In situ analysis and modeling of crack initiation and propagation within model fretting contacts using polymer materials

Crack initiation and growth under fretting-fatigue and fretting-wear contact conditions have been investigated using model epoxy materials which allowed an in situ visualization of damage processes within the contact zone. A fretting-fatigue predictive model has been used to analyze these experiments on the basis of an accurate determination of the contact conditions and knowledge of the bulk fatigue properties of the epoxy materials. A special emphasis has been directed towards crack nucleation and early growth during Stage I and Stage I-to-Stage II transition, Stage II crack growth. Photoelastic experiments especially showed that crack propagation under fretting-fatigue loading was strongly dependent upon the complex cyclic micro-sliding behaviour of the crack faces. Under a fretting-wear condition, the constancy of the local contact conditions within the gross slip regime allowed the derivation of realistic estimates of the crack initiation times from the theoretical model.