Effects of hygrothermal and thermal aging on the low-velocity impact properties of carbon fiber composites

The effects of hygrothermal and thermal aging on the low-velocity impact properties of carbon fiber composites were systematically investigated by comparing the mass loss, morphologies, dynamic mechanical properties, and chemical structures of aged and non-aged specimens. The relationships between dent depth, damage area, residual compression strength, and impact energy were also discussed in detail. The obtained results showed that the non-aged composite featured good fiber-resin bonding, whereas hygrothermal and thermal aging led to fiber-matrix interface damage. For thermally aged samples, dent depth rapidly increased with impact energy above the inflection point, and the corresponding amplitude was greater than those observed for non-aged and hygrothermally aged specimens. Notably, hygrothermal and thermal aging did not affect the impact-induced damage morphology and the after-impact compression failure mode. At a constant impact energy, the damage area of thermally aged samples exceeded those of non-aged and hygrothermally aged ones; moreover, thermal aging exhibited greater influence on residual compressive strength than hygrothermal aging. Finally, whereas hygrothermal aging reduced the glass transition temperature (Tg) and did not induce the formation of new materials or the occurrence of chemical reactions, thermal aging resulted in increased Tg and was accompanied by the concomitant occurrence of oxidation reactions.