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 thi ckness. An experimental correlation between residual stress and R(C) w as obtained. A relationship between the average pressure p of a spheri cal indenter, the yield strength S(y) and the residual stress of the m aterial was conceived and used in fitting the experimental data. In or der 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 str ess state under a spherical indenter, given in Shaw, Hoshi and Henry.1 A parameter a was introduced in our calculations to account for the e ffect of the nonperpendicularity of the residual stresses to the press ure p of the spherical indenter. The proposed model in large measure f its 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.