Issue 38

T. Morishita et alii, Frattura ed Integrità Strutturale, 38 (2016) 289-295; DOI: 10.3221/IGF-ESIS.38.39 292 Equivalent stress amplitude Δσ eq /2, MPa 200 175 150 Push-pull Circle 20 μm 20 μm 20 μm 20 μm 20 μm 20 μm Axial direction Figure 3: Observation of specimen surface after fatigue tests at Δσ eq /2=200MPa; 175MPa and 150MPa. Factor of 2 Method of universal slope curve 10 3 10 4 10 5 10 6 10 7 0.1 0.5 1 Number of cycles to failure N f , cycles Equivalent strain range  eq , % 2.0 1.0 Push-pull Rev.torsion Circle Figure 4: Correlation of N f with Δε eq . Applicability of Non-proportional Strain Range for Life Evaluation Itoh et al. have reported that the large reduction in failure life has a close relation with the strain path and the material [4;6;7;10;11] and they also proposed the non-proportional strain range Δε NP for life evaluation defined as eq NP ) 1(     f NP (2)