Temporal damage accumulation characteristics of plain weave composites under combined high and low cycle fatigue loading employing DIC and AE techniques

In this paper, a novel experimental investigation on the combined high and low cycle fatigue (CCF) behavior of plain weave composites (PWCs) is conducted, utilizing a specially designed fatigue loading block. Digital image correlation (DIC) and acoustic emission (AE) techniques are employed for comprehensive damage characterization. Superimposed high-cycle fatigue (HCF) loading is found to significantly reduce fatigue life, accelerate the accumulation of total and residual strain and lead to earlier damage of weft yarns. A fatigue damage mode identification method is developed by the k-means++ clustering analysis and macro/micro-scale damage observation, classifying fatigue AE signals into four modes. Notably, fatigue damage accumulation characteristics exhibit strong time dependency on the loading history. Under CCF loading, early damage primarily occurs during the HCF stage, while continued cycling causes substantial accumulation in both the load-rise and HCF stages. The superimposed HCF loading contributes to an increased number of cumulative AE hits across all loading stages. The presence of HCF loading maintains a consistently high damage accumulation rate for matrix cracking and fiber/matrix debonding throughout the fatigue process, which is the primary factor contributing to fatigue life reduction.