Issue 38

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

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.

2.0

Push-pull Rev.torsion Circle

Factor of 2

0.1 Equivalent strain range  eq , % 1.0 0.5 1

Method of universal slope curve

10 3

10 4

10 5

10 6

10 7

Number of cycles to failure N f

, cycles

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

   

f

1(

)

(2)

NP

NP

eq

292