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 (T-g) and did not induce the formation of new materials or the occurrence of chemical reactions, thermal aging resulted in increased T-g and was accompanied by the concomitant occurrence of oxidation reactions.