Analysis of corner filling behavior during tube hydro-forming of rectangular section based on Gurson-Tvergaard-Needleman ductile damage model

Friction plays an important role in the corner filling behavior during hydro-forming of rectangular section. In order to study the variation in corner filling behavior with internal pressure under the condition of different coefficients of friction, Gurson-Tvergaard-Needleman ductile damage model was used to describe material deformation involving damage evolution. First, an experimental-numerical hybrid method was applied to determine the parameters of critical porosity and failure porosity in Gurson-Tvergaard-Needleman ductile damage model. Second, a model describing the deformation behavior was established, in which the deformation zone was divided into three parts: sticking zone, sliding zone and corner zone. Third, the effect of coefficient of friction on the corner filling process was studied through simulation and experiments. The results show that as the internal pressure increases, the sticking zone starts at certain pressure and increases rapidly until taking over the whole contact length. Sticking friction will lead to greater thinning, and bursting occurs rapidly at the transition zone. Furthermore, the increase in the coefficient of friction will lead to greater variation in thinning and corner radius. For mu = 0.05 in experiments, corner filling is acceptable without bursting, correspondingly the final internal pressure is 67 MPa.