Strain rate-dependent constitutive modelling of stainless steels

A strain rate-dependent constitutive model for stainless steels, calibrated against 184 coupon test results assembled from the literature on austenitic, ferritic, duplex and martensitic alloys, is presented. The rate-dependent material behaviour of two austenitic stainless steels, EN 1.4307 and EN 1.4678, was first examined experimentally. A total of 46 coupon tests were conducted, at different strain rates ranging from 0.00018 s –1 to 2000 s –1 . The effect of strain rate on the strength and ductility of the tested stainless steels was analysed. The test results indicated that both the yield strength and ultimate strength of the two stainless steels are strain rate-dependent, though each exhibited distinct trends. As the strain rate increased, the yield strength exhibited an increasing trend, whereas the ultimate strength initially decreased at strain rates below 0.1 s –1 and then increased at higher strain rates. Compared to the normal-strength EN 1.4307 stainless steel, the high-strength EN 1.4678 stainless steel exhibited lower sensitivity to strain rates, as reflected by lower dynamic increase factors. The Johnson–Cook model was calibrated to match the observed response of the studied grades. Based on both the newly obtained test results, as well as additional experimental data collected from previous studies, a continuous dynamic constitutive model applicable to all stainless steels — expressed as a function of strain rate and yield strength — was developed by combining a modified Cowper–Symonds formulation for the strain rate effect with the two‑stage Ramberg–Osgood model for describing the stress-strain curve. The developed formulations are suitable for inclusion in advanced analytical models and numerical simulations of stainless steel elements under high strain rate loading scenarios. • Ultimate strength showed less strain-rate sensitivity than yield strength. • Johnson-Cook model was modified for EN 1.4307 and EN 1.4678 stainless steels. • Generalised rate-dependent constitutive model proposed for stainless steels. • Model accuracy validated against extensive experimental stress-strain data.