Preliminary Study Of Microvoid And Microcrack Evolution And Anisotropic Nature Of The Material

The works studied in the thesis are follows: Firstly, by means of controlling the macroscopic stress triaxiality and Lode's parameters of the cubic cell model, the void expanding analysis of penny-shaped crack and sphere-shaped void have been carried out by using finite element method. The results show that: when the stress triaxiality is low, the penny-shaped crack can lead to damage anistropy of a ductile material; and the variance of Lode's parameter will lead to the variance of the expanding rate and deformed shape of penny-shaped crack and sphere-shaped void. Secondly, to study the effect of the anisotropic property on void growth in orthotropic elastic-plastic matrix material, a three-dimensional cell model containing a spherical void is employed. The results show that: the orientation of principal stress of a cell has significant influence on void volume growth rates under a given stress triaxiality; the results also show that there is a higher void growth rate when the material is of stronger anisotropy or when the Lode parameter μ=-1, under low stress triaxiality. The analysis of this paper has demonstrated the damage development character of orthotropic elastic-plastic material. Thirdly, to study the distribution of the stress of the human femur under different loads, the three-dimensional finite element model of the human femur has been constructed, and the anisotropic property of bone has been considered. The results show that: the input of the internal fixation implant should be in accordance with the compressive trabeculae and be clingy with the femoral calcar; the stress distribution of the femur under external violence explained why the old people are easy to get the middle and low part fractures of the femoral neck and intertrochanteric fractures.