Some aspects of fretting fatigue under cyclic normal loading

Abstract

Fretting fatigue has been studied mainly under constant normal loading, as it requires simple equipment which can be assembled on a universal fatigue testing machine. Recently, we [1] have introduced an innovative fretting fatigue apparatus in which the contact pressure can independently be varied during the test. In a recent publication [2] we have investigated the effect of normal load frequency on fretting fatigue life of Al7075-T6 under cyclic normal load condition. It was found that the low frequency of normal load has drastic effect on fretting fatigue life. The effect, however, gradually diminishes with the frequency increase and vanishes at the frequency of around 80Hz. In another publication [3] we have compared the results of constant normal loading with those of in phase, 90^° and 180^° degrees out-of-phase loadings. It was found that the constant normal loading has the least fretting damage, while the maximum fretting damage occurs by in-phase loading. The results also showed that the out-of-phase loading had improving effect on fretting fatigue life with respect to the in-phase condition. Recently, Ciaverella [4] has published a discussion on our publications [2, 3]. He believes that some of our experimental results needs further discussion. Therefore, the objective of this article is to answer three main points he has raised in his article [4]. We hope that this discussion could lead to some progress.