Fatigue crack growth resistance and fracture toughness of pipe welds exposed to a blend of hydrogen and natural gas under high pressure

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Comportement de matériaux composites aéronautiques soumis à un chargement thermomécanique couplé

Un dispositif expérimental visant à déterminer l'influence d'une charge mécanique sur la tenue au feu de composites aéronautiques est présenté, afin de comprendre leur mode de dégradation sous sollicitation thermomécanique couplée. Il permet d'enregistrer l'évolution de la température et de la charge au cours d'un essai de flexion couplé à une source de chaleur (brûleur ou cône calorimètre). A partir de ces essais, une simulation par éléments finis est proposée, couplant le comportement mécanique, le transfert de chaleur et la combustion et permettant de retrouver la diminution progressive de la rigidité de l'échantillon

Soot Volume Fraction Measurements in a Three-Dimensional Laminar Diffusion Flame established in Microgravity

A methodology for the estimation of the soot volume fraction in a three-dimensional laminar diffusion flame is presented. All experiments are conducted in microgravity and have as objective producing quantitative data that can serve to estimate radiative heat transfer in flames representative of fires in spacecraft. The competitive nature of formation and oxidation of soot and its direct coupling with the streamlines (source of oxygen) require for these measurements to be conducted within the exact configuration. Thus three-dimensional measurements are needed. Ethylene is injected through a square porous burner and the oxidizer flows parallel to its surface. The methodology uses CH* chemiluminescence measurements to correct for three-dimensional effects affecting light attenuation measurements. Corrected local soot concentrations are thus obtained. All experiments are conducted during parabolic flights and the parameters varied are fuel and oxidizer flow rates

Modelling of thermomechanical behaviour of a wound carbon/epoxy composite exposed to fire

International audienceHydrogen is expected to be highly valuable energy carrier for the 21 th century as it should participate in answering main society and economical concerns. To exploit the benefits of this energy at large scale, further research and technological developments are required to secure its storage, especially during fire exposure. Thus, studies on the thermomechanical behaviour of the composite used in the manufacture of tanks for the storage of hydrogen are important. At present, the use of epoxy/carbon fibre composites is developed widely because of its low weight and its good mechanical properties. Thus, the present study focusses on the thermal decomposition property and the influence of a fire or a heating source on the residual mechanical behaviour of such materials. To account for this point, an experimental study is introduced to improve the understanding of thermal decomposition and fire exposure mechanisms of composite using different "elementary" samples. Firstly, to characterize the mechanical properties versus fire exposure, a thermal degradation is performed using a cone calorimeter on composite samples. These tests are led for various heat flux values and are stopped at different characteristic times. Then, the mechanical properties are characterized using tensile test on samples submitted at first to different fire time exposure. The evolution of the elastic properties and ultimate stress show that the density of energy is the main factor leading to a change of the mechanical properties and char thickness evolution. Secondly, to characterize the mechanical properties versus temperature, tensile tests are performed on samples submitted in situ to 4 homogeneous temperature conditions up to 150°C. Finally, A thermomechanical model is proposed to predict the behaviour of composite material

Composite pressure vessels for hydrogen storage in fire conditions: Fire tests and burst simulation

International audienceA type IV composite pressure vessel subjected to fire may burst because of the degradation of the outer layers, but when the inner pressure is less than a critical value, leak is observed instead of burst. This phenomenon is due to the heat transfer through the composite shell which leads to liner melting. In order to characterize this failure mechanisms, engulfing fire tests have been performed in the framework of the FireComp project whose objective is to understand and simulate the fire performance of hydrogen storage. An experimental set-up has been implemented to expose the cylinders to fire by the means of gas injectors. A simple FE model has been developed to simulate the coupled effects of mechanical damage and of temperature. This approach is found to accurately predict the time to burst of the composite tank, as well as the transition between burst and leak

Optimization of the Pressure Resistance Welding Process for Nuclear Fuel Cladding Coupling Experimental and Numerical Approaches

An approach coupling experimental tests and numerical simulation of the pressure resistance welding (PRW) process is proposed for optimizing fuel cladding welds for the new generation of nuclear reactors. Several experimental welds were prepared by varying the dissipated energy, which accounts for the effect of electric current and welding time applied during the PRW process. A working zone, a function of both applied dissipated weld energy and plug-displacement, was then identified on the basis of the microscopy observations of the weld defects. In addition, the numerical approach, based on a 2D axisymmetric multi-physics finite element model, was developed to simulate the PRW process in a plug-tube configuration. The proposed model accounted for interactions between the electrical, thermal and mechanical phenomena and the electro-thermo-mechanical contact between the pieces and electrodes. Numerical simulations were first validated by comparison to experimental measurements, notably by comparing the plug-displacement and the size and position of the heat-affected zone (HAZ). They were then used to assess the effect of the applied parameters on the maximum temperature and cumulated plastic strain reached during welding and the effect of the welding force on the quality of the weld. According to the numerical computations, the maximum temperature reached in the weld remains well below the melting temperature. Changing the welding force implies also modifying the applied energy in order to maintain the quality of the welds. Applied to different plug and clad geometries, the proposed model was shown to be useful for optimizing the joint plane for such a welding configuration

Comportement au feu de réservoirs composites de stockage d’hydrogène sous pression

International audienceA type IV composite pressure vessel subjected to fire may burst because of the degradation of the outer layers, but when the inner pressure is less than a critical value, leak is observed instead of burst. This phenomenon is due to the heat transfer through the composite shell which leads to liner melting. In order to characterize this failure mechanisms, engulfing fire tests have been performed in the framework of the FireComp project whose objective is to understand and simulate the fire performance of hydrogen storage. An experimental set-up has been implemented to expose the cylinders to fire by the means of gas injectors. A complete instrumentation of the tank was implemented to follow the behavior of its envelope during and after the fire using thermocouples located inside its composite wall, and pressure measurement inside the vessel. A simple Finite Element model has been developed to simulate the coupled effects of mechanical damage and temperature. This approach accurately predicts the time leading to burst of the composite tank, as well as the transition between burst and leak.L’utilisation de l’hydrogène à grande échelle, et notamment pour les véhicules, nécessite de maîtriser la fiabilité de stockage de ce gaz à très haute pression. Les réservoirs de type IV constitués d’une coque composite enroulée sur un revêtement en polymère, sont aujourd’hui considérés comme une technologie mature. Afin de mieux caractériser les conditions à éviter pour observer une défaillance de ce type de stockage dans des conditions accidentelles, en particulier un incendie, le projet FireComp (projet de recherche pré-normatif de trois ans) vise à caractériser le comportement thermomécanique de ce type de stockag

Optimization of the Pressure Resistance Welding Process for Nuclear Fuel Cladding Coupling Experimental and Numerical Approaches

International audienceAn approach coupling experimental tests and numerical simulation of the pressure resistance welding (PRW) process is proposed for optimizing fuel cladding welds for the new generation of nuclear reactors. Several experimental welds were prepared by varying the dissipated energy, which accounts for the effect of electric current and welding time applied during the PRW process. A working zone, a function of both applied dissipated weld energy and plug-displacement, was then identified on the basis of the microscopy observations of the weld defects. In addition, the numerical approach, based on a 2D axisymmetric multi-physics finite element model, was developed to simulate the PRW process in a plug-tube configuration. The proposed model accounted for interactions between the electrical, thermal and mechanical phenomena and the electro-thermo-mechanical contact between the pieces and electrodes. Numerical simulations were first validated by comparison to experimental measurements, notably by comparing the plug-displacement and the size and position of the heat-affected zone (HAZ). They were then used to assess the effect of the applied parameters on the maximum temperature and cumulated plastic strain reached during welding and the effect of the welding force on the quality of the weld. According to the numerical computations, the maximum temperature reached in the weld remains well below the melting temperature. Changing the welding force implies also modifying the applied energy in order to maintain the quality of the welds. Applied to different plug and clad geometries, the proposed model was shown to be useful for optimizing the joint plane for such a welding configuration

Effect of a coupled thermomechanical loading on the residual mechanical strength and on the surface temperature of wound carbon/epoxy composite

International audienceWound composite structures such as hyperbaric hydrogen tanks may experience accidental situations, for example in case of a fire. The FCH-JU project FireComp aims at better characterizing the conditions that need to be achieved in order to avoid a failure of a composite pressure vessel. This research program involves specific experiments to improve the understanding of loss of strength of composite high-pressure vessels in fire conditions. The present study investigates the effect of a coupled thermomechanical loading (cone calorimeter exposure and, simultaneously, mechanical stress) on the residual strength of a composite material. A specific device combining a cone and a four-point bending bench has been designed. The influence of the coupled aggression is addressed by comparing the temperature on the front and the rear sides, the mass loss, and the residual tensile strength of a set of samples subjected to a heat flux only and a set subjected to a heat flux and a four-point bending. The results do not exhibit a clear effect of the mechanical load: the thermomechanical properties of both sets of samples are similar