Mode II interlaminar delamination resistance and healing performance of 3D composites with hybrid z-fibre reinforcement

Resistance to impact induced delamination damage is critical to the safety of composite structures, and the extent of delamination depends on the mode II delamination toughness. This paper presents a novel three dimensional (3D) hybrid fibre technique for polymer matrix composites to resist and in-situ repair mode II delamination cracks. This hybrid fibre composite contains two types of through-the-thickness z-binders made of carbon fibre tows and thermoplastic filaments. The performance of this hybrid 3D composite is compared with 3D composites reinforced with only the carbon tows or the thermoplastic filaments. The results show that the hybrid z-binder reinforcements improve the mode II interlaminar fracture toughness (-75%) and in-situ reparability of mode II delamination. In this 3D hybrid composite, the carbon z-binders promote delamination toughness whereas the thermoplastic z-binders enable in-situ repair of delamination cracks. However, the levels of improvement to the mode H delamination resistance and healing efficiency are much less than those achieved under mode I loading. To understand the toughening mechanism of the hybrid z-binders, a finite element model was developed to simulate the mode II crack growth behaviour and fracture toughness properties of the composite materials. The finite element model is able to predict with good accuracy the mode II fracture properties of 3D hybrid composites.