Issue 37

K. Yanase et alii, Frattura ed Integrità Strutturale, 37 (2016) 101-107; DOI: 10.3221/IGF-ESIS.37.14

to that for tension-compression loading. Concerning the tension-compression loading, the area parameter model (cf. Eq. (3)) can be used for 17-4PH when  100μm area , which is much less than area < 1000 µm for the conventional carbon steels. Fig. 8 clearly shows that the aforementioned one-hole defect ( area = 70 µm) has negligible influence on fatigue limit under torsional loading. Finally, as some experimental data significantly deviate from the prediction line, a further study is necessary to elucidate the reasons behind these discrepancies.

600

 = 1.6HV



a

500

400

a  = 0.6  (1.6HV)



 area parameter model with k = 0               

300

Threshold for long crack

200

Failure Run‐out Prediction for fatigue limit Failure Run‐out Prediction for fatigue limit

Stress amplitude (MPa) Torsion

100

Tension‐Compression

0

10 1

10 2

10 3

 area (  m)

Figure 8: Relationship between stress amplitude and area .

C ONCLUSIONS

I

n this study, the torsional fatigue behavior of precipitation-hardened chromium-nickel-copper stainless steel 17-4PH was investigated in the presence of small defects. It was shown that the dimensions of defects can be evaluated by the square root of the projection area perpendicular to the major principal stress direction, area . The results pertaining to the fatigue crack growth behavior and fatigue limit demonstrate that the effect of biaxial stress on the surface of specimen is negligible and the major principal stress governs the fatigue behavior under torsional loading.

R EFERENCES

[1] Schönbauer, B.M., Yanase, K. and Endo, M., VHCF properties and fatigue limit prediction of precipitation hardened 17-4PH stainless steel, Int. J. Fatigue, 88 (2016) 205-216. DOI: 10.1016/j.ijfatigue.2016.03.034. [2] Schönbauer, B.M., Yanase, K. and Endo, M., to be submitted to Int. J. Fatigue. [3] Endo, M. and Ishimoto, I., The fatigue strength of steels containing small holes under out-of-phase combined loading, Int. J. Fatigue, 28 (2006) 592-597. DOI: 10.1016/j.ijfatigue.2005.05.013. [4] Endo, M. and Ishimoto, I., J. Solid Mech. Mater. Engng. (JSME), 1 (2007), 343-354, DOI: 10.1299/jmmp.1.343. [5] Yanase, K., A study on the multiaxial fatigue failure criterion with small defects, ASTM Mater. Perform. Charact., 2 (2013) 1-9. DOI: 10.1520/MPC20130013. [6] Yanase K., Endo M., Multiaxial high cycle fatigue threshold with small defects and cracks, Engng. Fract. Mech., 123 (2014) 182-196. DOI: 10.1016/j.engfracmech.2014.03.017.

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