Examination of ductile spall failure through direct numerical simulation

The effects of stress release from peak loading pressure on spall failure are examined by direct numerical simulation of void growth and coalescence from a population of thousands of void nucleating particles. The analyses examine the importance of strain rate and ramp release on spall stress, the impact of square wave release compared to ramp release, and how these are manifest in the free surface velocity profile. Availability of the complete internal state prior to and after spall facilitates a greater understanding of the process and provides insights into potential microstructure mechanisms for assessing the ramp-release response. An unanticipated result is that the peak pre-spall tensile stress from the square shaped pulse is greater than for the ramped release, but this higher stress is quickly subsumed and is not evident at the free surface. Mechanisms contributing to the release rate effects are discussed.