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The paper aims to develop a unified modeling to analyze the free vibrations and buckling of laterally functionally graded material columns. The columns of rectangular cross-section, in which the mass density and Young's modulus vary along the depth as a power-law function, were considered. The differential equation governing a mode shape of a deformed column was derived with the relevant boundary conditions, including the effect of rotatory inertia. The computation results for the natural frequencies and buckling load were compared well with those available in the open scientific literature. The effects of geometrical and material properties on natural frequencies and buckling loads with the mode shapes are highlighted. [ABSTRACT FROM AUTHOR]

Basalt-fiber-reinforced epoxy (BFRE) composite laminates fabricated using the vacuum infusion process were subjected to axial compression to assess their buckling behavior. The buckling responses of open-hole specimens were compared with those of plain ones. ABAQUS finite-element predictions of BFRE composite buckling agreed well with experimental results. A validated numerical model was used to perform a parametric investigation into the effects of open-hole specimen geometry and boundary conditions of specimens on their buckling behavior. A linear analysis was carried out to estimate the effect of geometric imperfections of specimens on their buckling. Also, glass-fiber-reinforced epoxy specimens were analyzed for their buckling response and compared with that of BFRE ones. The results of this study can be used for buckling-based designs of open-hole composite structures. [ABSTRACT FROM AUTHOR]

The optimum paths and orientations for curvilinear and straight fibers in composite cylindrical shells of variable and constant stiffness under external hydrostatic pressure are obtained and compared. The optimization was performed for several length-to-diameter ratios of the shells. Results showed that the buckling pressure of the variable-stiffness shell was by about 30℅ higher than that of the constant-stiffness one. This increase in the buckling pressure was obtained by locating fibers in the hoop direction in the middle of the cylinder and orienting the fibers toward the longitudinal direction on cylinder edges. [ABSTRACT FROM AUTHOR]

In order to determine the nonlocal critical buckling loads of chiral double-walled carbon nanotubes embedded in an elastic medium, the nonlocal Timoshenko beam theory is implemented. The solution for the nonlocal critical buckling loads is obtained using governing equations of the nonlocal theory. The effect of the elastic medium, the buckling mode number, chirality, and aspect ratio on the nonlocal critical buckling loads of double-walled carbon nanotubes are studied and discussed. The Young's modulus of three types of double-walled carbon nanotubes, with armchair, zigzag, and chiral tubules, are calculated based on molecular dynamics simulations. The nonlocal critical buckling loads in relation to the chirality of double-walled carbon nanotubes, buckling mode number, and length-to-diameter (aspect} ratio, in the presence and absence of an elastic medium, are examined. [ABSTRACT FROM AUTHOR]

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

The buckling of simply supported laminated composite plates is studied using various higher-order shear deformation theories. A Navier-type analytical method is used to solve the governing differential equations. The critical buckling loads of simply supported laminated composite plates under a uniaxial buckling load are calculated. The present results are compared with available published results to verify the accuracy of the higher-order shear deformation theories considered. [ABSTRACT FROM AUTHOR]

On the basis of the nonlocal elasticity theory, the Timoshenko beam model is utilized to investigate the elastic buckling of chiral single-walled carbon nanotubes (SWCNTs) under axial compression. Based on the governing equations of the nonlocal Timoshenko beam model, an analytical solution for nonlocal critical buckling loads is obtained. The influence of a nonlocal small-scale coefficient, the vibration mode number, the chirality of SWWCNTs, and their aspect ratio on the nonlocal critical buckling loads is studied and discussed. [ABSTRACT FROM AUTHOR]

The buckling behavior of a thin particle-reinforced composite plate under the influence of an unsteady temperature field and a temperature gradient across its thickness is investigated. An analytic solution for bending of the plate is obtained in the form of double trigonometric series. Based on the analytic result, a numerical test is carried out to study the thickness and time dependences of the buckling behavior of a plate made of a PVC matrix and titanium particles. [ABSTRACT FROM AUTHOR]

The nonlinear buckling and postbuckling of a shear-deformable anisotropic laminated cylindrical panel of finite length is investigated based on a boundary-layer theory for buckling. The layers of the panel are assumed to be linearly elastic. The governing equations are based on Reddy's higher-order shear deformation theory of shells and include the von Karman-type kinematic nonlinearity and extension/twist, extension/flexure, and flexure/twist couplings. The nonlinear prebuckling deformations and the initial geometric imperfections of the panel are both taken into account. The postbuckling behavior of the panel under axial compression is analyzed. A singular perturbation technique is employed to determine its buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling behavior of perfect and imperfect moderately thick anisotropic laminated cylindrical panels with different geometric parameters and stacking sequences. The new finding reveals that there arises a compressive stress along with an associate shear stress and twisting when a moderately thick anisotropic laminated cylindrical panel is subjected to axial compression. [ABSTRACT FROM AUTHOR]

The delamination buckling problem for a rectangular plate made of an orthotropic composite material is studied. The plate contains a band crack whose faces have an initial infinitesimal imperfection. The subsequent development of this imperfection due to an external compressive load acting along the crack is studied through the use of the three-dimensional geometrically nonlinear field equations of elasticity theory for anisotropic bodies. A criterion of initial imperfection is used in determining the critical forces. The corresponding boundary-value problems are solved by employing the boundary-form perturbation technique and the FEM. Numerical results for the critical force are presented. [ABSTRACT FROM AUTHOR]

The buckling of imperfect composite cylinders under concentric and eccentric compression is investigated experimentally and numerically, with particular attention given to the imperfection sensitivity of the shells. A series of glass-fiber-reinforced plastic cylinders have been tested under different load eccentricities to validate the corresponding nonlinear numerical analyses performed in this study. A good agreement between the experimental and numerical results was achieved through use of the ABAQUS/Explicit finite-element code and the introduction of initial imperfections. Both the experimental and the numerical results show that the knockdown factor increases as the loading eccentricity grows. [ABSTRACT FROM AUTHOR]

The postimpact buck ling loads of E-glass/epoxy laminates have been measured. Composite samples with the stacking sequence [+45/−45/90/0]2s were subjected to low-speed impact loadings at various energy levels. The tests were conducted on a specially developed vertical drop-weight testing machine. The main impact parameters, such as the peak load, absorbed energy, deflection at the peak load, and damage area, were evaluated and com pared. The damaged specimens were subjected to compressive axial forces, and their buckling loads were determined. The relation between the level of impact energy and buck ling loads is investigated. [ABSTRACT FROM AUTHOR]

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

A method is presented for determining the flexural strength of composites from tests on pinned specimens in axial compression. This scheme is close to the so-called Euler buckling model, but the load is applied eccentrically, and the bar is bent practically from the beginning of loading. An analytical model is proposed for calculating the flexural stress in longitudinal flexure of a thin bar in the case of large displacements. The problem is solved in elliptic integrals of the first and second kinds. The analytical model shows an excellent agreement with experiments. The results obtained are compared with experimental tension data. A device is also designed for testing composite bars in longitudinal flexure. The method offered has an obvious advantage over the conventional three- or four-point bending — the gage zone in this scheme is far away from the loading zone of the test specimen. [ABSTRACT FROM AUTHOR]