Thermal response to fire of a fibre-reinforced sandwich panel: Model formulation, selection of intrinsic properties and experimental validation

A predictive model is formulated for the fire response of a glass reinforced plastic panel, consisting of two glass-fibre/polyester skins and Vermiculux sandwich material (core) in between. Polymer conversion takes place according to a first-order decomposition reaction and an n-order combustion reaction both with an Arrhenius-type dependence on temperature. Intrinsic kinetic parameters have been estimated by re-examination of thermogravimetric data at four heating rates, resulting in activation energies for the two steps of 128 and 150 kJ/mol, respectively. Physical processes are modelled by the unsteady, onedimensional conservation equations taking into account heat transfer by convection and conduction, convective mass transfer, surface heat transfer, effective thermal conductivity, moisture evaporation, ablation of the heat-exposed surface at a critical temperature and property variation. Simulated process dynamics, using intrinsic values for all the model parameters, are highly influenced by the behaviour of the heat-exposed skin which shows three main regimes: I) very rapid conversion of a thin surface layer (fast heating regime), II) slowing down of the conversion processes following the formation of a thick insulating fibre glass layer (slow heating regime) and III) a new enhancement in the reaction rates as a consequence of surface collapse and ablation (ablation regime). Good agreement is obtained for the predicted and measured temperatures for both a single skin composite plate and a sandwich panel loaded with a hydrocarbon flame.