Baseline fatigue data are presented through a series of strain-controlled tension-compression-type fatigue tests on smooth specimens of a Type S1214 mild steel under various combinations of strain amplitudes and nonzero mean strains. The strainmagnitudes were chosen in the upper limit of the elastic range, in the plastic range, or in the transition area between the elastic and the plastic range. Experimental results show that for strain amplitudes in the upper limit of the elastic range,positive mean strains prolong fatigue life and negative mean strains shorten fatigue life. The observations are explained by the analysis of the basic material properties associated with the material concerned. The cyclic response behavior of thematerials, namely the Bauschinger effect, the cyclic softening, and the mean stress relaxation processes have been studied also to reveal the underlying fatigue mechanism. Several modified models have been proposed for life prediction under nonzero meanstrain and/or mean stress based on experimental observations. The comparison of the experimental results with the predictions made from the proposed models and from an existing model are also presented.
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