Effects of freeze–thaw cycles on mode I fracture toughness of adhesively bonded CFRP joints

The effects of freeze–thaw (FT) cycles on the mode I fracture toughness of adhesively bonded carbon fiber reinforced plastic joints were studied. Fracture toughness specimens were immersed in water and exposed to thermal cycles consisting of thawing (+60 °C) and freezing (−50 °C). Two types of fracture toughness specimen were prepared: those without mechanical loading (non-stressed) and those with mechanical loading using a wedge (stressed) during the environmental conditioning. Fracture toughness of the non-stressed specimens gradually decreased with increasing number of FT cycles, whereas that of the stressed specimens first increased and then gradually decreased. Fracture mechanisms are discussed on the basis of the results of fracture toughness tests, the tensile properties of bulk adhesives, and fracture morphologies.