Experimental research and model characterization on Mode I, Mode II and mixed-mode I/II delamination growth behavior of CFRP composites under quasi-static and fatigue loading

This paper seeks to comprehensively investigate the interlaminar delamination growth behavior of carbon fiber reinforced polymer (CFRP) composites under quasi-static and fatigue loading by experimental research and model characterization. Mode I, Mode II and Mixed-mode I/II quasi-static and fatigue delamination growth tests were systematically conducted on double cantilever beam (DCB), end-notched flexure (ENF) and mixed-mode bending (MMB) specimens, respectively. The results show that the fatigue delamination growth (FDG) rate decreases with the increase of stress ratio under the same mode mixture and with the increase of mode mixture under the same stress ratio. Meanwhile, the delamination damage of CFRP composites is much more sensitive to fatigue loading in Mixed-mode I/II compared to pure Mode I and Mode II. A new FDG model considering both stress ratio and mode mixture effects is developed to characterize the FDG behavior of CFRP composites, showing good correlation with the experimental data. In addition, it can be found from fractographic analysis that mode mixture, loading condition and stress ratio significantly affect the microscale damage mechanisms during delamination growth process. The comprehensive experimental findings of the FDG behavior of CFRP composites and the new FDG model considering both stress ratio and mode mixture effects can provide effective theoretical and data references for engineering practice.