Investigation into structural and mechanical aspects of localization of plastic deformation and fracture under dynamic loading

Abstract

An experimental testing technique was developed to conduct experimental study of plastic strain localization in specimens made of AMg6, D16 and Steel 3 alloys subject to dynamic torsion tests in the split Hopkinson pressure bar device fitted with infrared camera. The temperature values determined in-situ during dynamic torsion tests of the specimens made from AMg6, D16, Steel 3 alloys do not exceed 50° C, which indicates that temperature softening contributes insignificantly to the process of plastic strain localization. A method was developed and applied for determining the strain fields in the zone of plastic shear localization in the specimens made of AMg6, D16, and Steel 3 alloys, which were specially designed to study plastic strain localization during static deformation and dynamic loading on the split Hopkinson pressure bar using for this purpose the StrainMaster system. A comparison of the experimentally obtained strain fields with the results of numerical simulation, which was made using the kinetic equations for the evolution of defects of the mesoscale, yields rather good agreement to within 20%. This study examined post-test specimens specially designed for studying plastic deformation localization. The application of an optical interferometer-profilometer New View - 5010 allowed structural analysis of these specimens, processing of 3D data on the deformation relief and subsequent computation of the scale invariant (Hurst index) and the spatial scale of the zone where the correlated behavior of microshears is observed. The comparison of the scale invariant characteristics of the D16 alloy specimens obtained during static deformation and dynamic loading revealed a significant increase in the Hurst exponent (H~0,74) over a wide range of spatial scales (0,6-110,8 μm ) compared to the undeformed specimens (H~0,42 in the range of spatial scales 1,9-29,2 μm ). More meaningful results can be associated with the changes in both lower and upper scales, which indicates pronounced features of the localization of deformation. The structure of specimens made of AMg6 alloy, specially designed for studying the plastic strain localization after dynamic tests in the split Hopkinson pressure bar, was examined using the scanning electron microscope. The obtained data testify to significant evolutionary processes occurring in the defective subsystems undergoing dynamic deformations.