PSI - Issue 7

Hisao Matsunaga et al. / Procedia Structural Integrity 7 (2017) 460–467 Hisao Matsunaga / Structural Integrity Procedia 00 (2017) 000–000

466

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range, well-known for Mode I fatigue cracks, also exists in Mode II fatigue cracks, as can emanate under rolling contact. In Fig. 7, the threshold SIF ranges obtained in torsional fatigue tests under static compression by Matsunaga et al. (2011) were also indicated by a solid line, in good agreement with the ∆ K IIth obtained by the RCF tests. In consideration of the crack-size dependency shown in Fig. 7, the fatigue life data were again plotted in Fig. 8 as a relationship between ∆ K II, drill / d 1/3 and N f , in which all the data were unified within a narrow band. It is expected that such a modified S - N curve could be a design curve for bearings, relevant to a wide range of defect sizes, although some points remain unclear regarding the application for the flaking which originated from non-metallic inclusions, the future goal of this research.

20

3

10

1

∆ K IIth [MPa ・ m 1/2 ]

○ Unbroken bearing

tested up to N = 1 × 10 8 cycles Solid line: Result of torsional fatigue tests under a static compression

obtained by Matsunaga et al. (2011)

1

0.2

0.01

0.1

Diameter of drilled hole, d [mm]

Fig. 7: Relationship between Mode II threshold stress intensity factor range, ∆ K IIth , and the diameter of the drilled hole, d .

3.0

* Depth of hole edge ranges from 0.05 mm to 0.175 mm.

2.5

2.0

∆ K II, drill / d 1/3

1.5

1.0

d [mm]

d

0.05 0.08 0.1

Komata et al. ○

● ◆

Depth

0.5

6206

◇

×

51305

＋ ▲

0.0

10 8

10 9

10 6

10 7

Number of cycles to failure, N f

Fig. 8: Relationship between ∆ K II, drill / d

1/3 and fatigue life N f .