Co-authors​ :

 Marisa DE LA CRUZ MARTINEZ , Abishay MOHAN , Geoffrey NEALE (UNITED KINGDOM) 

The use of fibre reinforced composites continues to expand beyond their traditional base in aerospace. These materials are increasingly in demand across the wider transport, energy, space, and defence sectors as they strive to meet ambitious ‘Net Zero’ targets, for which composites are seen as a key enabling technology. As a result, there is an increasing need for embedded multifunctionality in composite structures to exhibit behaviours intrinsic in legacy materials like metals. In particularly high demand is efficient thermal energy transfer, though which a multitude of other functionalities can be derived e.g., self-healing, sensing (thermography), etc. Hybridisation via the addition of metallics to impart desirable functionality on the composite is well-established, but most approaches tend to add materials to the laminate interlayer providing planar properties without the much needed out-of-plane improvements. A specific use case is in automotive battery box/module cases where improved through thickness thermal conductivity is needed to conduct heat away from battery cells. Here we demonstrate that composite hybridisation by the addition of macroscale (>1 mm) through-thickness metallic pins can improve three-dimensional thermal energy transfer as well as provide effective tailoring of this property in composites. The use of fewer macroscale pins is significant as this allows for maximisation of the cross-sectional area of conductive material, which is crucial for improving heat flow. This work reports extensive thermomechanical characterisation of the carbon-benzoxazine fibre reinforced composite hybridised system hybridised with metallic pins that have been inserted during the pre-forming stage via static insertion. This feeds into experimentally validated macroscale (ply-level) finite element (FE) models which capture the thermomechanical behaviour of the hybridised system during operation (including stresses) and incorporate local fibre deviations due to the presence of the moulded-in pins. The metallic pin materials investigated are fabricated from stainless steel, magnesium, and copper, representing a wide range of thermal properties. Results show that z-direction oriented conductive metal pins can significantly improve local thermal energy transfer in both the planar and out-of-plane directions. By optimising material, pin proximity and pin quantity, pins exert a collective effect on the material and provide exceptional improvements to the hybridised system and is responsible for the increased in-plane thermal conductivity in the hybridised system. Results also show that these pins can be used to manipulate heat distribution across the material surface to exhibit a thermal cloaking effect, which is useful for controlling the location of hot and cool spots in the composite. The work demonstrates the positive implications for the use of this sort of through-thickness hybridisation for thermal management applications.