THE EFFECT OF RESIDUAL-STRESSES ON HARDNESS MEASUREMENTS

The Rockwell C hardness, R(C), was measured as a function of position on steel rings with different residual-stress profiles through the thickness. An experimental correlation between residual stress and R(C) was obtained. A relationship between the average pressure p of a spherical indenter, the yield strength S(y) and the residual stress of the material was conceived and used in fitting the experimental data. In order to model the effects of residual stresses on the measured hardness, the von Mises-Hencky (power) yield criterion was utilized, together with an adaptation for residual stresses of the expression for the stress state under a spherical indenter, given in Shaw, Hoshi and Henry.1 A parameter a was introduced in our calculations to account for the effect of the nonperpendicularity of the residual stresses to the pressure p of the spherical indenter. The proposed model in large measure fits experimental hardness versus residual stress data, and results are consistent with different samples. This model can be used as a basis for the measurement of residual stresses in steel or other materials.