Ductile fracture of materials with high void volume fraction

In the present paper, axisymmetric cell models containing one or two voids and a three-dimensional cell model containing two voids have been used to investigate void size and spacing effect on the ductile fracture in materials with high initial void volume fraction. They are performed for round smooth and round notched specimens under uniaxial tension. The example material used for comparison is a nodular cast iron material GGG-40 with initial void volume fraction of 7.7%. The parameters considered in this paper are void size and shape for axisymmetric cell models containing a single void, and void distribution pattern for axisymmetric and 3D cell models containing two voids of different sizes. The results obtained from these cell models by using FEM calculations are compared with the Gurson model, the Gurson-Tvergaard-Needleman model, the Rice-Tracey model and the modified Rice-Tracey model. It can be stated that the influence of void size and void spacing on the growth in volume of voids is very large, and it is dependent on the distribution of voids. Using non-uniform void distribution, the results of axisymmetric cell models can explain how a void can grow in an unstable state under very low stress triaxiality at very small strain as observed in experiments. Calculations using cell models containing two voids give very different results about the stable and unstable growth of voids which are strongly dependent on the configuration of cell model. (C) 1999 Elsevier Science Ltd. All rights reserved.