Evaluation for Nonlocal Damaged State in terms of Tesellation Analysis and an Anisotropic Yield Function

点击翻译按钮获取中文摘要

For ductile fracture of materials, the influence of damage due to voids on the mechanical property of materials is very important and it is necessary to clarify the relation between quantitative evaluation of damage and void growth. In this project, we propose a new method to evaluate the local damage state due to voids using the equivalent net stress. The equivalent net stress can be calculated from the applied stress and the damage tensor which is obtained form voronoi tessellation and the stereological method.Perforated sheets were set up as the plane models of damaged materials and were examined under the biaxial tensile condition in bulge testing machine, where the deformation of circular holes is measured. The deformation of circular holes becomes larger in severely damaged domain. The part where fracture of models starts is evaluated as severely damaged part. It is shown that the fracture of perforated sheets and local plastic deformation is well corresponding to the domain where the value of equivalent net stress is large. It is also shown that the deformation behavior depends highly on the distribution of holes and the arrangement of holes results in the anisotropy of yield stresses of perforated sheets, which is related to the stress concentration near the holes.As the three dimensional ideal model for real materials with damage, tensile specimens with the irregular distribution of holes are made by rapid prototyping method. Tensile test was carried out and the fracture state and the deformation of each hole are compared to the damage tensor distribution. It is found that the highly deformed region in the specimen corresponds to the part where the values of local damage tensor component are especially large.