Fatigue analysis of spherulitic semi-crystalline polymers: Unveiling the effects of microstructure and defect

A micromechanical model considering the spherulite structure of semi-crystalline polymers was established in this study. The micro stress-strain histories were captured by combining the constitutive equations and multi-axial fatigue criterion. The continuous damage theory was employed to describe the degradation of material properties during cycle loading. Based on the proposed model, the effects of microstructure features, such as grain anisotropy, defects, and crystallinity, on the fatigue performance was examined under multi-axial loading condition. The local material degradation and damage accumulation were then focused on to understand the underlying fatigue mechanisms with various microstructures. Meanwhile, the crack initiation site was precisely predicted and discussed. This research provides theoretical support for understanding the failure mechanisms of spherulitic semi-crystalline polymers, deepening the understanding of associated microstructural characteristics and strengthening the anti-fatigue design of semi-crystalline polymers. Highlights A microstructure model considering both crystalline and amorphous was established. Fatigue damage was captured at the grain level under multiaxial loading conditions. Micro-level fatigue behavior of semi-crystalline polymers was investigated. The interaction among microstructure features and their effects on damage were discussed.