Effect of ductile fracture criteria on chevron crack formation and evolution in drawing

The purpose of this study is to clarify the mechanics of ductile fracture in bulk metal forming processes by finite-element analysis and experiments. The author has developed a computer program, based on a conventional computer program involving the finite-element method, by which the behavior of crack propagation after ductile fracture can be analyzed. The phenomenon in which a ‘chevron crack’ appears periodically in the axial direction during drawing has been simulated using the developed computer program. Special attention is focused on the effect of various kinds of ductile fracture criteria on chevron crack formation and evolution during drawing. Results obtained are summarized as follows. First, the analytical results obtained using Gursonʹs fracture criterion and using Oyaneʹs fracture criterion agree well with the experimental result. Second, the analytical results using Cockcroft and Lathamʹs fracture criterion and using Brozzo et al.ʹs fracture criterion agree somewhat with the experimental result. Finally, the analytical result obtained using Freudenthalʹs fracture criterion does not agree with the experimental result.