Damage behavior and life prediction model of composite laminates under combined high and low cycle fatigue

In this paper, the mechanical property and damage behavior of T800/epoxy composite laminates under combined high and low cycle fatigue (CCF) are studied by combining digital image correlation, infrared thermal imaging and optical microscope. The effects of superimposed high cycle fatigue (HCF) on CCF are comprehensively examined by conducting an integrated analysis of fatigue life, stiffness degradation, energy dissipation, average surface temperature and damage morphology. The experimental results indicate that the CCF loads exhibit a pronounced effect on the fatigue life of composite laminates. According to the energy dissipation and stiffness degradation, the entire fatigue process of composite laminates under both LCF and CCF can be segmented into three distinct stages. The fatigue resistance of composite laminates under CCF loads decreases with the increasing superimposed HCF, and the damage accumulation under CCF loads is more severe due to the intricate load interactions. Particularly, a novel normalized fatigue life model is proposed to predict the CCF fatigue lives of composite laminates, which exhibits higher accuracy in comparison with other traditional prediction models.