Fretting fatigue crack initiation: An experimental and theoretical study

Fretting fatigue tests have been carried out on 7075-T6 aluminium alloy and En24 steel as a pad material to study the crack initiation behaviour. An asymptotic analysis is carried out to study the equivalence of stress state at the edge of a rectangular pad for complete contact for the Dundur's parameters, α, β and at notch root of an associated internal angle, 2γ and subsequently a model is developed giving the stress singularity, λ − 1 for the complete contact for dissimilar materials with friction. Further, a theoretical formulation is developed to predict the crack initiation angle using the stress singularity, λ − 1 and the strain energy density failure criteria. The crack initiation angle experimentally obtained through the scanning electron micrographs of the failed fretting fatigue specimens are compared with the predicted crack initiation angle using the strain energy density failure criteria. The experimental observations and the theoretical results suggest that the strain energy density failure criteria can be successfully used to predict the crack initiation angle under fretting fatigue loading conditions for the complete contact case with friction. Also it is observed that the crack initiation angle in general decreases with increase in coefficient of friction at the interface.