Finite element investigation of transmission conditions for thin interphases

Abstract

Nowadays, thin interphases are used for modern technology. A composite structure obtained in such a way exhibits a wide variety of thermal and mechanical properties. In this thesis, imperfect transmission conditions (ITCs) are discussed based on the finite element method (FEM) for a soft elasto-plastic interphase in a plane stress state, as well as thin reactive heat-conducting interphases, where the transmission conditions are nonlinear. The ITCs of a thin reactive two-dimensional interphase between two bonded materials in a dissimilar strip have been investigated. The validity of the transmission conditions for the heat conducting interphases has been analysed for three formulations of a reactive layer: with no source formulation, with constant source formulation, and with a temperature-dependent source formulation. In addition, the ITCs were evaluated in the most general form for several cases, demonstrating the high efficiency of the approach. This showed that it is possible to reconstruct the full solution inside the interphase using the information available for the respective imperfect interface of zero thickness. For the case of mechanical problems, it explains a thin elasto-plastic interphase layer, which is situated between two different elastic media. The intermediate layer consists of a soft elasto-plastic material with a small Young‘s modulus in comparison with those of the surrounding materials. The two-dimensional nonlinear transmission conditions for the bi-material structures were investigated using an asymptotic technique. This study evaluated the ITCs for a thin interphase layer with an adhesive joint, along with the mechanical behaviour of the bonded materials. Finally, the good accuracy of the nonlinear imperfect transmission conditions of the approach presented in this thesis is shown, along with the excellent performance of the finite element analysis of the thin elasto-plastic interphases and thin heat-conducting interphases