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

Thermomechanical and hygroelastic properties of an epoxy system under humid and cold-warm cycling conditions

In this paper, we study the hygrothermal aging of an anhydride-cured epoxy under temperature and hygrometry conditions simulating those experienced by an aircraft in wet tropical or subtropical regions. Gravimetric and dimensional measurements were performed and they indicate that there are three stages in this aging process: the first one, corresponding to the early cycles can be called the “induction stage”. The second stage of about 1000 cycles duration, could be named the “swelling stage”, during which the volume increase is almost equal to the volume of the (liquid) water absorbed. Both the first and second stages are accompanied by modifications of the mechanical properties and the glass transition temperature. During the third (“equilibrium”) stage, up to 3000 cycles, there is no significant change in the physical properties despite the continuous increase of water uptake. This can be explained by the fact that only physically sorbed water can influence physical properties

Construction of a micromechanics-based intralaminar mesomodel, and illustrations in ABAQUS/Standard

International audienceThe recent advances in the modeling of degradations in stratified composites have led to improved models on all scales. In particular, today, micromechanics derived in a generic framework enables one to define a reference virtual material which integrates most of the knowledge of a material. Thus, a model using damage mechanics on the mesoscale and usable for structural analysis can be built as a homogenized version of this reference model through previously-developed bridges. The objective is to derive a refined model worthy of micromechanics confidence, but transposable into a commercial code (here, ABAQUS/Standard)

Micromodel-based simulations for laminated composites

International audienceWe develop a calculation strategy for the simulation of a complete microscopic model. This strategy enables one to account for damage mechanisms in laminated composites. The model mixes discrete and continuous approaches by introducing potential rupture surfaces and a damageable continuous medium. This approach requires suitable calculation tools unavailable in industrial analysis codes. The strategy presented is multiscale in space and is based on a decomposition of the domain into substructures and interfaces. This strategy enables one to simulate complex problems with multiple cracks. In practice, to use such a model, the strategy must be improved in order to handle very large numbers of substructures and interfaces and to estimate the rupture criteria for the surfaces introduced into the model. We provide simple examples which demonstrate the capabilities of the microscopic model

Retours d'expériences sur la mise en oeuvre d'une Licence Professionnelle internationalisée en Réseaux et Télécommunications

Dossier spécial : Formations internationalesInternational audienceUn groupe d'étudiants de la Licence Professionnelle " Réseaux Sans Fil et Sécurité " de l'IUT de Grenoble a été internationalisé depuis la rentrée 2007. Ce groupe est constitué d'étudiants provenant de divers pays, en majorité non francophones, ce qui signifie que tous les enseignements sont en anglais. L'objectif de cette formation est de mettre en oeuvre une formation anglophone, dans un contexte international. Les étudiants préparent la Licence soit en inscription directe, soit par l'intermédiaire d'accord d'échanges bilatéraux (Brésil, bientôt Malaisie ou Palestine) ou d'accords ERASMUS, ils peuvent dans ces cadres obtenir pour certains un double-diplôme. La mobilité est encouragée, y compris pour les étudiants français qui participent à l'aventur

The effect of z-binding yarns on the electrical properties of 3D woven composites

Electrical resistance monitoring (ERM) has been used to study the effect of the z-binding yarns on the initial electrical resistance (ER) and its change of three architectures of 3D woven carbon fibre composites namely (orthogonal “ORT”, layer-to-layer “LTL” and angle interlock “AI”) when tested in tension. Specimens are loaded in on-axis “warp” and off-axis “45°” directions. In-situ ERM is achieved using the four-probe technique. Monotonic and cyclic “load/unload” tests are performed to investigate the effect of piezo-resistivity and residual plasticity on resistance variation. The resistance increase for the off-axis loaded specimens (∼90%) is found to be higher than that of their on-axis counterparts (∼20%). In the case of cyclic testing, the resistance increase upon unloading is irreversible which suggests permanent damage presence not piezo-resistive effect. At the moment, it is difficult to obtain a direct correlation between resistance variation and damage in 3D woven composites due to the complexity of the conduction path along the three orthogonal directions, however this study demonstrates the potential of using ERM for damage detection in 3D woven carbon fibre-based composites and highlights the challenges that need to be overcome to establish ERM as a Structural Health Monitoring (SHM) technique for such material systems

A fully coupled diffusion-reaction scheme for moisture sorptionedesorption in an anhydride-cured epoxy resin

Thermoset materials frequently display non-classical moisture sorption behaviors. In this paper, we investigated this issue from an experimental point of view as well as in terms of modeling the water transport. We used the gravimetric technique to monitor water uptake by epoxy samples, with several thicknesses exposed to different levels of humidity during absorption and desorption tests. Our results revealed that the polymer displays a two-stage behavior with a residual amount of water that is desorbed progressively. We proposed a phenomenological reaction-diffusion scheme to describe this behavior. The model describes water transport as a competition between diffusion and the reaction, during which the local diffusivity and solubility depend on the local advancement of the reaction. We then implemented our model using COMSOL Multiphysics and identified it using a MATLAB-COMSOL optimization tool and the experimental data. We discussed the relation between the hydrophilicity of the product of the reaction and the diffusion behavior. We examined the reaction-induced modification of the water concentration field. It is worth noting that part of the phenomenology can be explained by the presence of hydrolyzable groups