Polymeric adhesives play an increasingly critical role in today's engineering designs. When used, adhesively bonded components reduce or eliminate the need for bolted or welded connections. In many cases, this can reduce stress concentrations and weight. With energy dissipating adhesives, noise and vibration reduction are possible, as is the use of unique or complicated designs that could not otherwise be constructed. Adhesive properties however, can vary greatly with time, temperature, and environmental exposure conditions such as moisture. It is therefore critical, to understand the behavior of adhesives over the range of conditions that a bonded component might experience. In this work, the behavior of a urethane-based adhesive was characterized and long-term durability predictions were developed as a result of the data collected. The popular T-peel sample geometry has been used extensively in this study to explore the mechanics of a bonded system and the resulting impact on adhesive durability. The T-peel specimens used, consist of two aluminum sheets or adherends bonded together, with tabs bent back in the shape of a "T" for gripping in a universal load frame. Unlike some other test geometries, T-peel samples are often made with relatively thin adherends that may experience significant plastic deformation during testing. This extraneous energy dissipation greatly complicates the analysis to extract meaningful fracture properties of the adhesive. During testing, the load required to propagate a crack in the adhesive layer is measured at fixed displacement rates. The total system energy can then be partitioned into the energy dissipated within the adhesive (fracture energy), and the energy dissipated through plastic work in bending of the adherends. By performing these tests at different temperatures and rates, the calculated fracture energies span a wide range of possible material behavior. Using the principles of Time Temperature Superposition (TTS), the collected data can be shifted to different times or temperatures. This behavior is well understood in polymer physics, and is made possible with material specific "shift factors". By using the principles of TTS, data collected in in a relatively short experimental window, can be used to accurately predict the behavior of the adhesive in years or even decades. In this work, nearly 200 T-peel samples were tested in four different studies. A preliminary set of unaged specimens was used to develop testing and data analysis methodologies. A second set of unaged samples was tested over a wide range of temperatures and rates, in addition to a third group, subjected to constant moisture and cyclically varying temperature. The final set of specimens, was exposed to 20 separate isothermal aging conditions. The experimental data showed that the 400+ cycles, were insufficient to statistically distinguish these samples from their unaged counterparts. Additionally, samples aged for up to 2000 hours in a dry environment, or 500 hours in a wet environment, showed no reduction in fracture energies in comparison with unaged samples. Specimens aged for more than 500 hours however, were observed to have a significant decrease in fracture energy values. Strong correlations between the thickness of the adhesive layer and estimated fracture energy values were found in this study. As adhesive thickness varied substantially due to manufacturing differences in the specimens tested, new analysis techniques were developed to deal with the variations in adhesive thickness. A MATLAB code based on the ICPeel program, was written to provide a spatial variation of parameters such as adhesive thickness, peel load, and fracture energy. This provided additional insights into the behavior of these T-peel coupons, and prompted the investigation of the Universal Peel Diagram concept. While this diagram was not found to be applicable to the adhesive tested in this study, the analysis indicated that T-peel coupons could be multivalued. That is, a single measured load value does not always describe an adhesive's fracture energy (as is widely believed). Depending on the sample's geometry and material properties, several measured loads could cause debonding. This has potentially far reaching implications on the selection of appropriate T-peel test geometries, as a single measured load is often assumed to correlate to an adhesive's true fracture energy. In this work, both aged and unaged T-peel specimens were tested and the basis of the Universal Peel Diagram investigated. Given sufficient exposure times to moisture, elevated temperatures were found to significantly reduce the amount of energy dissipated in the urethane-based adhesive. Additionally, the Universal Peel Diagram indicated that for some systems, the load required for debond is in fact, multivalued. Therefore, care should be taken when designing a T-peel test configuration to avoid the multivalued regions. / Master of Science / Polymeric adhesives play an increasingly critical role in today's engineering designs. When used, adhesively bonded components reduce or eliminate the need for bolted or welded connections, reducing their weight in the process. With adhesives, noise and vibration reduction are possible, as is the use of unique or complicated designs that could not otherwise be constructed. Adhesive properties, however, can vary greatly with time, temperature, and other environmental exposure conditions such as moisture. It is therefore critical to understand the behavior of adhesives over the range of conditions that a bonded component might experience. In this work, the behavior of a urethane-based adhesive was characterized in order to develop long-term durability predictions. Numerous test methods have been developed to characterize the behavior of adhesively bonded joints. In this work, T-peel specimens were used consisting of two aluminum sheets (the adherends), bonded together with tabs bent back in the shape of a "T" for gripping in a universal load frame. During testing, the load required to propagate a crack in the adhesive layer is measured. An outcome of this measurement and subsequent data analysis is the fracture energy—a measure of the effectiveness of the adhesive in transferring loads. If we perform these tests at different temperatures and loading rates, we can determine fracture energy values which span a wide range of possible material behavior. Using principles from basic polymer physics, the collected data can be shifted to different times or temperatures enabling us to accurately predict the behavior of the adhesive over years or even decades. In this work, nearly 200 T-peel samples were tested in four different studies. A preliminary set of unaged specimens was used to develop testing and data analysis methodologies. Unaged and cyclically (temperature) aged samples were tested over a wide range of temperatures and rates. The fourth set of specimens was subjected to 20 separate isothermal aging conditions and also tested at different temperatures and rates. The experimental data showed that the 400+ temperature cycles were insufficient to damage these samples significantly. Additionally, samples aged for up to 2000 hours in a dry environment, or 500 hours in a wet environment showed no reduction in performance in comparison with unaged samples. Specimens aged for more than 500 hours in a wet environment however, demonstrated a significant decreases in fracture energy values. Strong correlations between the thickness of the adhesive layer and estimated fracture energy values were found in this study, and new analysis techniques were developed to analyze the effect of these thickness variations on the joint performance.

This thesis presents the results of testing and modeling conducted to characterize the performance of 3M™ VHB™ structural glazing tape in both shear and tension. Creep rupture testing results provided the failure time at a given static load and temperature, and ramp-to-fail testing results provided the ultimate load resistance at a given rate of strain and temperature. Parallel testing was conducted on three structural silicone sealants to compare performance. Using the time temperature superposition principle, master curves of VHB tape storage and loss moduli in shear and tension were developed with data from a dynamic mechanical analyzer (DMA). The thermal shift factors obtained from these constitutive tests were successfully applied to the creep rupture and ramp-to-fail data collected at 23°C, 40°C, and 60°C (73°F, 104°F, and 140°F), resulting in master curves of ramp-to-fail strength and creep rupture durability in shear and tension. A simple linear damage accumulation model was then proposed to examine the accumulation of wind damage if VHB tape is used to attach curtain wall glazing panels to building facades. The purpose of the model was to investigate the magnitude of damage resulting from the accumulation of sustained wind speeds that are less than the peak design wind speed. The model used the equation derived from tensile creep rupture testing, extrapolated into the range of stresses that would typically be generated by wind loading. This equation was applied to each individual entry in the data files of several real wind speed histories, and the fractions of life used at each entry were combined into a total percentage of life used. Although the model did not provide evidence that the established design procedure is unsafe, it suggested that the accumulation of damage from wind speeds below the peak wind speed could cause a VHB tape mode of failure that merits examination along with the more traditional peak wind speed design procedure currently recommended by the vendor. / Master of Science

L’objectif de cette thèse est de proposer une stratégie simplifiée et précise pour caractériser et modéliser le comportement mécanique des polymères amorphes de l'état quasi-fluide à l'état solide.L'étude a été réalisée sur des PMMA de masses molaires et de degré de réticulations différentes.D’abord, le comportement mécanique dans le domaine viscoélastique linéaire est étudié à l'aide de tests DMTA et rhéologiques. Il ressort de l’étude que l'augmentation de la masse molaire et du degré de réticulation augmentait les modules de stockage et de perte en tant que la transition α. En parallèle, l'utilisation du principe de superposition temps-température a permis de déterminer «des vitesses de déformation équivalentes à la température de référence».Ensuite, le comportement mécanique à grande déformation est étudié par essais cycliques en traction uni-axial et de cisaillement à haute température et couplés à la DIC. De plus, les effets de la vitesse de déformation et de la température ont été couplés grâce à "vitesse de déformation équivalent à la température de référence" extrait des observations dans le domaine linéaire. Les résultats ont montré que cibler la même vitesse de déformation équivalente conduira aux mêmes courbes contrainte-déformation, c'est-à-dire la même réponse mécanique. Ceci permet de réduire le nombre de tests expérimentaux nécessaires pour caractériser le comportement mécanique des polymères amorphes.Enfin, un modèle basée dans un cadre thermodynamique a été utilisée pour reproduire la réponse mécanique des PMMAs à grande déformation. Le modèle présentait un bon accord avec les données expérimentales, étant capable de reproduire des comportements visco-élasto-plastiques, viscoélastiques, hyperélastiques et visco-hyperelastiques pour la traction cyclique. / The present PhD thesis proposes a simplified and accurate strategy for characterising and modelling the mechanical behaviour of amorphous polymers from the quasi-fluid state up to the solid state.The study was carried out on PMMAs with different molar masses and crosslinking degree.First, we addressed the mechanical behaviour in the linear viscoelastic domain using DMTA and rheological tests. Results showed that increasing the molar mas and crosslinking degree increased the elastic and loss moduli as the α-transition. In parallel, using the time-temperature superposition principle allowed determining “equivalent strain rates at reference temperature”.Then, we performed uniaxial tensile and shear uploading-unloading tests at high temperature and coupled with DIC, to characterise the mechanical behaviour at large strain. Additionally, strain rate and temperature effects were coupled by means of the “equivalent strain rate at reference temperature” extracted from observations in the linear domain. Results showed that targeting the same equivalent strain rate lead to the same stress-strain curves, i.e. same mechanical response. This allows reducing the number of experimental tests needed to characterise the mechanical behaviour of amorphous polymers.Finally, a constitutive modelling based in a thermodynamics framework, was used to reproduce the mechanical response of the PMMAs at large deformation. The model presented a good agreement with the experimental data, being able to reproduce viscoelastoplastic, viscoelastic, hyperelastic and viscohyperelastic behaviours for cyclic loading tensile.

Le programme de recherche développé dans le cadre de cette thèse a pour principal objectif de concevoir, réaliser et valider une méthodologie d'étude des effets du vieillissement des interfaces collées, basée sur l'utilisation d'un dispositif de fluage innovant pouvant être couplé à un vieillissement hygrothermique. Celui-ci reprend la configuration classique de joint à double recouvrement mais permet de solliciter sous charge constante l'assemblage collé béton/composite. Il présente de plus certaines spécificités (zones de joint non sollicitées, compatibilité avec une machine d'essai à simple recouvrement existante,...) qui permettent de recueillir un grand nombre de résultat expérimentaux complémentaires. En premier lieux, nos travaux présentent une synthèse bibliographique retraçant le contexte du renforcement par composites collés et précisant les principaux mécanismes physico-chimiques susceptibles d'affecter la durabilité des adhésifs. Le manuscrit décrit ensuite les travaux expérimentaux menés pour étudier le comportement mécanique et physico-chimique des deux adhésifs sélectionnés pour la réalisation des joints collés béton/composites. Finalement, une approche prédictive basée sur i) des tests de fluage thermo-stimulés, ii) sur l'application du Principe de Superposition Temps-Température et iii) sur l'utilisation du modèle rhéologique de Burger, a permis de proposer un modèle de fluage non linéaire pour chacun des deux systèmes de colle. La seconde partie des travaux expérimentaux concerne la conception et la validation d'un dispositif innovant destiné à la caractérisation du comportement en fluage des interfaces collées béton/composite. Un élément important du cahier des charges de ce dispositif était d'en limiter l'encombrement, de sorte qu'il soit possible de tester plusieurs corps d'épreuve dans une chambre climatique au volume réduit, en vue d'étudier les effets synergiques du fluage et du vieillissement environnemental sur la durabilité des joints collés. Dans ce contexte, un prototype capable de solliciter en fluage trois corps d'épreuves à double recouvrement réalisés avec le procédé de renforcement Sika®Carbodur®S et connectés sur un unique circuit hydraulique, a été conçu et réalisé. Les résultats issus du prototype ont permis de le valider, en vérifiant notamment le maintient dans le temps de la charge appliquée, et le comportement symétrique des corps d'épreuve à double recouvrement. Le comportement mécanique des interfaces collées s'est révélé répétable, symétrique et conforme aux diverses modélisations réalisées, soit en calculant la réponse instantanée de l'interface au moyen d'un logiciel aux Eléments Finis (E.F.) ou à partir du modèle analytique de Volkersen, soit en calculant la réponse différée de l'interface en intégrant le modèle de fluage non linéaire de l'adhésif identifié précédemment dans le calcul aux E.F.. La dernière partie des travaux présentés dans le manuscrit concerne la réalisation d'un banc complet de fluage impliquant 14 corps d'épreuves à double recouvrement. Ces corps d'épreuve sont réalisés pour moitié avec le système de renforcement Sika®Carbodur®S et pour l'autre moitié avec le système Compodex. Le banc de fluage est installé dans la salle de vieillissement hygrothermique du Département Laboratoire d'Autun (40°C ; 95% H.R.). Tous les corps d'épreuves sont sollicités en fluage par un système de chargement alimenté par un circuit hydraulique similaire à celui utilisé pour le prototype, mais complété par une centrale hydraulique régulant la pression à partir de la mesure d'un capteur de pression. Pour compléter ces caractérisations sur interfaces collées, des essais de vieillissement sont également menés sur des éprouvettes d'adhésifs massiques stockées dans la salle climatique, certaines d'entre elles étant simultanément soumises à des sollicitations de fluage / The main objective of the present research is to design, realize and validate a methodology for studying ageing of bonded interfaces, based on the development of an innovative experimental creep device that can be coupled to hydrothermal aging. This device is based on the double-lap joint shear test configuration and enables to apply a constant load to the bonded assembly. In addition, this device combines other complementary features (unsolicited bonded joint zones, compatibility with an existing single lap shear test machine ...) that allows collecting useful complementary data. First, our work presents a literature review outlining the context of strengthening by bonded composite and specifying the main physicochemical mechanisms that may affect the durability of adhesive joints. Then, the manuscript describes the experimental characterizations carried out to assess both mechanical and physicochemical behaviors of the two adhesives selected for this study and which will be used to bond the composite on RC specimens in a later stage. Finally, a predictive approach based on i) thermo-stimulated creep tests, ii) on the application of the Time-Temperature-Superposition Principle and iii) on the use of the Burger's rheological model, allowed us to propose a non-linear creep model for each of the two adhesive systems. The second part of the experimental work is devoted to the design and validation of an innovative device for characterizing the creep behavior of concrete / composite adhesively bonded interfaces. An important requirement in the specifications was to reduce the size of the experimental device, so that several test specimens could be installed in a climatic room of limited volume, in order to study the synergistic effects of creep and hydrothermal ageing on the joint durability. In this line, a prototype involving three double-shear test-specimens loaded by flat jacks actuated by a centralized hydraulic system, was designed and realized (test-specimens were prepared using the Sika®Carbodur® S strengthening system). Collected data made it possible to validate the creep setup, by checking the constancy of the applied load over time, and the symmetrical behavior of the double lap shear test bodies. The mechanical behavior of the bonded interfaces was found to be repeatable, symmetrical and in a fair agreement with numerical and analytical modeling, done either by calculating the instantaneous response of the interface using a finite element (FE) approach and the analytical Völkersen's model, or by simulating the delayed creep response of the interface using a FE model in which the non-linear creep behavior of the adhesive layer had been implemented. The last chapter of the manuscript presents the realization of a full-scale creep setup involving fourteen double lap test specimens. Half of the test specimens were strengthened with Sika®Carbodur ® S and the other half with Compodex® C12 reinforcing composite system. This creep setup was installed in the climatic room of the Département Laboratoire d'Autun (40°C, 95% R.H.). Test specimens are creep loaded thanks to flat jacks powered by a hydraulic system similar to that used in the prototype, but supplemented by an electronic station that ensures pressure regulation in the circuit, based on the measurements of a pressure sensor. Beside these characterizations of bonded interfaces, complementary tests are also conducted on samples of the buk adhesive material stored in the climatic room, some of these samples being simultaneously subjected to creep loading