Residual stresses relaxation in surface-hardened half-space under creep conditions

We developed the method for solving the problem of residual stresses relaxation in surface-hardened layer of half-space under creep conditions. At the first stage we made the reconstruction of stress-strain state in half-space after plastic surface hardening procedure based on partial information about distribution for one residual stress tensor component experimentally detected. At the second stage using a numerical method we solve the problem of relaxation of self-balanced residual stresses under creep conditions. To solve this problem we introduce the following Cartesian system: $x0y$ plane is aligned with hardened surface of half-space and $0z$ axis is directed to the depth of hardened layer. We also introduce the hypotheses of plane sections parallel to $x0z$ and $y0z$ planes. Detailed analysis of the problem has been done. Comparison of the calculated data with the corresponding test data was made for plane specimens (rectangular parallelepipeds) made of EP742 alloy during $T=650^\circ$ C after the ultrasonic hardening with four hardening modes. We use half-space to model these specimens because penetration's depth of residual stresses is less than specimen general size in two digit exponent. There is enough correspondence of experimental and calculated data. It is shown that there is a decay (in modulus) of pressing residual stresses under creep in 1.4–1.6 times.