Scrutinising the isolated and combined effects of in-service temperature and moisture on mode I fatigue delamination of CFRPs

Given the long-term use of carbon fibre reinforced polymers (CFRP) in harsh environments, this study investigates the isolated and combined effects of temperature and moisture variations on mode I fatigue delamination propagation. Several levels of temperature and relative humidity were applied as preconditioning and as in-service during fatigue testing to evaluate their effects on the Paris curve. In addition, statistical analyses, including analysis of variance (ANOVA), semi-empirical interpolation modelling, and fractographic assessments, were conducted to provide a comprehensive understanding of the failure mechanisms. The results indicate that the moisture absorbed during hygrothermal preconditioning and the in-service temperature applied during fatigue test individually affect the Paris curve slope. These factors interact synergistically, significantly altering the fatigue crack growth rate. An empirical model capturing this interaction showed good agreement with experimental data, enabling reliable prediction of environmental degradation trends. Fractographic evidence supported the observed changes in fracture patterns, linking changes in fibre bridging formation, surface roughness, and energy dissipation to the observed shifts in fatigue behaviour.