Rate effect and mechanism analysis of mode I interlaminar fracture toughness of CF/PEEK thermoplastic composites

While increasingly used in aerospace, the dynamic interlaminar fracture toughness of high-performance thermoplastic composites like CF/PEEK is not well quantified, which limits the accurate simulation and prediction of their delamination behavior under dynamic loading. This study quantified the rate effect of Mode I interlaminar fracture toughness of CF/PEEK unidirectional laminates under different loading rates, and introduced dynamic crack tip temperature rise into the analysis of underlying mechanisms for the first time. Quasi-static and dynamic fracture tests were conducted using an electronic universal testing machine and a bidirectional electromagnetic Hopkinson bar respectively. The results indicated that the Mode I fracture toughness of CF/PEEK exhibits slight positive sensitivity to crack propagation velocity, and its rate-dependent parameters are much smaller than those of thermosetting CF/epoxy. Fracture surface morphology observation revealed the transformation of fracture mechanisms under quasi-static and dynamic conditions, and obvious temperature rise at the crack tip was observed during dynamic crack propagation. It can thus be inferred that the weak rate effect of the interlaminar fracture toughness of CF/PEEK may originate from the coupling effect between the strengthening effect induced by the transition from fiber debonding to matrix fracture under high strain rate loading, and the softening effect caused by local temperature rise. This study provides reliable parameters and a theoretical basis for the accurate modeling of the dynamic delamination behavior of advanced thermoplastic composites for engineering applications.