On the validity of the traditional measurement of spall strength

Basing on Gathers's work, a set of general equations for traditional determination of spall strength is given under some assumptions for the planar spall experiment with a low-impedance buffer placed behind the target. In the case of no buffer, the equations become the traditional expression given by Novikov within the acoustic approach. It is revealed that the propagation of wave profile in the spall scab is affected seriously by the damage evolution on the spall plane. Therefore, the free surface velocity profile of target or the stress profile of interface between target and low-impedance buffer depends critically on the damage evolution on the spall plane. It is concluded that the traditional determination of spall strength without taking into account the stress relaxation due to the damage evolution on the spall plane could be valid only for the numerically simulated 'pullback' by the simple spall cutoff criterion but not valid for the experimental 'pullback' in general.