Relaxation of residual stress in a surface-hardened prismatic sample in creep under biaxial loading

A mathematical model has been developed for calculating the relaxation of residual stresses in a surface-hardened prismatic sample in creep under biaxial loading. The calculation results were verified against experimental data for a surface-hardened sample of EP742 alloy after ultrasonic hardening under creep conditions at a temperature of 650$^\circ$C for 100 h. A detailed theoretical analysis of the influence of the type of stress state on the relaxation of residual stresses during thermal exposure (temperature exposure in the absence of mechanical stress) and under biaxial loading at a constant intensity of external stresses was performed. It is shown that under uniform tension in a plane stress state, the relaxation of residual stresses slows down, and under compression, the relaxation rate increases compared to the case of thermal exposure.