Numerical simulation of incremental sheet forming based on GTN damage model

An attempt was made to analyze the damage evolution and ductile fracture of incremental forming at the microscopic level. Firstly, an extended Gurson-Tvergaard-Needleman (GTN) model integrating with Hill'48 anisotropic yield criterion was established and numerically implemented by User-defined Material Subroutine (VUMAT) in the commercial finite element software ABAQUS. Then, the VUMAT program was verified via a single element test, and its damage parameters were determined through the combination of the simulation and the experiment of a tensile test. Afterwards, based on the extended GTN model, a finite element model of incremental forming was established and experimentally verified. And the influence of different values of two damage parameters, the volume fraction of void nucleating particles f (N) and the mean plastic strain value when voids nucleate epsilon (N), on the damage evolution of incremental forming was explored. It shows that there is almost no connection between the microscopic equivalent strain and the values of f (N) and epsilon (N). However, the maximum value of void volume fraction will increase significantly with the increase of f (N) or with the decrease of epsilon (N). Finally, void volume fraction was proved to be an effective index to predict crack occurrence of incremental forming.