Ductility of 304 stainless steel under pulsed uniaxial loading

The enhanced ductility that 304 stainless steel is exhibiting under pulsed loading (Zhang and Yuan, 2009) is investigated here using a combination of experiments and analysis. The simplest loading case, i.e., uniaxial tension, was selected to avoid the complicating effects of multiaxial stress states and/or contact and friction with a rigid die. Three types of tensile tests were performed: monotonic, pulsed and hold. For a range of strain rates, the pulsed and the hold tests exhibited different elongation-to-fracture from the monotonic tests. Digital image correlation and infrared thermography were employed to further probe this behavior. It was discovered that since the pulsed tests lasted longer than the corresponding monotonic ones (i.e., those with the same loading speed) but the total plastic work expended was comparable, milder deformation-induced heating developed in the pulsed tests. Since the resulting temperature gradients act as imperfections that trigger the localization of deformation, the enhanced elongation-to-fracture in the pulsed tests was attributed to the milder gradients that developed. Subsequently, a special isothermal tension test was used to de-couple the mechanical from the thermal behavior of the material and was repeated at various strain rates and temperatures. The material properties determined from this test were used as input to coupled, thermomechanical finite element simulations of the experiments. Despite numerous simplifications, such as constant thermal properties with temperature, the simulations captured the essential physics of the problem and yielded very close predictions of the elongation-to-fracture observed in the experiments.