Impact behavior and damage characteristics of hygrothermally conditioned carbon epoxy composite laminates

• Impact test was conducted on hygrothermally aged carbon/epoxy laminated composites.
• Mode I fracture toughness test was carried out on aged CFRP laminates.
• No structural defects were found in CFRP laminates exposed to hygrothermal ageing.
• Moisture significantly alleviated the impact induced damages in CFRP laminates.
• The mechanism for the enhanced impact response of aged CFRP laminates is proposed.

A novel finding about effects of moisture and cyclic hygrothermal conditions on the impact resistance of carbon fiber reinforced epoxy polymer (CFRP) composites are presented. The course of experiments began with the fabrication of specimens using unidirectional CFRP prepreg materials. As-fabricated specimens were exposed to two types of hygrothermal conditions which were designed to simulate in-service environment. Microstructure characterization of the specimens revealed that neither hygrothermal conditions brought about any evident defects to the laminates. Low-velocity impact testing was then carried out on the specimens with different moisture levels. It was found for the first time that moisture significantly alleviated impact induced damage in the CFRP unidirectional laminates. Detailed discussion about how the absorbed moisture influenced the impact behavior of the laminate was carried out based on the interpretation of the damage characteristics and impact testing data. The effects of absorbed moisture on the GIC of this material were explored to assist the understanding of the role played by the absorbed moisture during low-velocity impact testing.