Void growth and coalescence during high velocity impact

Abstract

Abstract The extent of void growth and cracking due to ductile fracture occurring during symmetric Taylor cylinder impact tests on leaded brass has been determined experimentally. Void growth occurs within these predominantly 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 measured porosities have been compared to predictions using a constitutive model based on the Gurson (1975, Ph.D. Thesis, Brown University) yield function, implemented within the DYNA2D finite element code. The initiation of void coalescence and subsequent crack development was also predicted using the approach of Tvergaard and Needleman (1984, Acta Metall. 32, 157) based on a critical porosity criterion. The calculations were able to qualitatively predict the development of the porous zone and void coalescence within the impact specimens; however, the predicted void growth exceeded that observed experimentally and the predicted extent of void coalescence was too large. It is suggested that the primary source of error lies in excessively high predicted void growth rates using the Gurson yield function at high stress triaxiality levels.