Fatigue failure, ratcheting behaviour and influence of pre-fatigue on fatigue behaviour were investigated under uniaxial cyclic loading for CK45 steel at room temperature. The fatigue life was recorded for various stress ratios, and then, three mean stress models were considered. The Walker model showed an acceptable accuracy in comparison with Smith–Watson–Topper and Park et al. models. The ratcheting strains were measured for various loading conditions in order to evaluate the impact of mean stress, stress amplitude and stress ratio on ratcheting behaviour. The experimental results showed that the ratcheting strain increased with increasing mean stress, stress amplitude and stress ratio. In addition, the results of the post-ratcheting-fatigue tests showed that although the fatigue life decreased with increasing pre-ratcheting strain (the ratcheting strain that is accumulated in pre-fatigue), the loading condition that pre-fatigue experiments were conducted has a significant effect on subsequent fatigue behaviour.

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