Issue 41

A. S. Cruces et alii, Frattura ed Integrità Strutturale, 41 (2017) 54-61; DOI: 10.3221/IGF-ESIS.41.08 59 Figure 4 : IP 1 – σ, τ and SKDP at max peak cycle (A) and min peak cycle (B) SKDP was computed for the test data shown in Tab. 4, and the material dependent parameters were optimized with a dual power law fit line. After several iterations of computations to optimize these damage parameter, it was observed that fit was good for larger w & k values for this data set. The direction of shear stress in this parameter is not taken into the account because both positive and negative shear stress create same crack initiation phenomenon. The damage parameter vs cycles to failure for the Suman-Kallmeyer damage parameter is shown in fig 5, and it can be observed from the curve that both LCF and HCF data have collapsed very well along the fitting line. Comparison of fig 3 and fig 5 appears to indicate that the Suman-Kallmeyer damage parameter provided better correlation for the test data. Figure 5 : Fatigue life correlation for St52-3N steel based on Sandip model (k=2.1, w=1.1). Life-Life plots were also created for the test data by using both Fatemi-Socie II [18] damage parameter and the damage parameter proposed by Suman-Kallmeyer [19]. Red square in fig 6 represent the life predicted by FSDP II, and green triangles represent the life predicted by SKDM model. By observing this plot (fig 6) and the data, the FSDP II tends to overestimate the fatigue life and the SKDP tends to underestimate the fatigue life. Similar level of correlation is observed on both damage parameters. The two new theories give overall good predictions for the test data under study.