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In order to understand the formation of one-dimension periodic structures by electrospinning, an approximate mechanical approach for the critical load and the number of half waves in the buckled shape have been conducted based on the energy method. Diameter of circular cross-section electrospun fiber is assumed to be equal to the length of the rectangular cross-section spitted fiber. Fiber with rectangular cross section buckles more easily than that with circular cross section because of the different flexural rigidity. For rectangular-section fiber, increase of length to width ratio can result in the increase of the number of half waves. Detailed simulation results for buckling responses of circular-section fiber and rectangular-section fiber have been conducted by commercial finite element analysis software (ABAQUS). [ABSTRACT FROM AUTHOR]

We present a nonlinear finite element method to investigate the nonlinear stability of stiffened functionally graded materials (FGM) plates considered as a whole unit. The plates are subjected to mechanical and thermal loads. The material properties are assumed to be temperature dependent and varied gradually across the thickness according to a power law distribution. The nonlinear equations of FGM plates are based on the first-order shear order plate theory. The influence of material, geometrical properties of stiffeners and initial deflections on the buckling and post-buckling response of the stiffened plates are studied in detail. Including the latest information no work has been oriented towards post-buckling analysis of stiffened FGM plates considered as a whole unit. [ABSTRACT FROM AUTHOR]

An analytical method for vibration and buckling behaviours of Functionally Graded (FG) beams with various boundary conditions under mechanical and thermal loads is presented. Based on linear strain-displacement relations, equations of motion and essential boundary conditions are derived from Hamilton’s principle. In order to account for thermal effects, three cases of the temperature rise through the thickness, which are uniform, linear and nonlinear, are considered. The exact solutions are derived using the state space approach. Numerical results are presented to investigate the effects of boundary conditions, temperature distributions, material parameters and slenderness ratios on the critical temperatures, critical buckling loads, and natural frequencies as well as load-frequencies curves, temperature-frequencies curves of FG beams under thermal/mechanical loads. The accuracy and effectiveness of proposed model are verified by comparison with previous research. [ABSTRACT FROM AUTHOR]

Abstract: Presented in this paper is analysis of buckling of double-orthotropic nanoplates based on nonlocal elasticity theory. It is assumed that two nanoplates are bonded by an internal elastic medium and surrounded by external elastic foundation. Three characteristic types of buckling are considered. Governing equations are derived based on nonlocal theory, while the expressions for the buckling load are given in explicit form for a nanoplate with all edges simply supported. Explained in detail is the influence of small scale coefficient, aspect ratio, and stiffness of internal elastic media and external elastic foundation, on the nondimensional buckling load. [Copyright &y& Elsevier]

Abstract: This paper presents an investigation into the effect of cutout and flange reinforcement on the buckling and post-buckling behaviour of a carbon/epoxy composite C-section structure. The C-section having a cutout in the web is clamped at one end and subjected to a shear load at the other free end. Three different stiffener reinforcements were investigated in finite element analysis by using MSC Nastran. Buckling load was predicted by using both linear and nonlinear FE analysis. Experiments were carried out to validate the numerical model and results. Subsequently post-buckling analysis was carried out by predicting the load–deflection response of the C-section beam in nonlinear analysis. Tsai-Wu failure criterion was used to detect the first-play-failure load. The effect of circular and diamond cutout shape and effective flange reinforcements were investigated. The results show that the cutout and reinforcement have little effect on the buckling stability. However an L-shape stiffener to reinforce the C-section flange can improve the critical failure load by 20.9%. [Copyright &y& Elsevier]

In this study, a buckling analysis was performed on square plates made of composite material with and without elliptical notch using the finite element method. The boron/epoxy laminated plates were asymmetrically orderly arranged into the following way [(θ/−θ)]. The resistance to buckling of the laminated plates subjected to mono-axial compression is highlighted according to the fiber orientations, the degree of anisotropy, size and the orientation of the notch. Results show that the minimum buckling load obtained corresponds to the largest ratio a/b =1 (circular notch), while maximum buckling loads correspond to the smallest ratio of the geometric defect a/b. More the size of the geometric defect is important less the buckling load will be. Thus, the amplification factor N ∗ grows with the increase of the ply thickness. When φ =0° and the angle of orientation of fibers is θ =0°, N ∗ is of the order of 5 and doubles when θ =90°. While for φ =90°, the maximum amplification is of the order of 4% for θ =45° corresponding to the minimum value of the first case where φ =0° and θ =0°. [ABSTRACT FROM AUTHOR]

Abstract: One of the most important mechanical behavior of composite beams subjected to certain external loads and boundary conditions is lateral buckling. The effects of hole dimension, shape and position, and beam thickness on the lateral buckling behavior of woven fabric laminated composite cantilever beams, having two square or two circular holes, were investigated. Firstly, the theoretical, experimental and numerical critical buckling loads of the beams without holes were found and compared with each other. It was shown that there is a good agreement among the theoretical, experimental and numerical results. ANSYS finite element (FEM) program was used for the numerical analyses. Therefore, the numerical analysis of some models with various hole dimensions, shapes (square or circular) and fiber directions were done by changing distance between the holes. It is concluded that the circular holes are advantageous compared to the square ones in terms of lateral buckling behavior. [Copyright &y& Elsevier]

Abstract: Elastic stability of fibers in fiber-reinforced composite materials subject to compressive loading is studied. The transversal buckling mode is considered, and two limiting cases, the dilute and non-dilute composites are analyzed. In the case of a non-dilute composite, the cylindrical model and the lubrication approximation are applied. The original problem is reduced to a problem of stability of a rod on elastic foundation. Through the solution of this problem a simple formula for the buckling load is obtained. In the case of a dilute composite, the solution of a problem of stability of a compressed rod in elastic plane is used. On the basis of the obtained solutions in two limiting cases the interpolation formulae are derived. These formulae describe buckling of fiber in the fiber-reinforced composite for any value of the fiber volume fraction. Comparison with known numerical and experimental results is carried out, and the sufficient accuracy of the derived formulae is demonstrated. [Copyright &y& Elsevier]

Buckling and postbuckling behavior of symmetric laminated composite plates with surface mounted and embedded piezoelectric actuators subjected to mechanical, thermal, electrical, and combined loads is studied. Formulation is based on the classical laminated plate theory with von-Karman non-linear kinematic relations. Initial geometrical imperfections are also accounted, and finally applying Galerkin procedure, the resulting equations are solved to obtain closed form expressions for non-linear equilibrium paths. Temperature dependency of thermo-mechanical properties is considered. Three cases of simply supported boundary conditions are investigated. Effects of in-plane compressive loading, temperature dependency and independency of properties, electrical loading, lay-up configuration, and geometric imperfection are discussed. Results for various states are verified with the known data in the literature. [ABSTRACT FROM AUTHOR]

Abstract: Critical local and global buckling loads of grid-stiffened carbon-fiber thin-shell structures, such as advanced grid-stiffened (AGS) conical shells relevant to aviation and aerospace applications, under uniform external transverse pressure were determined analytically using an equivalent stiffness model considering the influence of non-uniform grid distribution and the minimum potential energy principle. Experiments and finite-elements analysis have been carried out to assess the reliability of this analytical model. To maximize the buckling resistance for optimal design of the AGS conical shells, a hybrid genetic algorithm combining the genetic approach with a simulated annealing algorithm was developed, which considers the characteristics of multi-constraints and mixed discrete–continuous design variables. Comparisons between the benchmark results from the traditional genetic algorithm and simulated annealing algorithm confirmed the validity and efficiency of the hybrid genetic algorithms. Numerical examples show that the local-buckling constraint is a key factor for weight optimization of the AGS carbon-fiber conical. [Copyright &y& Elsevier]

Abstract: A closed-form solution is obtained to determine the buckling and post-buckling behavior of elastically restrained composite panels under compressive loading. The approach allows to study the response of stiffened panels undergoing local buckling modes, taking into account the restraints provided by the stiffeners to the rotation of the skin edges. The panels are modeled as thin plates referring to Marguerre type equations together with classical lamination theory. The equations are written in non-dimensional form, allowing for the study of a wide class of orthotropic laminates. The problem is formulated in terms of out of plane displacement, represented with a single-mode approximation, and Airy stress function. The compatibility equation is solved exactly, while the method of Galerkin is applied to impose the equilibrium. The buckling load, the out of plane displacement at different load levels, and the post-buckling stiffness are derived and compared with finite element analyses, revealing good accuracy. Sensitivity analyses are also performed obtaining design charts. [Copyright &y& Elsevier]

Abstract: Very large number of load steps is required to determine the buckling load based on the non-linear analysis in which the stability limit load is calculated from the non-linear load–deflection curve. In the present work, a simplified methodology is developed to predict the stability limit load that requires the consideration of only two load steps. The stability limit loads of the tapered curved plates are calculated using this methodology. Based on the first-ply failure analysis and the simplified non-linear buckling analysis, the critical sizes and parameters of the tapered curved plates that will not fail before global buckling are determined. The stability limit loads calculated using the present simplified methodology are shown to have good agreement with that calculated based on the non-linear load–deflection curve using the conventional non-linear buckling analysis methodology. [Copyright &y& Elsevier]

Abstract: Axial buckling analysis of double-walled Boron Nitride nanotubes (DWBNNTs) embedded in an elastic medium under combined electro-thermo-mechanical loadings is presented in this article. Virtual displacement method based on nonlocal cylindrical piezoelasticity continuum shell theory is employed to derive the equilibrium equations. Boron Nitride nanotube (BNNT) is assumed to be surrounded by a bundle of carbon nanotubes (CNTs) as elastic medium for reinforcement. The elastic medium is simulated as Winkler–Pasternak foundation, and adjacent layers interactions are assumed to have been coupled by van der Walls (vdW) force evaluated based on the Lennard–Jones model. The effects of parameters such as electric and thermal loads, elastic medium and small scale are investigated on the buckling behavior of the DWBNNTs. The electric field and its direction are found to have affected the magnitude of the critical buckling load. Moreover, an analysis is carried out to estimate the nonlocal critical electro-thermo-mechanical load for the axial buckling of embedded DWBNNTs. [Copyright &y& Elsevier]

Abstract: Accurate estimates of the orthotropic properties of nano-materials are usually not available due to the difficulties in making measurements at nano-scale. However the values of the elastic constants may be known with some level uncertainty. In the present study an ellipsoidal convex model is employed to study the biaxial buckling of a rectangular orthotropic nanoplate with the material properties displaying uncertain-but-bounded variations around their nominal values. Such uncertainties are not uncommon in nano-sized structures and the convex analysis enables to determine the lowest buckling loads for a given level of material uncertainty. The nanoplate considered in the present study is modeled as a nonlocal plate to take the small-size effects into account with the small-scale parameter also taken to be uncertain. Method of Lagrange multipliers is applied to obtain the worst-case variations of the orthotropic constants with respect to the critical buckling load. The sensitivity of the buckling load to the uncertainties in the elastic constants is also investigated. Numerical results are given to study the effect of material uncertainty on the buckling load. [Copyright &y& Elsevier]

Abstract: Nonlinear buckling response of a composite cylindrical shell made of polyvinylidene fluoride (PVDF), is investigated. A two-dimensional smart model surrounded by an elastic foundation subjected to combined electro–thermo-mechanical loading is considered. The nonlinear strain terms based on Donnell’s theory are taken into account using the first shear deformation theory. The Hamilton’s principle is employed to obtain coupled differential equations, containing displacement and electric potential terms. Harmonic differential quadrature method (HDQM) is applied to obtain the critical buckling load for clamped supported mechanical and free electric potential boundary conditions at both ends of the smart cylinder. Results indicate that the critical buckling load increases when piezoelectric effect is considered. [Copyright &y& Elsevier]

Abstract: Buckling of composite annular plates under uniform internal and external radial edge loads have been investigated using energy method. Trefftez rule is used in the stability equations. The symmetric buckling of symmetric cross-ply laminates is considered. In this paper, buckling behavior for the three laminates (90/0)2s , (90/02/90) s and (902/02) s are studied. Influence of some parameters such as thickness, stacking sequence, type of supports and the ratio of hole to sheet radius on buckling loads and modes are investigated. The results of the energy method are compared with the results of numerical method. Based on the results, in the plates with clamped boundary conditions the symmetric buckling assumption is not accurate, contrary to other boundary conditions. [Copyright &y& Elsevier]

The main objective of this paper is to present the buckling and vibration analysis of thermally pre-stressed functionally graded carbon-nanotube-reinforced composite (FG-CNTRC) annular sector plates resting on the elastic foundation via the variational differential quadrature (VDQ) method. The material properties of nanocomposite plate are considered to continuously vary across the thickness and are estimated according to the modified rule of mixture. The governing equations are derived on the basis of first order shear deformation theory. Applying two-dimensional generalized differential quadrature (GDQ) method, the energy functional of the structure is discretized. Then, based on Hamilton's principle and the VDQ method, the reduced forms of mass and stiffness matrices are obtained. After verifying the accuracy of the present method, comprehensive numerical results are presented to examine the effects of important parameters on the stability and vibrational behavior of the nanotube-reinforced composite annular sector plates. The results indicate that functionally graded distributions of CNTs in the thickness direction and the increase of elastic foundation coefficients can improve the stability of the structure. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the buckling and vibration analysis of isotropic and laminated plates by a first-order shear deformation theory. The numerical approach is based on collocation with radial basis functions. The model allows the analysis of arbitrary boundary conditions and irregular geometries. It is shown that the present method, based on a first-order shear deformation theory produces highly accurate natural frequencies and modes of vibration, as well as critical loads and modes. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to study the interaction curves along with buckling and postbuckling responses of a quasi-isotropic laminate with a centrally placed circular cutout of various sizes under uni-axial compression combined with in-plane shear loads (positive and negative). The present study is carried out using finite element method. The finite element formulation is based on the first order shear deformation theory and von Karman’s assumptions to incorporate geometric nonlinearity. The resulting nonlinear algebraic equations are solved by Newton–Raphson method. The 3-D Tsai-Hill criterion is used to predict the failure of a lamina while the onset of delamination is predicted by the interlaminar failure criterion. It is observed that pure compression- buckling, -first-ply failure and -ultimate failure strengths of the quasi-isotropic laminate with and without circular cutout decreases with increasing accompanying shear load. In addition, it is also noted that for a given uni-axial compression load, a quasi-isotropic laminate with and without a cutout can sustain higher negative shear load in comparison to the positive shear load. [Copyright &y& Elsevier]

A semi-analytical approach is presented for the analysis and optimization of laminated panels with non-symmetric lay-ups, and with the possibility of introducing requirements on the buckling load, the postbuckling response and the eigenfrequencies. The design strategy relies on the combined use of semi-analytical techniques for the structural analysis and genetic algorithms for the optimization. The structural analysis is performed with a highly efficient code based on thin plate theory, where the problem is formulated in terms of Airy stress function and out of plane displacement, expanded using trigonometric series. Eigenvalue analyses are performed to determine eigenfrequencies and buckling load, while an arc-length method is adopted for the postbuckling computation. The genetic algorithm is implemented with proper alphabet cardinalities to handle different steps for the angles of orientation, while specific mutation operators are used to guarantee good reliability of the optimization. To show the potentialities of the proposed optimization toolbox, two examples are presented regarding the design of balanced non-symmetric laminates subjected to linear and nonlinear constraints. The accuracy of the semi-analytical predictions is demonstrated by comparison with finite element results and benchmark cases taken from the literature. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, an investigation on the effects of flexural boundary conditions on prebuckling and postbuckling responses, failure loads and characteristics of a quasi-isotropic [i.e., (+45/−45/0/90)2s] square laminate with and without a central cutout of various shapes is carried out under combined in-plane loads [i.e., uni-axial compression combined with in-plane shear (positive and negative)] using finite element method. The finite element formulation is based on the first order shear deformation theory in conjunction with the von Karman’s assumptions to incorporate geometric nonlinearity. The 3-D Tsai-Hill criterion is used to predict the failure of a lamina while the onset of delamination is predicted by the interlaminar failure criterion. It is observed that under combined loading conditions, buckling and postbuckling strengths and failure loads of the laminate are reduced by the introduction of a cutout at the center of the laminate, irrespective of boundary conditions. It is also noted that the laminate with and without cutout has maximum buckling, first-ply failure and postbuckling strengths (at a particular value of transverse deflection) for BC3 (i.e., clamped on all edges) boundary conditions whereas these values are minimum for BC1 (i.e., simply-supported on all edges) boundary conditions, for both directions of shear load. [Copyright &y& Elsevier]

Abstract: The results of drop-weight impact tests and compression after impact (CAI) tests on carbon/epoxy laminates are presented. The experiments were carried out on specimens of two different geometries (rectangular and circular), according to two ASTM standards. Laminates of small thickness, thus prone to buckling under compression, were considered. Two different quasi-isotropic stacking sequences, obtained by cutting the specimens in two perpendicular directions, were also tested for each geometry, in order to study the influence of both these factors on the impact and post-impact response. In impact tests different dynamic behaviour, energy absorption and material damage were observed between coupons of different geometry; in the case of rectangular coupons, stacking sequence also affected the results. The behaviour of laminates under compression was always characterized by global buckling due to the small thickness. Different deformed shapes of the buckled specimens were observed, depending on geometry and lay-up, also by means of strain measurements. Finite element analysis was helpful in the interpretation of strain recordings in different positions of the laminates. Impact-induced damage did not affect the compressive behaviour and strength in every case, depending on the extent of delamination and the global buckling mode. In some cases the pre-existing damage was able to change the buckling mode and to lower the critical load as well as the ultimate compressive load. [Copyright &y& Elsevier]

The prime aim of the current investigation is to predict the nonlinear torsional buckling and postbuckling behavior of geometrically imperfect cylindrical nanoshells including surface stress effects. To this end, the size-dependent governing differential equations of cylindrical nanoshell based on von Karman–Donnell-type of kinematic nonlinearity are derived using a combination of Gurtin–Murdoch elasticity theory and the classical shell theory, and employing the principle of virtual work. Subsequently, by considering the transverse displacement and Airy stress function as independent variables, a boundary layer theory is put to use which takes surface stress effects into account in conjunction with the nonlinear prebuckling deformations, large postbuckling deflections and initial geometric imperfection. Finally, an efficient solution methodology based on a two-stepped singular perturbation technique is conducted to obtain the size-dependent postbuckling equilibrium paths of nanoshells. It is revealed that after the minimum point of postbuckling load, by increasing the value of applied torsional load, the difference between postbuckling load-deflection curves corresponding to the perfect and imperfect nanoshells tends to decrease. [ABSTRACT FROM AUTHOR]

Abstract: Cellular solids such as honeycombs and foams are widely used as structural materials for their low density and high specific stiffness. Under compression or shear loading buckling may occur in cells, and complex deformation modes can result in sudden variations in the strength characteristics of the cellular material. In this paper, the behaviour of regular hexagonal honeycombs under general in-plane loading (compression, traction and shear) is examined by experimental tests and numerical evaluation. In addition, the influence of geometrical imperfections on the failure process is considered. A set of uniform deformation fields is imposed on several honeycomb models with different imperfections in order to determine the overall strength properties, the principal buckling modes and the post-buckling behaviour. Experimental tests are properly designed in order to obtain a complete nonlinear in-plane mechanical characterisation of an Al 3033 honeycomb. Moreover, all the numerical analyses are performed by means of an in-house developed FE code. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to study stability and failure of a composite laminate with a centrally placed cutout of various shapes (i.e., circular, square, diamond, elliptical-vertical and elliptical-horizontal) under combined action of uni-axial compression and in-plane shear loads. The FEM formulation based on the first order shear deformation theory and von Karman’s assumptions has been utilized. Newton–Raphson method is used to solve nonlinear algebraic equations. Failure of a lamina is predicted by the 3-D Tsai–Hill criterion whereas the onset of delamination is predicted by the interlaminar failure criterion. The effects of cutout shape, direction of shear load and composite lay-up on buckling and postbuckling responses, failure loads and failure characteristics of the laminate has been discussed. An efficient utilization of material strength is observed in the case of laminate with circular cutout as compared to the laminate with other shaped cutouts. In addition, it is also concluded that although the buckling strength of the (0/90)4s laminate is lower than that of the (+45/−45/0/90)2s and (45/−45)4s laminates, but its strength is increased in the advanced stage of postbuckling deformation. [Copyright &y& Elsevier]

Abstract: A fiber-reinforced cylindrical shell with given geometry and material properties is optimized for maximum load-carrying capability under bending. The shell is assumed to be built using an advanced fiber-placement machine, which allows in-plane steering and overlapping of fibers, resulting in a so-called variable-stiffness shell. The design methodology for strength and stiffness variation in circumferential direction by means of fiber placement is explained and restrictions on the manufacturability are specified. Implementation in the commercially available finite element package ABAQUS® for structural analysis is described. Subsequently, the cylinder is optimized to carry a maximum buckling load under bending, while applying a strength constraint. Constraints on the global stiffness are imposed by means of comparison with a baseline quasi-isotropic shell, while a matrix dominated lay up is avoided at all locations in the laminate in order to ensure that the laminate is strong enough in all directions in case a hole is present. Optimization is done using a surrogate model in order to minimize the amount of finite element analyses. Improvements of up to 17% are obtained by changing the load path. The tension side is made stiffer and the compression side softer in longitudinal direction by changing the fiber orientation from near zero at the upper (tension) side to higher fiber angles at the lower (compression) side, such that load is relieved from the compression side. This results in a higher load-carrying capability of the cylinder. [Copyright &y& Elsevier]

Abstract: A postbuckling analysis is presented for nanocomposite cylindrical shells reinforced by single-walled carbon nanotubes (SWCNTs) subjected to combined axial and radial mechanical loads in thermal environment. Two types of carbon nanotube-reinforced composite (CNTRC) shells, namely, uniformly distributed (UD) and functionally graded (FG) reinforcements, are considered. The material properties of FG-CNTRCs are assumed to be graded in the thickness direction, and are estimated through a micromechanical model. The governing equations are based on a higher order shear deformation shell theory with a von Kármán-type of kinematic nonlinearity. The thermal effects are also included and the material properties of CNTRCs are assumed to be temperature-dependent. A boundary layer theory and associated singular perturbation technique are employed to determine the buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling behavior of perfect and imperfect, FG-CNTRC cylindrical shells under combined action of external pressure and axial compression for different values of load-proportional parameters. The results for UD-CNTRC shell, which is a special case in the present study, are compared with those of the FG-CNTRC shell. [Copyright &y& Elsevier]

Abstract: This work presents the results related to the behaviour of cylindrical concrete specimens reinforced by external wrappings made of unidirectional carbon fibre/epoxy and bidirectional glass/polyester layers. The specimens have been subjected to a new uni-axial compression technique, consisting in sequential loading of the same sample, with the first loadstep terminated prior to failure of the column. Four types of jacketed specimens by glass fibre (GFRP), and one by a carbon fibre (CFRP) composites have been examined. The results obtained show that the CFRP-reinforced columns provide a significant increase in ultimate compression stress compared to the GFRP-reinforced ones reinforced. The damage mechanisms of the columns wrapped by the composite layers strongly depend on the reinforcement chosen. The hybrid composite jackets proposed in this work show also a remarkable increase in compressive strength and maximum radial strains, coupled with a significant low cost of the raw materials involved. [Copyright &y& Elsevier]

The major goal of this research was to obtain a closed form of the solution for critical combined loads (combined effects of the axial load and l lateral pressure or the axial load and hydrostatic pressure) of functionally graded (FG) truncated conical shell in the framework of the shear deformation theory (SDT). The basic equations of FG truncated conical shell shells subjected to the combined loads are derived in the framework of the SDT. By using the Galerkin method to basic equations are obtained the expressions for critical combined loads of FG truncated conical shell in the framework of the SDT. In particular, similar expressions in the framework of the classical shell theory (CST) are obtained, also. Our numerical experiments reveal that the proposed solution may offer accurate critical combined loads for the FGM shells as compared with reference solutions available in the literature. Finally, the calculation and presentation of the effects of many parameters included in the analysis conclude the goals to be reached in the study. [ABSTRACT FROM AUTHOR]

A nonlinear analysis is presented for FGM cylindrical panels resting on elastic foundations subjected to the combined actions of uniform lateral pressure and compressive edge loads in thermal environments. The two cases of postbuckling of initially pressurized FGM cylindrical panels and of nonlinear bending of initially compressed cylindrical panels are considered. Heat conduction and temperature-dependent material properties are both taken into account. Material properties of functionally graded materials (FGMs) are assumed to be graded in the thickness direction based on Mori-Tanaka micromechanics model. The formulations are based on a higher order shear deformation theory and von Kármán strain displacement relationships. The panel-foundation interaction and thermal effects are also included. The governing equations are solved by a singular perturbation technique along with a two-step perturbation approach. The numerical illustrations concern the postbuckling behavior and the nonlinear bending response of FGM cylindrical panels with two constituent materials resting on Pasternak elastic foundations. The effects of volume fraction index, temperature variation, foundation stiffness as well as initial stress on the postbuckling behavior and the nonlinear bending response of FGM cylindrical panels are discussed in detail. [ABSTRACT FROM AUTHOR]

A multiobjective design and control optimization problem for functionally graded (FG) plates is presented using a first-order plate theory including the normal strain effect. The aim of the optimization is to minimize the vibrational response and to maximize the buckling loads of FG plates with constraints on the control energy and plate thickness. An integrated approach for the simultaneous design and active control optimization is presented to determine the optimal level of a closed loop control function. Plate thickness and a homogeneity parameter of FG plates are used as design variables. Numerical results for the optimal control force and the total energy of FG plates are presented in various cases of boundary conditions. The influence of the normal strain effect on the accuracy of the obtained results is illustrated. The effectiveness of the present control and design procedures are examined. [ABSTRACT FROM AUTHOR]

Abstract: A linear finite strip plate element based on the first order shear deformation theory is considered for the analysis of viscoelastic plates. The plate end conditions are considered to be simply supported and the polynomial shape functions are used to evaluate the deflection of plates in transverse direction. The mechanical properties of the material are considered to be linear viscoelastic by expressing the relaxation modulus in terms of Prony series. The time history of maximum deflection of viscoelastic plates subjected to loading and unloading is calculated. In addition, a nonlinear procedure is used to calculate the changing of in-plane critical load of plate with time. Moreover, the effect of thickness and the interaction of biaxial loading on critical load of plate are studied. [Copyright &y& Elsevier]

Abstract: This paper evaluates the humidity effect on the elastic properties and failure mechanism of two types of layered corrugated paperboard structures composed of entirely recycled material and virgin radiata pine (Pinus radiata D. Don) kraft and mixed fibre linerboards and fluting medium. Board samples and their component paper sheets were tested at 50% and 90% constant relative humidity (RH) under compression load and images of failure zones were obtained by serial sectioning and confocal microscopy. The compressive strength and modulus of elasticity of all components were found to be highest in the machine direction at 50% RH and lowest in the cross-machine direction at 90% RH. Virgin paper sheet components performed better in compressive performance than recycled components in both directions and at both relative humidities. In both types of corrugated board microscopic examination showed that failure under compression at 50% and 90% RH occurred along the adhesive line as well as by failure of inter-fibre bonds within the components. The combination of failure mechanisms resulted in local buckling of the boards. The elastic performance of recycled corrugated board was found to be inferior to that of virgin corrugated board at both RH conditions. [Copyright &y& Elsevier]

Abstract: Nomex™ honeycomb core sandwich panels with a bolt insert were load tested and modeled. The objective was to predict the honeycomb local buckling load and to identify a Nomex™ honeycomb constituent material model. Sandwich specimens were subjected to bolt pull-out load tests. The same sandwich structure was also tested in flat-wise tension with strain gages installed on the honeycomb walls. Finite element models of the flat-wise tension and bolt pull-out tests were built. The honeycomb geometry and strain gages were modeled with shell elements. An orthotropic honeycomb material model was identified by comparing the two test models to the experimental data. The material parameters identified are in the mid-range of previously published values. The pull-out test model was used to predict honeycomb wall buckling with a nodal rotation vector sum criterion. The buckling loads predictions closely corresponded to the start of the experimental load/displacement slope transition zone. [Copyright &y& Elsevier]

Abstract: This article provides an improvement of the technology of through-the-thickness reinforcement of thermosetting composite sandwiches by the insertion of stitching yarns. The aim of this work is to propose a model that would lead to the representation of the tri-dimensional elastic and ultimate performances of these 3D structures under out-of-plane shearing and compressive stress. To reach that goal, an analytical approach is proposed without the contribution of the numerical finite element technique. From experimental observations, this complex structure can be considered as a simple lattice made up of the stitches treated as bars composed of the UD impregnated yarns. The transverse compression and the out-of-plane shear module can be determined from the geometrical parameters of the structure. Moreover, the ultimate stress can be approximated once the cinematic of the failure of the structure has been experimentally identified for each stress case. Finally, the buckling of stitches ends up in the ruin of the material in each case. Thus, a classical theory of buckling can be used and a particular work has been done on the representation of the anchorage point of the stitches on the skin. The final model which is endowed with a good sensitivity enables us to predict the ultimate values in both loading cases. Finally, the variation of stitching angle allows to virtually optimize the material used according to the external loading. [Copyright &y& Elsevier]

Existing failure load prediction models for pultruded Fiber Reinforced Polymer (FRP) box beams are inaccurate when compared to experimental evaluations provided herein by the authors. This inaccuracy is attributed to improper identification of failure modes based on beam span-to-depth ratios and principal strain resulting in premature failure compared to elastic bending stress-based failures. Inclusion of stress intensity factors and computation of stress concentrations aids in consistently accurate results compared with experimental data. The proposed equations are predicting critical flexural load capacities within ±22% of experimental data for all cases. The failure model in tension is the most accurate one, while local buckling predictions in compression need further refinement. [ABSTRACT FROM AUTHOR]

This study investigated the energy absorption response and load carrying capability of woven natural silk/epoxy–triggered composite rectangular tubes subjected to an axial quasi-static crushing test. The rectangular composite tubes were prepared by hand lay-up technique. The tubes consisted of 12, 24, and 30 layers of natural woven silk/epoxy laminate and were 50, 80, and 120 mm long. The crashworthiness of the tubes was evaluated by measuring the specific energy absorption in quasi-static axial compression. Specific energy absorption was obtained from the load–displacement curve during testing. The failure mode of the tubes was analyzed from high resolution photographs obtained. Overall, the tube with 50 mm length and 30 layers showed the best crashworthiness among the tubes. The failure morphology showed that the specimens failed in two distinct modes: local and mid-length buckling. The triggered composite tubes exhibited progressive failure. [ABSTRACT FROM AUTHOR]

The effects of interfacial adhesion strength on the damage behavior and energy absorption characteristics of an aluminum (Al)/carbon fiber reinforced plastic (CFRP) short square hollow section (SHS) beam under three point bending loading was investigated. An Al SHS beam was wrapped by CFRP with a [0°/+45°/90°/−45°] n ( n = 1 or 2) stacking sequence, and four gradations of interfacial adhesion strength were caused by physical or chemical changes of the Al adherend with different mechanical abrasion and optimal Argon plasma treatment. A different level of appropriate interfacial adhesion strength existed for each hybrid specimen depending on the CFRP laminate thickness to obtain the highest energy absorption capability, and this was verified by detailed observation of the failure mechanism of the hybrid specimen. The specific energy absorbed (SEA) was improved by up to 57.2% in the Al/CFRP [0°/+45°/90°/−45°] 2 SHS beam compared to the Al SHS beam without compromising the crush force efficiency (CFE). [ABSTRACT FROM AUTHOR]

Abstract: Predicting torsional response of pultruded fiber reinforced polymer (FRP) composite member with closed cross-sections is complex due to the inhomogeneous nature of section properties, which are dependent on fiber architecture and constituent material properties. Presented herein are the methods and results of an experimental study on the response of such sections to torsional loading, including prediction of shear modulus (G) and angle of twist (θ). A literature review was performed, leading to many hypothesized methods for prediction. Results presented herein will exhibit the effectiveness of a Simplified Classical Laminate Theory analysis for shear modulus (G) determination (less than 5% error), and will demonstrate good correlation between full-scale and coupon test results. For this experiment, a torsional testing apparatus was designed and developed to accommodate samples up to 144in. in length and up to 6in. by 6in. cross-sectional dimensions. Failure behavior of the cross-sections was also examined, noting that all test samples failed after reaching maximum strength of the material and exhibiting no signs of local or global buckling. [Copyright &y& Elsevier]

Experimental and computational studies of the microscale mechanisms of damage formation and evolution in unidirectional glass fiber reinforced polymer composites (GFRP) under axial and off-axis compressive loading are carried out. A series of compressive testing of the composites with different angles between the loading vector and fiber direction were carried out under scanning electron microscopy (SEM) in situ observation. The damage mechanisms as well as stress strain curves were obtained in the experiments. It was shown that the compressive strength of composites drastically reduces when the angle between the fiber direction and the loading vector goes from 0° to 45° (by 2.3–2.6 times), and then slightly increases (when the angle approaches 80–90°). At the low angles between the fiber and the loading vector, fiber buckling and kinking are the main mechanisms of fiber failure. With increasing the angle between the fiber and applied loading, failure of glass fibers is mainly controlled by shear cracking. For the computational analysis of the damage mechanisms, 3D multifiber unit cell models of GFRP composites and X-FEM approach to the fracture modeling were used. The computational results correspond well to the experimental observations. [ABSTRACT FROM AUTHOR]

Energy absorption capability and bending collapse behavior of an aluminum (Al)/carbon fiber reinforced plastic (CFRP) short square hollow section (SHS) beam were investigated under transverse quasi-static loading. The Al SHS beam was reinforced by CFRP, and the specimen was co-cured via an autoclave curing process. Three-point bending test was performed with five different lay-up sequences and three different laminate thicknesses. Stable bending collapse accompanying plastic hinge was observed in all specimens. Individual bending collapse behaviors were different depending on the lay-up sequences. The specific energy absorbed (SEA) was improved by up to 29.6% in the Al/CFRP SHS beam specimen with a [0/+45°/90°/−45°] n lay-up sequence and laminate thickness of 1.168mm (thickness ratio of Al: CFRP=1: 0.87, 8 plies of prepreg) compared to the Al SHS beam. The SEA was not related with damage area of the Al/CFRP SHS beam. Finite element analysis and theoretical analysis based on Kecman’s model were performed to investigate the effect of reinforcement by CFRP on the Al SHS beam. [ABSTRACT FROM AUTHOR]

Abstract An analysis of the influence of fibre orientation on the interlaminar stresses near the free edge of composite laminates was carried out. The study of these stresses is relevant due to the fact that they contribute to a number of failure mechanisms, such as delamination and shear stress cracking at the laminate edge. The presence of a displacement gradient was demonstrated using a numerical model, which showed that the maximum value is dependent on the orientation of the plies in the laminate. A solid correlation of the model predictions with experimental results was obtained. A classic finite difference scheme similar to that proposed by Pipes and others was implemented, though on this occasion modified via the use of non-dimensional variables. The displacement gradient is related to interlaminar stresses, which in turn are dependent on fibre orientation. In order to study the dependence of the out-of-plane stresses on these two parameters, an analysis of symmetric laminates with varying stacking sequences and ply orientations was carried out. [ABSTRACT FROM AUTHOR]