Critical Conditions for Failure in Materials Subjected to High Rates of Loading

摘要

Dynamic shear band formation in steels has been investigated in torsional Kolsky bar experiments. Temperature profiles have been measured. Stress-time curves have been related to analytical predictions of localization in simple shear. Good agreement between theory and experiment is obtained when the effects of strain hardening, thermal softening, strain rate sensitivity, and geometric imperfections are included in the theory. The analysis of shear strain localization has been extended to the case of plane strain compression. Heat conduction has been included in the analysis of quasi-static deformations. Critical conditions for dynamic and quasi-static fracture initiation of AISI 1020 steel have been determined for three microstructures over the temperature range -150C to +150C. Fracture models for both cleavage fracture and ductile rupture have been developed for interpreting the observed behavior over the full range of temperatures and loading rates. The effect of loading rate on the fracture toughness of 4340 VAR steel has been investigated through experiments involving explosive loading of notched tensile bars and through plate impact experiments on pre-cracked plates. Numerical methods have been developed for the interpretation of the plate impact experiments. Analytical methods have been developed for understanding the effects of strong strain-rate sensitivity on dynamic crack propagation.