Fatigue life assessment of steel samples under various multiaxial loading spectra by means of Smith-Watson-Topper type damage descriptions

Fatigue damage and life of SS304, S45C, and SNCM630 steel samples tested at various irregular axial-torsional loading spectra were evaluated by means of 7 Smith-Watson-Topper (SWT) type damage descriptions. The overall damage was calculated over peak-valley events of counted cycles by means of the product of stress and strain corresponding to the areas within stress-strain hysteresis loops. Fatigue lives of 304 steel samples predicted by the SWT, Lorenzo-Laird, Szolwinski-Farris, and Chen-Xu-Huang models were found noticeably larger than those of experimentally obtained at various loading spectra. Predicted lives by these descriptions were found moderately in agreement with experimental data of S45C and SNCM630 steel samples. The predicted lives of steel samples by Socie, Lv et al, and the one presented in this study were closely agreed with experimental data due to their different descriptions. The modified SWT model further included the product of maximum shear stress and shear strain amplitude and related the overall damage to fatigue life through Coffin-Manson equation. The choice of model descriptions for damage assessment was discussed based on their terms, areas underneath of hysteresis loops, and material damage mechanism.