The effect of superimposed hydrostatic pressure on shear decohesion in round bar tensile specimens

The modified Gurson–Tvergaard–Needleman model, that considers shear decohesion as an increment in the total void volume fraction, is used to investigate the effect of superimposed hydrostatic pressure on the ductility of a round bar specimen. Experiments indicate that the fracture mode is not uniform across the cross section of a round bar specimen–no shear damage exists at the center while it is pronounced at the edge. The damage mechanisms of shear decohesion and void growth are delayed by applying superimposed hydrostatic pressure, which leads to an increase in the fracture strain and ductility. However, the effect of pressure on ductility depends on the location within the cross section. Void growth at both the center and the edge becomes increasingly delayed with increasing pressure, but this effect is more significant at the edge because of the existence of shear stress. Shear decohesion at the edge becomes the dominant damage mechanism, rather than void growth, when pressure is increased. The numerical results presented herein are used to explain and discuss this phenomenon in depth.