An Investigation into the Effect of Normal Load Frequency on Fretting Fatigue Behavior of Al7075-T6

Abstract

ABSTRACTMost previous studies on fretting fatigue have been accomplished under constant normal loading and less attention has been paid to cyclic normal loading. An innovative test apparatus was specially designed and manufactured for fretting fatigue tests under cyclic loading in this work and the fretting fatigue behavior of Al7075-T6 was investigated at different normal load frequencies. A finite element model was developed to study the effect of normal load frequency on the contact stress distribution. It was found that the cyclic normal load has a more damaging effect on fretting fatigue life compared to constant normal load, particularly at lower frequencies. The results showed that at the normal load frequency of f = 1 Hz, fatigue life decreased by 52% in the high cycle fatigue regime and 28% in the low cycle fatigue regime. The experimental results also indicated that at the normal load frequency of 80 Hz, the fretting fatigue life converged to its corresponding life under constant normal load condition. The fracture surface and the fretting area of the specimens were examined using both optical and scanning electron microscopy (SEM). The experimental observations showed that the dominant partial slip condition with a wider slip region compared to constant normal loading, severe delamination, and higher oxidation rate due to the normal load release at each cycle, are the most important reasons for significant reductions in fretting fatigue life, under cyclic normal loading, especially for low normal load frequencies.