The effect of material disorder on fatigue damage induced by unidirectional loading

Load reversals essentially contribute to the development of fatigue damage. However, experiments have shown that fatigue cracks do appear under unidirectional external forces in structures which are mechanically non-uniform. We apply the ‘strain-life’ approach of Coffin and Manson. Since fatigue damage in general is known to be due to local irreversibility of deformation, we apply the strain-life approach to deformations within volume elements of a material with a disorder in yield strain. We will first derive a formula for the effect of material disorder on the evolution of fatigue damage. Then, a simple distribution function for the yield strain will be introduced, and the effect of material disorder on the evolution of fatigue damage will be numerically elaborated, using this distribution function. Finally, the interplay between recoverable and irrecoverable strain will be discussed.