Influence of Low and Extreme Heat Fluxes on Thermal Degradation of Carbon Fibre-reinforced Polymers

Abstract

This study considers the influence of different irradiation scenarios on the thermal degradation of carbon fibre-reinforced polymers (CFRP). Real threats are simulated, such as fires with long-lasting low heat fluxes and nuclear heat flashes with short-lasting high heat fluxes. For this purpose, coated and uncoated quasi-isotropic samples of the commercially available CFRP HexPly® 8552/IM7 are thermally irradiated from one side by an electrical heater of a cone calorimeter and a xenon short-arc lamp of a laboratory heat flash simulator with heat fluxes between 5 and 175 W/cm2 at varying time intervals. The specimens’ temperature is recorded on the front and back side as well as at different laminate depths. The CFRP are analyzed with ultrasonic testing (UT), infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and micro-focused computed X-Ray tomography (μCT). Destructive tests are performed to determine the mechanical properties in terms of interlaminar shear, compressive and tensile strength. When samples of CFRP are exposed to higher heat flux, high temperatures and temperature gradient values occur along the cross-section. As a result, extreme damage gradients appear in the material, leading to changes in damage behavior and loss of mechanical properties within seconds. However, to ensure the safety of the material in case of thermal exposure, loading limits are introduced, indicating the threshold for strength collapse. In addition, with the application of coatings, thermal degradation of CFRP can be delayed. Finally, the time-heat flux superposition principle is established to predict the residual strength under different loading scenarios.