Effect of out-of-phase loading on fretting fatigue response of Al7075-T6 under cyclic normal loading using a new testing apparatus

In the present study, the effect of phase difference between axial and normal contact loads on fretting behavior of Aluminum alloy 7075-T6 is investigated using a new testing and numerical simulation using finite element method. The results showed that the phase differences ϕ = 90° and ϕ = 180° improved fretting fatigue life about 8-30% and 12-56%, respectively. The reduction in crack propagation lifetime was about 12-16% and 26-39%, for phase differences of ϕ = 90° and ϕ = 180°, respectively. The reason for improvement of fretting fatigue life can be attributed to the increase in crack initiation lifetime that happens due to (i) domination of gross slip regime that occurs for both of phase differences ϕ = 90° and ϕ = 180° compared to partial slip regime that occurs for in-phase condition and (ii) lower contact stresses that occur under out-of-phase loading noting that the fraction of total lifetime spent in crack initiation phase is mainly influenced by the contact stresses.