A novel, bioinspired, non-Newtonian energy absorption medium for the protection of composite laminates under Low Velocity Impact (LVI).

Sea cucumbers, marine animals members of the Echinoderms family, will react to an external stimulus by rapidly and reversibly increasing their skin stiffness in order to protect themselves [1-3]. This mechanism has been the source of inspiration for the development of a protective smart layer able to improve the impact resistance of Carbon Fibre Reinforced Polymer (CFRP) laminates. By exploiting a dynamic and autonomous phase transition, this novel, non-Newtonian medium acts as a protective layer on the surface of a laminate by changing its mechanical properties in response to an external stimulus, preventing impact damage such as delamination and microcracks. Low Velocity Impact (LVI) tests were employed at an energetic level of 15 J, to assess the energy absorption characteristics of the protective multi-layered coatings which were compared to an uncoated CFRP laminate. Results from LVI indicated that the proposed smart layers are able to modify the way the energy is distributed during the impact event, due to a dynamic transition between a viscous and rubbery phase of the embedded non-Newtonian material. These data were further confirmed by ultrasonic C-Scan analyses which showed an average reduction of 60% of the extent of the internal damage in comparison with the CFRPs laminates. These results demonstrate that the proposed medium possess unique energy absorption characteristics, thus providing an innovative solution for the protection of CFRP laminates in primary load-bearing applications where they might be subjected to out-of-plane impacts, such as in aerospace or railways components.