Synergistic Effect of Energy Absorption and Adiabatic Temperature on the Microstructural Evolution and Mechanical Properties During High-Speed Impacts

High speed impact at strain rates > 10(3) s(-1) has generic characteristics in context of energy absorption and adiabatic temperature rise. An ultra-high strength low alloy steel (USLA, 3.8 mm thick) subjected to high-speed impact has been investigated by focusing on energy absorption driven by thermo-kinetics phenomenon in correlation with the target plate thickness. Result was bulge and reduction in thickness up to 2 mm at impact point. An analytical model has been proposed by establishing a relation between absorbed energy and plate thickness to explain deformation characteristics. EBSD analysis was carried out at three specified points, i.e., impact zone (IZ), impact affected zones (IAZ; through-thickness direction near backside) and (IAZ; radial/circumferential direction) with in 3 mm diameter. Impact analysis was carried out in Ls Dyna computer code. EBSD and FE (finite element) analysis revealed that the shear wave velocity under the influence of adiabatic temperature rise up to 520 K has generated adiabatic shear bands in IZ and IAZ (through-thickness direction), however in the IAZ (radial direction), the plate experienced no adiabatic temperature and increased stress due to compressive wave velocity resulted in greater proportion of recrystallized grain structure which is 25.79% as compared to 10.98% in IAZ(through-thickness direction) and 6.19% in IZ (impact zone). Micro hardness testing of these three distinct zones also revealed that IAZ (radial direction) has higher hardness (630HV) than IZ (600HV) and IAZ (through-thickness direction) (570HV) owing to increased and evenly distributed fine-grained microstructure in IAZ (radial direction), and relatively less deformation damage.

Automated summary

High-speed impact at strain rates >10(3) s(-1) has common characteristics in energy absorption and adiabatic temperature rise. An ultra-high strength low alloy steel subjected to high-speed impact was studied, with a focus on energy absorption driven by thermo-kinetics phenomenon and its correlation with target plate thickness. Deformation characteristics were explained using an analytical model that relates absorbed energy and plate thickness. EBSD and FE analysis revealed the formation of adiabatic shear bands due to adiabatic temperature rise in specific zones, while the radial direction experienced increased stress resulting in a higher proportion of recrystallized grain structure. Micro hardness testing confirmed the differences in hardness between the distinct zones.