Mechanical Characterization of 304L-VAR Stainless Steel in Tension with a Full Coverage from Low, Intermediate, to High Strain Rates

A 304L-VAR stainless steel was mechanically characterized in tension over a full range of strain rates from low, intermediate, to high using a variety of apparatus. While low- and high-strain-rate tests were conducted with a conventional Instron and a Kolsky tension bar, the tensile tests at intermediate strain rates were conducted with a fast MTS and a Drop-Hopkinson bar. The fast MTS used in this study was able to obtain reliable tensile response at the strain rates up to 150 s−1, whereas the lower limit for the Drop-Hopkinson bar was determined to be 100 s−1. Combining the fast MTS and the Drop-Hopkinson bar fully closed the gap within the intermediate strain rate regime. Using these four apparatus, the tensile stress-strain curves of the 304L-VAR stainless steel were obtained at various strain rates on each order in magnitude ranging from 0.0001 to 2580 s−1. All tensile stress-strain curves exhibited linear elasticity followed by a significant work hardening prior to necking. After necking occurred, the specimen load decreased and the deformation became highly localized until fracture. The tensile stress-strain response the 304L-VAR stainless steel was also strain rate dependent. The flow stress increased with increasing strain rate. The strain-rate sensitivity was also observed to be strain-dependent, possibly due to thermosoftening caused by adiabatic heating at high strain rates. The 304L-VAR stainless steel also showed a significant ductility (or elongation to failure). The true failure strain was determined with the minimum diameter of the posttest specimen. The results showed that the true failure strains were approximately 210% at low strain rates, but were significantly lower (~110%) at high strain rates. The transition of true failure strain occurred within the intermediate strain rate range between 10−2 and 102 s−1.