Simulation of Material Fracture (Material Separation) in Tensile Test

首席研究员开发了一个新的计算程序，使用有限元法（FEM）。也就是说，开发了一种能够在材料断裂时将一个节点分解为两个节点的计算程序。利用该计算程序可以分析材料断裂后的裂纹扩展行为。在本研究中，利用首席研究员开发的计算程序，对具有代表性的材料试验之一拉伸试验中的材料断裂（材料分离）进行了模拟。首先，采用Gurson提出的屈服函数和首席研究员新提出的表示空隙体积分数变化的演化方程；在本文提出的演化方程中，假设当材料的无因次静水应力大于某一值时，空洞成核。此外，还采用了由首席研究员提出的基于微观角度的韧性断裂准则来判断材料的断裂。最后进行了拉伸试验，并将分析结果与实验结果进行了比较。确定了演化方程中各参数的取值，使分析结果与实验结果吻合。因此，材料断裂的评价可以通过拉伸试验来实现。

The head investigator has developed a new computation program using the Finite Element Method (FEM). In other words, a computation program which can separate one node into two nodes when the material fractures has been developed. The behavior of crack propagation after the material fractures can be analyzed using the computation program. In this research, the simulation of material fracture (material separation) in the tensile test which is one of the representative material tests has been performed using the computation program which the head investigator has developed. First, the yield function proposed by Gurson and the evolution equation which is newly proposed by the head investigator and which denotes the change in the void volume fraction is used. Here in the proposed evolution equation, it is assumed that the void nucleates when the non-dimensional hydrostatic stress of the material becomes larger than a certain value. Further the material fracture is judged using the ductile fracture criterion which is proposed by the head investigator and which is based on the microscopic point of view. Finally, the experiment of tensile test was performed and the analytical result is compared with the experimental result. The value of the parameter in the evolution equation is determined so that the analytical result coincides with the experimental result. Hence the evaluation of the material fracture can be achieved by the tensile test.