Multi-Scale Modeling And Simulation On Buckling And Wrinkling Phenomena Of Sandwich Structures

Sandwich structures have found more and more applications in engineering yields, such as space, aeronautics and automotive, where high structural performances are re-quired together with a reduced weight. It's well known that in-plane compressive stresses can cause the global and/or local instability phenomena in the skins of sandwich structures. Often the instability pattern is nearly spatially periodic and the wavelength is very small compared to the structure size. Direct simulation is not the best option for the following reasons:i) it's difficult to pilot the nonlinear simulation because too many solution paths exist around the useful one, and ii) direct simulation requires a large amount of elements and this leads to a high computational complexity.The central aim of this thesis is to develop advanced multi-scale modeling and simula-tion techniques to study the buckling and wrinkling phenomena of sandwich structures by combining the Technique of Slowly Variable Fourier Coefficients (TSVFC), the Bridging Techniques (BT) and the Asymptotic Numerical Method (ANM). Toward this end, the TSVFC and the BT have been firstly reviewed in the case of Winkler beams in order to evaluate the accuracy, the efficiency and the boundary effects of the Fourier-related macro-scopical model, and to investigate the coupling techniques between the macroscopical and microscopical models. Then, a one-dimensional (1D) microscopical model, a1D Fourier macroscopical model, a1D macro-micro multi-scale model, a two-dimensional (2D) mi-croscopical model, a2D Fourier macroscopical model have been successively established by choosing high-order layer-wise theory as the kinematics, by using the coefficients of Fourier series as the macroscopical envelopes, by applying the BT as the coupling tech-nique, by setting the ANM as the non-linear solver, to study the global buckling, the anti-symmetrical wrinkling, the symmetrical wrinkling and the globla-local-coupling in-stability of sandwich beams and plates. The numerical results show that the proposed multi-scale model is able to correctly simulate various instability phenomena of sandwich structures in a very efficient way.The results of these thesis are hoped to accurately and efficiently predict and pre-vent buckling and wrinkling of sandwich structures, and also to help to study the other instability phenomena with nearly periodic patterns.