Fouvry wrote an interesting article on the effect of plasticity on fretting wear in 2001. This investigation combined analytical and experimental work. The experimental part of the test was a fretting wear study performed in the gross slip regime; the analytical part was based on plasticity theories and equations.
Two different wear rates were observed at the different normal loads tested. It is a little difficult to tell for sure about the lower normal force because it is so small on the figures. With the test at a higher normal force the early part of the test had a higher wear rate than the later part of the test.
Fouvry connected this reduction in wear rate to the mean pressure of the contact dropping below 150 MPa. The tests were carried out with a Hertzian line contact, so the maximum and mean pressure drop throughout the test as the contact becomes wider. Once the mean contact pressure dropped below 225 MPa, the wear rate began to get smaller and it reached a fairly consistent low value by 150 MPa.
The cut off level for the wear rate was related to the plastic deformation of the surface. It was hypothesized that the transition pressure between high and low wear rates is related to the shakedown pressure. However, the shakedown pressure did not correspond well to the measured transition pressure. When assuming a smooth surface, the transition pressure was too low. When considering asperities, the transition pressure was too high. Fouvry felt that more effects need to be included to come up with an explanation of the transition criterion. Possibly the missing variable is related to the third body.
Another scientists named Kapoor had done similar work before and demonstrated that under lubricated sliding conditions plastic deformation determined a transition in the wear rate. However, using a parallel analysis under fretting conditions did not prove fruitful because of the high coefficient of friction characteristic of fretting. In this study the coefficient of friction was between 1.0 and 0.6 for all tests which is typical of fretting.
- Fouvry, S., 2001, “Shakedown analysis and fretting wear response under gross slip conditions,” Wear, Vol. 251, pp. 1320-1331.
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