سال:1388 | دوره: | شماره: |تعداد مقالات:8

The buckling and postbuckling behaviors of a composite beam with single delamination are investigated. A three-dimensional finite element model using the commercial code ANSYS is employed for this purpose. The finite elements analyses have been performed using a linear buckling model based on the solution of the eigenvalues problem, and a non-linear one based on an incremental-iterative method. The large displacements have been taken into account in the nonlinear analysis. Instead of contact elements a new delamination closure device using rigid compression-only beam elements is developed. Effect of delamination length, position through thickness and stacking sequence of the plies on the buckling and postbuckling of laminates is investigated. It has been found that significant decreases occur in the critical buckling loads after a certain value of the delamination length. The position of delamination and the fiber orientation also affect these loads.

We have solved the governing equations for the buckling of rectangular functionally graded plates which one of its edges has small non-zero deflection and moment. For the case that the material properties obey a power law in the thickness direction, an analytical solution is obtained using the perturbation series. The applied in-plane load is assumed to be perpendicular to the edge which has non-ideal boundary conditions. Making use of the Linshtead-Poincare perturbation technique, the critical buckling loads are obtained. The results were then verified with the known data in the literature.

This paper concentrates on the propagation of waves in a layer of binary mixture of elastic solids subjected to stress free boundaries. Secular equations for the layer corresponding to symmetric and antisymmetric wave modes are derived in completely separate terms. The amplitudes of displacement components and specific loss for both symmetric and antisymmetric modes are obtained. The effect of mixtures on phase velocity, attenuation coefficient, specific loss and amplitude ratios for symmetric and antisymmetric modes is depicted graphically. A particular case of interest is also deduced from the present investigation.

Using Donnell-type shell theory a simple and exact procedure is presented for linear buckling analysis of functionally graded conical shells under axial compressive loads and external pressure. The solution is in the form of a power series in terms of a particularly convenient coordinate system. By analyzing the buckling of a series of conical shells, under various boundary conditions and different material coefficients, the validity of the presented procedure is confirmed.

Thin plate structures are more widely used in many engineering applications as one of the structural members. Generally, buckling strength of thin shell structures is the ultimate load carrying capacity of these structures. The presence of cracks in a thin shell structure can considerably affect its load carrying capacity. Hence, in this work, static buckling strength of a thin square plate with a centre or edge crack under axial compression has been studied using general purpose Finite Element Analysis software ANSYS. Sensitivity of static buckling load of a plate with a centre or a edge crack for crack length variation and its vertical and horizontal orientations have been investigated. Eigen buckling analysis is used to determine the static buckling strength of perfect and cracked thin plates. First, bifurcation buckling loads of a perfect thin plate with its mode shapes from FE eigen buckling analysis are compared with analytical solution for validating the FE models. From the analysis of the cracked thin plates, it is found that vertical cracks are more dominant than horizontal cracks in reducing buckling strength of the thin plates. Further, it is also found that as the crack length increases, buckling strength decreases.

This paper studies dynamic stability of functionally graded beams with piezoelectric layers subjected to periodic axial compressive load that is simply supported at both ends lies on a continuous elastic foundation. The Young’s modulus of beam is assumed to be graded continuously across the beam thickness. Applying the Hamilton’s principle, the governing dynamic equation is established. The effects of the constituent volume fractions, the influences of applied voltage, foundation coefficient and piezoelectric thickness on the unstable regions are presented.

In this paper, the causes of the crack initiation in cast iron bullion moulds in Meybod Steel Corporation are investigated and then some new geometrical models are presented to replace the current moulds. Finally, among the new presented models and according to the life assessment, the best model is selected and suggested as the replaced one. For this purpose, the three recommended moulds were modeled and analyzed by ANSYS software. First, a thermal analysis and then a thermo-mechanical coupled field analysis were performed on each three model. The results of the analysis are used to determine the critical zone. The critical zone is selected on the symmetric axis of the inner surface of the mould. By comparing the principle stress contours and temperature distribution contours of three models, one of the suggested models was selected as optimized geometrical model. Then, the crack modeling and the life assessment on the optimized model were implemented and the total life of the model was calculated. Comparison of the life of the optimized and the initial models shows an increase in the life of the suggested model. The results are verified with the experiments.

One of the common failure modes of thin cylindrical shell subjected external pressure is buckling. The buckling pressure of these shell structures are dominantly affected by the geometrical imperfections present in the cylindrical shell which are very difficult to alleviate during manufacturing process. In this work, only three types of geometrical imperfection patterns are considered namely (a) eigen affine mode imperfection pattern, (b) inward half lobe axisymmetric imperfection pattern extended throughout the height of the cylindrical shell and (c) local geometrical imperfection patterns such as inward dimple with varying wave lengths located at the mid-height of the cylindrical shell. ANSYS FE non-linear buckling analysis including both material and geometrical non-linearities is used to determine the critical buckling pressure. From the analysis it is found that when the maximum amplitude of imperfections is 1t, the eigen affine imperfection pattern gives out the lowest critical buckling pressure when compared to the other imperfection patterns considered When the amplitude of imperfections is above 1t, the inner half lobe axisymmetric imperfection pattern gives out the lowest critical buckling pressure when compared to the other imperfection patterns considered.