Temperature effect on dynamic translaminar fracture of thermoplastic composites

Carbon fibre thermoplastic composites are emerging as an attractive alternative to thermoset composites for next-generation aerospace applications due to combination of manufacturing efficiency, mechanical performance, weight reduction, and sustainability benefits. The damage-tolerance of thermoplastic composite structures is influenced by their translaminar fracture toughness. Although temperature is known to influence the properties of these composites, its impact in the dynamic regime—particularly on the translaminar energy release rate related to fibre fracture—has not been extensively studied. This study shows, for the first time, the experimental characterisation of the dynamic mode-I translaminar critical energy release rate at various temperatures for a carbon fibre PEEK composite. An adaptation of the split Hopkinson pressure bar system was used to conduct compact tension experiments at high loading rates. Digital image correlation (DIC) analysis on ultra high-speed images was employed to extract the strain fields, crack tip location and the opening displacements in the different cases. By using the area method to evaluate the fracture energies, we found that the worst case for dynamic fracture, where the critical energy release rate was found to be minimum, was at 90 °C, showing 27 % lower energy than at room temperature. Specimens tested at -55 °C showed no significant difference to the room temperature high-rate experiments. DIC, micro-CT and SEM imaging offered insights on the underlying mechanisms behind these experimental observations.