Carbon fiber and matrix resin mechanical properties controlling statistical tensile fatigue life of unidirectional CFRP

The influence of carbon fiber and matrix resin mechanical properties on the statistical fatigue life of unidirectional CFRP under cyclic tension loadings is evaluated using the authors’ developed integrated accelerated testing methodology (Integrated ATM) based on the time–temperature superposition principle which holds for matrix resin viscoelasticity. First, the mechanisms governing the strength degradation because of cyclic loading of CFRP and its structures are presented and formulated. Second, the parameters in the formulations are inferred based on results of viscoelasticity tests of epoxy resin, and of static and fatigue tension tests of the resin-impregnated carbon fiber reinforced epoxy (CF/EP) strands using three kinds of carbon fiber as unidirectional CFRP. Finally, the influences of matrix resin viscoelasticity and carbon fiber mechanical properties on the statistical fatigue life of CF/EP strands are discussed. Results indicate that the CF/EP strand fatigue life depends on the ultimate strains and their scatter of carbon fibers. Strain ratio and matrix resin viscoelasticity effects on the fatigue life of CF/EP strand are also clarified.