Determination of the tensile residual properties of a wound carbon/epoxy composite first exposed to fire

Abstract

The use of carbon fiber/epoxy matrix composite is widely developed to store hydrogen at high pressure because of its low weight and its good specific mechanical properties. In order to secure this type of storage, it is necessary to tackle the thermal degradation and the influence of a fire or a heating source on the residual mechanical behavior of such materials. In the present study, carbon/epoxy composite samples with different fiber orientations are considered. The thermal aggression (representative of a fire) is performed by using a cone calorimeter apparatus (ISO 5660). The fire exposure is stopped at different time in order to study the influence of the thermal energy (different heat fluxes and exposure durations) on the residual mechanical tensile properties. The results obtained show that the residue thickness (char) of the samples is proportional to the incident energy. Strength and stiffness reduction can be observed even without ignition (i.e ., without combustion flame) when the mechanical properties are controlled only by the resin (fiber perpendicular to the loading axis). When the fibers are mechanically loaded (quasi-isotropic samples or ± 45° samples), a very little strength decrease is observed before ignition and accelerated after ignition. A proportional relationship between the ultimate stress of the exposed sample and the non-charred thickness is also observed.