Spall in Metals Induced by Explosive Shock Loadings and Protective Measures Using Momentum Traps.

Spall tests for three kinds of materials (A12024, SS41, Cu) are conducted using a newly developed testing device. This experimental assembly generates triangular stress waves with various gradients-in plate specimens (50×50×20mm) by direct explosive loadings. The relationship between measured spall layer thicknesses (5-15mm)and the explosive (PETN) thicknesses indicate that a time dependence exists in spall phenomena of the metals. A computer program with a cumulative damage model was constructed, which has reproduced the basic characteristics of the observed failure in the metals. It is known that the stress wave reflected at the free surface can be prevented from reaching the specimen plate by spallation of the momentum trap or spall plate, which is mounted in contact with the specimen. The following spall test results for A12024 have verified this effect and the numerical analysis also has simulated the phenomena successfully.