Dynamic and fractal properties of SP-28 steel under high-speed loading conditions

Using an interferometric method to record the velocity of the free surface of a target subjected to two-dimensional shock loading, it is shown experim entally that the decrease in the compression pulse amplitude is due to the nonstationary nature of mesoscale processes - the amplitude decrease is pro gressively larger for higher rates of change of the variance of the mesopar ticle velocity. It is shown theoretically that the loading rate influences the spallation strength of a material in a planar collision only if the var iance of the particle velocity is nonzero. A fractal analysis of the spalla tion surfaces of steel samples is performed by quantitative fractography me thods. An expression relating the fractal dimension of the spallation fract ure surface and the variance of the mesoparticle velocity is derived. For t ypical values of the load pulse parameters for which back-side spallation o ccurs the fractal dimension agrees satisfactorily with the fractal dimensio ns for triadic Koch islands. (C) 1998 American Institute of Physics. [S1063 -7842(98)00710-7].