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The present study employs a standardized progressive load scratch test (ASTM D7027/ISO 19252) to investigate the fundamental physical and mechanistic origins of scratch deformation in styrene-acrylonitrile (SAN) random copolymers. Previous findings from numerical simulation using finite element methods are used to establish correlation between mechanical properties and key scratch deformation mechanisms of the SAN model systems. For SAN, the acrylonitrile (AN) content and molecular weight (MW) can be changed to alter mechanical properties such as tensile strength and ductility. The key scratch deformation mechanisms are identified as: scratch groove formation, scratch visibility, periodic micro-cracking and plowing. Groove formation has been correlated to the secant modulus at the compressive yield point while micro-cracking and plowing are related to the tensile strength of the material. The fundamentals and physical origins of scratch visibility are discussed. It is explained how unbiased evaluation is accomplished by means of an automatic digital image analysis software package (ASV®). Frictional behavior and the effects of scratch speed and moisture absorption are also addressed. Increasing the AN content and/or the MW of the SAN random copolymers generally enhances the scratch resistance of the material with regard to the onset of the key deformation mechanisms. Increasing the scratch speed increases the brittleness of the material, resulting in failure at lower applied loads. Moisture absorption increases with AN content and imparts a degree of plasticization as the moisture diffuses into the sub-surface. This plasticization initially results in a degradation of scratch resistance with respect to the key deformation mechanisms, but then, after saturation, the moisture on the surface provides lubrication and improves the scratch resistance. It is important to note that polymers are fundamentally different in nature, but the findings of this study serve as an important stepping stone down the path to a deeper understanding of polymer scratch behavior.

Le plâtre est un matériau de grande disponibilité et très connu pour ses qualités : il est favorable à la protection de l’environnement, assez malléable, de faible densité, aux propriétés fonctionnelles remarquables (coupe-feu, isolant thermique, régulateur de l’hygrométrie des enceintes), décoratif, ... Ce qui justifie l’intérêt accordé à ce matériau pour les constructions. Sa grande fragilité préoccupante est à l’origine des travaux de recherches dans le monde entier en vue de son renforcement. Les fibres de verre et de sisal sont les renforts les plus utilisés à ce jour. Le renforcement par des fibres végétales est de plus en plus recherché. La texture micro structurale poreuse du plâtre favorise son caractère d’isolant thermique. Les textures mises en œuvre jusqu’à présent sont limitées à des porosités comprises entre 30 et 55%. La réduction du coût de ce matériau pour une large utilisation est encore possible et souhaitée. Deux leviers sont exploités dans ce travail, notamment un allègement de la masse de plâtre pour augmenter le taux de porosité et un renforcement de la tenue mécanique par incorporation de fibres végétales produites localement. L’objectif de ce travail est d’évaluer les caractéristiques mécaniques, thermiques et hygrométriques d’un matériau constitué de plâtre pris, à grande porosité, renforcé d’une nouvelle fibre végétale : le Rhecktophyllum Camerunense (RC), une fibre des forêts humides équatoriales. La fibre de sisal, d’utilisation connue pour le renforcement du plâtre, sert de référence à des fins de comparaison. Une série d’expérimentations est menée à cet effet. Une caractérisation physico-chimique des constituants est effectuée, des essais mécaniques de traction et de flexion sont effectués sur les constituants et les matériaux composites plâtre/fibres résultants, la cinétique d’adsorption d’humidité par les constituants et le matériau fibreux est suivie. Le comportement thermique des matériaux plâtre et plâtre/fibres est aussi mesuré. Les fibres utilisées, le sisal et le RC, sont à fort taux de cellulose (entre 49 et 78,8%), la fibre de RC est tubulaire avec 35,5% de porosité. Le plâtre est gâché à l’eau déminéralisée à un rapport massique E/P égal à 1 à partir de la poudre de semihydrate β. Sa microstructure cristalline est constituée de cristaux de gypse sous forme d’aiguilles enchevêtrées avec des vides intercristallins. Sur le plan du comportement mécanique, les résultats obtenus révèlent que le plâtre se montre fragile et présente un module d’élasticité en traction de 1,72 GPa, une résistance à la traction de 0,86 MPa et un allongement à la rupture de 1,16%. En flexion trois points, son module d’élasticité est de 0,64 GPa et sa contrainte à la rupture, de 0,13 MPa. La fibre de sisal est raide et fragile. Son module d’élasticité est compris entre 9 et 21 GPa, elle admet un allongement à rupture de 3 à 7%. Par contre, la fibre de RC est assez ductile avec un module d’Young moyen de 0,7 GPa et un allongement à rupture de 24,2%. L’adhésion du plâtre sur les fibres est faible : il adhère plus sur le sisal que sur le RC. Le sisal renforce mieux le plâtre par une augmentation plus sensible du module d’élasticité de 42,5%, contre 16,3% pour le RC, ce dernier lui apportant plutôt une grande ductilité élastique. Les fibres de RC apportent le maximum de renforcement en traction au plâtre lorsqu’elles sont tissées en unidirectionnel et en flexion lorsqu’elles sont uniformément réparties dans le volume suivant la direction longitudinale de la structure. (...) / The plaster is a material of high availability and very known for its qualities : it is favourable to the protection of the environment, quite malleable, of low density, its functional properties are remarkable (firewall, thermal insulation, regulator of the hygroscopy of enclosures), decorative, ... What justifies the interest attached to this material for constructions. Its great alarming brittleness is at the origin of the research tasks in the whole world for its strengthening. The glass fibers and sisal are the more used reinforcements to this day. The strengthening by plant fibers is more and more researched. The microstructure of the plaster is porous ; that promotes its heat insulation character. The textures implemented so far are limited to porosities ranging between 30 and 55%. The reduction of cost of this material for a wide use is still possible and desired. Two levers are exploited in this work, in particular a lightening of the plaster weight to increase the proportion of air voids and a reinforcement of the mechanical resistance with locally produced fibers. The objective of this work is to evaluate the mechanical, thermal and hygrometrical characteristics of a material made up of harden plaster, with high porosity, strengthened by a new plant fiber : the Rhecktophyllum Camerunense (RC), a fiber of humid equatorial forests. The sisal fiber, of known use for the strengthening of the plaster, serves as a reference for comparison purposes. A serie of experiments is conducted to this effect. A physicochemical characterization of constituents is performed. Mechanical tests of tensile and of bending are performed on the constituents and the resulting plaster/fiber composite materials. The kinetic adsorption of moisture by the constituents is followed. The thermal behaviour of plaster and plaster/fiber is also measured. The fibers used, sisal and RC are with high rates of cellulose (between 49 and 78.8% ), the fiber of RC is tubular with 35.5 % of porosity. The plaster is dissolved in demineralized water to a mass ratio W/P equals to 1 from the powder of semihydrate β. Its crystalline microstructure is composed of gypsum crystals in the form of needles tangled with the empty intercristallins. As far as the mechanical behavior is concerne, the result reveals that the plaster is weak, its Young’s modulus in tensile is 1.72 GPa, its tensile strength is 0.86 MPa and its elongation at break is 1.16 %. In three points bending test, its modulus of elasticity is 0.64 GPa and its constraint at break is 0.13 MPa. The sisal fiber is stiff and fragile. Its Young’s modulus is between 9 and 21 GPa, it admits an elongation at break of 3 to 7 %. On the other side, the fiber of RC is quite ductile : the means of Young’s module is 7 GPa and the elongation at break is 24.2 %. The adhesion of the plaster on the fiber surface is low : it adheres more on the sisal than on the RC. The sisal strengthened better the plaster with a sensitive increase of the Young’s modulus of 42.5 %, against 16.3 % for the RC. But the RC fiber gives rather high elastic ductility. The fibers of RC deliver maximum capacity in tensile to the plaster when they are woven into unidirectional. They offer high capacity in bending when they are uniformly distributed inside the volume according to the longitudinal direction of the structure. (...)

[pt] Geralmente, o ambiente marinho é o ambiente natural mais agressivo para tubulações metálicas, promovendo corrosão, levando a falhas catastróficas. O método de reparo tradicional metálico soldado é um método de reparo inconveniente e custoso para a indústria. Compósitos poliméricos (FRP) são um material com potencial para reparo devido a sua alta razão resistência/peso e alta resistência à corrosão e degradação ambiental. Porém, os compósitos poliméricos também são suscetíveis a degradação severa quando expostos a condições ambientais agressivas, incluindo absorção de água, temperatura, UV e pressão. Para um melhor entendimento do mecanismo de degradação, amostras de compósito de matriz polimérica reforçado por fibras de vidro e resina epóxi pura foram fabricados e analisados em função do tempo e temperatura de envelhecimento em uma atmosfera salina. Além disso, um grupo de compósitos tiveram suas bordas cobertas com resina epóxi para similar práticas reais comuns no campo, denominado coated FRP. Uma resina epóxi DGEBA bicomponente e um tecido bidirecional de fibras de vidro foram usados como matriz e reforço, respectivamente. O tecido de fibra de vidro detém de uma razão de fibras longitudinais por transversais de 2:1. Os materiais foram sujeitos a envelhecimento de névoa salina em três câmaras à 35, 55 e 70 Celsius por aproximadamente 15171 horas. A concentração de sal na solução usada foi 5.0 por cento por massa. As amostras foram periodicamente retiradas das câmaras de envelhecimento para terem seus ganhos de massa mensurados pelo método gravitacional. Suas mudanças dimensionais também foram capturadas para avaliação do comportamento de inchamento dos materiais. Análises térmicas com DSC e DMTA foram feitas para avaliar o grau de cura dos materiais poliméricos e os efeitos da temperatura na pós-cura do material. Análises químicas com testes FTIR foram feitas para investigar a ocorrência de processos de pós-cura, hidrólise e termo-oxidação durante o envelhecimento. Amostras de compósito para testes destrutivos de flexão e resistência ao cisalhamento (ILSS) foram testados periodicamente para terem suas degradações monitoradas com o tempo. Testes de Excitação por Impulso (IET) e Colorímetro foram realizados como testes não-destrutivos (NDT) complementares. A primeira parte deste trabalho foca na avaliação do comportamento de absorção de umidade nos compósitos e resina epóxi pura. A relação entre a capacidade de absorção de umidade dos materiais, considerando a fração volumétrica de fibras, foi investigada. Além disso, modelos de absorção não-Fickianos também foram aplicados aos dados experimentais do FRP e resina epóxi para considerar desvios do modelo Fickiano padrão. Com isso, relaxações poliméricas e interações polímero-água, assim como mudanças na rede polimérica induzidas por umidade e temperatura, foram investigados. Uma modificação ao modelo não-Fickiano de Berens-Hopfenberg (BH) foi proposta para incluir os efeitos de pós-cura na absorção de umidade; tal modificação aplicada a pós-cura não foi encontrada na literatura. Na segunda parte deste trabalho, o comportamento de inchamento da resina epóxi pura e compósitos revestidos e não-revestidos foi avaliado e correlacionado com a absorção de umidade. A ortotropia do compósito ficou evidente, visto que o material apresentou maior capacidade de inchamento na direção da espessura. Um modelo do tipo Fickiano foi implementado ao inchamento na espessura com o intuito de investigar deformação de inchamento de saturação e a frente de inchamento. A terceira parte deste trabalho foca nos testes destrutivos e na avaliação dos efeitos hidrotérmicos na degradação do material. A temperatura se mostrou um fator acelerador para degradação de propriedade. Além disso, uma metodologia para estimar a curva de serviço de sistemas de reparo e extrapolá-la para temperaturas mais baixas foi elaborada. Metodologias de extrapolação de propriedades para exposição hidrotérmica de longa duração não foram encontradas na literature. Parâmetros como platô de retenção de propriedade e taxa de degradação foram estimados para temperatura ambiente. Curvas de Arrhenius também foram plotadas para avaliar o tempo requerido para alcançar os níveis de retenção em cada temperatura testada. Por fim, duas técnicas não-destrutivas foram utilizadas no FRP e resina epóxi pura como testes complementares como forma de validar os resultados encontrados em outras técnicas. A Técnica de Excitação por Impulso (IET) foi realizada para obter o módulo de Young e boa correlação foi obtida entre o teste IET e o ensaio destrutivo de flexão. Através dos testes colorimétricos, os efeitos de umidade e temperatura foram visíveis, já que a mudança de cor da resina foi mais forte para tempos longos e temperaturas mais altas. / [en] Generally, the marine environment is the most aggressive natural environment for metallic pipelines, promoting corrosion, leading to catastrophic failures. The traditional welded metallic repairs are high-cost and inconvenient repair methods for the industry. Polymeric composites (FRP) are a potential repair material due to their high resistance/weight ratio and high resistance to corrosion and environmental degradation. However, polymeric composites are also susceptible to severe degradation when exposed to harsh environment conditions, including water absorption, temperature, UV and pressure. To better understand the degradation mechanism, glass-fiber reinforced polymer matrix composite (GFRP) and neat epoxy samples were fabricated and analyzed as a function of aging time and temperature in a saline atmosphere. In addition, a group of composites had their exposed edges coated with epoxy resin to simulate common real-life practices in the field, namely coated FRP. A two-component DGEBA epoxy resin and a bidirectional glass-fiber woven fabric were used as matrix and reinforcement, respectively. The fiberglass fabric had a longitudinal to transverse fiber ratio of 2:1. The materials were subjected to salt spray aging in three chambers at 35, 55 and 70 Celsius for approximately 15171 hours. The salt concentration in the solution used was 5.0 per cent by weight. Samples were periodically removed from the chambers to have their mass gain measured by the gravitational method. Their dimensional changes were also measured to evaluate the swelling behavior of the materials. Thermal analyses with DSC and DMTA were performed to evaluate the curing degree of the polymeric materials tested and the effects of temperature on the material’s post-curing. Chemical analyses with FTIR tests were performed to investigate the occurrence of post-curing, hydrolysis and thermo-oxidation processes during aging. Composite samples for bending and interlaminar shear strength (ILSS) destructive tests were periodically tested to have their degradation monitored over time. Impulse Excitation Technique and colorimetry tests were also performed as complementary non-destructive tests (NDT). The first part of this work focuses on the assessment of the moisture absorption behavior of both composite and neat epoxy resin. The relationship between the moisture gain capacity of the materials, considering the fiber volume fraction, was investigated. Besides, non-Fickian absorption models were also applied to the experimental data of FRP and neat epoxy resin to account for deviations from the standard Fickian model. Then, polymeric relaxations and polymer-water interactions, as well as network changes induced by moisture and temperature, were investigated. A modification to the Berens-Hopfenberg (BH) non-Fickian model was proposed to account for post-curing effects on the moisture absorption; such modification applied for post-curing was not found in literature. In the second part of this work, the swelling behavior of neat epoxy resin, uncoated and coated composites was evaluated and correlated with moisture absorption. The orthotropy of the composite was evident, since this material showed greater swelling capacity in the thickness direction. A Fickian-like model was implemented to the thickness swelling to investigate swelling strain saturation and swelling front. The third part of this work focuses on the destructive tests and evaluation of the hygrothermal effects on the material degradation. Temperature proved to be an accelerating factor for property degradation. In addition, a methodology to estimate the service-life curve of the repair systems and extrapolate it to lower temperatures was elaborated. The methodology of property extrapolation for long-term hygrothermal exposure in salt spray environments could not be found in literature. Parameters like property retention plateau and degradation rate were estimated for room temperature (25°C). Arrhenius curves were also plotted to evaluate the time required to reach the properties’ retention levels for each temperature. Finally, two non-destructive techniques were performed on the uncoated FRP and on neat epoxy resin as complementary tests in order to validate the results found in other techniques. The Impulse Excitation Technique (IET) was performed to evaluate the Young modulus and good correlation was found between IET and destructive bending tests. From the colorimetry tests, the effects of moisture and temperature were visible, as the resin s color change was stronger at longer aging time and higher temperatures.