COMPARATIVE ANALYSIS 2: MULTISCALE MECHANISMS OF DEFORMATION AND FRACTURE UNDER HIGH-VELOCITY PENETRATION

Abstract

Two kinds of aluminum alloy, 1561 and 1565 alloys, were tested in parallel within impact velocity range of 250–750 m/s in two schemes of shock loading: (i) under uniaxial strain conditions and (ii) in high velocity penetration. Combination of load regimes allows a formation of multiscale structure to be retraced. In both schemes of dynamic loading, the transition into structure-unstable state and change of scale level of dynamic deformation was found to occur under identical impact velocities. Formation of mesoscale-1 (1–10 µm) for both alloys is found to be identical – the mesoscale-1 structures are nucleated due to particle velocity fluctuations resulting from interaction of shock front with the structural hetero-geneities. The intensity of the velocity fluctuations is registered in real time in tests under uniaxial strain condition by using the interferometric technique. For the mesoscale-2 (50–150 µm), the formation of dynamic structures is studied by using microstructural data of post-shocked specimens. In 1561 alloy, the structural elements in the form of cell-structures of 50–150 µm are the result of collectivization of mesoscale-1 structures whereas in 1565 alloy the mesoscale-2 structures are the periodical fault-cellson the boundary of penetration cavern. The strength behavior of both kinds of aluminum alloys in different schemes of loading turns out to be opposite – where the resistance to penetration increases, the spall strength decreases.