Effect of fatigue-mediated secondary microcrack on crack resistance of twinned materials

Abstract

Accurately assessing fatigue crack growth resistance of structural materials is critical for service safety. We developed a theoretical model to describe the fatigue crack growth rate (FCGR) in an elastoplastic solid with fatigue-mediated random secondary microcracks. The model is applied to twinned materials. A special crack-microstructure interaction is examined which considers microcrack initiation occurs inside and outside twin ahead of the crack tip. The variations in spatial position and size characteristic of microcrack are considered using an extension of distributed dislocation technique. It is demonstrated that the FCGR exhibits significant dependence on fatigue-mediated microcrack for both the microcrack-inside and microcrack-outside cases. By solving the stress response near the crack tip, the combined effect of microcrack and twin lamella characteristics on FCGR is revealed. In parallel, we elucidate the competitive mechanism of the shielding and accelerating effects caused by microcrack. Besides, the effect of angle between the loading axial and the twin lamella is discussed. As the angle increases, the effects caused by secondary microcrack are weakening. This work expects to arouse new interest in the aspect of material crack resistance design concerning the influence of interaction between fatigue crack and fatigue-mediated microstructure.