Hygro effects on the low-velocity impact behavior of unidirectional CFRP composite plates for aircraft applications

Hygro effect on the impact resistance of unidirectional (UD) CFRP composite plates under low-velocity impact loading are studied experimentally. Before the test, the UD specimens were immersed in water at 80 °C for moisture absorption. Through the moisture ingress into the matrix–fiber interfacial region and resulting in the moisture swelling which may release the thermally induced residual compressive stresses around interfacial zone, certain degradation of disband at the interface of fiber and matrix was observed in the SEM pictures. The experimental results showed that the moisture content played a negative role by decreasing the impact resistance of composite plates. The composite plates with higher moisture level have small values of impact peak force, delamination threshold load, and initiation energy. The flexural rigidity of the unidirectional plates decreased as the moisture content increased, and the larger damage sizes were observed in wet specimens as compared to those of dry specimens.