Knockdown Factor Checkout Tests - TA01 and TA02
Thornburgh, Robert P.; Hilburger, Mark W.
2011-01-01
This report summarizes the pre-test analysis predictions for the SBKF-P2-CYL-TA01 and SBKF-P2-CYL-TA02 shell buckling tests conducted at the Marshall Space Flight Center (MSFC) in support of the Shell Buckling Knockdown Factor (SBKF) Project, NASA Engineering and Safety Center (NESC) Assessment. The test article (TA) is an 8-foot-diameter aluminum-lithium (Al-Li) orthogrid cylindrical shell with similar design features as that of the proposed Ares-I and Ares-V barrel structures. In support of the testing effort, detailed structural analyses were conducted and the results were used to monitor the behavior of the TA during the testing. A summary of predicted results for each of the five load sequences is presented herein.
Rengarajan, Govind; Aminpour, Mohammad A.; Knight, Norman F., Jr.
1992-01-01
An improved four-node quadrilateral assumed-stress hybrid shell element with drilling degrees of freedom is presented. The formulation is based on Hellinger-Reissner variational principle and the shape functions are formulated directly for the four-node element. The element has 12 membrane degrees of freedom and 12 bending degrees of freedom. It has nine independent stress parameters to describe the membrane stress resultant field and 13 independent stress parameters to describe the moment and transverse shear stress resultant field. The formulation encompasses linear stress, linear buckling, and linear free vibration problems. The element is validated with standard tests cases and is shown to be robust. Numerical results are presented for linear stress, buckling, and free vibration analyses.
Hilburger, Mark W.; Lovejoy, Andrew E.; Thornburgh, Robert P.; Rankin, Charles
2012-01-01
NASA s Shell Buckling Knockdown Factor (SBKF) project has the goal of developing new analysis-based shell buckling design factors (knockdown factors) and design and analysis technologies for launch vehicle structures. Preliminary design studies indicate that implementation of these new knockdown factors can enable significant reductions in mass and mass-growth in these vehicles. However, in order to validate any new analysis-based design data or methods, a series of carefully designed and executed structural tests are required at both the subscale and full-scale levels. This paper describes the design and analysis of three different orthogrid-stiffeNed metallic cylindrical-shell test articles. Two of the test articles are 8-ft-diameter, 6-ft-long test articles, and one test article is a 27.5-ft-diameter, 20-ft-long Space Shuttle External Tank-derived test article.
Hansbo, Peter; Larson, Mats G.
2015-11-01
Second order buckling theory involves a one-way coupled coupled problem where the stress tensor from a plane stress problem appears in an eigenvalue problem for the fourth order Kirchhoff plate. In this paper we present an a posteriori error estimate for the critical buckling load and mode corresponding to the smallest eigenvalue and associated eigenvector. A particular feature of the analysis is that we take the effect of approximate computation of the stress tensor and also provide an error indicator for the plane stress problem. The Kirchhoff plate is discretized using a continuous/discontinuous finite element method based on standard continuous piecewise polynomial finite element spaces. The same finite element spaces can be used to solve the plane stress problem.
Gherlone, Marco; Di Sciuva, Marco; Iurlaro, Luigi
2013-01-01
The Refined Zigzag Theory (RZT) belongs to the zigzag class of approximations for the analysis of laminated composite and sandwich structures. This paper presents the derivation of the non-linear equations of motion and consistent boundary conditions of RZT for multilayered plates. Subsequently, the equations are specialized to the linear boundary value problem of bending and the linear eigenvalue problems of free vibrations and buckling. In order to assess the accuracy of RZT, results concer...
Andrews, Blake M.; Song, Junho; Fahnestock, Larry A.
2009-09-01
Buckling-restrained braces (BRBs) have recently become popular in the United States for use as primary members of seismic lateral-force-resisting systems. A BRB is a steel brace that does not buckle in compression but instead yields in both tension and compression. Although design guidelines for BRB applications have been developed, systematic procedures for assessing performance and quantifying reliability are still needed. This paper presents an analytical framework for assessing buckling-restrained braced frame (BRBF) reliability when subjected to seismic loads. This framework efficiently quantifies the risk of BRB failure due to low-cycle fatigue fracture of the BRB core. The procedure includes a series of components that: (1) quantify BRB demand in terms of BRB core deformation histories generated through stochastic dynamic analyses; (2) quantify the limit-state of a BRB in terms of its remaining cumulative plastic ductility capacity based on an experimental database; and (3) evaluate the probability of BRB failure, given the quantified demand and capacity, through structural reliability analyses. Parametric studies were conducted to investigate the effects of the seismic load, and characteristics of the BRB and BRBF on the probability of brace failure. In addition, fragility curves (i.e., conditional probabilities of brace failure given ground shaking intensity parameters) were created by the proposed framework. While the framework presented in this paper is applied to the assessment of BRBFs, the modular nature of the framework components allows for application to other structural components and systems.
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Svetlana RADAVIČIENĖ
2012-12-01
Full Text Available In production of garments, embroidery carries out a variety of functions, one of which is the aesthetic appearance of the product improvement. The resulting defects, are seen as a negative indicator of the product quality. The discrepancy of the embroidered element to the digital design in size is a defect, which is influenced by the embroidery threads, embroidery materials properties and process parameters. The fabric sorrounded by the embroidery threads between adjancent needle penetrations inside of the embroidered element is compressed, buckling. The aim of this paper is to investigate the influence of the properties of embroidery threads on buckling of fabric inside of the embroidered element. For investigations specimens were prepared using different fibre composition, density and linear structure of the embroidery threads. Specimens were cut and photo-captured at the beginning, middle and end of the embroidered element. It was found, that different properties of the embroidery threads affecting on the different behavior of fabric inside of the embroidered element. The results of the investigations showed that the fabric inside of the embroidered element formed larger waves of buckling using the maximum elongation of the feedback exhibiting embroidery thread.DOI: http://dx.doi.org/10.5755/j01.ms.18.4.3100
LENUS (Irish Health Repository)
Gibran, S K
2012-02-03
AIMS: This pilot study uses Optical Coherence Tomography (OCT) imaging to compare the difference in foveal architecture after successful retinal detachment (RD) surgery by scleral buckling or pars plana vitrectomy (PPV). METHODS: Prospective recruitment of patients with macular off RDs. Detachment surgery was undertaken by scleral buckling, external drainage, and air injection (group 1) or by PPV (group 2). Postoperatively patients had clinical examinations and OCT at 1, 3, 6, and 12 months. If abnormalities persisted, a further OCT was obtained at 18 months. RESULTS: Retinal reattachment, including clinical macular reattachment, was achieved in all cases within 24 h postoperatively. In group 1 (n=22), postoperative OCT showed persistent foveal detachment in 63% of cases (n=14) at 1 and 3 months. At 6 and 12 months, 36% (n=8) and 9% (n=2) had a persistent foveal detachment, respectively, and at 18 months, foveal detachment eventually. In group 2 (n=21), postoperative OCT showed an attached fovea in all cases; however, foveal thickening suggesting intraretinal oedema was present in all cases. The oedematous appearance of retina on OCT settled in 1-3 months. No foveal abnormality was seen at 6 and 12 months postoperatively. CONCLUSIONS: A high proportion of patients with successful retinal reattachment surgery by scleral buckling had foveal detachments postoperatively. No cases who had PPV had foveal detachments; however, transient retinal oedema was evident in all cases. The aetiology of these changes is unknown and warrants further investigation, as there is the potential of a long-term effect on vision.
Anyi, Yin; Jiawei, Yan; Lin, Chen; shengfa, Zhu; zhong, Long; Liping, Fang; Tianwei, Liu
2017-11-01
The cracking evolution and failure mechanisms of Ti/TiN coatings on depleted uranium (DU) deposited by high power impulse magnetron sputtering were investigated by combing a compression-to-fail test and a numerical fracture modeling technique. The coating buckling and interface delamination were induced by unaxial compression tests, meanwhile the cracking pattern and the buckling characteristics were tracked and measured by an optical microscope (OM). A three dimensional (3D) cohesive fracture model considering both detailed coating cracking and interface cracking was developed to analyse the coating failure mechanism and to evaluate the interfacial adhesive properties. Our simulation results agree well with experiments. It is found that the coupled interacting of ridge crack and a pair of fringe cracks in coatings lead to a spontaneous self-replication propagation for the buckle; mode I fracture played a dominant role in the initiation and propagation of the ridge crack and fringe cracks; the top, the tails and the remained part of the curved interface crack front experienced pure mode I, pure mode II and mixed mode fracture, respectively. The interfacial adhesive strength of Ti/TiN coatings on DU was in the range of 80-100 Mpa, and the critical interfacial adhesive energy was in the range of 2-3 J/m2.
Morphable 3D mesostructures and microelectronic devices by multistable buckling mechanics.
Fu, Haoran; Nan, Kewang; Bai, Wubin; Huang, Wen; Bai, Ke; Lu, Luyao; Zhou, Chaoqun; Liu, Yunpeng; Liu, Fei; Wang, Juntong; Han, Mengdi; Yan, Zheng; Luan, Haiwen; Zhang, Yijie; Zhang, Yutong; Zhao, Jianing; Cheng, Xu; Li, Moyang; Lee, Jung Woo; Liu, Yuan; Fang, Daining; Li, Xiuling; Huang, Yonggang; Zhang, Yihui; Rogers, John A
2018-01-29
Three-dimensional (3D) structures capable of reversible transformations in their geometrical layouts have important applications across a broad range of areas. Most morphable 3D systems rely on concepts inspired by origami/kirigami or techniques of 3D printing with responsive materials. The development of schemes that can simultaneously apply across a wide range of size scales and with classes of advanced materials found in state-of-the-art microsystem technologies remains challenging. Here, we introduce a set of concepts for morphable 3D mesostructures in diverse materials and fully formed planar devices spanning length scales from micrometres to millimetres. The approaches rely on elastomer platforms deformed in different time sequences to elastically alter the 3D geometries of supported mesostructures via nonlinear mechanical buckling. Over 20 examples have been experimentally and theoretically investigated, including mesostructures that can be reshaped between different geometries as well as those that can morph into three or more distinct states. An adaptive radiofrequency circuit and a concealable electromagnetic device provide examples of functionally reconfigurable microelectronic devices.
Akkoyun, I; Pınarcı, E Y; Yesilirmak, N; Yılmaz, G
2014-10-01
Enhanced depth imaging (EDI) optical coherence tomography (OCT) provides high-definition cross-sectional images of the choroid. Information on alterations in choroidal thickness (CT) after scleral buckling surgery (SBS) is rare. The medical charts of 122 patients (122 eyes) who underwent SBS for macula-off rhegmatogenous retinal detachment (RRD) were retrospectively analyzed. Patients with a follow-up ≥ 6 months were included. Postoperative EDI-OCT images concerning CT were evaluated 1 week, 1 month and 6 months postoperatively in 4 groups: group 1 cerclage + cryopexy (n = 39 eyes), group 2 cerclage + cryopexy + sponge (n = 28 eyes), group 3 SBS + subretinal fluid drainage (SRD) (n = 25 eyes) and group 4 SBS + sponge + SRD (n = 30 eyes). Subfoveal CT was compared between the groups and with the non-operated fellow eye. Subfoveal CT in groups 1, 2, 3 and 4 was thicker 1 week postoperatively. There were no significant differences between the groups or when comparing the operated eye with the fellow eye 1 and 6 months postoperatively. There were no differences in subfoveal CT 1 and 6 months after SBS between the eye with macula-off RRD and the fellow eye. The use of a sponge or SRD induced no differences concerning subfoveal CT.
So, Hongyun
2013-10-31
© 2013, Springer-Verlag Berlin Heidelberg. This paper reports on a novel thermal actuator with sub-micron metallic structures and a buckling arm to operate with low voltages and to generate very large deflections, respectively. A lumped electrothermal model and analysis were also developed to validate the mechanical design and easily predict the temperature distribution along arms of the sub-micron actuator. The actuator was fabricated via the combination of electron beam lithography to form actuator arms with a minimum feature size of 200 nm and lift-off process to deposit a high aspect ratio nickel structure. Reproducible displacements of up to 1.9 μm at the tip were observed up to 250 mV under confocal microscope. The experimentally measured deflection values and theoretically calculated temperature distribution by the developed model were compared with finite element analysis results and they were in good agreement. This study shows a promising approach to develop more sophisticated nano actuators required larger deflections for manipulation of sub-micron scale objects with low-power consumption.
Directory of Open Access Journals (Sweden)
Roshan Lal
Full Text Available Abstract An investigation on the effect of uniform tensile in-plane force on the radially symmetric vibratory characteristics of functionally graded circular plates of linearly varying thickness along radial direction and resting on a Winkler foundation has been carried out on the basis of classical plate theory. The non-homogeneous mechanical properties of the plate are assumed to be graded through the thickness and described by a power function of the thickness coordinate. The governing differential equation for such a plate model has been obtained using Hamilton's principle. The differential transform method has been employed to obtain the frequency equations for simply supported and clamped boundary conditions. The effect of various parameters like volume fraction index, taper parameter, foundation parameter and the in-plane force parameter has been analysed on the first three natural frequencies of vibration. By allowing the frequency to approach zero, the critical buckling loads for both the plates have been computed. Three-dimensional mode shapes for specified plates have been plotted. Comparison with existing results has been made.
Baerveldt 250 mm2 Glaucoma Drainage Devices in Eyes With Preexisting Scleral Buckles.
Zhang, Linda; Blachley, Taylor S; Weizer, Jennifer S
2016-03-01
To evaluate eyes with preexisting scleral buckles (SBs) that underwent placement of a 250 mm Baerveldt glaucoma drainage device (GDD). Records of all patients with a preexisting SB who underwent 250 mm Baerveldt GDD placement at the Kellogg Eye Center between January 1, 2005 and September 30, 2012 were reviewed. Outcome measures included visual acuity (VA), intraocular pressure (IOP), and number of glaucoma medications prescribed. Seventeen eyes of 17 patients were analyzed. Mean follow-up was 23.9 months. Twelve eyes (70.6%) achieved successful control of IOP (IOP reduction procedures, and no devastating complications). Preoperatively, mean IOP was 25.5 mm Hg, mean number of glaucoma medications was 3.5, and mean logMAR VA was 1.1 (Snellen equivalent 20/200). At 1 and 2 years postoperatively, mean IOP was 9.2 and 8.8 mm Hg (Pglaucoma medications was 0.9 and 0.3 (Pdevice (2 eyes, 12%), phthisis (2 eyes, 12%), and hemorrhagic choroidal detachment (1 eye, 6%). In eyes with preexisting SBs, the Baerveldt 250 mm GDD effectively lowers IOP and reduces the number of glaucoma medications. Complications related to conjunctival dehiscence are not uncommon in these eyes with significantly scarred conjunctiva.
Adsorption of metal atoms at a buckled graphene grain boundary using model potentials
Directory of Open Access Journals (Sweden)
Edit E. Helgee
2016-01-01
Full Text Available Two model potentials have been evaluated with regard to their ability to model adsorption of single metal atoms on a buckled graphene grain boundary. One of the potentials is a Lennard-Jones potential parametrized for gold and carbon, while the other is a bond-order potential parametrized for the interaction between carbon and platinum. Metals are expected to adsorb more strongly to grain boundaries than to pristine graphene due to their enhanced adsorption at point defects resembling those that constitute the grain boundary. Of the two potentials considered here, only the bond-order potential reproduces this behavior and predicts the energy of the adsorbate to be about 0.8 eV lower at the grain boundary than on pristine graphene. The Lennard-Jones potential predicts no significant difference in energy between adsorbates at the boundary and on pristine graphene. These results indicate that the Lennard-Jones potential is not suitable for studies of metal adsorption on defects in graphene, and that bond-order potentials are preferable.
Compliant Buckled Foam Actuators and Application in Patient-Specific Direct Cardiac Compression.
Mac Murray, Benjamin C; Futran, Chaim C; Lee, Jeanne; O'Brien, Kevin W; Amiri Moghadam, Amir A; Mosadegh, Bobak; Silberstein, Meredith N; Min, James K; Shepherd, Robert F
2018-02-01
We introduce the use of buckled foam for soft pneumatic actuators. A moderate amount of residual compressive strain within elastomer foam increases the applied force ∼1.4 × or stroke ∼2 × compared with actuators without residual strain. The origin of these improved characteristics is explained analytically. These actuators are applied in a direct cardiac compression (DCC) device design, a type of implanted mechanical circulatory support that avoids direct blood contact, mitigating risks of clot formation and stroke. This article describes a first step toward a pneumatically powered, patient-specific DCC design by employing elastomer foam as the mechanism for cardiac compression. To form the device, a mold of a patient's heart was obtained by 3D printing a digitized X-ray computed tomography or magnetic resonance imaging scan into a solid model. From this model, a soft, robotic foam DCC device was molded. The DCC device is compliant and uses compressed air to inflate foam chambers that in turn apply compression to the exterior of a heart. The device is demonstrated on a porcine heart and is capable of assisting heart pumping at physiologically relevant durations (∼200 ms for systole and ∼400 ms for diastole) and stroke volumes (∼70 mL). Although further development is necessary to produce a fully implantable device, the material and processing insights presented here are essential to the implementation of a foam-based, patient-specific DCC design.
Buckling Instability Causes Inertial Thrust for Spherical Swimmers at All Scales
Djellouli, Adel; Marmottant, Philippe; Djeridi, Henda; Quilliet, Catherine; Coupier, Gwennou
2017-12-01
Microswimmers, and among them aspirant microrobots, generally have to cope with flows where viscous forces are dominant, characterized by a low Reynolds number (Re). This implies constraints on the possible sequences of body motion, which have to be nonreciprocal. Furthermore, the presence of a strong drag limits the range of resulting velocities. Here, we propose a swimming mechanism which uses the buckling instability triggered by pressure waves to propel a spherical, hollow shell. With a macroscopic experimental model, we show that a net displacement is produced at all Re regimes. An optimal displacement caused by nontrivial history effects is reached at intermediate Re. We show that, due to the fast activation induced by the instability, this regime is reachable by microscopic shells. The rapid dynamics would also allow high-frequency excitation with standard traveling ultrasonic waves. Scale considerations predict a swimming velocity of order 1 cm /s for a remote-controlled microrobot, a suitable value for biological applications such as drug delivery.
Takahashi, Kei; Toyota, Taro
2015-01-01
The cytosol of amoeba cells controls the membrane deformation during their motion in vivo. To investigate such ability of the cytosol of amoeba cell, Dictyostelium discoideum (Dictyostelium), in vitro, we used lipids extracted from Dictyostelium and commercially available phospholipids, and prepared substrate-supported lipid membrane patches on the micrometer scale by spin coating. We found that the spin coater holder, which has pores (pore size = 3.1 mm) of negative pressure to hold the cover glass induced the concave surface of the cover glass. The membrane lipid patches were formed at each position in the vicinity of the holder pores and their sizes were in the range of 2.7 to 3.2 × 10(4) μm(2). After addition of the cytosol extracted from Dictyostelium to the lipid membrane patches, through time-lapse observation with a confocal laser scanning fluorescence microscope, we observed an autonomous buckling of the Dictyostelium lipid patches and localized behaviours of proteins found within. The current method serves as the novel technique for the preparation of film patches in which the positions of patches are controlled by the holder pores without fabricating, modifying, and arranging the chemical properties of the solution components of lipids. The findings imply that lipid-binding proteins in the cytosol were adsorbed and accumulated within the Dictyostelium lipid patches, inducing the transformation of the cell-sized patch.
Buckled Thin-Film Transistors and Circuits on Soft Elastomers for Stretchable Electronics.
Cantarella, Giuseppe; Vogt, Christian; Hopf, Raoul; Münzenrieder, Niko; Andrianakis, Panagiotis; Petti, Luisa; Daus, Alwin; Knobelspies, Stefan; Büthe, Lars; Tröster, Gerhard; Salvatore, Giovanni A
2017-08-30
Although recent progress in the field of flexible electronics has allowed the realization of biocompatible and conformable electronics, systematic approaches which combine high bendability (3-4%), and low complexity in the fabrication process are still missing. Here, we show a technique to induce randomly oriented and customized wrinkles on the surface of a biocompatible elastomeric substrate, where Thin-Film Transistors (TFTs) and circuits (inverter and logic NAND gates) based on amorphous-IGZO are fabricated. By tuning the wavelength and the amplitude of the wrinkles, the devices are fully operational while bent to 13 μm bending radii as well as while stretched up to 5%, keeping unchanged electrical properties. Moreover, a flexible rectifier is also realized, showing no degradation in the performances while flat or wrapped on an artificial human wrist. As proof of concept, transparent TFTs are also fabricated, presenting comparable electrical performances to the nontransparent ones. The extension of the buckling approach from our TFTs to circuits demonstrates the scalability of the process, prospecting applications in wireless stretchable electronics to be worn or implanted.
Chow, W. T.; Atluri, S. N.
1996-07-01
An analytical investigation is conducted to predict the post-buckling strength of laminated composite stiffened panels under compressive loads. When a stiffened composite panel buckles, the skin would deform into a sinusoidal mode shape, and hence induces additional moments and forces near the skin-stiffener interface region. These induced loads would cause the existing small edge delamination cracks to propagate along the skin-stiffener interface, and this in turn would lead to the global failure of the stiffened panel. To reduce the cost of the analytical investigation, the failure of the stiffened panel under post-buckling loads is modeled in two stages: a global analysis to model the post-buckling behavior of the stiffened panel; and a local analysis to model the onset of propagation of the edge delamination crack at the skin-stiffener interface. The results from this study are compared with an experimental investigation conducted by Starnes, Knight, and Rouse (1987). It is found that for the eight different specimens that are considered in this study, the calculated critical energy release rate for the propagation of the edge delamination crack in each specimen differs substantially from those for the others; hence it may be concluded that the total energy release rate would not be a suitable fracture parameter for predicting the post-buckling strength of the stiffened panels. On the other hand, using the fracture criterion based on the critical mixed-mode stress intensity factors, the predicted post-buckling strength of the stiffened panels compares quite favorably with the experimental results and the standard deviation of the error of prediction is less than 10%. Furthermore, by applying the criterion of critical mixed-mode stress intensity factors on a simple damage model, the present analysis is able to predict the significant reduction in the post-buckling strenght of stiffened panels with a damage due to a low-speed impact at the skin
Chai, Yu-Yang; Song, Zhi-Guang; Li, Feng-Ming
2017-11-01
The lattice sandwich panels supported on elastic mediums are often applied in the construction of aerospace structures because of the low specific weight, excellent bending rigidity and outstanding vibration properties. This elastic medium can be any spring materials including damping tapes or heat shields which are attached to one side of the sandwich panel. Therefore, in this paper, aerothermoelastic flutter and thermal buckling characteristics of sandwich panels with the pyramidal lattice core resting on elastic foundations in supersonic airflow are studied. The influences of geometrical parameters and elastic foundation on the panel flutter and thermal buckling of the structures are analyzed in detail. In the structural modeling, the first-order shear deformation theory is applied, and the effective material properties of the lattice core are used. The aerodynamic pressure is evaluated by the supersonic piston theory. Hamilton's principle and the assumed modes method are applied to formulate the equation of motion. The highlight point of this investigation is that an effective thermal buckling suppression method utilizing the elastic foundation is proposed, based on which the thermal buckling of the structure can be completely eliminated with the natural frequencies remaining unchanged when the shearing layer parameter is equal to the thermal load. Through the numerical results, the influences of the elastic foundation, aspect ratio, core-to-facesheet thickness ratio, and inclination angle of the core truss on the aerothermoelastic behaviors of the lattice sandwich panel are analyzed, and the thermal buckling elimination effects are also examined.
Hilburger, Mark W.; Waters, W. Allen, Jr.; Haynie, Waddy T.; Thornburgh, Robert P
2017-01-01
Results from the testing of cylinder test article SBKF-P2-CYL-TA02 (referred to herein as TA02) are presented. TA02 is an 8-foot-diameter (96-inches), 78.0-inch-long, aluminum-lithium (Al-Li), orthogrid-stiffened cylindrical shell similar to those used in current state-of-the-art launch-vehicle structures and was designed to exhibit global buckling when subjected to combined compression and bending loads. The testing was conducted at the Marshall Space Flight Center (MSFC), February 3-6, 2009, in support of the Shell Buckling Knockdown Factor Project (SBKF). The test was used to verify the performance of a newly constructed buckling test facility at MSFC and to verify the test article design and analysis approach used by the SBKF researchers.
Kala, Zdeněk; Kala, Jiří
2012-09-01
The paper deals with the influence of correlation length, of Gauss random field, and of yield strength of a hotrolled I-beam under bending on the ultimate load carrying capacity limit state. Load carrying capacity is an output random quantity depending on input random imperfections. Latin Hypercube Sampling Method is used for sampling simulation. Load carrying capacity is computed by the programme ANSYS using shell finite elements and nonlinear computation methods. The nonlinear FEM computation model takes into consideration the effect of lateral-torsional buckling on the ultimate limit state.
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Filip-Vacarescu Norin
2016-03-01
Full Text Available This paper discusses the concept of a hybrid damper made from a combination of two dissipative devices. A passive hysteretic device like steel Buckling Restrained Brace (BRB can be combined with a magneto-rheological (MR Fluid Damper in order to obtain a hybrid dissipative system. This system can work either as a semi-active system, if the control unit is available, or as a passive system, tuned for working according to performance based seismic engineering (PBSE scale of reference parameters (i.e. interstory drift.
Carreno, Armando Arpys Arevalo
2015-10-27
The integration of thermal bimorph actuators and buckled cantilever structures to form an out-of-plane plate with adjustable angular positions is reported. This structure could be used as a platform to build other transducers such as optical micromirrors, scanning antennas, switches or low-frequency oscillators. The electromechanical characterisation has shown that these structures can adjust their angular position by 6° when they are operated using a DC source. The thermal characterisation performed by an infrared camera showed that the heat-affected zone reaches a maximum temperature of 125°C while the rest of the structure remains unaffected by the generated heat.
Mayers, J; Budiansky, Bernard
1955-01-01
An analysis is presented of the postbuckling behavior of a simply supported square flat plate with straight edges compressed beyond the buckling load into the plastic range. The method of analysis involves the application of a variational principle of the deformation theory of plasticity in conjunction with computations carried out on a high-speed calculating machine. Numerical results are obtained for several plate proportions and for one material. The results indicate plate strengths greater than those that have been found experimentally on plates that do not satisfy straight-edge conditions. (author)
Hilburger, Mark W.; Waters, W. Allen, Jr.; Haynie, Waddy T.
2015-01-01
Results from the testing of cylinder test article SBKF-P2-CYLTA01 (referred to herein as TA01) are presented. The testing was conducted at the Marshall Space Flight Center (MSFC), November 19?21, 2008, in support of the Shell Buckling Knockdown Factor (SBKF) Project.i The test was used to verify the performance of a newly constructed buckling test facility at MSFC and to verify the test article design and analysis approach used by the SBKF project researchers. TA01 is an 8-foot-diameter (96-inches), 78.0-inch long, aluminum-lithium (Al-Li), orthogrid-stiffened cylindrical shell similar to those used in current state-of-the-art launch vehicle structures and was designed to exhibit global buckling when subjected to compression loads. Five different load sequences were applied to TA01 during testing and included four sub-critical load sequences, i.e., loading conditions that did not cause buckling or material failure, and one final load sequence to buckling and collapse. The sub-critical load sequences consisted of either uniform axial compression loading or combined axial compression and bending and the final load sequence subjected TA01 to uniform axial compression. Traditional displacement transducers and strain gages were used to monitor the test article response at nearly 300 locations and an advanced digital image correlation system was used to obtain low-speed and high-speed full-field displacement measurements of the outer surface of the test article. Overall, the test facility and test article performed as designed. In particular, the test facility successfully applied all desired load combinations to the test article and was able to test safely into the postbuckling range of loading, and the test article failed by global buckling. In addition, the test results correlated well with initial pretest predictions.
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Mohammad Ghalambaz
2015-07-01
Full Text Available A new modified Adomian Decomposition Method (ADM is utilized to obtain an analytical solution for buckling of the nanocantilever actuators immersed in liquid electrolytes. The nanoactuators in electrolytes are subject to different nonlinear forces including ionic concentration, van der Waals, external voltage and electrochemical forces. The Duan–Rach modified Adomian decomposition method is utilized to obtain a full explicate solution for the buckling of nanoactuators free of any undetermined coefficients. The results are compared with the results of Wazwas ADM as well as the results of a finite element method available in the literature and found in excellent agreement.
Li, Yi-Wei; Elishakoff, Isaac; Starnes, James H., Jr.; Bushnell, David
1998-01-01
This study is an extension of a previous investigation of the combined effect of axisymmetric thickness variation and axisymmetric initial geometric imperfection on buckling of isotropic shells under uniform axial compression. Here the anisotropic cylindrical shells are investigated by means of Koiter's energy criterion. An asymptotic formula is derived which can be used to determine the critical buckling load for composite shells with combined initial geometric imperfection and thickness variation. Results are compared with those obtained by the software packages BOSOR4 and PANDA2.
Djomo Mbong, T. L. M.; Siewe Siewe, M.; Tchawoua, C.
2018-01-01
In this study, the effect of a controllable parametric excitation on both linear and nonlinear vibrational resonances on the dynamic of a buckled beam excited by a combination of uncontrollable low- and high-frequency periodic forces are investigated. First of all, the beam dynamic is assumed to be constrained by two periodic and independent ambient solicitations, such as wind and earthquake. An axial load of the beam represented by a periodic and parametric excitation is used to control the vibrational resonance phenomenon, induced by the presence of the two external excitations. Approximate analytical expressions for the linear response and the high-frequency force amplitude at which linear vibrational resonance occurs are obtained. An analytical expression of the amplitude of the nonlinear response at the superharmonic equal to the double of the low-frequency, is obtained. For all these expressions, we show the effect of the parametric excitation. We compare all the obtained results with the ones of the case where, the parametric force is absent. It is shown that, the presence of the parametric excitation permit the suppression of both linear and nonlinear vibrational resonances. Moreover, the vibration amplitudes of the buckled beam are significantly reduced, around certain threshold values for the amplitude and the frequency of the parametric excitation.
De Pascalis, Riccardo
2010-07-22
Euler\\'s celebrated buckling formula gives the critical load N for the buckling of a slender cylindrical column with radius B and length L as N/(π3B2)=(E/4)(B/L)2 where E is Young\\'s modulus. Its derivation relies on the assumptions that linear elasticity applies to this problem, and that the slenderness (B/L) is an infinitesimal quantity. Here we ask the following question: What is the first non-linear correction in the right hand-side of this equation when terms up to (B/L)4 are kept? To answer this question, we specialize the exact solution of incremental non-linear elasticity for the homogeneous compression of a thick compressible cylinder with lubricated ends to the theory of third-order elasticity. In particular, we highlight the way second- and third-order constants-including Poisson\\'s ratio-all appear in the coefficient of (B/L)4. © 2010 Springer Science+Business Media B.V.
Lovejoy, Andrew E.; Hilburger, Mark W.
2010-01-01
The Shell Buckling Knockdown Factor (SBKF) project includes the testing of sub-scale cylinders to validate new shell buckling knockdown factors for use in the design of the Ares-I and Ares-V launch vehicles. Test article cylinders represent various barrel segments of the Ares-I and Ares-V vehicles, and also include checkout test articles. Testing will be conducted at Marshall Space Flight Center (MSFC) for test articles having an eight-foot diameter outer mold line (OML) and having lengths that range from three to ten feet long. Both ends of the test articles will be connected to the test apparatus using attachment rings. Three multiple-piece and one single-piece design for the attachment rings were developed and analyzed. The single-piece design was chosen and will be fabricated from either steel or aluminum (Al) depending on the required safety factors (SF) for test hardware. This report summarizes the design and analysis of these attachment ring concepts.
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Roshan Lal
2013-01-01
Full Text Available The present work analyses the buckling and vibration behaviour of non-homogeneous rectangular plates of uniform thickness on the basis of classical plate theory when the two opposite edges are simply supported and are subjected to linearly varying in-plane force. For non-homogeneity of the plate material it is assumed that young's modulus and density of the plate material vary exponentially along axial direction. The governing partial differential equation of motion of such plates has been reduced to an ordinary differential equation using the sine function for mode shapes between the simply supported edges. This resulting equation has been solved numerically employing differential quadrature method for three different combinations of clamped, simply supported and free boundary conditions at the other two edges. The effect of various parameters has been studied on the natural frequencies for the first three modes of vibration. Critical buckling loads have been computed. Three dimensional mode shapes have been presented. Comparison has been made with the known results.
Johnston, William M.; Newman, James C., Jr. (Technical Monitor)
2001-01-01
A series of fracture test were conducted to determine the effects of specimen type specimen width and buckling on the fracture behavior of cracked thin sheet (0.063 inch thick) 2024-T3 aluminum alloy. A summary of the experimental measurements is presented for fracture tests conducted on two specimen types and various widths. Middle-crack tension M(T) and compact tension C(T) specimens were tested in the L-T and T-L orientation with duplicate tests for each condition. Four widths (W= 3, 12, 24, and 40 inch) were tested for the middle-crack tension specimens, and three widths (W=2, 4, and 6 inch) were tested for the compact tension specimens. The M(T) specimens were tested in either a constrained (out-of-plane displacements restrained with antibuckling guides) or unconstrained conditions were the specimen was free to buckle out of plane Measurements were made of load against crack extension for all specimens.
Influence of friction on buckling of a drill string in the circular channel of a bore hole
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Valery Gulyayev
2016-10-01
Full Text Available Abstract Enhancement of technology and techniques for drilling deep directed oil and gas bore hole is one of the most important problems of the current petroleum industry. Not infrequently, the drilling of these bore holes is attended by occurrence of extraordinary situations associated with technical accidents. Among these is the Eulerian loss of stability of a drill string in the channel of a curvilinear bore hole. Methods of computer simulation should play a dominant role in prediction of these states. In this paper, a new statement of the problem of critical buckling of the drill strings in 3D curvilinear bore holes is proposed. It is based on combined use of the theory of curvilinear elastic rods, Eulerian theory of stability, theory of channel surfaces, and methods of classical mechanics of systems with nonlinear constraints. It is noted that the stated problem is singularly perturbed and its solutions have the shapes of localized harmonic wavelets. The calculation results showed that the friction effects lead to essential redistribution of internal axial forces, as well as changing the eigenmode shapes and sites of their localization. These features make the buckling phenomena less predictable and raise the role of computer simulation of these effects.
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Solazzi L.
2010-06-01
Full Text Available This paper is concerned with the experimental mechanical analysis of a new design of a joint for a main components of a upper deck of a road bridge. These components are subject to the compression state stress induced by the weight and the load acting on the road. Each upper deck of a bridge (positioned on each side of the bridge is composed by four tubular structures that must be joint each together. The joint must to take in to account many aspects, for example that the length of each component is not the same (because, obviously, there is a mechanical tolerance. This phenomena induce different compression stress on each component and so is very important non only the critical buckling load but also the post buckling behaviour of the structure. It is very important that if a single tubular structure reaches the critical load of instability, it still has load capacity . This is to avoid that, in the case where a column reaches the instability, the entire load acting on a column increase the load on the remaining three. For this purpose many different geometrical solutions have been designed (elaborated by fem analyses and successively tested experimentally. This work reports the main experimental results on the best joint solution and how this increase the load capacity and the displacement respect to the solution without this flange.
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Badjian, H.; Setoodeh, A.R., E-mail: setoodeh@sutech.ac.ir
2017-02-15
Synthesizing inorganic nanostructures such as boron nitride nanotubes (BNNTs) have led to immense studies due to their many interesting functional features such as piezoelectricity, high temperature resistance to oxygen, electrical insulation, high thermal conductivity and very long lengths as physical features. In order to utilize the superior properties of pristine and defected carbon nanotubes (CNTs), a hybrid nanotube is proposed in this study by forming BNNTs surface coating on the CNTs. The benefits of such coating on the tensile and buckling behavior of single-walled CNTs (SWCNTs) are illustrated through molecular dynamics (MD) simulations of the resulted nanostructures during the deformation. The AIREBO and Tersoff-Brenner potentials are employed to model the interatomic forces between the carbon and boron nitride atoms, respectively. The effects of chiral indices, aspect ratio, presence of mono-vacancy defects and coating dimension on coated/non-coated CNTs are examined. It is demonstrated that the coated defective CNTs exhibit remarkably enhanced ultimate strength, buckling load capacity and Young's modulus. The proposed coating not only enhances the mechanical properties of the resulted nanostructure, but also conceals it from few external factors impacting the behavior of the CNT such as humidity and high temperature.
Impact of High Temperature Creep on the Buckling of Axially Compressed Steel Members
Włóka, Agata; Pawłowski, Kamil; Świerzko, Robert
2017-10-01
The paper presents results of the laboratory tests of the impact of creep on the buckling of axially compressed steel members at elevated temperatures. Tests were conducted on samples prepared of normal strength steel (S235JR) and high strength steel (S355J2). Samples were made in the form of a prismatic bar of a rectangular cross section 12 x 30 mm and a length of 500 mm. Support type of the specimens during tests was hinged on both ends. The tests were done at 600, 700 and 800°C. Experiments were carried out at static loads corresponding to values 0,8Ncr,T, 0,9Ncr,T, 1,0Ngr,T, where Ncr,T was theoretical value of Euler’s critical load at given temperature. Short-term creep analyses were performed in the universal testing machine Instron/Satec KN 600 equipped with a furnace for high-temperature testing type SF-16 2230, that enables testing at temperatures up to 1200°C. Temperature of the sample placed inside the furnace was verified and recorded with use of the compactRIO cRIO-9076 controller, equipped with a module for the connection of NI 9211 and K-type thermocouples. The system for the measurement and recording of the temperature of the analysed samples operated in the LabVIEW software environment. To measure lateral and longitudinal displacements LVTD Solatron ACR 100 displacement transducer was used. During the tests, the samples were heated to the given temperature (600, 700 or 800°C) and then subjected to a constant compressive load. During each test, for each sample following data was registered: the temperature on the surface of samples, longitudinal and lateral displacements in the middle of the sample. Basing on the conducted tests it was noted, for both analysed steel types, at the temperature of 800°C, growth of lateral displacements due to creep was very rapid, and tested elements were losing bearing capacity over the period of tens to hundreds of seconds, depending on stress level and the grade of the steel. At a temperature of 700°C growth
Salvekar, Abhijit Vijay; Huang, Wei Min; Xiao, Rui; Wong, Yee Shan; Venkatraman, Subbu S; Tay, Kiang Hiong; Shen, Ze Xiang
2017-02-21
-responsive shape memory embolization plug for temporary vascular occlusion. The plug consists of a composite with a poly(dl-lactide-co-glycolide) (PLGA) core (loaded with radiopaque filler) and cross-linked poly(ethylene glycol) (PEG) hydrogel outer layer. The device can be activated by body fluid (or water) after about 2 min of immersion in water. The whole occlusion process is completed within a few dozens of seconds. The underlying mechanism is water-responsive shape recovery induced buckling, which occurs in an expeditious manner within a short time period and does not require complete hydration of the whole hydrogel. In this paper, we experimentally and analytically investigate the water-activated shape recovery induced buckling in this biodegradable PEG hydrogel to understand the fundamentals in precisely controlling the buckling time. The molecular mechanism responsible for the water-induced SME in PEG hydrogel is also elucidated. The original diameter and amount of prestretching are identified as two influential parameters to tailor the buckling time between 1 and 4 min as confirmed by both experiments and simulation. The phenomenon reported here, chemically induced buckling via a combination of the SME and swelling, is generic, and the study reported here should be applicable to other water- and non-water-responsive gels.
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Panda Subrata Kumar
2017-01-01
Full Text Available The nonlinear finite element solutions for the buckling and post-buckling responses of the functionally graded shell panel subjected to the non-uniform thermal environment have been presented in this article. The thermal fields are assumed as uniform, linear and nonlinear temperature rise across the thickness of shell panel and the properties of each constituent are considered to be temperature dependent. The effective material properties of the graded structure are evaluated using the Voigt’s micromechanical rule in conjunction with power-law distribution. For the analysis purpose, a general nonlinear mathematical model of the functionally graded shell panel has been developed based on the higher order shear deformation theory and Green-Lagrange type geometrical nonlinear strains. The system governing equation of the panel structure is derived using the variational principle. Further, suitable nonlinear finite element steps have been adopted to discretize the model for the computation of the desired responses in association with the direct iterative method. The convergence and the validation behavior of the present numerical model are initially tested to demonstrate its efficacy and significance. Finally, the effects of curvature, power law index and different support conditions on the buckling and post-buckling responses of the functionally graded shell panels are investigated and discussed in details.
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Pham Minh Vuong
Full Text Available Abstract The main aim of this paper is to investigate analytically nonlinear buckling and post-buckling of functionally graded stiffened circular cylindrical shells filled inside by Pasternak two-parameter elastic foundations in thermal environments and under axial compression load and external pressure by analytical approach. Shells are reinforced by closely spaced rings and stringers. The material properties of shell and the stiffeners are assumed to be continuously graded in the thickness direction. Using the Reddy third order shear deformation shell theory, stress function method and Lekhnitskii smeared stiffeners technique, the governing equations are derived. The closed form to determine critical axial load and post-buckling load-deflection curves are obtained by Galerkin method. The effects of temperature, stiffener, foundation, material and dimensional parameters on the stability behavior of shells are shown. The accuracy of the presented method is affirmed by comparisons with well-known results in references. The results shown for thick cylindrical shells, the use of TSDT for determining their critical buckling load is necessary and more suitable.
STAVREV, A.
2013-03-01
The uncertainty of geometric imperfections in a series of nominally equal I-beams leads to a variability of corresponding buckling loads. Its analysis requires a stochastic imperfection model, which can be derived either by the simple variation of the critical eigenmode with a scalar random variable, or with the help of the more advanced theory of random fields. The present paper first provides a concise review of the two different modeling approaches, covering theoretical background, assumptions and calibration, and illustrates their integration into commercial finite element software to conduct stochastic buckling analyses with the Monte-Carlo method. The stochastic buckling behavior of an example beam is then simulated with both stochastic models, calibrated from corresponding imperfection measurements. The simulation results show that for different load cases, the response statistics of the buckling load obtained with the eigenmode-based and the random field-based models agree very well. A comparison of our simulation results with corresponding Eurocode 3 limit loads indicates that the design standard is very conservative for compression dominated load cases. © 2013 World Scientific Publishing Company.
Ajori, S.; Ansari, R.; Haghighi, S.
2018-01-01
The buckling behavior of cross-linked functionalized carbon nanotubes (CNTs) with polyethylene (PE) chains under physical adsorption of polymers (cfCNTs/polymer) is studied by classical molecular dynamics (MD) simulations, and the results are compared with those for the pure CNTs under the physical adsorption of polymers. Considering non-covalent functionalization, the effect of type of functional group, i.e. aramid and PE chains, on the interactions between polymers and cfCNTs is investigated. Based on the results, the gyration radius of cfCNTs/polymer increases by raising the weight percentage of non-covalent polymer chains. Also, the simulation results for most cases demonstrate that the gyration radius of cfCNTs/polymer is larger than that of pure CNTs/polymer for the similar weight percentage of non-covalent polymer chains. Moreover, the critical buckling force and the critical buckling strain of the cfCNTs/polymer are lower than those of pure CNT/polymer for the similar weight percentage of non-covalent polymer chains, although some exceptions can be observed. Besides, by raising the weight percentage of non-covalent polymer chains, the critical buckling force cfCNTs/polymer increases for a specific weight percentage of cross-linked PE chains.
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Zihao Yang
Full Text Available A microstructure-dependent model for the free vibration and buckling analysis of an orthotropic functionally graded micro-plate was proposed on the basis of a re-modified couple stress theory. The macro- and microscopic anisotropy were simultaneously taken into account by introducing two material length scale parameters. The material attributes were assumed to vary continuously through the thickness direction by a power law. The governing equations and corresponding boundary conditions were derived through Hamiltonâs principle. The Navier method was used to calculate the natural frequencies and buckling loads of a simply supported micro-plate. The numerical results indicated that the present model predicts higher natural frequencies and critical buckling loads than the classical model, particular when the geometric size of the micro-plates is comparable to the material length scale parameters, i.e., the scale effect is well represented. The scale effect becomes more noticeable as the material length scale parameters increase, the anisotropy weaken or the power law index increases, and vice versa. Keywords: Free vibration, Buckling, Functionally graded materials, Modified couple stress theory, Scale effect
Ansari, R.; Gholami, R.
2016-09-01
Considering the small scale effect together with the influences of transverse shear deformation, rotary inertia and the magneto-electro-thermo-mechanical coupling, the linear free vibration of magneto-electro-thermo-elastic (METE) rectangular nanoplates with various edge supports in pre- and post-buckled states is investigated herein. It is assumed that the METE nanoplate is subjected to the external in-plane compressive loads in combination with magnetic, electric and thermal loads. The Mindlin plate theory, von Kármán hypothesis and the nonlocal theory are utilized to develop a size-dependent geometrically nonlinear plate model for describing the size-dependent linear and nonlinear mechanical characteristics of moderately thick METE rectangular nanoplates. The nonlinear governing equations and the corresponding boundary conditions are derived using Hamilton’s principle which are then discretized via the generalized differential quadrature method. The pseudo-arc length continuation approach is used to obtain the equilibrium postbuckling path of METE nanoplates. By the obtained postbuckling response, and taking a time-dependent small disturbance around the buckled configuration, and inserting them into the nonlinear governing equations, an eigenvalue problem is achieved from which the frequencies of pre- and post-buckled METE nanoplates can be calculated. The effects of nonlocal parameter, electric, magnetic and thermal loadings, length-to-thickness ratio and different boundary conditions on the free vibration response of METE rectangular nanoplates in the pre- and post-buckled states are highlighted.
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Persson, R.; Andersson, A.J.W.; Wikdahl, C.E.
1966-11-15
Buckling determinations by means of flux mapping were performed in TZ up to 250 deg C on two lattices of Aagesta fuel assemblies in D{sub 2}O and on D{sub 2}O alone. Most of the flux measurements were made with fission counters in pressure thimbles. The perturbations caused by the thimbles were studied experimentally in various ways and compared with two group diffusion-theory calculations. In one of the lattices the effectiveness of a control rod (AglnCd) was also investigated. The results of the diffusion length experiments indicated some systematic error of the order of 0.15 - 0.10/m{sup 2} in the bucklings measured, though the temperature dependence should be well established. The bucklings of the two lattices studied (square pitches 24 and 27 cm) were found to be less sensitive to temperature than theoretical calculations predict, the temperature coefficient being more than 10 per cent smaller. The buckling changes from 20 to 250 deg C were about -2.4 and -1.8/m{sup 2}, respectively, for the two lattices. During part of the experimental period we had, for some unexplained reason, about 30 per cent excess absorption in the heavy water.
Mirshahi, Ahmad; Karkhaneh, Reza; Zamani Amir, Javad; Movassat, Morteza; Azadi, Pejvak
2014-01-01
To investigate the effect of intravitreal triamcinolone acetonide injection on the resolution of subretinal fluid (SRF), and its correlation with visual outcome after scleral buckle (SB) surgery. A prospective consecutive case series was conducted in patients who underwent SB surgery for macula-off rhegmatogenous retinal detachment (RRD) at Farabi Eye Hospital from February 1, 2012 to August 30, 2013. Exclusion criteria included previous ocular surgery (e.g. primary surgical failure) except cataract surgery, recurrent retinal detachment, macular hole, epiretinal membrane, proliferative vitreoretinopathy grade C, history of trauma, other retinal diseases, and diabetes mellitus. Patients were assigned to two groups. In group 1, patients received 2 mg of intravitreal triamcinolone acetonide injection at the end of surgery while patients in group 2 received intravitreal balanced saline solution for balancing the intraocular pressure (IOP). Patients were followed up at 1 day, 1 week, 1 month, 2 months and 3 months after the surgery by best-corrected visual acuity (BCVA), slitlamp examination, indirect ophthalmoscopy and optical coherence tomography (OCT). OCT (Heidelberg Engineering, Heidelberg, Germany) was used at all visits except day 1 after the surgery. Student's t test and χ(2) tests were used for comparisons; p value ≤ 0.05 was considered significant. Sixty-two eyes of 62 patients were enrolled in the study. There were 33 male patients (53%) and 29 female patients (47%). The average age was 43.8 years (18-72 years). The mean duration of symptoms was 34.7 ± 46.8 days. There were 29 eyes in group 1 and 33 eyes in group 2. Twelve weeks after the operation, 25 patients (40%) had SRF beneath the macula, but there was no significant difference (p = 0.24, χ(2) test) between the two groups. Improvement in BCVA in both groups was statistically significant (p ≤ 0.001) but did not differ between the two groups (p = 0.09) apart from week 12, in which the improvement
Meng, Lingbiao; Zhang, Yingjuan; Zhou, Minjie; Zhang, Jicheng; Zhou, Xiuwen; Ni, Shuang; Wu, Weidong
2018-02-08
Designing new materials with reduced dimensionality and distinguished properties has continuously attracted intense interest for materials innovation. Here we report a novel two-dimensional (2D) Zn2C monolayer nanomaterial with exceptional structure and properties by means of first-principles calculations. This new Zn2C monolayer is composed of quasi-tetrahedral tetracoordinate carbon and quasi-linear bicoordinate zinc, featuring a peculiar zigzag-shaped buckling configuration. The unique coordinate topology endows this natural 2D semiconducting monolayer with strongly strain tunable band gap and unusual negative Poisson ratios. The monolayer has good dynamic and thermal stabilities and is also the lowest-energy structure of 2D space indicated by the particle-swarm optimization (PSO) method, implying its synthetic feasibility. With these intriguing properties the material may find applications in nanoelectronics and micromechanics.
Potential of Transition Metal Atoms Embedded in Buckled Monolayer g-C3N4 as Single-Atom Catalysts
Li, Shu-Long
2017-10-27
We use first-principles calculations to systematically explore the potential of transition metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au) embedded in buckled monolayer g-C3N4 as single-atom catalysts. We show that clustering of Sc and Ti on g-C3N4 is thermodynamically impeded and that V, Cr, Mn, and Cu are much less susceptible to clustering than the other TM atoms under investigation. Strong bonding of the transition metal atoms in the cavities of g-C3N4 and high diffusion barriers together are responsible for single-atom fixation. Analysis of the CO oxidation process indicates that embedding of Cr and Mn in g-C3N4 gives rise to promising single-atom catalysts at low temperature.
Starnes, James H., Jr.; Hilburger, Mark W.
2003-01-01
The results of an experimental and analytical study of the effects of initial imperfections on the buckling response of unstiffened thin-walled compression-loaded graphite-epoxy cylindrical shells are presented. The analytical results include the effects of traditional and nontraditional initial imperfections and uncertainties in the values of selected shell parameters on the buckling loads of the shells. The nonlinear structural analysis results correlate very well with the experimental results. The high-fidelity nonlinear analysis procedure used to generate the analytical results can also be used to form the basis of a new shell design procedure that could reduce the traditional dependence on empirical results in the shell design process. KEYWORDS: high-fidelity nonlinear structural analysis, composite shells, shell stability, initial imperfections
Foroutan, Shahin; Haghshenas, Amin; Hashemian, Mohammad; Eftekhari, S. Ali; Toghraie, Davood
2018-03-01
In this paper, three-dimensional buckling behavior of nanowires was investigated based on Eringen's Nonlocal Elasticity Theory. The electric current-carrying nanowires were affected by a longitudinal magnetic field based upon the Lorentz force. The nanowires (NWs) were modeled based on Timoshenko beam theory and the Gurtin-Murdoch's surface elasticity theory. Generalized Differential Quadrature (GDQ) method was used to solve the governing equations of the NWs. Two sets of boundary conditions namely simple-simple and clamped-clamped were applied and the obtained results were discussed. Results demonstrated the effect of electric current, magnetic field, small-scale parameter, slenderness ratio, and nanowires diameter on the critical compressive buckling load of nanowires. As a key result, increasing the small-scale parameter decreased the critical load. By the same token, increasing the electric current, magnetic field, and slenderness ratio resulted in a decrease in the critical load. As the slenderness ratio increased, the effect of nonlocal theory decreased. In contrast, by expanding the NWs diameter, the nonlocal effect increased. Moreover, in the present article, the critical values of the magnetic field of strength and slenderness ratio were revealed, and the roles of the magnetic field, slenderness ratio, and NWs diameter on higher buckling loads were discussed.
Ahmadi, M.; Ansari, R.; Rouhi, H.
2017-09-01
Using a finite element-based multi-scale modeling approach, the bending, buckling and free vibration of hybrid polymer matrix composites reinforced by carbon fibers and carbon nanotubes (CF/CNT-RP) are analyzed herein. Thick composite plates with rectangular, circular, annular and elliptical shapes are considered. First, the equivalent material properties of CF/CNT-RP are calculated for different volume fractions of CF and CNT. To accomplish this aim, a two-step procedure is presented through which the coupled effects of nano- and micro-scale are taken into account. In the first step, modeling of dispersion of CNTs into the polymer matrix is done with considering interphase formed by their chemical interaction with the matrix, and the equivalent properties of resulting composite material are determined accordingly. CFs are then dispersed into CNT-RP which is considered a homogenous material in this step. Both distributions of CNTs and CFs are assumed to be random. After computing the equivalent properties of CF/CNT-RP for different volume fractions of its constituents, the bending, buckling and free vibration analyses of plates with different shapes are performed. It is shown that the reinforcement of the polymer matrix with both CF and CNT significantly affects the bending, buckling and free vibration characteristics of plates.
Thelen, Ulrich; Amler, Susanne; Osada, Nani; Gerding, Heinrich
2012-08-01
To evaluate the anatomical success rate of scleral buckling surgery in the treatment of rhegmatogenous retinal detachment and to evaluate the differences in outcome between patients suffering macula-off retinal detachment and those without a macular involvement. As a retrospective interventional case series, Munster Study on Therapy Achievements in Retinal Detachment (MUSTARD) is one of the largest ever established of retinal detachment patients and their outcome after buckling surgery, with 4325 patients who underwent surgery between 1980 and 2001. In 53.94% (n = 2134) of 3956 patients with nontraumatic retinal detachment, the macula was involved. The main outcome measure was the achievement of dry anatomical attachment of the retina. The success rate in patients with macula-off retinal detachment is 80.46% and thus 7.78% lower (p macula intact whose success rate amounted to 88.24%. The overall success rate of all 4325 MUSTARD patients was 83.98%. Scleral buckling is an established and mostly successful method for the treatment of retinal detachment. As our case series has demonstrated, even eyes with macula-off can be treated successfully by this procedure, thereby avoiding the complications of primary vitrectomy. © 2010 The Authors. Journal compilation © 2010 Acta Ophthalmol.
Isah, Olubukola Ajike; Okunade, Sunday Adewale; Aderinboye, Ronke Yemisi; Olafadehan, Olurotimi Ayobami
2015-08-01
The effect of browse plants (Piliostigma thonningii, Daniellia oliveri, Afzelia africana, Pterocarpus erinaceus and Annona senegalensis) supplementation on nutrient intake, digestibility, nutritive value and N utilization and growth performance of buckling goats fed threshed sorghum top (TST) was investigated using 24 Red Sokoto goats (9.0 ± 0.25 kg) body weight (BW) which were randomly assigned to one of the six diets in a completely random design. Intakes of dry matter (DM) and nutrients, feed conversion ratio, digestibility of nutrients except for neutral detergent fibre (NDF) and acid detergent fibre (ADF), digestible organic matter (DOM), digestible crude protein (DCP), energy concentration, N utilization and average daily gain were superior (P < 0.05) in TST-supplemented diets compared to sole TST diet. Among the supplemental fodders, intakes of forage, DM, condensed tannins and most of the nutrients; digestibility of DM, crude protein (CP) and non-fibre carbohydrate, DOM and DCP; and N absorbed, balance and retention were greater (P < 0.05) in A. africana relative to the other fodders. Results indicate that the entire browse fodders are good supplements to low quality TST, though A. africana appears to have a better nutritive value.
Eltanany, Ali M.; Yoshimura, Takeshi; Fujimura, Norifumi; Ebied, Mohamed R.; Ali, Mohamed G. S.
2017-10-01
In this study, we aim to examine the triggering force for an efficient snap-through solution of hand shaking vibrations of a piezoelectric bistable energy harvester. The proposed structure works at very low frequencies with nearly continuous periodic vibrations. The static characterizations are presented as well as the dynamic characterizations based on the phase diagrams of velocity vs displacement, voltage vs displacement, and voltage vs input acceleration. The mass attached to the bistable harvester plays an important role in determining the acceleration needed for the snap-through action, and the explanation for this role is complex because of mass dependence on frequency/amplitude vibration. Various hand shaking vibration tests are performed to demonstrate the advantage of the proposed structure in harvesting energy from hand shaking vibration. The minimum input acceleration for snap-through action was 11.59 m/s2 with peaks of 15.76 and 2 m/s2 in the frequency range of 1.3-2.7 Hz, when an attached mass of 14.6 g is used. The maximum generated power at a buckling state of 0.5 mm is 11.3 µW for the test structure at 26 g. The experimental results obtained in this study indicate that power output harvesting of slow hand shaking vibrations at 10 µW and a load resistance of 1 MΩ.
Xue, Jianghong; Xia, Fei; Ye, Jun; Zhang, Jianwen; Chen, Shuhua; Xiong, Ying; Tan, Zuyuan; Liu, Renhuai; Yuan, Hong
2017-06-30
This paper presents a multiscale approach to study the nonlinear vibration of fiber reinforced composite laminates containing an embedded, through-width delamination dividing the laminate into four sub-laminates. The equations of motion are established from macroscopic nonlinear mechanics for plates and shells and micro-mechanics of composite material to allow for the influences of large amplitude, membrane stretching in the neutral plane, and the interactions of the sublaminates. Analytical solutions obtained in this paper reveal that the interaction penalty at the interfaces plays a coupling effect between sublaminates, which eventually alters the vibration characters of the four-sublaminate lamina in macroscopic and microscopic mechanism. From a macro perspective, sub-laminates above and below the delamination vibrate in exactly the same mode in spite of their different stiffness and the four-sublaminate lamina has a consistent global vibration mode. In accompanying with the macro vibration, micro buckles occur on the interfaces of the delamination with amplitude about 10(-3) times of that of the global mode. It is found that the vibration frequency is an eigenvalue of the delaminated lamina determined only by the geometry of the delamination. Authentication of the multiscale study is fulfilled by comparing the analytical solutions with the FEA results.
Wong, Chee Wai; Yeo, Ian Yew San; Loh, Boon Kwang; Wong, Edmund Yick Mun; Wong, Doric Wen Kuan; Ong, Sze Guan; Ang, Chong Lye; Lee, Shu Yen
2015-12-01
To compare visual outcomes between pars plana vitrectomy (PPV) with or without scleral buckling (SB) and SB alone in the management of uncomplicated macula-off primary rhegmatogenous retinal detachment. Case-control study of 723 patients with uncomplicated macula-off primary rhegmatogenous retinal detachment seen at the Singapore National Eye Centre from 2005 to 2011. The primary outcome measure was the proportion of eyes achieving functional success, defined as logMAR best-corrected visual acuity of ≤0.3 logMAR at 6 months postoperatively. Multivariable logistic regression analysis was performed adjusting for the following preoperative covariates: age, gender, race, lens status, number of tears found, presence of proliferative vitreoretinopathy, operative procedure, logMAR best-corrected visual acuity, and duration of symptoms. Three hundred and eight eyes underwent SB alone, and 415 eyes underwent PPV ± SB. In the SB group, 133 eyes (43.2%) achieved functional success compared with 116 eyes (28.0%) in the PPV ± SB group. This difference was statistically significant on both univariate (P macula-off primary rhegmatogenous retinal detachment.
Paimushin, V. N.
2017-11-01
For an analysis of internal and external buckling modes of a monolayer inside or at the periphery of a layered composite, refined geometrically nonlinear equations are constructed. They are based on modeling the monolayer as a thin plate interacting with binder layers at the points of boundary surfaces. The binder layer is modeled as a transversely soft foundation. It is assumed the foundations, previously compressed in the transverse direction (the first loading stage), have zero displacements of its external boundary surfaces at the second loading stage, but the contact interaction of the plate with foundations occurs without slippage or delamination. The deformation of the plate at a medium flexure is described by geometrically nonlinear relations of the classical plate theory based on the Kirchhoff-Love hypothesis (the first variant) or the refined Timoshenko model with account of the transverse shear and compression (the second variant). The foundation is described by linearized 3D equations of elasticity theory, which are simplified within the framework of the model of a transversely soft layer. Integrating the linearized equations along the transverse coordinate and satisfying the kinematic joining conditions of the plate with foundations, with account of their initial compression in the thickness direction, a system of 2D geometrically nonlinear equations and appropriate boundary conditions are derived. These equations describe the contact interaction between elements of the deformable system. The relations obtained are simplified for the case of a symmetric stacking sequence.
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Hammouda Hamdy Ghoraba
2014-01-01
Full Text Available Purpose. To evaluate the efficacy of silicone oil (S.O reinjection without macular buckling for treatment of recurrent myopic macular hole retinal detachment (MHRD after silicone oil removal. Methods. A retrospective consecutive interventional study from medical reports on cases of myopic MHRD. Fifty-three eyes of 51 patients underwent silicone oil removal after successful repair of MHRD were reviewed. The main outcomes were the retinal status after silicone oil removal and management of recurrent cases. Results. The rate of recurrent RD (Re RD after silicone oil removal was 11.3% (6 out of 53 eyes. One case refused any other interference. In the remaining 5 eyes, 4 eyes (80% could be reattached by S.O re-injection and one eye (20% developed Re RD after S.O re-injection. Range of followup after management of recurrence was 5–53 months (mean 18.7 months. Conclusions. This case series concluded that the risk factors for recurrent RD after silicone oil removal from cases of myopic MHRD were high myopia, open flat MH, and large posterior staphyloma. Revision of vitrectomy and S.O re-injection can reattach most of recurrent cases.
Wu, Chih-Ping; Li, Wei-Chen
2017-05-01
A three-dimensional (3D) asymptotic formulation is developed for the buckling analysis of simply-supported, single-layered nanoplates/graphene sheets (SLNP and SLGS) embedded in an elastic medium and under biaxial compressive loads. In the formulation, the Eringen nonlocal elasticity theory is used to capture the small length scale effect, and the interaction between the SLNP/SLGS and its surrounding medium is simulated using a Pasternak-type foundation. After performing the mathematical processes of nondimensionalization, asymptotic expansion and successive integration, we finally obtain recursive sets of governing equations for various order problems. The nonlocal classical plate theory (CPT) is derived as a first-order approximation of the 3D nonlocal elasticity theory, and the governing equations for higher-order problems retain the same differential operators as those of nonlocal CPT, although with different nonhomogeneous terms. Some accurate nonlocal elasticity solutions of the critical load parameters of simply-supported, biaxially-loaded SLNP/SLGS with and without being embedded in the elastic medium are given to demonstrate the performance of the 3D asymptotic nonlocal elasticity theory.
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Thomas Sinn
2015-07-01
Full Text Available The use of morphing components on aerospace structures can greatly increase the versatility of an aircraft. This paper presents the design, manufacturing and testing of a new kind of adaptive airfoil with actuation through Shape Memory Alloys (SMA. The developed adaptive flap system makes use of a novel actuator that employs SMA wires in an antagonistic arrangement with a Post-Buckled Precompressed (PBP mechanism. SMA actuators are usually used in an antagonistic arrangement or are arranged to move structural components with linearly varying resistance levels similar to springs. Unfortunately, most of this strain energy is spent doing work on the passive structure rather than performing the task at hand, like moving a flight control surface or resisting air loads. A solution is the use of Post-Buckled Precompressed (PBP actuators that are arranged so that the active elements do not waste energy fighting passive structural stiffnesses. One major problem with PBP actuators is that the low tensile strength of the piezoelectric elements can often result in tensile failure of the actuator on the convex face. A solution to this problem is the use of SMA as actuator material due to their tolerance of tensile stresses. The power consumption to hold deflections is reduced by approximately 20% with the Post-Buckled Precompressed mechanism. Conventional SMAs are essentially non-starters for many classes of aircraft due to the requirement of holding the flight control surfaces in a given position for extremely long times to trim the vehicle. For the reason that PBP actuators balance out air and structural loads, the steady-state load on the SMAs is essentially negligible, when properly designed. Simulations and experiments showed that the SMAPBP actuator shows tip rotations on the order of 45°, which is nearly triple the levels achieved by piezoelectric PBP actuators. The developed SMAPBP actuator was integrated in a NACA0012 airfoil with a flexible skin
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Cunha, Divino J.S.; Benjamin, Adilson C. [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas
2005-07-01
Three analytical methods frequently used for analyzing upheaval buckling are presented and compared in this work: the Hobbs' method which is applied to straight pipelines, the Pedersen-Jensen's method and the JIP-Shell's method, both applied to pipelines containing initial imperfections. The basic equations of the three methods are outlined and its differences are appointed. Also it is studied the sensitivity of the response of the last two methods to the cover of soil and to the amplitude of the initial imperfection. (author)
Librescu, L.; Khdeir, A. A.; Frederick, D.
1989-01-01
This paper deals with the substantiation of a shear deformable theory of cross-ply laminated composite shallow shells. While the developed theory preserves all the advantages of the first order transverse shear deformation theory it succeeds in eliminating some of its basic shortcomings. The theory is further employed in the analysis of the eigenvibration and static buckling problems of doubly curved shallow panels. In this context, the state space concept is used in conjunction with the Levy method, allowing one to analyze these problems in a unified manner, for a variety of boundary conditions. Numerical results are presented and some pertinent conclusions are formulated.
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Nakai, H.; Kitada, T. [Osaka City Univ. (Japan); Oryu, T. [Kawasaki Heavy Industries Ltd., Kobe (Japan)
1998-10-21
Thin-walled box stub columns such as beams of cable-stayed bridge, suspension bridge tower, arch rib of arch bridge and steel piers and so forth can also bear torsion at the same time besides compression and bending. These thin-walled box stub columns may achieve ultimate condition before reaching to plastic condition due to the effect of local buckling and so forth. Accordingly, it is the important topic to study the properties regarding ultimate strength of thin-walled box members in order to evaluate correctly the effect on load bearing resistance of local buckling. In this report, validity of load bearing resistance curve and ultimate strength interaction curve proposed by authors was studied using load bearing capacity experiment results. As a result, all ultimate strengths obtained by the experiment were higher than the ultimate strengths estimated by load bearing capacity curve and ultimate strength interaction curve. Further, it was revealed that the specimens subjected to torsion or subjected to bending and torsion and so forth exceeded the plastic strength due to the effect of strain hardening. 12 refs., 14 figs., 4 tabs.
Carpineto, Paolo; Aharrh-Gnama, Agbeanda; Ciciarelli, Vincenzo; Borrelli, Enrico; Petti, Francesco; Aloia, Raffaella; Lamolinara, Alessia; Di Nicola, Marta; Mastropasqua, Leonardo
2016-12-01
To evaluate signal transduction and early apoptosis protein levels in subretinal fluid collected during scleral buckling surgery for macula-off rhegmatogenous retinal detachment (RRD). Our aim was to assess both their relation with RRD features and their influence on the posttreatment outcome. Thirty-three eyes of 33 RRD patients scheduled for scleral buckle surgery were enrolled in the study. Undiluted subretinal fluid samples were collected during surgery and analyzed via magnetic bead-based immunoassay. All patients underwent a complete ophthalmologic evaluation at baseline and at each follow-up visit (months 1, 3, and 6). Moreover, both at baseline and at the postsurgery month 6 visit, the patients were tested by means of spectral-domain optical coherence tomography (SD-OCT) in order to evaluate the average ganglion cell-inner plexiform complex thickness, as well as the photoreceptor inner segment/outer segment junction status. Patients' clinical features (retinal detachment size, detachment duration, and occurrence of proliferative vitreoretinopathy) were associated with several early apoptotic factors (caspase-8, caspase-9, and B-cell lymphoma 2 [Bcl-2]-associated death promoter [BAD]). Furthermore, both early apoptosis factors (caspase-8, Bcl-2, and p53) and signal-transduction proteins (ERK 1/2) were found to influence the postsurgery month 3 OCT characteristics. Signal-transduction proteins and early apoptosis proteins are associated with different clinical features and postsurgery outcomes.
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Wen-Fu Zhang
2017-01-01
Full Text Available Even for the doubly symmetric I-beams under linear distributed moment, the design formulas given by codes of different countries are quite different. This paper will derive a dimensionless analytical solution via linear stability theory and propose a new design formula of the critical moment of the lateral-torsional buckling (LTB of the simply supported I-beams under linear distributed moment. Firstly, the assumptions of linear stability theory are reviewed, the dispute concerning the LTB energy equation is introduced, and then the thinking of Plate-Beam Theory, which can be used to fully resolve the challenge presented by Ojalvo, is presented briefly; secondly, by introducing the new dimensionless coefficient of lateral deflection, the new dimensionless critical moment and Wagner’s coefficient are derived naturally from the total potential energy. With these independent parameters, the new dimensionless analytical buckling equation is obtained; thirdly, the convergence performance of the dimensionless analytical solution is discussed by numerical solutions and its correctness is verified by the numerical results given by ANSYS; finally, a new trilinear mathematical model is proposed as the benchmark of formulating the design formula and, with the help of 1stOpt software, the four coefficients used in the proposed dimensionless design formula are determined.
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Shi-Chao Yi
2017-01-01
Full Text Available Closed-form solution of a special higher-order shear and normal deformable plate theory is presented for the static situations, natural frequencies, and buckling responses of simple supported functionally graded materials plates (FGMs. Distinguished from the usual theories, the uniqueness is the differentia of the new plate theory. Each individual FGM plate has special characteristics, such as material properties and length-thickness ratio. These distinctive attributes determine a set of orthogonal polynomials, and then the polynomials can form an exclusive plate theory. Thus, the novel plate theory has two merits: one is the orthogonality, where the majority of the coefficients of the equations derived from Hamilton’s principle are zero; the other is the flexibility, where the order of the plate theory can be arbitrarily set. Numerical examples with different shapes of plates are presented and the achieved results are compared with the reference solutions available in the literature. Several aspects of the model involving relevant parameters, length-to-thickness, stiffness ratios, and so forth affected by static and dynamic situations are elaborate analyzed in detail. As a consequence, the applicability and the effectiveness of the present method for accurately computing deflection, stresses, natural frequencies, and buckling response of various FGM plates are demonstrated.
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Fujikubo, M.; Yao, T.; Varghese, B. [Hiroshima University, Hiroshima (Japan). Faculty of Engineering
1996-10-01
Elasto-plasticity analysis by using the finite element method was performed on a case that bi-axial compression and shear act on a thick rectangular plate, and applicability of the plasticity correction method was discussed. In the discussion, an investigation was made on effect of the loading method of a load on correlation between initial yield strength and ultimate strength of a rectangular plate under bi-axial compression. The analytical result from the finite element method was compared with estimated values derived by using the plasticity correction method with regard to the buckling strength. The result obtained may be summarized as follows: the effect of the loading method for combined load on the correlation between the initial yield strength and the ultimate strength is small; an approximation expression was derived for the upper limit of maximum initial bend of a deck panel of an actual vessel; the plasticity correction method for buckling strength as specified by classification societies has a certain applicability as a method to estimate ultimate strength on the safety side against plate thickness in a range of the upper limit of initial bend of an actual vessel; however, this method may estimate strength higher than the actual value depending on load ratio, hence attention is required. 5 refs., 8 figs.
Svalbonas, V.
1973-01-01
The User's manual for the shell theory automated for rotational structures (STARS) 2B and 2V (buckling, vibrations) is presented. Several features of the program are: (1) arbitrary branching of the shell meridians, (2) arbitrary boundary conditions, (3) minimum input requirements to describe a complex, practical shell of revolution structure, and (4) accurate analysis capability using a minimum number of degrees of freedom.
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Yamamoto, M.; Yao, T.; Yajima, H.; Miyamoto, H.; Morita, S. [Hiroshima University, Hiroshima (Japan). Faculty of Engineering; Ogihara, Y.; Ishikawa, T. [Nippon Steel Corp., Tokyo (Japan)
1996-10-01
Buckling and plastic breakdown strength characteristics of a structure fabricated by using new steel plates with surface layer made into ultra fine grain structure were analyzed and discussed by using a belt plate buckling and plasticity test and the finite element method. The tested steel plate has a thickness of 25 mm, and was fabricated for ocean vessel use, with surface layers on both sides of about 1/6 of the whole thickness having been made an ultra fine grain structure. As a result of a belt steel buckling and plasticity test on a steel plate with surface ratio of 29%, both of the initial yield stress and the buckling stress were found increased by about 4 to 10% as compared with a steel plate having surface ratio of 0%. An analysis by using the finite element method was made on square steel plates with a length of 80 cm, a width of 100 cm, and thicknesses of 12 mm and 24 mm. A result was obtained that, in the case of surface layer ratio of 33%, both of the initial yield stress and the maximum load withstanding force were higher by 5 to 16% than the case of surface ratio of 0%. Similar rise in strength was shown also in bend preventing plates which are basic constituting members of a vessel. 6 refs., 10 figs., 2 tabs.
Rio, G.
This paper concerns the inelastic stability of a thin plate under in-plane loading. In Love-Kirchhoffs approximation, using Hencky's relations and the Von Mises criterion, yield the particular stress distribution across the plate thickness for elastic and elastic-plastic prestress fields. The principle of virtual work is used to study the equilibrium of the bifurcated solution. This leads to the energy relations where explicit dependence between the stability equation coefficients and the solution is carried out. In the equilibrium equation, two nonquadratic additional terms are obtained which are neglected in the classical equation. Some applications are made using Ramberg-Osgood's formula to show the importance of the additional terms.
Fermions on the low-buckled honey-comb structured lattice plane and classical Casimir-Polder force
Goswami, Partha
2016-05-01
We start with the well-known expression for the vacuum polarization and suitably modify it for 2+1-dimensional spin-orbit coupled (SOC) fermions on the low-buckled honey-comb structured lattice plane described by the low-energy Liu-Yao-Feng-Ezawa (LYFE) model Hamiltonian involving the Dirac matrices in the chiral representation obeying the Clifford algebra. The silicene and germanene fit this description suitably. They have the Dirac cones similar to those of graphene and SOC is much stronger. The system could be normal or ferromagnetic in nature. The silicene turns into the latter type if there is exchange field arising due to the proximity coupling to a ferromagnet (FM) such as depositing Fe atoms to the silicene surface. For the silicene, we find that the many-body effects considerably change the bare Coulomb potential by way of the dependence of the Coulomb propagator on the real-spin, iso-spin and the potential due to an electric field applied perpendicular to the silicene plane. The computation aspect of the Casimir-Polder force (CPF) needs to be investigated in this paper. An important quantity in this process is the dielectric response function (DRF) of the material. The plasmon branch was obtained by finding the zeros of DRF in the long-wavelength limit. This leads to the plasmon frequencies. We find that the collective charge excitations at zero doping, i.e., intrinsic plasmons, in this system, are absent in the Dirac limit. The valley-spin-split intrinsic plasmons, however, come into being in the case of the massive Dirac particles with characteristic frequency close to 10 THz. Our scheme to calculate the Casimir-Polder interaction (CPI) of a micro-particle with a sheet involves replacing the dielectric constant of the sample in the CPI expression obtained on the basis of the Lifshitz theory by the static DRF obtained using the expressions for the polarization function we started with. Though the approach replaces a macroscopic constant by a microscopic
Rizzi, Stephen A.; Behnke, marlana N.; Przekop, Adam
2010-01-01
High-cycle fatigue of an elastic-plastic beam structure under the combined action of thermal and high-intensity non-Gaussian acoustic loadings is considered. Such loadings can be highly damaging when snap-through motion occurs between thermally post-buckled equilibria. The simulated non-Gaussian loadings investigated have a range of skewness and kurtosis typical of turbulent boundary layer pressure fluctuations in the vicinity of forward facing steps. Further, the duration and steadiness of high excursion peaks is comparable to that found in such turbulent boundary layer data. Response and fatigue life estimates are found to be insensitive to the loading distribution, with the minor exception of cases involving plastic deformation. In contrast, the fatigue life estimate was found to be highly affected by a different type of non-Gaussian loading having bursts of high excursion peaks.
Ozbasaran, Hakan
Trusses have an important place amongst engineering structures due to many advantages such as high structural efficiency, fast assembly and easy maintenance. Iterative truss design procedures, which require analysis of a large number of candidate structural systems such as size, shape and topology optimization with stochastic methods, mostly lead the engineer to establish a link between the development platform and external structural analysis software. By increasing number of structural analyses, this (probably slow-response) link may climb to the top of the list of performance issues. This paper introduces a software for static, global member buckling and frequency analysis of 2D and 3D trusses to overcome this problem for Mathematica users.
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Yao, T.; Fujikubo, M.; Yanagihara, D.; Irisawa, M. [Hiroshima University, Hiroshima (Japan). Faculty of Engineering
1997-10-01
Buckling and plastic collapse of upper decks and bottom outer plates of a hull results directly in longitudinal bending collapse of the hull. Therefore, discussions were given on analysis for pressure destruction strength of a detection control panel which assumes an upper deck and a bottom outer plate. Pressure destruction behavior of the panting panel is a complex phenomenon accompanying non-linearity and geometrical non-linearity of the materials. Its whole phenomenon may be analyzed by using the finite element method (FEM) as a principle, but the analysis is not efficient. Therefore, considerations were given in relation to modeling when using the FEM. The considerations were given on a panel attached with flat steel panting members with respect to the modeling scope which considers the buckling mode according to the aspect ratio of the panel partitioned by the deflection control members. If the local buckling mode of the panel is an even number wave mode in the longitudinal direction, a triple span model is required. A modeling scope for a case of being subjected to water pressure and in-plane compression was considered on a panel attached with angle-type steel members having non-symmetric cross section. In this case, a triple bay model is more preferable to reproduce the behavior under water pressure loading. 1 ref., 6 figs.
Nataf, David M.
2017-09-01
The assembly of the Milky Way bulge is an old topic in astronomy, one now in a period of renewed and rapid development. That is due to tremendous advances in observations of bulge stars, motivating observations of both local and high-redshift galaxies, and increasingly sophisticated simulations. The dominant scenario for bulge formation is that of the Milky Way as a nearly pure disk galaxy, with the inner disk having formed a bar and buckled. This can potentially explain virtually all bulge stars with [Fe/H] ≳ -1.0, which comprise 95% of the stellar population. The evidence is the incredible success in N-body models of this type in making non-trivial, non-generic predictions, such as the rotation curve and velocity dispersion measured from radial velocities, and the spatial morphologies of the peanut/X-shape and the long bar. The classical bulge scenario, whereby the bulge formed from early dissipative collapse and mergers, remains viable for stars with [Fe/H] ≲ -1.0 and potentially a minority of the other stars. A classical bulge is expected from Λ-CDM cosmological simulations, can accentuate the properties of an existing bar in a hybrid system, and is most consistent with the bulge abundance trends such as [Mg/Fe], which are elevated relative to both the thin and thick disks. Finally, the clumpy-galaxy scenario is considered, as it is the correct description of most Milky Way precursors given observations of high-redshift galaxies. Simulations predict that these star-forming clumps will sometimes migrate to the centres of galaxies where they may form a bulge, and galaxies often include a bulge clump as well. They will possibly form a bar with properties consistent with those of the Milky Way, such as the exponential profile and metallicity gradient. Given the relative successes of these scenarios, the Milky Way bulge is plausibly of composite origin, with a classical bulge and/or inner halo numerically dominant for stars with [Fe/H] ≲ -1.0, a buckling
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Anton Shterenlikht
2017-01-01
Full Text Available An automatic framework for tuning plastic constitutive models is proposed. It is based on multistart global optimisation method, where the objective function is provided by the results of multiple elastoplastic finite element analyses, executed concurrently. Wrapper scripts were developed for fully automatic preprocessing, including model and mesh generation, analysis, and postprocessing. The framework is applied to an isotropic power hardening plasticity using real load/displacement data from multiple steel buckling tests. M. J. D. Powell’s BOBYQA constrained optimisation package was used for local optimisation. It is shown that using the real data presents multiple problems to the optimisation process because (1 the objective function can be discontinuous, yet (2 relatively flat around multiple local minima, with (3 similar values of the objective function for different local minima. As a consequence the estimate of the global minimum is sensitive to the amount of experimental data and experimental noise. The framework includes the verification step, where the estimate of the global minimum is verified on a different geometry and loading. A tensile test was used for verification in this work. The speed of the method critically depends on the ability to effectively parallelise the finite element solver. Three levels of parallelisation were exploited in this work. The ultimate limitation was the availability of the finite element commercial solver license tokens.
Gharbiya, M; Malagola, R; Mariotti, C; Parisi, F; De Vico, U; Ganino, C; Grandinetti, F
2015-01-01
Purpose To determine the predictive value of markers for persistent subretinal fluid (SRF) absorption and the influence of subfoveal fluid on visual outcome after scleral buckle (SB) surgery for rhegmatogenous retinal detachment (RRD). Patients and methods This was a retrospective, observational study. We reviewed the medical records of 64 eyes of 64 patients who underwent SB surgery for macula-off RRD. Patients underwent clinical examination and spectral-domain optical coherence tomography before surgery, at 1 month and every 3 months postoperatively. The height and width of SRF bleb(s) were measured over time. Results Persistent SRF at 1 month was observed in 40 eyes (62.5%). SRF blebs were first detected 1.7±2.2 months postoperatively. In 29 cases that could be fully followed up, SRF blebs were completely absorbed 7.8±4.4 months postoperatively. Resolution of fluid was associated with an improvement of VA (P=0.003). Serial measurements of SRF bleb size showed that bleb width decreased significantly at all time points during the 12-month follow-up period (P0.05). The cut-off value of the bleb width-to-height ratio level for predicting bleb absorption at 6 months was 7, with 89% sensitivity and 83% specificity. Conclusions Visual improvement may occur with late resolution of residual subfoveal fluid. A bleb width-to-height ratio >7 indicates a higher risk of SRF to persist beyond 6 months after surgery. PMID:26139048
Pineda, Evan J.; Myers, David E.; Kosareo, Daniel N.; Kellas, Sotiris
2014-01-01
Four honeycomb sandwich panels, representing 1/16th arc segments of a 10 m diameter barrel section of the heavy lift launch vehicle, were manufactured under the NASA Composites for Exploration program and the NASA Constellation Ares V program. Two configurations were chosen for the panels: 6-ply facesheets with 1.125 in. honeycomb core and 8-ply facesheets with 1.000 in. honeycomb core. Additionally, two separate carbon fiber/epoxy material systems were chosen for the facesheets: inautoclave IM7/977-3 and out-of-autoclave T40-800B/5320-1. Smaller 3- by 5-ft panels were cut from the 1/16th barrel sections. These panels were tested under compressive loading at the NASA Langley Research Center. Furthermore, linear eigenvalue and geometrically nonlinear finite element analyses were performed to predict the compressive response of the 3- by 5-ft panels. This manuscript summarizes the experimental and analytical modeling efforts pertaining to the panel composed of 8-ply, T40-800B/5320-1 facesheets (referred to as Panel C). To improve the robustness of the geometrically nonlinear finite element model, measured surface imperfections were included in the geometry of the model. Both the linear and nonlinear, two-dimensional (2-D) and three-dimensional (3-D), models yield good qualitative and quantitative predictions. Additionally, it was predicted correctly that the panel would fail in buckling prior to failing in strength.
Pineda, Evan Jorge; Myers, David E.; Kosareo, Daniel N.; Zalewski, Bart F.; Kellas, Sotiris; Dixon, Genevieve D.; Krivanek, Thomas M.; Gyekenyesi, Thomas G.
2014-01-01
Four honeycomb sandwich panels, representing 1/16th arc segments of a 10-m diameter barrel section of the Heavy Lift Launch Vehicle, were manufactured and tested under the NASA Composites for Exploration and the NASA Constellation Ares V programs. Two configurations were chosen for the panels: 6-ply facesheets with 1.125 in. honeycomb core and 8-ply facesheets with 1.0 in. honeycomb core. Additionally, two separate carbon fiber/epoxy material systems were chosen for the facesheets: in-autoclave IM7/977-3 and out-of-autoclave T40-800b/5320-1. Smaller 3 ft. by 5 ft. panels were cut from the 1/16th barrel sections and tested under compressive loading. Furthermore, linear eigenvalue and geometrically nonlinear finite element analyses were performed to predict the compressive response of each 3 ft. by 5 ft. panel. To improve the robustness of the geometrically nonlinear finite element model, measured surface imperfections were included in the geometry of the model. Both the linear and nonlinear models yielded good qualitative and quantitative predictions. Additionally, it was correctly predicted that the panel would fail in buckling prior to failing in strength. Furthermore, several imperfection studies were performed to investigate the influence of geometric imperfections, fiber angle misalignments, and three-dimensional effects on the compressive response of the panel.
Mieszala, Maxime; Hasegawa, Madoka; Guillonneau, Gaylord; Bauer, Jens; Raghavan, Rejin; Frantz, Cédric; Kraft, Oliver; Mischler, Stefano; Michler, Johann; Philippe, Laetitia
2017-02-01
By designing advantageous cellular geometries and combining the material size effects at the nanometer scale, lightweight hybrid microarchitectured materials with tailored structural properties are achieved. Prior studies reported the mechanical properties of high strength cellular ceramic composites, obtained by atomic layer deposition. However, few studies have examined the properties of similar structures with metal coatings. To determine the mechanical performance of polymer cellular structures reinforced with a metal coating, 3D laser lithography and electroless deposition of an amorphous layer of nickel-boron (NiB) is used for the first time to produce metal/polymer hybrid structures. In this work, the mechanical response of microarchitectured structures is investigated with an emphasis on the effects of the architecture and the amorphous NiB thickness on their deformation mechanisms and energy absorption capability. Microcompression experiments show an enhancement of the mechanical properties with the NiB thickness, suggesting that the deformation mechanism and the buckling behavior are controlled by the brittle-to-ductile transition in the NiB layer. In addition, the energy absorption properties demonstrate the possibility of tuning the energy absorption efficiency with adequate designs. These findings suggest that microarchitectured metal/polymer hybrid structures are effective in producing materials with unique property combinations. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Pineda, Evan J.; Meyers, David E.; Kosareo, Daniel N.; Zalewski, Bart F.; Dixon, Genevieve D.
2013-01-01
Four honeycomb sandwich panel types, representing 1/16th arc segments of a 10-m diameter barrel section of the Heavy Lift Launch Vehicle (HLLV), were manufactured and tested under the NASA Composites for Exploration program and the NASA Constellation Ares V program. Two configurations were chosen for the panels: 6-ply facesheets with 1.125 in. honeycomb core and 8-ply facesheets with 1.000 in. honeycomb core. Additionally, two separate carbon fiber/epoxy material systems were chosen for the facesheets: in-autoclave IM7/977-3 and out-of-autoclave T40-800b/5320-1. Smaller 3- by 5-ft panels were cut from the 1/16th barrel sections. These panels were tested under compressive loading at the NASA Langley Research Center (LaRC). Furthermore, linear eigenvalue and geometrically nonlinear finite element analyses were performed to predict the compressive response of each 3- by 5-ft panel. This manuscript summarizes the experimental and analytical modeling efforts pertaining to the panels composed of 6-ply, IM7/977-3 facesheets (referred to as Panels B-1 and B-2). To improve the robustness of the geometrically nonlinear finite element model, measured surface imperfections were included in the geometry of the model. Both the linear and nonlinear models yield good qualitative and quantitative predictions. Additionally, it was correctly predicted that the panel would fail in buckling prior to failing in strength. Furthermore, several imperfection studies were performed to investigate the influence of geometric imperfections, fiber angle misalignments, and three-dimensional (3-D) effects on the compressive response of the panel.
Gama, I; Proença, H; Gonçalves, A; Faria, M; Almeida, L; Bernardo, T; Couceiro, R; Monteiro-Grillo, M
2017-12-01
To evaluate the macular choroidal thickness (CT) of eyes subjected to pars plana vitrectomy (PPV) whether or not combined with encircling scleral buckling (ESB) surgery for primary rhegmatogenous retinal detachment repair at 6 months or more after surgery. This observational study included: 15 eyes (15 patients) submitted to combined ESB+PPV; 15 eyes submitted to PPV and their respective 30 normal fellow eyes (FE). Two 6mm lineal perpendicular optical coherence tomography B-scans centred on the fovea with enhanced depth imaging were performed on each eye. CT was measured at several macular locations: subfoveal (SF-CT) and at a radius of 1, 2, and 3mm from the fovea. CTs of the eyes in the CE+PPV group were compared to CT in the PPV group and the CTs of all operated eyes were compared to the CTs of their FE. SF-CT of the eyes in the ESB+PPV group was significantly increased compared to their FE (P=.001). CT at a radius of 1, 2, and 3mm from the fovea of the ESB+PPV group were significantly increased (P=.001, P=.005, and P=.001, respectively). The SF-CT of the PPV group was similar to their FE (P=.691). The SF-CT of the ESB+PPV group was significantly increased compared to SF-CT of the PPV group (P=.019). The CT of the eyes subjected to combined ESB and PPV was significantly increased at 6 months or more after surgery compared to the CT of their FE and to the CT of the eyes subjected to PPV alone, which could be explained by a venous engorgement caused by the ESB. Copyright © 2017 Sociedad Española de Oftalmología. Publicado por Elsevier España, S.L.U. All rights reserved.
Directory of Open Access Journals (Sweden)
Alptekin YAVAŞ
2012-09-01
Full Text Available The Anatolian Seljuk Period is one of the underregognized periods of Turkish Art of Metal. Our knowledge concerning this period is limited to some objects, such as incense and candle holders made from percious metals. In this article, belts and hunger buckles are first promoted as wares of daily use in Medieval Turkish Period. The last 30 years-long excavations in Kubad-Abad Palace located in Beyşehir district of Konya, one of the best preserved palaces of the Anatolian Seljuk Period, made available to retrieve number of different objects asantiques giving insights into the Medieval times. Kubad-Abad is locatedon an alluvium plain on the south-western shores of Konya-BeyşehirLake, at the foot of the Anamas Mountain. It surrounds the Bronze Agemound. It is a large city-palace that stretches from the lake shore – evenfrom the islands in the lake – to the Anamas Mountain and holds tensof constructions. The metal findings of the palace famous with itsworldwide known tiles hold a very rich repertoire. The belts and hungerbuckles as poorly known finds provide solid evidence with regards torecognition of the wares of daily use in Seljuks. The nature of belt andbuckle straps pertain to the Medieval Turkish period has not beenattempted in detail so far. Among these, one-side written bordurehunger buckle is a rare object in the Anatolian Seljuk Period andpossibly belongs to sultan and his family circle. Anadolu Selçuklu dönemi, Türk Maden Sanatının en az bilinen dönemlerinden biridir. Bu döneme ilişkin veriler kıymetli metallerden yapılmış şamdan, buhurdan gibi objelerle sınırlıdır. Bu çalışmada Ortaçağ Türk Dönemi Kazıları arasında ilk kez gündelik kullanım eşyalarından kemer ve askı tokaları tanıtılacaktır. Anadolu Selçuklu döneminin günümüze en iyi durumda ulaşabilmiş saraylarından biri olan Konya-Beyşehir ilçesindeki Kubad-Abad Sarayında yaklaşık 30 yıldır süren kazı çalışmaları ile Orta
Computerized Buckling Analysis of Shells
1981-06-01
Flight Dynamics Laboratory (AFWAL/ FIBRA ) June 1981 AF Wright Aeronautical Laboratories (AFSC) 13 NI•RfPA;ES Wright-Patterson Air Force BWse OH 45433...tures." The work was administered by Lt Col J. D. Morgan (AFOSR) and Dr N. S. Khot (AFWAL/ FIBRA ) The contract work was performed between October 1977 and... coco -1 C,, Cý C c -. - .-. C) r) 10 10) q~ C) - col C) -i H H H H H- ’.0 m0 CD q) q k.0 10 m ) 10 10 10 ;r ’IT No r CD mO t.0 W. N- 4 N 10 N N Nr O C C
Dimple Patterns in Buckling Surfaces
Breid, Derek; Crosby, Alfred
2010-03-01
Surface wrinkling has attracted considerable attention in recent years for its ability to generate micro- and nano- scale surface structures via non-lithographic pathways. Although the wrinkle morphology has been considered from an energetic viewpoint for stresses exceeding the critical bifurcation stress, the wrinkle morphology for stress near the critical value is far less understood, in part due to a lack of experimental results in this regime. Recent models for this regime predict the formation of a dimple-phase morphology when the stress is equibiaxial, transitioning to aligned ridges when the stress is anisotropic. Here, we present an experimental investigation into the formation of dimple arrays through the control of the applied stress as well as the geometric parameters of the wrinkling system. We demonstrate the ability to develop dimple arrays over extensive lateral length scales, as well as dimples on the surface of a microscale hemisphere, resulting in a `golf ball' hierarchical structure. These results shed light on the morphology in the near-critical wrinkle regime and provoke many open questions about the underlying materials mechanics in the development of wrinkle surface structures.
Sequential buckling : a variational analysis
M.A. Peletier (Mark)
1999-01-01
textabstractWe examine a variational problem from elastic stability theory: a thin elastic strut on an elastic foundation. The strut has infinite length, and its lateral deflection is represented by $u:RtoR$. Deformation takes place under conditions of prescribed total shortening, leading to the
Stability Landscape of Shell Buckling
Virot, Emmanuel; Kreilos, Tobias; Schneider, Tobias M.; Rubinstein, Shmuel M.
2017-12-01
We measure the response of cylindrical shells to poking and identify a stability landscape, which fully characterizes the stability of perfect shells and imperfect ones in the case where a single defect dominates. We show that the landscape of stability is independent of the loading protocol and the poker geometry. Our results suggest that the complex stability of shells reduces to a low dimensional description. Tracking ridges and valleys of this landscape defines a natural phase-space coordinates for describing the stability of shells.
Energy Technology Data Exchange (ETDEWEB)
Asai, Shinichiro; Soda, Minoru; Kasatani, Kazuhiro; Ono, Toshio; Garlea, Vasile Ovidiu; Winn, Barry L.; Masuda, Takatsugu
2017-09-01
We carried out inelastic neutron scattering experiments on a buckled honeycomb lattice antiferromagnet Ba2NiTeO6 exhibiting a stripe structure at a low temperature. Magnetic excitations are observed in the energy range of ℏω≲10 meV having an anisotropy gap of 2 meV at 2 K. We perform spin-wave calculations to identify the spin model. The obtained microscopic parameters are consistent with the location of the stripe structure in the classical phase diagram. Furthermore, the Weiss temperature independently estimated from a bulk magnetic susceptibility is consistent with the microscopic parameters. The results reveal that a competition between the nearest-neighbor and next-nearest-neighbor interactions that together with a relatively large single-ion magnetic anisotropy stabilize the stripe magnetic structure.
Myers, David E.; Pineda, Evan J.; Zalewski, Bart F.; Kosareo, Daniel N.; Kellas, Sotiris
2013-01-01
Four honeycomb sandwich panels, representing 1/16th arc segments of a 10-m diameter barrel section of the heavy lift launch vehicle, were manufactured under the NASA Composites for Exploration program and the NASA Space Launch Systems program. Two configurations were chosen for the panels: 6-ply facesheets with 1.125 in. honeycomb core and 8-ply facesheets with 1.000 in. honeycomb core. Additionally, two separate carbon fiber/epoxy material systems were chosen for the facesheets: inautoclave IM7/977-3 and out-of-autoclave T40-800b/5320-1. Smaller 3.00- by 5.00-ft panels were cut from the 1/16th barrel sections. These panels were tested under compressive loading at the NASA Langley Research Center. Furthermore, linear eigenvalue and geometrically nonlinear finite element analysis was performed to predict the compressive response of the 3.00- by 5.00-ft panels. This manuscript summarizes the experimental and analytical modeling efforts pertaining to the panel composed of 8-ply, IM7/977-3 facesheets (referred to Panel A). To improve the robustness of the geometrically nonlinear finite element model, measured surface imperfections were included in the geometry of the model. Both the linear and nonlinear models yield good qualitative and quantitative predictions. Additionally, it was predicted correctly that the panel would fail in buckling prior to failing in strength. Furthermore, several imperfection studies were performed to investigate the influence of geometric imperfections, fiber misalignments, and three-dimensional (3 D) effects on the compressive response of the panel.
Directory of Open Access Journals (Sweden)
Iuuki Takasaka
2012-12-01
Full Text Available OBJETIVE: To describe the reattachment rate and visual acuity results of patients with uncomplicated rhegmatogenous retinal detachment who underwent segmental scleral buckle surgery. METHODS: Prospective case series of 100 patients with visual loss or symptoms (floaters and photopsia of less than 30 days' duration scheduled for surgery. No patient had a retinal break greater than 30°, a retinal detachment larger than 2 quadrants or proliferative vitreoretinopathy. RESULTS: The 1-week, 1-month, and 6-month anatomical success rates were 93%, 100%, and 100%, respectively. Seven patients underwent one additional retinal detachment surgery (pars plan vitrectomy after primary failure at 1-week follow-up. The preoperative, 1-month, and 6-month best correct visual acuity were 20/100, 20/80, and 20/50, respectively. The postoperative complications were: eyelid edema in 10% of the patients, transient ocular hypertension in 5%, macular pucker in 3%, transient diplopia in 3%, and hyphema (OBJETIVO: Descrever a taxa de reaplicação e os resultados da acuidade visual dos pacientes com descolamento de retina regmatogênico simples que se submeteram à cirurgia de introflexão escleral segmentar. MÉTODOS: Uma série de casos prospectivo de 100 pacientes com perda visual ou sintomas (floaters e fotopsia, com duração inferior a 30 dias, agendados para a cirurgia. Nenhum paciente apresentou uma ruptura da retina superior a 30°, um descolamento de retina maior que 2 quadrantes ou vitreorretinopatia. RESULTADOS: As taxas de sucesso anatômico em 1 semana, 1 mês e 6 meses foram de 93%, 100% e 100%, respectivamente. Sete pacientes foram submetidos à cirurgia de descolamento de retina adicional (vitrectomia via pars plana após falha primária em uma semana de seguimento. A melhor acuidade visual pré-operatória, 1 mês, e de 6 meses pós-operatório foram 20/100, 20/80 e 20/50, respectivamente. As complicações pós-operatórias foram: edema palpebral em 10
Buckling analysis of continuous welded rail track
Van, M.A.
1996-01-01
Continuous welded rail track, compared to jointed track not only reduces maintenance costs, but also increases life time of track components and the comfort of passengers. Since expansion of the rails is hardly possible in CWR-track, a temperature increase will result in high compressive stresses
Advances and Trends in Plate Buckling Research.
1982-12-01
Hydrostatic State of In- Plane Stress. Instituto de Mecanica Aplicada No. 79-21 (Puerto Belgrano, Argentina), June 1979, 10 pp. (to be published). 38. Leissa...and Elastic Stability of Circular Plates With Thickness Varying in a Bilinear Fashion. Instituto de Mecanica Aplicada No. 81-23 (Puerto Belgrano
FLEXURAL, TORSIONAL AND DISTORTIONAL BUCKLING OF ...
African Journals Online (AJOL)
ABSTRACT. Instability is an important branch of structural mechanics which examines alternate equilibrium states associated with large deformations. In this study, Varbanov's generalized strain fields and Vlasov's displacement equations were used to obtain a set of equations for neutral equilibrium of axially compressed ...
Buckling of Bucket Foundations During Installation
DEFF Research Database (Denmark)
Madsen, Søren
There is a great politically will to expand the green energy market in these times. A proven green technology is wind turbines. Wind turbines have been installed in great numbers on land over the last decades. However, the current development in wind turbine design leads to larger turbine sizes...... in order to reduce the cost of energy. This limits the on land application due to transportation limitations and unwillingness from prospect neighbours. Thus, offshore wind energy started developing over the last couple of years. Although installing the wind turbines offshore resolves the before men tioned...... issues, it brings up the cost of energy mainly due to increased installation and maintenance costs. A very large part—up to 30–50% using current technology—of the installation cost origins from the expenses related to the installation of foundations. A new foundation concept—the bucket foundation...
Yield stress independent column buckling curves
DEFF Research Database (Denmark)
Stan, Tudor‐Cristian; Jönsson, Jeppe
2017-01-01
in the definition of the normalised imperfection magnitudes. By introducing this factor it seems that the GMNIA analysis and knowledge of the independency of residual stress levels on the yield stress can be brought together and give results showing consistency between numerical modelling and a simple modified...... Ayrton‐Perry formulation. In this paper magnitudes of imperfections and residual stresses in relation to the Eurocode will be discussed. It will be shown that the use of equivalent imperfections may be very conservative if considered by finite element analysis as described in the current Eurocode code...
Different buckling regimes in direct electrospinning: A comparative approach to rope buckling
Shariatpanahi, S.P.; Etesami, Z.; Iraji zad, A.; Bonn, D.; Ejtehadi, M.R.
2015-01-01
Understanding the dynamics of direct electrospinning is the key to control fiber morphologies that are critical for the development of new electrospinning methods and novel materials. Here, we propose the theory for direct electrospinning based on theories for (liquid) "rope coiling" and
Sky dancer: the threshold of the buckling instability
Cros, Anne; Ibarra Nuño, Rodolfo; Michon, Bastien
2012-11-01
The sky dancer is a fabric-made large vertical tube which may ``dance'' above an air blower. We reproduced in laboratory reduced models, with diameters between 2.2 and 3 cm, and lengths varying from 45 to 95 cm. We measured the air speed and the pressure at the tube basis for the lower threshold of the tube. This threshold separates two regimes: the first one which appears for the lower velocities, when the tube falls down because of its own weight, from the second one, which corresponds to the stable regime, for which the tube stands up. Our measurements show that the air pressure thresholds get values equal to the pressure performed by the tube weight. We discuss our results and compare them with previous studies which dealt with thicker-walled tubes.
Elastic buckling analysis of corroded stiffened plates with irregular ...
Indian Academy of Sciences (India)
girders (figure 1), has been used as a main structural element in ship and offshore structures for their high strength-to-weight ... strength reduction of corroded deck plates in 20 years old ships under uniform longitudinal compression. General ..... Timoshenko S P and Gere J M 1961 Theory of elastic stability. 2nd ed, Eng.
Deformation and buckling of microcapsules in a viscoelastic matrix
Raffiee, Amir Hossein; Dabiri, Sadegh; Ardekani, Arezoo M.
2017-09-01
In this paper, we numerically study the dynamics of (1) a Newtonian liquid-filled capsule in a viscoelastic matrix and that of (2) a viscoelastic capsule in a Newtonian matrix in a linear shear flow using a front-tracking method. The numerical results for case (1) indicate that the polymeric fluid reduces the capsule deformation and aligns the deformed capsule with the flow direction. It also narrows the range of tension experienced by the deformed capsule for case (1), while the tank-treading period significantly increases. Interestingly, the polymeric fluid has an opposite effect on the tank-treading period and the orientation angle of case (2), but its effect on the deformation is similar to case (1).
Experimental investigations on buckling of cylindrical shells under ...
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
experimentally to validate the design. Keeping this in mind, a test programme has been for- mulated at the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam to carry out experimental studies on ..... mounting the specimen on the test bed with all its instrumentation, firstly the imperfection survey is carried out.
Parametric study on buckling behaviour of thin stainless steel ...
African Journals Online (AJOL)
user
imperfections are usually converted into a modal or Fourier series representation which can be easily used for analysis or design. Similar approach of imperfection studies were followed in other studies also. For example on thin metallic shells, Arbocz and Hol. (1991), Schneider (1996), Singer (1999) and Athiannan and ...
Buckling Load of Reinforced Concrete Frames in Fire Conditions
Bajc, Urška
2015-01-01
In the dissertation a failure scenarios of reinforced concrete columns in fire and for the scenarios suitable calculating procedure for determination of fire load capacity are introduced. The calculating procedures are numerical and, where is possible, semi-analytical as well. In the end all partial calculating procedures are combined in a global algorithm for determining the fire load capacity of reinforced concrete column. The main novelties of the global algorithm are, that we ...
Buckling of Bilayer Laminates - A Novel Approach to Synthetic Papillae
2013-10-01
Randolph St Arlington, VA 22203 A = Approved for public release; distribution is unlimited Cephalopods can reversibly change their appearance by...bilayer laminates‐ A novel approach to synthetic papillae Grant/Contract Number: FA9550‐10‐1‐0329 Final report Abstract Cephalopods can...reversibly‐texturing surfaces. Finally we have made progress in two projects that were not directly related to cephalopods , but nevertheless relevant to
A deflection, buckling and stress investigation into telescopic cantilever beams
Abraham, Jeevan George
2012-01-01
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University. The telescoping cantilever beam structure is applied in many different engineering sectors to achieve weight/space optimisation for structural integrity. There has been limited theory and analysis in the public domain of the stresses and deflections involved when applying a load to such a structure. This thesis proposes (a) The Tip Reaction Model, which adapts classical mechanics to predict...