A novel hybrid epoxy resin based on a dynamically active polyborosiloxane shear stiffening gel for highly impact resistant composite laminates

• A novel shear-dependent smart material was employed as a toughening material in hybrid epoxy based GFRP laminates. • Low Velocity Impact tests were conducted at various energy levels between unmodified GFRPs and hybrid ones at various stacking sequences. • Hybrid GFRPs displayed unprecedented impact resistance, with up to 79% reduction in damaged area compared to unmodified GFRPS. • Laminates prepared with hybrid epoxy matrix also displayed an improvement of damping properties of up to 66% and no significant effect on their flexural properties. The excellent benefits of composite laminates can be hindered by their poor performance to impact damage from foreign objects. In this work we present a new high performance and cost-effective hybrid resin matrix, which is able to enhance the impact resistance of composite laminates without affecting other desirable properties. This unique combination of properties is obtained by introducing a non-Newtonian, polyborosiloxane-based Shear Stiffening Gel (SSG) within a traditional epoxy resin. The SSG is able to autonomously respond to external impacts by activating a phase transition in its polymeric network, which provides high energy absorption while also avoiding any critical failure. A new manufacturing process to create the hybrid matrix was developed, which was incorporated into glass fibre laminates for a range of lay-up sequences to identify the optimal configurations. Detailed mechanical and chemical characterisation of the SSG, and the resulting hybrid matrix, enabled identification and extent of its dynamic properties. Flexural tests on laminates indicated that the SSG has a negligible effect on overall mechanical properties, while their damping properties were improved up to 66%, in comparison to laminates prepared with a traditional epoxy resin. Low velocity impact testing revealed an significant reduction of damaged areas of up to 79% for the new laminate configurations. This was further corroborated by non-destructive analysis post-impact. These results validate the unique properties of this new form of hybrid resin, which opens new possibilities to broaden the use of composite materials, improving their impact damage tolerance while reducing maintenance costs.