Unified kinetic continuous damage model for random LCF-HCF interaction

Obtaining representative results for a wide range of fatigue levels, as required for structures subjected to fluctuating loads, remains a challenge due to the different material degradation mechanisms involved. This contribution aims to provide a kinetic damage model capable of representing fatigue failure for the full range of stresses, from monotonic to high-cycle fatigue failure. The proposed continuous damage model is a two-scale extension of Lemaitre’s macroscopic damage model. It lies in the framework of standard generalised materials, in which damage growth is governed by a kinetic evolution law of the rate form D ̇ = … for the damage variable D . Naturally, any complex loading, proportional or not, can be considered. The cornerstone of the unified modelling is introducing a memory effect in the damage threshold and defining an apparent damage variable, which combines the damages at both mesoscopic and microscopic scales. The model is studied for complex loading, including sequential periodic loads and random loads both that combine low-cycle and high-cycle fatigue. • LCF and HCH mechanisms are represented by two damage variables at different scales. • An apparent damage variable unifies the two-scale fatigue material degradation. • Damage growth is governed by a kinetic (rate) evolution law. • The kinetic damage model handles fatigue failure for the full range of stress level. • It applies to any 3D complex loading, cyclic or random, coupling LCF and HCF.