PSI - Issue 7

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

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Load movement direction

d : Diameter of hole

h ': Depth of edge

Drilled hole after testing

Drilled hole before testing

Fig. 2: Example of the observation of a cross-section after RCF test (Inner ring of JIS-6206, d = 0.1 mm, h' = 0.063 mm, q max = 3.0 GPa, N f = 2.8 × 10 7 ).

3. Results and Discussion 3.1. Fatigue test results

Figure 3 reveals the q max – N f data for the rolling bearings with drilled holes. The diameter, d, and depth, h, of the holes greatly affected the fatigue lives of the specimens. As a reference, fatigue test results for flat-plate specimens with small drilled holes, as obtained by Komata et al. (2012, 2013) are also plotted in Fig. 3. Komata et al . conducted RCF tests of JIS-SUJ2 plate specimens having small drilled holes with various depths and diameters in the middle of the raceway. The RCF strength of the rolling bearings was considerably lower than that of the flat plate specimens. As shown in Fig. 2, all the fatigue cracks initiated at the edge of the drilled holes, later propagating by shear-mode. 3.2. Effect of depth of fatigue origin on rolling contact fatigue strength Figure 4 showcases the relationship between the nominal shear stress amplitude at the hole-edge, τ a , and N f . In Fig. 3 ( q max v.s. N f ), the experimental data exhibited a large scatter, whereas in Fig. 4 ( τ a v.s. N f ), much less was displayed. In the figure, τ a – N f data for d = 0.1 mm were unified within a narrow band, regardless of the variation of hole depth. On the other hand, the τ a – N f data for d = 0.05 mm were higher than those for d = 0.1 mm. Such an effect of hole diameter will be discussed in the following section. 3.3. Effect of size of fatigue origin on rolling contact fatigue strength In Part 1 of this research, via FEM, the authors analyzed the Mode II SIF range of ring-shaped cracks which originated in the vicinity of the edges of drilled holes during the passage of the rolling element, ∆ K II, drill . Based on the result of analyses, it was revealed that ∆ K II, drill can approximately be correlated with the SIF for penny-shaped