Mode I delamination behaviour of short fibre reinforced carbon fibre/epoxy composites following environmental conditioning

Carbon fibre laminates based on Newport Adhesives NCT-301 uniaxial pre preg were prepared for Mode I DCB testing. Polyamide and Polyolefin web materials supplied by Spunfab Ltd and Toyobos’ Zylon HM fibres were applied to the interlaminar region to enhance fracture toughness. Three of each specimen type were “treated”, subjected to immersion in 95 °C water for a period of 600 h. Two “untreated” control specimens of each type were aged at 21 °C and 40-95% relative humidity. Specimen weight gains in the order of 2% were found to occur in all immersed samples. Fracture toughness increases were evidenced in all treated samples with the exception of the Polyamide Web sample. Average GIc increases in treated samples were 250–300%. Untreated samples were found to have exclusively interlaminar crack propagation. Untreated samples containing Polyamide or Polyolefin Web reinforcement displayed increased fracture toughnesses. These toughness increases were attributed to improved interlaminar bonding.