Micro-spall damage and subsequent re-compaction of release melted lead under shock loading

Micro-spall is a large-area of liquid cavitation debris cloud formed near the free surface when metal melts during shocking or releasing process. We performed a molecular dynamics simulation to investigate the evolution of micro-spall and the related physical mechanism during the re-compaction process of a single crystal Pb by the second shock wave loading. The temperature and pressure obviously increase during re-compaction process. The ultra-high temperature-rise and local high pressure in the damage area is due to the collision between atoms and the collapse of voids. There is also one more pressure-rise and temperature-rise in the damage region, which is originated from the formation of high-speed internal micro jet and its striking on the back wall of large voids. Due to the uneven distribution of pressure and temperature after the 2nd shock wave passing through the micro spall damage region, the microstructures are also unevenly distributed. Besides, the damage region will swell due to the high temperature-rise during re-compaction process. Therefore, the micro-spall damaged region closed to the free surface is difficult to be compacted to dense state. Because that the voids in the damage region near the free surface are larger for the longer time interval, the temperature-rise originated from the collapse of voids is more severe. The wavefront plane is gradually broadened in the process of re-compaction.