Issue 38

T. Morishita et alii, Frattura ed Integrità Strutturale, 38 (2016) 289-295; DOI: 10.3221/IGF-ESIS.38.39

Δε p eq  N f ; the thin line shows the relationship of Δε p eq  N f

to be BN f 0.6 /(1+α f NP

assuming Δε p eq

). 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



.

BN

f



12.0

AN  



(5)

eq

f

+ 1 f 

NP

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.

2

0.5 1

p eq

6.0

   BN

f

0.01 Strain range  e eq ,  p eq , % 0.05 0.1

e eq

12.0

   AN

f

Push-pull (Elastic strain) Push-pull (Plastic strain) Rev. torsion (Elastic strain) Rev. torsion (Plastic strain) Circle (Elastic strain) Circle (Plastic strain)

6.0



BN  

p eq

f

1

f 

NP

10 2

10 3

10 4

10 5

10 6

10 7

Number of cycles to failure N f

, cycles

Figure 6: Correlations of N f

by Δε e eq

and Δε p eq .

10 7

Push-pull Rev.torsion Circle

10 3 Failure life in evaluation N f eva* , cycles Factor of 2 10 4 10 5 10 6

* eva

exp f N N 

f

10 2 10 3 10 4 10 5 10 6 10 7 10 2

exp , cycles

Failure life in experiment N f

Figure 7: Comparison of N f eva * and N f exp .

294