The translaminar fracture toughness of high-performance polymer fibre composites and their carbon fibre hybrids

The translaminar fracture toughness is a key property that governs the damage tolerance and notch sensitivity of fibre-reinforced composites. Compact tension tests were performed to investigate the translaminar fracture toughness of composites reinforced with three types of high-performance polymer fibres: polyarylate (PAR), polybenzobisoxazole (PBO) and aramid fibre. A carbon fibre composite was used as the reference system. The propagation translaminar fracture toughnesses of the PAR and PBO fibre composites were 492 kJ/m2 and 547 kJ/m2, respectively. These are among the highest translaminar fracture toughness values recorded in the literature. It was hypothesized that the fibrillation of the fibres upon failure was an important energy dissipating mechanism alongside pull-outs that were much longer than for carbon fibre. Replacing a small strip of a carbon fibre ply by a strip of PAR or PBO fibres successfully reinforced the material by locally arresting crack growth. By contrast, the performance of the aramid fibre composites and their hybrids with carbon fibre was lacklustre. The results presented in this work can be used to further improve the safety of composite parts by optimising the design for damage tolerance while also reducing the weight of the parts.