VOID GROWTH AND COALESCENCE DURING HIGH-VELOCITY IMPACT

The extent of void growth and cracking due to ductile fracture occurri ng during symmetric Taylor cylinder impact tests on leaded brass has b een determined experimentally. Void growth occurs within these predomi nantly compressively-loaded specimens through the development of large tensile hydrostatic stresses along the specimen axis near the impact face during expansion of the cylinder, termed ''mushrooming''. The mea sured porosities have been compared to predictions using a constitutiv e model based on the Gurson (1975, Ph.D. Thesis, Brown University) yie ld function, implemented within the DYNA2D finite element code. The in itiation of void coalescence and subsequent crack development was also predicted using the approach of Tvergaard and Needleman (1984, Acta M etall. 32, 157) based on a critical porosity criterion. The calculatio ns were able to qualitatively predict the development of the porous zo ne and void coalescence within the impact specimens; however, the pred icted void growth exceeded that observed experimentally and the predic ted extent of void coalescence was too large. It is suggested that the primary source of error lies in excessively high predicted void growt h rates using the Gurson yield function at high stress triaxiality lev els.