Residual Grinding Stresses in Mild Steel

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Abstract
A method for determining residual surface stresses is presented. For their determination, it is necessary to remove small layers from the part which has been bent by the residual stresses in the unrestrained state and to measure the resulting change in deflection and thickness of metal removed. Etching with a weak nitric acid and water solution was found to be a satisfactory method for removing surface metal without introducing additional stresses. Mild-steel bars were ground with a medium-soft grinding wheel in a surface grinder. The depth of surface layer containing residual stresses extended to approximately 0.012 in. to 0.018 in. below the surface for grinding cuts ranging in depth from 0.0003 in. to 0.003 in. The thickness of the layer containing residual stresses increases with increasing depth of grind. The maximum residual stress occurs on the surface and, for all depths of grinds, was considerably above the yield point of the original material. The maximum surface stresses when grinding mild steel within the foregoing range of depth of cut decreases with increasing depth. It is believed that this phenomenon can be explained by the possible partial recrystallization of the surface grains because of the higher surface temperatures obtained with heavy cuts.

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