Multi-physics modeling of the ignition of polymer matrix composites (PMCs) exposed to fire

Advanced polymer matrix composites are widely used in modern aircraft and as such have to withstand fire to comply with safety regulations. The thermal degradation of these lightweight materials is a complex process involving chemical reactions in the solid and gas phases, potentially leading to flaming combustion. Here, we numerically investigate the heat feedback from the ignition of outgassing at the surface of a structural polymer matrix composite exposed to a pilot flame. Our model couples the thermal, physical and chemical processes in the solid phase to compute the composite degradation, as well as the production and movements of pyrolysates. A counterflow diffusion flame is used to model the ignition of the combustible effluent close to the sample surface, where the hot jet of the pilot flame impinges. The predictive capabilities of the method are demonstrated considering a carbon/epoxy composite subjected to a small-scale fire test. As input data for our model, material properties have been measured for virgin and partially burned samples via Differential Scanning Calorimetry, Xenon Flash Analysis and Thermogravimetric Analysis. The model is able to predict the backface temperature and time-to-ignition of the composite sample exposed to a flame with a good degree of accuracy.