Multicracking in low cycle fatigue—a surface phenomenon?

A new description of LCF damage evolution taking into account the two-dimensional nature of short cracks is proposed. It appears that random character of the damage process is limited to the short crack nucleation. In the stage of short crack growth, the parameters related to the crack population (crack density, crack lengths) have no significant influence on damage evolution. When short cracks are considered as two-dimensional defects, the crack coalescence at surface does not lead to any significant acceleration of damage, as it is predicted by LCF models based on pure surface damage. The growth kinetics of the fatal crack appears as the essential parameter in HCF as well as in LCF providing a basis for a new generation of numerical simulation of fatigue damage.