Search

This paper investigates the instability and buckling characteristics of a porous microplate under the influence of electrostatic fields, taking into account the implications of the intermolecular Casimir forces. Employing the modified couple stress theory, this research formulates equations that encapsulate the interplay between electrostatic and Casimir forces within porous plates. The analysis integrates distributed support loads, employing both Galerkin mode summation and finite element methods to solve static deformation equations and determine pull-in instability voltages and buckling loads. A novel approach is introduced, and equilibrium relationships are derived with respect to displacement to determine both the buckling load and instability voltage. This study effectively compares classical and non-classical theories, scrutinizing the effects of dimensionless length scale parameters and porosity ratios on maximum displacement, pull-in instability voltages, and buckling loads. The results demonstrate that the analytical method converges swiftly and aligns with the findings of the finite element method. The method for deriving equilibrium relationships proves to be accurate in predicting both instability voltage and buckling load. Additionally, the instability voltage exhibits an almost linear relationship with variations in the percentage of porosity, and similarly, the buckling load undergoes linear changes with alterations in porosity percentage. Hence, formulas for the linear relationships are calculated for both of these associations. [ABSTRACT FROM AUTHOR]

Purpose: This article presents a Legendre-Ritz solution for free vibration and buckling analysis of porous microbeams. Background and Method: The beam model is based on the modified couple stress theory and higher-order shear deformation theory. Three porosity distributions of the beam, including uniform, symmetric, and asymmetric porosity distribution, are considered. The equation of motion is established from Lagrange's equation. The Legendre polynomial, which possesses the orthonormal and recursion properties, is developed to approximate the displacement field, and the Ritz procedure is used to find the porous microbeam's natural frequency and critical buckling load. Result: Numerical examples are conducted to assess the present method's efficiency and investigate the effect of the material length scale parameter, boundary condition, and porosity ratio on porous microbeams' frequency and critical buckling load. Conclusion: The study indicates that the Legendre-Ritz solution is simple and effective for analyzing porous microbeams' vibration and buckling behaviors. [ABSTRACT FROM AUTHOR]

During seismic events, cyclic demands exceeding the elastic limit load and buckling of steel reinforcing bars significantly impact the global response of thin and lightly reinforced concrete (TLRCW) wall buildings. This study evaluates the cyclic response of low-diameter steel reinforcing bars commonly used in thin RC walls. The experimental program of the study comprises the characterization and reversed cyclic tests of 60 specimens obtained from steel reinforcing bars grade 60 (420 MPa) with nominal diameters of 9.5 and 12.7 mm. An increasing, symmetrical strain protocol was used during the cyclic tests. The study analyses the stress–strain curves obtained in the cyclic tests of steel reinforcing bars and assesses the effect of parameters such as the slenderness ratio, bar diameter, and yield stress on the cyclic response of bars. The onset of buckling and its effects on the cyclic response of steel reinforcing bars, such as pinching and stress reduction in compression are also examined. The degradation of the mechanical properties of steel reinforcing bars obtained during cyclic tests was evaluated and compared to that obtained during monotonic tests. The study shows that low-diameter steel rebars under cyclic loading exhibit lower ductility and premature hardening in tension when compared to bars subjected to monotonic loading. Finally, fundamental properties of low-diameter steel reinforcing bars subjected to cyclic loads were established, such as ductility and hardening capacity. These properties will contribute to enhancing the understanding of the seismic behavior of TLRCW buildings. [ABSTRACT FROM AUTHOR]

Background: The modelling of the sheet metal forming operations requires accurate and precise data of the material plastic behaviour along non-proportional strain paths. However, the buckling phenomenon severely limits the compressive strain range that could be used to deform thin metal sheets. Objective: The main aim of this paper was to propose an effective device, that enables to determine of accurate stress-strain characteristics of thin metal sheet specimens subjected to axial deformation without buckling and with a special emphasis on friction correction. Methods: In this paper, an anti-buckling fixture was proposed to assess the deformation characteristics of X10CrMoVNb9-1 (P91) power engineering steel, and DP500 and DP980 dual-phase steels, under compression loading. The fixture enables monitoring of the friction between the specimen and supporting blocks during the test, and thus the precise stress response of the material could be determined. Results: The effectiveness of the fixture was evaluated under tension–compression cyclic loading and during the compression tests in which high-strength thin metal sheets were successfully deformed up to 10% without specimen buckling. Furthermore, the successful determination of a friction force variation between supporting blocks and the specimen during tests enabled to determine an actual force acting on the specimen. Conclusions: The proposed testing fixture was successfully assessed during the compression and cyclic tension–compression of high-strength thin metal sheets as no buckling was observed. Its advantage lies in adapting to change its length with specimen elongation or shrinkage during a test. The friction force generated from a movement of both parts of the device could be effectively monitored by the special strain gauge system during testing and thus its impact on the stress-strain characteristics could be successfully eliminated. [ABSTRACT FROM AUTHOR]

The nonlocal strain gradient and classical shell theories are used to derive the governing equations of functionally graded cylindrical nanopanels (open cylindrical shells). The properties of the nanopanel are graded as a power-law distribution through the thickness direction. The linearization stability equations are obtained using an adjacent equilibrium criterion. Governing equations are solved by Galerkin method to investigate the effects of the material length scale parameter, the nonlocal parameter, the geometric parameters, and the material properties on the buckling behavior of functionally graded cylindrical nanopanels. Numerical results are compared and discussed with available data. The solution of the closed cylindrical shell is recovered when the span angle is taken as 360 degrees. [ABSTRACT FROM AUTHOR]

This paper investigates the behavior of a medical guidewire within a vessel with a specific focus on its buckling, commonly known as tip load. The guidewire is simulated as a variable section microshaft embedded in an elastic environment, and a comprehensive buckling analysis is carried out based on the modified couple stress theory (MCST). The fundamental frequency is determined by applying Hamilton’s principle and Rayleigh’s method. A formula for calculating the buckling force is subsequently introduced. Numerical simulations were conducted to analyze the impact of the material properties, tapered tip length, core thickness, slenderness ratio, and material length scale parameter on the tip load and penetration force. Furthermore, a comparative study was carried out to validate the proposed formulation. The findings derived from this research can provide valuable insights for the optimization and exploration of various parameters related to medical guidewires. The findings indicate that coronary guidewires with lengths exceeding 10 cm exhibit minimal variations in tip load, whereas those with lengths below this threshold experience a substantial decrease of 65–75% in both tip load and penetration force when the length is doubled. In addition, nitinol guidewires demonstrate greater flexibility, with their tip load being nearly 75% lower than that of stainless steel guidewires of equivalent dimensions. Moreover, there is a notable increase in penetration force with an expanding radius, with tapered tips resulting in an approximate 20–30% increase in penetration force. [ABSTRACT FROM AUTHOR]

We developed and obtained close-form solutions for the buckling growth rate of microtubule (MT) bundles using the Timoshenko beam theory. We took into consideration the surface effects and the Poisson's ratio of the microtubules surrounded by neighbouring filaments in the viscous cytosol. We developed the motion equation by using the modified couple stress theory (MCST) which will take into account the small-scale effects of the microtubules. We then proceeded by studying the effects of various parameters on the buckling growth rate of microtubule bundles. Our results show that the internal material length scale parameter has a decreasing effect on the buckling growth rate of the microtubule bundle. And as microtubule added in the bundle increases, the buckling growth rate reduces further due to the effects of the surrounding microtubule-associated proteins (MAPs). On the contrary, the Poisson's ratio has an increasing effect on the value of the buckling growth rate of the microtubule bundle. We also investigated the effects of other parameters such as surface energy on the buckling growth rates of microtubule bundles and showed the validity of our model by comparing our results with those obtained by previous researchers. [ABSTRACT FROM AUTHOR]

The present study addresses a simplified topology optimization method to improve load bearing capacity. Topology optimization taking account of structurally nonlinear and complex behavior is an important topic from the viewpoint of mechanics. However, most methodologies require complex analytical derivation of sensitivity analysis and high computational cost to obtain the optimal solution. In light of this, we propose a practical design method employing the principal direction of Cauchy stress and the directional statistics, to improve load bearing capacity indirectly with much lower computational cost than those based on complex nonlinear structural analysis. Finally, we discuss setting of optimization problems, and demonstrate the accuracy and performance of the proposed method with a series of numerical examples. [ABSTRACT FROM AUTHOR]

This paper investigates the weight minimization of stiffened panels simultaneously optimizing sizing, layout, and topology under stress and buckling constraints. An effective topology optimization parameterization is presented using multiple level-set functions. Plate elements are employed to model the stiffened panels. The stiffeners are parametrized by implicit level-set functions. The internal topologies of the stiffeners are optimized as well as their layout. A free-form mesh deformation approach is improved to adjust the finite element mesh. Sizing optimization is also included. The thicknesses of the skin and stiffeners are optimized. Bending, shear, and membrane stresses are evaluated at the bottom, middle, and top surfaces of the elements. A p-norm function is used to aggregate these stresses in a single constraint. To solve the optimization problem, a semi-analytical sensitivity analysis is performed, and the optimization algorithm is outlined. Numerical investigations demonstrate and validate the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, the vibration and buckling behavior of a functionally graded piezoelectric porous cylindrical microshell under thermo-electro-mechanical loads are explored on the basis of modified couple stress theory and higher-order shear deformation theory. First, the model of a functionally graded piezoelectric porous cylindrical microshell composed of piezoelectric materials with gradient change in the thickness direction was described. Second, the governing equations of the microshell were derived by Hamilton's principle and Maxwell equation. Third, the modal frequency and buckling equations of the microshell with simply supported ends were obtained on the basis of harmonic trigonometric functions. Finally, the effects of parameters on the modal frequency and buckling behavior were carried out by case studies. The results show that the modal frequency of the microshell can be adjusted by changing the porosity volume fraction, power index, applied voltage, axial load and geometric dimensions. It is also found that the vibration of the microshell is suppressed by positive voltage and axial compression but is strengthened by negative voltage and axial tension, and the material length scale parameter increases stiffness. In addition, the effects of applied voltage and axial load on the buckling behavior are larger than those of temperature. Results can be used to guide the design and application of piezoelectric devices. [ABSTRACT FROM AUTHOR]

To assess the stability and postbuckling behavior of thin composite panels with additional repair lap plates, it is proposed to use relations that consider the unsymmetry of the structure. An analytical solution of the geometrically nonlinear problem is presented for smooth composite panels, whose shape is close to a square, loaded by tangential flows. The initial relations of the problem consider the possible unsymmetry of the structure and include mixed stiffnesses. The boundary conditions in this case correspond to a hinged support. An explicit expression is obtained for the critical stresses of the loss of stability under the action of tangential forces. Relations for the stress-strain state of a square composite panel at its geometrically nonlinear behavior are given. Examples of determination of the critical shear forces are presented, and the expediency of consideration of unsymmetry of the structure in verification calculations of thin composite panels is shown. [ABSTRACT FROM AUTHOR]

This study investigated the seismic demand of continuity plates (CP) in Special Moment Frames (SMFs), including built-up I-shape beams. Six reference experiments for SMF connections were considered, including beams with unequal depths on both sides of the column, to compare the seismic demand for CP with the corresponding value of the AISC code formula. The effects of beam shape properties, connection type, shear strain of the panel zone (PZ), different construction detailing and straight/inclined CP in dual/trapezoidal PZ were included in this study. In addition, companion analytical studies were performed to evaluate CP seismic demand. The results of the experiments and numerical analyses showed that the AISC code underestimates seismic demand for CP in joints with beams having sizes outside the geometries of hot-rolled structural sections. Poor seismic performance of the code-designed CP led to premature yielding and out-of-plane local buckling of CP, which were observed in the reference experiments and confirmed by numerical models. Finally, an equation for CP seismic demand was developed based on findings of this research. It was demonstrated that the proposed seismic demand met the required seismic criteria using this equation, and it also kept CP within the safe structural margins. [ABSTRACT FROM AUTHOR]

The necessity for considering both strength criteria and postbuckling effects in calculating the load-carrying capacity in compression of thin-wall composite structures with impact damage is substantiated. An original applied method ensuring solution of these problems with an accuracy sufficient for practical design tasks is developed. The main advantage of the method is its applicability in terms of computing resources and the set of initial data required. The results of application of the method to solution of the problem of compression of fragments of thin-wall honeycomb panel damaged by impacts of various energies are presented. After a comparison of calculation results with experimental data, a working algorithm for calculating the reduction in the load-carrying capacity of a composite object with impact damage is adopted. [ABSTRACT FROM AUTHOR]

The meshless analog equation method, a purely meshless method, is applied to the buckling analysis of moderately thick plates described by Mindlin's theory and resting on two-parameter elastic foundation (Pasternak type). The method is based on the concept of the analog equation, which converts the three governing second-order partial differential equations (PDEs) in terms of the three plate displacements (transverse displacement and two rotations) into three substitute equations, the analog equations. The analog equations constitute a set of three uncoupled Poisson's equations under fictitious sources, which are approximated by multi-quadric radial basis functions (MQ-RBFs) series. This enables the direct integration of the analog equations and allows the representation of the sought solution by new RBFs series. These RBFs approximate accurately not only the displacements but also their derivatives involved in the governing equations. Then, inserting the approximate solution in the original PDEs and in the associated boundary conditions (BCs) and collocating at mesh-free nodal points, a generalized eigenvalue problem is obtained, which allows the evaluation of the buckling load and the buckling modes. The studied examples demonstrate the efficiency of the presented method that is its ability to solve accurately and in a straightforward way difficult engineering problems. [ABSTRACT FROM AUTHOR]

This paper deals with a limit load assessment and preliminary experimental testing of a lattice-type steel tower used to support a newly designed, prototype small wind turbine having nine blades and a rotor diameter of 3.4 m. Small wind turbine and structural engineering codes of standards were followed with the purpose of implementing a system that meets European Union countries' legislation. The supporting lattice tower structure was subjected to a full-scale load test. This test verified that the structure can withstand the design loads. The finite element software ANSYS Mechanical was used to model and analyse the actual structure, and to determine the possible failure modes and their associated load levels. The most probable mode of failure for such a structure was found to be elastic buckling of the main corner posts. A number of finite element lattice tower models utilising different modelling strategies and solution methods are presented and analysed. The paper highlights the importance of using non-linear analyses as opposed to linear analyses and gives recommendations on the most reliable available modelling technique. Computational analyses' results are compared with measurements from a full-scale test on the tower structure. [ABSTRACT FROM AUTHOR]

The elastic buckling analysis and the static postbuckling response of the Euler-Bernoulli microbeams containing an open edge crack are studied based on a modified couple stress theory. The cracked section is modeled by a massless elastic rotational spring. This model contains a material length scale parameter and can capture the size effect. The von Kármán nonlinearity is applied to display the postbuckling behavior. Analytical solutions of a critical buckling load and the postbuckling response are presented for simply supported cracked microbeams. This parametric study indicates the effects of the crack location, crack severity, and length scale parameter on the buckling and postbuckling behaviors of cracked microbeams. [ABSTRACT FROM AUTHOR]

Structural topology optimisation has mainly been applied to strength and stiffness objectives, due to the ease of calculating the sensitivities for such problems. In contrast, dynamic and buckling objectives require time consuming central difference schemes, or inefficient non-gradient algorithms, for calculation of the sensitivities. Further, soft-kill algorithms suffer from numerous numerical issues, such as localised artificial modes and mode switching. This has resulted in little focus on structural topology optimisation for dynamic and buckling objectives. In this work it is found that nominal stress contours can be derived from applying the vibration and buckling mode shapes as displacement fields, defined as the dynamic and buckling von Mises stress, respectively. This paper shows that there is an equivalence between the dynamic von Mises stress and the frequency sensitivity numbers for element removal and addition in bidirectional evolutionary structural optimisation. Likewise, it was found that the contours of buckling von Mises stress and buckling sensitivity numbers are analogous; therefore, an equivalence is shown for element removal and addition. The examples demonstrate consistent resulting topologies from the two different formulations for both dynamic and buckling criteria. This article aims to develop a simple alternative, based on visual correlation with a mathematical verification, for topology optimisation with dynamic and buckling criteria. [ABSTRACT FROM AUTHOR]

Uniformly stretched thin plates do not buckle unless they are in special boundary conditions. However, buckling commonly occurs around discontinuities, such as cracks, cuts, narrow slits, holes, and different openings, of such plates. This study aims to show that buckling can also occur in thin plates that contain no defect or singularity when the stretching is local. This specific stability problem is analyzed with the finite element method. A brief literature review on stretched plates is presented. Linear and nonlinear buckling stress analyses are conducted for a partially stretched rectangular plate, and various load cases are considered to investigate the influence of the partial loading expanse on the critical tensile buckling load. Results are summarized in iso-stress areas, tables and graphs. Local stretching on one end of the plate induces buckling in the thin plate even without geometrical imperfection. [ABSTRACT FROM AUTHOR]

The paper presents results of two creep tests on pultruded open-section GFRP beams aimed to evaluate the long-term deformations, the residual deflection after unloading, and the influence of creep strains on the flexuraltorsional buckling phenomenon. Two beams were subjected to a constant load for about one year. Then one of the beams was unloaded to evaluate its residual deflection. For the other beam, the load was increased up to failure, and the residual buckling strength was compared with that of a similar beam tested up to failure. The parameters of the Findley power law are evaluated, and the experimental results are compared with those of numerical analyses and with available formulations for prediction of the time-dependent properties of composite beams. Results of the investigation testify, in particular, to a noninsignificant time-dependent increment in deflections of the beams and to a significant reduction in their buckling strength due to creep deformations. [ABSTRACT FROM AUTHOR]

In this paper, we continue the development of mathematically rigorous theory of 'near-flip' buckling of slender bodies of arbitrary geometry, based on hyperelasticity. In order to showcase the capabilities of this theory, we apply it to buckling of axially compressed circular cylindrical shells. The theory confirms the classical formula for the buckling load, whereby the perfect structure buckles at the stress that scales as the first power of shell's thickness. However, in the case of imperfections of load, the theory predicts scaling instability of the buckling stress. Depending on the type of load imperfections, buckling may occur at stresses that scale as thickness to the power 1.5 or 1.25, corresponding to the lower and upper ends, respectively, of the historically accumulated experimental data. [ABSTRACT FROM AUTHOR]

An axisymmetric problem of high strains in a spherical lead shell enclosed into an aluminum 'spacesuit' under the action of pulsed loading is considered. The shell straining is described with the use of equations of mechanics of elastoviscoplastic media in Lagrangian variables, and the kinematic relations are determined in the current state metrics. Equations of state are taken in the form of equations of the flow theory with isotropic hardening. The problem is solved numerically by using the variational difference method and the 'cross' explicit scheme of integration with respect to time. The influence of the yield stress as a function of the strain rate on changes in the shell shape is studied for different values of loading. The calculated final shape and residual strains are demonstrated to be in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

The critical-state response of granular assemblies composed of elastic spheres under generalised three-dimensional loading conditions was investigated using the discrete element method (DEM). Simulations were performed with a simplified Hertz-Mindlin contact model using a modified version of the LAMMPS code. Initially isotropic samples were subjected to three-dimensional stress paths controlled by the intermediate stress ratio, $$b=[(\sigma '_{2}-\sigma '_{3})/$$ $$(\sigma '_{1}-\sigma '_{3})]$$ . Three types of simulation were performed: drained (with $$b$$ -value specified), constant volume and constant mean effective stress. In contrast to previous DEM observations, the position of the critical state line is shown to depend on $$b$$ . The data also show that, upon shearing, the dilatancy post-peak increases with increasing $$b$$ , so that at a given mean effective stress, the void ratio at the critical state increases systematically with $$b$$ . Four commonly-used three-dimensional failure criteria are shown to give a better match to the simulation data at the critical state than at the peak state. While the void ratio at critical state is shown to vary with $$b$$ , the coordination number showed no dependency on $$b$$ . The variation in critical state void ratios at the same $$p'$$ value is apparently related to the directional fabric anisotropy which is clearly sensitive to $$b$$ . [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to avoid using C interpolation functions in finite element implementation of the previous zig-zag theories, artificial constraints, in which the first derivatives of transverse displacement will be replaced by the assumed variables, are usually employed. However, such assumption will violate continuity conditions of transverse shear stresses at interfaces. Differing from previous work, this paper will propose a C-type zig-zag theory for buckling analysis of laminated composite and sandwich plates with general configurations. The first derivatives of transverse displacement have been taken out from a displacement field of the proposed zig-zag theory. Thus, the C interpolation functions are only required in finite element implementations of the proposed model. Without use of any artificial constraints, an eight-node quadrilateral element based on the proposed model is presented by incorporating the terms associated with the geometric stiffness matrix. In order to verify performance of the proposed model, several buckling problems of sandwich plates with soft core have been analyzed. Numerical results show that the proposed model is able to predict accurately buckling loads of the soft-core sandwich plates with varying fiber orientations of face sheets. [ABSTRACT FROM AUTHOR]

This paper is concerned with effect of mismatched pressure on buckling of stressed thin films on a semi-infinite rigid substrate. Analytical approximate solutions are established in explicit form by using total potential energy of the system and the Rayleigh-Ritz's method, and their stabilities have also been determined. The dependences of the critical stress and film-center deflection on the mismatched pressure have been formulated. Results are compared with exact or numerical shooting solutions, and excellent agreements are observed for a large range of film-center deflection. These expressions are brief and can easily be used to derive the effects of various parameters on mechanical behavior of films. [ABSTRACT FROM AUTHOR]

The aim of the study was to develop an objective classification method for cross-country ski poles. A test device was designed to expose different pole models to maximal loading and impact tests. A load cell measured the axial forces in the pole shafts, and a laser distance meter measured shaft deflection when a load was applied via the wrist strap. In the loading tests, each shaft reached a plateau where no more force could be transferred. This maximal force transfer (MFT) value was a characteristic measure for flexural rigidity and thereby also strength. The developed test method enables a loading that is more similar to real-life skiing than a standard three-point bending test. Results show that the introduction of shaft indices for buckling strength is beneficial for comparison purposes. The MFT is a relevant parameter used in the characterization of poles. [ABSTRACT FROM AUTHOR]

A finite strain formulation is developed for elastic circular arches and rings in which the effects of shear deformations are included. Timoshenko beam hypothesis is adopted for incorporating shear. Finite strains are defined in terms of the normal and shear component of the longitudinal stretch. The constitutive relations for stress and finite strain are based on a hyperelastic constitutive model. Virtual work and equilibrium equations are derived. Closed-form in-plane buckling solutions are developed for circular rings and high arches under hydrostatic pressure. The effects of axial deformation prior to buckling as well as shear deformations are included in the buckling analysis. The formulation developed is compared with solutions in the literature and to the predictions of the finite element package ANSYS. The importance of including the effects of shear deformations for deep arches is investigated. [ABSTRACT FROM AUTHOR]

A numerical study was conducted using the finite element method to determine the effects of square and rectangular cutouts on the buckling behavior of a 16-ply quasi-isotropic graphite/epoxy symmetrically laminated rectangular composite plate. The square/ rectangular cutouts were subjected to uniaxial compression loading. This study addresses the effects of the size of the square/rectangular cutout, orientation of the square/rectangular cutout, plate aspect ratio (a/b), and plate length/thickness ratio (a/t) on the buckling behavior of the symmetrically laminated rectangular composite plate under uniaxial compression loading. Buckling loads were computed for seven different quasi-isotropic laminate configurations [0°/+45°/−45°/90°], [15°/+60°/−30°/−75°], [30°/+75°/−15°/−60°], [45°/+90°/0°/−45°], [60°/−75°/+15°/−30°], [75°/−60°/+30°/−15°], [90°/−45°/+45/°0°]. Results showed that the magnitudes of the buckling loads decrease with increasing cutout positioned angle as well as c/b and d/b ratios for plates with a rectangular cutout. The symmetrically laminated quasi-isotropic [0°/+45°/−45°/90°] composite plate is stronger than all other symmetrically analyzed laminated quasi-isotropic composite plates. The magnitudes of the buckling loads of a rectangular composite plate with square/rectangular cutout decrease with increasing plate aspect ratio (a/b) and plate length/thickness (a/t) ratio. [ABSTRACT FROM AUTHOR]

The nanomechanical properties, deformation, and shape recovery mechanism of NiTi nanowires (NWs) under torsion are studied using molecular dynamics simulations. The effects of loading rate, aspect ratio of NWs, and NW shape are evaluated in terms of atomic trajectories, potential energy, torque required for deformation, stress, shear modulus, centro-symmetry parameter, and radial distribution function. Simulation results show that dislocation nucleation starts from the surface and then extends to the interior along the {110} close-packed plane. For a high loading rate, the occurrence of torsional buckling of a NW is faster, and the buckling gradually develops near the location of the applied external loading. The critical torsional angle and critical buckling angle increase with aspect ratio of the NWs. Square NWs have better mechanical strength than that of circular NWs due to the effect of shape. Shape recovery naturally occurs before buckling. [ABSTRACT FROM AUTHOR]

This work investigates buckling behavior of thin film thermoelectrics subjected to a temperature gradient. Both a single-layer thermoelectric film and multilayered structures are studied. The multilayered structure consists of a p-type and n-type thermocouple separated by an insulating layer with or without additional supporting membrane layers. The temperatures, and thermoelectrically induced stresses and membrane forces are first presented. The elastic stability theories of homogeneous plates and laminated composites are subsequently used to determine the temperature differential between the hot and cold junctions that causes buckling of the thin film structures. The numerical results show that a single-layer thermoelectric film could buckle at a temperature differential of around 10 K for large length-to-thickness ratios. The multilayered thermoelectric thin film structures exhibit significantly higher buckling temperature differentials due to reduced overall length-to-thickness ratios. [ABSTRACT FROM AUTHOR]

Prestress in actin filaments plays an important role in the stability of cells and it strongly influences the cell stiffness. In this paper, we present a simple polygonal cytoskeleton model to study the influence of cell prestress. The existence of prestress is shown to facilitate cytoskeletal integrity. Remarkably, the optimum prestress is computed to be several kPa of extension, which is comparable to experimental results. This bio-self-optimized prestress can make the cells sufficiently stable, allowing them to endure external compressive loadings. The relationship between cell rigidity and the prestress is determined using the presented model and found to be linear, which also agrees with experimental results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The initiation, growth, and stability of buckling driven debonding in structural assemblies of stiff blocks, compliant joints, and adhesively bonded composite layers are analytically investigated. The model is developed with focus on masonry walls externally strengthened with composite materials where static and, mainly, dynamic loads may induce compression in the strengthening layers triggering a buckling driven debonding near the joints. The model introduces the interfacial nonlinearity (debonding) through a cohesive interface approach. The geometrical nonlinearity is introduced through the kinematics of intermediate class of deformation (large deflections, moderate rotations, small strains), and the material nonlinearity of the masonry construction is introduced through the constitutive law for the mortar joints. A numerical study of the debonding process in strengthened masonry walls is presented. The study uses the periodicity of the wall for sub-structuring and examines configurations that include composite strips or sheets, strengthening on one face of the wall or on both faces, and compliant mortar materials. Emphasis is placed on the localized debonding near the joint, its stability characteristics, and the possibility to detect the debonding process before it reaches the point of instability. [ABSTRACT FROM AUTHOR]

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 midsurface, geometrical features throughout the thickness, or multilayer structure under complex thermomechanical loading. The method is based on the geometrically nonlinear equations of three-dimensional thermoelasticity and the moment finite-element scheme. The method is justified numerically. Results of practical importance are obtained in analyzing poorely studied classes of inhomogeneous shells. These results provide an insight into the nonlinear deformation and buckling of shells under various combinations of thermomechanical loads. [ABSTRACT FROM AUTHOR]

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 buckling) behavior. Results are compared to the literature. In the case of cracking, the key role of a stress transfer correlation length ξ in establishing a scaling behavior for the brittle fracture of thin films is shown to extend to all geometrical and material properties involved. In the scaling regime of crack density in uniaxial tension cracking and delamination are found to occur simultaneously. In uniaxial tension of films with an internal biaxial compressive stress, the predicted initiation of buckles above delaminated areas near crack edges in the model is remarkably similar to experimental results. [ABSTRACT FROM AUTHOR]

The factors responsible for the errors often encountered in the stability analysis of elastic systems are found by testing the Bubnov-Galerkin method for the buckling problem of a single-layer flexible elastic bar. Refined formulas are obtained for the maximum deflection of a longitudinally compressed hinged three-layer bar. [ABSTRACT FROM AUTHOR]

Investigations of viscoelastic composite materials and structural members carried out using the TDLTSDB and initial-imperfection method are reviewed. The investigations address the internal and surface loss of stability of layered and fibrous composites, the loss of stability of plates, and the delamination (buckling) of plates with cracks. Each of these problems is reviewed separately. New areas of further research are proposed. The review focuses on the investigations carried out by the author and his students [ABSTRACT FROM AUTHOR]

We developed analytical models of the buckling failure of initially rectilinear pipeline in the environment. We specify the drawbacks of available analytical methods, which take no account of the possible longitudinal displacement of the pipeline points or the limited length of the pipeline portion, as well as, in the limiting case, fail to describe the experimental results of buckling failure in the air. The proposed models make it possible to provide analytical evaluation of the critical load, length and shape of the deformed pipeline in cases of its horizontal and vertical transversal deformations with the account of the above factors. The results obtained are corroborated by the numerical simulation of the deformation process, based on the procedure described by the authors in Part 1, as well as by the full-scale test results. [ABSTRACT FROM AUTHOR]

The axisymmetric strain problem for a shell in the direct phase transformation interval is formulated approximately as a nonlinear boundary-value thermoelastic problem with an implicit temperature dependence (through a phase parameter simulating the volume fraction of the new-phase crystals). The buckling problems for a circular plate and a shallow spherical dome of TiNi alloy loaded by normal pressure in the direct phase transformation interval are solved numerically. The branches of buckled equilibrium states are obtained for various values of the loading and phase parameters. It is found that the deflections increase abruptly with an increase in the phase parameter for a fixed value of the loading parameter. The evolution of the buckling modes and the phase-strain distribution along the meridian are studied. [ABSTRACT FROM AUTHOR]

In an attempt to simulate buckling of nonuniform coatings, we consider the problem of an embedded crack in a functionally graded coating bonded to a homogeneous substrate subjected to a compressive loading. The coating is graded in the thickness direction and the material gradient is orthogonal to the crack direction which is parallel with the free surface. The loading consists of a uniform compressive strain applied away from the crack region. The graded coating is modeled as a nonhomogeneous medium with an isotropic stress-strain law. Using a nonlinear continuum theory and a suitable perturbation technique, the plane strain problem is reduced to an eigenvalue problem describing the onset of buckling. Using integral transforms, the resulting plane elasticity equations are converted analytically into singular integral equations which are solved numerically to give the critical buckling strain and the corresponding crack opening displacement shapes. The main objective of the paper is to study the influence of material nonhomogeneity on the buckling resistance of the graded layer for various crack positions and coating thicknesses. [ABSTRACT FROM AUTHOR]

The loss of the load-carrying capacity of a nonlinearly elastic multilayer rod is investigated. The rod, whose layers have various thickness and are made of different materials, is rigidly fixed at both its ends. Rigid contact conditions between the layers are assumed. The problem posed is solved by using the variational method of mixed type in combination with the Rayleigh-Ritz method. The initial analysis is reduced to the solution of the Cauchy problem for a nonlinear ordinary differential equation solved for the first derivative. As the initial condition, the maximum initial eccentricity of the rod is assumed. In the case of zero eccentricity, the Shanley critical force for an axially compressed rod is determined. For a three-layer rod whose outer layers have equal thickness and are made of the same material, numerically, for various degrees of nonlinearity, the effect of physicomechanical and geometric parameters on the critical load of buckling instability is determined. It is found that, by matching the heterogeneity of the rod, it is possible to raise its load-carrying capacity. [ABSTRACT FROM AUTHOR]

The problem of a rod and a plate subjected to plane strain in the interval of the direct phase transformation is formulated as a nonlinear boundary-value thermoelastic problem with an implicit dependence on temperature (through a phase parameter simulating the volume fraction of new-phase crystals). An analytical solution of the problem of a rod bent into a ring and a plate bent into a tube as a result of phase strains under the action of a small end bending moment is given. A numerical analysis of the buckling problem of a titanium nickelide (alloy) rod (plate) under longitudinal compression in the interval of the direct phase transformation shows that buckling becomes possible if the compressive load is much lower than the Euler critical load calculated before the transformation. Branches of buckled equilibrium states corresponding to loads lower than the Euler load are plotted as functions of the phase parameter. In all cases considered, the deflections increase abruptly in the neighborhood of the critical points. The evolution of buckling modes is studied, and the phase-strain distributions along the rod (plate) are shown. [ABSTRACT FROM AUTHOR]

In engineering problems it is necessary to predict the deformations of structural elements subjected to shock waves. In the literature a wide range of structural theories, constitutive equations and simulation techniques is available in order to simulate the occurring deformations. However, an objective statement about the accuracy of calculated structural deformations is only possible by comparing these results to experiments. In the present work a measurement technique with shock tubes is introduced which was especially developed to measure fast deections of plates during the impulse duration. This technique provides a possibility to validate and to improve constitutive and structural theories. Furthermore, very precise measurements can be performed in order to observe limit states and buckling of repeatedly loaded plates. These applications are shown in this study. [ABSTRACT FROM AUTHOR]

The stability of elastic columns subjected to axial pressure is studied. An elastic multistepped column with rectangular cross sections are considered assuming that at the re-entrant corners of the column stable cracks are located. The influence of a crack on the loss of stability of the column is described by means of local flexibility and the function of compliance coupled with the stress intensity factor, which is known from the linear elastic fracture mechanics. A column with a single step is studied in more detail. The influence of crack location and length on the buckling load is assessed numerically. [ABSTRACT FROM AUTHOR]

A differential equation has been derived for the bending of a glued curvilinear rod with initial deflections of its elements. Adhesive joints work in shear. The 2D stability, collapse and buckling are investigated for a jointed rod, and the formulas are derived to determine the critical values of its element parameters. Some separate cases are considered and examples are given. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The nonlinear boundary-value problem of the axisymmetric buckling of a simply supported conical shell (dome) under a radial compressive load applied to the supported edge is formulated for a system of six first-order ordinary differential equations for independent fields of finite displacements and rotations. Multivalued solutions are obtained using the shooting method with specified accuracy. For various values of the loading parameter, bifurcation of the solutions of the problem is studied and a parametric branching diagram is constructed. The buckling modes are obtained for three branches of the solution. Curves of the buckling modes corresponding to three isolated branches of the solution are given. [ABSTRACT FROM AUTHOR]

The paper presents a method for stability analysis of an elastic system consisting of a ribbed cylindrical shell and noncrossing plates. The influence of the width and thickness of the plate on the buckling stresses and modes is analyzed [ABSTRACT FROM AUTHOR]

Three-dimensional finite element analysis is applied to verify mechanical behavior of spot welds for one, three and five spot welds under tensile and compressive loading conditions. The elastic-plastic stress distribution at edge of hot spot weld is used for strength calculations. To obtain exact and reliable results for finite element analysis of spot welds, which are generally very small relative to other dimensions, sub-modeling technique is applied. The proposed numerical calculation scheme allows one to take into account the material parameters and geometrical non-linearity effects related to a gap between thin plates, buckling, etc. We provide the analysis of elastic and elastoplastic behavior of specimens with various configuration of spot welds subjected to tensile and compressive axial loads. [ABSTRACT FROM AUTHOR]