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...
Vibration and buckling studies of pretensioned structures
Belvin, W. K.
1982-01-01
Results of analyses and tests of a simple pretensional structure are presented. Linear finite element analysis correlated well with experimental small amplitude vibration data. The buckling and vibration behavior of a pretensional stayed column was studied in detail. The bifurcation buckling load was also predicted accurately. Postbuckling behavior of the column was unusual and results in a post buckling restoring force of only 1/64 the bifurcation buckling load. Interaction between lateral accelerations and compressive load creates isolated stay slackening at loads above 50 percent of the buckling load. Further research will be required to fully understand their impact on the use of pretensioned structures as large space structures.
Structure of twisted and buckled bilayer graphene
Jain, Sandeep K.; Juričić, Vladimir; Barkema, Gerard T.
2017-03-01
We study the atomic structure of twisted bilayer graphene, with very small mismatch angles (θ ∼ {0.28}0), a topic of intense recent interest. We use simulations, in which we combine a recently presented semi-empirical potential for single-layer graphene, with a new term for out-of-plane deformations, (Jain et al 2015 J. Phys. Chem. C 119 9646) and an often-used interlayer potential (Kolmogorov et al 2005 Phys. Rev. B 71 235415). This combination of potentials is computationally cheap but accurate and precise at the same time, allowing us to study very large samples, which is necessary to reach very small mismatch angles in periodic samples. By performing large scale atomistic simulations, we show that the vortices appearing in the Moiré pattern in the twisted bilayer graphene samples converge to a constant size in the thermodynamic limit. Furthermore, the well known sinusoidal behavior of energy no longer persists once the misorientation angle becomes very small (θ \\lt {1}0). We also show that there is a significant buckling after the relaxation in the samples, with the buckling height proportional to the system size. These structural properties have direct consequences on the electronic and optical properties of bilayer graphene.
Theory of buckling and post-buckling behavior of elastic structures
Budiansky, B.
1974-01-01
The present paper provides a unified, general presentation of the basic theory of the buckling and post-buckling behavior of elastic structures in a form suitable for application to a wide variety of special problems. The notation of functional analysis is used for this purpose. Before the general analysis, simple conceptual models are used to elucidate the basic concepts of bifurcation buckling, snap buckling, imperfection sensitivity, load-shortening relations, and stability. The energy approach, the virtual-work approach, and mode interaction are discussed. The derivations and results are applicable to continua and finite-dimensional systems. The virtual-work and energy approaches are given separate treatments, but their equivalence is made explicit. The basic concepts of stability occupy a secondary position in the present approach.
Static and dynamic buckling of thin-walled plate structures
Kubiak, Tomasz
2013-01-01
This monograph deals with buckling and postbuckling behavior of thin plates and thin-walled structures with flat wall subjected to static and dynamic load. The investigations are carried out in elastic range. The basic assumption here is the thin plate theory. This method is used to determination the buckling load and postbuckling analysis of thin-walled structures subjected to static and dynamic load. The book introduces two methods for static and dynamic buckling investigation which allow for a wider understanding of the phenomenon. Two different methods also can allow uncoupling of the phenomena occurring at the same time and attempt to estimate their impact on the final result. A general mathematical model, adopted in proposed analytical-numerical method, enables the consideration of all types of stability loss i.e.local, global and interactive forms of buckling. The applied numerical-numerical method includes adjacent of walls, shear-lag phenomenon and a deplanation of cross-sections.
NONLINEAR BUCKLING CHARACTERISTIC OF GRADED MULTIWEB STRUCTURE OF HETEROGENEOUS MATERIALS
Institute of Scientific and Technical Information of China (English)
LI Yong; ZHANG Zhi-min
2005-01-01
The graded multiweb structure of heterogeneous anisotropic materials, which makes full use of the continuous, gradual and changing physical mechanical performance of material properties, has a widespread application in aeroplane aerofoil structure and automobile lightweight structure. On the basis of laminate buckling theory,the equivalent rigidity method is adopted to establish the corresponding constitutive relation and the non-linear buckling governing equation for the graded multiweb structure. In finding the solution, the critical load of buckling under different complicated boundary conditions together with combined loads were obtained and testification of the experimental analysis shows that the calculation results can satisfy the requirements of engineering design in a satisfactory way. Results obtained from the research say that: graded materials can reduce the concentrated stress on the interface in an effective way and weaken the effect of initial defect in materials and thereby improve the strength and toughness of materials.
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.
Robust simulation of buckled structures using reduced order modeling
Wiebe, R.; Perez, R. A.; Spottswood, S. M.
2016-09-01
Lightweight metallic structures are a mainstay in aerospace engineering. For these structures, stability, rather than strength, is often the critical limit state in design. For example, buckling of panels and stiffeners may occur during emergency high-g maneuvers, while in supersonic and hypersonic aircraft, it may be induced by thermal stresses. The longstanding solution to such challenges was to increase the sizing of the structural members, which is counter to the ever present need to minimize weight for reasons of efficiency and performance. In this work we present some recent results in the area of reduced order modeling of post- buckled thin beams. A thorough parametric study of the response of a beam to changing harmonic loading parameters, which is useful in exposing complex phenomena and exercising numerical models, is presented. Two error metrics that use but require no time stepping of a (computationally expensive) truth model are also introduced. The error metrics are applied to several interesting forcing parameter cases identified from the parametric study and are shown to yield useful information about the quality of a candidate reduced order model. Parametric studies, especially when considering forcing and structural geometry parameters, coupled environments, and uncertainties would be computationally intractable with finite element models. The goal is to make rapid simulation of complex nonlinear dynamic behavior possible for distributed systems via fast and accurate reduced order models. This ability is crucial in allowing designers to rigorously probe the robustness of their designs to account for variations in loading, structural imperfections, and other uncertainties.
DEFF Research Database (Denmark)
Henrichsen, Søren Randrup; Lindgaard, Esben; Lund, Erik
2015-01-01
Robust design of laminated composite structures is considered in this work. Because laminated composite structures are often thin walled, buckling failure can occur prior to material failure, making it desirable to maximize the buckling load. However, as a structure always contains imperfections...
DEFF Research Database (Denmark)
Madsen, Søren; Pinna, Rodney; Randolph, M. F.
2015-01-01
Using large monopod bucket foundations as an alternative to monopiles for offshore wind turbines offers the potential for large cost savings compared to typical piled foundations. In this paper, numerical simulations are carried out to assess the risk of structural buckling during installation...... is investigated. The effects of including soil restraint and soil–structure interaction on the buckling analysis are also addressed....
Micro-wrinkling and delamination-induced buckling of stretchable electronic structures
Oyewole, O. K.; Yu, D.; Du, J.; Asare, J.; Oyewole, D. O.; Anye, V. C.; Fashina, A.; Zebaze Kana, M. G.; Soboyejo, W. O.
2015-06-01
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.
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.
Structure buckling and non-probabilistic reliability analysis of supercavitating vehicles
Institute of Scientific and Technical Information of China (English)
AN Wei-guang; ZHOU Ling; AN Hai
2009-01-01
To perform structure buckling and reliability analysis on supercavitating vehicles with high velocity in the submarine, supercavitating vehicles were simplified as variable cross section beam firstly. Then structural buckling analysis of supercavitating vehicles with or without engine thrust was conducted, and the structural buckling safety margin equation of supercavitating vehicles was established. The indefinite information was de-scribed by interval set and the structure reliability analysis was performed by using non-probabilistic reliability method. Considering interval variables as random variables which satisfy uniform distribution, the Monte-Carlo method was used to calculate the non-probabilistic failure degree. Numerical examples of supercavitating vehi-cles were presented. Under different ratios of base diameter to cavitator diameter, the change tendency of non-probabilistic failure degree of structural buckling of supereavitating vehicles with or without engine thrust was studied along with the variety of speed.
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 introduced to reveal how sensitive the buckling load is to the mentioned imperfections. Including the first 21 mode shapes as imperfect geometries reduces the buckling pressure compared to only considering mode 1....
Predictive analysis of buckling distortion of thin-plate welded structures
Institute of Scientific and Technical Information of China (English)
杨新岐; 霍立兴; 张玉凤; 阎俊霞
2002-01-01
The welding buckling distortions of thin-plated structures were investigated based on finite element methods. An engineering treatment method for predicating the buckling distortion was proposed. The equivalent applied thermal-load was used to simulate the welding residual stress, thus the calculation of complex welding distortion can be transformed into 3D elastic structural applied-load analyses, which can reduce the quantities of calculating work effectively. The validation of the method was verified by comparison of the numerical calculation with experimental results. The prediction of buckling distortion for side-walled structures of passenger train was performed and the calculation was in agreement with measuring results in general. It is shown that the main factors for producing the buckling are the intermittent fillet and plug weld during welding the stiffened beams and columns to the panel.
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...... buckling of the column. The paper proposes use of plate buckling response, in terms of in-plane load and axial deformation, as modified stress-strain curves for use in column analysis. These curves can be derived from numerical analysis of such plates or may be based on experiments, where available. When...
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.
Optimization Formulations for the Maximum Nonlinear Buckling Load of Composite Structures
DEFF Research Database (Denmark)
Lindgaard, Esben; Lund, Erik
2011-01-01
This paper focuses on criterion functions for gradient based optimization of the buckling load of laminated composite structures considering different types of buckling behaviour. A local criterion is developed, and is, together with a range of local and global criterion functions from literature......, benchmarked on a number of numerical examples of laminated composite structures for the maximization of the buckling load considering fiber angle design variables. The optimization formulations are based on either linear or geometrically nonlinear analysis and formulated as mathematical programming problems...... solved using gradient based techniques. The developed local criterion is formulated such it captures nonlinear effects upon loading and proves useful for both analysis purposes and as a criterion for use in nonlinear buckling optimization. © 2010 Springer-Verlag....
Energy Technology Data Exchange (ETDEWEB)
Johnson, Ken I.; Deibler, John E.; Karri, Naveen K.; Pilli, Siva P. [Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Julyk, Larry J. [M and D Professional Services, Inc., Richland, Washington 99352 (United States)
2012-07-01
The U.S. Department of Energy, Office of River Protection has commissioned a structural analysis of record for the Hanford single shell tanks to assess their structural integrity. The analysis used finite element techniques to predict the tank response to the historical thermal and operating loads. The analysis also addressed the potential tank response to a postulated design basis earthquake. The combined response to static and seismic loads was then evaluated against the design requirements of American Concrete Institute standard, ACI-349-06, for nuclear safety-related concrete structures. Further analysis was conducted to estimate the plastic limit load and the elastic-plastic buckling capacity of the tanks. The limit load and buckling analyses estimate the margin between the applied loads and the limiting load capacities of the tank structure. The potential for additional dome loads from waste retrieval equipment and the addition of large dome penetrations to accommodate retrieval equipment has generated additional interest in the limit load and buckling analyses. This paper summarizes the structural analysis methods that were used to evaluate the limit load and buckling of the single shell tanks. This paper summarizes the structural analysis methods that were used to evaluate the limit load and buckling limit states of the underground single shell tanks at the Hanford site. The limit loads were calculated using nonlinear finite element models that capture the progressive deformation and damage to the concrete as it approaches the limit load. Both uniform and concentrated loads over the tank dome were considered, and the analysis shows how adding a penetration in the center of the tank would affect the limit loads. For uniform surface loads, the penetration does not affect the limit load because concrete crushing and rebar yielding initiates first at the top of the wall, away from the penetration. For concentrated loads, crushing initiates at the center of the
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...... example. The imperfection sensitivity of the optimized structure decreases during the recurrence optimization for both examples, hence robust buckling optimal structures are designed....
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...
Directory of Open Access Journals (Sweden)
Paulo B. Gonçalves
2008-01-01
Full Text Available Structural systems liable to asymmetric bifurcation usually become unstable at static load levels lower than the linear buckling load of the perfect structure. This is mainly due to the imperfections present in real structures. The imperfection sensitivity of structures under static loading is well studied in literature, but little is know on the sensitivity of these structures under dynamic loads. The aim of the present work is to study the behavior of an archetypal model of a harmonically forced structure, which exhibits, under increasing static load, asymmetric bifurcation. First, the integrity of the system under static load is investigated in terms of the evolution of the safe basin of attraction. Then, the stability boundaries of the harmonically excited structure are obtained, considering different loading processes. The bifurcations connected with these boundaries are identified and their influence on the evolution of safe basins is investigated. Then, a parametric analysis is conducted to investigate the influence of uncertainties in system parameters and random perturbations of the forcing on the dynamic buckling load. Finally, a safe lower bound for the buckling load, obtained by the application of the Melnikov criterion, is proposed which compare well with the scatter of buckling loads obtained numerically.
On the interaction of thermal buckling and debonding of patched structures
Carabetta, Pamela Marie
The widespread use of patched assemblies in engineering structures creates the need for better fundamental understanding of the failure phenomena of such structures to ensure their safe and effective usage. A structure possessing two substructures, the "patch" and "baseplate", with mismatched coefficients of thermal expansion is studied under thermal loading for two extreme edge conditions. The composite structure is taken as initially flawed, such that partial separation exists at the edges of the patch between the two substructures. Two relevant failure mechanisms are sling-shot buckling and edge debonding (separation). Sling-shot buckling, first observed for perfectly intact structures under thermal loads, occurs when the structure dynamically slings from one equilibrium configuration to another in an opposite sense of deflection at a critical load. It is desired to be able to predict and characterize buckling of the structure, and its coupling with debonding. The geometrically nonlinear problem is formulated via a variational formulation, which allows the boundaries of the domains of the structure to vary in addition to the displacements. The vanishing of the first variation of the potential energy yields governing equilibrium equations, boundary/matching conditions, and transversality conditions. The transversality condition yields a Griffith type delamination criterion. A closed-form solution is obtained after recasting the problem in a mixed formulation. A stability analysis is performed using the second variation of the potential energy functional. The partially debonded structure is seen to possess a "dual nature", where it is structurally different depending on the deflection, due to the existence of the initial flaw. It experiences sling-shot buckling, which, coupled with the structure's duality leads to what we refer to as "Buckle Trapping." It is suggested that, for certain critical temperature fields, the structure oscillates dynamically between
Limit Load and Buckling Analysis for Assessing Hanford Single-Shell Tank Dome Structural Integrity
Energy Technology Data Exchange (ETDEWEB)
Johnson, Kenneth I.; Deibler, John E.; Julyk, Larry J.; Karri, Naveen K.; Pilli, Siva Prasad
2012-12-07
The U.S. Department of Energy, Office of River Protection has commissioned a structural analysis of record (AOR) for the Hanford single shell tanks (SSTs) to assess their structural integrity. The analysis used finite element techniques to predict the tank response to the historical thermal and operating loads. The analysis also addressed the potential tank response to a postulated design basis earthquake. The combined response to static and seismic loads was then evaluated against the design requirements of American Concrete Institute (ACI) standard, ACI-349-06, for nuclear safety-related concrete structures. Further analysis was conducted to estimate the plastic limit load and the elastic-plastic buckling capacity of the tanks. The limit load and buckling analyses estimate the margin between the applied loads and the limiting load capacities of the tank structure. The potential for additional dome loads from waste retrieval equipment and the addition of large dome penetrations to accommodate retrieval equipment has generated additional interest in the limit load and buckling analyses. This paper summarizes the structural analysis methods that were used to evaluate the limit load and buckling of the single shell tanks.
Mullineux, G; Hicks, B J; Berry, C
2012-04-28
Understanding what happens in terms of delamination during buckling of laminate materials is of importance across a range of engineering sectors. Normally concern is that the strength of the material is not significantly impaired. Carton-board is a material with a laminate structure and, in the initial creation of carton nets, the board is creased in order to weaken the structure. This means that when the carton is eventually folded into its three-dimensional form, correct folding occurs along the weakened crease lines. Understanding what happens during creasing and folding is made difficult by the nonlinear nature of the material properties. This paper considers a simplified approach which extends the idea of minimizing internal energy so that the effects of delamination can be handled. This allows a simulation which reproduces the form of buckling-delamination observed in practice and the form of the torque-rotation relation.
Energy Technology Data Exchange (ETDEWEB)
Bejitual, T.S.; Morris, N.J.; Cairns, D.R.; Sierros, K.A., E-mail: kostas.sierros@mail.wvu.edu
2013-12-31
There is currently a great interest to design and fabricate novel flexible devices for solar cell, solid-state lighting, biomedical and energy harvesting applications. Such devices require the use of electrode components. Desired electrodes must exhibit structural integrity, low electrical resistivity and, in most cases, high optical transparency in the visible range. Despite growing efforts to replace them, transparent conducting oxide layers deposited on polymer substrates are still enjoying a dominant role as the electrode component. This is because of their excellent combination of electrical and optical properties. However, their performance when they are subjected to externally-applied mechanical stresses is limited. Such performance has been extensively investigated for the case of continuous brittle oxide films on polymer substrates. However, there is relatively little work reported to date on the mechanical behavior of patterned conducting layers on compliant substrates. In this study we report on the mechanical behavior of various patterned indium tin oxide shapes and sizes on polyethylene terephthalate. Micron-sized shapes include squares, circles, and zigzag-based structures. Controlled buckling experiments are performed in-situ using an optical microscope in order to monitor critical strains and potential failure mechanisms. In addition, ITO electrical resistance changes are continuously monitored during deformation. Furthermore, ex-situ characterization of the tested surfaces using scanning electron microscopy is conducted. Higher crack onset values are observed for the smaller size patterns. Also, square-shaped patterns are found to exhibit the lowest crack onset values. SEM observations suggest cracking-driven and buckling-driven delamination during ITO tensile and compressive buckling mode respectively. In both cases, failure is observed to initiate from the pattern edges. - Highlights: • In-situ experimental analysis of various patterned shapes
Ye, Hong-Ling; Wang, Wei-Wei; Chen, Ning; Sui, Yun-Kang
2017-03-01
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.
In-Plane Elastic Buckling of Arch
Institute of Scientific and Technical Information of China (English)
剧锦三; 郭彦林
2002-01-01
The in-plane elastic buckling behavior of arches is investigated using a new finite-element approach for the nonlinear analysis. The linear buckling, nonlinear primary buckling, and secondary bifurcation buckling behavior of arches are compared taking into account the large deformation and the effects of initial geometric imperfections or perturbations. The theoretical investigation emphasizes the nonlinear secondary bifurcation buckling behavior for a full span uniformly distributed load. The efficiency of compact method for tracing secondary buckling path is shown through several examples. Finally, a new structural design, which prevents the secondary bifurcation buckling by adding some crossed cables across the arch, is proposed to improve the limit load carrying capacity.
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.
Structural model for the dynamic buckling of a column under constant rate compression
Kuzkin, Vitaly A
2015-01-01
Dynamic buckling behavior of a column (rod, beam) under constant rate compression is considered. The buckling is caused by prescribed motion of column ends toward each other with constant velocity. Simple model with one degree of freedom simulating static and dynamic buckling of a column is derived. In the case of small initial disturbances the model yields simple analytical dependencies between the main parameters of the problem: critical force, compression rate, and initial disturbance. It is shown that the time required for buckling is inversely proportional to cubic root of compression velocity and logarithmically depends on the initial disturbance. Analytical expression for critical buckling force as a function of compression velocity is derived. It is shown that in a range of compression rates typical for laboratory experiments the dependence is accurately approximated by a power law with exponent equal to $2/3$. Theoretical findings are supported by available results of laboratory experiments. Keywords...
Fluid-Structure Interaction Study on a Pre-Buckled Deformable Flat Ribbon
Fovargue, Lauren; Shams, Ehsan; Watterson, Amy; Corson, Dave; Filardo, Benjamin; Zimmerman, Daniel; Shan, Bob; Oberai, Assad
2015-11-01
A Fluid-Structure Interaction study is conducted for the flow over a deformable flat ribbon. This mechanism, which is called ribbon frond, maybe used as a device for pumping water and/or harvesting energy in rivers. We use a lower dimensional mathematical model, which represents the ribbon as a pre-buckled structure. The surface forces from the fluid flow, dictate the deformation of the ribbon, and the ribbon in turn imposes boundary conditions for the incompressible Navier-Stokes equations. The mesh motion is handled using an Arbitrary Lagrangian-Eulerian (ALE) scheme and the fluid-structure coupling is handled by iterating over the staggered governing equations for the structure, the fluid and the mesh. Simulations are conducted at three different free stream velocities. The results, including the frequency of oscillations, show agreement with experimental data. The vortical structures near the surface of the ribbon and its deformation are highly correlated. It is observed that the ribbon motion exhibits deviation from a harmonic motion, especially at lower free stream velocities. The behavior of the ribbon is compared to swimming animals, such as eels, in order to better understand its performance. The authors acknowledge support from ONR SBIR Phase II, contract No. N0001412C0604 and USDA, NIFA SBIR Phase I, contract No. 2013-33610-20836 and NYSERDA PON 2569, contract No. 30364.
Abrosimov, N. A.
1999-11-01
Nonlinear three-dimensional problems of dynamic deformation, buckling, and posteritical behavior of composite shell structures under pulsed loads are analyzed. The structure is assumed to be made of rigidly joined plates and shells of revolution along the lines coinciding with the coordinate directions of the joined elements. Individual structural elements can be made of both composite and conventional isotropic materials. The kinematic model of deformation of the structural elements is based on Timoshenko-type hypotheses. This approach is oriented to the calculation of nonstationary deformation processes in composite structures under small deformations but large displacements and rotation angles, and is implemented in the context of a simplified version of the geometrically nonlinear theory of shells. The physical relations in the composite structural elements are based on the theory of effective moduli for individual layers or for the package as a whole, whereas in the metallic elements this is done in the framework of the theory of plastic flow. The equations of motion of a composite shell structure are derived based on the principle of virtual displacements with some additional conditions allowing for the joint operation of structural elements. To solve the initial boundary-value problem formulated, an efficient numerical method is developed based on the finite-difference discretization of variational equations of motion in space variables and an explicit second-order time-integration scheme. The permissible time-integration step is determined using Neumann's spectral criterion. The above method is especially efficient in calculating thin-walled shells, as well as in the case of local loads acting on the structural element, when the discretization grid has to be condensed in the zones of rapidly changing solutions in space variables. The results of analyzing the nonstationary deformation processes and critical loads are presented for composite and isotropic
Buckling of dislocation in graphene
Yao, Yin; Wang, Shaofeng; Bai, Jianhui; Wang, Rui
2016-10-01
The buckling of dislocation in graphene is discussed through the lattice theory of dislocation and elastic theory. The approximate solution of the buckling is obtained based on the inner stress distribution caused by different structure of dislocations and is proved to be suitable by the simulation. The position of the highest buckling is predicted to be at the vertex of the pentagon far away from the heptagon. The buckling is strongly influenced by the internal stress and the distance between the extrusive area and stretching area, as well as the critical stress σc. The SW defect is proved to be unbuckled due to its strong interaction between extrusion and stretching.
Buckling a Semiflexible Polymer Chain under Compression
Directory of Open Access Journals (Sweden)
Ekaterina Pilyugina
2017-03-01
Full Text Available Instability and structural transitions arise in many important problems involving dynamics at molecular length scales. Buckling of an elastic rod under a compressive load offers a useful general picture of such a transition. However, the existing theoretical description of buckling is applicable in the load response of macroscopic structures, only when fluctuations can be neglected, whereas membranes, polymer brushes, filaments, and macromolecular chains undergo considerable Brownian fluctuations. We analyze here the buckling of a fluctuating semiflexible polymer experiencing a compressive load. Previous works rely on approximations to the polymer statistics, resulting in a range of predictions for the buckling transition that disagree on whether fluctuations elevate or depress the critical buckling force. In contrast, our theory exploits exact results for the statistical behavior of the worm-like chain model yielding unambiguous predictions about the buckling conditions and nature of the buckling transition. We find that a fluctuating polymer under compressive load requires a larger force to buckle than an elastic rod in the absence of fluctuations. The nature of the buckling transition exhibits a marked change from being distinctly second order in the absence of fluctuations to being a more gradual, compliant transition in the presence of fluctuations. We analyze the thermodynamic contributions throughout the buckling transition to demonstrate that the chain entropy favors the extended state over the buckled state, providing a thermodynamic justification of the elevated buckling force.
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 an
Buckling failures in insect exoskeletons.
Parle, Eoin; Herbaj, Simona; Sheils, Fiona; Larmon, Hannah; Taylor, David
2016-02-01
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
Based on ANSYS buckling-restrained brace frame structure analysis%基于ANSYS约束屈曲支撑框架结构分析
Institute of Scientific and Technical Information of China (English)
费建伟
2011-01-01
传统的耗能支撑框架结构具有较好的经济性,但是,在中震和强震时,支撑会发生受压屈曲.利用ANSYS模拟约束屈曲支撑框架在地震作用下的结构响应,采用理想弹塑性模型模拟屈曲约束支撑的滞回性能,分别在中震烈度和大震烈度下,对一般框架结构和约束屈曲支撑框架结构进行非线性时程分析,得到结构响应.分析结果表明,约束屈曲支撑结构减震效果良好.%The traditional energy support frame structure with good efficiency, but in moderate earthquakes and strong earthquake support will occur pressure buckling. Using ANSYS simulation buckling-restrained brace framework response of the structure in earthquake. Using the ideal elastic-plastic model describe buckling-restrained brace hysteretic performance, in moderate earthquakes and strong earthquake, general framework and buckling-restrained brace framework for nonlinear time-history analysis, solving structural response. Analysis results show that buckling-restrained brace structure damping effect is good.
Bina, Craig; Cizkova, Hana
2014-05-01
Subducting slabs may exhibit buckling instabilities and consequent folding behavior in the mantle transition zone for various combinations of dynamical parameters, accompanied by temporal variations in dip angle, plate velocity, and trench retreat. Parameters governing such behavior include both viscous forces (slab and mantle rheology) and buoyancy forces (slab thermal structure and mineral phase relations). 2D numerical experiments show that many parameter sets lead to slab deflection at the base of the transition zone, typically accompanied by quasi-periodic oscillations (consistent with previous scaling analyses) in largely anticorrelated plate and rollback velocities, resulting in undulating stagnant slabs as buckle folds accumulate subhorizontally atop the lower mantle. Slab interactions with mantle phase transitions are important components of this process (Bina and Kawakatsu, 2010; Čížková and Bina, 2013). For terrestrial parameter sets, trench retreat is found to be nearly ubiquitous, and trench advance is quite rare - due to both rheological structure and ridge-push effects (Čížková and Bina, 2013). Recent analyses of global plate motions indicate that significant trench advance is also rare on Earth, being largely restricted to the Izu-Bonin arc (Matthews et al., 2013). Consequently, we explore the conditions necessary for terrestrial trench advance through dynamical models involving the unusual geometry associated with the Philippine Sea region. Detailed images of buckled stagnant slabs are difficult to resolve due to smoothing effects inherent in seismic tomography, but velocity structures computed for compositionally layered slabs, using laboratory data on relevant mineral assemblages, can be spatially low-pass filtered for comparison with tomographic images of corresponding resolution. When applied to P-wave velocity anomalies from stagnant slab material beneath northeast China, model slabs which undulate due to compound buckling fit
Directory of Open Access Journals (Sweden)
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.
Stress-driven buckling patterns in spheroidal core/shell structures.
Yin, Jie; Cao, Zexian; Li, Chaorong; Sheinman, Izhak; Chen, Xi
2008-12-09
Many natural fruits and vegetables adopt an approximately spheroidal shape and are characterized by their distinct undulating topologies. We demonstrate that various global pattern features can be reproduced by anisotropic stress-driven buckles on spheroidal core/shell systems, which implies that the relevant mechanical forces might provide a template underpinning the topological conformation in some fruits and plants. Three dimensionless parameters, the ratio of effective size/thickness, the ratio of equatorial/polar radii, and the ratio of core/shell moduli, primarily govern the initiation and formation of the patterns. A distinct morphological feature occurs only when these parameters fall within certain ranges: In a prolate spheroid, reticular buckles take over longitudinal ridged patterns when one or more parameters become large. Our results demonstrate that some universal features of fruit/vegetable patterns (e.g., those observed in Korean melons, silk gourds, ribbed pumpkins, striped cavern tomatoes, and cantaloupes, etc.) may be related to the spontaneous buckling from mechanical perspectives, although the more complex biological or biochemical processes are involved at deep levels.
Li, Bo; Wang, San-Min; Zhi, Chang-Jian; Xue, Xiang-Zhen; Makis, Viliam
2017-01-01
This paper aims at investigating the buckling load of fully deployed linear array deployable structure based on scissor-like element (SLE) under its own weight. The deployable structure has been widely researched both in geometric configurations and structural dynamic characteristics. However, when the number of elements or degree of deployment exceeds the predetermined range, even if there is no external load, deployable structure will automatically collapse under its own weight. To address this issue, this paper derives a new stability model based on linear elastic analysis and energy method to compute the buckling load caused by its own weight for avoiding the structural instability, which can be applied to a linear array deployable structure with n SLEs. In the process of calculation, the first SLE is taken for mechanical analysis and the results are extended to any unit. In the sequel of this process, the scissor deployable structure is equivalent to a uniform solid column and its buckling condition under self-weight is obtained based on the principle of potential energy. Also, the effect of various parameters that affect the instability of the structure, such as the number of elements, bar length and degree of deployment is investigated, and the results of the theoretical analysis are verified through a comparison with the simulation results in ANSYS, which show that the new stability model proposed here can predict the buckling load of scissor deployable structure.
Monn, Michael A.; Kesari, Haneesh
2017-01-01
We identify a new structure-property connection in the skeletal elements of the marine sponge Tethya aurantia. The skeletal elements, known as spicules, are millimeter-long, axisymmetric, silica rods that are tapered along their lengths. Mechanical designs in other structural biomaterials, such as nacre and bone, have been studied primarily for their benefits to toughness properties. The structure-property connection we identify, however, falls in the entirely new category of buckling resistance. We use computational mechanics calculations and information about the spicules’ arrangement within the sponge to develop a structural mechanics model for the spicules. We use our structural mechanics model along with measurements of the spicules’ shape to estimate the load they can transmit before buckling. Compared to a cylinder with the same length and volume, we predict that the spicules’ shape enhances this critical load by up to 30%. We also find that the spicules’ shape is close to the shape of the column that is optimized to transmit the largest load before buckling. In man-made structures, many strategies are used to prevent buckling. We find, however, that the spicules use a completely new strategy. We hope our discussion will generate a greater appreciation for nature’s ability to produce beneficial designs. PMID:28051108
Monn, Michael A; Kesari, Haneesh
2017-01-04
We identify a new structure-property connection in the skeletal elements of the marine sponge Tethya aurantia. The skeletal elements, known as spicules, are millimeter-long, axisymmetric, silica rods that are tapered along their lengths. Mechanical designs in other structural biomaterials, such as nacre and bone, have been studied primarily for their benefits to toughness properties. The structure-property connection we identify, however, falls in the entirely new category of buckling resistance. We use computational mechanics calculations and information about the spicules' arrangement within the sponge to develop a structural mechanics model for the spicules. We use our structural mechanics model along with measurements of the spicules' shape to estimate the load they can transmit before buckling. Compared to a cylinder with the same length and volume, we predict that the spicules' shape enhances this critical load by up to 30%. We also find that the spicules' shape is close to the shape of the column that is optimized to transmit the largest load before buckling. In man-made structures, many strategies are used to prevent buckling. We find, however, that the spicules use a completely new strategy. We hope our discussion will generate a greater appreciation for nature's ability to produce beneficial designs.
Monn, Michael A.; Kesari, Haneesh
2017-01-01
We identify a new structure-property connection in the skeletal elements of the marine sponge Tethya aurantia. The skeletal elements, known as spicules, are millimeter-long, axisymmetric, silica rods that are tapered along their lengths. Mechanical designs in other structural biomaterials, such as nacre and bone, have been studied primarily for their benefits to toughness properties. The structure-property connection we identify, however, falls in the entirely new category of buckling resistance. We use computational mechanics calculations and information about the spicules’ arrangement within the sponge to develop a structural mechanics model for the spicules. We use our structural mechanics model along with measurements of the spicules’ shape to estimate the load they can transmit before buckling. Compared to a cylinder with the same length and volume, we predict that the spicules’ shape enhances this critical load by up to 30%. We also find that the spicules’ shape is close to the shape of the column that is optimized to transmit the largest load before buckling. In man-made structures, many strategies are used to prevent buckling. We find, however, that the spicules use a completely new strategy. We hope our discussion will generate a greater appreciation for nature’s ability to produce beneficial designs.
Research on Seismic of Steel Structure with Buckling Restrained Brace%防屈曲支撑钢框架的抗震性能研究
Institute of Scientific and Technical Information of China (English)
刘伟; 李大鹏; 王光云
2012-01-01
本文采用ANSYS抗震性能软件,建立了防屈曲支撑钢框架有限元计算模型,通过建模计算验证了防屈曲支撑框架体系优越的结构性能.%This paper uses the ANSYS finite element analysis software,established the buckling-restrained braced frame model,and through the modeling result of buckling restrained braced frame system superior structural performance.
Buckling Analysis of Supporting Skirt of Security Injection Tank
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
The purpose of the calculating is to make a structural buckling analysis according to the code rules and the design requirements in order to judge whether the security injection tank have the ability to resist the buckling failure or not
Elastic buckling strength of corroded steel plates
Indian Academy of Sciences (India)
Ahmad Rahbar-Ranji
2013-02-01
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 irregular surfaces. Elastic buckling of simply supported rectangular corroded plates are studied with one- and both-sided irregular surfaces. Eigenvalue analysis by using ﬁnite element method (FEM) is employed for computing Euler stress. The inﬂuence of various geometric and corrosion characteristics are investigated and it is found that the aspect ratio of the plate, the average thickness diminution, the standard deviation of thickness diminution and the amount of corrosion loss have inﬂuence on the reduction of buckling strength of the corroded plates. Buckling strength of one- and both-sided corroded plates are the same. In plates with low value of aspect ratio, reduction of buckling strength is negligible. Reduction of buckling strength is more prominent in plates with higher aspect ratio. Reduction of buckling strength is very sensitive to the amount of corrosion loss; the higher the amount of corrosion loss, the more reduction of buckling strength. Reduction of buckling strength is less sensitive to the standard deviation of thickness diminution.
On the analysis of viscoplastic buckling
DEFF Research Database (Denmark)
Mikkelsen, Lars Pilgaard
1993-01-01
For elastic-viscoplastic structures the classical elastic-plastic bifurcation approach to inelastic buckling is not valid. Only an elastic bifurcation point exists in the el~tic-viscoplastic case, and the inelastic buckling behaviour is controlled by a strong sensitivity to small imperfections...
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...
Buckling of Bucket Foundations During Installation
DEFF Research Database (Denmark)
Madsen, Søren
axial and latteral pressure during the installation process buckling becomes a crucial design consideration. In 2005, a large wind turbine was to be installed nearshore the harbour in Wilhelmshaven, Germany. The windturbine was never erected since the skirt of the bucket foundation buckled during...... the suction assisted installation process. In this thesis, the phenomenon of buckling of the bucket foundation during installation is investigated by means of Finite Element Analysis. The influence of boundary conditions on the bucket foundation is adressed as well as the effect of including the surrounding...... soil and soil–structure interaction. Investigations are made regarding the buckling incident in Wilhelmshaven and the results are compared to current DNV and Eurocode standards. Finally, analysis of a new design of the cross section with a higher buckling capacity than an equivalent circular cross...
Design of Composite Material Structures for Buckling - An Evaluation of the State-of-the-Art
1981-03-01
REPORT DATE AFWAL/ FIBRA , U.S. Air Force, Aeronautical Systems March 1981 Division, Wright Patterson Air Force Base, Ohio 13. NUMBER OF PAGES 66 14...Structures." The project monitor for the contract was Dr Narendra S. Khot of the Structures and Dynamics Division (AFWAL/ FIBRA ). The technical work under
Micromechanics of collective buckling in CNT turfs
Torabi, Hamid; Radhakrishnan, Harish; Mesarovic, Sinisa Dj.
2014-12-01
Complex structures consisting of intertwined, nominally vertical carbon nanotubes (CNTs) are called turfs. Under uniform compression experiments, CNT turfs exhibit irreversible collective buckling of a layer preceded by reorientation of CNT segments. Experimentally observed independence of the buckling stress and the buckling wavelength on the turf width suggests the existence of an intrinsic material length. To investigate the relationship the macroscopic material properties and the statistical parameters describing the nano-scale geometry of the turf (tortuosity, density and connectivity) we develop a nano-scale computational model, based on the representation of CNT segments as elastica finite elements with van der Waals interactions. The virtual turfs are generated by means of a constrained random walk algorithm and subsequent relaxation. The resulting computational model is robust and is capable of modeling the collective behavior of CNTs. We first establish the dependence of statistical parameters on the computational parameters used for turf generation, then establish relationships between post-buckling stress, initial elastic modulus and buckling wavelength on statistical turf parameters. Finally, we analyze the reorientation of buckling planes of individual CNTs during the collective buckling process.
Stochastic behavior of nanoscale dielectric wall buckling
Friedman, Lawrence H.; Levin, Igor; Cook, Robert F.
2016-01-01
The random buckling patterns of nanoscale dielectric walls are analyzed using a nonlinear multi-scale stochastic method that combines experimental measurements with simulations. The dielectric walls, approximately 200 nm tall and 20 nm wide, consist of compliant, low dielectric constant (low-k) fins capped with stiff, compressively stressed TiN lines that provide the driving force for buckling. The deflections of the buckled lines exhibit sinusoidal pseudoperiodicity with amplitude fluctuation and phase decorrelation arising from stochastic variations in wall geometry, properties, and stress state at length scales shorter than the characteristic deflection wavelength of about 1000 nm. The buckling patterns are analyzed and modeled at two length scales: a longer scale (up to 5000 nm) that treats randomness as a longer-scale measurable quantity, and a shorter-scale (down to 20 nm) that treats buckling as a deterministic phenomenon. Statistical simulation is used to join the two length scales. Through this approach, the buckling model is validated and material properties and stress states are inferred. In particular, the stress state of TiN lines in three different systems is determined, along with the elastic moduli of low-k fins and the amplitudes of the small-scale random fluctuations in wall properties—all in the as-processed state. The important case of stochastic effects giving rise to buckling in a deterministically sub-critical buckling state is demonstrated. The nonlinear multiscale stochastic analysis provides guidance for design of low-k structures with acceptable buckling behavior and serves as a template for how randomness that is common to nanoscale phenomena might be measured and analyzed in other contexts. PMID:27330220
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.
Voltage-Induced Buckling of Dielectric Films using Fluid Electrodes
Tavakol, Behrouz
2016-01-01
Accurate and integrable control of different flows within microfluidic channels is crucial to further development of lab-on-a-chip and fully integrated adaptable structures. Here we introduce a flexible microactuator that buckles at a high deformation rate and alters the downstream fluid flow. The microactuator consists of a confined, thin, dielectric film that buckles into the microfluidic channel when exposed to voltage supplied through conductive fluid electrodes. We estimate the critical buckling voltage, and characterize the buckled shape of the actuator. Finally, we investigate the effects of frequency, flow rate, and the pressure differences on the behavior of the buckling structure and the resulting fluid flow. These results demonstrate that the voltage--induced buckling of embedded microstructures using fluid electrodes provides a means for high speed attenuation of microfluidic flow.
Uncertainty in Loading and Control of an Active Column Critical to Buckling
Directory of Open Access Journals (Sweden)
G.C. Enss
2012-01-01
Full Text Available Buckling of load-carrying column structures is an important design constraint in light-weight structures as it may result in the collapse of an entire structure. When a column is loaded by an axial compressive load equal to its individual critical buckling load, a critically stable equilibrium occurs. When loaded above its critical buckling load, the passive column may buckle. If the actual loading during usage is not fully known, stability becomes highly uncertain.
Buckling transition in long α-helices
Energy Technology Data Exchange (ETDEWEB)
Palenčár, Peter; Bleha, Tomáš, E-mail: bleha@savba.sk [Polymer Institute, Slovak Academy of Sciences, 845 41 Bratislava (Slovakia)
2014-11-07
The treatment of bending and buckling of stiff biopolymer filaments by the popular worm-like chain model does not provide adequate understanding of these processes at the microscopic level. Thus, we have used the atomistic molecular-dynamic simulations and the Amber03 force field to examine the compression buckling of α-helix (AH) filaments at room temperature. It was found that the buckling instability occurs in AHs at the critical force f{sub c} in the range of tens of pN depending on the AH length. The decrease of the force f{sub c} with the contour length follows the prediction of the classic thin rod theory. At the force f{sub c} the helical filament undergoes the swift and irreversible transition from the smoothly bent structure to the buckled one. A sharp kink in the AH contour arises at the transition, accompanied by the disruption of the hydrogen bonds in its vicinity. The kink defect brings in an effective softening of the AH molecule at buckling. Nonbonded interactions between helical branches drive the rearrangement of a kinked AH into the ultimate buckled structure of a compact helical hairpin described earlier in the literature.
Buckling analysis of planar compression micro-springs
Energy Technology Data Exchange (ETDEWEB)
Zhang, Jing; Sui, Li; Shi, Gengchen [School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Science and Technology on Electromechanical Dynamic Control Laboratory, 5 South Street Zhongguancun, Haidian 100081, Beijing (China)
2015-04-15
Large compression deformation causes micro-springs buckling and loss of load capacity. We analyzed the impact of structural parameters and boundary conditions for planar micro-springs, and obtained the change rules for the two factors that affect buckling. A formula for critical buckling deformation of micro-springs under compressive load was derived based on elastic thin plate theory. Results from this formula were compared with finite element analysis results but these did not always correlate. Therefore, finite element analysis is necessary for micro-spring buckling analysis. We studied the variation of micro-spring critical buckling deformation caused by four structural parameters using ANSYS software under two constraint conditions. The simulation results show that when an x-direction constraint is added, the critical buckling deformation increases by 32.3-297.9%. The critical buckling deformation decreases with increase in micro-spring arc radius or section width and increases with increase in micro-spring thickness or straight beam width. We conducted experiments to confirm the simulation results, and the experimental and simulation trends were found to agree. Buckling analysis of the micro-spring establishes a theoretical foundation for optimizing micro-spring structural parameters and constraint conditions to maximize the critical buckling load.
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...... are introduced, based on the buckling mode shapes from a linear eigenvalue buckling analysis. Different imperfect geometries are introduced to reveal how sensitive the buckling load is to these imperfections. Including the first 21 mode shapes as imperfect geometries will reduce the buckling pressure compared...... to only considering mode 1. The results of the finite element analysis are compared with current standards for evaluating buckling loads....
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.
Buckled graphene for efficient energy harvest, storage and conversion
Jiang, Jin-Wu
2016-10-01
Buckling is one of the most common phenomena in atom-thick layered structures like graphene. While the buckling phenomenon usually causes disaster for most nanodevices, we illustrate one positive application of buckled graphene for energy harvest, storage and conversion. More specifically, we perform molecular dynamical simulations to show that buckled graphene can be used to collect wasted mechanical energy and store the energy in the form of internal knotting potential. Through strain engineering, the knotting potential can be converted into useful kinetic (thermal) energy that is highly concentrated at the free edges of buckled graphene. The present study demonstrates potential applications of buckled graphene for converting dispersed wasted mechanical energy into concentrated useful kinetic (thermal) energy.
Buckled graphene for efficient energy harvest, storage and conversion.
Jiang, Jin-Wu
2016-10-01
Buckling is one of the most common phenomena in atom-thick layered structures like graphene. While the buckling phenomenon usually causes disaster for most nanodevices, we illustrate one positive application of buckled graphene for energy harvest, storage and conversion. More specifically, we perform molecular dynamical simulations to show that buckled graphene can be used to collect wasted mechanical energy and store the energy in the form of internal knotting potential. Through strain engineering, the knotting potential can be converted into useful kinetic (thermal) energy that is highly concentrated at the free edges of buckled graphene. The present study demonstrates potential applications of buckled graphene for converting dispersed wasted mechanical energy into concentrated useful kinetic (thermal) energy.
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
LOCALIZED BUCKLING OF THE SEMI-INFINITE ISOTROPIC PLATE NEAR ELASTICALLY FASTENED EDGE
Directory of Open Access Journals (Sweden)
Sharifian R.
2012-06-01
Full Text Available Localized buckling of a semi-infinite isotropic plate near elastically fastened edge has been investigated. Mathematical model is of structure is provided and characteristic equation of the problem is derived. The existence conditions of localized buckling are derived analytically. For the cases when localized buckling exists numerical solutions and plots for the critical loads are provided.
Institute of Scientific and Technical Information of China (English)
赵丰; 张崇厚
2013-01-01
斜交网筒结构具有较大的抗侧刚度,但其延性较差,通过设置屈曲约束支撑可改善斜交网筒结构延性.以30层的斜交网筒结构模型为研究对象,分别对普通斜交网筒结构和设置屈曲约束支撑斜交网筒结构进行静力弹塑性推覆(Pushover)分析.结果表明:屈曲约束支撑可有效改善斜交网筒结构延性.此外,对立面中部、立面角部、底部楼层、上部楼层共4种局部区域布置屈曲约束支撑的方案进行了结构延性分析.局部设置屈曲约束支撑斜交网筒结构的设计应确保斜柱处于弹性工作状态,屈曲约束支撑率先进入塑性耗能状态.建议采用立面中部布置屈曲约束支撑的方案,可实现在保证结构受剪承载力的前提下,较好地改善斜交网筒结构的延性,避免结构发生脆性破坏.%Diagrid tube structures have excellent lateral force resistance but poor structural ductility,which can be improved through buckling restrained brace.With respect to 30-story diagrid tube structures,nonlinear static analysis,i.e.pushover analysis was conducted respectively for the conventional diagrid tube structure and those with buckling restrained brace.The results show that the structural ductility is improved by utilizing buckling restrained brace.Furthermore,four schemes of diagrid tube structures partially with buckling restrained brace in different parts of the facades,including the corner and the middle,the bottom and the upper,were investigated for structural ductility.Diagrid tube structures partially with buckling restrained brace should be designed so that conventional brace remain in elastic state,while buckling restrained brace turn into plastic state in advance for energy dissipation.Diagrid tube structure with buckling restrained brace in the middle part of facade is recommended,which could effectively improve structural ductility to avoid brittle failure without decreasing shear load-bearing capacity.
Dynamic buckling of stiffened plates subjected to explosion impact loads
Wang, J.; Guo, J.; Yao, X. L.; Zhang, A. M.
2017-01-01
The dynamic buckling characteristics and criteria of a ship's structural stiffened plate subjected to underwater explosion impact loads are investigated in this study. Using the structural deformations observed in the experiments of underwater explosions against a plated grillage model, the mode shapes of the dynamic buckling were obtained. Through the construction of a computational model of stiffened plates subjected to an underwater explosion shock wave, the impact load was theoretically calculated and transformed into a rectangular pulse. According to the different response patterns of stiffened plates under different impact loads, a dynamic buckling criterion for the stiffened plates subjected to an explosion shock wave was proposed. Additionally, the static buckling phenomenon in the stiffened plates was analysed based on the minimum excess principle. In combination with the dynamic buckling criterion, the effects of various stiffening configurations on the dynamic and static buckling loads are discussed. The calculation results show that when the equivalent rectangular pulse is 2-3 times that of the static buckling load, the responses of the stiffened plates under the original shock load and the equivalent rectangular pulse are virtually identical. The impact load amplitude is the primary influencing factor in the dynamic buckling of stiffened plates subjected to underwater explosive impact loads. The stiffened plate aspect ratio has a substantial influence on the dynamic load factor. The analytical method and results are presented, which can be used to design stiffened optimum hull structures to enhance the dynamic load carrying capacity to withstand underwater shock damage.
Electrical characterization of a buckling thermal energy harvester
Trioux, E.; Rufer, L.; Monfray, S.; Skotnicki, T.; Muralt, P.; Basrour, S.
2015-12-01
This paper presents the electrical characterizations of a novel concept for thermal energy harvesting at micro scale. The devices presented here are based on a two-step transduction combining thermo-mechanical and piezoelectric conversion. The piezoelectric layer is directly integrated into a buckling bilayer plate made of aluminium and aluminium nitride. For the first time, we have characterized the structures electrically and we have investigated their output power during the buckling. Firstly, we have used an insulating tip to make the plate buckle in order to have an estimation of the output power due to piezoelectric contribution only, and to eliminate any pyroelectric contribution that might be present during the thermal actuation. Then, we heated up the structure and we collected the output signal with an instrumentation amplifier in order to measure the voltage generated during the buckling. The output power during the mechanical and the thermal buckling is compared in the paper.
Buckling of Carbon Nanotubes: A State of the Art Review
Directory of Open Access Journals (Sweden)
Hiroyuki Shima
2011-12-01
Full Text Available 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.
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.
Hyer, M. W.; Lee, H. H.
1990-01-01
The gains in buckling performance are explored that can be achieved by deviating from the conventional straightline fiber format and considering the situation whereby the fiber orientation in a layer, or a group of layers, can vary from point to point. The particular situation studied is a simply supported square plate with a centrally located hole loaded in compression. By using both a sensitivity analysis and a gradient-search technique, fiber orientation in a number of regions of the plate are selected so as to increase the buckling load relative to baseline straightline designs. The sensitivity analysis is used to determine which regions of the plate have the most influence on buckling load, and the gradient search is used to find the design that is believed to represent the absolute maximum buckling load for the conditions prescribed. Convergence studies and sensitivity of the final design are discussed. By examining the stress resultant contours, it is shown how the curvilinear fibers move the load away from the unsupported hole region of the plate to the supported edges, thus increasing the buckling capacity. The tensile capacity of the improved buckling design is investigated, and it is shown that both tensile capacity and buckling capacity can be improved with the curvilinear fiber concept.
Buckling of carbon nanotubes wrapped by polyethylene molecules
Wang, Q.
2011-01-01
The discovery of a buckling instability of a single-walled carbon nanotube wrapped by a polyethylene molecule subjected to compression is reported through molecular mechanics simulations. A decrease up to 44% in the buckling strain of the nano-structure owing to the van der Waals interaction between the two molecules is uncovered. A continuum model is developed to calculate both the interaction between the tube and the polymer and the decreased buckling strain of the structure by fitting the molecular mechanics results.
Buckling of carbon nanotubes wrapped by polyethylene molecules
Energy Technology Data Exchange (ETDEWEB)
Wang, Q., E-mail: Q_Wang@Umanitoba.c [Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg, Manitoba, R3T 5V6 (Canada)
2011-01-17
The discovery of a buckling instability of a single-walled carbon nanotube wrapped by a polyethylene molecule subjected to compression is reported through molecular mechanics simulations. A decrease up to 44% in the buckling strain of the nano-structure owing to the van der Waals interaction between the two molecules is uncovered. A continuum model is developed to calculate both the interaction between the tube and the polymer and the decreased buckling strain of the structure by fitting the molecular mechanics results.
Institute of Scientific and Technical Information of China (English)
赵杰; 孙晓艳; 霍林生
2015-01-01
This article briefly introduces the seismic safety community and the composition and performance parameters of buckling-restrained braces.The seismic safety community is the com-munity that experiences small destructive earthquakes.Specifically,these communities have car-ried out effective seismic fortification of all buildings in compliance with seismic hazard regula-tions.In the seismic safety community,improving the seismic performance of buildings is the pri-mary goal.Local seismic fortifications meet the minimum seismic requirements,and the level of fortification of buildings is increased using certain technical measures.The traditional method of seismic fortification is to increase the size of major structural components,such as beams,col-umns,and shear walls,and to improve the ratio of reinforcements to buildings.However,increas-ing the amount of material increases cost and reduces the usable area of buildings.The new meth-od calls for change to the seismic characteristics of the structure itself and improvements to its ca-pacity for energy dissipation through the use of isolation and dissipation technologies.In the struc-tural system,the seismic sections generally remain the same,and cost increases are small.Buck-ling-restrained braces have gained widespread application as measures for energy dissipation and earthquake resistance.They also overcome the disadvantages of traditional energy dissipation braces.The component’s full section will yield during compression,effectively minimizing local buckling failure and overall buckling failure.Therefore,the energy dissipation capacity of the com-ponents is maximized and the seismic response of the structure is reduced.The Dalian Aonan Mingxiu manor project described in the paper is a pilot project undertaken in the Dalian earth-quake safety community.The project addresses building security and earthquake safety at the de-sign stage.By installing buckling-restrained braces,the seismic characteristics of the
Institute of Scientific and Technical Information of China (English)
冯铭; 杨聪武; 曹志丹; 谭咏梅
2013-01-01
某高层钢结构住宅楼高48.6m,结构体系采用钢框架-支撑结构,主要抗侧力构件采用屈曲约束支撑.通过多种结构形式的对比分析阐述了框架-屈曲约束支撑结构体系地震作用效应小、塑性耗能能力优等结构特征.阐述了屈曲约束支撑设计控制内力的确定和支撑杆件与框架梁、柱连接节点设计等关键技术.通过多遇地震作用下结构整体计算分析、中震弹性分析和不考虑屈曲约束支撑作用的纯框架结构抗震验算,得出框架-屈曲约束支撑结构体系抗震性能优越、技术经济指标合理的结论.%A high-rise steel structure residence is 48. 6 meters high, structural system of the residence is the steel braced frame structure, and its main anti-lateral force components are buckling restrained braces. Through analysis of a variety of structural forms, structural features of the framework-buckling restrained brace structure system were elaborated, such as small seismic action effect and superior plastic energy dissipation capacity. Key technologies were introduced, including determination of design control internal force for the buckling restrained brace and design of connection nodes among the support rods, frame beams, and columns. Through the overall structure calculation under frequent earthquake, structural seismic elastic analysis under fortification intensity, and pure frame structure seismic calculation without regarding the effect of buckling restrained braces, it is concluded that seismic performance of the framework-buckling restrained brace structure is good and its technical and economic indicators are reasonable.
Global buckling assessment of high pressure and high temperature (HP/HT) offshore pipeline
Energy Technology Data Exchange (ETDEWEB)
Yang, Seung-Ho; Jung, Jong-Jin; Lee, Woo-Seob [Maritime Research Institute, Hyundai Heavy Industries, Ulsan, (Korea, Republic of); Kim, Yun-Hak; Kim, Jong-Bae [Offshore Installation Engineering Department, Hyundai Heavy Industries, Ulsan, (Korea, Republic of)
2010-07-01
High pressure and high temperature (HP/HT) offshore pipelines are frequently subjected to lateral buckling due to excessive compressive axial force. Several control processes have been designed such as sleepers to reduce lateral buckling. This paper investigated the effect of the introduction of sleepers as buckle triggers on the behavior of HP/HT pipelines. A 3D finite element analysis using ABAQUS software was performed to simulate concrete sleepers and a profile of the seabed. The analysis criteria were the buckling amplitude, Von Mises stress, equivalent plastic strain and the effective axial force on the pipeline. A case study for HP/HT pipeline was been carried out based on installation surveys. Comparisons between the results from a model without buckle trigger and those from a model with buckle trigger were carried out. It was found that the change to the support structure, adding a buckle trigger, affected the behaviour of the pipeline considerably.
Ko, William L.
1994-01-01
The combined load (mechanical or thermal load) buckling equations were established for orthotropic rectangular sandwich panels under four different edge conditions by using the Rayleigh-Ritz method of minimizing the total potential energy of a structural system. Two-dimensional buckling interaction curves and three-dimensional buckling interaction surfaces were constructed for high-temperature honeycomb-core sandwich panels supported under four different edge conditions. The interaction surfaces provide overall comparison of the panel buckling strengths and the domains of symmetrical and antisymmetrical buckling associated with the different edge conditions. In addition, thermal buckling curves of these sandwich panels are presented. The thermal buckling conditions for the cases with and without thermal moments were found to be identical for the small deformation theory.
Institute of Scientific and Technical Information of China (English)
李云勇; 郑七振; 安亚琳
2016-01-01
防屈曲支撑通过在杆件外围设置约束元件抑制受压时的屈曲,具有更好的耗能效果.为深入研究防屈曲支撑对钢框架结构抗震性能的影响,运用SAP2000有限元结构软件,对某钢框架在防屈曲支撑、普通中心支撑以及无支撑3种形式下的整体模型进行模态和时程分析.结果显示:采用防屈曲支撑钢框架的周期、层间位移角较纯框架均得到降低;在罕遇地震作用下,防屈曲支撑钢框架的顶层最大位移值、顶层加速度较普通支撑钢框架均有很大幅度的减小.表明采用防屈曲支撑可以明显提高钢框架结构的刚度,同时大幅度提高钢框架结构的抗震性能,耗能减震效应明显.%Through setting the constraints on the fringes of the bar element inhibition of compression buckling under pressure ,buckling-restrained support can achieve better effect of energy consumption. In order to further study the effect of anti buckling brace on the seismic behavior of steel frame structure, the paper used SAP2000 finite element software to analyze the mode and time of a steel frame of whole model under the condition of buckling brace, general center support and the forms of non support. The results showed that the period of buckling restrained brace steel frame and the displacement angle of the layer are all reduced compared with that that of the pure frame. In the case of rare earthquake, the top-maximum displacement value and the top acceleration of the steel frame are more significantly reduced than that of ordinary braced steel frame. The result indicated that the stiffness of steel frame can be obvi-ously improved by using the anti buckling brace, and the seismic performance of the steel frame structure is greatly improved, and the energy dissipation effect is obvious.
Optical manifestation of buckled configurations in graphene-like materials
Kazemlou, V.; Phirouznia, A.; Jamshidi-Ghaleh, K.
2017-04-01
In the present study, the effects of the configuration buckling on dielectric function of silicene, germanene and stanene are investigated. The behavior of the optical absorption spectrum and the refractive index dispersion are studied using the density functional theory in terms of incident photon energy at different buckling heights. The results show that for a fixed bond length, increasing the unit cell buckling height, increases the absorption and the refractive index in silicene and germanene but decreases in stanene. In addition, the absorption peaks shift toward the longer wavelengths (red shift) in the case of silicene and germanene by increasing the buckling height. For clear understanding of the mentioned results, the behavior of the optical absorption spectrum and refractive index dispersion at different buckling heights are studied within the present work. In the case of the silicene and germanene reduction of the band gap with increasing the buckling height could be regarded as the origin of this red shift. Meanwhile unlike the silicene and germanene, band-structure reshaping in stanene could explain the stanene blue shift as a result of the buckling height increment.
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.
The secondary buckling transition: wrinkling of buckled spherical shells.
Knoche, Sebastian; Kierfeld, Jan
2014-07-01
We theoretically explain the complete sequence of shapes of deflated spherical shells. Decreasing the volume, the shell remains spherical initially, then undergoes the classical buckling instability, where an axisymmetric dimple appears, and, finally, loses its axisymmetry by wrinkles developing in the vicinity of the dimple edge in a secondary buckling transition. We describe the first axisymmetric buckling transition by numerical integration of the complete set of shape equations and an approximate analytic model due to Pogorelov. In the buckled shape, both approaches exhibit a locally compressive hoop stress in a region where experiments and simulations show the development of polygonal wrinkles, along the dimple edge. In a simplified model based on the stability equations of shallow shells, a critical value for the compressive hoop stress is derived, for which the compressed circumferential fibres will buckle out of their circular shape in order to release the compression. By applying this wrinkling criterion to the solutions of the axisymmetric models, we can calculate the critical volume for the secondary buckling transition. Using the Pogorelov approach, we also obtain an analytical expression for the critical volume at the secondary buckling transition: The critical volume difference scales linearly with the bending stiffness, whereas the critical volume reduction at the classical axisymmetric buckling transition scales with the square root of the bending stiffness. These results are confirmed by another stability analysis in the framework of Donnel, Mushtari and Vlasov (DMV) shell theory, and by numerical simulations available in the literature.
LINEAR AND NONLINEAR BUCKLING ANALYSIS OF STIFFENED CYLINDRICAL SUBMARINE HULL
SREELATHA P.R; ALICE MATHAI
2012-01-01
Submarine is a watercraft capable of independent operation under water. Use of submarines includes marine science, offshore industry underwater exploration etc. The pressure hull of submarine is constructed as combination of cylinders and domes. The shell is subjected to very high hydrostatic pressure, which creates large compressive stress resultants. Due to this the structure is susceptible to buckling. The introduction of stiffeners in both directions considerably increases the buckling st...
A unified theory of plastic buckling of columns and plates
Stowell, Elbridge Z
1948-01-01
On the basis of modern plasticity considerations, a unified theory of plastic buckling applicable to both columns and plates has been developed. For uniform compression, the theory shows that long columns which bend without appreciable twisting require the tangent modulus and that long flanges which twist without appreciable bending require the secant modulus. Structures that both bend and twist when they buckle require a modulus which is a combination of the secant modulus and the tangent modulus. (author)
Buckling of polymerized monomolecular films
Bourdieu, L.; Daillant, J.; Chatenay, D.; Braslau, A.; Colson, D.
1994-03-01
The buckling of a two-dimensional polymer network at the air-water interface has been evidenced by grazing incidence x-ray scattering. A comprehensive description of the inhomogeneous octadecyltrichlorosilane polymerized film was obtained by atomic force microscopy and x-ray scattering measurements. The buckling occurs with a characteristic wavelength ~=10 μm.
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
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 bucket foundation during installation. Further, the effect of the lateral restraint offered by the surrounding soil on the buckling pressures is analysed. It is found that the new design enables a significantly larger buckling load compared to the traditional design....
The effect of temperature on the compressive buckling of boron nitride nanotubes
Energy Technology Data Exchange (ETDEWEB)
Shokuhfar, Ali; Ebrahimi-Nejad, Salman [Faculty of Mechanical Engineering, K.N. Toosi University of Technology, 19991-43344 Tehran (Iran, Islamic Republic of); Hosseini-Sadegh, Amin [Faculty of Petroleum Engineering, Petroleum University of Technology, 14539-53153 Tehran (Iran, Islamic Republic of); Zare-Shahabadi, Abolfazl [Department of Mechanical Engineering, Yazd Branch, Islamic Azad University, Yazd (Iran, Islamic Republic of)
2012-07-15
Inspired by the stability at high temperature and the high mechanical strength of boron nitride nanotubes (BNNTs), the effect of temperature on the compressive buckling of BNNTs has been investigated in this paper. Molecular dynamics (MD) simulations of BNNTs subjected to high temperatures (up to 3000 K) were performed and their structures were analyzed by studying their optimized structures at different temperatures through the radial distribution function (RDF). Then, the structural stability and compressive resistance properties of these nanotubes were investigated and the critical buckling loads and critical buckling strains of the nanotubes and their susceptibility to high temperatures were determined. The gradual decrease in the sharpness of the peaks of RDF plots of non-loaded nanotubes implies that at higher temperatures the structure displays greater deviations from that at room temperature. Results of buckling simulations also indicate a general weakening of the nanotubes and lower critical buckling loads and critical buckling strains at increased temperatures. The decrease in the critical buckling load is more significant for the longer nanotube (L {proportional_to} 6 nm) than the shorter one (L {proportional_to} 3 nm). The critical buckling strain experienced a drop of about 35-50% at temperatures higher than 1500 K. A transitional behavior was observed between T = 1000 and 2000 K. Temperature-dependent axial buckling behavior of boron nitride nanotubes. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
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 elim
Prediction of Buckling of Plain Knitted Fabric Sheets Subjected to Simple Shear in Wale Direction
Institute of Scientific and Technical Information of China (English)
ZHANG Yitong; AO Tao; XU Jiafu
2007-01-01
Knitted fabric is very different from woven fabric due to its more complicated knitting structures. The buckling of knitted fabric sheets subjected to simple shear in the wale direction is investigated analytically in consideration of the large deformation of fabric sheet in critical configuration. The theory on instability of finite deformation is applied to the analysis. All the stress boundary conditions of knitted fabric sheet are satisfied. An equation to determine the buckling direction angle is de-rived. It is shown that there are two possible buckling modes, flexural mode and barreling mode. The buckling condition equations for the flexural mode and barreling mode are also obtained respectively. Numerical illustrations reveal that only the flexural mode can actually occur and the barreling mode cannot, which agrees with the experimental observations. For a permitted buckling mode on margin boundaries, the critical value of shear amount and the buckling direction angle can be deter-mined.
Institute of Scientific and Technical Information of China (English)
张扬; 赵健; 张国伟; 吴徽
2014-01-01
A two-storey RC-frame-structure model was made as a substructure of an existing eight-storey RC building built in late 1970s with a scale of 1∶2.5.It was retrofitted with two buckling-restrained-braces frames by means of embedded bars and shear connectors respectively on the middle span of the three -span RC model structure on both sides.Pseudo-dynamic test had been carried out on the model frame substructure .The test results showed that the connecting methods of buckling-restrained braced frame performed excellent together with the existing frame structure under cyclic loading , and buckling-restrained braces increased the seismic performance of model structure , seismic energy to the structures during earthquake was mainly absorbed by buckling-restrained braces , leading to less damage on structure elements .%参照建于20世纪70年代末的具有代表性的八层混凝土框架结构，按照1∶2.5的比例进行缩尺，制作了一个两榀两层三跨的混凝土框架子结构模型。采用外贴防屈曲支撑混凝土框架的方式分别加固子结构模型每榀的中间跨，两榀框架的加固方式分别为植筋加固和抗剪键加固。对加固后的模型进行拟动力试验。试验结果表明，罕遇地震下结构的变形能够满足规范的要求，且依然具有变形的潜力；两种加固方法均安全可靠；防屈曲支撑加固后混凝土框架结构的抗震性能明显提高，防屈曲支撑耗散掉了大部分的地震能；与普通混凝土框架结构的滞回曲线相比，本结构具有更好的变形以及耗能能力。
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...... 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...
Studies on the Dynamic Buckling of Circular Plate Irradiated by Laser Beam
Institute of Scientific and Technical Information of China (English)
黄晨光; 段祝平
2002-01-01
The dynamic buckling of thin copper plate induced by laser beam, was analyzed with the numerical integration and disturbance methods of controlling equation. The buckling and post-buckling of thin plate were shown, with the consideration of the temperature distribution, inertia effect and initial deflection. At last, the buckling criterion about the circular plate was obtained and used to investigate the relation between the critical laser intensity and the ratio of thickness and diameter of the plate. The results fit the experimental observation and the FEM simulation very well, and benefit to the understanding of failure phenomenon of structures irradiated by laser beam.
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 crucial issue during installation. This paper addresses the hydrostatic buckling pressure of the bucket foundation using threedimensional, non-linear finite element analysis. The main finding of this paper is that introducing an imperfect geometry based on the first linear pre-buckling mode shape, can...... increase the buckling load significantly....
Buckling Characteristics of Cylindrical Pipes
Institute of Scientific and Technical Information of China (English)
Toshiaki Sakurai
2015-01-01
This paper describes the buckling pattern of the body frame by energy absorbed efficiency of crashworthiness related toresearch of the buckling characteristics of aluminum cylindrical pipes with various diameters formed mechanical tools. Experimentswere performed by the quasi-static test without lubrication between specimen and equipment. According to the change in the radiusversus thickness of the specimen, the buckling phenomena are transformed from folding to bellows and the rate of energy absorptionis understood. In crashworthiness, frames are characterized by the folding among three patterns from the absorbed energy efficiencypoint of view and weight reduction. With the development of new types of transport such as electric vehicles, innovated bodystructure should be designed.
Directory of Open Access Journals (Sweden)
Świta P.
2016-05-01
Full Text Available The main purpose is to present the stochastic perturbation-based Finite Element Method analysis of the stability in the issues related to the influence of high temperature resulting from a fire directly connected with the reliability analysis of such structures. The thin-walled beam structures with constant cross-sectional thickness are uploaded with typical constant loads, variable loads and, additionally, a temperature increase and we look for the first critical value equivalent to the global stability loss. Such an analysis is carried out in the probabilistic context to determine as precisely as possible the safety margins according to the civil engineering Eurocode statements. To achieve this goal we employ the additional design-oriented Finite Element Method program and computer algebra system to get the analytical polynomial functions relating the critical pressure (or force and several random design parameters; all the models are state-dependent as we consider an additional reduction of the strength parameters due to the temperature increase. The first four probabilistic moments of the critical forces are computed assuming that the input random parameters have all Gaussian probability functions truncated to the positive values only. Finally, the reliability index is calculated according to the First Order Reliability Method (FORM by an application of the limit function as a difference in-between critical pressure and maximum compression stress determined in the given structures to verify their durability according to the demands of EU engineering designing codes related to the fire situation.
Świta, P.; Kamiński, M.
2016-05-01
The main purpose is to present the stochastic perturbation-based Finite Element Method analysis of the stability in the issues related to the influence of high temperature resulting from a fire directly connected with the reliability analysis of such structures. The thin-walled beam structures with constant cross-sectional thickness are uploaded with typical constant loads, variable loads and, additionally, a temperature increase and we look for the first critical value equivalent to the global stability loss. Such an analysis is carried out in the probabilistic context to determine as precisely as possible the safety margins according to the civil engineering Eurocode statements. To achieve this goal we employ the additional design-oriented Finite Element Method program and computer algebra system to get the analytical polynomial functions relating the critical pressure (or force) and several random design parameters; all the models are state-dependent as we consider an additional reduction of the strength parameters due to the temperature increase. The first four probabilistic moments of the critical forces are computed assuming that the input random parameters have all Gaussian probability functions truncated to the positive values only. Finally, the reliability index is calculated according to the First Order Reliability Method (FORM) by an application of the limit function as a difference in-between critical pressure and maximum compression stress determined in the given structures to verify their durability according to the demands of EU engineering designing codes related to the fire situation.
Nonlinear Analysis of Buckling
Directory of Open Access Journals (Sweden)
Psotný Martin
2014-06-01
Full Text Available The stability analysis of slender web loaded in compression was presented. To solve this problem, a specialized computer program based on FEM was created. The nonlinear finite element method equations were derived from the variational principle of minimum of potential energy. To obtain the nonlinear equilibrium paths, the Newton-Raphson iteration algorithm was used. Corresponding levels of the total potential energy were defined. The peculiarities of the effects of the initial imperfections were investigated. Special attention was focused on the influence of imperfections on the post-critical buckling mode. The stable and unstable paths of the nonlinear solution were separated. Obtained results were compared with those gained using ANSYS system.
Institute of Scientific and Technical Information of China (English)
郭鹏; 张景旭; 杨飞; 赵宏超; 王富国
2015-01-01
30 m望远镜三镜为长轴3.594 m,短轴2.536 m的椭圆形微晶玻璃反射镜.其支撑结构采用了多种柔性结构,以释放非支撑方向的自由度. 使得轴向支承和侧向支撑能够相互解耦,并减小支撑结构与镜子材料的热胀系数不匹配带来的热应力.柔性件柔度越高,在望远镜观测条件的扰动下镜面面形越好.但过高的柔度会降低柔性件的屈曲临界载荷,导致结构发生屈曲失效.为此需要计算出望远镜观测过程中柔性结构所承受的最大压力载荷, 计算相应的屈曲安全系数SFBuckling. 对比了典型结构非线性屈曲分析和特征值屈曲分析的区别,不断迭代设计和分析,柔性元件的SFBuckling和柔度取得了一个较好的平衡点,热扰动下的面形也达到了设计要求.%Thirty Meter Telescopeˊs tertiary mirror is an elliptical ceramic glass reflector whose major axis is 3.594 m and minor axis is 2.536 m. Flexure structure was widely used in the mirrorˊs support structure to release all the other degree of freedom except those along the support direction. The design decoupled the axial and lateral support and reduce the thermal stress due to the material mismatch. The higher compliance would benefit the telescopeˊs mirror surface under distortion, but the buckling criteria load would decrease correspondingly, either. So the limit load of each flexure structure should be calculated as the design input. And the buckling safety factor SFBuckling was analyzed for each part under the limit loads. Eigenvalue buckling analysisand nonlinear buckling analysis were both taken and compared. Based on the analysis results, the design were optimized iteratively to achieve balanced values of compliance for all the flexure. The mirror surface error under thermal distortion met the design requirements.
Institute of Scientific and Technical Information of China (English)
王吉; 王肖钧; 王峰; 赵凯
2004-01-01
With finite-element software ANSYS 7.0 and simple thermal-mechanical coupling constitutive relations,the buckling failure of preloaded cylindrical shell irradiated by high power laser beam was studied by numerical simulations. The buckling mode and buckling critical loading were analysed for different preloading conditions. The influence of laser intensity, beam irradiation time, preloading conditions and geometric parameters of cylindrical shell on the buckling mode were discussed. The numerical results show that: ① the buckling deformation of the cylindrical shell was concentrated in the area of laser spot and the radial buckling was the main buckling mode, ② a linear relationship between the buckling eigenvalue and the maximum temperature at the center of laser spot was approached, ③ the buckling failure of cylindrical shell was attributed to the coupling effect of the material softening and the radial deformation in the laser spot, and hence to raise the stiffness of the material would enhance the ability for anti-irradiation of structure substantially.
Mechanical and thermal buckling analysis of sandwich panels under different edge conditions
Ko, William L.
1993-01-01
By using the Rayleigh-Ritz method of minimizing the total potential energy of a structural system, combined load (mechanical or thermal load) buckling equations are established for orthotropic rectangular sandwich panels supported under four different edge conditions. Two-dimensional buckling interaction curves and three dimensional buckling interaction surfaces are constructed for high-temperature honeycomb-core sandwich panels supported under four different edge conditions. The interaction surfaces provide easy comparison of the panel buckling strengths and the domains of symmetrical and antisymmetrical buckling associated with the different edge conditions. Thermal buckling curves of the sandwich panels also are presented. The thermal buckling conditions for the cases with and without thermal moments were found to be identical for the small deformation theory. In sandwich panels, the effect of transverse shear is quite large, and by neglecting the transverse shear effect, the buckling loads could be overpredicted considerably. Clamping of the edges could greatly increase buckling strength more in compression than in shear.
Creep buckling analysis of shells
Energy Technology Data Exchange (ETDEWEB)
Stone, C.M.; Nickell, R.E.
1977-01-01
The current study was conducted in an effort to determine the degree of conservatism or lack of conservatism in current ASME design rules concerning time-dependent (creep) buckling. In the course of this investigation, certain observations were made concerning the numerical solution of creep buckling problems. It was demonstrated that a nonlinear finite element code could be used to solve the time-dependent buckling problem. A direct method of solution was presented which proved to be computationally efficient and provided answers which agreed very well with available analytical solutions. It was observed that the calculated buckling times could vary widely for small errors in computed displacements. The presence of high creep strain rates contributed to the prediction of early buckling times when calculated during the primary creep stage. The predicted time estimates were found to increase with time until the secondary stage was reached and the estimates approached the critical times predicted without primary creep. It can be concluded, therefore, that for most nuclear piping components, whose primary creep stage is small compared to the secondary stage, the effect of primary creep is negligible and can be omitted from the calculations. In an evaluation of the past and current ASME design rules for time-dependent, load controlled buckling, it was concluded that current use of design load safety factors is not equivalent to a safety factor of ten on service life for low creep exponents.
Energy Technology Data Exchange (ETDEWEB)
Winton, B.R., E-mail: bwinton@gmail.com [ISEM, University of Wollongong, AIIM Facility, Innovation Campus, Squires Way, Fairy Meadow, NSW 2519 (Australia); Ionescu, M.; Dou, S.X.; Wexler, D.; Alvarez, G.A. [ISEM, University of Wollongong, AIIM Facility, Innovation Campus, Squires Way, Fairy Meadow, NSW 2519 (Australia)
2010-03-15
Elastomer films with three-dimensional features self-organized into coherent and semi-coherent buckling domains were created by implanting different species of metal ions and combinations thereof, using a metal evaporation ion source, into quality polydimethylsiloxane films. As a result of the implantation process, functionalized discrete regions of strain-induced surface buckling were created, taking the forms of domains of parallel surface waves, semi-ordered regions and disordered regions. In addition, deep, strain-induced, V-shaped cracks were observed to penetrate well into the elastomer matrix. Characterization was via optical microscopy, X-ray diffraction, atomic force microscopy and high-resolution scanning electron microscopy (SEM) in the form of field emission SEM. It was found that controlling the localized strain by altering the metal ion species can control the frequency of the V-shaped cracks and the properties of the buckled areas. These observations and possible mechanisms for the formation of the cracks and domains are discussed in this paper.
Buckling analysis of partially corroded steel plates with irregular surfaces
Indian Academy of Sciences (India)
Ahmad Rahbar-Ranji
2014-04-01
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 estimation of load carrying capacity reduction of corroded structures typically need a much higher level of accuracy, since the actual corroded plates would have irregular surfaces. The objective of this article is to determine the effect of general corrosion on reduction of elastic buckling strength of both-sided partially corroded plates with irregular surfaces. Eigenvalue analysis using finite element method is employed for Euler stress calculation of corroded plates. The effects of different influential parameters are investigated and it is found that, aspect ratio of plate, location of corroded area, standard deviation of thickness diminution and concentration of corrosion have influence on reduction of elastic buckling strength. Reduction of elastic buckling strength is very sensitive to the amount of corrosion loss. The higher the amount of corrosion loss, the more reduction of elastic buckling strength.
Buckling analysis of a laminate plate
Directory of Open Access Journals (Sweden)
Mamuzić, I.
2008-04-01
Full Text Available The paper deals with a modeling of laminate plates and with their buckling analysis. To predict the inception of buckling for plates in plane resultant forces must be included. The buckling analysis is made by the help of finite element method in program COSMOS/M. For rectangular laminate plate consisting of 4 layers with symmetric and antisymmetric stacking sequence a buckling analysis is carried out. In the illustrative example there are depicted buckling modes for symmetric laminates [30/-30]s, [45/-45]s, [60/-60]s, [90/-90]s and results of the buckling analysis for the symmetric and antisymmetric laminates.
Finite element based investigation of buckling and vibration behaviour of thin walled box beams
Directory of Open Access Journals (Sweden)
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.
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...... optimized design. A well-known issue in buckling topology optimization is artificial buckling modes in low density regions. The typical remedy applied for linear buckling does not have a natural extension to nonlinear problems, and we propose an alternative approach. Some possible negative implications...
Institute of Scientific and Technical Information of China (English)
朱江; 李帼昌; 马传正
2012-01-01
Computer models of buckling restrained braces-reinforced concrete frame and RC frame were set up,and seismic performances of the models were calculated by adopting response spectrum analysis and Pushover analysis based on SAP2000.The results show that the RC frame including buckling restrained braces will increase story-stiffness,decrease lateral deformation of frame structure significantly,and reach requirement of more defences in seismic concept design of buildings.%利用SAP2000软件建立包含和不包含屈曲约束支撑的钢筋混凝土框架计算模型,分别采用反应谱分析和Pushover分析方法对两种模型进行对比计算分析。结果表明：在纯钢筋混凝土框架结构中合理设置屈曲约束支撑,可以达到增加框架结构的侧向刚度、明显降低结构侧向变形、实现多道设防的效果。
FAKHIM, Y. G.; SHOWKATI, H.; K Abedi
2009-01-01
p. 2511-2522 The application of thin-walled cylindrical shells, as the essential structural members, has been known for engineers and functional duty of them is basic necessaries of modern industries. These structures are prone to fail by buckling under external pressure which could be happened during discharging or wind load. Although the buckling capacity of the shells depends principally on two geometric ratios of "length to radius" (L/R) and "radius to thickness" (R/t), but...
Buckling of microtubules: An insight by molecular and continuum mechanics
Energy Technology Data Exchange (ETDEWEB)
Zhang, Jin; Meguid, S. A., E-mail: meguid@mie.utoronto.ca [Mechanics and Aerospace Design Laboratory, Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario M5S 3G8 (Canada)
2014-10-27
The molecular structural mechanics method has been extended to investigate the buckling of microtubules (MTs) with various configurations. The results indicate that for relative short MTs the shear deformation effect, rather than the nonlocal effect, is mainly responsible for the limitation of their widely used Euler beam description and the observed length-dependence of their bending stiffness. In addition, the configuration effect of MTs is also studied and considered as an explanation for the large scattering of the critical buckling force and bending stiffness observed in existing experiments. This configuration effect is also found to mainly originate from the geometry of the MTs and is mainly determined by the protofilament number.
Quantum capacitance in monolayers of silicene and related buckled materials
Nawaz, S.; Tahir, M.
2016-02-01
Silicene and related buckled materials are distinct from both the conventional two dimensional electron gas and the famous graphene due to strong spin orbit coupling and the buckled structure. These materials have potential to overcome limitations encountered for graphene, in particular the zero band gap and weak spin orbit coupling. We present a theoretical realization of quantum capacitance which has advantages over the scattering problems of traditional transport measurements. We derive and discuss quantum capacitance as a function of the Fermi energy and temperature taking into account electron-hole puddles through a Gaussian broadening distribution. Our predicted results are very exciting and pave the way for future spintronic and valleytronic devices.
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...... buckling. The European buckling curves allowing deterministic analytical engineering analysis of members are based on large experimental and parametric measurement programs as well as analytical, numerical and probabilistic investigations. It is of enormous practical value that modern numerical...
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.
Influence of central buckle on suspension bridge dynamic characteristics and driving comfort
Institute of Scientific and Technical Information of China (English)
王达; 邓扬; 刘扬
2015-01-01
The central buckle, which is often used in a suspension bridge, can improve bridges’ performance in the actual operation condition. The influence of the central buckle on natural vibration characteristics and bridge-deck driving comfort of a long-span suspension bridge is studied by using a case study of Siduhe Suspension Bridge in China. Based on the finite element software ANSYS and independently complied program, the influence of the central buckle on the structure force-applied characteristics of a long-span suspension bridge has been explored. The results show that the huge increases of natural frequencies can result in the presence of central buckles because of the increases of bending and torsional rigidities. The central buckle basically makes the stiffening girders and cables within the triangular area covered as a relatively approximate rigid area. Hence, the central buckle can reduce the torsional displacement of the main girder. However, the increases of bending and torsional rigidities have little influence on the impact factor, which is obtained by using vehicle-bridge coupled vibration analysis. This means that the central buckle has little effect on the comfort indices. In addition, it is found that the central buckle can enhance the bridge deck’s driving stability due to the decrease of the torsional displacements of the main girder.
Computation Analysis of Buckling Loads of Thin-Walled Members with Open Sections
Directory of Open Access Journals (Sweden)
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.
Estimation of post-buckling fatigue damage for LMFBR reactor vessel under seismic load
Energy Technology Data Exchange (ETDEWEB)
Ogiso, S.; Sasaki, T.; Oooka, Y. [Kawasaki Heavy Industries, Ltd., Tokyo (Japan). Nuclear Systems Div.; Nakamura, H. [Central Research Inst. of Electric Power Industry, Chiba (Japan)
1995-12-31
Estimation of fatigue damage caused by buckling deformation is important to evaluate safety margin in a seismic buckling design criterion for LMFBR reactor vessels, in addition to limiting the buckling strength. An advanced buckling design guideline draft including the seismic margin criterion has been proposed under the sponsorship of MITI to date. An ultimate state in this criterion was defined as the condition that the maximum global displacement {delta}{sub max} reaches a critical displacement {delta}{sub u}. The authors have previously proposed an estimation method of the fatigue damage based on the post buckling fatigue tests 304 s.s. cylinders at room temperature. However, adoption of a modified 316 s.s named 316FR s.s is under development as the material of reactor vessel of the updated design of the Demonstration Fast Breeder Reactor. The buckling tests with 316FR s.s cylinders were performed under high temperature to obtain the skeleton curve of the relation between load and displacement. And the buckling behaviors under the cyclic loading were compared with those of 304 s.s. Objectives of the present study are: to apply the proposed estimation method to a reactor vessel made of 316FR s.s., and clarify the correlation between {delta}{sub max} and fatigue failure; to verify structural soundness of the ultimate state derived from the seismic margin criterion against the fatigue failure due to the buckling deformation. (author). 7 refs., 12 figs., 1 tab.
Elastic Buckling of Bionic Cylindrical Shells Based on Bamboo
Institute of Scientific and Technical Information of China (English)
Jian-feng Ma; Wu-yi Chen; Ling Zhao; Da-hai Zhao
2008-01-01
High load-bearing efficiency is one of the advantages of biological structures after the evolution of billions of years.Biomimicking from nature may offer the potential for lightweight design. In the viewpoint of mechanics properties, the culm of bamboo comprises of two types of cells and the number of the vascular bundles takes a gradient of distribution. A three-point bending test was carried out to measure the elastic modulus. Results show that the elastic modulus of bamboo decreases gradually from the periphery towards the centre. Based on the structural characteristics of bamboo, a bionic cylindrical structure was designed to mimic the gradient distribution of vascular bundles and parenchyma cells. The buckling resistance of the bionic structure was compared with that of a traditional shell of equal mass under axial pressure by finite element simulations. Results show that the load-bearing capacity of bionic shell is increased by 124.8%. The buckling mode of bionic structure is global buckling while that of the conventional shell is local buckling.
Large-Area Buckled MoS2 Films on the Graphene Substrate.
Kim, Seon Joon; Kim, Dae Woo; Lim, Joonwon; Cho, Soo-Yeon; Kim, Sang Ouk; Jung, Hee-Tae
2016-06-01
In this study, a novel buckled structure of edge-oriented MoS2 films is fabricated for the first time by employing monolayer graphene as the substrate for MoS2 film growth. Compared to typical buckling methods, our technique has several advantages: (1) external forces such as heat and mechanical strain are not applied; (2) uniform and controllable buckling over a large area is possible; and (3) films are able to be transferred to a desired substrate. Dual MoS2 orientation was observed in the buckled film where horizontally aligned MoS2 layers of 7 nm thickness were present near the bottom graphene surface and vertically aligned layers dominated the film toward the outer surface, in which the alignment structure was uniform across the entire film. The catalytic ability of the buckled MoS2 films, measured by performing water-splitting tests in acidic environments, shows a reduced onset potential of -0.2 V versus reversible hydrogen electrode (RHE) compared to -0.32 V versus RHE for pristine MoS2, indicating that the rough surface provided a higher catalytic activity. Our work presents a new method to generate a buckled MoS2 structure, which may be extended to the formation of buckled structures in various 2D materials for future applications.
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...
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...
Buckling of a single-layered graphene sheet on an initially strained InGaAs thin plate
Energy Technology Data Exchange (ETDEWEB)
Taziev, R M; Ya Prinz, V, E-mail: taziev@thermo.isp.nsc.ru [Institute of Semiconductor Physics, 630090, Novosibirsk (Russian Federation)
2011-07-29
The elastic buckling behavior of a defect-free single-layered graphene sheet deposited on a strained InGaAs substrate is investigated. Such a buckled sandwich structure can be formed by local etching of an initially strained InGaAs substrate. We numerically investigated the necessary buckling conditions for a single-layered graphene sheet of circular geometry on an initially strained InGaAs thin plate. A criterion for buckling for various axisymmetric buckling shapes was obtained. It is shown that for a thin circular InGaAs plate with a monolayer graphene sheet of radius 80 nm and thickness 4 nm three axisymmetric buckling shapes can be obtained. For an initial value of the elastic deformation of the plate of 3%, the in-plane strain in graphene can reach a value of 1%. This deformation is shown to be distributed inhomogeneously along the radius of the graphene monolayer.
On the buckling eigenvalue problem
Energy Technology Data Exchange (ETDEWEB)
Antunes, Pedro R S, E-mail: pant@cii.fc.ul.pt [Departamento de Matematica, Universidade Lusofona de Humanidades e Tecnologias, Av. do Campo Grande, 376, 1749-024 Lisboa (Portugal); Group of Mathematical Physics of the University of Lisbon, Complexo Interdisciplinar, Av. Professor Gama Pinto 2, P-1649-003 Lisboa (Portugal)
2011-05-27
We prove a density result which allows us to justify the application of the method of fundamental solutions to solve the buckling eigenvalue problem of a plate. We address an example of an analytic convex domain for which the first eigenfunction does change the sign and present a large-scale numerical study with polygons providing numerical evidence to some new conjectures.
Combined scleral buckling and phacoemulsification
Directory of Open Access Journals (Sweden)
Pukhraj Rishi
2009-01-01
Conclusion: Combined scleral buckling and phacoemulsification is a safe and effective procedure that spares the patient the burden of repeated surgeries. It may be considered as a treatment option in selected cases of rhegmatogenous retinal detachment with significant cataract with/without early PVR.
Uncertainty modelling of critical column buckling for reinforced concrete buildings
Indian Academy of Sciences (India)
Kasim A Korkmaz; Fuat Demir; Hamide Tekeli
2011-04-01
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 algorithms can be a solution to generate more dependable results. This study investigates 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 material properties were deﬁned to take uncertainties into account. The results show that uncertainties play an important role in stability analyses and should be considered in the design. The proposed approach is applicable to both future numerical and experimental researches. According to the study results, it is seen that, calculated buckling load values are stayed in lower and upper bounds while the load values are different for same concrete strength values by using different code formula.
DEFF Research Database (Denmark)
Neves, Miguel M.; Sigmund, Ole; Bendsøe, Martin P.
2002-01-01
The problem of determining highly localized buckling modes in perfectly periodic cellular microstructures of infinite extent is addressed. A double scale asymptotic technique is applied to the linearized stability problem for a periodic structure built from linearly elastic microstructures...... to design materials with optimal elastic properties that are less prone to localized instability in the form of local buckling modes at the scale of the micro structure. Copyright (C) 2002 John Wiley Sons, Ltd....
The elastic buckling of super-graphene and super-square carbon nanotube networks
Energy Technology Data Exchange (ETDEWEB)
Li Ying; Qiu Xinming [AML, Department of Engineering Mechanics, School of Aerospace, Tsinghua University, 100084 Beijing (China); Yin Yajun, E-mail: yinyj@tsinghua.edu.c [AML, Department of Engineering Mechanics, School of Aerospace, Tsinghua University, 100084 Beijing (China)] [Division of Mechanics, Nanjing University of Technology, 210009 Nanjing (China); Yang Fan [AML, Department of Engineering Mechanics, School of Aerospace, Tsinghua University, 100084 Beijing (China); Fan Qinshan [Division of Mechanics, Nanjing University of Technology, 210009 Nanjing (China)
2010-04-05
The super-graphene (SG) and super-square (SS) carbon nanotube network are built by the straight single-walled carbon nanotubes and corresponding junctions. The elastic buckling behaviors of these carbon nanotube networks under different boundary conditions are explored through the molecular structural mechanics method. The following results are obtained: (a) The critical buckling forces of the SG and SS networks decrease as the side lengths or aspect ratios of the networks increase. The continuum plate theory could give good predictions to the buckling of the SS network but not the SG network with non-uniform buckling modes. (b) The carbon nanotube networks are more stable structures than the graphene structures with less carbon atoms.
Buckling and Delamination of Ti/Cu/Si Thin Film During Annealing
Lin, Qijing; Yang, Shuming; Jing, Weixuan; Li, Changsheng; Wang, Chenying; Jiang, Zhuangde; Jiang, Kely
2014-09-01
In this paper, the formation of buckling and delamination of sandwiched stacking of Ti/Cu/Si thin film are investigated. The crystallization structures, the composition of the Cu/Ti thin films, and the surface morphology are measured during annealing. The results show that the solid-phase reaction between Cu and Ti occurs at the interface. Buckling is initiated in the thin film annealed at 600°C. The volume expansion promotes the buckling and further produces microcracks. With increasing volume expansion, there are cavities formed in the middle layer when the annealing temperature is up to 700°C. Finally, thin film is delaminated from the substrate.
Artery buckling analysis using a two-layered wall model with collagen dispersion.
Mottahedi, Mohammad; Han, Hai-Chao
2016-07-01
Artery buckling has been proposed as a possible cause for artery tortuosity associated with various vascular diseases. Since microstructure of arterial wall changes with aging and diseases, it is essential to establish the relationship between microscopic wall structure and artery buckling behavior. The objective of this study was to developed arterial buckling equations to incorporate the two-layered wall structure with dispersed collagen fiber distribution. Seven porcine carotid arteries were tested for buckling to determine their critical buckling pressures at different axial stretch ratios. The mechanical properties of these intact arteries and their intima-media layer were determined via pressurized inflation test. Collagen alignment was measured from histological sections and modeled by a modified von-Mises distribution. Buckling equations were developed accordingly using microstructure-motivated strain energy function. Our results demonstrated that collagen fibers disperse around two mean orientations symmetrically to the circumferential direction (39.02°±3.04°) in the adventitia layer; while aligning closely in the circumferential direction (2.06°±3.88°) in the media layer. The microstructure based two-layered model with collagen fiber dispersion described the buckling behavior of arteries well with the model predicted critical pressures match well with the experimental measurement. Parametric studies showed that with increasing fiber dispersion parameter, the predicted critical buckling pressure increases. These results validate the microstructure-based model equations for artery buckling and set a base for further studies to predict the stability of arteries due to microstructural changes associated with vascular diseases and aging.
Dynamic buckling of actin within filopodia
DEFF Research Database (Denmark)
Leijnse, Natascha; Oddershede, Lene B; Bendix, Pól Martin
2015-01-01
on external substrates.(1) These studies have revealed that internal actin flow can transduce a force across the cell surface through transmembrane linkers like integrins. In addition to the elongation-retraction behavior filopodia also exhibit a buckling and rotational behavior. Filopodial buckling...... a filopodium and holding it while measuring the cellular response, we also monitor and analyze the waiting times for the first buckle observed in the fluorescently labeled actin shaft....
A map of competing buckling-driven failure modes of substrate-supported thin brittle films
Energy Technology Data Exchange (ETDEWEB)
Jia, Zheng [Department of Mechanical Engineering and Maryland NanoCenter, University of Maryland, College Park, MD 20742 (United States); Peng, Cheng [Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005 (United States); Lou, Jun, E-mail: jlou@rice.edu [Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005 (United States); Li, Teng, E-mail: lit@umd.edu [Department of Mechanical Engineering and Maryland NanoCenter, University of Maryland, College Park, MD 20742 (United States)
2012-08-31
Our in situ experiments of polyimide-supported thin indium tin oxide (ITO) films reveal buckling-driven film cracking in some samples and buckling-driven interfacial delamination in other samples. Although studies of individual buckling-driven failure mode exist, it still remains unclear what governs the competition between these two different failure modes in a given film/substrate structure. Through theoretical analysis and numerical simulations, we delineate a map of competing buckling-driven failure modes of substrate-supported thin brittle films in the parameter space of interfacial adhesion and interfacial imperfection size. Such a map can offer insight on the mechanical durability of functional thin films. For example, interestingly, we show that strongly bonded thin brittle films are more prone to buckling-driven cracking, a more detrimental failure mode for thin brittle ITO transparent conductors widely used in displays and flexible electronics. - Highlights: Black-Right-Pointing-Pointer Map of buckling-driven failure modes of thin brittle films on substrates. Black-Right-Pointing-Pointer We study key parameters that govern buckling-driven failure modes. Black-Right-Pointing-Pointer The map offers insights on optimal design of functional thin films.
Reporting buckling strength and elastic properties of nanowires
Shaat, M.; Abdelkefi, A.
2016-12-01
Nanocrystalline-nanowires have been incorporated in many micro-/nano-scale applications. To design nanowires-based nano-devices, studies should be conducted on the characterization of the elastic properties and the buckling strengths of nanowires. The challenge associated with detecting the properties of nanowires is that their properties are size-dependent. This motivated us to propose a model for the mechanics of nanocrystalline nanowires. In the context of this model, new measures are incorportated to account for the nanowire material structure and size effects and to reflect the experimental observations of nanomaterials-nanowires. This model is then harnessed to report the ranges of the buckling strength and the elastic properties of nanowires made of nanocrystalline diamond, Si, Al, Cu, Ag, Au, and Pt, for the first time. First, we report the range of the grain boundary Young's modulus for the various nanocrystalline materials. Depending on the contents of the grain boundary and the amount of impurities, the grain boundary Young's modulus is likely to be within the reported ranges. Second, for each grain size (from 200 nm to 2 nm), we report the range of Young's modulus, shear modulus, bulk modulus, and mass density of the aforementioned nanocrystalline nanomaterials. Third, we report the buckling strength and the equivalent Young's modulus of nanowires with different sizes accounting for the nanowire surface effects. The reported ranges of the buckling strength and the elastic properties of nanowires are experimentally validated.
Exploiting Additive Manufacturing Infill in Topology Optimization for Improved Buckling Load
DEFF Research Database (Denmark)
Clausen, Anders; Aage, Niels; Sigmund, Ole
2016-01-01
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...... material, the buckling load may be more than four times higher than that of solid structures optimized under the same conditions....
Strain mapping on gold thin film buckling and siliconblistering
Energy Technology Data Exchange (ETDEWEB)
Goudeau, P.; Tamura, N.; Parry, G.; Colin, J.; Coupeau, C.; Cleymand, F.; Padmore, H.
2005-09-01
Stress/Strain fields associated with thin film buckling induced by compressive stresses or blistering due to the presence of gas bubbles underneath single crystal surfaces are difficult to measure owing to the microscale dimensions of these structures. In this work, we show that micro Scanning X-ray diffraction is a well suited technique for mapping the strain/stress tensor of these damaged structures.
Indian Academy of Sciences (India)
K Athiannan; R Palaninathan
2004-02-01
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 rolling and seam welding process and hence are expected to have imperfections more or less of a kind similar to that of real shell structures. The present work thus differs from most of the earlier investigations. The measured maximum imperfections $\\delta_{\\text{max}}$ are of the order of $\\pm 3t$ (t = thickness). The buckling loads obtained experimentally are compared with the numerical buckling values obtained through ﬁnite element method (FEM). In the case of axial buckling, the imperfect geometry is obtained in four ways and in the case of transverse shear buckling, the FE modelling of imperfect geometry is done in two ways. The initial geometric imperfections affect the load carrying capacity. The load reduction is considerable in the case of axial compression and is marginal in the case of transverse shear buckling. Comparisons between experimental buckling loads under axial compression, reveal that the extent of imperfection, rather than its maximum value, in a specimen inﬂuences the failure load. Buckling tests under transverse shear are conducted with and without axial constraints. While differences in experimental loads are seen to exist between the two conditions, the numerical values are almost equal. The buckling modes are different, and the experimentally observed and numerically predicted values are in complete disagreement.
Buckling of reconstruction elements of the edges of triple steps on vicinal Si(111) surfaces
Energy Technology Data Exchange (ETDEWEB)
Zhachuk, R. A., E-mail: zhachuk@gmail.com [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Coutinho, J. [University of Aveiro, Campus Santiago, I3N, Department of Physics (Portugal); Rayson, M. J. [University of Surrey, Department of Chemistry (United Kingdom); Briddon, P. R. [Newcastle University, School of Electrical, Electronic and Computer Engineering (United Kingdom)
2015-04-15
The structure of steps with a height of three (111) interplanar distances on vicinal Si(111) surfaces has been analyzed through density functional theory calculations. It has been shown that several stable atomic configurations are possible depending on the buckling of the reconstruction elements of edges of the steps on the surface. It has been found that the direction of the buckling of reconstruction elements in the ground state of the surface is determined by the Coulomb interaction with their nearest atomic environment.
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.
Institute of Scientific and Technical Information of China (English)
薛彦涛; 金林飞; 韩雪; 程小燕; 佟道林
2013-01-01
When buckling-restrained brace(BRB) is applied into structure system, it can strengthen lateral stiffness and shear strength of the structure, thus cut down the layer displacement and overall displacement of the structure. After brace is applied into the frame structure, its hysteretic curve has an essential change comparing with the traditional structure. For the influence of brace, the shape is full of energy. Furthermore, the capacity of energy consumption is improved to a large degree. The declined part of skeleton line of brace structure will not decline dramatically due to the increase of displacement like the common structure. Instead, the pace of decline slows down. The data show that it can be considered in design to adopt brace instead of shear wall in concrete structure system.%将屈曲约束支撑用于结构体系,增强了整体结构的抗侧刚度和抗剪强度,有利于减小结构的层间位移和总体位移.将支撑应用到框架中后,结构的滞回曲线较传统的框架形状更加饱满,说明结构耗能能力得到了大幅度提高.支撑框架的骨架线的下降段也不像普通框架那样随着位移的增加加速下降,而是有下降减缓的趋势.本文试图通过试验数据说明可以考虑用支撑代替混凝土剪力墙应用于混凝土结构体系中.
Directory of Open Access Journals (Sweden)
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.
Flexural buckling of fire exposed aluminium columns
Maljaars, J.; Twilt, L.; Soetens, F.
2009-01-01
In order to study buckling of fire exposed aluminium columns, a finite element model is developed. The results of this model are verified with experiments. Based on a parametric study with the finite element model, it is concluded that the simple calculation model for flexural buckling of fire expos
Numerical analysis and experiment to identify origin of buckling in rapid cycling synchrotron core
Energy Technology Data Exchange (ETDEWEB)
Morita, Y., E-mail: yuichi.morita@kek.jp [High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki (Japan); Kageyama, T. [High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki (Japan); Akoshima, M. [The National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki (Japan); Torizuka, S.; Tsukamoto, M. [National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki (Japan); Yamashita, S. [International Center for Elementary Particle Physics (ICEPP), University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo (Japan); Yoshikawa, N. [Institute of Industrial Science (IIS), University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo (Japan)
2013-11-11
The accelerating cavities used in the rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) are loaded with magnetic alloy (MA) cores. Over lengthly periods of RCS operation, significant reductions in the impedance of the cavities resulting from the buckling of the cores were observed. A series of thermal structural simulations and compressive strength tests showed that the buckling can be attributed to the low-viscosity epoxy resin impregnation of the MA core that causes the stiffening of the originally flexible MA–ribbon–wound core. Our results showed that thermal stress can be effectively reduced upon using a core that is not epoxy-impregnated. -- Highlights: • Study to identify the origin of buckling in the MA cores is presented. • Thermal stress simulations and compressive strength tests were carried out. • Results show that thermal stress is the origin of core buckling. • Thermal stress can be reduced by using cores without epoxy impregnation.
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.
Nemeth, Michael P.
2004-01-01
An approach for synthesizing buckling results for thin balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and elastically restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexural anisotropic plates that are subjected to combined mechanical loads. In addition, stiffness-weighted laminate thermal-expansion parameters and compliance coefficients are derived that are used to determine critical temperatures in terms of physically intuitive mechanical-buckling coefficients. Many results are presented for some common laminates that are intended to facilitate a structural designer s transition to the use of the generic buckling design curves. Several curves that illustrate the fundamental parameters used in the analysis are presented, for nine contemporary material systems, that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of the generic design curves.
Numerical Analysis Of Buckling Of Von Mises Planar Truss
Directory of Open Access Journals (Sweden)
Kalina Martin
2015-12-01
Full Text Available A computational algorithm of a discrete model of von Mises planar steel truss is presented. The structure deformation is evaluated by seeking the minimal potential energy. The critical force invented by mathematical solution was compared with solution by computer algorithm. Symmetric and asymmetric effects of initial shape of geometric imperfection of axis of struts are used in model. The shapes of buckling of von Mises planar truss of selected vertical displacement of top joint are shown.
Buckled graphene: A model study based on density functional theory
Khan, Mohammad A.
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.
Tailored Buckling Microlattices as Reusable Light-Weight Shock Absorbers.
Frenzel, Tobias; Findeisen, Claudio; Kadic, Muamer; Gumbsch, Peter; Wegener, Martin
2016-07-01
Structures and materials absorbing mechanical (shock) energy commonly exploit either viscoelasticity or destructive modifications. Based on a class of uniaxial light-weight geometrically nonlinear mechanical microlattices and using buckling of inner elements, either a sequence of snap-ins followed by irreversible hysteretic - yet repeatable - self-recovery or multistability is achieved, enabling programmable behavior. Proof-of-principle experiments on three-dimensional polymer microstructures are presented.
Controlled Buckling and Crumpling of Nanoparticle-Coated Droplets
Datta, Sujit S.; Shum, Ho Cheung; Weitz, David A.
2010-01-01
We introduce a new experimental approach to study the structural transitions of large numbers of nanoparticle-coated droplets as their volume is reduced. We use an emulsion system where the dispersed phase is slightly soluble in the continuous phase. By adding a fixed amount of unsaturated continuous phase, the volume of the droplets can be controllably reduced, causing them to buckle or crumple, thereby becoming nonspherical. The resultant morphologies depend both on the extent of volume red...
Advances in Shell Buckling: Theory and Experiments
Thompson, J. Michael T.
In a recent feature article in this journal, coauthored by Gert van der Heijden, I described the static-dynamic analogy and its role in understanding the localized post-buckling of shell-like structures, looking exclusively at integrable systems. We showed the true significance of the Maxwell energy criterion load in predicting the sudden onset of "shock sensitivity" to lateral disturbances. The present paper extends the survey to cover nonintegrable systems, such as thin compressed shells. These exhibit spatial chaos, generating a multiplicity of localized paths (and escape routes) with complex snaking and laddering phenomena. The final theoretical contribution shows how these concepts relate to the response and energy barriers of an axially compressed cylindrical shell. After surveying NASA's current shell-testing programme, a new nondestructive technique is proposed to estimate the "shock sensitivity" of a laboratory specimen that is in a compressed metastable state before buckling. A probe is used to measure the nonlinear load-deflection characteristic under a rigidly applied lateral displacement. Sensing the passive resisting force, it can be plotted in real time against the displacement, displaying an equilibrium path along which the force rises to a maximum and then decreases to zero: having reached the free state of the shell that forms a mountain-pass in the potential energy. The area under this graph gives the energy barrier against lateral shocks. The test is repeated at different levels of the overall compression. If a symmetry-breaking bifurcation is encountered on the path, computer simulations show how this can be suppressed by a controlled secondary probe tuned to deliver zero force on the shell.
Institute of Scientific and Technical Information of China (English)
刘淼鑫; 魏路; 伍阳; 钟维浩
2014-01-01
以某实际高层框筒结构工程为例，根据规范设定较高的抗震性能目标，研究分析屈曲约束支撑体系对提高结构的整体抗震性能的效果。分别进行多遇地震作用下的弹性反应谱分析和罕遇地震作用下的推覆分析，结果表明：加设屈曲约束支撑后结构的抗震性能得到明显加强。在多遇地震作用下，屈曲约束支撑体系减小层间位移角；在罕遇地震作用下，屈曲约束支撑体系有效耗散地震能量，减小主体结构变形和损伤，形成合理的整体型结构屈服机制。%In this paper, Based on the higher seismic performance objectives set by the code, a real high-rise framed-tube building is established to research and analysis the overall seismic performance and to investigate damping control effect of the anti-buckling brace. Respectively, the elastic earthquake response spectrum analysis and rare earthquake pushover analysis show that anti-buckling brace has significantly enhanced the seismic performance of the structure.The results show that anti-buckling brace system significantly reduces drift angle in the weak earthquake and in rare earthquake, the anti-buckling brace system effectively dissipate seismic energy, reducing the main structural damage and form a reasonable yield mechanism to the overall structure.
Observation of optomechanical buckling transitions
Xu, H.; Kemiktarak, U.; Fan, J.; Ragole, S.; Lawall, J.; Taylor, J. M.
2017-03-01
Correlated phases of matter provide long-term stability for systems as diverse as solids, magnets and potential exotic quantum materials. Mechanical systems, such as buckling transition spring switches, can have engineered, stable configurations whose dependence on a control variable is reminiscent of non-equilibrium phase transitions. In hybrid optomechanical systems, light and matter are strongly coupled, allowing engineering of rapid changes in the force landscape, storing and processing information, and ultimately probing and controlling behaviour at the quantum level. Here we report the observation of first- and second-order buckling transitions between stable mechanical states in an optomechanical system, in which full control of the nature of the transition is obtained by means of the laser power and detuning. The underlying multiwell confining potential we create is highly tunable, with a sub-nanometre distance between potential wells. Our results enable new applications in photonics and information technology, and may enable explorations of quantum phase transitions and macroscopic quantum tunnelling in mechanical systems.
Nitinol stent design - understanding axial buckling.
McGrath, D J; O'Brien, B; Bruzzi, M; McHugh, P E
2014-12-01
Nitinol׳s superelastic properties permit self-expanding stents to be crimped without plastic deformation, but its nonlinear properties can contribute towards stent buckling. This study investigates the axial buckling of a prototype tracheobronchial nitinol stent design during crimping, with the objective of eliminating buckling from the design. To capture the stent buckling mechanism a computational model of a radial force test is simulated, where small geometric defects are introduced to remove symmetry and allow buckling to occur. With the buckling mechanism ascertained, a sensitivity study is carried out to examine the effect that the transitional plateau region of the nitinol loading curve has on stent stability. Results of this analysis are then used to redesign the stent and remove buckling. It is found that the transitional plateau region can have a significant effect on the stability of a stent during crimping, and by reducing the amount of transitional material within the stent hinges during loading the stability of a nitinol stent can be increased.
Directory of Open Access Journals (Sweden)
Kaspars Kalnins
2015-01-01
Full Text Available Nondestructive methods, to calculate the buckling load of imperfection sensitive thin-walled structures, such as large-scale aerospace structures, are one of the most important techniques for the evaluation of new structures and validation of numerical models. The vibration correlation technique (VCT allows determining the buckling load for several types of structures without reaching the instability point, but this technique is still under development for thin-walled plates and shells. This paper presents and discusses an experimental verification of a novel approach using vibration correlation technique for the prediction of realistic buckling loads of unstiffened cylindrical shells loaded under axial compression. Four different test structures were manufactured and loaded up to buckling: two composite laminated cylindrical shells and two stainless steel cylinders. In order to characterize a relationship with the applied load, the first natural frequency of vibration and mode shape is measured during testing using a 3D laser scanner. The proposed vibration correlation technique allows one to predict the experimental buckling load with a very good approximation without actually reaching the instability point. Additional experimental tests and numerical models are currently under development to further validate the proposed approach for composite and metallic conical structures.
Torres, Fernando G; Troncoso, Omar P; Diaz, John; Arce, Diego
2014-11-01
Porcupine quills are natural structures formed by a thin walled conical shell and an inner foam core. Axial compression tests, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) were all used to compare the characteristics and mechanical properties of porcupine quills with and without core. The failure mechanisms that occur during buckling were analyzed by scanning electron microscopy (SEM), and it was found that delamination buckling is mostly responsible for the decrease in the measured buckling stress of the quills with regard to predicted theoretical values. Our analysis also confirmed that the foam core works as an energy dissipater improving the mechanical response of an empty cylindrical shell, retarding the onset of buckling as well as producing a step wise decrease in force after buckling, instead of an instantaneous decrease in force typical for specimens without core. Cell collapse and cell densification in the inner foam core were identified as the key mechanisms that allow for energy absorption during buckling.
Energy Technology Data Exchange (ETDEWEB)
Potoczny, G.A. [School of Metallurgy and Materials, University of Birmingham, Edgbaston, B15 2TT Birmingham (United Kingdom); Bejitual, T.S. [Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, 26506, West Virginia (United States); Abell, J.S. [School of Metallurgy and Materials, University of Birmingham, Edgbaston, B15 2TT Birmingham (United Kingdom); Sierros, K.A. [Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, 26506, West Virginia (United States); Cairns, D.R., E-mail: Darran.Cairns@mail.wvu.edu [Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, 26506, West Virginia (United States); Kukureka, S.N. [School of Metallurgy and Materials, University of Birmingham, Edgbaston, B15 2TT Birmingham (United Kingdom)
2013-01-01
The flexibility and electrical stability of highly conductive and transparent amorphous indium tin oxide (a-ITO) films coated on polyethylene terephthalate and polyethylene naphthalate substrates were investigated by buckling tests with in situ monitoring of the electrical resistance. Monotonic and cyclic loading tests of the ITO/polymer systems were conducted. The results show that monotonic buckling in tension is more critical for electromechanical stability of ITO films than in compression (an increase in electrical resistance was observed at a critical radius of curvature, of ∼ 3 and ∼ 1 mm, respectively for both cases investigated). In contrast, cyclic loading tests show that the compression mode is more critical than the tensile mode which may be a result of the residual stress present in the film structure. Failure of the ITO film was caused by buckling-driven delamination observed using scanning electron microscopy after the tests. The presence of residual stress could mean that buckling-driven delamination is the dominant failure mode for ITO/polymer systems under repeated flexing. In general, comparable electromechanical stability was observed in both cases. Investigating the electromechanical response of such material systems is important for polymer substrate selection and life-time prediction of flexible polyester-based electronic devices. - Highlights: ► Cyclic buckling investigation of flexible electrodes. ► Importance of ITO surface compression mode as opposed to tension. ► Role of ITO residual stresses on controlled buckling investigations.
Development of Finite Element Model for the Static Buckling Behavior of the Spacer Grid
Energy Technology Data Exchange (ETDEWEB)
Yoo, Young Ik; Park, Nam Gyu; Kim, Kyoung Ju; Suh, Jung Min [Kepco Nuclear Fuel, Daejeon (Korea, Republic of)
2013-10-15
In this study, finite element model was proposed to evaluate the buckling characteristics and structural behavior of partial spacer grids. A two-dimensional model was developed to simplify a real spacer gird model and save analysis time. And it was validated for comparison with experimental tests. A non-linear analysis method was introduced to perform realistic simulation. Later, the buckling analysis of the full size grid will be performed based on the analysis results of partial spacer grids. A study was conducted to develop the simplified model of a spacer grid and provide a prediction of buckling behavior. The FE analysis results are quite similar to the experimental tests. · The deformed geometry of FE model after compression is consistent and very similar to that of real situation, and the non-linear analysis method used in this model can simulate buckling and post-buckling behavior well. · The buckling strength obtained by FEM shows a very good agreement with the physical tests.
Buckling instability of squeezed droplets
Elfring, Gwynn J
2015-01-01
Motivated by recent experiments, we consider theoretically the compression of droplets pinned at the bottom on a surface of finite area. We show that if the droplet is sufficiently compressed at the top by a surface, it will always develop a shape instability at a critical compression. When the top surface is flat, the shape instability occurs precisely when the apparent contact angle of the droplet at the pinned surface is pi, regardless of the contact angle of the upper surface, reminiscent of past work on liquid bridges and sessile droplets as first observed by Plateau. After the critical compression, the droplet transitions from a symmetric to an asymmetric shape. The force required to deform the droplet peaks at the critical point then progressively decreases indicative of catastrophic buckling. We characterize the transition in droplet shape using illustrative examples in two dimensions followed by perturbative analysis as well as numerical simulation in three dimensions. When the upper surface is not f...
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.
Scleral buckle infection with Alcaligenes xylosoxidans.
Hsu, Chih-Kang; Chang, Yun-Hsiang; Chen, Jiann-Torng
2014-06-01
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.
Thermal buckling analysis of truss-core sandwich plates
Institute of Scientific and Technical Information of China (English)
陈继伟; 刘咏泉; 刘伟; 苏先樾
2013-01-01
Truss-core sandwich plates have received much attention in virtue of the high values of strength-to-weight and stiffness-to-weight as well as the great ability of impulse-resistance recently. It is necessary to study the stability of sandwich panels under the influence of the thermal load. However, the sandwich plates are such complex three-dimensional (3D) systems that direct analytical solutions do not exist, and the finite element method (FEM) cannot represent the relationship between structural parameters and mechanical properties well. In this paper, an equivalent homogeneous continuous plate is idealized by obtaining the effective bending and transverse shear stiffness based on the characteristics of periodically distributed unit cells. The first order shear deformation theory for plates is used to derive the stability equation. The buckling temperature of a simply supported sandwich plate is given and verified by the FEM. The effect of related parameters on mechanical properties is investigated. The geometric parameters of the unit cell are optimized to attain the maximum buckling temperature. It is shown that the optimized sandwich plate can improve the resistance to thermal buckling significantly.
Fabrication and buckling dynamics of nanoneedle AFM probes
Energy Technology Data Exchange (ETDEWEB)
Beard, J D; Gordeev, S N, E-mail: jdb28@bath.ac.uk [Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY (United Kingdom)
2011-04-29
A new method for the fabrication of high-aspect-ratio probes by electron beam induced deposition is described. This technique allows the fabrication of cylindrical 'nanoneedle' structures on the atomic force microscope (AFM) probe tip which can be used for accurate imaging of surfaces with high steep features. Scanning electron microscope (SEM) imaging showed that needles with diameters in the range of 18-100 nm could be obtained by this technique. The needles were shown to undergo buckling deformation under large tip-sample forces. The deformation was observed to recover elastically under vertical deformations of up to {approx} 60% of the needle length, preventing damage to the needle. A technique of stabilizing the needle against buckling by coating it with additional electron beam deposited carbon was also investigated; it was shown that coated needles of 75 nm or greater total diameter did not buckle even under tip-sample forces of {approx} 1.5 {mu}N.
A Reduction Factor for Buckling Load of Spherical Cap Shells
Directory of Open Access Journals (Sweden)
P.N. Khakina
2011-12-01
Full Text Available The classical buckling theory usually overestimates the buckling load of shells. In this study, a reduction factor is determined using geometrical parameters so as to reduce the classical buckling load to a more realistic value based on the post-buckling load. It is observed that the buckling load is directly proportional to the thickness and rise and inversely proportional to the span of the spherical cap. Finite element modeling and simulation using ABAQUS was conducted to determine the buckling behavior of a spherical cap shell subjected to different initial geometrical imperfections. The load-deflection curves drawn from the simulation formed a plateau at the post-buckling load. It is observed that as the initial geometrical imperfection is increased, the value of the initial buckling load is almost the same as the value of the post-buckling load on the plateau. The results obtained from different shells were used to derive a formula for the reduction factor.
Scleral buckle infection with aspergillus flavus
Directory of Open Access Journals (Sweden)
Bouhaimed Manal
2008-01-01
Full Text Available Purpose: To present a case of scleral buckle infection with Aspergillus flavus in a tertiary eye center in Saudi Arabia. Methods: A retrospective case report of a 28-year-old Saudi male who presented with a six-month history of conjunctival injection and discharge from the left eye which had undergone uncomplicated conventional retinal detachment surgery, at the King Khaled Eye Specialist Hospital in Riyadh, Saudi Arabia, in the form of cryopexy, subretinal fluid drainage and scleral buckle (grooved segmental sponge and circumferential band with sleeve for a macula on retinal detachment four years earlier. A diagnosis of infected extruded scleral buckle was made and the buckle was removed. Results: The infected scleral buckle was removed under local anesthesia with administration of sub-conjunctival irrigation of 50 mg solution of Vancomycin, and sub-conjunctival injection of 25mg of Vancomycin. Post operative microbiological studies revealed infection with silver staining of moderate Aspergillus flavus hyphae. Visual acuity of the left eye improved from 20/200 before surgery to 20/60 in the two years follow-up visit. Conclusion: This case report indicates the importance of considering infection with multiple organisms - including fungal ones - in cases of scleral buckle infections in our population.
Buckling Behavior of Substrate Supported Graphene Sheets
Directory of Open Access Journals (Sweden)
Kuijian Yang
2016-01-01
Full Text Available The buckling of graphene sheets on substrates can significantly degrade their performance in materials and devices. Therefore, a systematic investigation on the buckling behavior of monolayer graphene sheet/substrate systems is carried out in this paper by both molecular mechanics simulations and theoretical analysis. From 70 simulation cases of simple-supported graphene sheets with different sizes under uniaxial compression, two different buckling modes are investigated and revealed to be dominated by the graphene size. Especially, for graphene sheets with length larger than 3 nm and width larger than 1.1 nm, the buckling mode depends only on the length/width ratio. Besides, it is revealed that the existence of graphene substrate can increase the critical buckling stress and strain to 4.39 N/m and 1.58%, respectively, which are about 10 times those for free-standing graphene sheets. Moreover, for graphene sheets with common size (longer than 20 nm, both theoretical and simulation results show that the critical buckling stress and strain are dominated only by the adhesive interactions with substrate and independent of the graphene size. Results in this work provide valuable insight and guidelines for the design and application of graphene-derived materials and nano-electromechanical systems.
Cholesterol-Induced Buckling in Physisorbed Polymer-Tethered Lipid Monolayers
Directory of Open Access Journals (Sweden)
Christoph A. Naumann
2013-04-01
Full Text Available The influence of cholesterol concentration on the formation of buckling structures is studied in a physisorbed polymer-tethered lipid monolayer system using epifluorescence microscopy (EPI and atomic force microscopy (AFM. The monolayer system, built using the Langmuir-Blodgett (LB technique, consists of 3 mol % poly(ethylene glycol (PEG lipopolymers and various concentrations of the phospholipid, 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC, and cholesterol (CHOL. In the absence of CHOL, AFM micrographs show only occasional buckling structures, which is caused by the presence of the lipopolymers in the monolayer. In contrast, a gradual increase of CHOL concentration in the range of 0–40 mol % leads to fascinating film stress relaxation phenomena in the form of enhanced membrane buckling. Buckling structures are moderately deficient in CHOL, but do not cause any notable phospholipid-lipopolymer phase separation. Our experiments demonstrate that membrane buckling in physisorbed polymer-tethered membranes can be controlled through CHOL-mediated adjustment of membrane elastic properties. They further show that CHOL may have a notable impact on molecular confinement in the presence of crowding agents, such as lipopolymers. Our results are significant, because they offer an intriguing prospective on the role of CHOL on the material properties in complex membrane architecture.
Arjmand, T.; Bagheri Tagani, M.; Rahimpour Soleimani, H.
2017-03-01
In this paper, we consider zigzag-edge germanene nanoribbons with small buckling and even (symmetric) or odd (asymmetric) widths. Although the band structures of these two type structures are the same, they are noticeably different in terms of conductivity and current. In previous works on silicene, the role of buckling to dominate the effect of symmetry has been ignored and just the buckling changes of the symmetry space group from σ to C 2 are shown. In this case, buckling is the main factor responsible for differences in conductivity and current. Fluorine, hydroxyl, and hydrogen are used to passivate the nanoribbon edges. Results show that the current and conductivity are strongly dependent on the kinds of substitutional atoms/groups used to passivate the structure. It is found that symmetry breaking is not the only effective factor in the creation of current—buckling and backscattering are also important.
Mathematical modeling and full-scale shaking table tests for multi-curve buckling restrained braces
Institute of Scientific and Technical Information of China (English)
C. S. Tsai; Yungchang Lin; Wenshin Chen; H. C. Su
2009-01-01
Buckling restrained braces (BRBs) have been widely applied in seismic mitigation since they were introduced in the 1970s. However, traditional BRBs have several disadvantages caused by using a steel tube to envelope the mortar to prevent the core plate from buckling, such as: complex interfaces between the materials used, uncertain precision, and time consumption during the manufacturing processes. In this study, a new device called the multi-curve buckling restrained brace (MC-BRB) is proposed to overcome these disadvantages. The new device consists of a core plate with multiple neck portions assembled to form multiple energy dissipation segments, and the enlarged segment, lateral support elements and constraining elements to prevent the BRB from buckling. The enlarged segment located in the middle of the core plate can be welded to the lateral support and constraining elements to increase buckling resistance and to prevent them from sliding during earthquakes. Component tests and a series of shaking table tests on a full-scale steel structure equipped with MC-BRBs were carried out to investigate the behavior and capability of this new BRB design for seismic mitigation. The experimental results illustrate that the MC-BRB possesses a stable mechanical behavior under cyclic loadings and provides good protection to structures during earthquakes. Also, a mathematical model has been developed to simulate the mechanical characteristics of BRBs.
Institute of Scientific and Technical Information of China (English)
贺强; 艳芳; 苏三庆
2016-01-01
The floor mass center and stiffness center are deviated about irregular frame structure, lead to struc-ture’ s torsion under seismic performance.For high intensity area, the torsion effect more apparent in the irregular reinforced concrete structure.The practical engineering model use response spectrum analysis and time history anal-ysis under severe earthquake action, and the results show that the RBR-RC ( buckling-restrained braced frame) can improve the structure torsion.The structure of torsion period ratio, inter-story displacement angle and torsional dis-placement ratio can conform to the requirements of the specification.Under rare earthquake action, adding BRB between pillars of frame have the uniform torsional displacement ratio, the maximum of 1.17, and inter-story tor-sion deformation is controlled.The BRBs have full hysteretic curve in frame bottom, and dissipative damping effect is obvious.%不规则框架结构楼层的质量中心和刚度中心偏离，导致结构在地震作用下容易发生扭转。对于高烈度设防区的不规则钢筋混凝土结构，产生的扭转效应更加明显。结合实际工程案例对计算模型进行反应谱分析和罕遇地震作用下的时程分析。结果表明：屈曲约束支撑能够改善结构整体的扭转效应，结构的扭转周期比、层间位移角和扭转位移比均能符合规范要求。罕遇地震作用下，在柱间增设屈曲约束支撑的框架扭转位移比变化均匀，最大值为1.17，层间扭转变形得到控制。框架底层屈曲约束支撑滞回曲线饱满，耗能减震效果明显。
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....
Reber, J. E.; Schmalholz, S. M.; Burg, J.-P.
2010-10-01
Two orthogonal sets of veins, both orthogonal to bedding, form chocolate tablet structures on the limbs of folded quartzwackes of Carboniferous turbidites in SW Portugal. Structural observations suggest that (1) mode 1 fractures transverse to the fold axes formed while fold amplitudes were small and limbs were under layer-subparallel compression and (2) mode 1 fractures parallel to the fold axes formed while fold amplitudes were large and limbs were brought to be under layer-subparallel tension. We performed two- and three-dimensional numerical simulations investigating the evolution of stress orientations during viscous folding to test whether and how these two successive sets of fractures were related to folding. We employed ellipses and ellipsoids for the visualization and quantification of the local stress field. The numerical simulations show a change in the orientation of the local σ1 direction by almost 90° with respect to the bedding plane in the fold limbs. The coeval σ3 direction rotates from parallel to the fold axis at low fold amplitudes to orthogonal to the fold axis at high fold amplitudes. The stress orientation changes faster in multilayers than in single-layers. The numerical simulations are consistent with observation and provide a mechanical interpretation for the formation of the chocolate tablet structures through consecutive sets of fractures on rotating limbs of folded competent layers.
Cylindrical shell buckling through strain hardening
Energy Technology Data Exchange (ETDEWEB)
Bandyopadhyay, K.; Xu, J.; Shteyngart, S. [Brookhaven National Lab., Upton, NY (United States); Gupta, D. [USDOE, Germantown, MD (United States)
1995-04-01
Recently, the authors published results of plastic buckling analysis of cylindrical shells. Ideal elastic-plastic material behavior was used for the analysis. Subsequently, the buckling analysis program was continued with the realistic stress-strain relationship of a stainless steel alloy which does not exhibit a clear yield point. The plastic buckling analysis was carried out through the initial stages of strain hardening for various internal pressure values. The computer program BOSOR5 was used for this purpose. Results were compared with those obtained from the idealized elastic-plastic relationship using the offset stress level at 0.2% strain as the yield stress. For moderate hoop stress values, the realistic stress-grain case shows a slight reduction of the buckling strength. But, a substantial gain in the buckling strength is observed as the hoop stress approaches the yield strength. Most importantly, the shell retains a residual strength to carry a small amount of axial compressive load even when the hoop stress has exceeded the offset yield strength.
The origin of magnetic alloy core buckling in J-PARC 3 GeV RCS
Energy Technology Data Exchange (ETDEWEB)
Nomura, M., E-mail: masahiro.nomura@j-parc.j [JAEA, 2-4, Shirakata-shirane, Tokai, Ibaraki 319-1195 (Japan); Yamamoto, M.; Schnase, A.; Shimada, T.; Suzuki, H.; Tamura, F. [JAEA, 2-4, Shirakata-shirane, Tokai, Ibaraki 319-1195 (Japan); Hara, K.; Hasegawa, K.; Ohmori, C.; Toda, M.; Yoshii, M. [KEK, Tsukuba, Ibaraki 305-0801 (Japan)
2010-11-21
We have been operating ten RF cavities loaded with magnetic alloy (MA) cores with a high field gradient of more than 20 kV/m in Japan Proton Accelerator Research Complex (J-PARC) 3 GeV Rapid Cycling Synchrotron (RCS) since September 2007. During 3 years operation, we detected three times the impedance reductions of RF cavities resulting from the buckling of MA cores. To find out the origin of the MA core buckling, we evaluated the thermal stress inside the MA cores in operation and studied the relationship between the MA core buckling and core structure. We figured out that the MA core buckling was caused by the thermal stress that was enhanced due to the impregnation with low viscosity epoxy resin. We improved the MA cores without the low viscosity epoxy resin impregnation and replaced all the cores in one RF cavity with them in March 2010. Up to now we operated the RF cavity loaded with the improved MA cores for 1500 h, it showed no impedance reduction and no buckling.
Buckling Behavior of Long Anisotropic Plates Subjected to Fully Restrained Thermal Expansion
Nemeth, Michael P.
2003-01-01
An approach for synthesizing buckling results and behavior for thin, balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and which are fully-restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined mechanical loads and is based on useful nondimensional parameters. In addition, stiffness-weighted laminate thermal-expansion parameters are derived and used to determine critical temperature changes in terms of physically intuitive mechanical buckling coefficients. The effects of membrane orthotropy and anisotropy are included. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of the generic buckling design curves that are presented in the paper. Several generic buckling design curves are presented that provide physical insight into buckling response and provide useful design data. Examples are presented that demonstrate the use of generic design curves. The analysis approach and generic results indicate the effects and characteristics of laminate thermal expansion, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general, unifying manner.
Institute of Scientific and Technical Information of China (English)
张癑; 高向宇; 尹学军; 付学智
2014-01-01
Using the orthogonal test theory,five full sized tuning mass damped buckling-restrained brace (TMD-BRB)specimens were designed,manufactured and tested.The influence factors included work period,contact surface craft and springs layout.There were 3 levels for work period and 2 levels for the other two.The effects of spring,friction between contact surfaces and force form on the dynamic behavior of specimens were investigated in detail.In addition,the performance of BRBs in the related structures was tested.The tests included free vibration,resonance tests under common seismic intensity and cyclic static tests.Spectral characteristics of specimens,change laws of dynamic coefficients and damping ratios,and hysteretic curves were analyzed.The results showed that the specimens with symmetrical springs and wheels have a high tuning precision,strong TMD properties and standard index for BRB performance to realize a structural balance between composite vibration reduction functions.%借鉴正交试验理论，设计，制作并测试了5个足尺调谐质量型防屈曲支撑试件。影响因素包括工作周期、接触工艺和弹簧布置。其中工作周期3水平，其它因素2水平。重点考察弹簧、接触面摩擦、受力形式等对试件动力性能的影响，以及相关构造条件下 BRB 的性能表现。试验包括自由振动，常见地震烈度条件下共振试验和静力拉压试验。研究分析了试件频谱特性，动力系数和阻尼比变化规律，拉压滞回性能。试验结果表明，对称弹簧布置的轮式构造试件调谐精度高，TMD 特性明显，BRB 相关性能指标能够满足行业规定，实现复合减震功能在构造上的“兼顾”。
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...
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.
Bauer, Christina T; Kroner, Elmar; Fleck, Norman A; Arzt, Eduard
2015-12-01
Nature uses hierarchical fibrillar structures to mediate temporary adhesion to arbitrary substrates. Such structures provide high compliance such that the flat fibril tips can be better positioned with respect to asperities of a wavy rough substrate. We investigated the buckling and adhesion of hierarchically structured adhesives in contact with flat smooth, flat rough and wavy rough substrates. A macroscopic model for the structural adhesive was fabricated by molding polydimethylsiloxane into pillars of diameter in the range of 0.3-4.8 mm, with up to three different hierarchy levels. Both flat-ended and mushroom-shaped hierarchical samples buckled at preloads one quarter that of the single level structures. We explain this behavior by a change in the buckling mode; buckling leads to a loss of contact and diminishes adhesion. Our results indicate that hierarchical structures can have a strong influence on the degree of adhesion on both flat and wavy substrates. Strategies are discussed that achieve highly compliant substrates which adhere to rough substrates.
MODELING OF NONLINEAR DEFORMATION AND BUCKLING OF ELASTIC INHOMOGENEOUS SHELLS
Directory of Open Access Journals (Sweden)
Bazhenov V.A.
2014-06-01
Full Text Available The paper outlines the fundamentals of the method of solving static problems of geometrically nonlinear deformation, buckling, and postbuckling behavior of thin thermoelastic inhomogeneous shells with complex-shaped mid-surface, geometrical features throughout the thickness, and multilayer structure under complex thermomechanical loading. The method is based on the geometrically nonlinear equations of three-dimensional thermoelasticity and the moment finiteelement scheme. The method is justified numerically. Comparing solutions with those obtained by other authors and by software LIRA and SCAD is conducted.
Buckling and Multiple Equilibrium States of Viscoelastic Rectangular Plates
Institute of Scientific and Technical Information of China (English)
无
1999-01-01
On the basis of Karman's theory of thin plates with large deflection, the Boltzmann law on linear viscoelastic materials and the mathematical model of dynamic analysis on viscoelastic thin plates, a set of nonlinear integro-partial-differential equations is first presented by means of a structural function introduced in this paper. Then,by using the Galerkin technique in spatial field and a backward difference scheme in temporal field, the set of nonlinear integro-partial-differential equations reduces to a system of nonlinear algebraic equations. After solving the algebraic equations, the buckling behavior and multiple equilibrium states can be obtained.
Buckling instability in amorphous carbon films
Zhu, X. D.; Narumi, K.; Naramoto, H.
2007-06-01
In this paper, we report the buckling instability in amorphous carbon films on mirror-polished sapphire (0001) wafers deposited by ion beam assisted deposition at various growth temperatures. For the films deposited at 150 °C, many interesting stress relief patterns are found, which include networks, blisters, sinusoidal patterns with π-shape, and highly ordered sinusoidal waves on a large scale. Starting at irregular buckling in the centre, the latter propagate towards the outer buckling region. The maximum length of these ordered patterns reaches 396 µm with a height of ~500 nm and a wavelength of ~8.2 µm. However, the length decreases dramatically to 70 µm as the deposition temperature is increased to 550 °C. The delamination of the film appears instead of sinusoidal waves with a further increase of the deposition temperature. This experimental observation is correlated with the theoretic work of Crosby (1999 Phys. Rev. E 59 R2542).
Energy Technology Data Exchange (ETDEWEB)
Sugawara, Takanori, E-mail: sugawara.takanori@jaea.go.j [Japan Atomic Energy Agency, Shirakata Shirane 2-4, Tokai-mura, Naka-gun, Ibaraki, 319-1195 (Japan); Kikuchi, Kenji; Nishihara, Kenji; Oigawa, Hiroyuki [Japan Atomic Energy Agency, Shirakata Shirane 2-4, Tokai-mura, Naka-gun, Ibaraki, 319-1195 (Japan)
2010-03-15
The investigation of the beam window, which is a key component in the conceptual design of an Accelerator Driven System, has been performed. In the past studies, it was found that buckling failure due to hydrostatic pressure in the liquid lead bismuth was critical failure mode for the beam window and detailed structural analyses were performed. These investigations, however, did not consider irradiation effects by neutrons and protons. In this study, investigations based on the latest knowledge for irradiation effects obtained in the spallation target irradiation program are presented. By using the experimental data, it was found that the buckling pressure increased about 80% by the irradiation (20 dpa). It was assumed that if the beam window had integrity in the unirradiated condition, the buckling failure would not be critical issue during the ADS operation.
Semi-Analytical Finite Strip Transfer Matrix Method for Buckling Analysis of Rectangular Thin Plates
Directory of Open Access Journals (Sweden)
Li-Ke Yao
2015-01-01
Full Text Available Plates and shells are main components of modern engineering structures, whose buckling analysis has been focused by researchers. In this investigation, rectangular thin plates with loaded edges simply supported can be discretized by semi-analytical finite strip technology. Then the control equations of the strip elements of the buckling plate will be rewritten as the transfer equations by transfer matrix method. A new approach, namely semi-analytical Finite Strip Transfer Matrix Method, is developed for the buckling analysis of plates. This method requires no global stiffness matrix of the system, reduces the system matrix order, and improves the computational efficiency. Comparing with some theoretical results and FEM’s results of two illustrations (the plates and the ribbed plates under six boundary conditions, the method is proved to be reliable and effective.
Designing pinhole vacancies in graphene towards functionalization: Effects on critical buckling load
Georgantzinos, S. K.; Markolefas, S.; Giannopoulos, G. I.; Katsareas, D. E.; Anifantis, N. K.
2017-03-01
The effect of size and placement of pinhole-type atom vacancies on Euler's critical load on free-standing, monolayer graphene, is investigated. The graphene is modeled by a structural spring-based finite element approach, in which every interatomic interaction is approached as a linear spring. The geometry of graphene and the pinhole size lead to the assembly of the stiffness matrix of the nanostructure. Definition of the boundary conditions of the problem leads to the solution of the eigenvalue problem and consequently to the critical buckling load. Comparison to results found in the literature illustrates the validity and accuracy of the proposed method. Parametric analysis regarding the placement and size of the pinhole-type vacancy, as well as the graphene geometry, depicts the effects on critical buckling load. Non-linear regression analysis leads to empirical-analytical equations for predicting the buckling behavior of graphene, with engineered pinhole-type atom vacancies.
Molecular dynamics simulations of the buckling of graphyne and its family
Energy Technology Data Exchange (ETDEWEB)
Salmalian, K., E-mail: kavehsalmalian@iaul.ac.ir; Rouhi, S.; Mehran, S.
2015-01-15
Molecular dynamics simulations are employed to study the instability characteristics of graphyne and its family under compressive loads. The effects of nanosheet side length and aspect ratio on the critical compressive force and critical strain are investigated. It is shown that increasing aspect ratio leads to decreasing the critical compressive force. Besides, the effect of atomic structure on the compressive behavior of nanosheets is explored. It is observed that the zigzag graphynes have larger buckling forces than the armchair graphynes with same geometries. Finally, the buckling behavior of different nanosheets from the graphyne family is studied. It is represented that the nanosheets with more acetylene links have smaller critical compressive forces.
Institute of Scientific and Technical Information of China (English)
周云; 尹庆利; 林绍明; 邓雪松
2012-01-01
该文设计制作两榀带防屈曲耗能腋撑钢筋混凝土框架模型和一榀普通钢筋混凝土框架模型，分别对其进行低周反复荷载作用下的抗震性能试验。研究两类框架结构的破坏特征、滞回特性、强度和刚度退化、耗能能力以及关键测点应变变化情况，并采崩有限元软件SeismoStruct对其进行模拟对比分析。研究结果表明：设置防屈曲耗能腋撑提高框架结构的初始刚度和承载能力，延缓裂缝的开展；提高结构的整体耗能能力；改变框架结构的受力模式，使塑性铰的发展从梁端和柱端转到腋撑连接处，减小梁柱节点区的受力，有效地保护了梁柱节点；防屈曲耗能腋撑框架的破坏特征与普通框架相同，均由柱脚形成塑性铰而破坏。%Two models of RC frame structures with buckling-restrained haunch braces (BRHB) and a genera] RC frame structure model were designed and their seismic performances were tested under low frequency cyclic loading. Seismic behaviors such as failure modes, hysteretic performance, strength and stiffness degradation, energy dissipation capacity and reinforcement strain of key measure points of these specimens were investigated. The finite-element software SeismoStruct was employed for simulation analysis of the models. The investigation results indicated that the initial stiffness and bearing capacity of the RC frame structure with BRHB were enhanced, the development of crack could be delayed, and the bearing mode of the frame structure was changed. The stress of beam-column joints was reduced, which could effectively protect the beam-celumn joint, the development of the plastic hinges on the end of column and beam transferred to the joint of haunch brace, also the energy dissipation capacity of the RC frame structure with BRHB was improved. Compared with general RC frame structure, the failure modes of the RC frame structure with BRHB was the same, as the plastic
SHEAR BUCKLING ANALYSIS OF WEB OF LATTICE ENHANCED FOAM SANDWICH STRUCTURE%格构增强型泡沫夹层结构腹板剪切屈曲分析
Institute of Scientific and Technical Information of China (English)
洪俊青; 刘伟庆; 方海
2014-01-01
Based on model of Pasternak elastic foundation, shear buckling strength of web of lattice-enhanced foam-sandwich structure was analysed and probed under pure shear stress, due to the existence of foam core.The applicable condition of the analytic model was discussed, whose rationality was confirmed in comparison with the data of FEM model.The results show that the analytic model can match with the FEM model very well if the core thickness could be guaranteed to some degree.The existence of the core can enhance the web stability effectively.The shear stiffness provided by foam core to the web stability is still of great significance, even if the Young's modulus of the core material is low.But with the increase of ratio of height to thickness of web, and the augmentation of the young's modulus of the core material, the normal stiffness from the foam core play a more controlled role on the web shear stability.The ratio of length to height could be omitted for the perspective of engineering application.%基于双参数地基模型，分析了格构式增强型泡沫夹层结构的腹板在纯剪作用下的弹性稳定问题，讨论了泡沫芯材的存在对夹层结构腹板剪切稳定的影响规律、该理论分析模型的适用条件，通过有限元方法验证了该模型分析结果的合理性。分析表明，泡沫芯材的存在可以有效提高腹板的剪切稳定性能。即使芯材弹性模量较低，其提供的剪切刚度对于腹板的稳定也有着重要意义。随着腹板高厚比和芯材弹性模量的增加，泡沫对腹板提供的法向刚度控制作用越明显。芯材厚度是该模型结果准确与否的重要前提。从工程实用的角度，腹板区格的长高比对腹板剪切稳定的影响可以忽略不计。
Buckling modes of elastic thin films on elastic substrates
Mei, Haixia; Huang, Rui; Chung, Jun Young; Stafford, Christopher M.; Yu, Hong-Hui
2007-04-01
Two buckling modes have been observed in thin films: buckle delamination and wrinkling. This letter identifies the conditions for selecting the favored buckling modes for elastic films on elastic substrates. Transition from one buckling mode to another is predicted as the stiffness ratio between the substrate and the film or is predicted for variation of the stiffness ratio between the substrate and the film or variation of theinterfacial defect size. The theoretical results are demonstrated experimentally by observing the coexistence of both buckling modes and mode transition in one film-substrate system.
Elastoswellability: Will it bend or will it buckle?
Holmes, Douglas; Pandey, Anupam
2013-03-01
Soft mechanical structures such as biological tissues and gels exhibit motion, instabilities, and large morphological changes when subjected to external stimuli. Swelling is a robust approach for inducing structural change as it occurs naturally in humid environments and can be easily adapted for industrial design. Small volumes of fluid that interact favorably with a material can cause large, dramatic, and geometrically nonlinear deformations including beam bending, plate buckling, and surface wrinkling. In this talk we address an overarching question regarding swelling-induced deformations: will the structural change occur globally, or will it be confined to the material's surface? We introduce a materials and geometry defined transition point that describes a fluid-structure's characteristic ``elastoswellability'' lengthscale. By locally swelling unconstrained slender beams and plates with solvents of varying solubility, we identify a transition between local surface wrinkling and global structural bending.
Plastic Buckling of Cylindrical Shells Under Transverse Loading
Institute of Scientific and Technical Information of China (English)
ZHANG Chonghou; LIU Yansheng; Yoshiaki Goto
2008-01-01
Thick cylindrical shells under transverse loading exhibit an elephant foot buckling mode, whereas moderately thick cylindrical shells show a diamond buckling mode. There exists some intermediate geome- try at which the transition between buckling modes can take place. This behavior is significantly influenced by the radius-to-thickness ratio and the material yield strength, rather than the length-to-radius ratio and the axial force. This paper presents a critical value at which the transition of buckling modes occurs as a func- tion of the radius-to-thickness ratio and the material yield strength. The result shows that the circumferential wave number of the diamond buckling mode increases with decreasing wall thickness. The strain concentra- tion is also intensified for the diamond buckling modes compared with the elephant foot buckling modes.
Buckling behavior of pipes in oil and gas wells
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Based on the non-linear differential equations of buckled pipes, the buckling behavior of pipes in different wellbores has been analyzed. The relation between the deflection of buckled pipe and the loads on it has been given, and the critical loads for sinusodal and helical buckling within different wellbores subjected to axial and torsional loads have been determined. Therefore, the profile of load increase during the post-buckling process and the bending moments in the buckled pipe can be determined. In addition, the effects of down-hole packer as fixed end on the helical buckling behavior of pipes have been investigated. These results can be applied to the related engineering design and construction.
Buckling analysis of a cylindrical shell, under neutron radiation environment
Energy Technology Data Exchange (ETDEWEB)
Arani, A. Ghorbanpour [Department of Mechanical Engineering, School of Engineering, University of Kashan, Kashan (Iran, Islamic Republic of); Ahmadi, M. [School of Research and Development of Nuclear Reactors and Accelerators, Nuclear Science and Technology (Iran, Islamic Republic of); Ahmadi, A. [Department of Management, University of Tehran, Tehran (Iran, Islamic Republic of); Rastgoo, A. [Department of Mechanical Engineering, School of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Sepyani, H.A., E-mail: hosepiani@yahoo.com [Department of Mechanical Engineering, School of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of)
2012-01-15
Highlights: Black-Right-Pointing-Pointer The work investigates the buckling of a shell in the neutron radiation environment. Black-Right-Pointing-Pointer Radiation induced porosity in elastic materials affects the material's properties. Black-Right-Pointing-Pointer The data based technique was used to determine the volume fraction porosity. Black-Right-Pointing-Pointer The theoretical formulations are presented based on the classical shell theory (CST). Black-Right-Pointing-Pointer It was concluded that both T and neutron induced swelling have significant effects. - Abstract: This research investigates the buckling of a cylindrical shell in the neutron radiation environment, subjected to combined static and periodic axial forces. Radiation induced porosity in elastic materials affects the thermal, electrical and mechanical properties of the materials. In this study, the data based technique was used to determine the volume fraction porosity, P, of shell material. A least-squares fit of the Young's module data yielded the estimated Young's modulus. The shell assumed made of iron irradiated in the range of 2-15e-7 dPa/s at 345-650 Degree-Sign C and theoretical formulations are presented based on the classical shell theory (CST). The research deals with the problem theoretically; keeping in mind that one means of generating relevant design data is to investigate prototype structures. A parametric study is followed and the stability of shell is discussed. It is concluded that both temperature and neutron induced swelling have significant effects on the buckling load.
Edmondson, S; Frieda, K; Comrie, JE; Onck, PR; Huck, WTS
2006-01-01
Buckle-driven delamination and subsequent collapse of strained thin polymer films upon triggered release from the substrate is exploited to fabricate striking, well-defined ridging patterns (see figure). An analysis of these patterns is presented, including the effects of film thickness and the exte
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...
Crack buckling in soft gels under compression
Institute of Scientific and Technical Information of China (English)
Rong Long; Chung-Yuen Hui
2012-01-01
Recent interest in designing soft gels with high fracture toughness has called for simple and robust methods to test fracture behavior.The conventional method of applying tension to a gel sample suffers from a difficulty of sample gripping.In this paper,we study a possible fracture mechanism of soft gels under uni-axial compression.We show that the surfaces of a pre-existing crack,oriented parallel to the loading axis,can buckle at a critical compressive stress.This buckling instability can open the crack surfaces and create highly concentrated stress fields near the crack tip,which can lead to crack growth.We show that the onset of crack buckling can be deduced by a dimensional argument combined with an analysis to determine the critical compression needed to induce surface instabilities of an elastic half space.The critical compression for buckling was verified for a neoHookean material model using finite element simulations.
Dynamic Pulse Buckling--Theory and Experiment
1983-02-01
34Buckling of Bars Subject to Axial Shock," Studii si Cercetari de Mecanica Applicata (Roumania), 7, 1, pp. 173-178, January 1956. 26. A.F. Schmitt, "A...Procopovici, "Transverse Deformation of an Elastic Bar Subjected to an Axial Impulsive Force," Studii si Ceretari de Mecanica Applicata. 8, 3, pp. 839
Lower Bound Approximation for Elastic Buckling Loads
Vrouwenvelder, A.; Witteveen, J.
1975-01-01
An approximate method for the elastic buckling analysis of two-dimensional frames is introduced. The method can conveniently be explained with reference to a physical interpretation: In the frame every member is replaced by two new members: - a flexural member without extensional rigidity to transmi
Weil, Arlo; Gutiérrez-Alonso, Gabriel; Johnston, Stephen; Pastor Galán, Daniel
2013-04-01
latest Carboniferous, which agrees well with recent geodynamical models and structural data that relate oroclinal buckling with lithospheric delamination in the Variscan.
Selective buckling via states of self-stress in topological metamaterials
Paulose, Jayson; Meeussen, Anne S.; Vitelli, Vincenzo
2015-01-01
States of self-stress—tensions and compressions of structural elements that result in zero net forces—play an important role in determining the load-bearing ability of structures ranging from bridges to metamaterials with tunable mechanical properties. We exploit a class of recently introduced states of self-stress analogous to topological quantum states to sculpt localized buckling regions in the interior of periodic cellular metamaterials. Although the topological states of self-stress arise in the linear response of an idealized mechanical frame of harmonic springs connected by freely hinged joints, they leave a distinct signature in the nonlinear buckling behavior of a cellular material built out of elastic beams with rigid joints. The salient feature of these localized buckling regions is that they are indistinguishable from their surroundings as far as material parameters or connectivity of their constituent elements are concerned. Furthermore, they are robust against a wide range of structural perturbations. We demonstrate the effectiveness of this topological design through analytical and numerical calculations as well as buckling experiments performed on two- and three-dimensional metamaterials built out of stacked kagome lattices. PMID:26056303
Selective buckling via states of self-stress in topological metamaterials.
Paulose, Jayson; Meeussen, Anne S; Vitelli, Vincenzo
2015-06-23
States of self-stress--tensions and compressions of structural elements that result in zero net forces--play an important role in determining the load-bearing ability of structures ranging from bridges to metamaterials with tunable mechanical properties. We exploit a class of recently introduced states of self-stress analogous to topological quantum states to sculpt localized buckling regions in the interior of periodic cellular metamaterials. Although the topological states of self-stress arise in the linear response of an idealized mechanical frame of harmonic springs connected by freely hinged joints, they leave a distinct signature in the nonlinear buckling behavior of a cellular material built out of elastic beams with rigid joints. The salient feature of these localized buckling regions is that they are indistinguishable from their surroundings as far as material parameters or connectivity of their constituent elements are concerned. Furthermore, they are robust against a wide range of structural perturbations. We demonstrate the effectiveness of this topological design through analytical and numerical calculations as well as buckling experiments performed on two- and three-dimensional metamaterials built out of stacked kagome lattices.
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
Flutter and thermal buckling control for composite laminated panels in supersonic flow
Li, Feng-Ming; Song, Zhi-Guang
2013-10-01
Aerothermoelastic analysis for composite laminated panels in supersonic flow is carried out. The flutter and thermal buckling control for the panels are also investigated. In the modeling for the equation of motion, the influences of in-plane thermal load on the transverse bending deflection are taken into account, and the unsteady aerodynamic pressure in supersonic flow is evaluated by the linear piston theory. The governing equation of the structural system is developed applying the Hamilton's principle. In order to study the influences of aerodynamic pressure on the vibration mode shape of the panel, both the assumed mode method (AMM) and the finite element method (FEM) are used to derive the equation of motion. The proportional feedback control method and the linear quadratic regulator (LQR) are used to design the controller. The aeroelastic stability of the structural system is analyzed using the frequency-domain method. The effects of ply angle of the laminated panel on the critical flutter aerodynamic pressure and the critical buckling temperature change are researched. The flutter and thermal buckling control effects using the proportional feedback control and the LQR are compared. An effective method which can suppress the flutter and thermal buckling simultaneously is proposed.
Shear-lag model of diffusion-induced buckling of core-shell nanowires
Li, Yong; Zhang, Kai; Zheng, Bailin; Yang, Fuqian
2016-07-01
The lithiation and de-lithiation during the electrochemical cycling of lithium-ion batteries (LIBs) can introduce local deformation in the active materials of electrodes, resulting in the evolution of local stress and strain in the active materials. Understanding the structural degradation associated with lithiation-induced deformation in the active materials is one of the important steps towards structural optimization of the active materials used in LIBs. There are various degradation modes, including swelling, cracking, and buckling especially for the nanowires and nanorods used in LIBs. In this work, a shear-lag model and the theory of diffusion-induced stress are used to investigate diffusion-induced buckling of core-shell nanowires during lithiation. The critical load for the onset of the buckling of a nanowire decreases with the increase of the nanowire length. The larger the surface current density, the less the time is to reach the critical load for the onset of the buckling of the nanowire.
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.
Dynamic buckling behavior of thin metal film lines from substrate
Wu, Dan; Xie, Huimin; Wang, Heling; Zhang, Jie; Li, Chuanwei
2014-10-01
The dynamic buckling behavior of thin films from substrate is studied in this work. The experimental results show that the buckling morphology of the constantan film lines from the polymer substrate is inconsistent and non-sinusoidal, which is different from the sinusoidal form of the buckling morphology under static loads. The plastic deformation of the film lines results in the non-sinusoidal buckling morphology and residual deformation when unloaded. Finite element modeling results with regard to the plastic dissipation of the constantan film lines reveal that the plastic dissipation suppresses the buckling-driven delaminating under impact loads. This study will give some new perspectives on the buckling behavior of thin film from substrate.
Buckling of stepped beams with elastic supports
Institute of Scientific and Technical Information of China (English)
ZHANG Hong-sheng; LU Nian-li; LAN Peng
2009-01-01
The tangent stiffness matrix of Timoshenko beam element is applied in the buckling of multi-step beams under several concentrated axial forces with elastic supports. From the governing differential equation of lateral deflection including second-order effects, the relationship of force versus displacement is established. In the formulation of finite element method ( FEM), the stiffness matrix developed has the same accuracy with the solution of exact differential equations. The proposed tangent stiffness matrix will degenerate into the BernoulliEuler beam without the effects of shear deformation. The critical buckling force can be determined from the determinant element assemblage by FEM. The equivalent stiffness matrix constructed by the topmost deflection and slope is established by static condensation method, and then a recurrence formula is proposed. The validity and efficiency of the proposed method are shown by solving various numerical examples found in the literature.
Wang, Qinghua; Xie, Huimin; Lu, Jian; Chen, Pengwan; Zhang, Qingming
2011-06-15
Measurement of interfacial toughness of a metal film wire and a flexible substrate is a challenging issue for evaluating the interfacial bonding capacity of the film-wire/substrate systems. In this paper, an electricity induced buckling method is proposed to measure the interfacial toughness between a metal film wire and a polymer membrane, which does not use a pre-existing weak interface. This method relies on causing a buckling driven delamination of the metal film wire from the polymer membrane, by inducing a compressive stress due to electrification of the film wire. For a sort of structure formed by a constantan film wire and a polymer membrane, the current density range under which the buckling of the film wire will emerge is obtained from experiments. The average interfacial toughness of one typical sample is measured to be 31.6 J/m(2). According to the buckling topographies under different current densities, the interfacial toughness of the constantan film wire and the polymer substrate is found to vary from 10 J/m(2) to 60 J/m(2).
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.
Buckling Behavior of Long Anisotropic Plates Subjected to Elastically Restrained Thermal Expansion
Nemeth, Michael P.
2002-01-01
An approach for synthesizing buckling results for, and behavior of, thin balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and elastically restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined mechanical loads and is based on useful nondimensional parameters. In addition, stiffness-weighted laminate thermal-expansion parameters and compliance coefficients are derived that are used to determine critical temperatures in terms of physically intuitive mechanical-buckling coefficients. The effects of membrane orthotropy and membrane anisotropy are included in the general formulation. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of generic buckling design curves. Several curves that illustrate the fundamental parameters used in the analysis are presented, for nine contemporary material systems, that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of generic design curves. The analysis approach and generic results indicate the effects and characteristics of elastically restrained laminate thermal expansion or contraction, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general and unifying manner.
Remaining local buckling resistance of corroded pipelines
Energy Technology Data Exchange (ETDEWEB)
Chen, Qishi [C-FER Technologies, Edmonton, AB (Canada); Khoo, Heng Aik [Carleton University, Ottawa, Ontario (Canada); Cheng, Roger [University of Alberta, Edmonton, AB (Canada); Zhou, Joe [TransCanada Pipelines Limited, Calgary, AB (Canada)
2010-07-01
The Pipeline Research Council International has undertaken a multi-year research program to investigate the local buckling (or wrinkling) of onshore pipelines affected by corrosion. Local buckling resistance depends on wall thickness and seems to be considerably reduced by metal-loss defects. Experimental data were lacking, which led to the use of overly conservative assumptions. C-FER and the University of Alberta conducted research in three phases in order to develop local buckling criteria for pipelines with corrosion defects. In Phase 1, the influence of various corrosion defect features was assessed with finite element analysis, and the ranking of key parameters was determined. On this basis, Phase 2 consisted in developing a test matrix and carrying out 10 full-scale tests to collect data. In Phase 3, finite element models were used to analyze over 150 parametric cases and develop criteria for assessing maximum moment and compressive strain limit. These criteria were applied to in-service pipelines with general corrosion features.
Liu, J. C.; Zhang, Y. Q.; Fan, L. F.
2017-04-01
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.
Buckling analysis of curved composite sandwich panels subjected to inplane loadings
Cruz, Juan R.
1993-01-01
Composite sandwich structures are being considered for primary structure in aircraft such as subsonic and high speed civil transports. The response of sandwich structures must be understood and predictable to use such structures effectively. Buckling is one of the most important response mechanisms of sandwich structures. A simple buckling analysis is derived for sandwich structures. This analysis is limited to flat, rectangular sandwich panels loaded by uniaxial compression (N(sub x)) and having simply supported edges. In most aerospace applications, however, the structure's geometry, boundary conditions, and loading are usually very complex. Thus, a general capability for analyzing the buckling behavior of sandwich structures is needed. The present paper describes and evaluates an improved buckling analysis for cylindrically curved composite sandwich panels. This analysis includes orthotropic facesheets and first-order transverse shearing effects. Both simple support and clamped boundary conditions are also included in the analysis. The panels can be subjected to linearly varying normal loads N(sub x) and N(sub y) in addition to a constant shear load N(sub xy). The analysis is based on the modified Donnell's equations for shallow shells. The governing equations are solved by direct application of Galerkin's method. The accuracy of the present analysis is verified by comparing results with those obtained from finite element analysis for a variety of geometries, loads, and boundary conditions. The limitations of the present analysis are investigated, in particular those related to the shallow shell assumptions in the governing equations. Finally, the computational efficiency of the present analysis is considered.
Energy Technology Data Exchange (ETDEWEB)
Abebe, Daniel Yeshewawork; Choi, Jae Hyouk; Kim, Jin Hyang [Chosun Univ., Gwangju (Korea, Republic of)
2013-01-15
Progressive collapse is a chain reaction of failures propagating throughout a portion of a structure that is disproportionate to the original local failure. When column members are subjected to unexpected load (compression load), they will buckle it the applied load is greater than the critical load the induces buckling. The post buckling strength of the columns will decrease rapidly, but if there is enough residual strength, the members will absorb the potential energy generated by the impact load to prevent progressive collapse. Thus, it is necessary to identify the relationship of the load deformation of a column member in the progressive collapse of a structure up to final collapse. In this study, we carried out nonlinear FEM analysis and based on deflection theory, we investigated the load deformation relationship of H section steel columns when both ends were fixed.
Energy Technology Data Exchange (ETDEWEB)
Watashi, K. [PNC, Ibaraki (Japan). OEC; Iwata, K. [PNC, Ibaraki (Japan). OEC
1995-01-01
Two remarkable thermally induced deformation mechanisms of pipes which may have serious effects on structural integrity, thermal buckling and progressive ovalization, were observed on the horizontal piping of the sodium test facility, called TTS, with which cyclic thermal transient tests of structures had been conducted. The thermal buckling, which was caused by thermal stratification, occurred at a circumferentially welded region of the pipe where a noticeable geometrical imperfection existed. The buckling was analyzed comprehensively for this pipe, using both the finite element method and a simplified method based on Gellin`s analysis results. The predictions were reasonable and gave confidence in accounting for the sodium leakage encountered at the TTS. It was also demonstrated by the finite element analyses that the progressive ovalization of the pipe cross-section from a circular to a downward triangular shape can be caused by cyclic thermal stratification under the existence of cover gas in the pipe. ((orig.)).
Buckling failure of the automated planet finder spectrometer determinate spaceframe
Radovan, Matthew V.; Cabak, Gerald F.
2012-09-01
The Ken and Gloria Levy Spectrometer is now operational at a new 2.4 meter telescope on Mt. Hamilton. Together the spectrometer and telescope comprise the Automated Planet Finder (APF), a radial velocity instrument. A catastrophic failure occurred during transit as the instrument was being shipped to the observatory. Several struts buckled in the space frame that supported the echelle grating. This event has caused UCO/Lick to re-evaluate design methodology and how engineering safety factors apply to this type of structure. This paper describes the shipping container design, events during shipment, the failure mechanism, testing and analysis of a remedy, and its implementation. We also suggest design changes to prevent similar failures in the future.
Buckling induced delamination of graphene composites through hybrid molecular modeling
Cranford, Steven W.
2013-01-01
The efficiency of graphene-based composites relies on mechanical stability and cooperativity, whereby separation of layers (i.e., delamination) can severely hinder performance. Here we study buckling induced delamination of mono- and bilayer graphene-based composites, utilizing a hybrid full atomistic and coarse-grained molecular dynamics approach. The coarse-grain model allows exploration of an idealized model material to facilitate parametric variation beyond any particular molecular structure. Through theoretical and simulation analyses, we show a critical delamination condition, where ΔD∝kL4, where ΔD is the change in bending stiffness (eV), k the stiffness of adhesion (eV/Å4), and L the length of the adhered section (Å).
Buckling Behavior of Cold-Formed Studs with Thermal Perforations
Directory of Open Access Journals (Sweden)
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.
Electrostatics-Driven Hierarchical Buckling of Charged Flexible Ribbons
Yao, Zhenwei; Olvera de la Cruz, Monica
2016-04-01
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.
Dynamic torsional buckling of multi-walled carbon nanotubes embedded in an elastic medium
Institute of Scientific and Technical Information of China (English)
Chengqi Sun; Kaixin Liu; Guoxing Lu
2008-01-01
In this paper the dynamic torsional buckling of multi-walled carbon nanotubes (MWNTs) embedded in an elastic medium is studied by using a continuum mechan-ics model. By introducing initial imperfections for MWNTs and applying the preferred mode analytical method, a buck-ling condition is derived for the buckling load and associ-ated buckling mode. In particular, explicit expressions are obtained for embedded double-walled carbon nanotubes (DWNTs). Numerical results show that, for both the DWNTs and embedded DWNTs, the buckling form shifts from the lower buckling mode to the higher buckling mode with increasing the buckling load, but the buckling mode is invari-able for a certain domain of the buckling load. It is also indicated that, the surrounding elastic medium generally has effect on the lower buckling mode of DWNTs only when compared with the corresponding one for individual DWNTs.
Energy Technology Data Exchange (ETDEWEB)
Familiar Solano, Rafael; Reis Antunes, Bruno; Santos Hansen, Alexandre [PETROBRAS, Rio de Janeiro, (Brazil)
2010-07-01
Offshore pipelines can be subject to lateral buckling; some strategies are applied to prevent buckle initiation by monitoring the buckling behaviour. Some pipelines have been modified by PETROBRAS with triggers and sleepers; and distributed buoyancies have been added along the pipeline route. This paper investigated the thermo-mechanical design of the pipeline to avoid buckling and its consequences. Both planned buckles at dual sleepers and at distributed buoyancy modules and unplanned buckles were studied. Comparisons between the results obtained in design with finite element analysis and observed during operation with sidescan images were made. Seven planned buckles and two unplanned buckles were mapped and analyzed. It was found that the maximum stress, strain and fatigue damage at the buckle locations were fairly low. The mapping tests showed that the lengths and amplitudes of the buckles were compatible with lateral buckles in the design of pipelines.
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
Elastic buckling analysis of corroded stiffened plates with irregular surfaces
Indian Academy of Sciences (India)
Ahmad Rahbar-Ranji
2015-02-01
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 patterns, amount of corrosion loss and roughness of surface are investigated. Ratio of Euler stress of corroded stiffened plate over Euler stress of un-corroded stiffened plate is used to characterize the effects of corrosion on reduction of buckling strength. Results show that reduction of buckling strength is very sensitive to the amount of corrosion loss and roughness of surface, but less sensitive to the location of corroded region. The potential for decrease in buckling strength as a consequence of corrosion is found to depend on the dominant buckling mode. Residual buckling strength is reduced by as much as 12% for the interaction of plate-web-torsional buckling mode, and by 2% for column buckling.
Flow sensing by buckling monitoring of electrothermally actuated double-clamped micro beams
Kessler, Yoav; Liberzon, Alex
2016-01-01
We report on a flow sensing approach based on deflection monitoring of micro beams buckled by the compressive thermal stress due to electrothermal Joules 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 was obtained from the deflections measurements. The quasi-static responses of 2000 microns long, 10 microns wide and 30 microns high single crystal silicon beam transduced using image processing were consistent with the prediction of the reduced order model, which couples thermoelectric, thermofluidic and structural domains. The deflection sensitivity of 1.5 microns/(m/s) and the critical current sensitivity of 0.4 mA/(m/s) were registered in the experiments. Our model and experimental results collectively demonstrate feasibility of the sensing approach and further suggest that simple, robust and potentially downscalable beam-type devices may have use ...
Directory of Open Access Journals (Sweden)
Guan Quan
2016-04-01
Full Text Available In this study, an analytical model of the combination of beam-web shear buckling and bottom-flange buckling at elevated temperatures has been introduced. This analytical model is able to track the force-deflection path during post-buckling. A range of 3D finite element models has been created using the ABAQUS software. Comparisons have been carried out between the proposed analytical model, finite element modelling and an existing theoretical model by Dharma (2007. Comparisons indicate that the proposed method is able to provide accurate predictions for Class 1 and Class 2 beams, and performs better than the existing Dharma model, especially for beams with high flange-to-web thickness ratios. A component-based model has been created on the basis of the analytical model, and will in due course be implemented in the software Vulcan for global structural fire analysis.
Global lateral buckling analysis of idealized subsea pipelines
Institute of Scientific and Technical Information of China (English)
刘润; 刘文彬; 吴新利; 闫澍旺
2014-01-01
In order to avoid the curing effects of paraffin on the transport process and reduce the transport difficulty, usually high temperature and high pressure are used in the transportation of oil and gas. The differences of temperature and pressure cause additional stress along the pipeline, due to the constraint of the foundation soil, the additional stress can not release freely, when the additional stress is large enough to motivate the submarine pipelines buckle. In this work, the energy method is introduced to deduce the analytical solution which is suitable for the global buckling modes of idealized subsea pipeline and analyze the relationship between the critical buckling temperature, buckling length and amplitude under different high-order global lateral buckling modes. To obtain a consistent formulation of the problem, the principles of virtual displacements and the variation calculus for variable matching points are applied. The finite element method based on elasto-plastic theory is used to simulate the lateral global buckling of the pipelines under high temperature and pressure. The factors influencing the lateral buckling of pipelines are further studied. Based upon some actual engineering projects, the finite element results are compared with the analytical ones, and then the influence of thermal stress, the section rigidity of pipeline, the soil properties and the trigging force to the high order lateral buckling are discussed. The method of applying the small trigging force on pipeline is reliable in global buckling numerical analysis. In practice, increasing the section rigidity of a pipeline is an effective measure to improve the ability to resist the global buckling.
Chen, Licui; Jia, Nana; Gao, Lianghui; Fang, Weihai; Golubovic, Leonardo
2013-04-11
We explore the effects of the peripheral and transmembrane antimicrobial peptides on the lipid bilayer membrane by using the coarse grained Dissipative Particle Dynamics simulations. We study peptide/lipid membrane complexes by considering peptides with various structure, hydrophobicity and peptide/lipid interaction strength. The role of lipid/water interaction is also discussed. We discuss a rich variety of membrane morphological changes induced by peptides, such as pore formation, membrane corrugation and Euler buckling.
PANDA2: Program for Minimum Weight Design of Stiffened, Composite, Locally Buckled Panels
1986-09-01
stiffened cylinders under axial compression," AIA i, Vol. 13, pp 750-755 (1975) [34] I. Sheinman and G. J. Simitses, "Buckling analysis of geometrically...J. Simitses and I. Sheinman , "Optimization of geometrically imperfect stiffened cylindrical shells under axial compression," Comp. Struct, Vol. 9, pp...Structures, Vol. 6, pp. 221-239 (1976) (60] G. J. Simitses and I. Sheinman , "Accurate predic- tion of critical conditions for shear-loaded panels," A.IA
2009-08-01
Crushing damage of barge headlog ................................................................................. 37 Tables Table 3.1. Three design load...types of structures as the geometry of the contact area is the same for both.) The photograph on the cover of this report shows a badly damaged barge...structural concept can be explained as follows. Because of the elastoplastic and limiting strain material characteristics of steel combined with the
Biaxially stretchable supercapacitors based on the buckled hybrid fiber electrode array
Zhang, Nan; Zhou, Weiya; Zhang, Qiang; Luan, Pingshan; Cai, Le; Yang, Feng; Zhang, Xiao; Fan, Qingxia; Zhou, Wenbin; Xiao, Zhuojian; Gu, Xiaogang; Chen, Huiliang; Li, Kewei; Xiao, Shiqi; Wang, Yanchun; Liu, Huaping; Xie, Sishen
2015-07-01
In order to meet the growing need for smart bionic devices and epidermal electronic systems, biaxial stretchability is essential for energy storage units. Based on porous single-walled carbon nanotube/poly(3,4-ethylenedioxythiophene) (SWCNT/PEDOT) hybrid fiber, we designed and fabricated a biaxially stretchable supercapacitor, which possesses a unique configuration of the parallel buckled hybrid fiber array. Owing to the reticulate SWCNT film and the improved fabrication technique, the hybrid fiber retained its porous architecture both outwardly and inwardly, manifesting a superior capacity of 215 F g-1. H3PO4-polyvinyl alcohol gel with an optimized component ratio was introduced as both binder and stretchable electrolyte, which contributed to the regularity and stability of the buckled fiber array. The buckled structure and the quasi one-dimensional character of the fibers endow the supercapacitor with 100% stretchability along all directions. In addition, the supercapacitor exhibited good transparency, as well as excellent electrochemical properties and stability after being stretched 5000 times.In order to meet the growing need for smart bionic devices and epidermal electronic systems, biaxial stretchability is essential for energy storage units. Based on porous single-walled carbon nanotube/poly(3,4-ethylenedioxythiophene) (SWCNT/PEDOT) hybrid fiber, we designed and fabricated a biaxially stretchable supercapacitor, which possesses a unique configuration of the parallel buckled hybrid fiber array. Owing to the reticulate SWCNT film and the improved fabrication technique, the hybrid fiber retained its porous architecture both outwardly and inwardly, manifesting a superior capacity of 215 F g-1. H3PO4-polyvinyl alcohol gel with an optimized component ratio was introduced as both binder and stretchable electrolyte, which contributed to the regularity and stability of the buckled fiber array. The buckled structure and the quasi one-dimensional character of the
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.
Seismic Energy Demand of Buckling-Restrained Braced Frames
Choi, Hyunhoon; Kim, Jinkoo
2008-07-01
In this study seismic analyses of steel structures were carried out to examine the effect of ground motion characteristics and structural properties on energy demands using 60 earthquake ground motions recorded in different soil conditions, and the results were compared with those of previous works. Analysis results show that ductility ratios and the site conditions have significant influence on input energy. The ratio of hysteretic to input energy is considerably influenced by the ductility ratio and the strong motion duration. It is also observed that as the predominant periods of the input energy spectra are significantly larger than those of acceleration response spectra used in the strength design, the strength demand on a structure designed based on energy should be checked especially in short period structures. For that reason framed structures with buckling-restrained-braces (BRBs) were designed in such a way that all the input energy was dissipated by the hysteretic energy of the BRBs, and the results were compared with those designed by conventional strength-based design procedure.
The electromechanical response of silicon nanowires to buckling mode transitions
Energy Technology Data Exchange (ETDEWEB)
Wong, Chee Chung; Liao, Kin [Division of Bioengineering, Nanyang Technological University (Singapore); Reboud, Julien; Neuzil, Pavel; Soon, Jeffrey; Agarwal, Ajay; Balasubramanian, Naranayan, E-mail: pavel@kist-europe.de, E-mail: askliao@ntu.edu.sg [Institute of Microelectronics, A-STAR (Agency for Science, Technology, and Research) (Singapore)
2010-10-08
Here we show how the electromechanical properties of silicon nanowires (NWs) are modified when they are subjected to extreme mechanical deformations (buckling and buckling mode transitions), such as those appearing in flexible devices. Flexible devices are prone to frequent dynamic stress variations, especially buckling, while the small size of NWs could give them an advantage as ultra-sensitive electromechanical stress sensors embedded in such devices. We evaluated the NWs post-buckling behavior and the effects of buckling mode transition on their piezoresistive gauge factor (GF). Polycrystalline silicon NWs were embedded in SiO{sub 2} microbridges to facilitate concurrent monitoring of their electrical resistance without problematic interference, while an external stylus performed controlled deformations of the microbridges. At points of instability, the abrupt change in the buckling configuration of the microbridge corresponded to a sharp resistance change in the embedded NWs, without altering the NWs' GF. These results also highlight the importance of strategically positioning the NW in the devices, since electrical monitoring of buckling mode transitions is feasible when the deformations impact a region where the NW is placed. The highly flexible NWs also exhibited unusually large fracture strength, sustaining tensile strains up to 5.6%; this will prove valuable in demanding flexible sensors.
Institute of Scientific and Technical Information of China (English)
严俊; 庞金来; 施卫星
2015-01-01
For the lack of researches of the longitudinal framing of fabricated structure with weak lateral stiffness, non-damped, buckling-restrainedbrace and damped structure finite element analysis models were es-tablished .The three models'earthquake reaction in the longitudinal system were compared by the nonlinear time history analysis method .Analysis shows that the similar structure with damper can significantly improve the damping effect , and keep the structure in the elastic stage under the major earthquake .The paper can provide a reference for damper's application in the longitudinal framing .%针对抗侧刚度较弱的装配式结构纵向框架研究较少的现状，建立了纯框架、增设防屈曲支撑及增设阻尼器的装配式框架有限元分析模型，通过非线性的时程对比分析了在地震作用下三种模型纵向体系的结构反应。分析表明，在类似结构中增设阻尼器，可显著提高减震效果，使结构在大震中依然处于弹性状态。对于进一步提高阻尼器在纵向框架的应用水平具有一定的借鉴意义。
MERIDIONAL TILT OF THE STELLAR VELOCITY ELLIPSOID DURING BAR BUCKLING INSTABILITY
Energy Technology Data Exchange (ETDEWEB)
Saha, Kanak [Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany); Pfenniger, Daniel [Geneva Observatory, University of Geneva, CH-1290 Sauverny (Switzerland); Taam, Ronald E., E-mail: saha@mpe.mpg.de [Institute of Astronomy and Astrophysics, Academia Sinica-TIARA, Taiwan (China)
2013-02-20
The structure and evolution of the stellar velocity ellipsoid play an important role in shaping galaxies undergoing bar-driven secular evolution and the eventual formation of a boxy/peanut bulge such as is present in the Milky Way. Using collisionless N-body simulations, we show that during the formation of such a boxy/peanut bulge, the meridional shear stress of stars, which can be measured by the meridional tilt of the velocity ellipsoid, reaches a characteristic peak in its time evolution. It is shown that the onset of a bar buckling instability is closely connected to the maximum meridional tilt of the stellar velocity ellipsoid. Our findings bring a new insight to this complex gravitational instability of the bar which complements the buckling instability studies based on orbital models. We briefly discuss the observed diagnostics of the stellar velocity ellipsoid during such a phenomenon.
Institute of Scientific and Technical Information of China (English)
Hong-Ling Ye; Wei-Wei Wang; Ning Chen; Yun-Kang Sui
2016-01-01
In this paper, a model of topology optimization with linear buckling constraints is established based on an independent and continuous mapping method to minimize the plate/shell structure weight. A composite exponential function (CEF) is selected as filtering functions for element weight, the element stiffness matrix and the element geomet-ric stiffness matrix, which recognize the design variables, and to implement the changing process of design variables from“discrete”to“continuous”and back to“discrete”. The buck-ling constraints are approximated as explicit formulations based on the Taylor expansion and the filtering function. The optimization model is transformed to dual programming and solved by the dual sequence quadratic programming algo-rithm. Finally, three numerical examples with power function and CEF as filter function are analyzed and discussed to demonstrate the feasibility and efficiency of the proposed method.
Weil, A. Brandon; Gutiérrez-Alonso, G.; Johnston, S. T.; Pastor-Galán, D.
2013-01-01
latest Carboniferous, which agrees well with recent geodynamical models and structural data that relate oroclinal buckling with lithospheric delamination in the Variscan.
Liu, Xiaolong; Eckert, Andreas; Connolly, Peter
2016-06-01
Buckle folds of sedimentary strata commonly feature a variety of different fracture sets. Some fracture sets including outer arc tensile fractures and inner arc shear fractures at the fold hinge zones are well understood by the extensional and compressional strain/stress pattern. However, other commonly observed fracture sets, including tensile fractures parallel to the fold axis, tensile fractures cutting through the limb, extensional faults at the fold hinge, and other shear fractures of various orientations in the fold limb, fail to be intuitively explained by the strain/stress regimes during the buckling process. To obtain a better understanding of the conditions for the initiation of the various fractures sets associated with single-layer cylindrical buckle folds, a 3D finite element modeling approach using a Maxwell visco-elastic rheology is utilized. The influences of three model parameters with significant influence on fracture initiation are considered: burial depth, viscosity, and permeability. It is concluded that these parameters are critical for the initiation of major fracture sets at the hinge zone with varying degrees. The numerical simulation results further show that the buckling process fails to explain most of the fracture sets occurring in the limb unless the process of erosional unloading as a post-fold phenomenon is considered. For fracture sets that only develop under unrealistic boundary conditions, the results demonstrate that their development is realistic for a perclinal fold geometry. In summary, a more thorough understanding of fractures sets associated with buckle folds is obtained based on the simulation of in-situ stress conditions during the structural development of buckle folds.
Nüchter, Jens-Alexander
2017-01-01
The paper introduces the mechanism of buckling-enhanced aperture growth for syn-tectonic veins that formed in simple-shear dominated kinematic frameworks in the middle or lower crust. Apart from the well understood concepts of fracture widening driven by effective tensile stresses, buckling-enhanced fracture aperture growth relates widening to active outward buckling of more viscous incipient cement layers precipitated as hydrothermal minerals for the pore fluid on the walls of juvenile syn-tectonic veins, driven by fracture-parallel compressive creep strain in the host rocks. Thus, the mechanism proposed here follows similar principles as tectonic folding, although important differences exist. Inspired by the structural record of low-aspect ratio veins exposed in HP/LT metamorphic rocks cropping out on south Evia island, Greece, generic numerical models are calculated to study development of buckling instabilities in such incompletely cemented veins and their impact on aperture growth rates. The models indicate (1) that aperture growth rates increase with increasing viscosity contrast between the host rocks and the cement layers, (2) an increase in the thickness of the cement layers cause acceleration of aperture growth, (3) that support of restraining forces at the vein tips offered by the host rocks against buckling of the cement layers cause fully compressive states of stress ahead the fracture tips, and (4) that fracture aperture growth is possible against fully compressive fracture-normal stresses. The buckling-enhanced vein aperture growth mechanism yields important implications for the maintenance and decay of fracture-bound permeability and for the mechanical state of the middle and lower crust in seismically active regions.
ANALYSIS OF DYNAMICAL BUCKLING AND POST BUCKLING FOR BEAMS BY FINITE SEGMENT METHOD
Institute of Scientific and Technical Information of China (English)
YIN Xue-gang; DU Si-yi; HU Ji-yun; DING Jian-ping
2005-01-01
Based on the multi-rigid body discretization model, namely, finite segment model,a chain multi-rigid-body-hinge-spring system model of a beam was presented,then a nonlinear parametrically exacted vibration equation of multi-degrees of freedom system was established using the coordination transformation method, and its resonance fields were derived by the restriction parameter method, that is, the dynamical buckling analysis of the beam. Because the deformation of a beam is not restricted by the discrete model and dynamic equation, the post buckling analysis can be done in above math model. The numerical solutions of a few examples were obtained by direct integrated method, which shows that the mechanical and math model gotten is correct.
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...... problem is integrated and this results in a second order differential equation of the Fuchs type, which allows an asymptotic expansion of the buckling equation. By means of Lyapunov and Chetaev functions, a rigorous proof is given that the loss of stability of the trivial equilibrium shape occurs for any...
Buckling Analysis of Debonded Sandwich Panel Under Compression
Sleight, David W.; Wang, John T.
1995-01-01
A sandwich panel with initial through-the-width debonds is analyzed to study the buckling of its faceskin when subject to an in-plane compressive load. The debonded faceskin is modeled as a beam on a Winkler elastic foundation in which the springs of the elastic foundation represent the sandwich foam. The Rayleigh-Ritz and finite-difference methods are used to predict the critical buckling load for various debond lengths and stiffnesses of the sandwich foam. The accuracy of the methods is assessed with a plane-strain finite-element analysis. Results indicate that the elastic foundation approach underpredicts buckling loads for sandwich panels with isotropic foam cores.
Electromechanical Dynamics Analysis of Buckling Microstructure For Micromirror
Energy Technology Data Exchange (ETDEWEB)
Jia, Jianyuan; Chen, Guimin; Fan, Guobin [Xidian Univ., Jiangxi (China)
2002-11-15
The electromechanical dynamics characteristic and emulation of buckling microstructure for digital micromirror device are studied. The microstructure of digital micromirror device based on buckling theory is designed and its electromechanical dynamics model is established. The hidden functions in the dynamics model are found out by numerical methods such as Runge-Kutta method and Finite Element method. A numerical emulation to the whole motion differential equation has been presented, and a continuous angular displacement curve of micro-reflectmirror is obtained. At last, it is concluded that the buckling microstructure has an advantage of light beam stability.
Measurement of buckling load for metallic plate columns in severe accident conditions
Energy Technology Data Exchange (ETDEWEB)
Jo, Byeongnam, E-mail: jo@vis.t.u-tokyo.ac.jp; Sagawa, Wataru, E-mail: sagawa@vis.t.u-tokyo.ac.jp; Okamoto, Koji, E-mail: okamoto@n.t.u-tokyo.ac.jp
2014-07-01
Highlights: • Buckling load was experimentally measured in a wide range of temperature up to 1200 °C. • Two different test methods for measuring buckling failure load were suggested and compared. • Creep buckling under compressive load was performed to explain results of buckling tests. • Reduced buckling load was explained by effects of creep buckling, geometrical imperfection, and thermal stress. • Buckling processes were visualized by a high speed camera. - Abstract: In severe accidents, a reactor pressure vessel, its components, and piping have to be under extremely high temperature and high pressure conditions, which results in failure modes like rupture by internal pressure, buckling, creep, and their combinations. In this study, buckling (failure) load was experimentally measured for metallic columns under the compressive force from room temperature up to 1200 °C. A stainless steel was chosen to be a test material to measure the buckling load. Two different test methods were employed to explore the effect of thermal history of the material on the buckling load. Particularly, the effect of creep under a compressive load was considered as a reason for the reduced buckling load at high temperatures. Additionally, finite element simulations were also conducted to predict buckling load for both an ideal column and a column with geometrical imperfection as well. Moreover, buckling process was visualized using a high speed camera to understand buckling processes.
Forced Vibrations of Silos Leading to Buckling
FLORES, FERNANDO G.; GODOY, LUIS A.
1999-07-01
The large-amplitude force vibrations of steel thin-walled silos when empty are investigated. The basic geometry configuration modelled is a cylinder clamped at the bottom with a top conical roof. Wind pressure distributions are assumed as non-axisymmetric in the circumferential direction and with a rectangular impulse or step distribution in time. Instability is identified from finite-element computations of the time response of the shell using a criterion due to Budianski and Roth. Results are computed for silos made with plain as well as with corrugated sheets, and the influences of geometric imperfections and the stiffening due to the roof are included in the analysis. The problems are also modelled with static pressures using both continuation techniques and bifurcation analysis from a linear fundamental path. Additional results have been obtained to estimate the dynamic buckling load for step loading using energy procedures. All results are computed using finite-element codes developed by the authors.
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.
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......, the ordinary finite element method slightly overestimates the buckling load, and with a very few number of elements high rate of convergence to the exact results is observed. If the bending rigidity field is modelled using random fields, stochastic finite element method is utilized. The discretization...... is performed using weighted intergrals. Then, the buckling load becomes a random variable. The sensitivity of the lower order moments of the buckling load with respect to the mesh size, the correlation length and coefficient of variation of the random field are examined. The reliability of columns designed...
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......, but where subsequently the load starts to increase again, it is found that near the local load minimum, the buckling pattern switches back to a periodic type of pattern. The inelastic material behavior of the panel is described in terms of J(2) corner theory, which avoids the sometimes unrealistically high...
Scale effects on thermal buckling properties of carbon nanotube
Energy Technology Data Exchange (ETDEWEB)
Wang Yize, E-mail: wangyize@gmail.co [P.O. Box 137, School of Astronautics, Harbin Institute of Technology, Harbin 150001 (China); Department of Mechanical Sciences and Engineering, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8552 (Japan); Li Fengming, E-mail: fmli@hit.edu.c [P.O. Box 137, School of Astronautics, Harbin Institute of Technology, Harbin 150001 (China); Kishimoto, Kikuo [Department of Mechanical Sciences and Engineering, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8552 (Japan)
2010-11-01
In this Letter, the thermal buckling properties of carbon nanotube with small scale effects are studied. Based on the nonlocal continuum theory and the Timoshenko beam model, the governing equation is derived and the nondimensional critical buckling temperature is presented. The influences of the scale coefficients, the ratio of the length to the diameter, the transverse shear deformation and rotary inertia are discussed. It can be observed that the small scale effects are significant and should be considered for thermal analysis of carbon nanotube. The nondimensional critical buckling temperature becomes higher with the ratio of length to diameter increasing. Furthermore, for smaller ratios of the length to the diameter and higher mode numbers, the transverse shear deformation and rotary inertia have remarkable influences on the thermal buckling behaviors.
Study of Buckling Restrained Braces in Steel Frame Building
Directory of Open Access Journals (Sweden)
Mr. Y. D. Kumbhar
2014-08-01
Full Text Available Conventional braces have limited deformation ductility capacity, and exhibit unsymmetrical hysteretic cycles, with marked strength deterioration when loaded in compression. To overcome the above mentioned problems, a new type of brace was developed in Japan called as buckling restrained braces, designated as BRB’s. These braces are designed such that buckling is inhibited to occur, exhibiting adequate behavior and symmetrical hysteretic curves under the action of both tensile and compressive cycles, produced by the action of seismic and wind forces. This paper presents experimental results concerning the lateral load carrying capacity of steel frame model by use of buckling restrained brace. This paper also includes the comparative study of lateral load carrying capacity of frame model for bare frame, frame with Conventional brace and frame with buckling restrained brace.
Buckling analysis of a ring stiffened hybrid composite cylinder
Potluri, Rakesh; Eswara Kumar, A.; Navuri, Karteek; Nagaraju, M.; Mojeswara Rao, Duduku
2016-09-01
This study aims to understand the response of the ring stiffened cylinders made up of hybrid composites subjected to buckling loads by using the concepts of Design of Experiments (DOE) and optimization by using Finite Element Method (FEM) simulation software Ansys workbench V15. Carbon epoxy and E-glass epoxy composites were used in the hybrid composite. This hybrid composite was analyzed by using different layup angles. Central composite design (CCD) was used to perform design of experiments (D.O.E) and kriging method was used to generate a response surface. The response surface optimization (RSO) was performed by using the method of the multi-objective genetic algorithm (MOGA). After optimization, the best candidate was chosen and applied to the ring stiffened cylinder and eigenvalue buckling analysis was performed to understand the buckling behavior. Best laminate candidates with high buckling strength have been identified. A generalized procedure of the laminate optimization and analysis have been shown.
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.
Salehi-Khojin, Amin; Jalili, Nader
2007-04-01
Unlike widely-used carbon nanotubes, boron nitride nanotubes (BNNTs) have shown to possess stable semiconducting behavior and strong piezoelectricity. Such properties along with their outstanding mechanical properties and thermal conductivity, make BNNTs promising candidate reinforcement materials for a verity of applications especially nanoelectronic and nanophotonic devices. Motivated by these abilities, we aim to study the buckling behavior of BNNT-reinforced piezoelectric polymeric composites when subjected to combined electro-thermo-mechanical loadings. For this, the multi-walled structure of BNNT is considered as elastic media and a set of concentric cylindrical shell with van der Waals interaction between them. Using three-dimensional equilibrium equations, Donnell shell theory is utilized to show that the axially compressive resistance of BNNT varies with applying thermal and electrical loads. The effect of BNNT piezoelectric property on the buckling behavior of the composites is demonstrated. More specifically, it is shown that applying direct and reverse voltages to BNNT changes the buckling loads for any axial and circumferential wavenumbers. Such capability could be uniquely utilized when designing BNNT-reinforced composites.
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.
Buckling Analysis of Functionally Graded Plates with Simply Supported Edges
Directory of Open Access Journals (Sweden)
Megueni ABDELKADER
2009-12-01
Full Text Available Thermal buckling analyses of S-FGM are investigated by using first order shear deformation theory. Material properties are varied continuously in the thickness direction according to a sigmoid distribution. The thermal buckling behaviours under uniform, linear and sinusoidal temperature rise across the thickness are analyzed. 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 classic plate theory (CPT.
Institute of Scientific and Technical Information of China (English)
Cheng-Qi Sun; Kai-Xin Liu; You-Shi Hong
2012-01-01
The paper studies the axisymmetric compressive buckling behavior of multi-walled carbon nanotubes (MWNTs) under different boundary conditions based on continuum mechanics model.A buckling condition is derived for determining the critical buckling load and associated buckling mode of MWNTs,and numerical results are worked out for MWNTs with different aspect ratios under fixed and simply supported boundary conditions.It is shown that the critical buckling load of MWNTs is insensitive to boundary conditions,except for nanotubes with smaller radii and very small aspect ratio.The associated buckling modes for different layers of MWNTs are in-phase,and the buckling displacement ratios for different layers are independent of the boundary conditions and the length of MWNTs.Moreover,for simply supported boundary conditions,the critical buckling load is compared with the corresponding one for axial compressive buckling,which indicates that the critical buckling load for axial compressive buckling can be well approximated by the corresponding one for axisymmetric compressive buckling.In particular,for axial compressive buckling of double-walled carbon nanotubes,an analytical expression is given for approximating the critical buckling load.The present investigation may be of some help in further understanding the mechanical properties of MWNTs.
Combined torsional buckling of multi-walled carbon nanotubes
Lu, Y. J.; Wang, X.
2006-08-01
This paper reports the results of an investigation on combined torsional buckling of an individual multi-walled carbon nanotube (MWNT) under combined torque and axial loading. Here, a multiple shell model is adopted and the effect of van der Waals forces between two adjacent tubes is taken into account. According to the ratio of radius to thickness, MWNTs discussed in this paper are classified into three types: thin, thick and nearly solid. The critical shear stress and the combined buckling mode are calculated for three types of MWNTs under combined torque and axial loading. Results carried out show that the buckling mode (m, n) corresponding to the critical shear stress is unique, which is obviously different from the purely axial compression buckling of an individual MWNT. Numerical results also show that the critical shear stresses and the corresponding buckling modes of MWNTs under combined torque and axial loading are dependent on the axial loading form and the types of MWNTs. The new features and meaningful numerical results in the present work on combined buckling of MWNTs under combined torque and axial loading may be used as a useful reference for the designs of nano-drive devices and rotational actuators in which MWNTs act as basic elements.
Flexural-torsional buckling behavior of aluminum alloy beams
Institute of Scientific and Technical Information of China (English)
Xiaonong GUO; Zhe XIONG; Zuyan SHEN
2015-01-01
This paper presents an investigation on the flexural-torsional buckling behavior of aluminum alloy beams （AAB）. First, based on the tests of 14 aluminum alloy beams under concentrated loads, the failure pattern, load- deformation curves, bearing capacity and flexural-torsional buckling factor are studied. It is found that all the beam specimens collapsed in the flexuml-torsional buckling with excessive deformation pattern. Moreover, the span, loading location and slenderness ratio influence the flexural-torsional buckling capacity of beams significantly. Secondly, besides the experiments, a finite element method （FEM） analysis on the flexural-torsional buckling behavior of AAB is also conducted. The main parameters in the FEM analysis are initial imperfection, material property, cross-section and loading scheme. According to the analytical results, it is indicated that the FEM is reasonable to capture mechanical behavior of AAB. Finally, on the basis of the experimental and analytical results, theoretical formulae to estimate the flexural- torsional buckling capacity of AAB are proposed, which could improve the application of present codes for AAB.
BUCKLING ANALYSES OF A HEAVY COLUMN CONSIDERATED IN WATER
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Yeliz PEKBEY
2008-02-01
Full Text Available In 1744, the critical buckling load with the assumption of uniform cross-section without weight of column were computed by Euler. Whenever an economical solution is required, the weight of column must be considered for solution of buckling analyses. In literature, the critical buckling load and asymptotic behaviour of heavy column in condition of atmosphere have inverstigated for ten different support types. When this literature is examined, it is stated that the differential equations of for four different suppport types in condition of water is similar to condition of atmosphere. However, the differential equations of other four different suppport types in condition of water is different from to condition of atmosphere. And it is stated that the critical buckling load these different suppport types in condition of water is not calculated from condition of atmosphere. The goals of this paper are to develop self weight buckling of column at its top fixed and lower end fixed-roller supported in condition of water. This paper, presents a analytical method for calculating the critical buckling load of the heavy column.
Strengthening of Steel Columns under Load: Torsional-Flexural Buckling
Directory of Open Access Journals (Sweden)
Martin Vild
2016-01-01
Full Text Available The paper presents experimental and numerical research into the strengthening of steel columns under load using welded plates. So far, the experimental research in this field has been limited mostly to flexural buckling of columns and the preload had low effect on the column load resistance. This paper focuses on the local buckling and torsional-flexural buckling of columns. Three sets of three columns each were tested. Two sets corresponding to the base section (D and strengthened section (E were tested without preloading and were used for comparison. Columns from set (F were first preloaded to the load corresponding to the half of the load resistance of the base section (D. Then the columns were strengthened and after they cooled, they were loaded to failure. The columns strengthened under load (F had similar average resistance as the columns welded without preloading (E, meaning the preload affects even members susceptible to local buckling and torsional-flexural buckling only slightly. This is the same behaviour as of the tested columns from previous research into flexural buckling. The study includes results gained from finite element models of the problem created in ANSYS software. The results obtained from the experiments and numerical simulations were compared.
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)
Are buckling force measurements reliable in nocturnal penile tumescence studies?
Nofzinger, E A; Fasiczka, A L; Thase, M E; Reynolds, C F; Frank, E; Jennings, J R; Garamoni, G L; Matzzie, J V; Kupfer, D J
1993-02-01
The study of nocturnal penile tumescence (NPT) is frequently used to evaluate male erectile dysfunction. Buckling force, a measure of rigidity, is an important part of this evaluation, but its reliability is unknown. Accordingly, we studied the reliability of buckling force measurement and the stability of "maximum buckling force" between consecutive NPT series repeated in the same subject. For individual subjects, we correlated buckling forces for separate episodes of sleep-related tumescence that were of comparable fullness (0-100%) as rated by a technician's visual estimates. For healthy control subjects, test-retest correlations were > 0.8 both within-night and across study series separated by an average of 70 weeks. In depressed men, correlations within nights were > 0.9, but fell to 0.64 across study series separated by an average of 21 weeks. Despite the high reliability of buckling force measurement, we found little stability of "maximum buckling force" between NPT series for individual subjects. Considerable variability in the maximum degree of penile rigidity was seen over time despite a constant level of reported daytime erectile function. We conclude that although penile rigidity is one of the more important variables in the assessment of male erectile dysfunction and can be measured reliably, the instability of maximum rigidity during sleep-related erections suggests that it is, at best, an imprecise correlate of daytime erectile function.
Buckle Driven Delamination in Thin Hard Film Compliant Substrate Systems
Moody, N. R.; Reedy, E. D.; Corona, E.; Adams, D. P.; Kennedy, M. S.; Cordill, M. J.; Bahr, D. F.
2010-06-01
Deformation and fracture of thin films on compliant substrates are key factors constraining the performance of emerging flexible substrate devices. [1-3] These systems often contain layers of thin polymer, ceramic and metallic films and stretchable interconnects where differing properties induce high normal and shear stresses. [4] As long as the films remain bonded to the substrates, they may deform far beyond their freestanding form. Once debonded, substrate constraint disappears leading to film failure. [3] Experimentally it is very difficult to measure properties in these systems at sub-micron and nanoscales. Theoretically it is very difficult to determine the contributions from the films, interfaces, and substrates. As a result our understanding of deformation and fracture behavior in compliant substrate systems is limited. This motivated a study of buckle driven delamination of thin hard tungsten films on pure PMMA substrates. The films were sputter deposited to thicknesses of 100 nm, 200 nm, and 400 nm with a residual compressive stress of 1.7 GPa. An aluminum oxide interlayer was added on several samples to alter interfacial composition. Buckles formed spontaneously on the PMMA substrates following film deposition. On films without the aluminum oxide interlayer, an extensive network of small telephone cord buckles formed following deposition, interspersed with regions of larger telephone cord buckles. (Figure 1) On films with an aluminum oxide interlayer, telephone cord buckles formed creating a uniform widely spaced pattern. Through-substrate optical observations revealed matching buckle patterns along the film-substrate interface indicating that delamination occurred for large and small buckles with and without an interlayer. The coexistence of large and small buckles on the same substrate led to two distinct behaviors as shown in Figure 2 where normalized buckle heights are plotted against normalized film stress. The behaviors deviate significantly from
Buckle Driven Delamination in Thin Hard Film Compliant Substrate Systems
Directory of Open Access Journals (Sweden)
Bahr D.F.
2010-06-01
Full Text Available Deformation and fracture of thin films on compliant substrates are key factors constraining the performance of emerging flexible substrate devices. [1-3] These systems often contain layers of thin polymer, ceramic and metallic films and stretchable interconnects where differing properties induce high normal and shear stresses. [4] As long as the films remain bonded to the substrates, they may deform far beyond their freestanding form. Once debonded, substrate constraint disappears leading to film failure. [3] Experimentally it is very difficult to measure properties in these systems at sub-micron and nanoscales. Theoretically it is very difficult to determine the contributions from the films, interfaces, and substrates. As a result our understanding of deformation and fracture behavior in compliant substrate systems is limited. This motivated a study of buckle driven delamination of thin hard tungsten films on pure PMMA substrates. The films were sputter deposited to thicknesses of 100 nm, 200 nm, and 400 nm with a residual compressive stress of 1.7 GPa. An aluminum oxide interlayer was added on several samples to alter interfacial composition. Buckles formed spontaneously on the PMMA substrates following film deposition. On films without the aluminum oxide interlayer, an extensive network of small telephone cord buckles formed following deposition, interspersed with regions of larger telephone cord buckles. (Figure 1 On films with an aluminum oxide interlayer, telephone cord buckles formed creating a uniform widely spaced pattern. Through-substrate optical observations revealed matching buckle patterns along the film-substrate interface indicating that delamination occurred for large and small buckles with and without an interlayer. The coexistence of large and small buckles on the same substrate led to two distinct behaviors as shown in Figure 2 where normalized buckle heights are plotted against normalized film stress. The behaviors deviate
Institute of Scientific and Technical Information of China (English)
姜正荣; 石开荣; 徐牧; 蔡健
2011-01-01
以一31．1m×24．1m跨度的椭圆抛物面辐射式张弦梁结构为分析对象，考虑几何非线性、初始几何缺陷、材料弹塑性及活载的半跨布置，对其非线性屈曲性能进行研究。采用分批分阶段的拉索张拉施工方案，通过对张拉全过程的仿真分析，得到直接指导施工的各组拉索张拉力。研究表明：初始几何缺陷按最低阶屈曲模态分布时，稳定承载力系数并非最小；荷载不对称分布对结构的稳定性更为不利；材料非线性对结构稳定性影响较大；初始几何缺陷取短轴跨度的1／500较为适宜；各组拉索的实际施工张拉力与目标索力差别较小，张拉过程中，群索之间索力的相互影响不大。%The nonlinear buckling behavior of an elliptic paraboloid radial beam string structure （BSS） of span 31.1 m × 24.1 m is investigated by introducing geometric nonlinearity, initial geometric imperfection, material elastic-plasticity and half-span distribution of live loads. The actual cable tension forces in different batches and stages are determined from simulation of the overall process, in order to guide the construction. The study shows that the coefficient of stable bearing capacity usually is not minimal when the initial geometric imperfection configuration is taken as the first order buckling mode, but rather, the unsymmetrical loading distribution and the material nonlinearity might have significant effects on the coefficient. A 1/500 of the span of minor axis could be appropriately taken as the maximum value of initial geometric imperfection. The simulation analysis of the construction demonstrates that the differences between the actual cable tension forces and the design values are very small, and the correlations between groups of cables during the tensioning are rather minor.
Ma, Weilin; Liu, Jiande; Dong, Sheng; Zhang, Xin; Ma, Xiaozhou
2017-02-01
In order to theoretically study the buckle propagation of subsea pipelines with slip-on buckle arrestors, a two-dimensional ring model was set up to represent the pipeline and a nonlinear spring model was adopted to simulate the contact between pipeline's inner walls and between pipeline's outer wall and slip-on buckle arrestor's inner wall during buckle propagation. In addition, some reverse springs are added to prevent the wall of left and right sides separating from the inner wall of slip-on buckle arrestors. Considering large deformation kinematics relations and the elastic-plastic constitutive relation of material, balance equations were established with the principle of virtual work. The variation of external pressure with respect to the cross-sectional area of pipelines was analyzed, and the lower bound of the crossover pressure of slip-on buckle arrestors was calculated based on Maxwell's energy balance method. By comparing the theoretical results with experiment and finite element numerical simulation, the theoretical method is proved to be correct and reliable.
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.
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
Buckling of open-section bead-stiffened composite panels
Laananen, D. H.; Renze, S. P.
Stiffened panels are structures that can be designed to efficiently support inplane compression, bending, and shear loads. Although the stiffeners are usually discrete elements which are fastened or bonded to a flat or continuously curved plate, manufacturing methods such as thermoforming allow integral formation of the stiffeners in a panel. Such a configuration offers potential advantages in terms of a reduced number of parts and manufacturing operations. For thermoplastic composite panels stiffened by integrally formed open-section beads, the effects of bead spacing and bend cross-section geometry on the initiation of buckling under uniaxial compression and uniform shear loading were investigated. Finite elements results for a range of stiffened panel sizes and bead geometries are presented and compared with approximate closed-form solutions based on an effective flat plate size. Experimental verification of analytical predictions for one of the shear panels and one of the compression panels is described. Compensation of the forming tool to reduce the degree of initial curvature of the panels was found to be necessary.
Production TTR modeling and dynamic buckling analysis
Institute of Scientific and Technical Information of China (English)
Hugh Liu; John Wei; Edward Huang
2013-01-01
In a typical tension leg platform (TLP) design,the top tension factor (TTF),measuring the top tension of a top tensioned riser (TTR) relative to its submerged weight in water,is one of the most important design parameters that has to be specified properly.While a very small TTF may lead to excessive vortex induced vibration (ⅤⅣ),clashing issues and possible compression close to seafloor,an unnecessarily high TTF may translate into excessive riser cost and vessel payload,and even has impacts on the TLP sizing and design in general.In the process of a production TTR design,it is found that its outer casing can be subjected to compression in a worst-case scenario with some extreme metocean and hardware conditions.The present paper shows how finite element analysis (FEA) models using beam elements and two different software packages (Flexcom and ABAQUS) are constructed to simulate the TTR properly,and especially the pipe-in-pipe effects.An ABAQUS model with hybrid elements (beam elements globally + shell elements locally) can be used to investigate how the outer casing behaves under compression.It is shown for the specified TTR design,even with its outer casing being under some local compression in the worst-case scenario,dynamic buckling would not occur; therefore the TTR design is adequate.
DYNAMIC BUCKLING OF DOUBLE-WALLED CARBON NANOTUBES UNDER STEP AXIAL LOAD
Institute of Scientific and Technical Information of China (English)
Chengqi Sun; Kaixln Liu
2009-01-01
An approximate method is presented in this paper for studying the dynamic buckling of double-walled carbon nanotubes (DWNTs) under step axial load. The analysis is based on the continuum mechanics model, which takes into account the van der Waals interaction between the outer and inner nanotubes. A buckling condition is derived, from which the critical buckling load and associated buckling mode can be determined. As examples, numerical results are worked out for DWNTs under fixed boundary conditions. It is shown that, due to the effect of van der Waals forces, the critical buckling load of a DWNT is enhanced when inserting an inner tube into a single-walled one. The paper indicates that the critical buckling load of DWNTs for dynamic buckling is higher than that for static buckling. The effect of the radii is also examined. In addition, some of the results are compared with the previous ones.
Perturbation analysis on post-buckling behavior of pile
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The nonlinear large deflection differential equation, based on the assumption that the subsoil coefficient is the 2nd root of the depth, was established by energy method. The perturbation parameter was introduced to transform the equation to a series of linear differential equations to be solved, and the deflection function according with the boundary condition was considered. Then,the nonlinear higher-order asymptotic solution of post-buckling behavior of a pile was obtained by parameter-substituting. The influencing factors such as bury-depth ratio and stiffness ratio of soil to pile, slenderness ratio on the post-buckling behavior of a pile were analyzed. The results show that the pile is more unstable when the bury-depth ratio and stiffness ratio of soil to pile increase,and although the buckling load increases with the stiffness of soil, the pile may ruin for its brittleness. Thus, in the region where buckling behavior of pile must be taken into account, the high grade concrete is supposed to be applied, and the dynamic buckling behavior of pile needs to be further studied.
THERMAL POST-BUCKLING OF FUNCTIONALLY GRADED MATERIAL TIMOSHENKO BEAMS
Institute of Scientific and Technical Information of China (English)
LI Shi-rong; ZHANG Jing-hua; ZHAO Yong-gang
2006-01-01
Analysis of thermal post-buckling of FGM (Functionally Graded Material)Timoshenko beams subjected to transversely non-uniform temperature rise is presented.By accurately considering the axial extension and transverse shear deformation in the sense of theory of Timoshenko beam, geometrical nonlinear governing equations including seven basic unknown functions for functionally graded beams subjected to mechanical and thermal loads were formulated. In the analysis, it was assumed that the material properties of the beam vary continuously as a power function of the thickness coordinate. By using a shooting method, the obtained nonlinear boundary value problem was numerically solved and thermal buckling and post-buckling response of transversely non-uniformly heated FGM Timoshenko beams with fixed-fixed edges were obtained. Characteristic curves of the buckling deformation of the beam varying with thermal load and the power law index are plotted. The effects of material gradient property on the buckling deformation and critical temperature of beam were discussed in details. The results show that there exists the tension-bend coupling deformation in the uniformly heated beam because of the transversely non-uniform characteristic of materials.
Circumferential nonlocal effect on the buckling and vibration of nanotubes
Energy Technology Data Exchange (ETDEWEB)
Wang, Cheng Yuan, E-mail: cywang@ujs.edu.cn; Li, Xiao Hu; Luo, Ying
2016-04-01
The nonlocal beam theories are widely used to study the mechanics of cylindrical nanotubes (NTs). The one-dimensional models however are unable to account for the nonlocal effect in the circumferential direction, which may substantially affect the applicability of the nonlocal beam models. To address the issue this letter examines the circumferential nonlocal effect (CNE) on the buckling and vibration of the NTs. Here the CNE is characterized by the difference between the nonlocal beam model considering the axial nonlocal effect only and the nonlocal shell model with both axial and circumferential nonlocal effects. The aspect ratio and radius-dependence of the CNE are calculated for the singlewall carbon NTs selected as a typical example. The results show that the CNE is substantial for the buckling and vibration of the NTs with small radius (e.g., <1 nm) and aspect ratio (e.g., <15). It however decreases with the rising radius and the aspect ratio, and turns out to be small for relatively wide and long NTs. The nonlocal beam theories thus may overestimate the buckling load and vibration frequency for the thin and short NTs. - Highlights: • First revealed the substantial circumferential nonlocal effect (CNE) on nanotube buckling. • Achieved radius/aspect ratio-dependence of CNE on nanotube buckling and vibration. • Located the range of applicability of the nonlocal beam theory without CNE.
Buckling in polymer monolayers: Molecular-weight dependence
Energy Technology Data Exchange (ETDEWEB)
Srivastava, S.; Basu, J.K.; (IIS)
2010-11-12
We present systematic investigations of buckling in Langmuir monolayers of polyvinyl acetate formed at the air-water interface. On compression the polymer monolayers are converted to a continuous membrane with a thickness of {approx}2-3 nm of well-defined periodicity, {lambda}{sub b}. Above a certain surface concentration the membrane undergoes a morphological transition buckling, leading to the formation of striped patterns. The periodicity seems to depend on molecular weight as per the predictions of the gravity-bending buckling formalism of Milner et al. for fluidlike films on water. However anomalously low values of bending rigidity and Young's modulus are obtained using this formalism. Hence we have considered an alternative model of buckling-based solidlike films on viscoelastic substrates. The values of bending rigidity and Young's modulus obtained by this method, although lower than expected, are closer to the bulk values. Remarkably, no buckling is found to occur above a certain molecular weight. We have tried to explain the observed molecular-weight dependence in terms of the variation in isothermal compressive modulus of the monolayers with surface concentration as well as provided possible explanations for the obtained low values of mechanical properties similar to that observed for ultrathin polymer films.
Buckling analysis of composite cylindrical shell using numerical analysis method
Energy Technology Data Exchange (ETDEWEB)
Jung, Hae Young; Bae, Won Byung [Pusan Nat' l Univ., Busan (Korea, Republic of); Cho, Jong Rae [Korea Maritime Univ., Busan (Korea, Republic of); Lee, Woo Hyung [Underwater Vehicle Research Center, Busan (Korea, Republic of)
2012-01-15
The objective of this paper is to predict the buckling pressure of a composite cylindrical shell using buckling formulas (ASME 2007, NASA SP 8007) and finite element analysis. The model in this study uses a stacking angle of [0/90]12t and USN 125 composite material. All specimens were made using a prepreg method. First, finite element analysis was conducted, and the results were verified through comparison with the hydrostatic pressure bucking experiment results. Second, the values obtained from the buckling formula and the buckling pressure values obtained from the finite element analysis were compared as the stacking angle was changed in 5 .deg. increments from 20 .deg. to 90 .deg. The linear and nonlinear results of the finite element analysis were consistent with the results of the experiment, with a safety factor of 0.85-1. Based on the above result, the ASME 2007 formula, a simplified version of the NASA SP 8007 formula, is regarded as a buckling formula that provides a reliable safety factor.
Molecular dynamics analysis on buckling of defective carbon nanotubes
Energy Technology Data Exchange (ETDEWEB)
Kulathunga, D D T K; Ang, K K [Department of Civil Engineering, National University of Singapore (Singapore); Reddy, J N, E-mail: cveangkk@nus.edu.s [Department of Mechanical Engineering, Texas A and M University, College Station, TX 77843-3123 (United States)
2010-09-01
Owing to their remarkable mechanical properties, carbon nanotubes have been employed in many diverse areas of applications. However, similar to any of the many man-made materials used today, carbon nanotubes (CNTs) are also susceptible to various kinds of defects. Understanding the effect of defects on the mechanical properties and behavior of CNTs is essential in the design of nanotube-based devices and composites. It has been found in various past studies that these defects can considerably affect the tensile strength and fracture of CNTs. Comprehensive studies on the effect of defects on the buckling and vibration of nanotubes is however lacking in the literature. In this paper, the effects of various configurations of atomic vacancy defects, on axial buckling of single-walled carbon nanotubes (SWCNTs), in different thermal environments, is investigated using molecular dynamics simulations (MDS), based on a COMPASS force field. Our findings revealed that even a single missing atom can cause a significant reduction in the critical buckling strain and load of SWCNTs. In general, increasing the number of missing atoms, asymmetry of vacancy configurations and asymmetric distribution of vacancy clusters seemed to lead to higher deterioration in buckling properties. Further, SWCNTs with a single vacancy cluster, compared to SWCNTs with two or more vacancy clusters having the same number of missing atoms, appeared to cause higher deterioration of buckling properties. However, exceptions from the above mentioned trends could be expected due to chemical instabilities of defects. Temperature appeared to have less effect on defective CNTs compared to pristine CNTs.
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.
Electrical Bending and Mechanical Buckling Instabilities in Electrospinning Jets
Han, Tao; Reneker, Darrell H.
2007-03-01
The electrospinning jet was a continuous fluid flow ejected from the surface of a fluid when the applied electrical force overcomes the surface tension. The jet moved straight away from the tip and then became unstable and bent into coils. This phenomenon is the electrical bending instability [1]. When the distance between the tip and collector was reduced to less than the maximal straight segment length, the electrical bending instability did not occur. The periodic buckling of a fluid jet incident onto a surface is a striking fluid mechanical instability [2]. When axial compressive stress along the jet reached a sufficient value, it produced the fluid mechanics analogue to the buckling of a slender solid column. In the electrospinning, the buckling instability occurred just above the collector where the jet was compressed as it encountered the collector. The buckling frequencies of these jets are in the range of 10^4 to 10^5 Hz. The buckling lengths of these jets are in the range of 10 to 100μm. *Reneker,D.H.; Yarin, A. L.; Fong, H.; Koombhongse, S., Journal of Applied Physics, 87, 4531, 2000 *Tchavdarov B.; Yarin, A. L.; Radev S., Journal of Fluid Mechanics; 253, 593,1993
Buckling of hybrid nanocomposites with embedded graphene and carbon nanotubes
Chandra, Y.; Saavedra Flores, E. I.; Scarpa, F.; Adhikari, S.
2016-09-01
With the aid of atomistic multiscale modelling and analytical approaches, buckling strength has been determined for carbon nanofibres/epoxy composite systems. Various nanofibres configurations considered are single walled carbon nano tube (SWCNT) and single layer graphene sheet (SLGS) and SLGS/SWCNT hybrid systems. Computationally, both eigen-value and non-linear large deformation-based methods have been employed to calculate the buckling strength. The non-linear computational model generated here takes into account of complex features such as debonding between polymer and filler (delamination under compression), nonlinearity in the polymer, strain-based damage criteria for the matrix, contact between fillers and interlocking of distorted filler surfaces with polymer. The effect of bridging nanofibres with an interlinking compound on the buckling strength of nano-composites has also been presented here. Computed enhancement in buckling strength of the polymer system due to nano reinforcement is found to be in the range of experimental and molecular dynamics based results available in open literature. The findings of this work indicate that carbon based nanofillers enhance the buckling strength of host polymers through various local failure mechanisms.
Fatigue Crack Propagation in Steel A131 Under Ice Loading of Crushing, Bending and Buckling
Institute of Scientific and Technical Information of China (English)
DUAN Menglan(段梦兰); SONG Lisong(宋立崧); FAN Xiaodong(樊晓东); James C.M.LId; FANG Huacan(方华灿)
2001-01-01
Three types of ice loading, which are most commonly present when ice acts on structures,are chosen and simulated for use of fatigue crack propagation tests on offshore structural steel Al31. The three types of ice categorized in accordance with the failure modes when acting on structures called crushing ice, bending ice, and buckling ice,respectively. This paper presents an experimental investigation on the fatigue crack propagation behavior of widely used high strength steel A 131 for offshore jackets in the loading environment of ice crushing, bending, and buckling. The test results of fatigue crack propagation in steel A 13 l under these simulated ice loading at temperature 292K are presented and analyzed in detail in this paper. The amplitude root mean square stress intensity factor is optimized to be the fundamental parameter of fatigue crack propagation for all types of ice loading histories. The results are also compared with constant amplitude fatigue crack propagation conclusions as in wave load mode, and a joint investigation on the results from ice forces, ice-induced vibrations, and ice-induced fatigue crack propagation is conducted, Conclusions are drawn for reference in structural design and material selection for offshore structures in ice environments.
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.
Energy Technology Data Exchange (ETDEWEB)
Khedmati, Mohammad Reza; Nouri, Zorareh Hadj Mohammad Esmaeil; Roshanali, Mohammad Mahdi [Amirkabir University of Technology, Tehran (Iran, Islamic Republic of)
2012-03-15
Post-buckling behaviour and ultimate strength of imperfect corroded steel plates used in ships and other related marine structures are investigated. Nonlinear elastic-plastic large deflection finite element analyses are performed on corroded steel plates. General corrosion wastage is considered to be distributed randomly on either one or both surfaces of the analyzed plates. The effects of general corrosion are introduced into the finite element models using a random thickness surface model. The effects of corroded plate parameters on the plate post-buckling and ultimate strengths are evaluated in detail. It was realized that the aspect ratio and thickness (slenderness) of the corroded plates affects their strength characteristics. Age of the plate models affects mainly their post-buckling-strength regimes and degrades their buckling/ultimate strength. Also, nonlinear post-buckling characteristics of the plates suffering either one-side or both-side random corrosion exhibit some differences. Finally, simple empirical formulations are proposed in order to give rough estimations of the ultimate strength of randomly corroded plates.
Schaeffner, Maximilian; Götz, Benedict; Platz, Roland
2016-06-01
Buckling of slender beam-columns subject to axial compressive loads represents a critical design constraint for light-weight structures. Active buckling control provides a possibility to stabilize slender beam-columns by active lateral forces or bending moments. In this paper, the potential of active buckling control of an axially loaded beam-column with circular solid cross-section by piezo-elastic supports is investigated experimentally. In the piezo-elastic supports, lateral forces of piezoelectric stack actuators are transformed into bending moments acting in arbitrary directions at the beam-column ends. A mathematical model of the axially loaded beam-column is derived to design an integral linear quadratic regulator (LQR) that stabilizes the system. The effectiveness of the stabilization concept is investigated in an experimental test setup and compared with the uncontrolled system. With the proposed active buckling control it is possible to stabilize the beam-column in arbitrary lateral direction for axial loads up to the theoretical critical buckling load of the system.
Ansari, R.; Ajori, S.; Hassani, R.
2016-09-01
The buckling behavior of a novel three-dimensional metallic carbon nanostructure known as T6 is investigated herein employing the molecular dynamics (MD) simulations. The models are prepared on the basis of two beam- and plate-like structures to study the effects of size and geometry on the critical buckling force and critical strain. It is observed that the range of critical force for the beam-like and plate-like T6 with different geometrical parameters is approximately identical. Moreover, it is demonstrated that the critical buckling force decreases and increases by increasing the length and the width of T6, respectively. Moreover, it is shown that critical strain of beam-like T6 decreases by increasing the length, whereas, in the case of plate-like T6, the critical strain only fluctuates around 2% by increasing the width. It is further found that the buckling parameters of T6 are not comparable with those of single-walled carbon nanotubes (SWCNTs) and graphene with a relatively similar dimension. The critical buckling force and critical strain of T6 are considerably smaller than those of SWCNT and larger than those of graphene.
Jamalpoor, A.; Ahmadi-Savadkoohi, A.; Hosseini-Hashemi, Sh
2016-10-01
This paper deals with the theoretical analysis of free vibration and biaxial buckling of magneto-electro-elastic (MEE) microplate resting on Kelvin-Voigt visco-Pasternak foundation and subjected to initial external electric and magnetic potentials, using modified strain gradient theory (MSGT). Kirchhoff plate model and Hamilton’s principle are employed to extract the governing equations of motion. Governing equations were analytically solved to obtain clear closed-form expression for complex natural frequencies and buckling loads using Navier’s approach. Numerical results are presented to reveal variations of natural frequency and buckling load ratio of MEE microplate against different amounts of the length scale parameter, initial external electric and magnetic potentials, aspect ratio, damping and transverse and shear stiffness parameters of the visco-Pasternak foundation, length to thickness ratio, microplate thickness and higher modes. Numerical results of this study illustrate that by increasing thickness-to-material length scale parameter ratio, both natural frequency and buckling load ratio predicted by MSGT and modified couple stress theory are reduced because the non-dimensional length scale parameter tends to decrease the stiffness of structures and make them more flexible. In addition, results show that initial external electric and initial external magnetic potentials have no considerable influence on the buckling load ratio and frequency of MEE microplate as the microplate thickness increases.
Institute of Scientific and Technical Information of China (English)
ZHU Yong-an; WANG Fan; LIU Ren-huai
2008-01-01
The nonlinear thermal buckling of symmetrically laminated cylindrically orthotropic shallow spherical shell under temperature field and uniform pressure including transverse shear is studied.Also the analytic formulas for determining the critical buckling loads under different temperature fields are obtained by using the modified iteration method.The effect of transverse shear deformation and different temperature fields on critical buckling load is discussed.
Active stabilization of thin-wall structures under compressive loading
Welham, Jared; Calius, Emilio P.; Chase, J. Geoffrey
2003-08-01
The active suppression of elastic buckling instability has the potential to significantly increase the effective strength of thin-wall structures. Despite all the interest in smart structures, the active suppression of buckling has received comparatively little attention. This paper addresses the effects of embedded actuation on the compression buckling strength of laminated composite plates through analysis and simulation. Numerical models are formulated that include the influence of essential features such as sensor uncertainty and noise, actuator saturation and control architecture on the buckling process. Silicon-based strain sensors and diffuse laser distance sensors are both considered for use in the detection of incipient buckling behavior due to their increased sensitivity. Actuation is provided by paired distributions of piezo-electric material incorporated into both sides of the laminate. Optimal controllers are designed to command the structure to deform in ways that interfere with the development of buckling mode shapes. Commercial software packages are used to solve the resulting non-linear equations, and some of the tradeoffs are enumerated. Overall, the results show that active buckling control can considerably enhance resistance to instability under compressive loads. These buckling load predictions demonstrate the viability of optimal control and piezo-electric actuation for implementing active buckling control. Due to the importance of early detection, the relative effectiveness of active buckling control is shown to be strongly dependent on the performance of the sensing scheme, as well as on the characteristics of the structure.
Limit-point buckling analyses using solid, shell and solid.shell elements
Energy Technology Data Exchange (ETDEWEB)
Killpack, Marc; Abed-Meraim, Farid [CNRS, Metz Cedex (France)
2011-05-15
In this paper, the recently-developed solid-shell element SHB8PS is used for the analysis of a representative set of popular limit-point buckling benchmark problems. For this purpose, the element has been implemented in Abaqus/Standard finite element software and the modified Riks method was employed as an efficient path-following strategy. For the benchmark problems tested, the new element shows better performance compared to solid elements and often performs as well as state-of-the-art shell elements. In contrast to shell elements, it allows for the accurate prescription of boundary conditions as applied to the actual edges of the structure.
Energy Technology Data Exchange (ETDEWEB)
MACKEY, T.C.
2006-03-17
This report documents a detailed buckling evaluation of the primary tanks in the Hanford double shell waste tanks. The analysis 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 raise by the Office of Environment, Safety, and Health (ES&H) Oversight (EH-22) during a review (in April and May 2001) of work being performed on the double-shell tank farms, and the operation of the aging waste facility (AWF) primary tank ventilation system.
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.
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.
Axisymmetric buckling of laminated thick annular spherical cap
Dumir, P. C.; Dube, G. P.; Mallick, A.
2005-03-01
Axisymmetric buckling analysis is presented for moderately thick laminated shallow annular spherical cap under transverse load. Buckling under central ring load and uniformly distributed transverse load, applied statically or as a step function load is considered. The central circular opening is either free or plugged by a rigid central mass or reinforced by a rigid ring. Annular spherical caps have been analysed for clamped and simple supports with movable and immovable inplane edge conditions. The governing equations of the Marguerre-type, first order shear deformation shallow shell theory (FSDT), formulated in terms of transverse deflection w, the rotation ψ of the normal to the midsurface and the stress function Φ, are solved by the orthogonal point collocation method. Typical numerical results for static and dynamic buckling loads for FSDT are compared with the classical lamination theory and the dependence of the effect of the shear deformation on the thickness parameter for various boundary conditions is investigated.
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.
Buckling-driven delamination of carbon nanotube forests
Pour Shahid Saeed Abadi, Parisa; Hutchens, Shelby B.; Greer, Julia R.; Cola, Baratunde A.; Graham, Samuel
2013-06-01
We report buckling-driven delamination of carbon nanotube (CNT) forests from their growth substrates when subjected to compression. Macroscale compression experiments reveal local delamination at the CNT forest-substrate interface. Results of microscale flat punch indentations indicate that enhanced CNT interlocking at the top surface of the forest accomplished by application of a metal coating causes delamination of the forest from the growth substrate, a phenomenon not observed in indentation of as-grown CNT forests. We postulate that the post-buckling tensile stresses that develop at the base of the CNT forests serve as the driving force for delamination.
Dynamic Buckling of Column Impacted by a Rigid Body
Institute of Scientific and Technical Information of China (English)
Zhijun Han; Hongwei Ma; Shanyuan Zhang
2004-01-01
The dynamic buckling of an elastic column subjected to axial impact by a rigid body is discussed in accordance with the energy law in this paper. The equation of lateral disturbance used to analysis the problem is developed by taking into account the effect of stress wave. The power series solution of this problem has been obtained by using the power series approach. The buckling criterion of this problem is proposed by analyzing the characteristics of the solution. The relationships between critical velocity and impacting mass as well as critical velocity and critical length are given by using theoretical analysis and numerical computation.
On the buckling behavior of piezoelectric nanobeams: An exact solution
Energy Technology Data Exchange (ETDEWEB)
Jandaghian, Ali Akbar; Rahmaini, Omid [University of Zanjan, Zanjan (Iran, Islamic Republic of)
2015-08-15
In this paper, thermoelectric-mechanical buckling behavior of the piezoelectric nanobeams is investigated based on the nonlocal theory and Euler-Bernoulli beam theory. The electric potential is assumed linear through the thickness of the nanobeam and the governing equations are derived by Hamilton's principle. The governing equations are solved analytically for different boundary conditions. The effects of the nonlocal parameter, temperature change, and external electric voltage on the critical buckling load of the piezoelectric nanobeams are discussed in detail. This study should be useful for the design of piezoelectric nanodevices.
NASTRAN buckling study of a linear induction motor reaction rail
Williams, J. G.
1973-01-01
NASTRAN was used to study problems associated with the installation of a linear induction motor reaction rail test track. Specific problems studied include determination of the critical axial compressive buckling stress and establishment of the lateral stiffness of the reaction rail under combined loads. NASTRAN results were compared with experimentally obtained values and satisfactory agreement was obtained. The reaction rail was found to buckle at an axial compressive stress of 11,400 pounds per square inch. The results of this investigation were used to select procedures for installation of the reaction rail.
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
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.
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...... tendency towards pressure induced buckling due to some combination of excessive out-gassing, fragility, radiation damage, magnetic field distortion,. The analysis for design is complicated because elliptical shell chambers display a complex form of nonlinear snap buckling behavior under the external...... 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 weld reinforcement on axial plastic buckling of welded steel cylindrical shells
Institute of Scientific and Technical Information of China (English)
Chu-lin YU; Zhi-ping CHEN; Ji WANG; Shun-juan YAN; Li-cai YANG
2012-01-01
The effect of weld reinforcement on axial plastic buckling of welded steel cylindrical shells is investigated through experimental and numerical buckling analysis using six welded steel cylindrical shell specimens.The relationship between the amplitude of weld reinforcement and the axial plastic buckling critical load is explored.The effect of the material yield strength and the number of circumferential welds on the axial plastic buckling is studied.Results show that circumferential weld reinforcement represents a severe imperfect form of axially compressed welded steel cylindrical shells and the axial plastic buckling critical load decreases with the increment of the mean amplitude of circumferential weld reinforcement.The material yield strength and the number of circumferential welds are found to have no significant effect on buckling waveforms; however,the axial plastic buckling critical load can be decreased to some extent with the increase of the number of circumferential welds.
A survey of buckling of conical shells subjected to axial compression and external pressure
Directory of Open Access Journals (Sweden)
O. Ifayefunmi
2014-07-01
Full Text Available The paper reviews literature on buckling of conical shells subjected to three loading conditions: (i axial compression only, (ii external pressure only and (iii combined loading. The review is from the theoretical as well as experimental points of view. This review covers known experiments on cones from (1958 – 2012. The literature review is split thematically into the following categories: theoretical prediction of axially compressed cones, theoretical prediction of externally pressurized cones, theoretical prediction of cones under combined loading, buckling experiments on axially compressed cones, buckling experiments on externally pressurized cones, buckling experiments on cones subjected to combined loading, buckling experiments on composite conical shells, equivalent cylinder approach, effect of initial geometric imperfection on the buckling behaviour of cones and effect of imperfect boundary conditions on the buckling behaviour of cones.
Buckling of Thin Films in Nano-Scale
Wang, S.; Jia, H. K.; Sun, J.; Ren, X. N.; Li, L. A.
2010-06-01
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.
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.
Effect of Physical Nonlinearity on Local Buckling in Sandwich Beams
Koissin, Vitaly; Shipsha, Andrey; Skvortsov, Vitaly
2010-01-01
This article deals with experimental, theoretical, and FE characterization of the local buckling in foam-core sandwich beams. In the theoretical approach, this phenomena is considered in a periodic formulation (unbounded wrinkle wave); a nonlinear stress—strain response of the face material is accou
Buckling and dynamic analysis of drill strings for core sampling
Energy Technology Data Exchange (ETDEWEB)
Ziada, H.H., Westinghouse Hanford
1996-05-15
This supporting document presents buckling and dynamic stability analyses of the drill strings used for core sampling. The results of the drill string analyses provide limiting operating axial loads and rotational speeds to prevent drill string failure, instability and drill bit overheating during core sampling. The recommended loads and speeds provide controls necessary for Tank Waste Remediation System (TWRS) programmatic field operations.
Motor-Driven Bacterial Flagella and Buckling Instabilities
Vogel, Reinhard
2012-01-01
Many types of bacteria swim by rotating a bundle of helical filaments also called flagella. Each filament is driven by a rotary motor and a very flexible hook transmits the motor torque to the filament. We model it by discretizing Kirchhoff's elastic-rod theory and develop a coarse-grained approach for driving the helical filament by a motor torque. A rotating flagellum generates a thrust force, which pushes the cell body forward and which increases with the motor torque. We fix the rotating flagellum in space and show that it buckles under the thrust force at a critical motor torque. Buckling becomes visible as a supercritical Hopf bifurcation in the thrust force. A second buckling transition occurs at an even higher motor torque. We attach the flagellum to a spherical cell body and also observe the first buckling transition during locomotion. By changing the size of the cell body, we vary the necessary thrust force and thereby obtain a characteristic relation between the critical thrust force and motor torq...
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 n
Finite Element Modeling of the Buckling Response of Sandwich Panels
Rose, Cheryl A.; Moore, David F.; Knight, Norman F., Jr.; Rankin, Charles C.
2002-01-01
A comparative study of different modeling approaches for predicting sandwich panel buckling response is described. The study considers sandwich panels with anisotropic face sheets and a very thick core. Results from conventional analytical solutions for sandwich panel overall buckling and face-sheet-wrinkling type modes are compared with solutions obtained using different finite element modeling approaches. Finite element solutions are obtained using layered shell element models, with and without transverse shear flexibility, layered shell/solid element models, with shell elements for the face sheets and solid elements for the core, and sandwich models using a recently developed specialty sandwich element. Convergence characteristics of the shell/solid and sandwich element modeling approaches with respect to in-plane and through-the-thickness discretization, are demonstrated. Results of the study indicate that the specialty sandwich element provides an accurate and effective modeling approach for predicting both overall and localized sandwich panel buckling response. Furthermore, results indicate that anisotropy of the face sheets, along with the ratio of principle elastic moduli, affect the buckling response and these effects may not be represented accurately by analytical solutions. Modeling recommendations are also provided.
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
Directory of Open Access Journals (Sweden)
S. S. Daimi
2014-08-01
Full Text Available Functionally graded materials (FGMs are microscopically inhomogeneous spatial composite materials, typically composed of a ceramic-metal or ceramic-polymer pair of materials. Therefore, it is important to investigate the behaviors of engineering structures such as beams and plates made from FGMs when they are subjected to thermal loads for appropriate design. Therefore, using an improved third order shear deformation theory (TSDT based on more rigorous kinetics of displacements to predict the behaviors of functionally graded plates is expected to be more suitable than using other theories. In this paper, the improved TSDT is used to investigate thermal buckling of functionally graded plates. Temperature dependent material property solutions are adopted to investigate thermal buckling results of functionally graded plates. To obtain the solutions, the Ritz method using polynomial and trigonometric functions for defining admissible displacements and rotations is applied to solve the governing equations.
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.
Institute of Scientific and Technical Information of China (English)
谭燕秋; 王颖欣
2013-01-01
By using finite element analysis software SPA2000, 12 layers of steel frame structure were set up. In X direction and Y direction of original framework bottom column, BRC structure was constructed. The top maximum displacement, base shear and top absolute acceleration time history of three structure scheme under the action of seismic wave as follow EL - Centra wave, Taft wave and TRI_TREASURE ISLAND_90 were analyzed. The results show that comparing with the traditional steel structure, the natural vibration period of BRC structure increased. The control effect of top floor of the maximum displacement and basal shear control is very apparent. This structure has obvious damping effect.%利用有限元分析软件SPA2000,建立12层的钢框架结构,在原框架底层柱X方向、Y方向添加BRC结构.分析三种结构方案在EL-Centro波、Taft波和TRI_TREASURE ISLAND_90这三种地震波作用下的顶层最大位移、基底剪力和顶层绝对加速度时程分析这几种结构反应.结果表明:BRC结构与传统钢结构相比,自振周期有所增加,对顶层最大位移和基底剪力的控制效果非常明显,具有显著的减震效果.
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.
Lei, Xiao; Narsu, B.; Yun, Guohong; Li, Jiangang; Yao, Haiyan
2016-05-01
Surface effects play a deterministic role in the physical and mechanical properties of nanosized materials and structures. In this paper, we present a self-consistent theoretical scheme for describing the elasticity of nanowires. The natural frequency and the critical compression force of axial buckling are obtained analytically, taking into consideration the influences of lower symmetry, additional elastic parameters, surface reconstruction, surface elasticity, and residual surface stress. Applications of the present theory to elastic systems for the axially oriented Si and Cu nanowires and Ag axially oriented nanowires yield good agreement with experimental data and calculated results. The larger positive value of the new elastic parameter c12α taken into account for Si oriented nanowires drives the curves of natural frequency and critical compression force versus thickness towards the results obtained from density functional theory simulation. Negative surface stress decreases the critical load for axial buckling, thus making the nanowires very easy to bend into various structures. The present study is envisaged to provide useful insights for the design and application of nanowire-based devices.
Flow sensing by buckling monitoring of electrothermally actuated double-clamped micro beams
Kessler, Y.; Krylov, S.; Liberzon, A.
2016-08-01
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.
Birman, Victor; Byrd, Larry W.
2008-02-01
The interest to functionally graded materials (FGM) and structures has been generated by their potential advantages, including enhanced thermal properties, reduced or eliminated delamination concerns, a potential for an improved stress distribution, etc. Various aspects of the processing, design, micromechanics and analysis of FGM have been outlined in a number of reviews, mentioned here are [1-3]. In particular, functionally graded panels may be advantageous compared to their conventional counterparts in numerous applications. However, a typical FGM panel is asymmetric about its middle plane resulting in lower buckling loads and fundamental frequencies as well as higher stresses and deformations than the counterpart with a symmetric distribution of the same constituents. The reduced stiffness of FGM panels can be compensated by reinforcing them with stringers. For example, metallic stringers at the metal-rich surface of a FGM ceramic-metal panel may provide an efficient solution enabling a designer to increase both buckling loads as well as natural frequencies. The list of studies on optimization of FGM is extensive as could be anticipated for such tailored structural elements. For example, recent papers by Batra and his collaborators present optimization of the natural frequencies of a FGM plate through material grading [4] and through the graded fiber orientation [5]. The present paper is concerned with an optimum design of the system of stringers for a specified FGM panel. The task is to design the lightest system of stringers enabling the panel to achieve prescribed buckling loads or fundamental frequency.
Institute of Scientific and Technical Information of China (English)
Blake M. Andrews; Junho Song; Larry A. Fahnestock
2009-01-01
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.
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.
ON THE ORIENTATION OF BUCKLING DIRECTION OF ANISOTROPIC ELASTIC PLATE UNDER UNIAXIAL COMPRESSION
Institute of Scientific and Technical Information of China (English)
Zhang Yitong
2001-01-01
The theory of small deformation superimposed on a large deformation of an elastic solid is used to investigate the buckling of anisotropic elastic plate under uniaxial compression. The buckling direction (the direction of buckling wave) is generally not aligned with the compression direction. The equation for determining the buckling direction is obtained. It is found that the out-of-plane buckling of anisotropic elastic plate is possible and both buckling conditions for flexural and extensional modes are presented. As a specific case of buckling of anisotropic elastic plate, the buckling of an orthotropic elastic plate subjected to a compression in a direction that forms an arbitrary angle with an elastic principal axis of the materials is analyzed. It is found that the buckling direction depends on the angle between the compression direction and the principal axis of the materials, the critical compressive force and plate-thickness parameters.In the case that the compression direction is aligned with the principal axis of the materials, the buckling direction will be aligned with the compression one irrespective of critical compressive force and plate-thickness.
Post-buckling behaviour of carbon-nanotube-reinforced nanocomposite plate
Indian Academy of Sciences (India)
ASHISH SRIVASTAVA; DINESH KUMAR
2017-01-01
The aim of the present paper is to investigate the buckling and post-buckling behaviour ofnanocomposite plate having randomly oriented carbon nanotubes (CNTs) reinforced in magnesium (Mg) under uni-axial compression. The effect of non-bonded interaction at the interface between CNT and matrix is considered through a cohesive zone model, used to predict the elastic property of the interphase, while evaluating the elastic properties of the nanocomposite using a representative volume element. A special purpose program based on finite-element formulation is developed to study the buckling and post-buckling behaviour of nanocomposite plate. The formulation is based on first-order shear deformation theory in conjunction with geometrical non-linearity as per von Karman’s assumptions. A parametric study is conducted to investigate theeffects of interphase between CNT and matrix, short-CNT and long-CNT reinforcements and boundary conditions on buckling and post-buckling response of nanocomposite plate. It is found that imperfect bonding between CNT and Mg results in the loss of buckling and post-buckling strength, as compared with perfect bonding, of CNT–Mg nanocomposite plate. It is also concluded that buckling and post-buckling strength ishigher for long-CNT-reinforced nanocomposite plate than that of short-CNT einforcement, irrespective of bonding between CNT and matrix material.
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.
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.
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...
BUCKLING ANALYSIS UNDER COMBINED LOADING OF THIN-WALLED PLATE ASSEMBLIES USING BUBBLE FUNCTIONS
Institute of Scientific and Technical Information of China (English)
Gao Xuanneng; Zou Yinsheng; Zhou Xuhong
2000-01-01
Bubble functions are finite element modes that are zero on the boundary of the element but nonzero at the other point. The present paper adds bubble functions to the ordinary Complex Finite Strip Method(CFSM) to calculate the elastic local buckling stress of plates and plate assemblies. The results indi cate that the use of bubble functions greatly improves the convergence of the Finite Strip Method(FSM) in terms of strip subdivision, and leads to much smaller storage required for the structure stiffness and stability matrices. Numerical examples are given, including plates and plate structures subjected to a combination of longitudinal and transverse compression, bending and shear. This study illustrates the power of bubble func tions in solving stability problems of plates and plate structures.
Saavedra, K.; Allix, O.; Gosselet, P.
2012-08-01
This paper investigates a computational strategy for studying the interactions between multiple through-the-width delaminations and global or local buckling in composite laminates taking into account possible contact between the delaminated surfaces. In order to achieve an accurate prediction of the quasi-static response, a very refined discretization of the structure is required, leading to the resolution of very large and highly nonlinear numerical problems. In this paper, a nonlinear finite element formulation along with a parallel iterative scheme based on a multiscale domain decomposition are used for the computation of 3D mesoscale models. Previous works by the authors already dealt with the simulation of multiscale delamination assuming small perturbations. This paper presents the formulation used to include geometric nonlinearities into this existing multiscale framework and discusses the adaptations that need to be made to the iterative process in order to ensure the rapid convergence and the scalability of the method in the presence of buckling and delamination. These various adaptations are illustrated by simulations involving large numbers of DOFs.
Institute of Scientific and Technical Information of China (English)
梁珂; 孙秦; Zafer Gurdal
2013-01-01
基于Koiter的初始后屈曲理论以及Newton法的增量迭代技术,提出了一种能够自动跟踪非线性平衡路径的降阶方法.降阶模型中摄动载荷以及主路径上变形位移的引入使摄动展开能够在平衡路径上的任意一点处进行；在每个摄动步中将求解降阶模型得到的非线性解作为结构响应的初始预测,然后采用有限元模型计算的残余力对解进行修正,最后以修正后的解作为下一个摄动步的已知展开点,并通过更新降阶模型来反映当前结构刚度的变化.算例分析表明,该方法不仅具有很高的非线性分析精度,而且需要计算的线性方程组(阶数与有限元全模型阶数相当)的数目远小于常规的非线性有限单元法.%A kind of solar heat reflection material, Na2O-ZnO-Fe2O3-P2O5, was prepared via coprecipitation and was characterized by means of UV-Vis-NIR spectroscopy and XRD. The results show that (1) when the Zn/Fe molar ratio is 9.00, the phase composition of the products calcined at 7001 varies with the Zn/P molar ratio (1. 52, 1. 02, 0. 76 and 0. 61) , in which a Zn/P molar ratio of 0. 61 may result in a single-phase NaZnPO4 structure while the other ratios may result in multiphase structures; (2) when the Zn/P molar ratio is 0. 61 , the phase composition of the products calcined at 700℃ is independent of the Zn/Fe molar ratio (19. 00 , 9. 00 , 5. 67 and 4. 00) , with all the products being of a single-phase NaZnPO4 structure, however, these products become dark and the reflectance decreases with the decrease of the Zn/Fe molar ratio; and (3) at a Zn/P molar ratio of 0.61 and a Zn/Fe molar ratio of 9.00, the products calcined at 500 ~ 800℃ are all of a single-phase NaZnPO4 structure, and the products become dark and the reflectance decreases with the increase of the calcination temperature, for instance, the products calcined at 600 and 7001 are respectively orange and red, with their reflectance being 80. 7% and 72
Directory of Open Access Journals (Sweden)
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
Oblique and Herringbone Buckling Analysis of Steel Strip by Spline FEM
Institute of Scientific and Technical Information of China (English)
QIN Jian; ZHANG Qing-dong; HUANG Ke-fu
2011-01-01
The tilted waves in steel strip during rolling and leveling of sheet metal can be classified into two different types of buckling, oblique and herringbone buckling, respectively. Numerical considerations of oblique and herringbone buckling phenomena are dealt with by the spline finite element method （FEM）. It is pointed out that the shear stress due to residual strains caused by the rolling process or applied non-uniform loading is the main reason of oblique and herringbone buckle. According to the analysis of stress distribution in plane, the appropriate initial strain patterns are adopted and the corresponding buckling modes are calculated by the spline FEM. The developed numerical model provides an estimation of buckling critical load and wave configuration.
Buckling Response of Pipe-in-Pipe Systems Subjected to Bending
Institute of Scientific and Technical Information of China (English)
王哲; 陈志华; 刘红波; 何永禹; 马克俭
2015-01-01
The buckling response of pipe-in-pipe(PIP)systems subjected to bending is investigated in this paper. A set of parameterized models are established to explore the bending characteristics of the PIP systems through eigen-value buckling analysis and nonlinear post-buckling analysis. The results show that the length of PIP systems and the height of centralizers are the most significant factors that influence the buckling moment, ultimate bending mo-ment and buckling mode; the other geometric characteristics, such as initial geometric imperfection and friction between centralizers and outer pipes, evidently influence the post-buckling path and ductility of PIPs; the equivalent bending stiffness is dependent on the length and centralizers. Moreover, the range of equivalent bending stiffness is also discussed.
Flexural-torsional buckling analysis of angle-bar stiffened plates
Energy Technology Data Exchange (ETDEWEB)
Ahmad, Rahbar Ranji [Amirkabir University of Technology, Tehran (Iran, Islamic Republic of)
2015-09-15
The interaction of flexural-torsional buckling modes is critical for stiffened plates with asymmetric stiffeners. However, this interaction is ignored in all design rules because it is complex to characterize. In the literature, the presence of an attached plate is ignored, and stiffened plate is treated as an ordinary asymmetric beam. In the flexural buckling mode, stiffener and the attached plate buckle together; in the torsional buckling mode, the attached plate cannot freely rotate with stiffener. Basic equations of the flexural-torsional buckling modes are deduced based on hybrid beam concept and a new strain distribution assumption for sideway bending of stiffeners. Elastic buckling stresses of different angle-bar stiffened plates are calculated and compared with those generated by the Finite element method (FEM) and those available in the literature. The present method has better agreements with FEM.
BEAM 1.7: development for modelling fuel element and bundle buckling strength
Energy Technology Data Exchange (ETDEWEB)
Cheng, G.; Xu, S.; Xu, Z.; Paul, U.K. [Atomic Energy of Canada, Mississauga, Ontario (Canada)
2010-07-01
This paper describes BEAM, an AECL developed computer program, used to assess mechanical integrity of CANDU fuel bundles. The BEAM code has been developed to satisfy the need for buckling strength analysis of fuel bundles. Buckling refers to the phenomenon where a compressive axial load is large enough that a small lateral load can cause large lateral deflections. The buckling strength refers to the critical compressive axial load at which lateral instability is reached. The buckling strength analysis has practical significance for the design of fuel bundles, where the buckling strength of a fuel element/bundle is assessed so that the conditions leading to bundle jamming in the pressure tube are excluded. This paper presents the development and qualification of the BEAM code, with emphasis on the theoretical background and code implementation of the newly developed fuel element/bundle buckling strength model. (author)
Caught in the Act: Direct Detection of Galactic Bars in the Buckling Phase
Erwin, Peter
2016-01-01
The majority of massive disk galaxies, including our own, have stellar bars with vertically thick inner regions -- so-called "boxy/peanut-shaped" (B/P) bulges. The most commonly suggested mechanism for the formation of B/P bulges is a violent vertical "buckling" instability in the bar, something that has been seen in N-body simulations for over twenty years, but never identified in real galaxies. Here, we present the first direct observational evidence for ongoing buckling in two nearby galaxies (NGC 3227 and NGC 4569), including characteristic asymmetric isophotes and (in NGC 4569) stellar-kinematic asymmetries that match buckling in simulations. This confirms that the buckling instability takes place and produces B/P bulges in real galaxies. A toy model of bar evolution yields a local fraction of buckling bars consistent with observations if the buckling phase lasts ~0.5--1 Gyr, in agreement with simulations.
Elastocapillary instability under partial wetting conditions: bending versus buckling
Andreotti, Bruno; Das, Siddhartha; Snoeijer, Jacco H
2011-01-01
The elastocapillary instability of a flexible plate plunged in a liquid bath is analysed theoretically. We show that the plate can bend due to two separate destabilizing mechanisms, when the liquid is partially wetting the solid. For contact angles $\\theta_e > \\pi/2$, the capillary forces acting tangential to the surface are compressing the plate and can induce a classical buckling instability. However, a second mechanism appears due to capillary forces normal to surface. These induce a destabilizing torque that tends to bend the plate for any value of the contact angle $\\theta_e > 0$. We denote these mechanisms as "buckling" and "bending" respectively and identify the two corresponding dimensionless parameters that govern the elastocapillary stability. The onset of instability is determined analytically and the different bifurcation scenarios are worked out for experimentally relevant conditions.
Buckling of Bilayer Laminates - A Novel Approach to Synthetic Papillae
2013-10-01
a very small region. This method of immobilization was used in some experiments. We also d indentatio with a sin this layer scale inde be measu...must select the lowest energy mode. (Fig. 8). (3) Radial buckling of an annulus where the buckling mode cannot be predicted by linear stability...conductivity, volume conservation can be approximated, at least for small deformations. We considered two typical forms of the anisotropic thermal expansion
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.
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
Orbital cellulitis following silicone-sponge scleral buckles
Nemet AY; Ferencz JR; Segal O; Meshi A
2013-01-01
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 i...
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.
A buckling mechanism for ESCRT-III budding
Lenz, Martin; Joanny, Jean-François
2009-01-01
The ESCRT-III protein complex binds to the membrane of eukaryotic cells, causing it to bud into long tubes. Here we propose that this budding is akin to a buckling instability. We analyze the linear stability of flat ESCRT-III-dressed membranes and account for the formation of long tubes. We study strongly deformed dressed membranes and their bifurcation diagram numerically. Our mechanism is compatible with reasonable in vivo parameter values and we propose an experiment allowing its validation.
Li, Yupeng; Kim, Hyung-Ick; Wei, Bingqing; Kang, Junmo; Choi, Jae-Boong; Nam, Jae-Do; Suhr, Jonghwan
2015-08-01
The local buckling behavior of vertically aligned carbon nanotubes (VACNTs) has been investigated and interpreted in the view of a collective nanotube response by taking van der Waals interactions into account. To the best of our knowledge, this is the first report on the case of collective VACNT behavior regarding van der Waals force among nanotubes as a lateral support effect during the buckling process. The local buckling propagation and development of VACNTs were experimentally observed and theoretically analyzed by employing finite element modeling with lateral support from van der Waals interactions among nanotubes. Both experimental and theoretical analyses show that VACNTs buckled in the bottom region with many short waves and almost identical wavelengths, indicating a high mode buckling. Furthermore, the propagation and development mechanism of buckling waves follow the wave damping effect.The local buckling behavior of vertically aligned carbon nanotubes (VACNTs) has been investigated and interpreted in the view of a collective nanotube response by taking van der Waals interactions into account. To the best of our knowledge, this is the first report on the case of collective VACNT behavior regarding van der Waals force among nanotubes as a lateral support effect during the buckling process. The local buckling propagation and development of VACNTs were experimentally observed and theoretically analyzed by employing finite element modeling with lateral support from van der Waals interactions among nanotubes. Both experimental and theoretical analyses show that VACNTs buckled in the bottom region with many short waves and almost identical wavelengths, indicating a high mode buckling. Furthermore, the propagation and development mechanism of buckling waves follow the wave damping effect. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03581c
Controlled buckling of thin film on elastomeric substrate in large deformation
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
Electronic systems with large stretchability have many applications.A precisely controlled buckling strategy to increase the stretchability has been demonstrated by combining lithographically patterned surface bonding chemistry and a buckling process.The buckled geometry was assumed to have a sinusoidal form,which may result in errors to determine the strains in the film.A theoretical model is presented in this letter to study the mechanics of this type of thin film/substrate system by discarding the ass...
Low voltage driven RF MEMS capacitive switch using reinforcement for reduced buckling
Bansal, Deepak; Bajpai, Anuroop; Kumar, Prem; Kaur, Maninder; Kumar, Amit; Chandran, Achu; Rangra, Kamaljit
2017-02-01
Variation in actuation voltage for RF MEMS switches is observed as a result of stress-generated buckling of MEMS structures. Large voltage driven RF-MEMS switches are a major concern in space bound communication applications. In this paper, we propose a low voltage driven RF MEMS capacitive switch with the introduction of perforations and reinforcement. The performance of the fabricated switch is compared with conventional capacitive RF MEMS switches. The pull-in voltage of the switch is reduced from 70 V to 16.2 V and the magnitude of deformation is reduced from 8 µm to 1 µm. The design of the reinforcement frame enhances the structural stiffness by 46 % without affecting the high frequency response of the switch. The measured isolation and insertion loss of the reinforced switch is more than 20 dB and 0.4 dB over the X band range.
Nonlinear features identified by Volterra series for damage detection in a buckled beam
Directory of Open Access Journals (Sweden)
Shiki S. B.
2014-01-01
Full Text Available The present paper proposes a new index for damage detection based on nonlinear features extracted from prediction errors computed by multiple convolutions using the discrete-time Volterra series. A reference Volterra model is identified with data in the healthy condition and used for monitoring the system operating with linear or nonlinear behavior. When the system has some structural change, possibly associated with damage, the index metrics computed could give an alert to separate the linear and nonlinear contributions, besides provide a diagnostic about the structural state. To show the applicability of the method, an experimental test is performed using nonlinear vibration signals measured in a clamped buckled beam subject to different levels of force applied and with simulated damages through discontinuities inserted in the beam surface.
Xu, Sheng; Yan, Zheng; Jang, Kyung-In; Huang, Wen; Fu, Haoran; Kim, Jeonghyun; Wei, Zijun; Flavin, Matthew; McCracken, Joselle; Wang, Renhan; Badea, Adina; Liu, Yuhao; Xiao, Dongqing; Zhou, Guoyan; Lee, Jungwoo; Chung, Ha Uk; Cheng, Huanyu; Ren, Wen; Banks, Anthony; Li, Xiuling; Paik, Ungyu; Nuzzo, Ralph G; Huang, Yonggang; Zhang, Yihui; Rogers, John A
2015-01-01
Complex three-dimensional (3D) structures in biology (e.g., cytoskeletal webs, neural circuits, and vasculature networks) form naturally to provide essential functions in even the most basic forms of life. Compelling opportunities exist for analogous 3D architectures in human-made devices, but design options are constrained by existing capabilities in materials growth and assembly. We report routes to previously inaccessible classes of 3D constructs in advanced materials, including device-grade silicon. The schemes involve geometric transformation of 2D micro/nanostructures into extended 3D layouts by compressive buckling. Demonstrations include experimental and theoretical studies of more than 40 representative geometries, from single and multiple helices, toroids, and conical spirals to structures that resemble spherical baskets, cuboid cages, starbursts, flowers, scaffolds, fences, and frameworks, each with single- and/or multiple-level configurations.
Buckling Experiment on Anisotropic Long and Short Cylinders
Directory of Open Access Journals (Sweden)
Atsushi Takano
2016-07-01
Full Text Available A buckling experiment was performed on anisotropic, long and short cylinders with various radius-to-thickness ratios. The 13 cylinders had symmetric and anti-symmetric layups, were between 2 and 6 in terms of the length-to-radius ratio, between 154 and 647 in radius-to-thickness ratio, and made of two kinds of carbon fiber reinforced plastic (CFRP prepreg with high or low fiber modulus. The theoretical buckling loads for the cylinders were calculated from the previously published solution by using linear bifurcation theory considering layup anisotropy and transverse shear deformation and by using deep shell theory to account for the effect of length and compared with the test results. The theoretical buckling loads for the cylinders were calculated from the previously published solution by using linear bifurcation theory considering layup anisotropy and transverse shear deformation and by using deep shell theory to account for the effect of length. The knockdown factor, defined as the ratio of the experimental value to the theoretical value, was found to be between 0.451 and 0.877. The test results indicated that a large length-to-radius ratio reduces the knockdown factor, but the radius-to-thickness ratio and other factors do not affect it.
Buckling patterns of gold thin films on silicon substrates: Formation of superimposed blisters
Colin, J.; Coupeau, C.; Durinck, J.; Grilhé, J.
2009-06-01
Buckling phenomena leading to the formation of superimposed blisters have been experimentally observed with the help of a confocal interferometric microscope onto the surface of gold thin films deposited on silicon substrates. Assuming that residual folding effects resulting from plastic deformation mechanisms take place in the film during its morphological evolution, different probable scenarios for the formation of the observed buckling patterns are elaborated in the framework of the Föppl-von Karman's theory of thin plates. Multi-step buckling with growing interface delamination is considered for the first scenario while a single or multi-step buckling at a given delamination width is assumed for the other ones.
Molecular dynamics simulation on the buckling behavior of GaN nanowires under uniaxial compression
Energy Technology Data Exchange (ETDEWEB)
Wang, Zhiguo; Zu, Xiaotao; Yang, Li; Gao, Fei; Weber, William J
2008-01-01
Molecular dynamics simulation is one of the most promising methods for investigating the mechanical behavior of nanostructures, such as nanowires and nanotubes. Atomistic simulations are performed to investigate the buckling properties of [001], [11¯0] and [110] oriented GaN nanowires under uniaxial compression, these three types of nanowires correspond to experimentally synthesized nanowires. The effects of simulation temperature, and wire length on the buckling behavior are investigated. The simulation results show that critical stress decreases with the increase of wire length, which is in agreement with the Euler theory. Buckling occurs as a result of dynamic processes, buckling strain (and corresponding stress) decreases as temperature is increased.
Ko, William L.; Jackson, Raymond H.
1991-01-01
Combined compressive and shear buckling analysis was conducted on flat rectangular sandwich panels with the consideration of transverse shear effects of the core. The sandwich panel is fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that the square panel has the highest combined load buckling strength, and that the buckling strength decreases sharply with the increases of both temperature and panel aspect ratio. The effect of layup (fiber orientation) on the buckling strength of the panels was studied in detail. The metal matrix composite sandwich panel was much more efficient than the sandwich panel with nonreinforced face sheets and had the same specific weight.
Energy Technology Data Exchange (ETDEWEB)
Yao, T.; Fujikubo, M.; Yanagihara, D. [Hiroshima University, Hiroshima (Japan). Faculty of Engineering
1996-04-10
A hull structure is constituted by thin panels, and reinforced longitudinally and laterally by stiffened members to increase the effectiveness of the structure. In order to attain findings on buckling and plastic collapse behavior of stiffened plates, this paper describes analysis of elasto-plastic large deflection by using the finite element method on thin stiffened plates having flat-bars and angle-bars. The analysis includes the case of an aspect ratio being 5.0 and the case to consider welding residual stress. Considerations were given on cross sectional shape, panel aspect ratio and effects of initial welding imperfections against the buckling and plastic collapse behavior of the stiffened plates. The angle-bars tend to cause secondary buckling more easily because it has greater bending and twisting rigidity, and stronger constraint against deflection than the flat-bars. When the aspect ratio is larger and the span is longer, the ultimate strength declines, and the withstand power after the ultimate strength decreases rapidly. Existence of the residual stress tends to make the secondary buckling occur more easily. The secondary buckling affects little the withstand power after the ultimate strength. 3 refs., 7 figs., 1 tab.
Investigation of scleral buckling by CO{sub 2} laser
Energy Technology Data Exchange (ETDEWEB)
Maswadi, S
2001-05-01
This thesis investigates the effect of using the infrared wavelength CO{sub 2} laser (10.6{mu}m) as a localised heat source for inducing scleral buckling on eyes. Retinal detachment disease is a major cause of blindness and the scleral buckling is an important technique used in treatment. A radio-frequency excited 10.6{lambda}m laser source is used to heat collagen in the sclera above its shrinkage temperature so as to produce a localised indentation and deformation in the human eye (in vitro). Basic measurements of the onset shrinkage temperatures of porcine and human sclera are taken. Optical properties of sclera tissue at 10.6{mu}m are also determined to provide information about the interaction of the CO{sub 2} laser with the sclera. It is found that CO{sub 2} laser radiation is highly absorbed by the scleral water. Optical diffraction technique is investigated to quantify in-plane deformation in the sclera tissue as result of heating by producing grating on porcine and human sclera using the ArF laser (193nm). Photothermal deflection technique is also used to investigate scleral ablation by using the TEA and Ultrapulse CO{sub 2} laser. This technique provides a useful guide to the regime where ablation rather than heat shrinkage of collagen in the sclera will dominate using the Ultrapulse CO{sub 2} laser. A quantitative assessment of buckling using the technique of projection moire interferometry is described which allows a non-contact measurement to be made of the out-of-plane displacement by laser radiation. In-plane surface strain (shrinkage) has also been demonstrated using in-situ optical microscopy of the laser treated eye. The moire method is suitable to obtain information on buckling in real time and to obtain a three-dimensional view of the eye surface as laser treatment proceeds. A theoretical heat flow model is described for predicting the temperature profile produced in the sclera using the Ultrapulse CO{sub 2} laser. For appropriate exposure
On dynamic buckling of cylindrical shell in soil subjected to blast loads%爆炸荷载作用下土埋圆柱壳动力屈曲分析
Institute of Scientific and Technical Information of China (English)
刘新宇; 马林建; 方秦; 张川; 马淑娜
2012-01-01
To investigate the dynamic stability of cylindrical shell in shallow soil,the calculation model of soil spring-shell interaction was established based on the stress characteristic of the shell subjected to blast loads. The nonlinear FEM method was utilized to solve the structural dynamic responses. The B-R buckling rule was applied to determining the critical buckling load following the numerical simulation of the shell buckling progress. The influence of the soil layer deformation on the structural buckling load was analyzed in detail. The quantitative relationship between the buckling load of the structure and the elastic modulus of the soil was obtained. The results indicate that the structural buckling load increases nonlinear-ly with the soil elastic modulus.%为研究爆炸动载作用下土中圆柱壳结构的动力稳定特性,依据爆炸动载作用下土埋圆柱壳的受力特征,建立了考虑土与圆柱壳相互作用的土弹簧一柱壳计算模型,应用非线性有限元方法进行了数值计算.在圆柱壳结构动力屈曲过程数值分析的基础上,运用B-R屈曲准则判定土埋圆柱壳在爆炸动载作用下的屈曲临界荷载,并重点讨论了土层变形性质对圆柱壳屈曲荷载的影响,得到了土中圆柱壳屈曲荷载和土体弹性常数K的定量关系.结果表明,屈曲荷载随土体弹性常数的增大而非线性增大.
Buckle, ruck and tuck: A proposed new model for the response of graphite to neutron irradiation
Energy Technology Data Exchange (ETDEWEB)
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.
Saavedra, Karin; Gosselet, Pierre; 10.1002/nme.4305
2012-01-01
This paper investigates a computational strategy for studying the interactions between multiple through-the-width delaminations and global or local buckling in composite laminates taking into account possible contact between the delaminated surfaces. In order to achieve an accurate prediction of the quasi-static response, a very refined discretization of the structure is required, leading to the resolution of very large and highly nonlinear numerical problems. In this paper, a nonlinear finite element formulation along with a parallel iterative scheme based on a multiscale domain decomposition are used for the computation of 3D mesoscale models. Previous works by the authors already dealt with the simulation of multiscale delamination assuming small perturbations. This paper presents the formulation used to include geometric nonlinearities into this existing multiscale framework and discusses the adaptations that need to be made to the iterative process in order to ensure the rapid convergence and the scalabi...
How the antimicrobial peptides destroy bacteria cell membrane: Translocations vs. membrane buckling
Golubovic, Leonardo; Gao, Lianghui; Chen, Licui; Fang, Weihai
2012-02-01
In this study, coarse grained Dissipative Particle Dynamics simulation with implementation of electrostatic interactions is developed in constant pressure and surface tension ensemble to elucidate how the antimicrobial peptide molecules affect bilayer cell membrane structure and kill bacteria. We find that peptides with different chemical-physical properties exhibit different membrane obstructing mechanisms. Peptide molecules can destroy vital functions of the affected bacteria by translocating across their membranes via worm-holes, or by associating with membrane lipids to form hydrophilic cores trapped inside the hydrophobic domain of the membranes. In the latter scenario, the affected membranes are strongly corrugated (buckled) in accord with very recent experimental observations [G. E. Fantner et al., Nat. Nanotech., 5 (2010), pp. 280-285].
Da Silva, Andre; Limam, Ali; Lorioux, Fabien; Radulovic, Serge; Taponier, Vincent; Leudiere, Vincent
2012-07-01
The results of an experimental study on the buckling of thin cylindrical shells (R/t = 450, 675, 1350) subjected to combined loads are presented here. The aim of the present study is to improve the design of shells in the aerospace industry, which mainly uses the NASA SP8007 rule, established in the late 1960s. Two load cases are examined: combined internal pressure and bending; and combined internal pressure and compression. The tests point out the two main flaws of the NASA SP8007. First, it is obviously over- conservative for low values of internal pressure, which has been widely acknowledged. Then, the experiments show the effect of plasticity for higher internal pressures, which is not well accounted for in the SP8007 design rule, and leads to a drop in the load-bearing capacity of the structure.
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.
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.
Directory of Open Access Journals (Sweden)
Rubens Camargo Siqueira
2007-03-01
Full Text Available PURPOSE: To compare the surgical results of vitrectomy with and without scleral buckling for rhegmatogenous retinal detachment (RD. METHODS: Fifty-one patients with rhegmatogenous retinal detachment with proliferative vitreoretinopathy (PVR at different stages were submitted to pars plana vitrectomy as the primary surgery, 23 patients (45.09% with scleral buckle (group I and 28 (54.90% without scleral buckle (group II. Visual acuity, anterior segment complications, intraocular pressure, strabismus and retina reattachment rate were evaluated in both groups. RESULTS: The anatomical success and postoperative complications were similar in both groups. Retinal reattachment was achieved in 20 of 23 eyes (87% of group I and in 24 of 28 eyes (85.7% of group II after the initial surgery (p=1.000. Elevated intraocular pressure was noted in 2 eyes (8.7% of group I and 1 eye (3.6% of group II (p=0.583. Corneal abnormalities were seen in 3 eyes (13% of group I and 2 eyes (7.19% of the group II (p=0.647. Visual acuity improved from a preoperative median of 20/200 to a median of 20/100 in group 1 and from 20/400 to 20/100 in group 2; the difference between the two groups was statistically significant (pOBJETIVOS: Comparar os resultados cirúrgicos da vitrectomia com e sem "buckle" escleral para descolamento da retina regmatogênico (DR. MÉTODOS: Cinqüenta e um pacientes com descolamento da retina regmatogênico com proliferação vitreorretiniana (PVR em diferentes estádios foram submetidos a vitrectomia pars plana como cirurgia primária; 23 pacientes (45,09% com buckle escleral (grupo 1 e 28 pacientes (54,90% sem "buckle" escleral (grupo 2. Acuidade visual, complicações do segmento anterior, pressão intra-ocular, estrabismo e razão do redescolamento da retina foram avaliados em ambos os grupos. RESULTADOS: O sucesso anatômico e complicações pós-operatórias foram semelhantes em ambos os grupos. A reaplicação da retina foi obtida em 20 dos 23
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.
Buckling of composite beams with two enveloped delaminations: Lower and upper bounds
Parlapalli, M.S.R.; Shu, Dongwei; Chai, Gin B.
2008-01-01
Lower and upper bounds of the buckling load of a composite beam with two enveloped delaminations are obtained from newly developed analytical models. The characteristic equation, governing the delamination buckling is derived by using Euler–Bernoulli beam and classical lamination theory, performing
Numerical and Exact Solution of Buckling Load For Beam on Elastic Foundation
Directory of Open Access Journals (Sweden)
Roland JANČO
2013-06-01
Full Text Available In this paper we will be presented the exact solution of buckling load for supported beam on elastic foundation. Exact solution will be compared with numerical solution by FEM in our code in Matlab. Implementation of buckling to FEM will be presented here.
Energy Technology Data Exchange (ETDEWEB)
Shen Huishen, E-mail: hsshen@mail.sjtu.edu.c [Department of Engineering Mechanics, Shanghai Jiao Tong University, Shanghai 200030 (China); State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200030 (China)
2010-08-30
A nonlocal shear deformable shell model is developed for buckling of microtubules embedded in an elastic matrix of cytoplasm under bending in thermal environments. The results reveal that the lateral constraint has a significant effect on the buckling moments of a microtubule when the foundation stiffness is sufficiently large.
A Nonlinear Theory of Bending and Buckling of Thin Elastic Shallow Spherical Shells
Kaplan, A; Fung, Y C
1954-01-01
The problem of the finite displacement and buckling, of a shallow spherical dome is investigated both theoretically and experimentally. Experimental results seem to indicate that the classical criterion of buckling is applicable to very shallow spherical domes for which the theoretical calculation was made. A transition to energy criterion for higher domes is also indicated.
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
Institute of Scientific and Technical Information of China (English)
Yitong Zhang; Cuiyu Li; Jiafu Xu
2005-01-01
With the aid of the micro-mechanical model of knitted fabric proposed in Part 1 we analyze the buckling of a knitted fabric sheet when it is subjected to a tension along the wale direction. The large deformation of the fabric sheet in the critical configuration is considered and, to avoid possible deviation due to the approximation of the theory of thin plate, the three-dimensional theory of instability is used.The fabric sheet is considered as a three-dimensional body and all boundary conditions are satisfied. It is shown that the buckling of the fabric sheet is possible, two buckling modes and the corresponding buckling conditions are obtained, but only the flexural mode is physically possible as observed in experiments.
Distortional buckling modes of semi-discretized thin-walled columns
DEFF Research Database (Denmark)
Andreassen, Michael Joachim; Jönsson, Jeppe
2012-01-01
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...... for column buckling analysis and identification of buckling modes. The extension is based on an initial stress approach by addition of the related potential energy terms. The potential energy of a single deformation mode is formulated based on a discretization of the cross section. Through variations...... eigenvalue problem. This gives the buckling mode shapes and the associated eigenvalues corresponding to the bifurcation load factors. Thus the buckling modes are found directly by the analytical solution of the coupled GBT-equations without modal decomposition. Illustrative examples showing global column...
BUCKLING ANALYSIS OF WOVEN FABRIC UNDER UNIAXIAL TENSION IN ARBITRARY DIRECTION
Institute of Scientific and Technical Information of China (English)
张义同; 徐家福
2002-01-01
The buckling of a fabric sheet subjected to a uniaxial tension in a direction mak-ing arbitrary angle, θ (0°＜θ＜ 90°) say, with respect to that of warp is investigated.The equation to determine the buckling direction angle, β say, was obtained and, as illus-tration, the solution curves of the equation for θ = 45° and θ = 30° were plotted. It is shownthat when the fabric sheet is subjected to tension in non-warp/non-weft direction the out-of-plane buckling of fabric is possible, two buckling modes (flexural and extensional modes)and the both corresponding buckling conditions are obtained. The results given by ZHANGand FU ( 2001 ) are the special cases of this paper.
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....... The local buckling caused high strains and stresses in the surrounding of the delamination, which exceeded the material design properties and therefore should be considered as dangerous. Delaminations placed near the mid-surface of the cap did not have a significant effect on the blade response under normal...... operation conditions. In the simulations the static load exceeded the design load by more than 40% before delamination growth or cap buckling occurred. It could be concluded that delamination induced near-surface buckling modes have to be considered critical due to an onset of local sublaminate buckling...
Khang, Dahl-Young; Xiao, Jianliang; Kocabas, Coskun; MacLaren, Scott; Banks, Tony; Jiang, Hanqing; Huang, Yonggang Y; Rogers, John A
2008-01-01
We have studied the scaling of controlled nonlinear buckling processes in materials with dimensions in the molecular range (i.e., approximately 1 nm) through experimental and theoretical studies of buckling in individual single-wall carbon nanotubes on substrates of poly(dimethylsiloxane). The results show not only the ability to create and manipulate patterns of buckling at these molecular scales, but also, that analytical continuum mechanics theory can explain, quantitatively, all measurable aspects of this system. Inverse calculation applied to measurements of diameter-dependent buckling wavelengths yields accurate values of the Young's moduli of individual SWNTs. As an example of the value of this system beyond its use in this type of molecular scale metrology, we implement parallel arrays of buckled SWNTs as a class of mechanically stretchable conductor.
Dynamic buckling of actin within filopodia
DEFF Research Database (Denmark)
Leijnse, Natascha; Oddershede, Lene B; Bendix, Pól Martin
2015-01-01
Filopodia are active tubular structures protruding from the cell surface which allow the cell to sense and interact with the surrounding environment through repetitive elongation-retraction cycles. The mechanical behavior of filopodia has been studied by measuring the traction forces exerted...... in conjunction with rotation enables the cell to explore a much larger 3-dimensional space and allows for more complex, and possibly stronger, interactions with the external environment.(2) Here we focus on how bending of the filopodial actin dynamically correlates with pulling on an optically trapped...
Basu, Saptarshi; Bansal, Lalit; Miglani, Ankur
2016-06-14
The evaporation of a nanocolloidal sessile droplet exhibits preferential particle assembly, nanoporous shell formation and buckling to form cavities with unique morphological features. Here, we have established many universal trends that explain the buckling dynamics under one umbrella irrespective of hydrophobicity, evaporation mode and particle loading. We provide a regime map explaining the droplet morphology and buckling characteristics for droplet evaporation on various substrates. Specifically, we find that the final droplet volume and the radius of curvature at the buckling onset are universal functions of particle concentration. Furthermore, we establish that post-buckling cavity growth is evaporation driven regardless of the substrate.
Modeling the buckling and delamination of thin films
Jagla, E. A.
2007-02-01
I study numerically the problem of delamination of a thin film elastically attached to a rigid substrate. A nominally flat elastic thin film is modeled using a two-dimensional triangular mesh. Both compression and bending rigidities are included to simulate compression and bending of the film. The film can buckle (i.e., abandon its flat configuration) when enough compressive strain is applied. The buckled configurations of a piece of film with stripe geometry are investigated as a function of the compressive strain. It is found that the stable configuration depends strongly on the applied strain and the Poisson ratio of the film. Next, the film is considered to be attached to a rigid substrate by springs that can break when the detaching force exceeds a threshold value, producing partial delamination of the film. Delamination is induced by a mismatch of the relaxed configurations of film and substrate. The morphology of the delaminated film can be followed and compared with available experimental results as a function of model parameters. “Telephone-cord,” polygonal, and “brainlike” patterns qualitatively similar to experimentally observed configurations are obtained in different parameter regions. The main control parameters that select the different patterns are the strain mismatch between film and substrate and the degree of in-plane relaxation within the unbuckled regions.
Nonlinear Dynamic Buckling of Damaged Composite Cylindrical Shells
Institute of Scientific and Technical Information of China (English)
WANG Tian-lin; TANG Wen-yong; ZHANG Sheng-kun
2007-01-01
Based on the first order shear deformation theory(FSDT), the nonlinear dynamic equations involving transverse shear deformation and initial geometric imperfections were obtained by Hamilton's philosophy. Geometric deformation of the composite cylindrical shell was treated as the initial geometric imperfection in the dynamic equations, which were solved by the semi-analytical method in this paper. Stiffness reduction was employed for the damaged sub-layer, and the equivalent stiffness matrix was obtained for the delaminated area. By circumferential Fourier series expansions for shell displacements and loads and by using Galerkin technique, the nonlinear partial differential equations were transformed to ordinary differential equations which were finally solved by the finite difference method. The buckling was judged from shell responses by B-R criteria, and critical loads were then determined. The effect of the initial geometric deformation on the dynamic response and buckling of composite cylindrical shell was also discussed, as well as the effects of concomitant delamination and sub-layer matrix damages.
Buckling of Single-Crystal Silicon Nanolines under Indentation
Directory of Open Access Journals (Sweden)
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.
Nonlinear buckling analyses of a small-radius carbon nanotube
Energy Technology Data Exchange (ETDEWEB)
Liu, Ning, E-mail: liuxiao@ase.buaa.edu.cn; Li, Min; Jia, Jiao [School of Aeronautic Science and Engineering, Beihang University, Beijing 100091 (China); Wang, Yong-Gang [Department of Applied Mechanics, China Agricultural University, Beijing 100083 (China)
2014-04-21
Carbon nanotube (CNT) was first discovered by Sumio Iijima. It has aroused extensive attentions of scholars from all over the world. Over the past two decades, we have acquired a lot of methods to synthesize carbon nanotubes and learn their many incredible mechanical properties such as experimental methods, theoretical analyses, and computer simulations. However, the studies of experiments need lots of financial, material, and labor resources. The calculations will become difficult and time-consuming, and the calculations may be even beyond the realm of possibility when the scale of simulations is large, as for computer simulations. Therefore, it is necessary for us to explore a reasonable continuum model, which can be applied into nano-scale. This paper attempts to develop a mathematical model of a small-radius carbon nanotube based on continuum theory. An Isotropic circular cross-section, Timoshenko beam model is used as a simplified mechanical model for the small-radius carbon nanotube. Theoretical part is mainly based on modified couple stress theory to obtain the numerical solutions of buckling deformation. Meanwhile, the buckling behavior of the small radius carbon nanotube is simulated by Molecular Dynamics method. By comparing with the numerical results based on modified couple stress theory, the dependence of the small-radius carbon nanotube mechanical behaviors on its elasticity constants, small-size effect, geometric nonlinearity, and shear effect is further studied, and an estimation of the small-scale parameter of a CNT (5, 5) is obtained.
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.
Euler buckling and nonlinear kinking of double-stranded DNA.
Fields, Alexander P; Meyer, Elisabeth A; Cohen, Adam E
2013-11-01
The bending stiffness of double-stranded DNA (dsDNA) at high curvatures is fundamental to its biological activity, yet this regime has been difficult to probe experimentally, and literature results have not been consistent. We created a 'molecular vise' in which base-pairing interactions generated a compressive force on sub-persistence length segments of dsDNA. Short dsDNA strands (Euler buckling'. We monitored the buckling transition via Förster Resonance Energy Transfer (FRET) between appended fluorophores. For low-to-moderate concentrations of monovalent salt (up to ∼150 mM), our results are in quantitative agreement with the worm-like chain (WLC) model of DNA elasticity, without the need to invoke any 'kinked' states. Greater concentrations of monovalent salts or 1 mM Mg(2+) induced an apparent softening of the dsDNA, which was best accounted for by a kink in the region of highest curvature. We tested the effects of all single-nucleotide mismatches on the DNA bending. Remarkably, the propensity to kink correlated with the thermodynamic destabilization of the mismatched DNA relative the perfectly complementary strand, suggesting that the kinked state is locally melted. The molecular vise is exquisitely sensitive to the sequence-dependent linear and nonlinear elastic properties of dsDNA.
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.
Full scale tests of all-steel buckling restrained braces
Ma, Ning; Wu, Bin; Li, Hui; Ou, Jinping; Yang, Weibiao
2009-03-01
Buckling-restrained braces (BRBs) are widely used seismic response-controlling members with excellent energy dissipation capacity without buckling at design deformation. However, the property of all-steel BRBs with cruciform cross section encased in a square steel tube remains insufficiently studied. In this paper, the properties of this kind of BRBs, which were used in two office buildings in Beijing, were examined by full-scale test. First, initial design was done according to the client's requirement. Then, two full-scale specimens were tested under uniaxial quasi-static cyclic loading. The test results indicate that there should be no welding in yielding portion of the core. Finally, the full-scale subassemblage test was done with an improved BRB and gusset plates installed in a frame. The result shows that the brace exhibited high energy dissipation capacity and stable hysteretic characteristic. According to the results from above tests, some important issues are summarized to provide advices for practical applications.
Mechanical Buckling Analysis of Composite Panels with/without Cutouts
Institute of Scientific and Technical Information of China (English)
Oana Zenaida PASCAN; ZHANG Wei-hong; Jean Philippe PONTHOT
2012-01-01
A simplified analytical solution suitable for simple stacking sequences was developed using the Euler buck- ling theory, the structure＇s equations of equilibrium and laminate panel mathematical formulation. Comparing these results with numerical results reveals the accuracy of the method and even more, allows us to validate the nu- merical analysis. Therefore, two important results are obtained： a simplified analytical solution for the buckling problem and validation of the numerical results. Another important and novel finding is related to the influence of the angle ply orientation and of the cutouts, on the buckling load. Under symmetrical boundary conditions and loading case, rectangular panels with elliptical cutouts, give better results for 90~ oriented plies than for 0 oriented ones. With a compression load applied in the X direction, and with material properties 10 times better in X direction than in Y direction, the best results are obtained when the load is aligned with the Y direction associated to the ma- terial reference frame. Moreover, panels with cutouts seem to behave better than panels without cutouts under cer- tainply orientation angles.
Nonlinear buckling analyses of a small-radius carbon nanotube
Liu, Ning; Wang, Yong-Gang; Li, Min; Jia, Jiao
2014-04-01
Carbon nanotube (CNT) was first discovered by Sumio Iijima. It has aroused extensive attentions of scholars from all over the world. Over the past two decades, we have acquired a lot of methods to synthesize carbon nanotubes and learn their many incredible mechanical properties such as experimental methods, theoretical analyses, and computer simulations. However, the studies of experiments need lots of financial, material, and labor resources. The calculations will become difficult and time-consuming, and the calculations may be even beyond the realm of possibility when the scale of simulations is large, as for computer simulations. Therefore, it is necessary for us to explore a reasonable continuum model, which can be applied into nano-scale. This paper attempts to develop a mathematical model of a small-radius carbon nanotube based on continuum theory. An Isotropic circular cross-section, Timoshenko beam model is used as a simplified mechanical model for the small-radius carbon nanotube. Theoretical part is mainly based on modified couple stress theory to obtain the numerical solutions of buckling deformation. Meanwhile, the buckling behavior of the small radius carbon nanotube is simulated by Molecular Dynamics method. By comparing with the numerical results based on modified couple stress theory, the dependence of the small-radius carbon nanotube mechanical behaviors on its elasticity constants, small-size effect, geometric nonlinearity, and shear effect is further studied, and an estimation of the small-scale parameter of a CNT (5, 5) is obtained.
Wiggins, Andrew D.
Bow seals are critical components on advanced marine vehicles that rely on aerostatic support to reduce drag. They consist of a series of open-ended fabric cylinders ("fingers") that contact the free surface and, when inflated, form a compliant pressure barrier. Bow seals are unique in that, unlike a majority of structures in civil and mechanical engineering, bow seals operate in a buckled state. The response characteristics of these structures are of practical interest due to unacceptable wear rates on seal components and difficulties in predicting seal performance. Despite this, the hydroelastic response of the seal system, particularly basic information on seal vibration modes and the mechanisms responsible for seal wear, remains largely unknown. Similarly, estimates of the hydrodynamic loads on the seal system are inaccurate and based on heuristic scaling of data from small-scale experiments, where similitude is challenging to maintain. Thus, a large-scale test system is necessary to obtain accurate estimates of bow seal response. The work is comprised of three parts. Part one presents detailed observations of bow seal response acquired using a large-scale test platform developed as part of the present study. These high-resolution observations, the first of their kind, show bow seal response to be characterized by complex post-buckling behavior. Part two proposes an analytical framework for interpreting the wide range of behavior observed at large scale. Using this framework, key parameters driving seal conformation and stability are identified. It is found that, due to their buckled state, bow seals are highly susceptible to a mode switching instability, which may be a potential mechanism responsible for the damaging vibrations. In part three, a benchtop experiment is used to demonstrate that the scalings identified in this study hold across a wide range of bending rigidities. This work has implications for improving drag and wear characteristics in future bow
Post-buckling analysis of composite beams: A simple intuitive formulation
Indian Academy of Sciences (India)
Jagadish Babu Gunda; G Venkateswara Rao
2013-06-01
Post-buckling analysis of composite beams with axially immovable ends is investigated using an Intuitive formulation. Intuitive formulation uses two parameters namely critical buckling load and axial stretching force developed in the post-buckled domain of composite beam. Geometric nonlinearity of von-Karman type is taken into consideration which accounts for membrane stretching action of the beam. Axial stretching force developed in post-buckled domain of composite beam is evaluated by using an axial governing equation and is expressed either in terms of lateral displacement function as an integrated value, or as a function of both axial and lateral displacement functions at any discrete location of the beam. The available expressions of critical buckling load and derived expressions of axial stretching force developed in the beam are used for obtaining an approximate closed-form expressions for the post-buckling loads of various beam boundary conditions. Numerical accuracy of the proposed analytical closed-form expressions obtained from the intuitive formulation are compared to the available ﬁnite element solutions for symmetric and asymmetric lay-up schemes of laminated composite beam. Effect of central amplitude ratio and lay-up orientation on post-buckling load variation is brieﬂy discussed for various beam boundary conditions considered in this study.
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.
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.
Effect of surface layer thickness on buckling and vibration of nonlocal nanowires
Energy Technology Data Exchange (ETDEWEB)
Hu, Kai-Ming; Zhang, Wen-Ming, E-mail: wenmingz@sjtu.edu.cn; Zhong, Zuo-Yang; Peng, Zhi-Ke; Meng, Guang
2014-01-31
In this Letter, the buckling and vibration behavior of nonlocal nanowires by incorporating surface elasticity is investigated. A modified core–shell model is developed to depict the size effect of Young's modulus and validated by the reported experimental data. Our results show that the buckling load and natural frequency of nanowires increase when the effect of surface layer thickness is taken into account. Moreover, as the diameter of nanowires is smaller than 50 nm, the influence of surface layer thickness becomes obvious. This work can be helpful in characterizing and predicting the buckling and vibration behavior of NWs.
Buckling analysis of stringer-stiffened laminated cylindrical shells with nonuniform eccentricity
Energy Technology Data Exchange (ETDEWEB)
Sadeghifar, M. [Islamic Azad University, Department of Mechanical Engineering, Nowshahr Branch, Nowshahr (Iran, Islamic Republic of); Bagheri, M. [Sattari Air University, Faculty of Aerospace Engineering, Tehran (Iran, Islamic Republic of); Jafari, A.A. [K.N. Toosi University of Technology, Faculty of Mechanical Engineering, Tehran (Iran, Islamic Republic of)
2011-07-15
In this study, the influence of nonuniformity of eccentricity of stringers on the general axial buckling load of stiffened laminated cylindrical shells with simply supported end conditions is investigated. The critical loads are calculated using Love's First-order Shear Deformation Theory and solved using the Rayleigh-Ritz procedure. The effects of the shell length-to-radius ratio, shell thickness-to-radius ratio, number of stringers, and stringers depth-to-width ratio on the buckling load of nonuniformly eccentric shells, are examined. The research demonstrates that an appropriate nonuniform distribution of eccentricity of stringers leads the buckling load to increase significantly. (orig.)
An epibulbar chocolate cyst: a rare complication of silicone-based scleral buckle.
Venkatesh, Pradeep; Gogia, Varun; Gupta, Shikha; Nayak, Bhagabat
2015-08-03
A patient with a history of vitreoretinal surgery presented with nasal dystopia, diplopia and epibulbar bluish black mass simulating a chocolate cyst in the right eye. After a non-conclusive ocular examination, he underwent CT of the orbit along with volume rendition and three-dimensional reconstruction, which demonstrated intact globe with laterally displaced band-buckle assembly along with peri-scleral buckle element (SBE) soft tissue proliferation. Imaging-assisted exploration of the lesion was performed and retained scleral buckle element (SBE) was removed in toto; thus relieving the patient long-standing dystopia.
Mechanical behavior of carbon nanotubes in the rippled and buckled phase
Jackman, H.; Krakhmalev, P.; Svensson, K.
2015-02-01
We have studied the mechanical behavior of multi-walled carbon nanotubes for bending strains beyond the onset for rippling and buckling. We found a characteristic drop in the bending stiffness at the rippling and buckling onset and the relative retained stiffness was dependent on the nanotube dimensions and crystallinity. Thin tubes are more prone to buckle, where some lose all of their bending stiffness, while thicker tubes are more prone to ripple and on average retain about 20% of their bending stiffness. In defect rich tubes, the bending stiffness is very low prior to rippling, but these tubes retain up to 70% of their initial bending stiffness.
Timoshenko beam model for buckling of piezoelectric nanowires with surface effects.
Samaei, Arash Tourki; Bakhtiari, Majid; Wang, Gang-Feng
2012-03-27
This paper investigates the buckling behavior of piezoelectric nanowires under distributed transverse loading, within the framework of the Timoshenko beam theory, and in the presence of surface effects. Analytical relations are given for the critical force of axial buckling of nanowires by accounting for the effects of surface elasticity, residual surface tension, and transverse shear deformation. Through an example, it is shown that the critical electric potential of buckling depends on both the surface stresses and piezoelectricity. This study may be helpful in the characterization of the mechanical properties of nanowires and in the calibration of the nanowire-based force sensors.
Study of Dynamic Buckling of FG Plate Due to Heat Flux Pulse
Directory of Open Access Journals (Sweden)
Czechowski L.
2015-02-01
Full Text Available The paper deals with a FEM analysis of dynamic buckling of functionally graded clamped plates under heat flux loading with huge power. The materials of structures as well as their properties are varying in each layer across the plate thickness formulated by the power law distribution. The heat flux was applied evenly to the whole ceramic surface. The analysis was developed in the ANSYS 14.5 software. The duration of the heat flux loading equal to a period of natural fundamental flexural vibrations of given structures was taken into consideration. To implement large deflections of structures, the Green-Lagrange nonlinear-displacement equations and the incremental Newton-Raphson algorithm were applied. An evaluation of the dynamic response of structures was carried out on basis of the Budiansky-Hutchinson criterion. The studies were conducted for different volume fraction distributions and different shapes of the heat flux loading. The computation results of the heat flux versus maximal plate deflection are shown and discussed.
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 shape...... of the substrate, a new non-dimensional geometrical parameter enters the conditions for steady-state delamination. It is shown that this additional geometrical parameter in most cases of practical relevance has insignificant influence on the fracture mechanical parameters involved for the problem. The consequence...... is that solutions need to be mapped as a function of one rather than two dimensionless parameters. Furthermore, the shape of the substrate has profound influence especially on initiation of delamination growth....
Buckling-driven delamination in layered spherical shells
Sørensen, Kim D.; Jensen, Henrik M.
An analysis of buckling-driven delamination of a layer in a spherical, layered shell 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 the sense that additional to the effect of the shape of the substrate, a new non-dimensional geometrical parameter enters the conditions for steady-state delamination. It is shown that this additional geometrical parameter in most cases of practical relevance has insignificant influence on the fracture mechanical parameters involved for the problem. The consequence is that solutions need to be mapped as a function of one rather than two dimensionless parameters. Furthermore, the shape of the substrate has profound influence especially on initiation of delamination growth.
Buckling and unstable collapse of seamless pipes and tubes
Energy Technology Data Exchange (ETDEWEB)
Jakani, S.; Van den Abeele, F. [ArcelorMittal Global RnD Ghent, Zelzate, (Belgium); Bar, J. [ArcelorMittal Tubular Products Ostrava, Ostrava, (Czech Republic)
2010-07-01
Off-shore pipelines and high pressure casings are subject to buckling and unstable collapse. This paper investigated the unstable collapse of seamless pipes under compressive loading. Collapse pressure tests for high collapse casing grades L80HC and P110HC were carried out by enclosing end-capped specimens in a pressure vessel, and applying hydrostatic pressure. Analytical calculations were performed to predict the critical collapse pressure for pipes with different values of diameter to wall thickness. Four regimes were identified and studied: yielding collapse, plastic collapse, transition range and elastic collapse. Simplified design equations were produced for each regime to estimate the collapse pressure more efficiently. The influence of initial geometric imperfections and material properties was studied with the aim of developing a modified design equation for collapse able to predict the critical collapse pressure of dented seamless pipes. Experimental tests showed that the pipes complied with API standards and the modified equation was validated.
Buckling Analysis of Unidirectional PolymerMatrix Composite Plates
Directory of Open Access Journals (Sweden)
Jawad Kadhim Uleiwi
2006-01-01
Full Text Available This study deals with the estimation of critical load of unidirectional polymer matrix composite plates by using experimental and finite element techniques at different fiber angles and fiber volume fraction of the composite plate.Buckling analysis illustrated that the critical load decreases in nonlinear relationship with the increase of the fiber angle and that it increases with the increase of the fiber volume fraction.The results show that the maximum value of the critical load is (629.54 N/m at (? = 0? and (Vf = 40 % for the finite element method, while the minimum value of the critical load is (49 N/m at (? = 90? and (Vf = 10 % for the experimental results. The results also indicated that the maximum difference between the finite element analysis and experimental work is about (11 % at ( ? = 0? and (Vf = 40 %
Periumbilical allergic contact dermatitis: blue jeans or belt buckles?
Byer, Tara T; Morrell, Dean S
2004-01-01
Nickel is the most ubiquitous contact allergen among children and adolescents. Metal blue jeans buttons and belts have been noted to cause nickel dermatitis around the umbilicus. For these children, traditional teaching is strict avoidance of all pants with metal snaps/buttons, particularly blue jeans. In this study we tested 90 pairs of blue jeans and 47 belts for nickel using the dimethylglyoxime spot test. Only 10% of blue jeans tested positive, while 53% of belts tested positive. Furthermore, 10 pairs of nickel-negative blue jeans remained negative after 10 washings. Overall we found no resistance to testing in clothing stores. From these results, we recommend that patients with allergic contact dermatitis secondary to nickel need not strictly avoid blue jeans and metal belt buckles. Rather, families should be encouraged to use the dimethylglyoxime spot test to test these items for nickel prior to purchase.
Bending and buckling behavior analysis of foamed metal circular plate.
Fan, Jian Ling; Ma, Lian Sheng; Zhang, Lu; De Su, Hou
2016-07-04
This paper establishes a density gradient model along the thickness direction of a circular plate made of foamed material. Based on the first shear deformation plate theory, the result is deduced that the foamed metal circular plate with graded density along thickness direction yields axisymmetric bending problem under the action of uniformly distributed load, and the analytical solution is obtained by solving the governing equation directly. The analyses on two constraint conditions of edge radial clamping and simply supported show that the density gradient index and external load may affect the axisymmetric bending behavior of the plate. Then, based on the classical plate theory, the paper analyzes the behavior of axisymmetric buckling under radial pressure applied on the circular plate. Shooting method is used to obtain the critical load, and the effects of gradient nature of material properties and boundary conditions on the critical load of the plate are analyzed.
Buckling of elliptical rings under uniform external pressure
Energy Technology Data Exchange (ETDEWEB)
Tang, Y.
1991-04-03
A thin, elastic elliptical ring is subjected to uniform external pressure. The lowest critical pressure is computed and presented for various ratio of the major axis to the minor axis of the elliptical ring. It is found that the critical pressure for an elliptical ring is higher than that for the circular ring whose diameter is equal to the major axis of the elliptical ring. It can be shown that under the same external pressure, the axial force developed in the elliptical ring is less than that developed in the corresponding circular ring. Thus, a higher pressure is required to buckle the elliptical rings. Therefore, by changing the shape of the ring from circular to elliptical, the capability of the ring to sustain the external pressure can be increased substantially. The results of this study can be useful in the design of elliptical reinforcing rings and thin-walled tubes subjected to external pressure.
Graphene-like monolayer low-buckled honeycomb germanium film
He, Yezeng; Luo, Haibo; Li, Hui; Sui, Yanwei; Wei, Fuxiang; Meng, Qingkun; Yang, Weiming; Qi, Jiqiu
2017-04-01
Molecular dynamics simulations have been performed to study the cooling process of two-dimensional liquid germanium under nanoslit confinement. The results clearly indicates that the liquid germanium undergoes an obvious liquid-solid phase transition to a monolayer honeycomb film with the decrease of temperature, accompanying the rapid change in potential energy, atomic volume, coordination number and lateral radial distribution function. During the solidification process, some hexagonal atomic islands first randomly emerge in the disordered liquid film and then grow up to stable crystal grains which keep growing and finally connect together to form a honeycomb polycrystalline film. It is worth noting that the honeycomb germanium film is low-buckled, quite different from the planar graphene.
Axisymmetric buckling of laminated, moderately thick shallow conical cap
Energy Technology Data Exchange (ETDEWEB)
Dumir, P.C.; Dube, G.P.; Joshi, S. [Applied Mechanics Dept., I.I.T. Delhi, New Delhi (India)
2001-05-01
Axisymmetric buckling and postbuckling analysis is presented for a moderately thick, laminated shallow conical cap under static transverse load. Marguerre-type, first-order shear deformation shallow-shell theory is formulated in terms of transverse deflection w, the rotation {psi} of the normal to the midsurface and the stress function {phi}. The governing equations are solved by the orthogonal point-collocation method. Clamped conical caps and simple supports with movable and immovable edge conditions are considered. Typical numerical results are presented, illustrating the effect of various parameters. The dependence of the effect of the shear deformation on the thickness parameter, boundary conditions, ratio of Young's moduli and cap height is investigated. (orig.)
Buckling analysis of an orthotropic thin shell of revolution using differential quadrature
Energy Technology Data Exchange (ETDEWEB)
Redekop, D. [Department of Mechanical Engineering, University of Ottawa, 161 Louis Pasteur, Ottawa, ON, K1N 6N5 (Canada)]. E-mail: dredekop@tesla.cc.uottawa.ca
2005-08-01
A method is developed to predict the buckling characteristics of an orthotropic shell of revolution of arbitrary meridian subjected to a normal pressure. The solution is given within the context of the linearized Sanders-Budiansky shell buckling theory and makes use of the differential quadrature method. Numerical results for buckling pressures and mode shapes are given for complete toroidal shells. Both completely free shells and shells with circumferential line restraints are covered. The loadings considered consist either of uniform pressure or circumferential bands of constant pressure. It is demonstrated that the differential quadrature method is numerically stable and converges. For isotropic toroidal shells, good agreement is observed with previously published analytical and finite element results. New results for buckling pressures and mode numbers are given for orthotropic shells and for band loaded shells.
Size-dependent thermal buckling of heated nanowires with ends axially restrained
Wang, Yu; Wang, Zhi-Qiao; Lv, Jian-Guo
2014-02-01
Nanowires (NWs) are being actively explored for applications as nanoscale building blocks of sensors, actuators and nanoelectromechanical systems (NEMS). Temperature changes can induce an axial force within NWs due to the thermal expansion and may lead to buckling. The thermal buckling behaviors of ends-axially-restrained nanowires, subjected to a uniform temperature rise, are studied based on Bernoulli-Euler beam theory including the surface thermoelastic effects. Besides the surface elastic modulus, the influences of surface thermal expansion coefficient are incorporated into the model presented herein to describe size-dependent thermoelastic behaviors of nanowires. The results show that the critical buckling temperature and postbuckling deflection are significantly affected by surface thermoelastic effects and the influences become more prominent as the thickness of nanowire decreases. The corresponding influences of the slenderness ratio are also discussed. This research is helpful not only in understanding the thermal buckling properties of nanowires but also in designing the nanowire-based sensor and thermal actuator.
Ali, Elaf Jaafar; Gao, David Yang
2016-10-01
The goal of this paper is to solve the post buckling phenomena of a large deformed elastic beam by a canonical dual mixed finite element method (CD-FEM). The total potential energy of this beam is a nonconvex functional which can be used to model both pre-and post-buckling problems. Different types of dual stress interpolations are used in order to verify the triality theory. Applications are illustrated with different boundary conditions and external loads by using semi-definite programming (SDP) algorithm. The results show that the global minimum of the total potential energy is stable buckled configuration, the local maximum solution leads to the unbuckled state, and both of these two solutions are numerically stable. While the local minimum is unstable buckled configuration and very sensitive to both stress interpolations and the external loads.
Buckling and Delamination Growth Analysis of Composite Laminates Containing Embedded Delaminations
Hosseini-Toudeshky, H.; Hosseini, S.; Mohammadi, B.
2010-04-01
The objective of this work is to study the post buckling behavior of composite laminates, containing embedded delamination, under uniaxial compression loading. For this purpose, delamination initiation and propagation is modeled using the softening behavior of interface elements. The full layer-wise plate theory is also employed for approximating the displacement field of laminates and the interface elements are considered as a numerical layer between any two adjacent layers which delamination is expected to propagate. A finite element program was developed and the geometric non-linearity in the von karman sense is incorporated to the strain/displacement relations, to obtain the buckling behavior. It will be shown that, the buckling load, delamination growth process and buckling mode of the composite plates depends on the size of delamination and stacking sequence of the laminates.
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.
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...... and the buckling Elastica solution for an original compliant mechanism kinematic analysis. New compliant mechanism designs are presented to highlight where such combined kinematic analysis is required....
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
An analysis of buckling/snapping and bending behaviors of magneto-elastic-plastic interaction and coupling for cantilever rectangular soft ferromagnetic plates is presented. Based on the expression of magnetic force from the variational principle of ferromagnetic plates, the buckling and bending theory of thin plates, the Mises yield criterion and the increment theory for plastic deformation, we establish a numerical code to quantitatively simulate the behaviors of the nonlinearly multi-fields coupling problems by the finite element method. Along with the phenomena of buckling/snapping and bending, or the characteristic curve of deflection versus magnitude of applied magnetic fields being numerically displayed, the critical loads of buckling/snapping,and the influences of plastic deformation and the width of plate on these critical loads, the plastic regions expanding with the magnitude of applied magnetic field, as well as the evolvement of deflection configuration of the plate are numerically obtained in a case study.
External Pressure Forming and Buckling Analysis of Tubular Parts with Ribs
Institute of Scientific and Technical Information of China (English)
Gang LIU; Xuelian YIN; Shijian YUAN
2006-01-01
Buckling and forming processes of tubes with varying slenderness ratio(ratio of length to diameter)under external hydraulic pressure were analyzed with three-dimensional finite element method(FEM)for studying tube external pressure forming(EPF). Buckling pressures for different tube blanks without mandrel were predicted, and an EPF of a carbon steel tube onto a mandrel with six ribs was simulated. Both thickness distribution and buckling pressure from the simulations were found to be in agreement with those from experiments. Buckling pressures are shown to be a function of the slenderness ratio. The tubular part with six ribs produced by EPF has a uniform thickness distribution, whose maximum thinning rate is only 5.9%.
Research Progress of Buckling Propagation Experiment of Deep-Water Pipelines
Institute of Scientific and Technical Information of China (English)
余建星; 吴梦宁; 孙震洲; 段晶辉
2016-01-01
In recent years, the extraction of fossil resources, especially oil and gas in deep and ultra-deep water areas has been playing a more important role and been paid more attention to. For this reason, the working depth of subma-rine pipelines, which are used for the transportation of oil and gas, has been increasing sharply. As the main failure pattern of deep-water pipelines, buckling and its propagation problem have drawn more attention of many research institutions and engineering units around the world. Based on the existing research, the summary of experiments and their outcomes of deep-water pipeline buckling failure is made in this paper. Research status and developing prospects of the experiments of buckling propagation and buckle arrestor are discussed in detail.
Variational principles for buckling and vibration of MWCNTs modeled by strain gradient theory
Institute of Scientific and Technical Information of China (English)
徐晓建; 邓子辰
2014-01-01
Variational principles for the buckling and vibration of multi-walled carbon nanotubes (MWCNTs) are established with the aid of the semi-inverse method. They are used to derive the natural and geometric boundary conditions coupled by small scale parameters. Hamilton’s principle and Rayleigh’s quotient for the buckling and vibration of the MWCNTs are given. The Rayleigh-Ritz method is used to study the buckling and vibration of the single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) with three typical boundary conditions. The numerical results reveal that the small scale parameter, aspect ratio, and boundary conditions have a profound effect on the buckling and vibration of the SWCNTs and DWCNTs.
Critical buckling strain in high strength steel pipes using isotropic kinematic hardening
Energy Technology Data Exchange (ETDEWEB)
Fathi, A.; Roger Cheng, J. J.; Adeeb, Samer [Department of Civil and Environmental Engineering, University of Alberta (Canada); Zhou, Joe [TransCanada Pipelines Ltd. (Canada)
2010-07-01
In the natural gas sector, the use of high strength steel pipelines (HSSP) to transport huge volumes over long distances is increasing as it yields important savings in both capital and operational expenditures. In order to design HSSP, the critical buckling strain as to be taken into consideration but the models so far developed have been for isotropic materials while important material anisotropy is observed on HSSP due to their manufacturing process. The paper presents a model to assess the critical buckling strain of HSSP. An isotropic-kinematic hardening material model was developed and isotropic and anisotropic models were used to simulate pressurized and non-pressurized HSSP and were compared to test results. Results showed that the isotropic model is not suitable for predicting the buckling strain of HSSP but that the isotropic-kinematic hardening material model is. A model to better predict the buckling strain of HSSP was developed and successfully tested herein.
Size-dependent thermal buckling of heated nanowires with ends axially restrained
Energy Technology Data Exchange (ETDEWEB)
Wang, Yu [School of Engineering and Technology, China University of Geosciences, Beijing 100083 (China); Key Laboratory on Deep GeoDrilling Technology, Ministry of Land and Resources, China University of Geosciences, Beijing 100083 (China); Wang, Zhi-Qiao, E-mail: zqwang@cugb.edu.cn [School of Engineering and Technology, China University of Geosciences, Beijing 100083 (China); Key Laboratory on Deep GeoDrilling Technology, Ministry of Land and Resources, China University of Geosciences, Beijing 100083 (China); Lv, Jian-Guo [School of Engineering and Technology, China University of Geosciences, Beijing 100083 (China); Key Laboratory on Deep GeoDrilling Technology, Ministry of Land and Resources, China University of Geosciences, Beijing 100083 (China)
2014-02-01
Nanowires (NWs) are being actively explored for applications as nanoscale building blocks of sensors, actuators and nanoelectromechanical systems (NEMS). Temperature changes can induce an axial force within NWs due to the thermal expansion and may lead to buckling. The thermal buckling behaviors of ends-axially-restrained nanowires, subjected to a uniform temperature rise, are studied based on Bernoulli–Euler beam theory including the surface thermoelastic effects. Besides the surface elastic modulus, the influences of surface thermal expansion coefficient are incorporated into the model presented herein to describe size-dependent thermoelastic behaviors of nanowires. The results show that the critical buckling temperature and postbuckling deflection are significantly affected by surface thermoelastic effects and the influences become more prominent as the thickness of nanowire decreases. The corresponding influences of the slenderness ratio are also discussed. This research is helpful not only in understanding the thermal buckling properties of nanowires but also in designing the nanowire-based sensor and thermal actuator.
Contractile Units in Disordered Actomyosin Bundles Arise from F-Actin Buckling
Lenz, Martin; Thoresen, Todd; Gardel, Margaret L.; Dinner, Aaron R.
2012-06-01
Bundles of filaments and motors are central to contractility in cells. The classic example is striated muscle, where actomyosin contractility is mediated by highly organized sarcomeres which act as fundamental contractile units. However, many contractile bundles in vivo and in vitro lack sarcomeric organization. Here we propose a model for how contractility can arise in bundles without sarcomeric organization and validate its predictions with experiments on a reconstituted system. In the model, internal stresses in frustrated arrangements of motors with diverse velocities cause filaments to buckle, leading to overall shortening. We describe the onset of buckling in the presence of stochastic motor head detachment and predict that buckling-induced contraction occurs in an intermediate range of motor densities. We then calculate the size of the “contractile units” associated with this process. Consistent with these results, our reconstituted actomyosin bundles show contraction at relatively high motor density, and we observe buckling at the predicted length scale.
Indian Academy of Sciences (India)
Hesheng Tang; Yu Su; Jiao Wang
2015-08-01
The paper describes a procedure for the uncertainty quantification (UQ) using evidence theory in buckling analysis of semi-rigid jointed frame structures under mixed epistemic–aleatory uncertainty. The design uncertainties (geometrical, material, strength, and manufacturing) are often prevalent in engineering applications. Due to lack of knowledge or incomplete, inaccurate, unclear information in the modeling, simulation, measurement, and design, there are limitations in using only one framework (probability theory) to quantify uncertainty in a system because of the impreciseness of data or knowledge. Evidence theory provides an alternative to probability theory for the representation of epistemic uncertainty that derives from a lack of knowledge with respect to the appropriate values to use for various inputs to the model. Unfortunately, propagation of an evidence theory representation for uncertainty through a model is more computationally demanding than propagation of a probabilistic representation for uncertainty. In order to alleviate the computational difficulties in the evidence theory based UQ analysis, a differential evolution-based computational strategy for propagation of epistemic uncertainty in a system with evidence theory is presented here. A UQ analysis for the buckling load of steel-plane frames with semi-rigid connections is given herein to demonstrate accuracy and efficiency of the proposed method.
The computer simulation of portal rigid frame static buckling%门式刚架静力屈曲的计算机模拟
Institute of Scientific and Technical Information of China (English)
杨卫奇
2015-01-01
This paper made linear static buckling simulation to portal rigid frame steel structure using ANSYS finite element analysis software, given first-order static buckling mode,buckling load,the calculation length coefficient of column of a time frame,analyzed the relationship be-tween column calculation length coefficient computer simulation value with the theoretical value,provided basis for the research on similar problems.%采用ANSYS有限元分析软件对门式刚架结构进行线性静力屈曲模拟，给出了某一时刻刚架的一阶屈曲模态、屈曲载荷、柱的计算长度系数，分析了柱的计算长度系数计算机模拟值与理论值的关系，为类似问题的研究提供了依据。
Buckling of Euler Columns with a Continuous Elastic Restraint via Homotopy Analysis Method
Directory of Open Access Journals (Sweden)
Aytekin Eryılmaz
2013-01-01
Full Text Available Homotopy Analysis Method (HAM is applied to find the critical buckling load of the Euler columns with continuous elastic restraints. HAM has been successfully applied to many linear and nonlinear, ordinary and partial, differential equations, integral equations, and difference equations. In this study, we presented the application of HAM to the critical buckling loads for Euler columns with five different support cases continuous elastic restraints. The results are compared with the analytic solutions.
Nemeth, Michael P.
2013-01-01
Nondimensional linear-bifurcation buckling equations for balanced, symmetrically laminated cylinders with negligible shell-wall anisotropies and subjected to uniform axial compression loads are presented. These equations are solved exactly for the practical case of simply supported ends. Nondimensional quantities are used to characterize the buckling behavior that consist of a stiffness-weighted length-to-radius parameter, a stiffness-weighted shell-thinness parameter, a shell-wall nonhomogeneity parameter, two orthotropy parameters, and a nondimensional buckling load. Ranges for the nondimensional parameters are established that encompass a wide range of laminated-wall constructions and numerous generic plots of nondimensional buckling load versus a stiffness-weighted length-to-radius ratio are presented for various combinations of the other parameters. These plots are expected to include many practical cases of interest to designers. Additionally, these plots show how the parameter values affect the distribution and size of the festoons forming each response curve and how they affect the attenuation of each response curve to the corresponding solution for an infinitely long cylinder. To aid in preliminary design studies, approximate formulas for the nondimensional buckling load are derived, and validated against the corresponding exact solution, that give the attenuated buckling response of an infinitely long cylinder in terms of the nondimensional parameters presented herein. A relatively small number of "master curves" are identified that give a nondimensional measure of the buckling load of an infinitely long cylinder as a function of the orthotropy and wall inhomogeneity parameters. These curves reduce greatly the complexity of the design-variable space as compared to representations that use dimensional quantities as design variables. As a result of their inherent simplicity, these master curves are anticipated to be useful in the ongoing development of
Directory of Open Access Journals (Sweden)
Tongqing Lu
2014-01-01
Full Text Available In a thin film-substrate system in-plane compressive stress is commonly generated in the film due to thermal mismatch in operation or fabrication process. If the stress exceeds a critical value, part of the film may buckle out of plane along the defective interface. After buckling delamination, the interface crack at the ends may propagate. In the whole process, the compliance of the substrate compared with the film plays an important role. In this work, we study a circular film subject to compressive stress on an infinitely thick substrate. We study the effects of compliance of the substrate by modeling the system as a plate on an elastic foundation. The critical buckling condition is formulated. The asymptotic solutions of post-buckling deformation and the corresponding energy release rate of the interface crack are obtained with perturbation methods. The results show that the more compliant the substrate is, the easier for the film to buckle and easier for the interface crack to propagate after buckling.
An Analytical Solution for Lateral Buckling Critical Load Calculation of Leaning-Type Arch Bridge
Directory of Open Access Journals (Sweden)
Ai-rong Liu
2014-01-01
Full Text Available An analytical solution for lateral buckling critical load of leaning-type arch bridge was presented in this paper. New tangential and radial buckling models of the transverse brace between the main and stable arch ribs are established. Based on the Ritz method, the analytical solution for lateral buckling critical load of the leaning-type arch bridge with different central angles of main arch ribs and leaning arch ribs under different boundary conditions is derived for the first time. Comparison between the analytical results and the FEM calculated results shows that the analytical solution presented in this paper is sufficiently accurate. The parametric analysis results show that the lateral buckling critical load of the arch bridge with fixed boundary conditions is about 1.14 to 1.16 times as large as that of the arch bridge with hinged boundary condition. The lateral buckling critical load increases by approximately 31.5% to 41.2% when stable arch ribs are added, and the critical load increases as the inclined angle of stable arch rib increases. The differences in the center angles of the main arch rib and the stable arch rib have little effect on the lateral buckling critical load.
Determination of the critical buckling pressure of blood vessels using the energy approach.
Han, Hai-Chao
2011-03-01
The stability of blood vessels under lumen blood pressure is essential to the maintenance of normal vascular function. Differential buckling equations have been established recently for linear and nonlinear elastic artery models. However, the strain energy in bent buckling and the corresponding energy method have not been investigated for blood vessels under lumen pressure. The purpose of this study was to establish the energy equation for blood vessel buckling under internal pressure. A buckling equation was established to determine the critical pressure based on the potential energy. The critical pressures of blood vessels with small tapering along their axis were estimated using the energy approach. It was demonstrated that the energy approach yields both the same differential equation and critical pressure for cylindrical blood vessel buckling as obtained previously using the adjacent equilibrium approach. Tapering reduced the critical pressure of blood vessels compared to the cylindrical ones. This energy approach provides a useful tool for studying blood vessel buckling and will be useful in dealing with various imperfections of the vessel wall.
Fracture and buckling of piezoelectric nanowires subject to an electric field
Energy Technology Data Exchange (ETDEWEB)
Zhang, Jin; Wang, Chengyuan, E-mail: chengyuan.wang@swansea.ac.uk; Adhikari, Sondipon [College of Engineering, Swansea University, Singleton Park, Swansea, Wales SA2 8PP (United Kingdom)
2013-11-07
Fracture and buckling are major failure modes of thin and long nanowires (NWs), which could be affected significantly by an electric field when piezoelectricity is involved in the NWs. This paper aims to examine the issue based on the molecular dynamics simulations, where the gallium nitride (GaN) NWs are taken as an example. The results show that the influence of the electric field is strong for the fracture and the critical buckling strains, detectable for the fracture strength but almost negligible for the critical buckling stress. In addition, the reversed effects are achieved for the fracture and the critical buckling strains. Subsequently, the Timoshenko beam model is utilized to account for the effect of the electric field on the axial buckling of the GaN NWs, where nonlocal effect is observed and characterized by the nonlocal coefficient e{sub 0}a=1.1 nm. The results show that the fracture and buckling of piezoelectric NWs can be controlled by applying an electric field.
Cui, Zhen; Guo, Jian-Gang
2016-12-01
Two interfacial failure modes, shear sliding and buckling, of graphene on a flexible substrate subjected to uniaxial compression are investigated. The shear sliding starts at the edge region, and buckling starts at the middle region of graphene. Using shear-lag cohesive zone models and finite element (FE) simulations, the critical strain and maximum strain of graphene are predicted for the interfacial sliding failure. Then, the critical strain for the onset of buckling is derived via the theory of continuum mechanics with the van der Waals (vdW) interaction between graphene and the substrate surface taken into consideration. By comparison of the two critical failure strains and maximum strain of graphene, it is found that there exists a critical length of graphene. As the graphene length is larger than it, interfacial failure goes through four stages of development with increasing loading, including sliding and buckling. Conversely, the buckling of graphene will not occur. Finally, the influence of the interfacial adhesion energy and geometric size of graphene on the critical strains for interfacial sliding and buckling are discussed.
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.
Buckling failure of square ice-nanotube arrays constrained in graphene nanocapillaries
Zhu, YinBo; Wang, FengChao; Wu, HengAn
2016-08-01
Graphene confinement provides a new physical and mechanical environment with ultrahigh van der Waals pressure, resulting in new quasi-two-dimensional phases of few-layer ice. Polymorphic transition can occur in bilayer constrained water/ice system. Here, we perform a comprehensive study of the phase transition of AA-stacked bilayer water constrained within a graphene nanocapillary. The compression-limit and superheating-limit (phase) diagrams are obtained, based on the extensive molecular-dynamics simulations at numerous thermodynamic states. Liquid-to-solid, solid-to-solid, and solid-to-liquid-to-solid phase transitions are observed in the compression and superheating of bilayer water. Interestingly, there is a temperature threshold (˜275 K) in the compression-limit diagram, which indicates that the first-order and continuous-like phase transitions of bilayer water depend on the temperature. Two obviously different physical processes, compression and superheating, display similar structural evolution; that is, square ice-nanotube arrays (BL-VHDI) will bend first and then transform into bilayer triangular AA stacking ice (BL-AAI). The superheating limit of BL-VHDI exhibits local maxima, while that of BL-AAI increases monotonically. More importantly, from a mechanics point of view, we propose a novel mechanism of the transformation from BL-VHDI to BL-AAI, both for the compression and superheating limits. This structural transformation can be regarded as the "buckling failure" of the square-ice-nanotube columns, which is dominated by the lateral pressure.
Institute of Scientific and Technical Information of China (English)
Su-deok SHON; Seung-jae LEE; Kang-guk LEE
2013-01-01
This study investigated characteristics of bifurcation and critical buckling load by shape imperfection of space truss,which were sensitive to initial conditions.The critical point and buckling load were computed by the analysis of the eigenvalues and determinants of the tangential stiffness matrix.The two-free-nodes example and star dome were selected for the case study in order to examine the nodal buckling and global buckling by the sensitivity to the eigen buckling mode and the analyses of the influence,and characteristics of the parameters as defined by the load ratio of the center node and surrounding node,as well as rise-span ratio were performed.The sensitivity to the imperfection of the initial shape of the two-free-nodes example,which occurs due 1o snapping at the critical point,resulted in bifurcation before the limit point due to the buckling mode,and the buckling load was reduced by the increase in the amount of imperfection.The two sensitive buckling patterns of the numerical model are established by investigating the displaced position of the free nodes,and the asymmetric eigenmode greatly influenced the behavior of the imperfection shape whether it was at limit point or bifurcation.Furthermore,the sensitive mode of the two-free-nodes example was similar to the in-extensional basis mechanism of a simplified model.The star dome,which was used to examine the influence among several nodes,indicated that the influence of nodal buckling was greater than that of global buckling as the rise-span ratio was higher.Besides,global buckling is occurred with reaching bifurcation point as the value of load ratio was higher,and the buckling load level was about 50％-70％ of load level at limit point.
Experimental Study of Nano-Film Buckling Mode%纳米薄膜屈曲模式的实验研究
Institute of Scientific and Technical Information of China (English)
贾海坤; 王世斌; 李林安; 佟景伟
2011-01-01
Film/substrate system plays a very important role in information science and microelectro-mechanical system (MEMS). Film/substrate structure works commonly under the combination of applied stress and residual stress due to the regular existence of residual stress in film. The load is different due to the different functions of film, which leads different damage modes of film. Buckling under compressive loading is one of the main damage mode of film/substrate structure. This paper focuses on the buckling process of compressed thin titanium film (150nm) and aluminium film (150nm) deposited on an organic glass substrate by using magnetron sputtering technology. In order to simulate film working and to produce regular buckle mode, external uniaxial compression was exerted to specimen. Under the condition of combination effect of axial compressive stress and residual stress, whole process from delamination to bulking was investigated. Mechanism of straight-sided bulking, the propagation of bulking driven delamintaion and the conversion from straight side bucklings to telephone cord buckling were analyzed.%薄膜/基底系统在信息科学以及微电子机械系统中有着十分重要的地位.薄膜中常会有压或拉的残余应力,因此薄膜/基底结构通常是工作在残余应力以及外加应力的联合作用下.根据结构的功用不同,其载荷方式也有不同,从而也导致了不同的破坏模式.压缩载荷下的脱粘屈曲是薄膜基底结构主要的破坏形式之一.本文使用磁控溅射镀膜技术,制作了压缩薄膜试件.选用表面抛光的有机玻璃作为基底,制作了厚度为150nm的铝薄膜和150nm的钛薄膜.在实验中,使用一台光学显微镜观测膜层表面的形貌及其变化.考虑了薄膜在残余应力、外加轴向压应力共同作用下的屈曲破坏模式,并对屈曲的力学行为进行了分析.
Ko, William L.
1995-01-01
Thermal buckling characteristics of hypersonic aircraft sandwich panels of various aspect ratios were investigated. The panel is fastened at its four edges to the substructures under four different edge conditions and is subjected to uniform temperature loading. Minimum potential energy theory and finite element methods were used to calculate the panel buckling temperatures. The two methods gave fairly close buckling temperatures. However, the finite element method gave slightly lower buckling temperatures than those given by the minimum potential energy theory. The reasons for this slight discrepancy in eigensolutions are discussed in detail. In addition, the effect of eigenshifting on the eigenvalue convergence rate is discussed.
Ko, William L.
1996-01-01
Mechanical and thermal buckling behavior of monolithic and metal-matrix composite hat-stiffened panels were investigated. The panels have three types of face-sheet geometry: Flat face sheet, microdented face sheet, and microbulged face sheet. The metal-matrix composite panels have three types of face-sheet layups, each of which is combined with various types of hat composite layups. Finite-element method was used in the eigenvalue extractions for both mechanical and thermal buckling. The thermal buckling analysis required both eigenvalue and material property iterations. Graphical methods of the dual iterations are shown. The mechanical and thermal buckling strengths of the hat-stiffened panels with different face-sheet geometry are compared. It was found that by just microdenting or microbulging of the face sheet, the axial, shear, and thermal buckling strengths of both types of hat-stiffened panels could be enhanced considerably. This effect is more conspicuous for the monolithic panels. For the metal-matrix composite panels, the effect of fiber orientations on the panel buckling strengths was investigated in great detail, and various composite layup combinations offering, high panel buckling strengths are presented. The axial buckling strength of the metal-matrix panel was sensitive to the change of hat fiber orientation. However, the lateral, shear, and thermal buckling strengths were insensitive to the change of hat fiber orientation.
Institute of Scientific and Technical Information of China (English)
Bai Jiangbo; Xiong Junjiang
2014-01-01
This paper seeks to outline the temperature effect on the buckling properties of ultra-thin-walled lenticular collapsible composite tube (LCCT) subjected to axial compression. The buckling tests of the LCCT specimens subjected to axial compression were carried out on INSTRON-500N servo-hydraulic machine in dry state and at the temperatures of 25 ?C, 100 ?C and ?80 ?C. The load-displacement curves and buckling initiation loads were measured and the buckling initiation mechanism was discussed from experimental observations. Experiments show that the buckling initiation load, on average, is only about 2.2% greater at the low temperature of ?80 ?C than at the room temperature of 25 ?C due to the material hardening, demonstrating an insignificant increase in the buckling initiation load, whereas it is about 19.5%lower at the high temperature of 100 ?C than at the room temperature owing to the material softening, implying a significant decrease in the buckling initiation load. The failure mode of the LCCT in axial compres-sion tests at three different temperatures can be reckoned to be characteristic of the buckling initi-ation and propagation around the central region until rupture. The finite element (FE) model is presented to simulate the buckling initiation mechanism based on the eigenvalue-based methodol-ogy. Good correlation between experimental and numerical results is achieved.
Institute of Scientific and Technical Information of China (English)
Zhang Shanyuan; Lei Jianping; Zhao Longmao; Cheng Guoqiang; Lu Guoyun
2000-01-01
This article reports an experimental investigation on the axial impact buckling of thin metallic cylindrical shells fully filled with water. Low velocity impact tests are carried out by DHR-9401 drop hammer rig. The whole process of dynamic buckling is simulated using LS-DYNA computer code. The consistency between experimental observation and numerical simulation is quite satisfactory. The investigation indicates that quite high internal hydrodynamic pressure occurs inside the shell during the impact process. Under the combined action of the high internal pressure and axial compression plastic buckling occurs easily in the thin walled shells and buckling modes take on regular and axisymmetric wrinkles.
Institute of Scientific and Technical Information of China (English)
ZHANG Yitong; LI Cuiyu; XU Jiafu
2004-01-01
The typical micro-knitting structure of knitted fabric, which makes it very different from woven fabric, is described. The tensile tests of knitted fabric are reported. The deformations of the micro-knitting structures are carefully studied. The study indicates that when a knitted fabric sheet is subjected to a tension along w-direction an extra compressive stress field inside loop in c-direction is induced. The extra stress field is also determined through analysis. Finally, a micro-mechanical model of knitted fabric is proposed. This work paves the way for the simulations of buckling modes of a knitted fabric sheet as are observed in experiments.
Finite element analysis of sandwich overall buckling and wrinkling%夹层梁总体屈曲及皱曲的有限元计算
Institute of Scientific and Technical Information of China (English)
梁嫄; 余音; 汪海
2011-01-01
皱曲是夹层结构的一种短波屈曲模式，通常发生于夹心较厚或夹心刚度较低的情况。由于模型规模的限制，在常规有限元建模时通常将夹层板模拟为二维板单元，这种方法忽略了面板和夹心在厚度方向上的相互作用，无法计算出皱曲模式。针对上述问题，本文首先介绍了一个计算夹层结构总体屈曲和皱曲的统一理论，并将此理论的计算结果作为理论解。为了同时计算总体屈曲和皱曲，本文利用MSC．Patran／Nastran有限元软件，建立夹层梁和夹层板的二维截面细节模型，分析了两种不同结构夹层梁的控制屈曲模式，并与理论解进行比较。最后讨论了当夹层板面板为复合材料时，铺层角度对屈曲载荷的影响，并与常规建模方式进行了对比。通过对结果的分析，给出了对夹层结构屈曲及皱曲分析的几点参考。%Wrinkling, a kind of short-wave buckling mode of sandwich Structures, usually occurs when the core is thick or soft. Limited by model scale sandwich panel is usually modeled using shell element during finite element buckling analysis. This approach ignores the interactions of the face sheet and the core in the thickness direction and can not calculate the wrinkling mode. This paper developed a two-dimensional cross-section finite element model of the sandwich panels to analysis overall buckling and wrinkling together. Firstly, a unified theory was presented for overall buckling and wrinkling of sandwich structures. In order to calculate the overall buckling and wrinkling simultaneously, a two-dimensional cross-section details model was developed in MSC. Patran/Nastran software to analyze the control modes of two sandwich beams. The analytical results of sandwich structures were compared with the theoretical solutions. Then the ply angle effect of composite face sheet on buckling is discussed. The result obtained from the method of this paper was
Directory of Open Access Journals (Sweden)
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
Degradation and buckling of metal tubes under cyclic bending and external pressure
Corona, Edmundo
The response and stability of long tubular components under bending and external pressure were investigated. The behavior of the structure under monotonic as well as cyclic bending was examined through combined experimental and analytical efforts. The experiments involved metal seamless tubes with diameter-to-thickness ratios in the range of 17 to 35. Long specimens were tested under combined bending and pressure in a specially developed test facility. Bending-pressure interaction collapse envelopes were first generated for monotonically increasing loading histories. The two loads were found to interact strongly through the ovalization of the cross section and the collapse envelopes to depend on the loading history followed. Cyclic bending under various curvature controlled and moment controlled histories was considered. The factors influencing the rate of accumulation of ovalization and the resulting instabilities were studied parametrically. Buckling under cyclic loads occurred when the ovalization of the tubes reached a critical value approximately equal to the critical value developed under the corresponding monotonically applied loads. The problem was analyzed numerically using kinematics which capture the ovalization of the cross section. The predicted response was found to be very sensitive to the elastic-plastic constitutive models used. This sensitivity was carefully analyzed using state-of-the-art models. In the case of cyclic loading histories, the hardening rules used in such models were found to play a pivotal role in the accuracy of the predictions. The reasons for this sensitivity were studied through a parallel investigation of the behavior of the material under cyclic loads.
Polymer Thin Film Buckling: Wrinkling and Strain Localizations
Ebata, Yuri; Croll, Andrew B.; Crosby, Alfred J.
2011-03-01
Out of plane deformations of thin films are observed in everyday life, e.g. wrinkled aging human skin or folded fabrics. Recently, these deformations are being pursued for fabricating unique patterned surfaces. In this study, the transition from wrinkling, a low-strain buckling behavior, to localized deformations such as fold and delamination, is investigated for polystyrene films with thickness ranging from 5nm to 180nm. The thin films are attached to a uniaxially strained polydimethysiloxane substrate and the strain is released incrementally to apply increasing compressive strain to the attached film. The wavelength and the amplitude of local out-of-plane deformation are measured as global compression is increased to distinguish between wrinkling, folding, and delamination. The transition from wrinkling to strain localizing events is observed by tracking the statistics of amplitude distribution sampled across a large lateral area. A critical strain map is constructed to denote the strain regimes at which wrinkle, fold, and delamination occur. NSF-DMR 0907219.
Buckling delamination induced microchannel: Flow regulation in microfluidic devices
Kang, Jingtian; Wang, Changguo; Xue, Zhiming; Liu, Mengxiong; Tan, Huifeng
2016-09-01
The buckling delamination induced microchannel is employed to regulate fluid flow as a microvalve which can be utilized in microfluidic devices. This microvalve consists of a soft substrate and a stiff thin film, between which there is a pre-set small imperfection. Two critical strain values, namely, on-off strain and failure strain, have been proposed to determine the working strain interval using analytical predictions. Within this interval, the cross-sectional area of the microchannel can be controlled and predicted by different compressive strains of the film/substrate system. The fluid flow rate within this microchannel can be then estimated by both analytical and numerical simulations and adjusted to satisfy different values by alternating the compressive strain. In addition, a demonstrative experiment has been taken to verify the feasibility of this approach. This flexible microvalve has potential in the application where the use of traditional rigid microvalves is improper in flexible microfluidic devices. The method and approach of this paper can provide a general guide for flow rate control in microfluidic devices.
Buckling of Flat Thin Plates under Combined Loading
Directory of Open Access Journals (Sweden)
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.
Aeroelastic Deformation and Buckling of Inflatable Wings under Dynamic Loads
Simpson, Andrew; Smith, Suzanne; Jacob, Jamey
2006-11-01
Inflatable wings have recently been used to control a vehicle in flight via wing warping. Internal pressure is required to maintain wing shape and externally mounted mechanical actuators are used to asynchronously deform the wing semi-spans for control. Since the rigidity of the inflatable wing varies as a function of inflation pressure, there is a need to relate the wing shape with aerodynamic loads. Via wind tunnel tests, span-wise deformations, twist and flutter have been observed under certain dynamic loading conditions. Photogrammetry techniques are used to measure the static aeroelastic deformation of the wings and videogrammetry is used to examine the dynamic shape changes (flutter). The resulting shapes can be used to determine corresponding aerodynamic characteristics. For particular inflation pressures, buckling can be induced at sufficiently high dynamic loads either through high dynamic pressure or large angle of attack. This results in a set of critical loading parameters. An inflatable winged vehicle would require operation within these limits. The focus of the presentation will be on defining and exploring the unsuitable operating conditions and the effects these conditions have on the operation of the wing.
Pneumatic retinopexy versus scleral buckling: a randomised controlled trial.
Mulvihill, A; Fulcher, T; Datta, V; Acheson, R
1996-01-01
Pneumatic retinopexy (PR) is a technique for repairing certain retinal detachments which is easier to perform than conventional sceral buckling (SB) surgery but has comparable results. We performed a prospective, randomised, controlled trial to determine for ourselves whether PR is a safe and acceptable procedure. Twenty patients presenting consecutively with retinal detachments which fulfilled the selection criteria were randomised to have their detachments repaired by either PR or SB, ten patients in each group. The suitable patients had a single retinal break or small group of breaks of not greater than one clock hour in size, situated within the superior eight clock hours of retina. Patients with significant proliferative vitreoretinopathy or other fundus disorders were excluded. All patients in the PR group had local anaesthesia while all those in the SB group had general anaesthesia. Successful reattachment of the retina was achieved with one or more procedures in 90 percent of the PR group and in 100 percent of the SB group. We feel that narrowing the selection criteria for PR may further improve the success rate.
Variational Principles for Buckling of Microtubules Modeled as Nonlocal Orthotropic Shells
Directory of Open Access Journals (Sweden)
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.
Energy Technology Data Exchange (ETDEWEB)
Sahmani, S.; Ansari, R. [University of Guilan, Rasht (Iran, Islamic Republic of)
2011-09-15
Buckling analysis of nanobeams is investigated using nonlocal continuum beam models of the different classical beam theories namely as Euler-Bernoulli beam theory (EBT), Timoshenko beam theory (TBT), and Levinson beam theory (LBT). To this end, Eringen's equations of nonlocal elasticity are incorporated into the classical beam theories for buckling of nanobeams with rectangular cross-section. In contrast to the classical theories, the nonlocal elastic beam models developed here have the capability to predict critical buckling loads that allowing for the inclusion of size effects. The values of critical buckling loads corresponding to four commonly used boundary conditions are obtained using state-space method. The results are presented for different geometric parameters, boundary conditions, and values of nonlocal parameter to show the effects of each of them in detail. Then the results are fitted with those of molecular dynamics simulations through a nonlinear least square fitting procedure to find the appropriate values of nonlocal parameter for the buckling analysis of nanobeams relevant to each type of nonlocal beam model and boundary conditions analysis.
Elasto-plastic buckling analysis of laminated plates including interfacial damage
Energy Technology Data Exchange (ETDEWEB)
Tian, Yanping; Fu, Yiming [Hunan University, State Key Laboratory of Advanced Technology of Design and Manufacturing for Vehicle Body, College of Mechanics and Aerospace, Changsha (China)
2010-06-15
Elasto-plastic buckling of orthotropic laminated plates, which include interfacial damage, is analyzed in detail. Firstly, a novel mixed hardening yield criterion, as an improvement of Hill's counterpart, is proposed for the orthotropic materials on the basis of the plastic theory. And differing from Hill's theory, the present yield criterion is related to the spherical tensor of stress. Then, the incremental elasto-plastic constitutive relations of the mixed hardening orthotropic materials are presented. Secondly, the incremental static equilibrium equations for laminated plates including interfacial damage are established based on Von-Karman type theory and the principle of minimum potential energy. Finally, the elasto-plastic buckling of laminated plates are solved by adopting the Galerkin method and iteration scheme. The numerical results show that buckling of the plate occurs easier due to the existence of interfacial damage, and the critical load trends to constant when the interfacial damage approaches a certain degree. Also, the effect of anisotropy on buckling is obvious and the analysis of elasto-plastic buckling is necessary. (orig.)
On the Minimum Safety Factor in Elastic Buckling of Fuel Rod
Energy Technology Data Exchange (ETDEWEB)
Kim, Hyung Kyu; Kim, Jae Yong; Yoon, Kyung Ho; Lee, Young Ho; Lee, Kang Hee; Kang, Heung Seok; Song, Kun Woo [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2010-10-15
Elastic buckling of a thin tube is an instantaneous collapse phenomenon due to an external pressure. This should be prohibited for a PWR (Pressurized Water Reactor) fuel rod. There is an engineering formula of it; however, safety factor used to be applied to the calculation results since there will be uncertainty in the parameters of the formulae such as dimensional tolerances, environmental conditions and so forth. It is a designer's responsibility to determine an appropriate safety factor that is acceptably economically conservative. Mechanical properties of a material are usually adopted from a material handbook. However, they are usually different from the measured values of the material actually used. A local dimension anomaly critically affects the elastic buckling. Conventional safety factors against the elastic buckling seemed to be large (more than 3.5). However, the reason for this is rarely found. Engineering experience may be incorporated. Therefore, it is highly necessary to propose a minimum safety factor on the elastic buckling while accommodating the above mentioned uncertainties. It is so especially for the dual cooled fuel rod since it has never been used before. The primary purpose of this work is to quantify the aforementioned uncertainties of the parameters in the elastic buckling formula, especially for an outer cladding of the currently studied dual cooled fuel rod. It is extended from the previous theoretical and experimental study
MAGNETIC-ELASTIC BUCKLING OF A THIN CURRENT CARRYING PLATE SIMPLY SUPPORTED AT THREE EDGES
Institute of Scientific and Technical Information of China (English)
WANG Zhiren; WANG Ping; BAI Xiangzhong
2008-01-01
The magnetic-elasticity buckling problem of a current plate under the action of a mechanical load in a magnetic field was studied by using the Mathieu function. According to the magnetic-elasticity non-linear kinetic equation, physical equations, geometric equations, the expression for Lorenz force and the electrical dynamic equation, the magnetic-elasticity dynamic buckling equation is derived. The equation is changed into a standard form of the Mathieu equation using Galerkin's method. Thus, the buckling problem can be solved with a Mathieu equation. The criterion equation of the buckling problem also has been obtained by discussing the eigenvalue relation of the coefficients λ and η in the Mathieu equation. As an example, a thin plate simply supported at three edges is solved here. Its magnetic-elasticity dynamic buckling equation and the relation curves of the instability state with variations in some parameters are also shown in this paper. The conclusions show that the electrical magnetic forces may be controlled by changing the parameters of the current or the magnetic field so that the aim of controlling the deformation, stress, strain and stability of the current carrying plate is achieved.
Sadamoto, S.; Ozdemir, M.; Tanaka, S.; Taniguchi, K.; Yu, T. T.; Bui, T. Q.
2017-02-01
The paper is concerned with eigen buckling analysis of curvilinear shells with and without cutouts by an effective meshfree method. In particular, shallow shell, cylinder and perforated cylinder buckling problems are considered. A Galerkin meshfree reproducing kernel (RK) approach is then developed. The present meshfree curvilinear shell model is based on Reissner-Mindlin plate formulation, which allows the transverse shear deformation of the curved shells. There are five degrees of freedom per node (i.e., three displacements and two rotations). In this setting, the meshfree interpolation functions are derived from the RK. A singular kernel is introduced to impose the essential boundary conditions because of the RK shape functions, which do not automatically possess the Kronecker delta property. The stiffness matrix is derived using the stabilized conforming nodal integration technique. A convected coordinate system is introduced into the formulation to deal with the curvilinear surface. More importantly, the RKs taken here are used not only for the interpolation of the curved geometry, but also for the approximation of field variables. Several numerical examples with shallow shells and full cylinder models are considered, and the critical buckling loads and their buckling mode shapes are calculated by the meshfree eigenvalue analysis and examined. To show the accuracy and performance of the developed meshfree method, the computed critical buckling loads and mode shapes are compared with reference solutions based on boundary domain element, finite element and analytical methods.
Institute of Scientific and Technical Information of China (English)
WANG Hao; LI AiQun; GUO Tong; MA Shuang
2009-01-01
Runyang Suspension Bridge (RSB) with the main span of 1490 m is the longest bridge in China and the third longest one in the world. In this bridge the rigid central buckle is employed for the first time in the mid-span of the suspension bridge in China. For such a super-long-span bridge, the traditional finite element (FE) modeling technique and stress analysis methods obviously cannot satisfy the needs of conducting accurate stress analysis on the central buckle. In this paper, the submodel method is introduced and for the first time used in analyzing the stresses of the central buckle. After an accurate FE submodel of the central buckle was specially established according to the analysis results from the whole FE model, the connection technique between the two-scale FE models was realized and the accurate stresses of the central buckle under various vehicle load cases were then conducted based on the submodel method. The calculation results were testified to be accurate and reliable by the field measurements, which show the efficiency and reliability of the submodel method on analyzing the mechanical condition of the central buckle of long-span suspension bridges. Finally, the working behavior and mechanical characteristics of the central buckle of the RSB under vehicle loads were analyzed based on the calculation and measurement results. The results obtained in this paper can provide theoretic references for analyzing and designing the rigid central buckle in long-span suspension bridges in future.
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Runyang Suspension Bridge (RSB) with the main span of 1490 m is the longest bridge in China and the third longest one in the world. In this bridge the rigid central buckle is employed for the first time in the mid-span of the suspension bridge in China. For such a super-long-span bridge, the traditional finite element (FE) modeling technique and stress analysis methods obviously cannot satisfy the needs of conducting accurate stress analysis on the central buckle. In this paper, the submodel method is in- troduced and for the first time used in analyzing the stresses of the central buckle. After an accurate FE submodel of the central buckle was specially established according to the analysis results from the whole FE model, the connection technique between the two-scale FE models was realized and the ac- curate stresses of the central buckle under various vehicle load cases were then conducted based on the submodel method. The calculation results were testified to be accurate and reliable by the field measurements, which show the efficiency and reliability of the submodel method on analyzing the mechanical condition of the central buckle of long-span suspension bridges. Finally, the working be- havior and mechanical characteristics of the central buckle of the RSB under vehicle loads were ana- lyzed based on the calculation and measurement results. The results obtained in this paper can provide theoretic references for analyzing and designing the rigid central buckle in long-span suspension bridges in future.
Buckling of Rectangular Delamination Bridged by Fibers%有纤维搭桥的矩形脱层屈曲
Institute of Scientific and Technical Information of China (English)
翟三栋; 张扬; 李四平
2011-01-01
The problem of buckling of delamination stitched with fiber-bridge in 3D composites was solved by FEA.Linear springs of tension-only or compression-only distributed on the nodes of delamination cells are used to simulate the fibers and substrate respectively.The problem of eigenvalue buckling is transformed into the problem of geometric nonlinearities with an initial imperfection and solved by FEA of incremental non-linear structural analysis.The results show that there are period contact points（districts） between delamination and substrate.And as the elastic coefficient of the fiber bridge increases,the critical buckling loads may also increase.The relation of the characteristic length and fiber-bridge is expressed by mathematical formula.%用有限元方法求解了3D复合材料中有纤维搭桥的矩形脱层屈曲问题.搭桥纤维和基体分别用分布于脱层单元节点上的只拉不压和只压不拉的线性弹簧单元来模拟,并把有纤维搭桥脱层屈曲的特征值问题转化成考虑初始缺陷的结构几何非线性强度问题,用增量非线性结构分析的有限元方法求解.结果表明,引进纤维搭桥后,脱层屈曲模态上存在与基体周期性的接触点（区）,屈曲临界载荷随着纤维搭桥刚度的增加而增加.最后,通过数学公式给出了脱层屈曲的特征长度与纤维搭桥的关系式.
Stroud, W. J.; Anderson, M. S.; Hennessy, K. W.
1977-01-01
A structural synthesis computer code which accounts for first order effects of an initial bow and which can be used for sizing stiffened composite panels having an arbitrary cross section is used to study graphite blade-stiffened panels. The effect of a small initial bow on both the load carrying ability of panels and on the mass of panels designed to carry a specified load is examined. Large reductions in the buckling load caused by a small initial bow emphasize the need for considering a bow when a panel is designed.
Analysis of polysilicon micro beams buckling with temperature-dependent properties
Shamshirsaz, M; Asgari, M B; Tayefeh, M
2008-01-01
The suspended electrothermal polysilicon micro beams generate displacements and forces by thermal buckling effects. In the previous electro-thermal and thermo-elastic models of suspended polysilicon micro beams, the thermo-mechanical properties of polysilicon have been considered constant over a wide rang of temperature (20- 900 degrees C). In reality, the thermo-mechanical properties of polysilicon depend on temperature and change significantly at high temperatures. This paper describes the development and validation of theoretical and Finite Element Model (FEM) including the temperature dependencies of polysilicon properties such as thermal expansion coefficient and Young's modulus. In the theoretical models, two parts of elastic deflection model and thermal elastic model of micro beams buckling have been established and simulated. Also, temperature dependent buckling of polysilicon micro beam under high temperature has been modeled by Finite Element Analysis (FEA). Analytical results and numerical results ...
Micro-scale delaminating and buckling of thin film on soft substrate
Wu, Dan; Xie, Huimin; Yin, Yajun; Tang, Minjin
2013-03-01
In this paper, a simple process is suggested to estimate the interfacial toughness of the material system ‘aluminum film/soft PDMS substrate’. The specimen, i.e. the aluminum film deposited on the soft polydimethylsiloxane (PDMS) substrate, is subject to a tensile load, and delaminating and buckling of aluminum film are observed in the perpendicular direction to the tensile strain. With the aid of the buckling blisters, the interfacial toughness of the material system is estimated. Large deformation is considered during the buckling of the thin film, and the interfacial toughness is deduced from a fracture theory. Besides, the evolution from one single blister to three blisters and then four blisters is observed in situ under microscope. This simplified method has potential applications to flexible electronics in which interfacial toughness of the metal film/soft substrate must be well controlled.
DYNAMIC BUCKLING OF ELASTIC-PLASTIC COLUMN IMPACTED BY RIGID BODY
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The dynamic buckling of an elastic-plastic column subjected to an axial impact by a rigid body was discussed by using the energy law. The traveling process of elastic-plastic waves under impact action was analyzed by characteristics method. The equation of lateral disturbance used to analyze the problem was developed by taking into account the effect of elastic-plastic stress wave. The power series solution of this problem has been the power series approach. The buckling criterion of this problem was proposed by analyzing the characteristics of the solution. The relationship among critical velocity and impact mass, critical buckling length, hardening modulus was given by using theoretical analysis and numerical computation.
THE DYNAMIC BUCKLING OF ELASTIC-PLASTIC COLUMN SUBJECTED TO AXIAL IMPACT BY A RIGID BODY
Institute of Scientific and Technical Information of China (English)
Han Zhijun; Wang Jingchao; Cheng Guoqiang; Ma Hongwei; Zhang Shanyuan
2005-01-01
The dynamic buckling of an elastic-plastic column subjected to axial impact by a rigid body has been discussed in this paper. The whole traveling process of elastic-plastic waves under impact action is analyzed with the characteristics method. The regularity of stress changes in both column ends and the first separating time of a rigid body and column are obtained. By using the energy principle and taking into account the propagation and reflection of stress waves the lateral disturbance equation is derived and the power series solution is given. In addition,the critical buckling condition can be obtained from the stability analysis of the solution. By numerical computation and analysis, the relationship among critical velocity and impact mass,hardening modulus, and buckling time is given.
End boundary effects on local buckling response of high strength linepipe
Energy Technology Data Exchange (ETDEWEB)
Fatemi, Ali [IMV Projects Atlantic and Memorial University of Newfoundland (Canada); Kenny, Shawn [Memorial University of Newfoundland (Canada); Taheri, Farid [Dalhousie University (Canada); Duan, Da-Ming; Zhou, Joe [TransCanada PipeLines (Canada)
2010-07-01
In the natural gas sector, when long distance transportation of large volumes is required, high strength pipelines are usually used, due to their economic benefits. These pipelines are often installed in harsh environments with high strain conditions and limit state functions need to be set up. The aim of this paper is to study the length to diameter ratio effect on the local buckling response. In order to predict the local buckling response, a model was developed with ABAQUS/Standard, a finite element software, and was adjusted with experimental data. Results showed that conventional methods might not be completely accurate when determining compressive strength limits for short pipeline segments while the model developed herein showed a good prediction. This study highlighted the limits of current methods and showed that end effects on the local buckling response must be addressed; the calibrated finite element model developed can mitigate it but needs further validation.
Energy Technology Data Exchange (ETDEWEB)
Firouz-Abadi, R. D.; Fotouhi, M. M.; Permoon, M. R.; Haddadpour, H. [Sharif University of Technology, Tehran (Iran, Islamic Republic of)
2012-02-15
The small-scale effect on the natural frequencies and buckling of pressurized nanotubes is investigated in this study. Based on the firstorder shear deformable shell theory, the nonlocal theory of elasticity is used to account for the small-scale effect and the governing equations of motion are obtained. Applying modal analysis technique and based on Galerkin's method a procedure is proposed to obtain natural frequencies of vibrations. For the case of nanotubes with simply supported boundary conditions, explicit expressions are obtained which establish the dependency of the natural frequencies and buckling loads of the nanotube on the small-scale parameter and natural frequencies obtained by local continuum mechanics. The obtained solutions generalize the results of nano-bar and -beam models and are verified by the literature. Based on several numerical studies some conclusions are drawn about the small-scale effect on the natural frequencies and buckling pressure of the nanotubes.
Buckling analysis of thick isotropic plates by using exponential shear deformation theory
Directory of Open Access Journals (Sweden)
Sayyad A. S.
2012-12-01
Full Text Available In this paper, an exponential shear deformation theory is presented for the buckling analysis of thick isotropic plates subjected to uniaxial and biaxial in-plane forces. The theory accounts for a parabolic distribution of the transverse shear strains across the thickness, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. Governing equations and associated boundary conditions of the theory are obtained using the principle of virtual work. The simply supported thick isotropic square plates are considered for the detailed numerical studies. A closed form solutions for buckling analysis of square plates are obtained. Comparison studies are performed to verify the validity of the present results. The effects of aspect ratio on the critical buckling load of isotropic plates is investigated and discussed.
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
Magnetic field effects on buckling behavior of smart size-dependent graded nanoscale beams
Ebrahimi, Farzad; Reza Barati, Mohammad
2016-07-01
In this article, buckling behavior of nonlocal magneto-electro-elastic functionally graded (MEE-FG) beams is investigated based on a higher-order beam model. Material properties of smart nanobeam are supposed to change continuously throughout the thickness based on the power-law model. Eringen's nonlocal elasticity theory is adopted to capture the small size effects. Nonlocal governing equations of MEE-FG nanobeam are obtained employing Hamilton's principle and they are solved using the Navier solution. Numerical results are presented to indicate the effects of magnetic potential, electric voltage, nonlocal parameter and material composition on buckling behavior of MEE-FG nanobeams. Therefore, the present study makes the first attempt in analyzing the buckling responses of higher-order shear deformable (HOSD) MEE-FG nanobeams.
Highly stretchable carbon nanotube transistors enabled by buckled ion gel gate dielectrics
Energy Technology Data Exchange (ETDEWEB)
Wu, Meng-Yin; Chang, Tzu-Hsuan; Ma, Zhenqiang [Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Zhao, Juan [School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054 (China); Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Xu, Feng; Jacobberger, Robert M.; Arnold, Michael S., E-mail: michael.arnold@wisc.edu [Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
2015-08-03
Deformable field-effect transistors (FETs) are expected to facilitate new technologies like stretchable displays, conformal devices, and electronic skins. We previously demonstrated stretchable FETs based on buckled thin films of polyfluorene-wrapped semiconducting single-walled carbon nanotubes as the channel, buckled metal films as electrodes, and unbuckled flexible ion gel films as the dielectric. The FETs were stretchable up to 50% without appreciable degradation in performance before failure of the ion gel film. Here, we show that by buckling the ion gel, the integrity and performance of the nanotube FETs are extended to nearly 90% elongation, limited by the stretchability of the elastomer substrate. The FETs maintain an on/off ratio of >10{sup 4} and a field-effect mobility of 5 cm{sup 2} V{sup −1} s{sup −1} under elongation and demonstrate invariant performance over 1000 stretching cycles.
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.
Institute of Scientific and Technical Information of China (English)
SHA Feng-huan; ZHAO Long-mao; YANG Gui-tong
2005-01-01
The dynamic response of a double-walled carbon nanotube embedded in elastic medium subjected to periodic disturbing forces is investigated. Investigation of the dynamic buckling of a double-walled carbon nanotube develops continuum model. The effect of the van der Waals forces between two tubes and the surrounding elastic medium for axial dynamic buckling are considered. The buckling model subjected to periodic disturbing forces and the critical axial strain and the critical frequencies are given. It is found that the critical axial strain of the embedded multi-walled carbon nanotube due to the intertube van der Waals forces is lower than that of an embedded single-walled carbon nanotube. The van der Waals forces and the surrounding elastic medium affect region of dynamic instability. The van der Waals forces increase the critical frequencies of a double-walled carbon nanotube. The effect of the surrounding elastic medium for the critical frequencies is small.
Overcurvature describes the buckling and folding of rings from curved origami to foldable tents
Mouthuy, Pierre-Olivier; Coulombier, Michael; Pardoen, Thomas; Raskin, Jean-Pierre; Jonas, Alain M.
2012-12-01
Daily-life foldable items, such as popup tents, the curved origami sculptures exhibited in the Museum of Modern Art of New York, overstrained bicycle wheels, released bilayered microrings and strained cyclic macromolecules, are made of rings buckled or folded in tridimensional saddle shapes. Surprisingly, despite their popularity and their technological and artistic importance, the design of such rings remains essentially empirical. Here we study experimentally the tridimensional buckling of rings on folded paper rings, lithographically processed foldable microrings, human-size wood sculptures or closed arcs of Slinky springs. The general shape adopted by these rings can be described by a single continuous parameter, the overcurvature. An analytical model based on the minimization of the energy of overcurved rings reproduces quantitatively their shape and buckling behaviour. The model also provides guidelines on how to efficiently fold rings for the design of space-saving objects.
Contractile units in disordered actomyosin bundles arise from F-actin buckling
Lenz, Martin; Gardel, Margaret L; Dinner, Aaron R
2012-01-01
Bundles of filaments and motors are central to contractility in cells. The classic example is striated muscle, where actomyosin contractility is mediated by highly organized sarcomeres which act as fundamental contractile units. However, many contractile bundles in vivo and in vitro lack sarcomeric organization. Here we propose a model for how contractility can arise in actomyosin bundles without sarcomeric organization and validate its predictions with experiments on a reconstituted system. In the model, internal stresses in frustrated arrangements of motors with diverse velocities cause filaments to buckle, leading to overall shortening. We describe the onset of buckling in the presence of stochastic actin-myosin detachment and predict that buckling-induced contraction occurs in an intermediate range of motor densities. We then calculate the size of the "contractile units" associated with this process. Consistent with these results, our reconstituted actomyosin bundles contract at relatively high motor dens...
The buckling response of symmetrically laminated composite plates having a trapezoidal planform area
Radloff, H. D., II; Hyer, M. W.; Nemeth, M. P.
1994-08-01
The focus of this work is the buckling response of symmetrically laminated composite plates having a planform area in the shape of an isosceles trapezoid. The loading is assumed to be inplane and applied perpendicular to the parallel ends of the plate. The tapered edges of the plate are assumed to have simply supported boundary conditions, while the parallel ends are assumed to have either simply supported or clamped boundary conditions. A semi-analytic closed-form solution based on energy principles and the Trefftz stability criterion is derived and solutions are obtained using the Rayleigh-Ritz method. Intrinsic in this solution is a simplified prebuckling analysis which approximates the inplane force resultant distributions by the forms Nx=P/W(x) and Ny=Nxy=0, where P is the applied load and W(x) is the plate width which, for the trapezoidal planform, varies linearly with the lengthwise coordinate x. The out-of-plane displacement is approximated by a double trigonometric series. This analysis is posed in terms of four nondimensional parameters representing orthotropic and anisotropic material properties, and two nondimensional parameters representing geometric properties. For comparison purposes, a number of specific plate geometry, ply orientation, and stacking sequence combinations are investigated using the general purpose finite element code ABAQUS. Comparison of buckling coefficients calculated using the semi-analytical model and the finite element model show agreement within 5 percent, in general, and within 15 percent for the worst cases. In order to verify both the finite element and semi-analytical analyses, buckling loads are measured for graphite/epoxy plates having a wide range of plate geometries and stacking sequences. Test fixtures, instrumentation system, and experimental technique are described. Experimental results for the buckling load, the buckled mode shape, and the prebuckling plate stiffness are presented and show good agreement with the
Non-drainage scleral buckling with solid silicone elements
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Pukhraj Rishi
2014-01-01
Full Text Available Background: With the increasing number of cataract surgeries, incidence of posterior segment complications including rhegmatogenous retinal detachment (RRD is likely to rise. Scleral buckling (SB surgery is an effective and less expensive option. The primary advantage of non-drainage procedure is avoidance of possible complications associated with trans-choroidal drainage. The aim of present study is to describe the clinical profile of subjects undergoing non-drainage SB surgery with solid silicone elements for RRD and analyze their treatment outcomes. Materials and Methods: This was a retrospective, non-randomized, interventional study at a tertiary care center. Three hundred and six eyes of 298 patients undergoing non-drainage SB surgery with solid silicone elements from year 2000 to 2006 were included. Inclusion criteria were primary RRD, peripheral depressible retinal break, media clarity affording peripheral retinal view and proliferative vitreo-retinopathy (PVR up to grade C2. Uni- and multivariate analyses was done to analyze factors affecting anatomical and visual outcomes. Statistical analysis was performed using SPSS Version 10. Results: Mean follow-up was 303 ± 393.33 days. Primary anatomical success was obtained in 279 (91.2% eyes; primary functional success in 286 (93.5% eyes. PVR (grade B or C, intraocular pressure <10 mm Hg and the inability to find a retinal break were significantly associated with final anatomical failure. Baseline vision ≤3/60 was significantly associated with poor visual recovery. Conclusions: SB surgery is reasonably safe and highly efficacious. Solid silicone elements are effective in non-drainage SB surgery. However, case selection is important.
Atomistic study of the buckling of gold nanowires
Energy Technology Data Exchange (ETDEWEB)
Olsson, Paer A.T., E-mail: par.olsson@mek.lth.se [Division of Mechanics, Lund University, PO Box 118, SE-221 00 Lund (Sweden); Park, Harold S., E-mail: parkhs@bu.edu [Department of Mechanical Engineering, Boston University, Boston, MA 02215 (United States)
2011-06-15
In this work, we present results from atomistic simulations of gold nanowires under axial compression, with a focus on examining the effects of both axial and surface orientation effects on the buckling behavior. This was accomplished by using molecular statics simulations while considering three different crystallographic systems: <1 0 0>/{l_brace}1 0 0{r_brace}, <1 0 0>/{l_brace}1 1 0{r_brace} and <1 1 0>/{l_brace}1 1 0{r_brace}{l_brace}1 0 0{r_brace}, with aspect ratios spanning from 20 to 50 and cross-sectional dimensions ranging from 2.45 to 5.91 nm. The simulations indicate that there is a deviation from the inverse square length dependence of critical forces predicted from traditional linear elastic Bernoulli-Euler and Timoshenko beam theories, where the nature of the deviation from the perfect inverse square length behavior differs for different crystallographic systems. This variation is found to be strongly correlated to either stiffening or increased compliance of the tangential stiffness due to the influence of nonlinear elasticity, which leads to normalized critical forces that decrease with decreasing aspect ratio for the <1 0 0>/{l_brace}1 0 0{r_brace} and <1 0 0>/{l_brace}1 1 0{r_brace} systems, but increase with decreasing aspect ratio for the <1 1 0>/{l_brace}1 1 0{r_brace}{l_brace}1 0 0{r_brace} system. In contrast, it was found that the critical strains are all lower than their bulk counterparts, and that the critical strains decrease with decreasing cross-sectional dimensions; the lower strains may be an effect emanating from the presence of the surfaces, which are all more elastically compliant than the bulk and thus give rise to a more compliant flexural rigidity.
Okajima, Kenji; Imai, Junichi; Tanaka, Tadatsugu; Iida, Toshiaki
Damage to piles in the liquefied ground is frequently reported. Buckling by the excess vertical load could be one of the causes of the pile damage, as well as the lateral flow of the ground and the lateral load at the pile head. The buckling mechanism is described as a complicated interaction between the pile deformation by the vertical load and the earth pressure change cased by the pile deformation. In this study, series of static buckling model tests of a pile were carried out in dried sand ground with various thickness of the layer. Finite element analysis was applied to the test results to verify the effectiveness of the elasto-plastic finite element analysis combining the implicit-explicit mixed type dynamic relaxation method with the return mapping method to the pile buckling problems. The test results and the analysis indicated the possibility that the buckling load of a pile decreases greatly where the thickness of the layer increases.
Prediction of the critical buckling load of multi-walled carbon nanotubes under axial compression
Timesli, Abdelaziz; Braikat, Bouazza; Jamal, Mohammad; Damil, Noureddine
2017-02-01
In this paper, we propose a new explicit analytical formula of the critical buckling load of double-walled carbon nanotubes (DWCNT) under axial compression. This formula takes into account van der Waals interactions between adjacent tubes and the effect of terms involving tube radii differences generally neglected in the derived expressions of the critical buckling load published in the literature. The elastic multiple Donnell shells continuum approach is employed for modelling the multi-walled carbon nanotubes. The validation of the proposed formula is made by comparison with a numerical solution. The influence of the neglected terms is also studied.
POST-BUCKLING OF A CANTILEVER ROD WITH VARIABLE CROSS-SECTIONS UNDER COMBINED LOAD
Institute of Scientific and Technical Information of China (English)
吴莹; 李世荣; 滕兆春
2003-01-01
Based on the geometrically nonlinear theory of axially extensible elastic rods,the governing equations of post-buckling of a clamped-free rod with variable cross-sections,subjected to a combined load, a concentrated axial load P at the free end and a nonuniformly distributed axial load q, are established. By using shooting method, the strong nonlinear boundary value problems are numerically solved. The secondary equilibrium paths and the post-buckling configurations of the rod with linearly varied cross-sections are presented.
WEIGHTED SOLUTION OF SMALL-DEFLECTION BUCKLING EQUATION OF THIN SHELL
Institute of Scientific and Technical Information of China (English)
王宗利; 王熙; 郝文华
2001-01-01
Based on small-deflection buckling equation, a weighted solution for critical load is presented. Usually, it is very difficult to solve the equation for general problems,especially those with complicated boundary conditions. Axisymmetric problem was studied as an example. Influencing factors were found from the equation and averaged as the buckling load by introducing weights. To determine those weights, some special known results were applied. This method solves general complicated problems by using the solutions of special simple problems, simplifies the solving procedure and expands the scope of solvable problem. Compared with numerical solution, it also has fine precision.
Nonlinear dynamic buckling of stiffened plates under in-plane impact load
Institute of Scientific and Technical Information of China (English)
张涛; 刘土光; 赵耀; 罗家智
2004-01-01
This paper presents a simple solution of the dynamic buckling of stiffened plates under in-plane impact loading. Based on large deflection theory, a discretely stiffened plate model has been used. The tangential stresses of stiffeners and in-plane displacement are neglected. Appling the Hamilton's principle, the motion equations of stiffened plates are obtained. The deflection of the plate is taken as Fourier series, and using Galerkin method the discrete equations can be deduced, which can be solved easily by Runge-Kutta method. The dynamic buckling loads of the stiffened plates are obtained form Budiansky-Roth criterion.
DYNAMIC BUCKLING OF STIFFENED PLATES UNDER FLUID-SOLID IMPACT LOAD
Institute of Scientific and Technical Information of China (English)
张涛; 刘土光; 熊有伦; 张维衡
2004-01-01
A simple solution of the dynamic buckling of stiffened plates under fluid-solid impact loading is presented. Based on large deflection theory, a discretely stiffened plate model has been used. The tangential stresses of stiffeners and in-plane displacement are neglected. Applying the Hamilton' s principle, the motion equations of stiffened plates are obtained. The deflection of the plate is taken as Fourier series, and using Galerkin method,the discrete equations can be deduced, which can be solved easily by Runge-Kutta method.The dynamic buckling loads of the stiffened plates are obtained from Budiansky-Roth ( B-R )curves.
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.
Growth of buckling instabilities during radial collapse of an impulsively-loaded cylindrical shell
Energy Technology Data Exchange (ETDEWEB)
Duffey, T.A.; Warnes, R.H.; Greene, J.M.
1987-01-01
Conditions leading to the growth of initial imperfections for rings or cylindrical shells subjected to initial uniform inward impulsive velocity loading are investigated. The work is motivated by a need to prevent buckling of rings during the contracting ring test, which is used to determine intermediate strain rate compressive stress-strain data. A previous analysis by Abrahamson is extended to include deceleration of the ring during inward motion; and the results of this deceleration are found to greatly influence the growth of imperfections (buckling). Qualitative comparisons with experimental data are presented.
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.
Dynamic and buckling analysis of a thin elastic-plastic square plate in a uniform temperature field
Institute of Scientific and Technical Information of China (English)
Shifu Xiao; Bin Chen
2005-01-01
The nonlinear models of the elastic and elasticlinear strain-hardening square plates with four immovably simply-supported edges are established by employing Hamilton's Variational Principle in a uniform temperature field. The unilateral equilibrium equations satisfied by the plastically buckled equilibria are also established. Dynamics and stability of the elastic and plastic plates are investigated analytically and the buckled equilibria are investigated by employing Galerkin-Ritz's method. The vibration frequencies, the first critical temperature differences of instability or buckling, the elastically buckled equilibria and the extremes depending on the final loading temperature difference of the plastically buckled equillibria of the plate are obtained. The results indicate that the critical buckling value of the plastic plate is lower than its critical instability value and the critical value of its buckled equilibria turning back to the trivial equilibrium are higher than the value. However, three critical values of the elastic plate are equal. The unidirectional snap-through may occur both at the stress-strain boundary of elasticity and plasticity and at the initial stage of unloading of the plastic plate.
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 buck
The effect of interface adhesion on buckling and cracking of hard thin films
Flores-Johnson, E. A.; Shen, L.; Annabattula, R. K.; Onck, P. R.; Shen, Y. G.; Chen, Z.
2014-01-01
The physics behind the strain-released buckling patterns including telephone cords and straight-sided wrinkles with and without cracks, as experimentally observed in sputter-deposited Ti-Si-N thin films on Si substrates, is investigated with model-based simulations by varying the mechanical properti
The Mexican hat effect on the delamination buckling of a compressed thin film
Zhang, Yin; Liu, Yun
2014-12-01
Because of the interaction between film and substrate, the film buckling stress can vary significantly, depending on the delamination geometry, the film and substrate mechanical properties. The Mexican hat effect indicates such interaction. An analytical method is presented, and related dimensional analysis shows that a single dimensionless parameter can effectively evaluate the effect.
Dynamic buckling of elastic-plastic cylindrical shells and axial stress waves
Institute of Scientific and Technical Information of China (English)
徐新生; 苏先樾; 王仁
1995-01-01
The mechanism for bifurcation of elastic-plastic buckling of the semi-infinite cylindrical shell under impacting axial loads is proposed based on the theory of stress wave. Numerical results on three kinds of end supports and step and impulse loads are given.
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
DEFF Research Database (Denmark)
Pedersen, Niels Leergaard; Nielsen, A.
2004-01-01
and the objective of the optimizations is minimum mass with constraints on (possibly multiple) eigenfrequencies, displacements, and stresses. For the case of stress constraints, we deal differently with tensile and compressive stresses, for which we control buckling on the element level. The stress constraints...
Institute of Scientific and Technical Information of China (English)
PENG Fan; FU YiMing; LIU YiFan
2008-01-01
Based on the first order shear deformation theory and classic buckling theory, the paper investigates the creep buckling behavior of viscoelastic laminated plates and laminated circular cylindrical shells. The analysis and elaboration of both instantaneous elastic critic load and durable critic load are emphasized. The buckling load in phase domain is obtained from governing equations by applying Laplace transform, and the instantaneous elastic critic load and durable critic load are determined according to the extreme value theorem for inverse Laplace transform. It is shown that viscoelastic approach and quasi-elastic approach yield identical solutions for these two types of critic load respectively. A transverse disturbance model is developed to give the same mechanics significance of durable critic load as that of elastic critic load. Two types of critic loads of boron/epoxy composite laminated plates and circular cylindrical shells are discussed in detail individually, and the influencing factors to induce creep buckling are revealed by examining the viscoelasticity incorporated in transverse shear deformation and in-plane flexibility.
Directory of Open Access Journals (Sweden)
Yokoyama T
2015-01-01
Full Text Available Toshiyuki Yokoyama, Koki Kanbayashi, Tamaki YamaguchiDepartment of Ophthalmology, Juntendo University Nerima Hospital, Tokyo, JapanPurpose: To assess the treatment of pediatric patients with rhegmatogenous retinal detachment (RRD by scleral buckling with chandelier illumination.Methods: Three eyes were treated in three patients, healthy boys aged 7 years, 12 years, and 11 years, with RRD, macular involvement, and small retinal holes, of which two were preoperatively undetectable. Conventional scleral buckling with cryoretinopexy was performed under the contact lens for vitreous surgery or noncontact wide-angle viewing system using 27-gauge twin chandelier illumination.Results: The only known predisposing factor for retinal detachment was myopia stronger than 3 D with lattice retinal degeneration in two of the three patients. Retinal reattachment was achieved in all cases without intra- or postoperative complications. However, visual recovery was limited in one of the three patients.Conclusion: Scleral buckling with chandelier illumination is effective for pediatric RRD, especially if the retinal hole is difficult to detect preoperatively. However, visual recovery was sometimes limited because of macular involvement due to late diagnosis, which is one of the characteristic features of pediatric RRD.Keywords: pediatric rhegmatogenous retinal detachment, chandelier illumination, scleral buckling
Mesozoic(?) lithosphere-scale buckling of the East European Craton in southern Ukraine
DEFF Research Database (Denmark)
Starostenko, V.; Janik, T.; Lysynchuk, D.
2013-01-01
by compressional lithospheric-scale buckling and ascribed to Late Jurassic–Early Cretaceous and/or end Cretaceous collision-related tectonic events associated with closing of the Palaeotethys and Neotethys oceans in this part of Europe. To our knowledge, no such spectacular folds deforming the Moho, have been...
Thermal Buckling and Free Vibration Analysis of Heated Functionally Graded Material Beams
Directory of Open Access Journals (Sweden)
Khalane Sanjay Anandrao
2013-05-01
Full Text Available 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 terms of buckling temperatures and frequencies, is presented, considering the temperature independent and temperature dependent material properties. The buckling temperature and fundamental frequency obtained using the temperature independent material properties is higher than that obtained by using the temperature dependent material properties, for all the material distributions, geometrical parameters in terms of length to thickness ratios and the boundary conditions considered. It is also observed that the frequencies of the FGM beam will reduce with the increase in temperature. This observation is applicable for the higher modes of vibration also. The necessity of considering the temperature dependency of material properties in determining thermal buckling and vibration characteristics of FGM beams is clearly demonstrated.Defence Science Journal, 2013, 63(3, pp.315-322, DOI:http://dx.doi.org/10.14429/dsj.63.2370
Rigorous buckling analysis of size-dependent functionally graded cylindrical nanoshells
Sun, Jiabin; Lim, C. W.; Zhou, Zhenhuan; Xu, Xinsheng; Sun, Wei
2016-06-01
This paper presents new analytical solutions for buckling of carbon nanotubes (CNTs) and functionally graded (FG) cylindrical nanoshells subjected to compressive and thermal loads. The model applies Eringen's nonlocal differential constitutive relation to describe the size-dependence of nanoshells. Based on Reddy's higher-order shear deformation theory, governing equations are established and solved by separating the variables. The analysis first re-examines the classical buckling of single-walled CNTs. Accurate solutions are established, and it is found that the buckling stress decreases drastically when the nonlocal parameter reaches a certain value. For CNTs with constant wall-thickness, the buckling stress eventually decreases with enhanced size effect. By comparing with CNTs molecular dynamic simulations, the obtained nonlocal parameters are much smaller than those proposed previously. Subsequently, FG cylindrical nanoshells are analyzed, and it is concluded that similar behavior that has been observed for CNTs is also valid for FG cylindrical nanoshells. The paper further discusses in detail the effects of different geometric parameters, material distribution, and temperature field.
Ansari, R.; Norouzzadeh, A.
2016-10-01
The size-dependent static buckling responses of circular, elliptical and skew nanoplates made of functionally graded materials (FGMs) are investigated in this article based on an isogeometric model. The Eringen nonlocal continuum theory is implemented to capture nonlocal effects. According to the Gurtin-Murdoch surface elasticity theory, surface energy influences are also taken into account by the consideration of two thin surface layers at the top and bottom of nanoplate. The material properties vary in the thickness direction and are evaluated using the Mori-Tanaka homogenization scheme. The governing equations of buckled nanoplate are achieved by the minimum total potential energy principle. To perform the isogeometric analysis as a solution methodology, a novel matrix-vector form of formulation is presented. Numerical examples are given to study the effects of surface stress as well as other important parameters on the critical buckling loads of functionally graded nanoplates. It is found that the buckling configuration of nanoplates at small scales is significantly affected by the surface free energy.
Buckling and postbuckling of radially loaded microtubules by nonlocal shear deformable shell model.
Shen, Hui-Shen
2010-05-21
This paper presents an investigation on the buckling and postbuckling of microtubules (MTs) subjected to a uniform external radial pressure in thermal environments. The microtubule is modeled as a nonlocal shear deformable cylindrical shell which contains small scale effects. The governing equations are based on higher order shear deformation shell theory with a von Kármán-Donnell-type of kinematic nonlinearity and include the extension-twist and flexural-twist couplings. The thermal effects are also included and the material properties are assumed to be temperature-dependent. A singular perturbation technique is employed to determine the buckling pressure and postbuckling equilibrium paths. The small scale parameter e(0)a is estimated by matching the buckling pressure of MTs measured from the experiments with the numerical results obtained from the nonlocal shear deformable shell model. The numerical results show that buckling pressure and postbuckling behavior of MTs are very sensitive to the small scale parameter e(0)a. The results reveal that the 13_3 microtubule has a stable postbuckling path, whereas the 13_2 microtubule has an unstable postbuckling behavior due to the presence of skew angles.
Post-buckled precompressed (PBP) subsonic micro flight control actuators and surfaces
Barrett, R.; Vos, R.; De Breuker, R.
2007-01-01
This paper describes a new class of flight control actuators using Post-Buckled Precompressed (PBP) piezoelectric elements to provide much improved actuator performance. These PBP actuator elements are modeled using basic large deflection Euler-beam estimations accounting for laminated plate effects
Advanced control techniques for post-buckled precompressed (PBP) flight control actuators
Groen, M.; Van Schravendijk, M.; Barrett, R.; Vos, R.
2009-01-01
The dynamic response of a new class of flight control actuators that rely on post-buckled recompressed (PBP) piezoelectric elements is investigated. While past research has proven that PBP actuators are capable of generating deflections three times higher than conventional bimorph actuators, this pa
Zhen, Wu; Wanji, Chen
2007-05-01
Buckling response of angle-ply laminated composite and sandwich plates are analyzed using the global-local higher order theory with combination of geometric stiffness matrix in this paper. This global-local theory completely fulfills the free surface conditions and the displacement and stress continuity conditions at interfaces. Moreover, the number of unknowns in this theory is independent of the number of layers in the laminate. Based on this global-local theory, a three-noded triangular element satisfying C1 continuity conditions has also been proposed. The bending part of this element is constructed from the concept of DKT element. In order to improve the accuracy of the analysis, a method of modified geometric stiffness matrix has been introduced. Numerical results show that the present theory not only computes accurately the buckling response of general laminated composite plates but also predicts the critical buckling loads of soft-core sandwiches. However, the global higher-order theories as well as first order theories might encounter some difficulties and overestimate the critical buckling loads for soft-core sandwich plates.
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...
Institute of Scientific and Technical Information of China (English)
Zhang Yongcun; Li Xiaobin; Liu Shutian
2016-01-01
Auxetic materials have previously been shown to enhance various performances due to its unusual property of becoming fatter when uniaxially stretched and thinner when uniaxially com-pressed (i.e., the materials exhibit a negative Poisson’s ratio). The current study focuses on assessing the potential of an auxetic material to enhance the buckling capacity of a rectangular plate under uniaxial compression. The in-plane translational restraint along the unloaded edges that was often neglected in open literature is taken into consideration in our buckling model proposed in this study. The closed-form expressions for the critical buckling coefficient of the rectangle are provided and the predicted results agree well with those determined by the finite element method. Further-more, the results indicate that the buckling performance of a rectangular plate under uniaxial com-pression can be significantly improved by replacing the traditional material that has a positive Poisson’s ratio with an auxetic material when there is in-plane translation restraint along the unloaded edges.
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.
Post-Buckled Precompressed (PBP) piezoelectric actuators for UAV flight control
Vos, R.; Barrett, R.; Krakers, L.; Van Tooren, M.
2006-01-01
This paper presents the use of a new class of flight control actuators employing Post-Buckled Precompressed (PBP) piezoelectric elements in morphing wing Uninhabited Aerial Vehicles (UAVs). The new actuator relieson axial compression to amplify deflections and control forces simultaneously. Two desi
Buckling Capacity Curves for Steel Spherical Shells Loaded by the External Pressure
Directory of Open Access Journals (Sweden)
Błażejewski Paweł
2015-03-01
Full Text Available Assessment of buckling resistance of pressurised spherical cap is not an easy task. There exist two different approaches which allow to achieve this goal. The first approach involves performing advanced numerical analyses in which material and geometrical nonlinearities would be taken into account as well as considering the worst imperfections of the defined amplitude. This kind of analysis is customarily called GMNIA and is carried out by means of the computer software based on FEM. The other, comparatively easier approach, relies on the utilisation of earlier prepared procedures which enable determination of the critical resistance pRcr, the plastic resistance pRpl and buckling parameters a, b, h, l 0 needed to the definition of the standard buckling resistance curve. The determination of the buckling capacity curve for the particular class of spherical caps is the principal goal of this work. The method of determination of the critical pressure and the plastic resistance were described by the authors in [1] whereas the worst imperfection mode for the considered class of spherical shells was found in [2]. The determination of buckling parameters defining the buckling capacity curve for the whole class of shells is more complicated task. For this reason the authors focused their attention on spherical steel caps with the radius to thickness ratio of R/t = 500, the semi angle j = 30o and the boundary condition BC2 (the clamped supporting edge. Taking into account all imperfection forms considered in [2] and different amplitudes expressed by the multiple of the shell thickness, sets of buckling parameters defining the capacity curve were determined. These parameters were determined by the methods proposed by Rotter in [3] and [4] where the method of determination of the exponent h by means of additional parameter k was presented. As a result of the performed analyses the standard capacity curves for all considered imperfection modes and
Institute of Scientific and Technical Information of China (English)
PENG Fan; FU YiMing; CHEN YaoJun
2008-01-01
The effect of matrix cracking on the bifurcation creep buckling of viscoelastic laminated circular cylindrical shells is investigated. The viscoelastic behavior of laminas is modeled by Schapery's integral constitutive equation with growing ma-trix cracks. The values of damage variables are correlated to non-dimensional density of matrix cracks relying on the formulas from meso-mechanics approach, and the evolution equation predicting the growth rate of density of matrix cracks is assumed to follow a power type relation with transverse tensile stress. The gov-erning equations for pre-buckling creep deformation and bifurcation buckling of laminated circular cylindrical shells under axial compression are obtained on the basis of the Donnell type shallow shell theory and Karman-Donnell geometrically nonlinear relationship. Corresponding solution strategy is constructed by inte-grating finite-difference technique, trigonometric series expansion method and Taylor's numerical recursive scheme for convolution integration. The bifurcation creep buckling of symmetrically laminated glass-epoxy circular cylindrical shells with matrix creep cracking coupled are examined for various geometrical parame-ters and parameters of damage evolution as well as boundary conditions. The nu-merical results show that matrix creep cracking remarkably shortens the critic time of bifurcation buckling and reduces the durable critic loads, and its effects become weak and finally vanish with the increase of the ratio of radius to thickness in the case of short laminated circular cylindrical shells, also the influence of the matrix creep cracking is mainly dependent on the boundary conditions at two ends for moderately long circular cylindrical shells.
Determination of buckling in the IPEN/MB-01 Reactor in cylindrical configuration
Energy Technology Data Exchange (ETDEWEB)
Purgato, Rafael Turrini; Bitelli, Ulysses d' Utra; Aredes, Vitor Ottoni; Silva, Alexandre F. Povoa da; Santos, Diogo Feliciano dos; Mura, Luis Felipe L.; Jerez, Rogerio, E-mail: rtpurgato@ipen.br, E-mail: ubitelli@ipen.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)
2013-07-01
One of the key parameters in reactor physics is the buckling of a reactor core. It is related to important parameters such as reaction rates, nuclear power operation, fuel burning, among others. In a critical reactor, the buckling depends on the geometric and material characteristics of the reactor core. This paper presents the results of experimental buckling in the reactor IPEN/MB-01 nuclear reactor in its cylindrical configuration with 28 fuel rods along its diameter. The IPEN/MB-01 is a zero power reactor designed to operate at a maximum power of 100 watts, it is a versatile nuclear facility which allows the simulation of all the characteristics of a large nuclear power reactor and ideal for this type of measurement. We conducted a mapping of neutron flux inside the reactor and thereby determined the total buckling of the cylindrical configuration. The reactor was operated for an hour. Then, the activation of the fuel rods was measured by gamma spectrometry on a rod scanner HPGe detector. We analyzed the gamma photons of the {sup 239}Np (276,6 keV) for neutron capture and the {sup 143}Ce (293,3 keV) for fission on both {sup 238}U and {sup 235}U, respectively. We analyzed the axial and radial directions. Other measurements were performed using wires and gold foils in the radial and axial directions of the reactor core. The results showed that the cylindrical configuration compared to standard rectangular configuration of the IPEN/MB-01 reactor has a higher neutron economy, since in this configuration there is less leakage of neutrons. The Buckling Total obtained from the three methods was 95.84 ± 2.67 m{sup -2}. (author)
Institute of Scientific and Technical Information of China (English)
梅卫进; 杨昌锦
2015-01-01
Devices of layered combination structure consisting of piezoelectric substrate and metal electrode are widely used in electric engineering. But, delaminate buckling of such layered structures may occur easily in the interface under the applied loading. In order to study critical delamination buckling load and the influence of the electromechanical coupling effect on the critical buckling load, and to provide a guidance for the design of such layered devices, the ABAQUS code was used to study the circular delamination buckling problem. Results of the finite element analysis are compared with those by the elastic stability theory of the simply supported and clamped circular delamination thin discs, and the correctness of the finite element analysis is verified.%由压电材料层与金属电极组合的层状结构功能器件应用很广，但在工程应用时因受荷载作用此类层合结构很容易在层间界面出现脱层屈曲现象。为了研究脱层屈曲时的临界荷载、力电耦合效应对屈曲临界载荷的影响，为此类层状器件的设计提供参考，本文用ABAQUS对压电层表面金属层圆形脱层的屈曲问题进行有限元研究，并将有限元解与利用弹性稳定理论将圆形脱层简化成薄圆板在考虑简支和固支边界时的结果进行对比分析，用以说明有限元结果的正确性。
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.
Thermal post-buckling of slender composite and FGM columns through a simple and novel FE formulation
Indian Academy of Sciences (India)
G VENKATESWARA RAO; K SANJAY ANANDRAO; R K GUPTA
2016-08-01
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 additional thermal load beyond critical temperature, which can be obtained using von-Karman geometric nonlinearity, applicable for moderately large deflections. In the present study, the solution of the nonlinear post-buckling problem is obtained by treating it as a linear eigenvalue problem using the concept of effective stiffness. Here, the total degrees of freedom (dof) of the discretized column are reduced and the postbuckling load is obtained without the need for iterative analysis. Comparison of the numerical results obtainedfrom this FE formulation is in very good agreement with those obtained from the earlier FE formulations.
Alart, P.; Barboteu, M.; Gril, J.
2004-09-01
In this paper a numerical modelling of non linear problems involving large deformations and frictional contact conditions is proposed. The motivation of this work comes from the study of the cellular materials (such as wood or foams) undergoing strong deformations. We restrict our study to a regular cellular network of hexagonal cells with thin walls. Strong loadings can generate at first buckling phenomena, then self-contact in the cell. Renouncing homogenization procedures, not always pertinent in this case, we have developed direct simulations. After giving the mechanical and mathematical formulations of the problem, we present two advanced numerical tools to solve large non linear frictional multicontact problems. This numerical modelling is based on an arc-length continuation method which permits to snap through singular points due to buckling phenomena and on an optimal domain decomposition method adapted to frictional contact problems. Finally, mechanical investigations of the contactless buckling and the post-buckling provide some pertinent parameters controlling the deformation process.