Effects of sample geometry and loading rate on tensile ductility of TRIP800 steel

The effects of sample geometry and loading rate on the tensile ductility of a commercial grade Transformation Induced Plasticity (TRIP) steel are examined in this paper. Quasi-static tensile tests were performed for the 1.2 mm gauge TRIP800 steel sheets with two geometries: sub-sized ASTM E-8 and a custom designed miniature tensile sample. Sample geometry effects on post-uniform elongation are discussed together with other experimental data reported in the open literature. Further discussions on the effects of sample geometry are cast in the context of mesh-size dependent ductility in finite element-based engineering simulations. The quasi-static tensile curve for the miniature sample is then compared with the split Hopkinson bar results at the loading rates of 1700-s−1 and 2650-s−1 with the same sample design. In contrary to the typical strain rate sensitivity results for mild steel where the dynamic strength increase at high strain rate usually occurs at the price of ductility reduction, our results show that the TRIP800 under examination has positive strain rate sensitivity on both strength and ductility. Images of the deformation process captured by high speed camera together with scanning electron microscopy (SEM) near the fracture zone are also used to elucidate the different deformation modes at different loading rates.

► Miniature tensile sample has higher ultimate ductility than ASTM E-8 samples.
► TRIP800 has positive strain rate sensitivity on both strength and ductility.
► Ultimate ductility is not an intrinsic material property.