General stability analysis of composite sandwich plates under thermal load

In structures subjected to high temperature change such as high-speed aircraft the panels are stressed more significantly under thermal loading than mechanical loading. This can produce instability within the structure; therefore, the thermal loading may become the primary factor in the design of the structure. For example, buckling and facesheet wrinkling are two major failure modes of the composite sandwich plates subjected to various loadings. The goal of this dissertation is to study the stability analysis of composite sandwich plates due to buckling and wrinkling subjected to thermal loading. The primary objective is to find out the critical failure mode and the associated critical temperature change causing it. For thermal buckling and wrinkling analysis, the critical temperature change Delta Tcr, is of more interest than the critical thermal load.;In this study, two different approaches of the stability problem of the composite sandwich plate subjected to thermally induced load are developed. In the first approach, the wrinkling analysis and buckling analysis are performed separately to evaluate their associated critical wrinkling and buckling temperature changes. For the face-wrinkling problem, two different models, the linear decaying Hoff model and exponential decaying Chen model are employed. The global buckling analysis is based on the energy method. The second approach is based on the unified theory of Benson and Mayers. In such an approach, the critical temperature change for both the global buckling and face wrinkling can be evaluated simultaneously. A potential energy based variation principle has been applied to formulate the problem. The Lagrange multipliers are used to satisfy the face-core continuity conditions. The buckling and wrinkling can be analyzed and calculated simultaneously. Therefore, the critical wrinkling temperature and the critical buckling temperature are found in a single analysis.;The critical buckling and wrinkling stresses subjected to temperature changes are evaluated for composite sandwiches with various lay-up of facesheet , core thickness, core normal and shear stiffness, the thermal expansion coefficients of facesheet material, and plate aspect ratios. The numerical results show that the critical temperature change of a simply supported composite sandwich plate with identical symmetric layup of faces is dependent upon the core to face thickness ratio, facesheet lay-up, and thermal expansion coefficients of the facesheet and the aspect ratio of the structure. Decreasing the core thickness will change the type of failure mode from global buckling to facesheet wrinkling, while increasing the core stiffness will change the failure mode from local wrinkling to global buckling mode. In addition, comparisons between the two different approaches and with other available theoretical results are presented and a good agreement is reported.