Ductile fracture modeling based on a mesh objective element removal technology

Övrigt konferensbidrag, 2014

The phenomenological Johnson-Cook continuum and failure models constitute a simple ap- proach to the modelling of ductile fracture in metals. Even though the model is simple, it catches the material behavior at high speed/temperature with a relatively few material parameters. This is an obvious advantage, in addition to its widespread use in commercial softwares, which makes it so often used in many applications, and, in particular, machining simulations of metal cutting processes. Even though there are advantages with the model, a major drawback from our expe- rience1 is that the JC–material model exhibits a significant mesh size dependence in orthogonal machining simulations. In order to overcome this difficulty a mesh objective element removal technology is devised based on a smeared out type of dissipation concept to represent the fracture energy. The tech- nology is investigated for the ductile failure modeling of the pearlite phase in a cast iron mi- crostructure with the objective to obtain a mesh size independent computational tool. In order to obtain mesh objective element deletion, an element removal criterion is defined on the plastic strain energy prior to fracture state is considered as fracture energy. A fracture state is achieved in a gauss-point when the accumulated effective plastic strain equals the fracture strain, com- puted with the Johnson-Cook fracture model. Then a total scaled fracture dissipation energy is computed based on the current accumulated dissipation. The figures below show the model set up, a shear loaded plate, and the computed reaction force, where vertical displacements are pre- scribed, for different mesh sizes. Indeed, our experience is that the model exhibits a significant mesh size dependence without the proper scaling of the energy dissipation.