Study of influence of superimposed hydrostatic pressure on bendability of sheet metals

The effect of superimposed hydrostatic pressure on the bendability of sheet metal is investigated using the finite element method employing the Gurson-Tvergaard-Needleman (GTN) model. It is shown that bendability and fracture strain increase significantly by imposing hydrostatic pressure as it delays the growth and coalescence of microvoids but it has insignificant effect on void nucleation using the GTN model, which is strain controlled for void nucleating. Furthermore, the effect of superimposed hydrostatic pressure on tensile test simulation under plane strain state is investigated and the predicted fracture strains are compared with those corresponding to bending tests. It is demonstrated that ductility under various superimposed hydrostatic pressures for bending test are higher than those predicted in tensile tests. Lastly, the sensitivity of ductile fracture parameters in the GTN model on bendability is considered. Numerical results are found to be in good agreement with experimental observations.