An analysis of the influence of overloads on the fatigue life of 45-steel within the range of low-cycle fatigue

The results of our investigations into the influence of overloads on a fatigue life and the course of some phenomena concomitant with a fatigue process within the range of low-cycle fatigue are presented in this paper. Overloads were realized as a block of cycles or single cycles with amplitudes significantly greater than the base strain amplitude. Investigations were performed for the base total strain epsilon_ac=0.008, whereas overloads were realized at levels: epsilon_ac_p=2.0epsilon_ac; 2.5epsilon_ac; 3.0epsilon_ac, respectively. An analysis of the test results showed that in all cases of overloads the fatigue lives of specimens were less than the one obtained under the base strain conditions. The value of fatigue life depended on the load program. In all cases general hardening followed, as a result of overload, while an analysis of stress courses against the total strain in phase with overload amplitude changes, showed the exi-stance of typical ranges of hardening, stabilization (relaxation, saturation) and softening. What can be treated as an evidence of a change in the fatigue properties of 45-steel as a consequence of overload.