Influence of overloading on fatigue durability and stability of residual stresses in shot peened normalized steel

The present investigation deals with the effect of overloads on the stress relaxation and fatigue life time of shot-peened near-pearlitic steels. Single cycles with a total strain amplitude of 0.6% with start in tension or compression were exerted either at the very beginning or after 1000 cycles and superimposed on the constant total strain amplitude test at 0.3%. The results were compared with the constant amplitude test data. It was shown that such overloading can reduce the fatigue life time by 25–60% of the life time obtained in constant amplitude tests. Maximum amount of reduction was obtained in overloading histories started with straining in tension. The stress amplitudes and corresponding mean stress development after overloading were also recorded and used to interpret the effects of overloads on the fatigue life times. In addition the residual stress relaxation throughout the whole lifetime was followed.