Molecular dynamics study on the shock induced spallation of polyethylene

Macroscopic experimental results of the plate impact tests of polymers are generally interpreted using the free surface approximation and the acoustic approximation. However, their validity over a range of shock pressures has not been thoroughly investigated yet. We conducted molecular dynamics simulations of plate impact tests of polyethylene to obtain molecular-level insights on those two common approximations associated with the interpretation of shock pressure and spall strength. Our results revealed that the free surface approximation could slightly underpredict the shock pressure in the polymer. The spall strength computed from the free surface velocity history can be significantly smaller than the actual tensile stress in the region of spallation.