Adhésion | EPFL Graph Search

En physique et en mécanique, l’adhésion est l’ensemble des phénomènes physico-chimiques qui se produisent lorsque l’on met en contact intime deux matériaux, dans le but de créer une résistance mécanique à la séparation. Une fois le contact établi, l’énergie nécessaire pour réaliser la séparation s’appelle énergie d’adhésion (énergie par unité de surface). Elle ne doit pas être confondue avec l’adhérence, qui est au contraire la force (par unité de surface) nécessaire pour réaliser cette même séparation. L’adhésion est soit directe, soit médiée par un matériau intermédiaire. Adhésion directe L'adhésion directe entre matériaux est rare. Elle a lieu uniquement pour des matériaux très lisses et extrêmement propres (mica ou silicium par exemple), que l'on parvient à mettre en contact intime, c'est-à-dire à des distances de l'ordre de la taille atomique (nanomètre). Elle est donc souvent impossible si les surfaces sont rugueuses. L'adhésion directe est liée principalement, mais

Couplage d'une loi d'adhésion à une loi de contact avec frottement pour l'étude de la décohésion dans les matériaux composites

Christian Talon

In this thesis, an original law of adhesion is developed and then coupled to the classical law of unilateral contact with threshold friction, in order to study the phenomenon of fibre/matrix debonding in composite materials. This tribological law is developed within the framework of standard generalized materials adapted to interfaces. Thus, the law is derived from a free energy potential ψc and a dissipation potential Φc. The adhesive interface is interpreted as a bundle of links connecting the two contact surfaces. Each link is assumed to have a plastic behavior with softening and damage, caused by stretching, to represent the loss of adhesion. An internal variable ga measuring an irreversible adhesive gap is introduced and associated by energetic duality to an adhesive stress pa. The ranges of ga and pa are limited by two characteristic constants of adhesion, gM and pM respectively. pM is the maximum adhesive tension below which the links remain elastic. Above this limit, debonding and damage of the links occur as ga increases. Once ga reaches the value gM, total rupture of the adhesive bond occurs. This adhesion law is then mounted in parallel to the contact and friction laws into a unique law. The law is regularized using either the approximate penalty method or the exact augmented Lagrangian method, in option. The regularized laws are implemented in a node-to-node contact element of the finite element code TACT. The adhesive force is computed by means of a predictor-corrector with projection algorithm for integrating the evolution of ga, and the relevant Jacobian tensors required for the resolution of non-linearities by the iterative scheme of Newton are calculated. This is accomplished for the penalty and the augmented Lagrangian regularizations. A traction test of a glass/epoxy interface in the normal direction is designed and used to experimentally determine the parameters pM and gM of such an interface (pM directly and gM indirectly). Numerical simulations of adhesion between a rigid punch and an elastic half-space enable the comparison of the proposed model of adhesion to the classical theories of adhesion. A numerical simulation of the standard pull-out test of a fibre embedded in a matrix is then performed, and the numerical shear distribution along the interface is compared to the analytical one existing for this experiment. The results are in good agreement with existing ones. Finally, a crack propagation in a fibrous composite is simulated.

EPFL2002

Biodegradation and Antimicrobial Properties of Zinc Oxide-Polymer Composite Materials for Urinary Stent Applications

Lorenzo Lucherini

Research advancements in the field of urinary stents have mainly been in the selection of materials and coatings to address commonly faced problems of encrustation and bacterial adhesion. In this study, polylactic acid (PLA) and polypropylene (PP) were evaluated with zinc oxide (ZnO) coating to assess its ability to reduce or eliminate the problems of encrustation and bacteria adhesion. PLA and PP films were prepared via twin screw extrusion. ZnO microparticles were prepared using sol-gel hydrothermal synthesis. The as-prepared ZnO microparticles were combined in the form of a functional coating and deposited on both polymer substrates using a doctor blade technique. The ZnO-coated PP and PLA samples as well as their uncoated counterparts were characterized from the physicochemical standpoints, antibacterial and biodegradation properties. The results demonstrated that both the polymers preserved their mechanical and thermal properties after coating with ZnO, which showed a better adhesion on PLA than on PP. Moreover, the ZnO coating successfully enhanced the antibacterial properties with respect to bare PP/PLA substrates. All the samples were investigated after immersion in simulated body fluid and artificial urine. The ZnO layer was completely degraded following 21 days immersion in artificial urine irrespective of the substrate, with encrustations more evident in PP and ZnO-coated PP films than PLA and ZnO-coated PLA films. Overall, the addition of ZnO coating on PLA displayed better adhesion, antibacterial activity and delayed the deposition of encrustations in comparison to PP substrates.

MDPI2020

Couplage d'une loi d'adhésion à une loi de contact avec frottement pour l'étude de la décohésion dans les matériaux composites

Christian Talon

EPFL2002