脆性材料的扩展裂纹前缘形态与三维J积分

本文利用超声波断口图技术对不同类型的PMMA试件进行了测试。这些试件为承受均匀拉伸或三点弯曲变形的带单侧贯穿裂纹的PMMA板，其中拉伸试件又分为光面和带表面沟槽的两种。得到了这些试件断口上的超声波线。发现它们为平面线．其凸凹方向与试件的表面状态有关。基于有限元法，计算了试件的三维J积分，考察了杨氏模量和泊松比对其的影响．结果发现泊松比影响J积分曲线形状，而杨氏模量只影响其绝对数值，不影响其曲线形状。得到的试件在不同裂纹长度下的三维J积分与它们断口图上的超声波线的形状和凸凹方向相似。说明在脆性材料中，扩展裂纹前缘曲线形态是三维J积分的作用的结果。

Configuration of Propagating Crack Front in Brittle Material and Three Dimensional J Integral

In this paper, ultrasonic fractography method is used to test several types of PMMA specimens. They are uniform tensile and three-point bending ones with one-side-through crack. And tensile specimens have two kinds: one with surface notches; another without surface notches. The ultrasonic lines remained in the fracture surface of these specimens are obtained and they are plane curves. These lines' protruding and concave configurations depend upon the specimen's surface status. Three simensional J integrals of the specimens are evaluated based on finite element method. The effect of Young's modulus and Poisson's ratio on J integral is investigated. As a result, Poisson's ratio affects the shape of J integral curve and Young's modulus doesn't affect the shape but absolute values of J integral curve. There are similarities between three dimensional J integrals evaluated under different crack lengths and ultrasonic lines remained in the specimens'fracture surfaces in shape and protruding direction, which indicates the configurations of propagating crack fronts in brittle materials are decided by the three dimensional J integral.