Abstract: Delamination of hole exit zone in carbon fibre-reinforced plastics is the most severer section in whole hole zone existing delamination defect caused by drilling. Main reason for causing the delamination of hole exit zone is the opening mode (mode Ⅰ) fracture in interplies which due to thrust force. Uncut layers in front of drill is called remaining layer, and its distribution of stiffness is the key factor to determine the delamination shapes of the interplies. As a result, based on analyzing the distribution of stiffness of the remaining layer, forming mechanism of elliptic delamination of hole exit zone in multi-directional carbon fiber-reinforced plastics caused by drilling is presented theoretically. On the other hand, orientation producing maximum delamination defect is as same as direction with maximum stiffness on the remaining layer. So based on determination of maximum stiffness orientation of the remaining layer, calculating method of major axis angle of the elliptic delamination is established.

Key words: Carbon fibre-reinforced plastics(CFRP), Drilling, Elliptic delamination, Major axis angle, Remaining layer