Studying the Localized Shear Fracture Mechanism in Alloys under Dynamic Loading

Abstract

Experiments on the dynamic loading of specimens from AMg6 alloy were conducted on a split Hopkinson–Kolsky bar and with target perforation. The thermodynamics of the deformation process was studied in situ by recording temperature fields using a CEDIP Silver 450M high-speed infrared camera in order to reveal the characteristic stages of strain localization. The temperature measurements in the localization zones do not confirm the traditional concept of the strain localization mechanism caused by thermoplastic instability. Dynamic tests of specimens made of Steel 3, AMg6, and D16 alloys of a special shape designed to study the localization of plastic deformation on a split Hopkinson–Kolsky bar were conducted using the StrainMaster noninvasive strain measurement system. The displacements and strain fields in these specimens are constructed. A comparison of the experimentally measured temperature and strain fields with the results of numerical simulation with allowance for the mesodefect accumulation kinetics in the material gives a satisfactory agreement within ~20%. In the specimens after the experiments, the surface relief was analyzed using a NewView-5010 optical surface profiler with subsequent processing of the 3D strain relief data and calculation of the scale invariant (Hurst index) and the spatial scale of the region on which the correlated behavior of mesodefects is observed. The data of the experiments and analysis of the surface relief of deformed specimens, as well as the data of numerical simulation taking the mesodefects accumulation kinetics in the material into account, suggest that one of the plastic strain localization mechanisms under high-speed loading is caused by jump-wise processes in the defect structure of materials.