The Bauschinger Effect for Cold Finished Mild Steel after Friction Stir Processing

摘要

This paper considers the Bauschinger effect on workpieces subjected to friction stir processing. Cold finished, mild steel was selected as the base material for this study. Four-point bend tests were performed on material specimens in a forward direction to 2% of true strain, followed by reverse bending by 4% of true strain or until failure. Strain gauges were mounted to the specimens to measure strain while the vertically applied bending force was measured with a high precision load cell. Test results show that friction stir processing, despite having a highly refined microstructure, exhibits a Bauschinger effect response slightly higher than that of unaltered base material. It is suggested that the increased response is due to a residual dislocation density induced by friction stir processing and a strong fiber orientation transverse to the direction of processing, which coincides with the major strain axis in bending. It is also concluded that the Bauschinger effect response of friction stir processed material is independent of orientation relative to the rolling direction of the plate, despite anisotropic effects present in strength.