Control of unstable crack propagation through bio-inspired interface modification

Selective toughening can be used to improve specific interfaces in a fibre reinforced polymer (FRP) component which may otherwise act as crack initiation sites. Interfacial tougheners (such as interleaves and powder treatments) have typically been deployed in a simplistic manner. However, by discretely and judiciously introducing toughening agents, taking inspiration from nature, a step change in toughness characteristics can be demonstrated. Cracks propagating through these toughened regions give rise to interesting fracture phenomena. The work presented herein shows that by incorporating regions of variable toughness, unstable crack propagation can be avoided and graceful degradation to failure demonstrated. Using both Mode I double cantilever beam testing and finite element modelling this study shows how selective toughening can be used without unstable crack growth.