Compréhension et maîtrise de l’adhésion aux interfaces lors du surmoulage d’élastomères thermoplastiques

Static sealing solutions in the automotive industry are produced with vulcanized thermoplastic elastomers. These parts are manufactured by overmolding, a process which consists in joining two extruded profiles by injection. The development of adhesion at the interface of this type of polymers is strongly thermo-dependent. The quality of the contact can be studied from a thermal or mechanical point of view. This thesis aims at establishing, for the first time, a link between the thermal and mechanical quality of the contact at the interface between these materials. For this purpose, an original instrumented device of overmolding has been developed, allowing to calculate by inverse method the surface temperatures and the heat flux densities, and thus the thermal resistance of contact, reflecting the thermal quality of the contact. This device is also used to perform double cantillever beam tests, allowing to quantify the quality of the interface from a mechanical point of view. A correlation is then established between these two quantities. Finally, the knowledge acquired during the study is applied on the industrial device, and the process and material improvement are detailed.Les solutions d’étanchéité statiques dans le secteur automobile sont produites en élastomères thermoplastiques vulcanisés. Ces pièces sont fabriquées par surmoulage, en assemblant par injection deux profils en élastomères thermoplastiques vulcanisés extrudés. Le développement de l’adhésion à l’interface de ce type de polymères est fortement thermo-dépendant. La qualité du contact peut être étudiée d’un point de vue thermique ou mécanique. Ce travail de thèse s’attache à établir, pour la première fois, un lien entre la qualité thermique et mécanique du contact à l’interface entre ces matériaux. Pour cela, un dispositif original instrumenté de surmoulage a été développé, permettant de calculer par méthode inverse les températures de surface et les densités de flux de chaleur, et donc la résistance thermique de contact, reflétant la qualité thermique du contact. Ce dispositif est également utilisé pour réaliser des essais de double cantillever beam, permettant de quantifier d’un point de vue mécanique la qualité de l’interface. Une corrélation est ensuite établie entre ces deux grandeurs. Enfin, les connaissances acquises lors de l’étude sont appliquées sur le dispositif industriel, et des pistes d’amélioration procédé et matière sont détaillées

Understanding and control of adhesion at interfaces during the overmolding of thermoplastic elastomers

Les solutions d’étanchéité statiques dans le secteur automobile sont produites en élastomères thermoplastiques vulcanisés. Ces pièces sont fabriquées par surmoulage, en assemblant par injection deux profils en élastomères thermoplastiques vulcanisés extrudés. Le développement de l’adhésion à l’interface de ce type de polymères est fortement thermo-dépendant. La qualité du contact peut être étudiée d’un point de vue thermique ou mécanique. Ce travail de thèse s’attache à établir, pour la première fois, un lien entre la qualité thermique et mécanique du contact à l’interface entre ces matériaux. Pour cela, un dispositif original instrumenté de surmoulage a été développé, permettant de calculer par méthode inverse les températures de surface et les densités de flux de chaleur, et donc la résistance thermique de contact, reflétant la qualité thermique du contact. Ce dispositif est également utilisé pour réaliser des essais de double cantillever beam, permettant de quantifier d’un point de vue mécanique la qualité de l’interface. Une corrélation est ensuite établie entre ces deux grandeurs. Enfin, les connaissances acquises lors de l’étude sont appliquées sur le dispositif industriel, et des pistes d’amélioration procédé et matière sont détaillées.Static sealing solutions in the automotive industry are produced with vulcanized thermoplastic elastomers. These parts are manufactured by overmolding, a process which consists in joining two extruded profiles by injection. The development of adhesion at the interface of this type of polymers is strongly thermo-dependent. The quality of the contact can be studied from a thermal or mechanical point of view. This thesis aims at establishing, for the first time, a link between the thermal and mechanical quality of the contact at the interface between these materials. For this purpose, an original instrumented device of overmolding has been developed, allowing to calculate by inverse method the surface temperatures and the heat flux densities, and thus the thermal resistance of contact, reflecting the thermal quality of the contact. This device is also used to perform double cantillever beam tests, allowing to quantify the quality of the interface from a mechanical point of view. A correlation is then established between these two quantities. Finally, the knowledge acquired during the study is applied on the industrial device, and the process and material improvement are detailed

Thermal and mechanical interface behaviour of overmoulded vulcanized thermoplastic elastomers

International audienceVulcanized thermoplastic elastomers (TPV) are widely used in the automotive industry for the manufacturing of weather seals by overmoulding a TPV on an extrudate TPV. This process is assumed to be a fusion bonding in which the quality of the thermal contact is essential to develop the mechanical strength of the assembly. From a thermal point of view, the contact can be quantified by a thermal contact resistance (TCR) which consider the flux lines constriction and their lengthening. From a mechanical point of view, the contact can be qualified by Double Cantilever Beam tests through the calculation of the critical energy restitution rate. The influence of the overmoulding conditions on the contact thermal resistance value and on the critical energy restitution rate is discussed. A correlation was found between these two quantities

Développement d'un dispositif expérimental de surmoulage permettant la mesure de la résistance thermique de contact pièce polymère/pièce polymère en conditions industrielles

International audienceDans l'industrie automobile, les joints d'étanchéité sont fabriqués par surmoulage de profils en élastomères extrudés. Les élastomères thermoplastiques vulcanisés (TPV) constituent un des types d'élastomères utilisés. Lors du procédé de surmoulage, la qualité du contact thermique est essentielle pour développer la résistance mécanique de l'assemblage. Cet article vise à évaluer, pour la première fois, la qualité du contact thermique entre le TPV extrudé et le TPV injecté pendant les phases de maintien et de refroidissement en conditions procédé. A cette fin, un moule expérimental instrumenté a été conçu, permettant de mesurer les champs de température dans chaque polymère pendant le cycle de surmoulage. Les relevés de température ainsi que les positions des thermocouples servent alors de données d’entrée à la méthode séquentielle inverse de Beck. Les informations quantitatives non intrusives de température de surface et de flux de chaleur ainsi obtenues, permettent d’identifier la Résistance Thermique de Contact (RTC) sur le cycle d’élaboration complet. Il a été observé que les variations de la RTC à l’interface polymère semblent être liées au déséquilibre thermique engendré lors du procédé qui génère un champ de transformation hétérogène

Thermomechanical Behaviour and Interface of Overmoulded Soft Thermoplastic Vulcanizate Elastomers

International audienceThe influence of melt injection temperature on the thermomechanical behaviour of soft–soft overmoulded vulcanized thermoplastic elastomers (TPV) with different elastic properties was studied. Samples with two different overmoulding temperatures were tested under uniaxial loading conditions. The full deformation and temperature fields in each TPV were determined using digital image correlation technique and infrared thermography, respectively. The maximum interface strength was found to be equal to 70N for a maximum injection temperature of 260∘C, which is consistent with the fact that high temperatures promote interdiffusion between the molten TPV and the TPV insert. The two TPV have different stiffness, leading to a significant change of the interface position along the specimens during stretching and to a significant necking in the softer material. The zone of influence of the interface in terms of stretch gradient is very different in size from one TPV to the other. In addition, thermal investigations have shown that the elasticity of the two TPV is due to both entropic and non-entropic effects, the former being the most significant at large strains

Low incidence of SARS-CoV-2, risk factors of mortality and the course of illness in the French national cohort of dialysis patients

International audienceThe aim of this study was to estimate the incidence of COVID-19 disease in the French national population of dialysis patients, their course of illness and to identify the risk factors associated with mortality. Our study included all patients on dialysis recorded in the French REIN Registry in April 2020. Clinical characteristics at last follow-up and the evolution of COVID-19 illness severity over time were recorded for diagnosed cases (either suspicious clinical symptoms, characteristic signs on the chest scan or a positive reverse transcription polymerase chain reaction) for SARS-CoV-2. A total of 1,621 infected patients were reported on the REIN registry from March 16th, 2020 to May 4th, 2020. Of these, 344 died. The prevalence of COVID-19 patients varied from less than 1% to 10% between regions. The probability of being a case was higher in males, patients with diabetes, those in need of assistance for transfer or treated at a self-care unit. Dialysis at home was associated with a lower probability of being infected as was being a smoker, a former smoker, having an active malignancy, or peripheral vascular disease. Mortality in diagnosed cases (21%) was associated with the same causes as in the general population. Higher age, hypoalbuminemia and the presence of an ischemic heart disease were statistically independently associated with a higher risk of death. Being treated at a selfcare unit was associated with a lower risk. Thus, our study showed a relatively low frequency of COVID-19 among dialysis patients contrary to what might have been assumed