Macro- and micro-interfacial properties of carbon fiber reinforced epoxy resin composite under hygrothermal treatments

Short beam shear test and single-fiber fragmentation test with an energy-based model were employed to investigate the changes of interfacial properties of carbon fiber/epoxy resin composites under hygrothermal treatments, including 70â.,water immersion, boiling water immersion and re-drying. Scanning electron microscope pictures of shear fracture section in short beam shear and polarized photos at first fiber break in single-fiber fragmentation test were used to analyze the failure mode at interphase region before and after water aging. Furthermore, the similarities and differences between macro- and micro-interfacial properties were compared for two kinds of carbon fiber composites. The experimental results show the consistency of interfacial hygrothermal resistance based on the results from short beam shear and single-fiber fragmentation test. The resin tensile modulus, interlaminar shear strength from short beam shear and interfacial fracture energy from single-fiber fragmentation test all decrease after water aging and recovery to certain extents in re-drying treatment. The failure mode is different for different treated samples, especially showing irreversible change after boiling water immersion. Moreover, the obvious differences between the retention rates of interfacial fracture energy and those of interlaminar shear strength indicate the discrepancy between the micro-interfacial property and the macro-interfacial property on hygrothermal resistance.