Laboratory-Scale Assessment of Carbon-Epoxy Structural U-Channels Exposed to Flange Heating

Abstract

This study investigates the combined thermal and mechanical response of pre-loaded woven carbon-epoxy U-channels subjected to radiant heating conditions similar to those experienced by aircraft structures in the event of a fire. A custom-built laboratory scale test rig was used to combine the mechanical loads and thermal boundary conditions. The main experimental aim was to measure failure times, failure modes, displacement and temperature distribution of the U-channels. The results show that the U-channels undergo multiple phases of decomposition when exposed to heat. These phases include physico-chemical changes such as bubble formation, visible charring, and epoxy resin pyrolysis. Additionally, the U-channels experience mechanical degradation through thermal-induced delamination and torsional deformation, causing the flange furthest from the heat source to buckle. The rate of decomposition and loss of load-bearing capacity are directly proportional to heat flux, with higher heat fluxes accelerating these processes. Analysis of displacement data reveals that higher heat fluxes correlate with lower displacement variability over time for U-channels under identical thermal conditions. Temperature measurements indicate that higher heat fluxes result in higher temperatures but lower temperature gradients, directly influencing failure times and modes. Consequently, higher temperatures lead to shorter failure times, while lower temperatures extend failure times. The findings from this study will provide valuable knowledge to inform optimised approaches, especially in the domain of aircraft structural fire safety.