In this study, an aerospace thermosetting composite was co-curing joined by Polyether-ether-ketone (PEEK) and Polyethylenimine (PEI) films, with an aim of developing advanced composite joints. The semi-crystalline PEEK films were surface activated upon a UV-irradiation technique to obtain a strong film–composite interface, while the amorphous PEI films could be directly used. The fracture behaviour of the composite joints was evaluated and compared with benchmark aerospace adhesive joints. The experimental results proved remarkable mode-I and mode-II fracture resistance of the PEEK co-cured joints at 22 °C and 130 °C, while the PEI co-cured joints exhibited excellent mode-I fracture resistance at 22 °C and mode-II fracture resistance in both testing temperature cases. Extensive elongation, tearing and fracture of the PEEK/PEI plastics were proved to be the main mechanisms for toughness enhancement. Overall, this work had successfully demonstrated the effectiveness of developing advanced composite joints via a co-curing process using high-performance thermoplastic films.

The mechanical characterization of textile composites is a challenging task, due to their nonuniform deformation and complicated failure phenomena. This article introduces a three-dimensional mesoscale finite element model to investigate the progressive damage behavior of a notched single-layer triaxially-braided composite subjected to axial tension. The damage initiation and propagation in fiber bundles are simulated using three-dimensional failure criteria and damage evolution law. A traction-separation law has been applied to predict the interfacial damage of fiber bundles. The proposed model is correlated and validated by the experimentally measured full field strain distributions and effective strength of the notched specimen. The progressive damage behavior of the fiber bundles is studied by examining the damage and stress contours at different loading stages. Parametric numerical studies are conducted to explore the role of modeling parameters and geometric characteristics on the internal damage behavior and global measured properties of the notched specimen. Moreover, the correlations of damage behavior, global stress-strain response, and the efficiency of the notched specimen are discussed in detail. The results of this paper deliver a throughout understanding of the damage behavior of braided composites and can help the specimen design of textile composites.