A tyre is a complex object composed of a stack of steel cables in an elastomer matrix composite plies. One cable is an assembly of drawn pearlitic steel wires. The wires in service are subjected to mechanical (tension and bending) and chemical (diffusion of species) cyclic loading leading to fatigue damage. Responding to environmental issues requires reducing the weight of tires without reducing their performance, especially their fatigue life.

A fatigue model of the steel wire has been developed, based on the assumption of existing defects at the surface of the steel wires, from which crack initiate. A crack propagation law was determined from tensile cyclic tests on single wire, under synchrotron beam to measure crack shape and length. The distribution of defect sizes has been measured from fracture surface analysis, whereas other model parameters have been obtained by inverse method from Wöhler curves.

The model is able to simulate accurately the number of cycles to failure of wires submitted to a constant loading but also to variable loading.