Modélisation de la dégradation d'un matériau composite carbone-époxy soumis à une sollicitation thermo-mécanique couplée. Application aux réservoirs d'hydrogène de type IV

Abstract : Composite materials made of carbon fibres and epoxy resin have remarkable specific properties that make them suitable for large-scale use in many areas where mass savings are required, such as transport. An example is the type IV hydrogen tank in motor vehicles. In the context of the safety of persons, the fire risk must then be considered: when a hydrogen tank undergoes thermal aggression such as a fire, its composite shell is subject to thermal decomposition which, coupled with heat transfers and damage due to mechanical loading, can lead to burst of the structure. To numerically predict the behaviour of tanks subjected to coupled load (thermal and mechanical), a model based on the phenomena having a major impact on the behaviour of the material has been developed. It involves, in a thermodynamic framework, matrix microcracking, fibre failure and fibre/matrix interfaces decohesion as well as delamination and represents the effects of temperature on mechanical properties. To this mechanical damage is added the thermal decomposition due to high temperatures (>350°C). It induces structural changes in the material due to the gasification of the epoxy resin, a change in thermal parameters (which has an influence on heat transfers) and a loss of mechanical properties.At the specimen scale, calculations are carried out to determine the parameters of the different sub-models. This includes initiation criteria and damage evolution laws, reaction parameters for thermal decomposition and thermal parameters (density, thermal capacity and conductivity) for each decomposition state. A method is proposed to determine the key parameters of thermomechanical coupling, namely the influence of thermal decomposition on mechanical behaviour. Fully coupled calculations are also performed to determine the weight of each phenomenon (temperature, thermal decomposition and mechanical damage) on the final failure of the material under fire exposure conditions.At the hyperbaric tank scale, burst pressure predictions, in a fire situation and at room temperature, are carried out. At room temperature, the role of each damage process in the ultimate pressure is evaluated to determine their relative weight in the modelling. Under fire conditions, the time to burst is evaluated when the tank is subjected to different internal pressures. The model is able to correctly predict the transition from a burst mode at high pressure to leak mode at lower pressure due to melting of the liner before the stress level is critical in the composite shell and leads to burst. This approach, implemented at the scale of the tank, therefore makes it possible to establish the sequence of events leading to burst (plies in which damage occurs, temperature field in the composite wall, burst time).
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Camille Mercadé. Modélisation de la dégradation d'un matériau composite carbone-époxy soumis à une sollicitation thermo-mécanique couplée. Application aux réservoirs d'hydrogène de type IV. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2017. Français. ⟨NNT : 2017ESMA0027⟩. ⟨tel-01696237⟩

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