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To reveal the compression failure modes of one-dimensional hierarchical double-shell octagonal lattice truss composite structures (DLTCSs), finite element modeling and equivalent continuum models were developed. DLTCS has three typical failure modes: (a) fracture of the strut, (b) global buckling, and (c) local buckling. Failure mode maps were constructed. It is found that column of long enough length will collapse at global buckling. When the column length decreases, the failure mode will turn to local buckling and strut fracture successively. Bay length greatly influences the buckling mode. Longer bay length could change the buckling mode from global buckling to local buckling. Compared with single-shell lattice truss composite structure, DLTCS has advantage in load carrying when the column fails at strut fracture or global buckling, while local buckling tolerance of DLTCS is smaller. [ABSTRACT FROM AUTHOR]

The results of an experimental study on the buckling behavior of thin-walled GFRP-stiffened cylindrical shells are presented. The buckling behavior of stiffened shells, with lozenge and triangular grids, and unstiffened shells were studied under quasi-static axial loading at room temperature. The effect of the number of helical ribs and grid shapes was thoroughly investigated. During the experimental study, local skin buckling mode was observed on all specimens. Based on the findings from this work, a minimum number of stiffeners should be present in a structure in order to play an effective role in its strength. Furthermore, it was concluded that under axial loading, increasing the number of helical ribs is more effective than adding hoop rings and changing the grid types. [ABSTRACT FROM AUTHOR]

Buckling analysis of symmetric and antisymmetric cross-ply laminated hybrid composite plates with an inclined crack subjected to a uniform compression is investigated in this article. The first-order shear deformation theory in conjunction with the variational energy method is employed in the mathematical formulation. The effects of crack size, crack inclination angle, and lay-up sequences on the buckling loads are investigated. The results are shown in graphical form for various conditions. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) finite element analysis has been conducted to examine the local buckling behavior of foam-cored composite sandwich panels containing a face core debond. The influences of core stiffness and debond size and shape are examined. The core stiffness was found to have a profound influence on the local buckling load, especially for low modulus cores and smaller debonds. Panels with square debonds buckled at lower loads than those with circular debonds of the same dimension, and buckling loads for both circular and square debonds decreased with increased debond size. The results of the analysis were compared to local buckling loads determined experimentally. Reasonable agreement was found between the predicted and experimentally measured local buckling loads for both circular and square debonds. [ABSTRACT FROM AUTHOR]

Edgewise compression (buckling) tests were performed on unstitched and stitched sandwich specimens made of glass/epoxy face-sheets and polyurethane foam core. The buckling characteristics of the specimens with through-the-thickness stitches and the influence of strain rate on buckling were investigated. Ultimate load carrying capacity of the specimens was determined. Modes and causes of failure along with their relation to the buckling properties were identified. The effect of stitch row spacing on the instability preceding the crush failure was investigated using finite element analyses, which were found to explain the fracture and debonding phenomena accurately. The average sustained critical compression load increased with reduced stitch row spacing and the total buckling load decreased with decrease in strain rate, as revealed by the buckling experimental studies. [ABSTRACT FROM AUTHOR]

Thermal buckling analysis of symmetric and antisymmetric laminated composite plates with clamped and simply supported edges, and containing a hole is presented in this paper. The first-order shear deformation theory in conjunction with the variational energy method is employed in mathematical formulation. The eight-node Lagrangian finite element technique is used to find thermal buckling temperatures of isotropic, glass-epoxy and boron-epoxy laminates. The effects of hole size, angle of ply orientation, lay-up sequences, and boundary conditions on thermal buckling temperatures are investigated. The result is shown in graphical forms for various boundary conditions. [ABSTRACT FROM AUTHOR]

In the present article, the variational energy principle is used to derive the expression for energy release rate in buckled composite laminate containing through-the-width delamination, subjected to in-plane strains. Boundary conditions are clamped at both edges. Buckling and post-buckling solutions are obtained and expressions for critical buckling load and post-buckling deflection have been developed. A through-the-width delamination model has been considered and formulations are based on higher order shear deformation theory. The effects of considering the higher order shear deformation theory on equivalent bending rigidity, buckling load, and energy release rate have been investigated. Finally, the results of current study have been compared with the results of finite element method analysis by Abaqus/CAE and those available in the literature. [ABSTRACT FROM AUTHOR]

An investigation is carried out to understand the non-linear thermal buckling behaviour of local delamination near the surface of fiber reinforced laminated plates. The shape of the delaminated region considered is rectangular, elliptic or triangular. The mechanical properties and the thermal expansion coefficient of the fiber material are treated as a function of temperature, which leads to the force in the middle plane of the laminated plates a non-linear function of temperature. The critical temperatures of laminated plates with variously shaped local delamination and different stacking patterns are obtained by making use of the energy principle. It has been found that linear solutions of the critical buckling temperature give a higher value than that from non-linear consideration. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore post-buckling strength potential of two different stiffener types and evaluate structural efficiencies of those by making a comparison. This has been done by first determining the buckling and post-buckling behavior of J- and hat-stiffened composite panels under compression loading. By making a structural efficiency definition, the experimental results of J- and hat-stiffened panels for initial buckling and post-buckled responses of the panels were compared with predicted and analytical results. [ABSTRACT FROM AUTHOR]

In this article, we combine the Carrera's Unified Formulation, CUF (Carrera E. Theories and Finite elements for multilayered plates and shells: A unified compact formulation with numerical assessment and benchmarking. Arch. Comput. Methods Eng., 2003; 10: 215–297.) and a radial basis function collocation technique for predicting the static deformations, free vibrations and buckling behavior of thin and thick cross-ply laminated plates. We develop by the CUF two Zig-Zag theories according to Murakami's Zig-Zag function. Both theories account for through-the-thickness deformations, allowing the analysis of thick plates. The accuracy and efficiency of this collocation technique for static, vibration, and buckling problems are demonstrated through numerical examples. [ABSTRACT FROM AUTHOR]

Experimental determination of the flexural and torsional properties of pultruded FRP profiles, based on full section and coupon tests, is described. Results for a range of I-profiles indicates that transverse shear moduli, determined from full section three point bending tests, are influenced significantly by localised deformation at the supports. Closed form solutions for the influence of shear deformation on global flexural, torsional and lateral buckling of pultruded FRP profiles have been developed. Parametric studies for a range of I-profiles indicate that shear deformation can reduce flexural and torsional buckling loads by up to 10%. For wide flange I-profiles pre-buckling displacements can increase lateral buckling moments by more than 20% while the influence of shear deformation is relatively minor. [ABSTRACT FROM AUTHOR]

As one of the most common defects induced by Automated Fiber Placement, in-plane fiber micro-buckling is characterized by a macroscopic value and its influence on composites tensile properties are studied in this article. The mathematical relationship between fiber microscopic distribution and geodesic curvature of non-geodesic fiber path is derived. Influences of in-plane fiber micro-buckling on tensile properties are analyzed by off-axis tensile theory and finite element analysis, and verified by experiments. Actual fiber microscopic distribution of in-plane fiber micro-buckling shows that it is reasonable to evaluate the scale of fiber micro-buckling by the geodesic curvature radius of curved fiber trajectory. Longitudinal tensile properties of lamina are dramatically influenced by in-plane fiber micro-buckling, while the influences of in-plane fiber micro-buckling on transversal tensile properties can be ignored. When A/L reaches 0.023, the longitudinal tensile modulus and strength of lamina decreased by 25.5% and 57.7%, respectively, compared with the lamina without any defects. Based on the conclusions made in this article, the scale of in-plane fiber micro-buckling can be predicted without metallographic observation. And the increase of structural efficiency and the loss of mechanical performance in consequence of non-geodesic fiber path could be evaluated for the optimization of fiber trajectory. [ABSTRACT FROM AUTHOR]

Focuses on a study which analyzed the buckling of an orthopedic layer bonded to half-space with an interface crack subjected to compressive load under plane strain. Formulation of the problem; Solution procedures; Conclusions.

Tapered composite beams are increasingly being used in various engineering applications such as helicopter yoke, robot arms, and turbine blades. In the present work, the buckling analysis of laminated tapered composite beams is conducted using a higher order finite element formulation. In tapered laminates, the material and geometric discontinuities at ply drop-off locations lead to significant discontinuities in stress distributions. Higher order formulation ensures the continuity of the stress distribution through the thickness of a laminate as well as across the element interfaces, which is very important for the analysis of tapered laminates. In addition, higher order finite element formulation requires lesser number of elements in order to achieve reasonably accurate results in buckling analysis. The stiffness coefficients of the tapered laminated beam are determined in the present work based on the stress and strain transformations and the classical laminate theory. A detailed parametric study on various types of tapered composite beams is conducted. [ABSTRACT FROM AUTHOR]

The buckling of laminated metal-matrix composite (MMC) plates with a central square cutout were analyzed under compressive biaxial loading using the finite element approach. The MMC plates displayed some interesting buckling patterns and initial buckling shapes when subjected to different combination of hole sizes and boundary conditions. In the case of anti-symmetric, free-free boundary conditions, the MMC plates with central square cutout resist higher buckling loads as the hole size increased. Two laminated stacking sequences [90/0/0/90]2 and [45/-45/-45/45]2 were used in this study. For the same hole size, plate aspect ratio, and boundary conditions, the results showed that the critical buckling behavior of the plates were primarily influenced by the edge boundary conditions rather than by the laminated stacking sequences. The overall critical buckling analysis indicated that plates with clamped boundary conditions will take higher compressive loads than that of simply supported boundary conditions by a ratio of 2 to 1. [ABSTRACT FROM AUTHOR]

The objective of this article is to introduce and assess a new plate buckling analysis procedure which can be used for quick, approximate analysis of buckling loads in preliminary design. The method is applied to a range of plate edge support condition combinations including many where results are not readily available. The results obtained using the new procedure were compared against theoretical formulae available in the literature and by finite element analyses with good agreement. [ABSTRACT FROM PUBLISHER]

This article presents analytical solutions for buckling analysis of functionally graded plate based on a refined plate theory. Based on the refined shear deformation theory, the position of neutral surface is determined and the governing stability equations based on neutral surface are derived. There is no stretching–bending coupling effect in the neutral surface-based formulation, and consequently, the governing equations and boundary conditions of functionally graded plates based on neutral surface have the simple forms as those of isotropic plates. The closed-form solutions of buckling load are obtained for rectangular plates with various boundary conditions. The accuracy of neutral surface-based model is verified by comparing the obtained results with those reported in the literature. Finally, parameter studies are carried out to study the effects of power law index, thickness ratio, and aspect ratio on the critical buckling load of functionally graded plates. [ABSTRACT FROM AUTHOR]

Based on Reddy's third-order shear deformation theory, an exact closed-form solution is proposed to describe linear buckling of transversely isotropic laminated rectangular plates under either mono- or bi-axial compressive in-plane loads. To this end, the coupled governing equations are exactly converted to two sets of uncoupled equations for in-plane and transverse deformations of symmetric laminated plates. The new uncoupled equations are analytically solved by applying both Navier and Lévy-type solution methods. The validity and high accuracy of the current exact solution are evaluated by comparing the present results with their counterparts reported in literature. [ABSTRACT FROM AUTHOR]

The fabric buckling model proposed by Grosberg and Swani has been modified by incorporating Huang's bilinear bending rule. The proposed model is an extension of the present model and also covers the special cases. The numerical results appear realistic and conform to the trend observed by other researchers. The effects of fabric bending parameters on the buckling behavior of woven fabrics were explored by numerical computations. The second part of this paper includes the recovery from large-scale buckling of woven fabric. [ABSTRACT FROM AUTHOR]

Post-buckling behaviors of rectangular composite plates with multiple circular delaminations are studied experimentally and numerically. The plate is fixed at its loading edges and simply-supported at its side edges considering the CAI test method recommended by SACMA. Multiple circular delaminations are placed at regular intervals in the thickness direction at the plate center. The diameters of the delaminations are increased from the top surface to the bottom surface, which is an idealized pattern of foreign object impact damage of composite laminates as reported by many researchers. A three-dimensional brick element is adopted. The contact problem of the delaminated surfaces is approximately considered by placing spring elements between the double nodes at the upper and lower delamination surfaces, which have no resistance in the tensile direction and high stiffness in the compressive direction. The numerical results are compared with experiment and found to be consistent with the experiment. The effects of the delaminations on the post-buckling behavior of the laminates are discussed parametrically through finite element results. [ABSTRACT FROM AUTHOR]

The influence of cutout shape upon the buckling stability of multilayered rectangular epoxy plates reinforced by glass fiber, with different orientation angles is investigated. U-shaped cutouts are made on the long sides symmetrically. The investigated plates are simply supported on the loaded edges (i.e. short sides) and free on the unloaded edges. The plates without cutouts are examined theoretically to confirm experimental and Finite Element (FE) results. The FE and experimental results are round out for different U-shaped cutouts sizes. U-notch shape effects are examined depending on notch depth and notch root radius. According to results, the effect of notch depth is stronger than that of the notch root radius on buckling loads of plates. But, in some cases, although plates containing U-notch, no reduction is obtained in buckling loads. Obtained results with experimental, theoretical, and FE are in good agreement with each other. [ABSTRACT FROM AUTHOR]

Post-buckling behaviors of laminated composite and isotropic rectangular plates subjected to various thermal changes are studied. Geometric imperfections are taken into account since they play a fundamental role. The plate is modeled using a nonlinear, higher order shear deformation theory. Plates with clamped edges are considered. A pseudo-arc length continuation method is used to obtain numerical results. Laboratory experiments have been performed in order to compare to the numerical calculations. [ABSTRACT FROM PUBLISHER]

In this article, we assess the feasibility of energy harvesting from mechanical buckling of ionic polymer metal composites induced by a steady fluid flow. Specifically, we consider an underwater energy harvester composed of a paddle wheel, a slider-crank mechanism, and two ionic polymer metal composites clamped at both their ends. To enhance electromechanical transduction, the electrodes of the ionic polymer metal composites are split into three parts via a selective platinum deposition process. The system is installed in a water tunnel and experiments are performed to elucidate the influence of both the flow speed and the shunting resistance on energy harvesting. To provide a theoretical interpretation of the experimental results, the classical post-buckling theory of inextensible elastic beams is adapted to predict mechanical deformations and a lumped-circuit model is utilized to estimate the harvested power. [ABSTRACT FROM AUTHOR]

In the present study, unified shear deformation theory which was proposed by Soldatos, K.P. and Tımarcı, T. (1993). A Unified Formulation of Laminated Composite, Shear Deformable Five-degrees-of-freedom Cylindrical Shells on the Basis of a Unified Shear Deformable Shell Theory, Compos. Struct., 25(1-4): 165-171 is used to analyze simply supported symmetric cross-ply rectangular plates for deflections, stresses, natural frequencies, and buckling loads. This theory enables the selection of different in-plane displacement components to represent shear deformation. Exponential shear deformation theory, which is proposed by Karama et al., 40(6) (2003). Mechanical Behavior of Laminated Composite Beam by New Multi-layered Laminated Composite Structures Model with Transverse Shear Stress Continuity, Int J Solids Struct., 40: 1525-1546, is used for the first time to analyze the problem considered. Results which are found by exponential theory are compared with those obtained by using the parabolic shear deformation theory of Reddy, J.N., 51(4) (1984). A Simple Higher-order Theory for Laminated Composite Plates, J Appl Mech., 51: 745-752, the trigonometric shear deformation theory of Touratier, M., 29(8) (1991). An Efficient Standard Plate Theory, Int. Jnl. Engng. Sci., 29(8): 901-916, the hyperbolic shear deformation theory of Soldatos, K.P., 94(3-4) (1992). A Transverse Shear Deformation Theory for Homogeneous Monoclinic Plates, Acta Mech., 94: 1995-220 and with the available three-dimensional elasticity solutions. The study shows that while the transverse displacement and the stresses are best predicted by the exponential shear deformation theory, the parabolic shear deformation and the hyperbolic shear deformation theories yield more accurate predictions for the natural frequencies and the buckling loads. [ABSTRACT FROM AUTHOR]

Numerical simulation has been carried out to analyze several unique buckling and postbuckling behaviors of superelastic shape memory alloy (SMA) columns observed from experimental evidences. Comparison of the experimental critical load with analytical predictions verifies the fact that physical nonlinearity should be taken into account to comprehensively analyze the buckling behaviors of SMA columns. Thus, based on the nonlinear stress-strain relations as well as the large deformation theory, the load-deformation curves of the columns during a complete loading-unloading cycle have been predicted by using the FEM code ANSYS. Simulation has also been performed for the stainless steel (SUS304) columns. The total strain distributions in the column materials have been calculated at different states of loading. Precise and quantitative analyses of the results verify that the unique behaviors of the SMA columns could be attributed to the special nature of the stress-strain curves. It is found that the slender SMA column buckles in the austenite phase. Due to SMA's high strength for large strains, the slender columns can sustain the load with a very small change in magnitude for the postbuckling compression. A special method has been devised to simulate the unique unloading path of the slender superelastic SMA columns and its usefulness has been demonstrated. It has been found that defining a few intermediate unloading curves between the actual loading and unloading curves can help to minimize the stress discontinuity at the beginning of unloading. Simulation results also verify that because of the elastic shape recovery of the buckled slender SMA columns, the load increases when they are unloaded. [ABSTRACT FROM AUTHOR]

Generally, a grid layer is used as an orthotropic layer to reinforce plates and shells or as an independent structural element. The proposed laminated grid plate is composed of different grid layers with different orientations. Consequently, the grid layers with different fibers, patterns and orientations can be used, resulting in laminates with enhanced stiffness and coupling effects. In the present study, to investigate the efficiency of the laminated grids, the vibration and buckling responses of a conventional and laminated grid plates are compared. The first-order shear deformation plate theory along with Ritz method is used to obtain the buckling load and natural frequencies of the plates. The effectiveness of increasing the number of layers on mechanical responses of the laminated grids is also studied. The analytical results of vibration frequencies are compared and validated by finite element method and experimental analysis of two manufactured grid plates. The results indicate that thoughtful selection of stacking sequences of the laminated grids considerably enhances the response of the laminated grids in comparison with conventional grids. [ABSTRACT FROM AUTHOR]

The effect of fiber weight fraction on buckling of laminated composite plates has been investigated in the present study. The elastic properties of individual laminae are calculated from the elastic properties of fiber and matrix materials. The laminated plate has been modeled using eight noded isoparametric quadratic plate bending element using first order shear deformation theory. The buckling parameter of laminated composite plate has been calculated and compared with those available in literature. A detailed parametric study has been performed to investigate the effect of fiber weight fraction on buckling of laminated composite plates. [ABSTRACT FROM AUTHOR]

Buckling-restrained braced frames are steadily replacing concentrically braced frames because buckling-restrained brace can yield without buckling when subjected to both tension and compression. Though buckling-restrained brace frames are being widely used as framing structures for construction in high seismicity areas, it is shown that at large strains, a considerable amount of permanent deformation is produced at the support connector between the brace and the frame. This drawback can be overcome by providing recentering capabilities to the braced frame system. By applying the concept of a recentering system to the design of buckling-restrained brace frames, we developed braced frames that incorporate buckling-restrained braces with superelastic shape memory alloy end-support connectors. Owing to the recentering capability, shape memory alloy materials have been used in the place where large deformation may feasibly occur. The primary advantages of the innovative braced frames proposed herein are verified through nonlinear pushover analyses. Analytical frame models are developed to estimate theultimate and residual inter-story drifts. The analysis results suggest that buckling-restrained brace frames with superelastic shape memory alloy bracing systems are more effective in controlling residual inter-story drifts than those with conventional steel bracing systems owing to the inherent self-healing characteristics of superelastic shape memory alloys. [ABSTRACT FROM AUTHOR]

The torsional buckling of an individual multi-walled carbon nanotube under two different loading conditions is studied in this article. The multiple shell model is adopted and the effects of van der Waals forces between adjacent nanotubes are taken into account. An examination with an individual double-walled carbon nanotube shows that the effect of the change of interlayer spacing on the torsional buckling force can be neglected if only the innermost radius is larger than a certain value. Under this condition, single buckling equations are derived and explicit formulas for the critical torsional loads in terms of the buckling modes are obtained. It is found that the critical torsional load of a multi-walled carbon nanotube with torque exerted on the outermost tube is higher than that of the same multi-walled carbon nanotubes under the torques being proportionally applied to each individual layer of the multi-walled carbon nanotubes. For thin multi-walled carbon nanotubes with large radii, the critical torque linearly scales with its thickness, but the critical shear force (per unit length) of the multi-walled carbon nanotubes uniformly twisted along the cross-section does not increase as its layer number (thickness) increases, which is due to the interlayer slips between adjacent nanotubes. [ABSTRACT FROM AUTHOR]

In a previous paper published in this journal, an attempt was made to study vibration and buckling analysis of axially functionally graded beams. Further studies on this subject show that an additional term needed to be included in the solution of the governing equations that lead to incorrect results. So the aim of the present study is to correct the solution of this problem. [ABSTRACT FROM PUBLISHER]

To achieve high energy absorption under edgewise compression loading, sandwich composites must experience a progressive failure that includes compression failure of the facesheets. This investigation focused on sandwich core design for energy absorption through the use of failure mode maps. Predictive models for global buckling, facesheet wrinkling, and facesheet compression failure were used to construct failure mode maps as a function of sandwich core thickness and density. Predicted failure loads and initial failure modes were found to be in good agreement with results from edgewise compression testing. Sandwich configurations experiencing facesheet compression failure as the initial failure mode were found to produce the highest energy absorption. These results suggest that sandwich composites may be designed for enhanced energy absorption through the proper selection of core materials and geometries. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of damage characteristics and local curvature change on the residual compressive strength (RCS) of flat 4-mm thick carbon/epoxy panels through the examination of their buckling behavior. The damage was induced by impact, quasi-static loading and embedment of artificial delamination for a variety of damage areas, intensities and different local curvature changes. The embedment technique of artificial delaminations allowed the separation of the damage from the local curvature change. Panels with no or less significant damage in conjunction with no or little local curvature change failed in end crushing because of large membrane reaction, in-plane shear resistance and flexural rigidity. Prebuckling and Poisson's effect dictated their compressive behavior. Panels with significant damage followed the sequential behavior of prebuckling, local buckling, global buckling and ultimate failure in the mid-section region. Their RCSs were dictated by a combination of delamination size, intensity and local curvature change. Propagation of the damage with certain size and intensity associated with reduced flexural rigidity in the damaged area led to the local-to-global buckling transition and the panels failed at the global buckling-to-postbuckling transition at a nodal line. The effect of increasing the panel thickness on the ratio of RCS to a baseline value was not straightforward due to the end crushing failure of the thicker intact panels. [ABSTRACT FROM AUTHOR]

In this article, a novel numerical approach for the delamination growth simulation in composite panels under compressive load is proposed. This approach, suitable for preliminary design and optimization purposes, is able to simulate the delamination propagation by means of a limited number of linear analyses. It is based on the determination of the delamination buckling and on the evaluation of the energy released during the delamination propagation by means of eigenvalue and linear static analyses. The proposed approach has been implemented into the finite element code ANSYS and applied to composite panels with circular embedded and rectangular through-the-width delaminations under compressive load. A first validation has been carried out by comparing the results in terms of delamination growth load and energy release rate distributions along the delamination front to two-dimensional and three-dimensional nonlinear results taken from literature. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of precondition characteristics on the residual compressive strength (RCS) of 16-ply carbon/epoxy panels through the establishment of their compressive and buckling response characteristics. The preconditions of varying sizes include impact damage and embedded artificial delaminations of both circular and elliptical shapes. A sequence of prebuckling, local and global buckling, and postbuckling is found in both the longitudinal and transverse directions. The possibility of delamination propagation is examined using the response characteristics on the basis of the sequences. A damage threshold is found at the 25% panel width or 455mm² damage area. Both the global buckling loads and the RCSs suffer substantial degradation but in a different manner, depending on the threshold. For small damages, the global buckling loads are unaffected but the RCSs suffer substantial degradation, though there is little evidence for the delamination propagation. For large damages, while the global buckling loads are reduced moderately with an increase of the damages due likely to the unstable global buckling-to-postbuckling transition, the RCSs do not suffer further reduction, though evidence is found for the delamination propagation. These panels fail soon after the unstable global buckling-to-postbuckling transition. Panels with multiple delaminations suffer a greater reduction in RCS than the impact-damaged panels. A combination of the delamination size and number is shown to have the most dominant effect on the RCSs. It is demonstrated that the present method of embedding artificial delaminations proves to be very useful for studying the RCS of impact-damaged panels via the establishment of response characteristics and their links to the effects of the preconditions on them. [ABSTRACT FROM AUTHOR]

An improved transverse shear stiffness for vibration and buckling analysis of functionally graded sandwich plates based on the first-order shear deformation theory is proposed in this paper. The transverse shear stress obtained from the in-plane stress and equilibrium equation allows to analytically derive an improved transverse shear stiffness and associated shear correction factor of the functionally graded sandwich plate. Sandwich plates with functionally graded faces and both homogeneous hardcore and softcore are considered. The material property is assumed to be isotropic at each point and vary through the plate thickness according to a power-law distribution of the volume fraction of the constituents. Equations of motion and boundary conditions are derived from Hamilton’s principle. The Navier-type solutions are obtained for simply supported boundary conditions, and exact formulae are proposed and compared with the existing solutions to verify the validity of the developed model. Numerical results are obtained for simply supported functionally graded sandwich plates made of three sets of material combinations of metal and ceramic, Al/Al2O3, Al/SiC and Al/WC to investigate the effects of the power-law index, thickness ratio of layer, material contrast on the shear correction factors, natural frequencies and critical buckling loads as well as load–frequency curves. [ABSTRACT FROM PUBLISHER]

Three-dimensional spacer fabric is a type of one-piece sandwich structure consisting of two outer layers and vertical and inclined spacer monofilaments. It behaves like a cushioning material, having linear, plateau, and densification stages under compression. This article elucidates the compression mechanism of a typical spacer fabric in terms of global deformation, local deformation, and internal contact behavior of spacer monofilaments through finite element simulation. While the linear stage is post-buckling of spacer monofilaments with tight constraints, the plateau stage is a combination of post-buckling, torsion, rotation, and contact of spacer monofilaments. The densification stage is attributed to the contact between spacer monofilaments and outer layers, which decreases the effective length to bear the load and enhances the constraints on the spacer monofilaments. The vertical spacer monofilaments with almost triple the normal strains of the inclined ones contribute more to compression resistance. [ABSTRACT FROM AUTHOR]

This paper provides useful insights into the nonlinear buckling phenomenon of fibrous materials. In the analysis, a fiber is considered to be a rectangular, prismatic, inextensible column with no shear effect, whose constitutive equation corresponds to a Ludwick or modified Ludwick type. Governing equations of the buckling of a fiber as a nonlinear elastic column are established and solved. These equations cover not only the buckling situation of the column but also three other loading conditions: a horizontal direction of point load and a vertical direction of the distributed load, a vertical direction of point load and horizontal direction of distributed load, and a vertical direction of both point and distributed loads. As a result, in a linear material, the shape of the deflected fiber is fully described by the geometric boundary conditions of the path. In a nonlinear material, however, the shape depends on many other factors, including the cross-section, stress-strain response, and loading. Moreover, the deflected shape of a fiber with specified angles at both ends is almost the same for point or combined loading, regardless of the choice of constitutive relationship. What makes difference between the choices of constitutive equations is the load level. In a nonlinear fiber, the same deflected shape can be achieved at different load levels from the linear case. Another distinctive feature in nonlinear fiber is that the solution has double roots of the load parameter β at the same value of tip slope angle, whereas it has only one root for the linear case. Finally, the accuracy of the solution is estimated by comparing the results with well-known elliptic integral solutions for a linear elastic case under point load. Selected examples of the deflected shape are also provided. [ABSTRACT FROM AUTHOR]

There are currently no specialized test methods for the characterization of specific energy absorption (SEA) of composite materials. Based on an original concept developed by NASA in the early 1990s, a test method that utilizes a flat plate-like specimen and a modified anti-buckling fixture is presented here that introduces a region of unsupported material in the proximity of the crush front, and allows the specimen to deform freely. A systematic experimental investigation is conducted with two unidirectional tapes to verify the general applicability of the test method to screen candidate material systems, and to isolate the effect of the unsupported distance on the measured SEA values. In general, it is found that there are four failure mechanisms (fragmentation, frond formation, local, and global buckling) that compete as the dominating mode according to the chosen unsupported distance. The specimen and fixture combination presents several limitations, but with a properly selected unsupported distance it could be used to assess the SEA of material and structures whose dominating failure mechanism is frond formation. [ABSTRACT FROM AUTHOR]

Elastic memory composite (EMC) can endure a much higher nominal bending strain than the ultimate strain of reinforced fibers. Experimental studies have confirmed that microbuckling and post-microbuckling response for compressively loaded fibers in the soft matrix are the primary deformation mechanism for EMC to realize a large bending deformation. However, classical buckling solutions developed for hard-matrix composites cannot effectively predict the microbuckling onset and post-microbuckling response of soft-matrix composites under bending. In this study, a simplified 1D solution is proposed by combining matrix shear energy with Timoshenko's elastic foundation energy. Based on the experiment results of carbon-fiber/resin EMC laminates under bending, the new solution exhibits to be effective in predicting the microbuckling wavelength and the onset of critical compressive stress and strain. In addition, the location of neutral-strain surface and failure modes are also discussed. [ABSTRACT FROM AUTHOR]

The in-plane longitudinal compressive strength of continuous fiber-reinforced composites is significantly less than their tensile strength, a phenomenon that is still not well understood. Dow and Rosen attempted in 1965 to explain this phenomenon through a fiber microbuckling model, in which each fiber was modeled as a beam-on-an-elastic-foundation. The model, however, grossly overestimates the compressive strength; researchers have since focused on introducing factors that reduce the predicted compressive strength to fit experimentally observed values. These include initial fiber waviness, fiber and matrix properties, the interfacial strength, and interphase properties. While empirical results have demonstrated the influences of some of these factors, an analytical model that can accurately predict the strength while taking into account the underlying failure mechanism is still lacking. The present study treats the compressive strength prediction of continuous fiber-reinforced composites using a different approach. Here, the matrix surrounding the fiber is not assumed to be homogeneous, but is divided into a discrete interphase region adjacent to the fiber and bulk matrix phase beyond the interphase. The three-phase model is shown to provide a more accurate prediction of the compressive strength of typical high-performance composites, such as glass and carbon fiber-reinforced epoxy. The present model's prediction agrees well with the trends shown in the experimental database available in the literature. [ABSTRACT FROM AUTHOR]

An efficient global zigzag theory (GZIGT) is developed for elastic laminated plates, by approximating the in-plane displacements by a cubic expansion in thickness coordinate along with a global zigzag function, which takes values ±1 at successive interfaces. The deflection is approximated to account explicitly for transverse thermal strain. The displacement variables are reduced to five, the same as used in first-order shear deformation theory, by imposing the conditions on transverse shear at three a priori selected interfaces/faces. A third order theory (TOT1) is also developed with similar expression of deflection. GZIGT and TOT1 are assessed by comparison with exact three-dimensional solutions for simply-supported square plates for sinusoidal pressure and thermal loads, natural frequencies and buckling. In general, GZIGT yields good results for two-ply, three-ply and four-ply composite plates, but it is inaccurate for a highly inhomogeneous test plate. [ABSTRACT FROM AUTHOR]

Multi-segment shell typical of underwater vehicles is currently important underwater equipment. Stealth performance is a key indicator to improve the working capacity of underwater vehicles. Low-noise design is an important means to improve stealthy performance. Accurate and effective identification of its structure Frequency Response Function (FRF) is the premise of low-noise design. However, the multi-section shell joint interface has many connection points, complex transmission path and typical nonlinear characteristics, which challenges the acquisition of its structural FRF. The Receptance Coupling Substructure Analysis (RCSA) is used to segment the multi-stage shell, which can realize the integration of finite element method and experimental method, and provide an effective way to obtain the FRF of multi-segment shell. At the same time, the multi-segment shell is a typical thin-wall structure, and its actual buckling process under impact is a nonlinear (large deformation) process. Therefore, the nonlinear joint interface is constructed based on linear connection, and the RCSA for nonlinear joint interface is studied. On the basis of accurately obtaining the FRF, it is of theoretical and application significance to study the low noise design of shell. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesting from ambient vibrations is well studied, but harvesting from quasi-static responses is not yet fully explored. The lack of attention is because quasi-static actions are much slower than the resonance frequency of piezoelectric oscillators to achieve optimal outputs; however, they can be a common mechanical energy resource: from large civil structure deformations to biomechanical motions. The recent advances in bio-micro-electro-mechanical systems and wireless sensor technologies are motivating the study of piezoelectric energy harvesting from quasi-static conditions for low-power budget devices. This article presents a new approach of using quasi-static deformations to generate electrical power through an axially compressed bilaterally constrained strip with an attached piezoelectric layer. A theoretical model was developed to predict the strain distribution of the strip’s buckled configuration for calculating the electrical energy generation. Results from an experimental investigation and finite element simulations are in good agreement with the theoretical study. Test results from a prototyped device showed that a peak output power of 1.33 μW/cm2 was generated, which can adequately provide power supply for low-power budget devices. And a parametric study was also conducted to provide design guidance on selecting the dimensions of a device based on the external embedding structure. [ABSTRACT FROM AUTHOR]

A nonlocal sinusoidal plate model for micro/nanoscale plates is developed based on Eringen’s nonlocal elasticity theory and sinusoidal shear deformation plate theory. The small-scale effect is considered in the former theory while the transverse shear deformation effect is included in the latter theory. The proposed model accounts for sinusoidal variations of transverse shear strains through the thickness of the plate, and satisfies the stress-free boundary conditions on the plate surfaces, thus a shear correction factor is not required. Equations of motion and boundary conditions are derived from Hamilton’s principle. Analytical solutions for bending, buckling, and vibration of simply supported plates are presented, and the obtained results are compared with the existing solutions. The effects of small scale and shear deformation on the responses of the micro/nanoscale plates are investigated. [ABSTRACT FROM PUBLISHER]

A triangular composite stiffened plate/shell element is developed to analyze the advanced grid stiffened (AGS) structures based on Mindlin shear deformation theory. The rotations of ribs and skin are interpolated, respectively, while the conditions of displacement compatibility are satisfied along the interface of rib and skin. There are no restrictions on the number, positions, and orientation of the ribs in establishing element mesh. The numerical results indicate its effectiveness, especially for the case of the AGS structures of higher ribs. Stability analyses for an ortho-grid plate and iso-grid cylindrical shell are also carried out. [ABSTRACT FROM AUTHOR]

In this article, the governing equations of motion for a functionally graded material plate (FGP) based on a higher-order deformation theory in a general state of non-uniform initial stress are derived. The properties of FGP are assumed varied continuously along the thickness of the plate, according to a simple power law of volume fractions of constituents. With the derived governing equations, the natural frequencies and buckling loads of ceramic--FGM--metal plates subjected to an initial stress are investigated. The initial stress is taken to be a combination of a uniaxial extensional stress and a pure bending stress. A ceramic--FGM--metal plate can become an all-FGM, all-ceramic plate, or all-metal plate by modifying the value of material parameter and volume fraction index. The effects of various parameters and initial stresses on the natural frequencies and buckling loads of FGPs are studied. [ABSTRACT FROM AUTHOR]

To increase understanding of damage evolution in advanced composite material systems, a series of large deflection bending-compression experiments and model predictions have been performed for a woven glass-epoxy composite material system. Theoretical developments employing both small and large deformation models and computational studies are performed. Results (a) show that the Euler–Bernoulli beam theory for small deformations is adequate to describe the shape and deformations when the axial and transverse displacement are quite small, (b) show that a modified Drucker's equation effectively extends the theory prediction to the large deformation region, providing an accurate estimate for the buckling load, the post-buckling axial load-axial displacement response of the specimen and the axial strain along the beam centerline, even in the presence of observed anticlastic (double) specimen curvature near mid-length for all fiber angles (that is not modeled), and (c) for the first time the quantities σeff – ɛeff are shown to be appropriate parameters to correlate the material response on both the compression and tension surfaces of a beam-compression specimen in the range 0 ≤ ɛeff < 0.005 as the specimen undergoes combined bending-compression loading. In addition, computational studies indicate that the experimental σeff – ɛeff results are in reasonable quantitative agreement with unwoven laminate finite element simulation predictions in the range 0 ≤ ɛeff < 0.010, with the effect of the woven structure appearing to provide the key constraint for various fiber angles that leads to the observed consistency in the experimental σeff – ɛeff results on both surfaces. [ABSTRACT FROM AUTHOR]

Bistable generator for vibration energy harvesting is one of the most promising solutions to reach practically enhanced performance. Due to the buckled–spring–mass–specific behavior, the deformation of the piezoelectric transducer is nonlinearly dependent on the displacement, especially in the inter-well motion case. An analytical model is developed using harmonic balance analysis for the buckled–spring–mass generator architecture. Contrary to the usual method, a special doubled frequency voltage solution in the inter-well motion case is assumed in harmonic balance analysis to obtain an accurate predictive model, which is validated by experimental results. The influence of five critical parameters on the performance is thoroughly discussed. Design rules are then deduced: low damping ratio, properly high coupling level, matched load, optimal buckling level, and low characteristic frequency are required to get optimal performance in the inter-well motion case. Besides, we show some interesting results about the parameter optimization study. [ABSTRACT FROM AUTHOR]

In the present era, the use of CFST members has become quite popular in the construction industry and at the same time, aging of metallic structures and member deterioration have also been often reported. Therefore, actions such as implementation of new materials and strengthening techniques have become essential to combat this problem. It has already been proved that FRP composites significantly improved the strength of reinforced concrete structures. The application of these materials is implemented in the high-performance steel structures. With this aim, an experimental study has been carried out to investigate the suitability of unidirectional CFRP fabrics in strengthening CFST members under axial compression. The size and height of the specimens used in this study are 91.5 × 91.5 × 3.6 mm and 600 mm, respectively. Out of 21 columns, 18 columns were externally bonded by CFRP strips having a constant width of 50 mm with spacing values of 20 mm and 30 mm and the remaining three columns were unbonded. The effect of CFRP layers on the load-carrying capacity of CFST columns was investigated. The strengthened columns exhibited FRP rupture failure due to outward buckling of steel tube. Experimental results also revealed that external bonding of CFRP strips considerably provides the confining pressure to the CFST column and as a result, CFRP-confined columns sustained higher ultimate load and larger axial deformation compared to control column. An analytical model was also proposed herein for predicting the axial load capacity of CFRP-confined CFST columns. The average percentage of difference between the analytical and the experimental loads was found as ±4%. [ABSTRACT FROM PUBLISHER]

Low-velocity dynamic compression tests were carried out to reveal the failure mechanism and the energy absorption capacity of multilayered woven lattice sandwich panels. Dynamic compression coupled with shear deformation results in typical softening deformation after the peak stress. The load–displacement curve is characterized by a long zigzag deformation. Multilayered woven lattice sandwich panels have deformation characteristics of type II structure. Compared with the quasi-static compressed panel, the impacted woven textile sandwich has similar failure mode but excellent energy absorption induced by greater dynamic strength. Strain rate effect of the structure was explained by dynamic buckling theory. Gradient structure, placing the hardest layer as the first impacted layer and the weakest as the last, has great benefits in terms of energy absorption efficiency and should be ideal to serve as an energy-absorbing structure. [ABSTRACT FROM AUTHOR]