The coffin-manson law as a consequence of the statistical nature of the LCF surface damage

The transition between the Coffin-Manson law in low cycle fatigue and the Basquin law in high cycle fatigue is shown to be closely related to the microstructural aspects of damage accumulation in the two different fatigue domains. In LCF, the surface extension of microcracks is predominant whereas their bulk propagation is dominating in HCF. Along these lines, the Coffin-Manson law is derived using standard methods of statistical physics of disordered systems. The universality of the Coffin-Manson exponent for single-phased materials is shown to be a direct consequence of the statistical nature of damage accumulation due to the growth and the interaction of surface microcracks.