Effects Of The Surface Perturbation And The External Stress On The Evolutons Of Microcracks

The evolution of microcracks in materials has a great value in theoretical study and engineering practices. As a nonbalanced thermodynamic process, the evolution is determined by many factors, such as the environment, the stress state and the geometrical shape of the microcracks. In this dissertation, based on a basic framework of the thermal kinetics theory of mass transportation in materials, a finite element method is developed to study the evolution processes of damage microcracks in materials. And many influencing factors are analyzed in the processes. The main contents are summarized as follows:First of all, based on the classical theory of surface diffusion and its weak statement, a finite element scheme is implemented, and a program is developed for simulating the evolution of two-dimensional microcracks within grains, or perpendicular to the grain boundary.Then, a simplified model of microcracks with surface perturbation is established, and a new module is added to the computer program for analyzing the effects of the surface perturbation. The evolution processes for the two-dimensional microcracks within grains or perpendicular to the grain boundary are simulated by the finite element method developed in this paper. For microcracks, the cylinderization time and the critical aspect ratio of splitting vary with the changing of the amplitude and frequency of surface perturbation. These effects are investigated detailedly in the dissertation.At last, for the microcracks in complex stressed elastic solid, an expression of chemical potential for atoms is derived based on elastic mechanics and energy theory. With the expression, the finite element method can be improved for simulating the evolution of microcracks with small aspect ratio in complex stressed elastic solid. A prime study on the effects of stress for cylinderization time is performed in the end.