Monitoring and simulations of hydrolysis in epoxy matrix composites during hygrothermal aging

In this paper, we studied the water transport in thermoset matrices. We used Fourier Transform Infrared analysis (FTIR) during sorption/desorption experiments to investigate the interaction between sorbed water and the epoxy network. Our results demonstrated that the polymer matrix undergoes hydrolysis. We found that the chemical species involved in the reaction process was the residual anhydride groups. These results support the physical basis of the three-dimensional (3D) diffusion/reaction model. We finally showed that this model is able to reproduce multi-cycle sorption/desorption experiment, as well as water uptake in hybrid metal/epoxy samples. We simulated the 3D distributions of the diffusing water and the reacted water

Modélisation multiphysique et simulation numérique des bains de soudage TIG

It is well reported in the literature that the characteristics of the weld joint and the heat transfer at the solid/liquid interface are highly dependent on the fluid flow in the weld pool. In the present work, we numerically investigate the effects of welding parameters on GTA weld pools developments. A 2D model including the cathode, arc plasma and anode domains is developed to study in-depth stationary GTAW. This also permits to quantify the effects of the chemical composition of the shielding gas, and to study new welding techniques such as GTAW with alternate supply of shielding gases. The study of moving GTAW with filler metal is performed using a hybrid 2D-3D approach. The numerical simulations conducted for horizontal-position welding reveal a huge asymmetry of the weld towards the opposite gravity direction, which is numerically found to be the effect of buoyancy-induced flows and asymmetrical free surface deformation. This defect can be significantly reduced in dissimilar sulfur content welds by placing the low sulfur plate at the bottom.Il est bien rapporté dans la littérature que les caractéristiques du joint soudé ainsi que le transfert de chaleur à l'interface liquide/solide sont fortement dépendants de l'écoulement du métal liquide. Ce travail porte sur l'étude numérique de l'influence des paramétres opératoires de soudage sur les bains de fusion TIG. Un modéle 2D incluant la cathode, le plasma d'arc et l'anode est développé pour l'étude du soudage TIG spot. Il permet également de quantifier les effets de la composition chimique du gaz, et de simuler des techniques innovantes tel que le soudage avec gaz pulsé. Le soudage TIG avec torche mobile et apport de matiére est modélisé à l'aide d'une approche hybride 2D-3D. Les simulations numériques pour des positions de soudages horizontales révèlent une dissymétrie de la soudure dans la direction opposée à la gravité, ce qui est dû à l'action de la flottabilité et à la déformation assymétrique de la surface libre. Ce défaut peut être considérablement réduit lors du soudage de matériaux à taux de soufre différents, en plaçant la pièce bas soufre en bas