双向载荷下威布尔应力参量的研究

STUDY ON PARAMETER OF WEIBULL STRESS UNDER BIAXIAL LOAD

以往对双轴断裂的研究多采用线弹性断裂力学参量且限于弹性材料 ,局部法理论提出了威布尔应力参量 ,威布尔应力作为度量脆性断裂概率的参量已广泛采用。为研究双向载荷对威布尔应力的影响 ,文中开发了威布尔应力计算程序并进行考核验证 ,以威布尔应力为参量 ,以ASTMA3 6钢中心裂纹板为研究对象 ,结合有限元分析方法 ,研究二维裂纹问题在不同双向载荷比下威布尔应力参量的变化规律 ,从而得到双向载荷对脆断概率的影响。计算结果表明 ,平面应力状态下 ,双向载荷对威布尔应力和脆断概率基本上没有影响 ;而在平面应变状态下 。

During the past years, much effort has been concentrated on the effect of biaxial load on fracture character. But fracture parameters often studied are line elastic fracture parameters such as stress intensity factor K and energy release ratio G , which are used for elastic materials. It is not appropriate for pressure vessel steels which are often elastic plastic material. The development of local approach to fracture put forward a new parameter, Weibull stress, which is widely used as a measure of the probability of brittle failure of elastic plastic steel. In order to find the effect of biaxial load on Weibull stress, a computer program of Weibull stress is developed and is tested and proved true. Finite element method has been adopted to analyze the stress and strain fields of a finite plate containing a through thickness crack. The finite plate is made of ASTM A36 steel and is subjected to biaxial load under plane stress and plane strain conditions. Combined the finite element calculation results and the Weibull stress computer program, the Weibull stress and the brittle fracture probability of the finite plate under different biaxial load are analyzed. The calculation results show that the biaxial load almost has no effect on Weibull stress and on brittle fracture probability under plane stress condition, however, Weibull stress and brittle fracture probability increase with the increase of the ratio of biaxial load under plane strain condition. When the load ratio is 0.9 and the ratio of biaxial load equals to 2, the difference between the Weibull stress under biaxial load and that under axial load is maximal and it reaches 29%.