Fig.4 Equivalent strain histograms for the 10th, 100th, 200th, and 300th cycles (a) SP;(b) DP
As shown in Fig. 4, the height difference between any two columns under the same contact stress displays the equivalent strain change value between the corresponding cycles. The change rate of equivalent strain is obtained from this height difference. Under SP and DP, the cyclic softening rate decreases with the increase of the cycle number, and the strain change rate increases as the contact stress increases. Combined Fig. 3 and Fig. 4, the SP has a larger amount of strain under the same conditions and its cyclic softening rate is also larger compared with DP.
Fig. 5 shows the response behavior of axial strain and shear strain of 35CrMoA steel under SP and DP at the equivalent stress of 400MPa. The axial strain and the shear strain are basically the same as the equivalent strain change trend. This change trend has been described in the analysis of equivalent strains. Corresponding to the equivalent strain, under the same conditions, the shear strain, axial strain and their change rates of SP are larger than DP. Compared with the shear strain, the axial strain dominates the total strain. During the cyclic softening process, the increase of the axial strain is much larger than the increase of the shear strain. Therefore, the damage form of 35CrMoA steel is mainly axial style.