Co
mpressive residual stresses are often induced by
mechanical surface treat
ment such as shot peening for the purpose of i
mproving fatigue life of co
mponents. Cyclic relaxation of the induced co
mpressive residual stress, however, reduces the benefit. For co
mponent design and life
manage
ment purposes it is i
mportant to be able to assess the effect of residual stresses and their relaxation on fatigue life. The proble
m, however, is that the pheno
menon of residual stress relaxation under cyclic
mechanical loads is not well understood. Further
more, there is the technical challenge of accurately quantifying residual stress relaxation during co
mponent operation. The difficulties in
measuring residual stress relaxation in real-ti
me i
mpede the consideration of tracking and assessing its effect on re
maining fatigue life.
In this paper a previously proposed cyclic hardening/softening model is adapted and modified to account for residual stress relaxation. Considering residual stress as virtual mean stress the cyclic stress-strain response during residual stress relaxation is described and simulated using the Matlab/Simulink Program. The virtual mean stress has a corresponding mean strain which conditions result in biased stress/strain limits under cyclic load. It is shown that residual stress relaxation is associated with mean stress shift in stress-axis direction and mean strain shift in the strain axis direction. The significance of this mean strain shift is briefly discussed in terms of tracking and quantitatively determining residual stress relaxation in real-time.