Analysis Of Fracture Problem In Piezoelectric Semiconductor Film

Piezoelectric semiconductor film materials have been widely used in vehicle with the rapid development of auto industry. The defects in the materials and devices called extensive attentions to the study of their fracture properties. In this thesis, both theoretical and numerical methods are employed to study the fracture problem and to model the indentation experiment of piezoelectric semiconductor materials. The main contributions of this thesis are as follows:(1) Fracture analysis of piezoelectric semiconductor films: 1) General solutions of displacement and stress fields are obtained based on the theory of differential operators and the generalized Almansi’s theorem. 2) Based on the derived general solutions, the extended displacement discontinuity fundamental solutions are obtained by virtue of Hankel transform. 3) The extended displacement discontinuity boundary element method(EDDBEM) is obtained for the fracture problem in three-dimensional transversely isotropic piezoelectric semiconductors. 4) A penny shaped crack in such piezoelectric semiconductor media is studied, and the extended displacement discontinuity fields on the crack surface and the extended intensity factors at the crack front are analyzed.(2) Modeling of indentation experiment of multilayer film-substrate systems: 1) The influence factors of the elastic modulus and yield strength of the film-substrate on the load-displacement function are considered. The finite element method(FEM) was employed to simulate the indention test of a single-layer-film-over-the-substrate model and a semi-empirical formula is obtained in terms of the elastic modulus radio, yield strength radio and indentation depth to describe the relationship between the load applied to the composite structure and those applied to the film and substrate individually.2) A double-layer-film-over-the-substrates model is also considered. Via the computational iteration approach, the equivalent elastic modulus and yield strength are presented. 3) A semi-empirical formula for multilayered film-substrate system is further proposed based on the iterative method introduced in this thesis.