Application of Complete Gurson Model for prediction of ductile fracture in welded steel joints

摘要

Ductile fracture process includes three stages: void nucleation, their growth and coalescence. The voids nucleate due to the fracture or separation of non-metallic inclusions and secondary-phase particles from the material matrix. Micromechanical models based on the Gurson plastic flow criterion are often used for analysis of ductile fracture. They consider the material as a porous medium in which the effect of voids on the stress-strain state and plastic flow cannot be neglected. Another important property of the Gurson criterion is that the hydrostatic stress component influences the plastic flow of the material. Two models that include the Gurson plastic flow criterion are frequently used: GTN (Gurson-Tveergard-Needleman) and recently CGM (Complete Gurson Model). Their application includes a combination of experimental and numerical procedure. The problem with the GTN model is determining the critical void volume fraction at the beginning of void coalescence, because this parameter depends on geometry and the initial state of the material. The CGM eliminates the critical void volume fraction as a failure criterion, which is an important advantage of this model. In this paper, a detail insight into the GTN and the CGM is given, including the application of the CGM in numerical simulation of ductile fracture of a pre-cracked specimen. Inhomogeneous materials (welded joints) are analysed, considering the influence of initial parameters and the size of the finite elements near the crack tip.