Effect of sliding contact on fatigue properties of low alloy steel

Abstract

Stress distribution of brake disks during braking is complicated due to sliding contact and frictional heat. To investigate the effect of sliding contact on the fatigue properties of low alloy steel, a new fatigue test method that enables the application of cyclic loading with sliding contact has been developed. Two main results have been obtained by this method. Firstly, the specimens with sliding contact had longer life than those without sliding contact (normal test) under a finite life regime. Secondly, the fatigue limit with sliding contact was 26% lower than that without sliding contact. Moreover, the results of normal test result showed no fatigue failure at more than 106 cycles, whereas the tests with sliding contact had fatigue failure even over 106 cycles. To clarify the fatigue limit reduction caused by sliding contact, fatigue tests applying sliding contact prior to cyclic loading (pre-wear) has been conducted. The results of pre-wear showed no fatigue failure at more than 106 cycles, which is similar to the normal test, but the fatigue limit is lower compared to that in the normal test. The effect of sliding contact on the fatigue properties is discussed from point of wear and surface roughness. Thickness of the test specimens was reduced by wear with an increase of sliding contact duration. This suggests that the sliding contact was possibly contributed to have longer life in the fatigue tests than the normal tests because of elimination of fatigue damaged surface layers. Surface roughness also increased due to sliding contact. This leads decreasing of fatigue limits. √area parameter calculated from surface roughness was used to predict the fatigue limits with sliding contact. The predicted fatigue limits corresponded well to experiment fatigue limits if surface roughness was considered as a single notch. Therefore, it is concluded that surface roughness variation due to sliding contact affects the fatigue strength of the tested low alloy steel.

Keywords

• sliding contact
• fatigue test
• fatigue properties
• fatigue limit
• wear
• surface roughness
• √area parameter models