개선된 전단변형 이론을 이용한 복합재료 및 샌드위치 적층 구조물에 대한 효율적 열-기계 연성 해석 기법에 대한 연구

Abstract

In this dissertation, efficient and accurate models based on enhanced theories (enhanced first-order theories, enhanced higher-order theories and enhanced zig-zag theory) are proposed for the thermo-mechanical analysis of laminated composite and sandwich plates. In addition, co-rotational formulation with enhanced first-order theory is developed to investigate the geometrically nonlinear behaviors. In enhanced models, a couple of displacement fields are independently assumed to provide a reasonable compromise between solution accuracy and efficiency. The main objective of this dissertation is to systematically establish the relationships between two independent fields through the mixed variational theorem (MVT) as well as the strain energy transformation. According to the relationships, enhanced models have the same computational advantage of the simple models (conventional FSDT, HSDT, LCW, etc.) while improving upon its performance by utilizing the post-process procedure. Additionally, the convolution theorem of Laplace transformation is applied to circumvent the complexity of dealing with linear viscoelastic materials. The enhanced theories proposed in this dissertation have the following advantages.  Transverse shear stress continuity conditions at the interfaces between layers are satisfied.  Transverse shear free conditions at the top and bottom surfaces of the composite and sandwich plates are satisfied.  The number of primary variables is independent of the number of layers.  C0 interpolation function is only required in the finite element implementation, so computational efficiency can be further improved. The robustness, accuracy and computational efficiency of the enhanced models are demonstrated by comparing numerical results obtained herein to those of the 3-D exact solution, 3-D FEM solution as well as other theories available in the open literature.