Élaboration d'une solution de collage pour les assemblages travaillant à haute et basse température : le Joint Multi-Adhésifs. Mise en oeuvre de la solution technologique et prédiction de son comportement en service.

Une solution d'assemblage par collage des modules de puissance utilisés dans le ferroviaire à basse et haute température est développée dans ce travail. Nous proposons l'utilisation d'un Joint Multi-Adhésifs (JMA) qui se compose de deux types d'adhésifs, un adhésif résistant à haute température et un adhésif résistant à basse température. Ces deux adhésifs sont disposés sous forme de trois joints séparés et mis côte à côte. Afin de valider ce concept pour notre application, nous avons formulé des adhésifs hybrides époxyde/silicone de différentes nuances. Puis, une caractérisation thermomécanique globale a justifié la sélection de deux nuances à utiliser au sein du JMA. L'étude de leur tenue au vieillissement thermo-oxydatif isotherme a permis de déduire les mécanismes de dégradation les plus probables. De plus, lors du vieillissement isotherme des adhésifs, la prédiction de la perte de masse est réalisée par la technique de la courbe maîtresse, et le comportement en fluage par la méthode de la superposition temps/temps de vieillissement. Des simulations numériques ont permis de dresser une cartographie des contraintes lors dune sollicitation dynamique telle que le fluage. ABSTRACT : This work is dealing with a bonding solution associating two adhesives in a same joint without interdiffusion for railways transport application. This concept, called Multi-Adhesive Joint, is a combination of an adhesive for high temperatures use (High Temperature Adhesive (HTA)) and another for low temperatures (LTA) because of a large temperature range in use. We have formulated and thermo-mechanically tested epoxy/silicone "hybrid" adhesive by changing the silicone content. From ageing studies in several thermal conditions, degradation behaviours are investigated and predictive laws are established. In addition, numerical simulations modelize the mixed-joints behaviour subjected to creep solicitations

Impact resistance of composite materials under biaxal preloading

The first aim of this study is to analyze the impact behavior of pre-loaded composite. Indeed, a bi-axial load is applied to the composite specimen, in order to keep in touch with a real case of composite fuselage. Then, this pre-loaded specimen is impacted by a pendulum. The used energy and velocity are weak in order to be in the case of low-energy and low-velocity impact. The second aim of this study is to develop and design a pendulum device to be integrated to the biaxial fatigue loading. Moreover, two Non Destructive Inspections (Sonoscan and InfraRed Thermography) is used in order to establish links between pre-load and induced impact damage

Evaluation of the real contact area in three-body dry friction by micro-thermal analysis

Many tribological properties and wear mechanisms occurring on the micro-and nanoscale are strongly controlled by the so-called real contact area (Ar) which is a small fraction of the nominal or apparent contact area (Aa). The determination of Ar is often based on either (i) a geometrical approach describing the real geometry of contacting surfaces or (ii) a mechanical approach involving contact mechanics and physical-mechanical properties. In addition some experimental methods have also been attempted but they generally do not take into account the presence of third body at the interface—i.e. the wear debris trapped within the contact. In this paper we propose an experimental approach to estimate the dynamic real contact area from the operating parameters (Fn, v, T) and the tribological responses (μ, Ft) in presence of third body. A scanning thermal microscope (SThM) is used for determining both the thermal conductivity of the third body and the relationship between the contact temperature and the thermal power really dissipated at the micro-asperity level. These results are combined with a thermal model of the macro-tribocontact for computing the real contact area and the real contact pressure. Validation of these results is carried out using a classical Greenwood Williamson model and finite element models built from the real AFM maps

Élaboration d'une solution de collage pour les assemblages travaillant à haute et basse température (le Joint Multi-adhésif)

Une solution d'assemblage par collage des modules de puissance utilisés dans le ferroviaire à basse et haute température est développée dans ce travail. Nous proposons l'utilisation d'un Joint Multi-Adhésifs (JMA) qui se compose de deux types d'adhésifs, un adhésif résistant à haute température et un adhésif résistant à basse température. Ces deux adhésifs sont disposés sous forme de trois joints séparés et mis côte à côte. Afin de valider ce concept pour notre application, nous avons formulé des adhésifs hybrides époxyde/silicone de différentes nuances. Puis, une caractérisation thermomécanique globale a justifié la sélection de deux nuances à utiliser au sein du JMA. L'étude de leur tenue au vieillissement thermo-oxydatif isotherme a permis de déduire les mécanismes de dégradation les plus probables. De plus, lors du vieillissement isotherme des adhésifs, la prédiction de la perte de masse est réalisée par la technique de la courbe maîtresse, et le comportement en fluage par la méthode de la superposition temps/temps de vieillissement. Des simulations numériques ont permis de dresser une cartographie des contraintes lors dune sollicitation dynamique telle que le fluage.This work is dealing with a bonding solution associating two adhesives in a same joint without interdiffusion for railways transport application. This concept, called Multi-Adhesive Joint, is a combination of an adhesive for high temperatures use (High Temperature Adhesive (HTA)) and another for low temperatures (LTA) because of a large temperature range in use. We have formulated and thermo-mechanically tested epoxy/silicone "hybrid" adhesive by changing the silicone content. From ageing studies in several thermal conditions, degradation behaviours are investigated and predictive laws are established. In addition, numerical simulations modelize the mixed-joints behaviour subjected to creep solicitations.TOULOUSE-ENSEEIHT (315552331) / SudocTARBES-ENIT (654402301) / SudocSudocFranceF

Bi-axial fatigue analysis by stereo-correlation measurement

This paper deals with the development of an experimental method to make measurements by the digital image correlation technique during a dynamic test on a biaxial tensile system. The aim of this method is to be able to cover a complete cycle of a dynamic test, regardless of its form and to follow a position during a long time test. Results are presented for different measurement fields

Rheological and crystallization behaviors of low processing temperature poly(aryl ether ketone)

International audienceA new low melting temperature poly(aryl ether ketone) (PAEK) thermoplasticpolymer (Victrex AE 250) was investigated through thermal and rheologicalanalysis of films and flakes. DSC was assigned to evaluate the influence ofcooling rate on crystallinity and thermal transitions. Rheometry was used toassess its flowing behavior through the evaluation of dynamic moduli andcomplex viscosity in the melted state. The relaxation times were found fromthe rheological curves: they are between a few ms to 200 ms for AE 250, lowerthan those found for PEEK 450, meaning a faster mobility of macromolecules.The thermal activation energy,Eaobtained from Time Temperature Superposi-tion is the same for films and flakes in spite of a lower viscosity for flakes. Themolecular weight between entanglements is evaluated at 8000 g.mol1forFMc and 13,000 for FLc, it is compared to the value of about 2000 g.mol1found for PEEK 450 with the same procedure. Also, the viscosity was com-pared to other commercial PAEK such as PEEK and PEKK based on data fromthe literature. This polymer appears very efficient to compete with high perfor-mance thermoplastics to be processed by compression molding, out of auto-clave consolidation, additive manufacturing, and welding

Mechanical behavior of amorphous PEEK in the rubbery state

International audienceThe mechanical behavior of amorphous poly(etheretherketone) (PEEK) was investigated just above the glass-transition temperature (Tg). In the rubbery state, the mobility of the macromolecular chains reveals a drop of mechanical properties with the onset of cold-crystallization as limit, as shown by dynamic-mechanical and thermal analysis. For an isothermal at 155°C, the onset of cold-crystallization begins after 40 minutes, this delay is long enough to perform static mechanical analysis. Thus, the understanding of the mechanical behavior was thoroughly investigated. From this study, different contributions are highlighted in the rubbery state: viscous and elastoplastic

Ultrasonic welding of CF/PEEK composites: Influence of welding parameters on interfacial temperature profiles and mechanical properties

International audienceThis work focuses on ultrasonic (US) welding of CF/PEEK composite containing a PEI layer at the interface. Welding time, load and amplitude are defined as the welding parameters. The influence of each parameter is assessed by temperature measurement and mechanical tests on US welding specimens. 80-μm diameter thermocouples are integrated into the interfacial polymer layer for in-situ monitoring of the maximum temperature profile during the welding phase. Only welding time and welding load have an influence on both temperatures and lap shear strengths (LSS). The highest LSS are close to 50 MPa, and the temperature achieved in those cases is around 580◦C. Interfacial fractures occur in both PEI and PEEK. PEI-based fracture is mostly brittle whereas PEEK-based fracture is a competition between brittle and ductile fracture. Finally, a fracture within the PEI/PEEK blend can occur. Raman spectroscopy is effectively used to quantify the thickness of this blend zone, it is about 0.075 mm