Thermal ageing mitigation of frp composites using vascular networks

Incorporation of multifunctionality to fibre reinforced polymer composite materials delivers many benefits. One example includes improved longevity of components through increasing permissible temperatures of operation, which could be achieved via in-situ cooling. As the temperature of composite components approaches the glass transition temperature (Tg) of the matrix, thermal stress induced ageing greatly increases [1], [2], thus the incentive for integrated cooling. In order to assess the damage, which could be caused by exposure to elevated temperatures, isothermal ageing was performed at a temperature 15° C lower than the materials Tg (2200 hours at 110° C). Material used in this study is a carbon/epoxy prepreg system (Gurit, SE70), with a T g of 126° C when cured at 110° C. Results have shown a significant drop in Short Beam Shear (SBS) Strength starting after exposure for 1700h and increase in fibre bridging seen in mode I Double Cantilever Beam (DCB) testing. Fracture surface analysis using SEM indicated that fibres were generally less well bonded to the matrix, with visible changes began occurring as early as 1000h exposure. These results indicate that extended exposure of a material at near T g temperatures has a detrimental effect on material properties. To mitigate against this phenomenon, a series of tests were performed on SBS and DCB specimens in a raised temperature (110° C) environment, which incorporated in-situ cooling. The specimens were placed in an oven at 110° C and were cooled down to a constant temperature of 60° C via the internal vascular cooling arrangement. Further testing is underway to assess the inhibition of ageing and maintenance of the original composite material by active cooling using embedded vascular networks.