Full-range strain-dependent dynamic increase factor (DIF) model for Q355 steel

Structural materials experience high strain rates when subjected to high-speed impact and explosion, and their constitutive behaviour changes significantly due to strain rate effect. This effect has already been found to be dependent on strain, e.g., the dynamic increase factor (DIF) on yield stress is typically higher than that on tensile strength. However, systematic investigations on the dependence of strain rate effect on strain are inadequate, and the underlying microscopic mechanisms are still unclear. In this study, a series of Q355 tensile coupons was designed and tested, with the coupon dimensions and loading schemes specifically designed to achieve five near-constant true strain rates (ranging 0.001 s^‐1– 4460 s^‐1). True stress-strain relationships corresponding to all strain rates were determined and full-range DIF curves were then obtained. Significant strain rate-induced strengthening effect was observed, and the effect became less prominent with the increase in strain. Based on the experimental findings, a new full-range strain-dependent DIF model was accordingly proposed. The proposed model exhibits consistently high performance in predicting the full-range dynamic response of various structural metals under different strain rates, achieving a 24 % ∼ 62 % increase in predictive accuracy compared to traditional models (e.g. the C-S and J-C models). Microstructural characterizations were conducted on three post-test coupons subjected to different strain rates, and on each coupon, four locations corresponding to distinct strains were examined. Combinative influences of dislocation multiplication, grain refinement and crystal orientation evolution well elaborate the macroscopic dependence of strain rate effect on strain.