Free surface effect on the strain localization in metals

The effect of free surface on strain localization is presented on the examp le of a type 316 austenitic stainless steel deformed in two test environmen ts lair and vacuum). Specimens strained in vacuum exhibit systematically hi gher resistance to plastic deformation and lower strain rate sensitivity. S uch a behavior of the material is explained in terms of free-surface soften ing due to stress concetrations at oxide-substrate interface and oxidized g rain boundaries in the near-surface zone.