Size Effects and Hygrothermal Aging on Mode II Interlaminar Fracture Toughness of Thick CFRP Composites

ABSTRACT The size effects and hygrothermal aging behavior of Mode II interlaminar fracture toughness ( G II c ) for thick composites are investigated. Experimental results demonstrate that increasing specimen thickness leads to a rise in G II c for NPC and PC tests from 0.99 and 0.64 kJ/m 2 to 1.41 and 0.97 kJ/m 2 , respectively. FE simulation results indicate that the increase in the fracture process zone (FPZ) area plays a crucial role in contributing to the size effects observed in G II c . The ENF specimens exhibit a significant decrease in glass transition temperature ( T g ) along with noticeable changes in fracture morphology. The G II c values obtained from NPC tests are significantly lower than those of unaged specimens. However, hygrothermal aging has no effect on the crack propagation behavior and G II c values in PC tests. These findings provide practical insights for designing and predicting the service life of composite components exposed to humid and high‐temperature environments.