Polyborosiloxane-based, dynamic shear stiffening multilayer coating for the protection of composite laminates under Low Velocity Impact

This work presents a novel shear-dependant, smart layer consisting of a polyborosiloxane (PBS)-based Shear Stiffening Gel (SSG), encapsulated in crosslinked vinyl-terminated polydimethylsiloxane (VPDMS), acting as a protective layer on the surface of Carbon Fibre Reinforced Polymer (CFRP) laminates reducing impact damage. The frequency-dependant reversible network structure of the PBS smart layer acts as a dynamic responding energy absorption medium (DrEAM), able to autonomously stiffen in response to an external stimulus. Low Velocity Impact (LVI) tests were employed to assess the energy absorption characteristics of the smart layers which were compared to a VPDMS film and an uncoated CFRP laminate. Results indicated that DrEAM smart layers are able to modify the way the energy is distributed due to the dynamic phase transition of the embedded SSG. These were further confirmed by Non-Destructive Testing analyses, where DrEAM coatings allowed for an average reduction of 65% of the extent of the internal damage in comparison with the CFRPs and outperformed VPDMS by showing a further reduction of 33% at low energy (10 J) and by more than 50% for higher energy (20 J), providing a complete low-cost solution for the protection of CFRP laminates subjected to out-of-plane impacts such as in aerospace or railways components.