Some Quantitative Data Bearing on the Scabbing of Metals under Explosive Attack

Abstract

Fracturing, or scabbing, of a material near a free surface as the result of a transient compressional stress wave of high intensity impinging on that surface has been observed for many years; however, little quantitative data that relate the fracture to the nature of the stress wave and the physical properties of the material seem to exist. The phenomenon has been investigated for five metals, 1020 steel, 4130 steel, 24S‐T4 aluminum alloy, brass, and copper, by using an explosive charge to induce a high intensity stress wave in the metal. The distribution of pressure within the wave was determined by a modified Hopkinson‐bar type of experiment. Scabbing has been found to be governed principally by the spatial distribution of pressure within the wave and a critical normal fracture stress σ_c that is characteristic of the material and perhaps the state of stress. Numerical values of σ_c were obtained for each of the five metals.