Issue 38

T. Morishita et alii, Frattura ed Integrità Strutturale, 38 (2016) 289-295; DOI: 10.3221/IGF-ESIS.38.39 294 Δε p eq  N f ; the thin line shows the relationship of Δε p eq  N f assuming Δε p eq to be BN f 0.6 /(1+α f NP ). The relationships of Δε p eq  N f are drawn by separate lines in the proportional loading and the non-proportional loading. This results show that the elastic deformation behaviour may be independent on the non-proportional loading becomes of the smaller chance of interaction of slip systems due to non-proportional loading [2;3;6;12]. In order to estimate the effect of non-proportional loading in the lower stress/strain level; the modified equation is presented as NP . 12.0 + 1 f BN AN       f f eq (5) Fig. 7 shows comparison between N f eva * and N f exp . N f eva * is evaluated by the modified non-proportional strain range defined in Eq. (5). In Fig. 7; almost of the data are replotted within the factor of 2 band and the correlation becomes better in comparison with that in Fig. 5 (b). Therefore the modified non-proportional strain range becomes a suitable parameter for life evaluation in the high and the low strain levels under non-proportional loading. However; the definition of α still needs more discussion with additional experimental results in future studies. 10 2 10 3 10 4 10 5 10 6 10 7 0.01 0.05 0.1 0.5 1 Number of cycles to failure N f , cycles Strain range  e eq ,  p eq , % Push-pull (Elastic strain) Push-pull (Plastic strain) Rev. torsion (Elastic strain) Rev. torsion (Plastic strain) Circle (Elastic strain) Circle (Plastic strain) 12.0 f e eq    AN 6.0 f p eq    BN NP 6.0 f p eq 1 f BN     2 Figure 6: Correlations of N f by Δε e eq and Δε p eq . 10 2 10 3 10 4 10 5 10 6 10 7 10 2 10 3 10 4 10 5 10 6 10 7 Failure life in experiment N f exp , cycles Failure life in evaluation N f eva* , cycles exp f * eva f N N  Factor of 2 Push-pull Rev.torsion Circle Figure 7: Comparison of N f eva * and N f exp .