COMPARATIVE ANALYSIS 1: INCIPIENT STAGE OF DYNAMIC DEFORMATION AND FRACTURE IN 1561 AND 1565 ALUMINUM ALLOYS
Received by the Editor 2022/06/15 Transition of dynamically deformed solids into structure-unstable state is analyzed theoretically and experimentally from the physical kinetics approach. Propagation of shock wave in heterogeneous medium is considered to be in the form of superposition of two modes: (i) propagation of plane front with the mean velocity u(x,t) and (ii) random motions of local regions of medium because of chaotic stress fields. resulting from interaction of shock wave with the heterogeneous medium. This interaction results in particle velocity distribution, the quantitative characteristic of which is the particle velocity dispersion. Transition from one scale of dynamic deformation to another is found to be the so-called defect (decrease) of the particle velocity which characterizes the intensity of energy and momentum exchange between scale levels. Both characteristics are registered in real time in the process of shock-wave tests by using precise interferometric technique. Two materials, 1561 and 1565 aluminum alloys, were tested under uniaxial strain conditions within impact velocity range of 250-750 m/s. Owing to fine focusing of laser beam of interferometer up to 50-70 µm, the registered dynamic strength (spall strength) of material corresponds to single mesoscale structural element, which allows the incipient stage of dynamic fracture to be revealed in detail. The incipient strength is found to be maximum when velocity variation becomes equal to the velocity defect.