PSI - Issue 19

Yuya Tanaka et al. / Procedia Structural Integrity 19 (2019) 320–327 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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This difference may be related to the heat production during sliding. In the case of high sliding speed condition ( f = 1 and 10Hz), the melting of wear particles could be promoted so that the sliding surfaces can stick easily to each other. The asperities shown in Figure 7 (a)-(d) indicate the severe adhesive wear and the material transfer. On the other hand, under low sliding velocity ( f = 0.1Hz), friction heat might not enough to fuse debris. Therefore, it is supposed that abrasion powder, which piled up on the worn surface due to the difficulty of wear particle ejection, plays a role as a lubricant, decreasing μ k down to about 0.6 with increasing N as shown in Figure 6. In order to verify the effect of sliding velocity on the value of μ k , an additional experiment was carried out. The mean sliding speed can be calculated approximately by following equation: V s = 4 S a ∙ f (5) With this equation, V s = 40 μm /s was obtained under the conditions of p = 10 MPa, f = 0.1Hz and S a ≈ 100 μm. Additional test was conducted under the conditions of p = 10 MPa, f = 1Hz and S a ≈ 10 μm in order to accommodate the sliding speed to 40 μm/s, at which the lowest kinetic friction coefficient was observed. Figure 8 shows the result. The result of additional test was in good agreement with the target experiment. Thereafter, it is concluded that the coefficient of kinetic friction under cyclic reciprocating contact has a dependence on sliding speed and the threshold value is between 40-400 μm/s. 3.4. Dependence of sliding speed on kinetic friction coefficient

Fig. 8. Variations of μ k as a function of N . ( V s = 40 μm/s)

4. Conclusions

In this study, the cyclic reciprocating sliding contact test for a JIS SUJ2 bearing steel was conducted with a newly developed ring-on-ring testing method. Especially, the effect of sliding speed on the test results was discussed in detail. The obtained results are summarized as follows: 1. The relationship between tangential force, F , and relative displacement, S , exhibits squared-shaped hysteresis loop. 2. Nominal contact pressure, p , and arithmetic mean roughness, R a , have no influence on the coefficient of kinetic friction, μ k .