Fracture Behaviour of Polyetherimide (PEI) and Interlaminar Fracture of CF/PEI Laminates at Elevated Temperatures

(2005) Fracture behavior of polyetherimide (PEI) and interlaminar fracture of CF/PEI laminates at elevated temperatures. Abstract To investigate effects of environmental temperature on fracture behaviour of a polyetherimide (PEI) thermoplastic polymer and its carbon fibre (CF/PEI) composite, experimental and numerical studies were performed on compact tension (CT) and double cantilever beam (DCB) specimens under mode-I loading. The numerical analyses were based on 2-D large deformation finite element analyses (FEA). Elevated temperatures greatly released the crack tip triaxiality (constraint) and promoted matrix deformation due to low yield strength and enhanced ductility of the PEI matrix, which resulted in the greater plane-strain fracture toughness of the bulk PEI polymer and the interlaminar fracture toughness of its composite during delamination propagation with increasing temperature. Furthermore, the high triaxiality was developed around the delamination front tip in the DCB specimen, which accounted for the poor translation of matrix toughness to the interlaminar fracture toughness by suppressing the matrix deformation and reducing the plastic energy dissipated in the plastic zone. Especially, at delamination initiation, the weakened fibre/matrix adhesion at elevated temperatures leaded to premature failure of fibre/matrix interface, suppressing matrix deformation and preventing the full utilization of matrix toughness. Consequently, the low interlaminar fracture toughness was obtained at elevated temperatures.