Engine fire in an aircraft is a situation where polymer-based composites structural parts surrounding the engine can be exposed to extreme heat of be impacted by a flame. Current regulations impose a minimum flight capacity of 15 min after fire break out. Aeronautics manufacturers validate their composites solutions by checking that the flame does not get through the composite plate impacted by the flame. For the development and the integration of new materials, e.g. thermoplastic-based composites, a detailed characterization of the mechanisms involved in the situation of a thermal aggression is first necessary. This can be achieved partially by experimental analyses [1]. Modelling provides a complementary mean to describe the complex interplays between thermal transfers and mechanical properties degradation and to predict the phenomena of stress redistribution during one-face fire exposure [2]. This presentation will first give an overview of the complex multiphysical problem at stake: a large variety of mechanisms, directly related to the nature of materials at play and the wide range of temperatures encountered, the rapidity of the evolutions, the concurrent role of through thickness thermal gradients and mesostructure of the laminate. Then, the focus will be on modelling the thermomechanical behavior of a laminates representative volume element from the ambiant to the temperature of polymer decomposition onset. It is based on an explicit meshing of the matrix-yarn meso-structure and on the finite element resolution. A complete methodology for the identification of the thermomechanical parameters has been developped for a range of temperatures including both the glass transition and the melting of the matrix. The methodology has been applied and validated for a CPPS composite, after a comprehensive set of thermal and mechanical analyses. Supplementary considerations will be made on the damage occuring above the temperature of decomposition of the polymer matrix. Current developments are made on an experiments-based modelling of porosity formation (pyrolysis of the polymer) to predict the connectivity depth of the porosity network and the moment of the thermal aggression where a flame can get through the laminate. REFERENCES [1] Y. Carpier, B. Vieille, A. Coppalle, F. Barbe, Polymer Composites, 9:3552–3563, 2020 [2] Y. Carpier, B. Vieille, F. Barbe, A. Coppalle, Composites Part A, 162:107165, 2022