Un composite époxy/fibre de verre élaboré à partir de matériaux simplifiés a été soumis en parallèle à du vieillissement artificiel (UV et thermohydrique) et à du vieillissement naturel (climat tropical humide). Une étude des matériaux (résine seule et composite) à travers un large panel de techniques de caractérisation physico-chimiques, mécaniques et de moyens d’observation (MEB, AFM) a permis d’identifier clairement la structure, la morphologie et les principales propriétés du réseau époxy-amine de l’état initial. Une caractérisation systématique des échantillons par couches de 20 microns d’épaisseur a permis, en particulier, d’identifier un gradient de structure et de propriétés dans les 200 premiers microns à la surface des plaques de résine et de composite. Ce gradient est attribué à l’évaporation du durcisseur amine lors de l’élaboration des matériaux. Dans les plaques de composites, le DMA ainsi que l’AFM ont permis de mettre en évidence une zone d’interphase autour des fibres pour laquelle le réseau époxy-amine présente des caractéristiques différentes de celles de la résine en masse.La même méthodologie a été adoptée pour suivre l’évolution de ces matériaux lors des vieillissements artificiels et naturels.Les études séparées des vieillissements UV et thermohydrique ont permis de mettre en évidence les altérations chimiques et physico-chimiques de la matrice seule d’une part, et des interphases fibres/matrice d’autre part. Le vieillissement photochimique se montre le plus dégradant pour la surface des plaques, alors que les effets du vieillissement thermohydrique sont principalement observés au niveau des interfaces fibres/matrice dans les composites. Dans les deux cas également, nous pouvons proposer des mécanismes simplifiés de dégradation de la résine époxy-amine.Enfin, les résultats de caractérisation après le vieillissement naturel nous permettent de faire des corrélations avec les vieillissements artificiels et de pointer les effets prépondérants des deux paramètres de vieillissement, ainsi que d’avancer un facteur d’accélération. / A simplified glass fiber/epoxy composite was exposed to artificial ageing conditions (UV and Hygrothermal) and natural ageing (humid tropical climate). A wide range of physicochemical, mechanical and observation techniques (SEM, AFM) were used to clearly identify the structure, morphology and the main properties of the epoxy-amine network of the resin alone and composite in the initial state. A gradient in structure and properties was shown up in the first 200 microns of resin and composite plates surfaces thanks to the systematic characterization of sample layers of 20 microns thickness. It is attributed to an amine deficit during the sample elaboration process. In composite plates, DMA and AFM measurements have highlighted the existence of an interphase area around the fibers with a higher molecular mobility and a lower stiffness than the epoxy-amine network in the bulk resinThe same methodology was used to follow the materials evolution during artificial and natural ageing.The effects of UV and hygrothermal ageing were analyzed independently on the resin and on the composite in order to identify the chemical and physicochemical alterations of the matrix on one hand and of fiber/matrix interphases on the other hand. Photochemical ageing effects are mainly localized on materials surfaces, while the hygrothermal ageing affects mainly fiber/matrix interfaces in composite. In both cases simplified degradation mechanisms of epoxy-amine network are proposed.Finally, the characterization results after natural exposure allow us to establish correlations with artificial ageing. Predominant effects are identified and an acceleration factor is proposed.

La caractérisation et l’évaluation des propriétés physiques, chimiques, physico-chimiques et mécaniques sont un point important dans la compréhension du comportement des assemblages collés polymère/substrat. La spectroscopie diélectrique est une méthode de caractérisation efficace permettant d’étudier la dynamique moléculaire, et permettre aussi un suivi in situ de joints collés. La modélisation mathématique de résultats expérimentaux par la méthode de l’analyse par intervalle permet de s’affranchir de nombreux défauts de logiciels utilisés couramment (erreur expérimentale prise en compte dans les calculs du modèle, permet d’accepter ou de rejeter un modèle, …). Il a été démontré qu’en présence d’un substrat métallique, une compétition avait lieu entre la réaction de polymérisation et des réactions entre les monomères et les substrats métalliques, menant à une interphase (i.e. interface d’épaisseur non nulle) ayant des propriétés différentes des propriétés du même polymère en volume. Ces propriétés influent sur l’adhérence entre le polymère époxydeamine et le substrat d’aluminium. L’adhérence sera caractérisée par un test normé et reliée aux propriétés de l’interphase par diverses techniques. Des vieillissements de systèmes DGEBAanime/ aluminium ont été effectués. Durant ces vieillissements, des tests destructifs et non destructifs ont été effectués afin d’avoir un suivi sur les propriétés des interphases et interfaces de ces joints collés. Les résultats obtenus ont été mis en corrélation afin de pouvoir être capable par l’utilisation de tests non destructifs in situ, de pouvoir prévenir une rupture à l’interphase/interface entre l’adhésif et le substrat / Characterization and evaluation of physical, chemical, physico-chemical and mechanical properties are an important point in the comprehension of the behavior of bonded polymer/substrate assemblies. Dielectric spectroscopy is an effective method of characterization to study molecular dynamics, and also allow in situ monitoring of bonded joints. Mathematical modeling of experimental results by the method of interval analysis overcomes many shortcomings of commonly used software (experimental error taken into account, accept or reject a model ...). It has been shown that in the presence of a metal substrate, a competition was held between the polymerization reaction and the reactions between the monomers and metal substrates, leading to an interphase (i.e. non-zero thickness of interface) having properties different than these of the bulk. These properties influence the adhesion between the epoxy-amine polymer and the aluminum substrate. Adhesion will be characterized by a standardized test and related to the properties of the interphase by various techniques. The aging of DGEBA-anime/aluminum system have been done during this study. During the aging, destructive and non-destructive tests were carried out in order to have a follow-up on the properties of interfaces and interphases of these bonded joints. The results were correlated in order to be able to use an in situ non-destructive testing to prevent the rupture at the interphase/interface between the adhesive and the substrate

No description available.

Tübingen, Univ., Diss., 2001.

Tübingen, Univ., Diss., 2005.

The aqueous suspension prepregging technique was used to fabricate PEEK and PPS matrix composites with polyimide interphases of tailored properties. The structure-property relationships of Ultem-type polyimide and BisP-BTDA polyimide which were made from various water soluble polyamic acid salts were studied. The molecular weight of the polyimides was shown to be dependant upon the selection of the base used for making the polyamic acid salt. The development of an Ultem-type polyimide with controlled molecular weight and properties similar to commercial Ultem 1000 was accomplished with the Ultem-type TPA+ polyamic acid salt. Both the Ultem-type polyimides and the BisP-BTDA polyimides derived from the NH4+ salt and the TMA+ salt were shown to crosslink at elevated temperatures. Blends of Ultem-type polyimide with PEEK and BisP-BTDA polyimide with PEEK were prepared to study the structure-property relationships of model composite matrices. Since both polyimides are miscible with PEEK, interdiffusion of the polyimides with PEEK is expected, however, the interdiffusion behavior is complicated by the crosslinking mechanism of the polyimides. Ultem-type polyimide interphase, PEEK matrix composites and BisP-BTDA polyimide interphase, PEEK matrix composites were fabricated using the aqueous suspension prepregging technique and evaluated to determine the effects of the interphase properties on the bulk composite performance and durability. Three different Ultem-type polyimides from the NH4+, TMA+ and TPA+ polyamic acid salts were used and two different BisP-BTDA polyimides from the NH4+ and TMA+ polyamic acid salts were used. The transverse flexure strength was used to qualitatively rank the composites by level of interfacial shear strength. The longitudinal tensile strength of the composites was shown to vary with relative interfacial shear strength. The trend of these data qualitatively support the existence of a maximum longitudinal tensile strength at an optimum interfacial shear strength. Notched fatigue testing of the Ultem-type polyimide interphase, PEEK matrix composites showed that the initial split growth rate increased with decreasing relative interfacial shear strength. Ultem-type polyimide interphase, PPS matrix composites were fabricated using the aqueous suspension prepregging technique and evaluated to determine the effects of the interphase properties on the bulk composite performance. Three different Ultem-type polyimides from the NH4+, TMA+ and TPA+ polyamic acid salts were used. The transverse flexure strength was used to qualitatively rank the composites by level of interfacial shear strength. The longitudinal tensile strength of the composites was shown to vary with relative interfacial shear strength. The trend of these data qualitatively support the existence of a maximum longitudinal tensile strength at an optimum interfacial shear strength. / Ph. D.

Current technology of polymer nanocomposites (PNC) emphasizes the need for fundamental understanding of the links between manufacturing method and macro-scale properties in order to engineer processing and performance of PNCs. The manufacturing method is one key variable that dramatically defines interfacial interactions on the nano-scale and thus the properties of polymer near the interface of nanomaterial/polymer or interphase, level of dispersion and the crystallization behavior of semi-crystalline PNCs. These factors in particular govern reinforcing mechanisms at the interface and consequently impart important properties to PNCs. The current approach to manufacturing PNCs involves trial and error with elaborate, costly and time consuming experimental characterization of PNCs. Therefore, a deep insight into the links among manufacturing method, interfacial interactions and bulk properties is essential in order to design and fabricate PNCs with engineered performance. The main goal of this study was to provide a better understanding of the effect of manufacturing methods on the macro-scale properties of PNCs, with a focus on the role of interfacial interactions, that can lead to fabrication of PNCs with multifunctional performance. The objectives of this research were to: i) determine the detail correlations among manufacturing method, nano- and microstructure and macro-scale properties of multifunctional exfoliated graphite nanoplatelets/polyamide 12 polymer nanocomposites with enhanced mechanical and electrical performance through systematic manufacturing and experimental methodologies, ii) understand correlations among nano-scale interfacial interactions, physical and structural properties of the polymer at the interface and macro-scale behavior of PNCs, and iii) evaluate effect of manufacturing method on electrical behavior of PNCs with directionally dependent performance. This study demonstrated key correlations among manufacturing techniques, interfacial interactions and macro-scale properties of PNCs. A methodology was introduced to understand and determine the characteristics of a complex constrained region produced at the interface of nanomaterials and polymer in semi-crystalline PNCs. Finally, the study illustrated superior electrical and morphological properties of selective laser sintering (SLS) processed parts over injection molded PNCs and thus confirmed the capability of SLS in the development of electrically conductive PNCs that exhibit multifunctional performance. In conclusion, the study provided an insight into the links among process, nano-scale interfacial interactions and microstructure to better understand effects of manufacturing technique on macro-scale properties of PNCs, which enables fabrication of conductive PNCs with multifunctional performance.

No description available.

In this study, liquid-vapor vertical upflow has been research with the intent of finding an improved method of modelling the interphase friction in two-phase vertical flow in nuclear thermal-hydraulic codes. An improved method of modelling interphase friction should allow for better prediction of pressure gradient, void fraction and the phasic velocities. Data has been acquired from several available published resources and analyzed to determine the interphase friction using a force balance between the liquid and vapor phases. Using the Buckingham Pi Theorem, a dimensionless interphase friction force was tested and refined before being compared against seven other dimensionless parameters. Three correlations have been developed that establish a dimensionless interphase friction force as a function of the Weber number, the Froude number and the mixture Froude number. Statistical analysis of the three correlations shows that the mixture Froude number correlation should be the most accurate correlation. The correlations have a weakness that makes them ineffective mostly for bubbly flow and some slug flow scenarios, while they should perform significantly better for annular flow cases. Comparisons have been made against the interphase friction calculations published in the manuals of RELAP5/MOD2, RELAP5/MOD3.3, RELAP5-3D and TRACE. The findings have generally shown that the equations in the manuals provide very inaccurate approximations of the interphase friction compared to the interphase friction that was found via force balance. When analyzing the source code of RELAP5/MOD3.3, several differences were noticed between the source code and manual, which have been discussed. Calculations with the source code equations reveal that the source code provides a modestly improved prediction of the interphase friction force, but still has significant errors. Despite the fact that the manual and source code equations indicate that RELAP5/MOD3.3 should perform poorly in modelling interphase friction, actual RELAP5/MOD3.3 model runs perform very well in predicting pressure gradient, void fraction, the liquid and vapor velocities and the interphase friction force. This is largely due to RELAP5/MOD3.3 being able to adjust parameters to converge to a solution that fits within the boundary conditions established in the input file. Modifications to the RELAP5/MOD3.3 code were first made with the three correlations developed using dimensionless parameters, and were tested with data points that the RELAP5/MOD3.3 flow regime map had predicted would be annular flow. While the mixture Froude number correlation has been analyzed to be the most statistically accurate of the three correlations, it was found that the Weber number correlation performed best when implemented into RELAP5/MOD3.3. In a parametric study of the Weber number correlation, it performed optimally at 150% of the original correlation, improving upon the original RELAP model in almost every metric examined. Additional investigations were performed with individual annular flow correlations that model specific physical parameters. Results with the annular flow physical models were inconclusive as no particular model provided a significant improvement over the original RELAP5/MOD3.3 model, and there was no clear indication that combining the models would provide significant improvement. / Ph. D.

Les copolymères à blocs (BCP) sont des macromolécules capables de s’auto-assembler produisant des morphologies bien définies à l’échelle nanométrique. Un certain nombre de leurs propriétés macroscopiques peuvent être largement modifiées par des effets de confinement à l’échelle moléculaire, mais aussi par des effets de cisaillement (l’orientation des structures et donc un comportement mécanique fortement anisotrope). L’une des technologies permettant d’étudier ces effets sur la structuration des BCP est la coextrusion multinanocouches, qui permet de produire à grande échelle des matériaux sous forme de films possédant deux ou plusieurs constituants organisées en milliers de couches alternées ayant chacune une épaisseur nanométrique. À l’aide de ce procédé, des films constitués du tribloc poly(méthacrylate de méthyle-b-butyle acrylate-b-méthacrylate de méthyle) et des homopolymères polyméthacrylate de méthyle, polystyrène et polycarbonate (ayant donc différentes interfaces) ont été fabriqués en variant la composition du mélange et les conditions de coextrusion afin d’obtenir différentes épaisseurs du film (et donc différentes épaisseurs de couche). Une caractérisation multi-échelle a été effectuée en couplant différentes techniques, notamment AFM, MET (après une étape préalable de marquage) et SAXS. Elle a permis d’identifier les structures locales au sein des couches et de mieux comprendre la relation procédé-structure-propriétés suite à des essais en traction uni-axiale montrant de meilleures propriétés dans le cas de structures multicouches. Une faible stabilité thermique, à de temps comparables à ceux du procédé, a montré une influence sur la structuration de ce type de BCP. Nous avons mis en évidence un changement dans la morphologie du tribloc à partir d’une structure lamellaire, lorsque le matériau se trouve dans un état proche de l’équilibre thermodynamique, vers une structure cylindrique au sein du système multicouche et maintenue, quelle que soit l’épaisseur de couche, à grande distance. La maitrîse des procédés de transformation de matériaux à base de polymère à l’échelle micro ou nanométrique prend ainsi toute son importance afin de mieux contrôler, dans le cas des BCP, la structuration lors d’une production à grande échelle de matériaux hiérarchisés constitués de ces matériaux, ce qui influence fortement leurs propriétés macroscopiques. / Block copolymers (BCP) have proven to be of great interest, especially for their ability to spontaneously self-assemble in ordered and well-defined nanostructures. Some of their macroscopic properties can be altered by physical effects such as confinement (constraining domains at molecular scale) or shear (predominant orientation of domains with anisotropic mechanical response). Here, the study of these effects over the BCP structuration is achieved by using an industrially scalable technique, nanolayer coextrusion, which allows fabrication of macroscopic films made of thousands of alternating layers with individual thickness tuned down to a few tens of nanometers. Films are then coextruded using the triblock : poly(methyl methacrylate-b-butyl acrylate-b-methyl methacrylate) and the polymers : polymethyl methacrylate, polystyrene and polycarbonate (having different interfaces) by varying weight proportions and process parameters to target different layer thicknesses. A multi-scale characterization by coupling different technics as AFM, TEM (after samples staining) and SAXS allowed the local identification of nano-domains and the better understanding of process-structures-properties relation as a result of tensile tests showing improved mechanical behavior for these films. A low thermic stability for comparable process times showed a clear influence over structuration of this kind of BCP. We have observed a change in the triblock morphology from lamellar structures, when it is a close to thermodynamic equilibrium state, to cylindrical structures within the multilayer system which is maintained over long distances indistinct of layer thickness. The well understanding of the forming process parameters to create polymer-based materials at micro- or nanoscale scale is therefore an important factor in order to control nano-structures during a large-scale production of hierarchized materials consisting of BCP, which could strongly influence their macroscopic properties.