Surface temperature of carbon composite samples during thermal degradation

An infrared camera and a Fourier transform infrared spectrometer were used simultaneously to observe the radiation from the surface of carbon composite samples during thermal degradation experiments. Surface temperatures were estimated from radiation measurements conducted during cone calorimeter tests. Infrared spectra and images were post-processed involving a subtraction method between successive images, to withdraw the high incident flux from the cone calorimeter partly reflected by the sample. The surface intensities were first evaluated as a function of time. Then, an identification step was implemented linking the rise in intensity between two time steps with the increase in sample temperature. Corrections were introduced for the reflection of the incident radiation from the heater and for the true emissivity of the material. Both experimental devices - camera and spectrometer - showed temperature evolutions in a good agreement. The sharp temperature increase of the sample and the auto-ignition of the pyrolysis gases on the surface were observed and evaluated for various incident fluxes from the cone between 20 and 65 kW/m2. Measurements carried out with a short time step down to 0.2 s further allowed an evaluation of the supplementary flux due to the auto-ignition with a peak up to 20 kW/m2 for an incident flux of 35 kW/m2 on a carbon composite sample with surface 50 mm × 300 mm and thickness 5 mm.