Initiation of fretting fatigue cracks in spiral multi-layer strands
The present work deals with the prediction of the fatigue resistance of spiral strands undergoing cyclic bending deformations in service conditions. The prediction of fretting fatigue crack initiation at the inter-wire contacts of a spiral strand is proposed for the simple loading case of the spiral strand axially tensioned and bent with a uniform radius of curvature. The amplitudes of the bending stresses and the friction forces related to the strand curvature are calculated at the outside inter-layer contact patches of the spiral strand. The fretting fatigue limit of the steel wire is calculated taking into account the contact parameters of the theory of Hertz and Midlin and the basic tensile fatigue characteristics of the material. The fatigue limit and the conditions of occurrence of fretting fatigue cracks in spiral strands are discussed with the fatigue criterion of Goodman adjusted to take into account the high stress gradient in the subsurface. The conditions of representative experimental fretting fatigue simulations and the limits of the theoretical predictions are also addressed.