Thermo-viscoplastic behavior and constitutive relations for 304 austenitic stainless steel over a wide range of strain rates covering quasi-static, medium, high and very high regimes

Using the recently developed single shear specimen, deformation behavior of 304 austenitic stainless steel is studied systematically over a wide range of strain rates, covering quasi-static (0.001-0.1 s⁻¹), medium (1-10 s⁻¹), high (3000-6000 s⁻¹) and very high (13000-39000 s⁻¹) regimes, and temperatures between 77 and 1073 K were considered. The experimental flow stress curves show that: (1) the flow stress increases slightly at strain rates below 6000 s⁻¹; concerning strain rates above 13000 s⁻¹, however, an obvious flow stress upturn exists; (2) dynamic strain aging (DSA) occurs within the temperature range of 673 to 873 K and strain rates lower than 10 s⁻¹; (3) both temperature sensitivity and strain rate sensitivity of the material are affected by DSA, and bell-shaped sensitivity curves form; (4) with increasing strain rates, peaks of the bell-shaped temperature sensitivity curves move to higher temperature regimes, and the evolution law is equally valid for the influence of temperature on the strain rate sensitivity curves. According to experiments, eight constitutive relations, including three phenomenological, four physical-based, and an artificial neural network, are established, including viscous drag effect at very high strain rates but excluding DSA phenomenon. Prediction capacities of the established constitutive models are checked by testing condition jump tests at randomly chosen strain rates and temperatures. Description capacities of the constitutive models in terms of strain hardening rate, temperature sensitivity and strain rate sensitivity are also analyzed.