Esse trabalho tem por objetivo desenvolver uma ferramenta para previsão das características da cura em borrachas, através da análise numérica de modelos fenomenológicos de vulcanização correlacionados às análises térmicas via método dos elemento finitos. A metodologia é baseada em simular o processo de vulcanização no molde, estimando-se a energia de ativação e simulando o histórico de temperaturas dentro do molde, estratificando o volume do componente por faixas de vulcanização. A partir da caracterização mecânica da borracha nos seus diversos estados de cura, as propriedades constitutivas são especificadas de forma segregada para cada diferente região do componente, que então é simulado em situação de operação. Desta forma, é possível analisar as consequências sobre o comportamento mecânico de componentes parcialmente curados ou melhorar o processo de moldagem a fim de minimizar as diferenças decorrentes do processo. Usam-se como objeto de estudo apoios elastoméricos de pontes não fretados, comparando alterações na resposta do componente perfeitamente curado com situações industriais onde isso não é possível. Como resultado, obtém-se uma estratificação de cura com erros de aproximadamente 2% para percentuais de cura superiores a 50% e diferenças consideráveis para o estado de tensões do modelo com cura homogênea e estratificada. / This work develops a tool to predict vulcanization properties in rubber, based on numerical analysis of phenomenological model correlated with the thermal history of rubber in mold vulcanization. This methodology simulates mold cure process by finite element method, estimating the activation energy and dividing the component into different cure regions. After the mechanical characterization of the rubber with different cure percentages, the constitutive properties are specified in a segregate form in each different cure region of the component, emulating the mechanical behavior of the component in operation. This way it is possible to analyze stresses and strains in components with 100% of cure and in components with incomplete cure. The methodology is applied to a thick rubber piece used to support the track in road bridges. As result, the mean error is about 2% for cure level above 50% and the stratified model present different state of stress in comparison with the homogeneous cure model.

O aumento da vida útil de pneus tem sido uma incessante busca de seus fabricantes. Aumentar a vida de um pneu não significa somente prolongar sua vida, mas também manter estáveis as características e propriedades, para as quais os compostos foram projetados. Para manter estáveis as propriedades e características dos compostos, deve-se ter a estabilidade das ligações cruzadas formadas durante a vulcanização do pneu. Em condições normais de uso, os principais causadores da degradação das ligações cruzadas em compostos de pneus são os ataques térmicos e oxidativos. O objetivo deste trabalho é avaliar a estabilidade de um composto de borracha natural frente às solicitações térmica e oxidativa das ligações cruzadas formadas sob diferentes condições de vulcanização e sistemas vulcanizantes. Foram elaboradas cinco formulações baseadas em borracha natural do tipo RSS-3 e com variações na dosagem de enxofre e óxido de zinco, utilizando sistemas de vulcanização convencional e eficiente. Todos os compostos foram vulcanizados em duas condições, 170°C e 140°C. Os compostos vulcanizados foram avaliados em ensaios físicos e químicos, incluindo medições de módulos de armazenamento e de perda, tensão e alongamentos à ruptura, resistência à laceração, densidade de ligações cruzadas e cinética de vulcanização nas condições novo (original) e envelhecidos na presença e na ausência de oxigênio. Os resultados obtidos permitem afirmar que a utilização de oxido de zinco de alta área superficial e de sistemas de vulcanização eficientes tornam este tipo de composto mais resistentes ao envelhecimento térmico e oxidativo. / The increment of the service life of tires has been a constant challenge for their manufacturers. Increasing the life of a tire does not mean only prolong his life, but also maintain its characteristics and properties stable, whatever the compounds were designed for. To keep stable the properties and characteristics of the compounds, we must have the stability of the crosslinks formed during the vulcanization of the tire. In normal use, the main causes of the degradation of the crosslinks are due to the thermal and oxidative attacks. The objective of this study is to evaluate the thermal and oxidative stability of the crosslinks formed under different conditions and curing systems in a compound with natural rubber. Five formulations were prepared based on the natural rubber RSS-3 and variations in the dosage of sulfur and zinc oxide, as well as the type of the vulcanization system, conventional or efficient, were introduced. All compounds were cured in two conditions, 170°C and 140°C. The vulcanized compounds were evaluated by physical and chemical tests, including measurements of the storage and loss moduli, tension and stretching to break, tear resistance, crosslinking density and kinetics of curing. The performance of the compounds was evaluated under three conditions, namely new (original) and after aging in the presence and in the absence of oxygen. The results allowed us to conclude that the use of zinc oxide of high surface area and the efficient vulcanization systems are more resistant to thermal and oxidative aging.

Dans cette thèse, nous avons travaillé sur la mise au point de surfaces superhydrophobes modèles dont la mouillabilité peut être contrôlée par un stimulus externe. Composées de forêts de piliers micrométriques élastomères à forts rapports d'aspect dans lesquels sont incorporées des particules magnétiques, les surfaces présentent, via l'application d'un champ magnétique externe, une orientation modulable des piliers, donc une rugosité de surface adaptable. En faisant varier la géométrie, l'élasticité et l'aimantation de ces derniers, nous avons pu mettre en évidence les points suivants. Nous avons vu dans un premier temps qu’en accord avec la littérature, et en l’absence de champ magnétique, l’hystérèse de mouillage augmente avec la fraction de surface. Cependant, elle reste constante lorsque l’élasticité des piliers varie. Résultat déroutant, car à l’échelle du pilier, il existe bel et bien une différence de mobilité des piliers entre les piliers les plus rigides et les plus complaisants qui subissent la traction de la ligne triple.Nous avons ensuite montré que l’orientation des piliers changeait significativement l’angle de glissement via l’application d’un champ magnétique. De plus, le glissement de la goutte sur la surface est favorisé lorsque les piliers sont orientés à l’opposé de la pente. Enfin, nous avons pu contrôler la façon dont une goutte d’eau se déplace sur une surface inclinée en deçà de l’angle de glissement, puisqu’elle n’avance vers le bas de la surface que si une actuation magnétique est appliquée. Ces surfaces seront une source d’étude intéressante pour comprendre comment moduler le mouillage ou l’écoulement de liquide en état fakir. / During this thesis, we have developped superhydrophobic surfaces whose wettability can be controlled by an external magnetic stimulus. Formulating a network of elastomeric and magnetic micro-pillars with high aspect ratio allows the orientation of the pillars through magnetic forces, hence an adaptable surface roughness. Moreover, modulating the geometry, elasticity and magnetization of pillars allowed us to highlight the following conclusions.We have seen first that in agreement with the literature, without magnetic field, the wetting hysteresis increased with the surface fraction. However, it remains constant varying the elasticity of pillars. This conclusion is confusing, because at the pillar scale, there is indeed a difference of mobility between rigid and flexible pillars due to the force exerted by the triple line.We then demonstrated that the deflexion of the pillars can change significantly the sliding angle due to the applied magnetic field. Moreover, sliding of the droplet on such a surface is promoted when pillars are deflected against the slope.Finally, we managed to control the displacement of a droplet on a surface which is tilted with an angle below the sliding angle : it moves forward from the surface only if magnetic actuation is applied. This surfaces will be an attractive source of study in order to understand how to modulate wetting and liquid flow in fakir state.

La détermination des distributions de contrainte et de déformation dans des matériaux opaques est une question clé pour évaluer leur comportement sous des conditions de chargement souvent complexes. La plupart des méthodes expérimentales utilisées aujourd’hui pour traiter ce problème sont des méthodes invasives ou bien inefficaces pour les matériaux opaques. Dans ce contexte nous proposons d’utiliser le signal de Résonance Quadripolaire Nucléaire (RQN) de petits cristaux, utilisés comme charge, dans des matériaux peu ou pas conducteurs. Les contraintes transmissent par la matrice au cristal induisent une déformation de son réseau cristallin qui à son tour induit une modification de sa fréquence RQN. La RQN est, par conséquent, sensible aux déformations induites par une contrainte mécanique externe et le cristal agit comme une jauge de contrainte à l’échelle du micron. Nous appelons cette méthode la piézospectroscopie RQN.L’objectif de cette étude est de prouver que l’on peut utiliser la piézospectroscopie RQN pour mesurer des contraintes au sein de matériaux opaques et plus précisément au sein d’élastomères. Le lien fondamental entre la variation de fréquence RQN et le tenseur de contrainte appliqué au cristal a été étudié. Pour cela nous avons choisi le 63Cu dans la cuprite comme sonde RQN. Expérimentalement, la dépendance à la contrainte de la fréquence RQN est mesurée en utilisant différentes sollicitations mécaniques générées par des montages originaux intégrant mesure de contrainte et de RQN. Les résultats ainsi obtenus sont discuté en regard de calculs quantiques basés sur la DFT.En outre, comme preuve de concept de la piézospetroscopie RQN, nous avons réalisé des expériences supplémentaires en utilisant des conditions de chargement qui nous ont permis de démontrer, sans faire d’hypothèses sur les propriétés mécaniques du Cu2O, que la variation de fréquence RQN est représentative de la composante hydrostatique du champ de contrainte interne de l’élastomère. Nous avons ensuite étudié la capacité de cette méthode à cartographier un champ de contrainte hétérogène. / The determination of stress and strain distributions in opaque materials is a key issue to evaluate their mechanical behavior. However, most of the methods used today to measure stress are either extremely invasive or ineffective for opaque materials. Within this context, we propose to use the Nuclear Quadrupolar Resonance (NQR) signal of small crystals, embedded within non, or poorly, conductive materials. Stresses transferred by the matrix to the crystal induce a deformation of its lattice which in turn results in a modification of the Electric Field Gradient (EFG) at the nucleus of interest. NQR is, as a consequence, sensitive to deformations induced by external mechanical stress and the crystals act as local stress gauges at the micron-scale. We call this method NQR piezospectroscopy.The objective of this study is to prove that NQR piezospectroscopy can be used to measure stress within opaque materials and more precisely within elastomer. The fundamental link between the NQR frequency variation and the stress tensor applied to the crystal has been studied. For that purpose, 63Cu in cuprite has been selected as a NQR probe. The stress dependence of its NQR frequency is investigated experimentally using different mechanical loadings generated within an original integrated NQR – stress device and discussed in the light of DFT ab-initio calculations.In addition, as proof-of-concept of NQR piezospectroscopy, additional experiments were carried out using loading conditions proving, without hypothesis on cuprite’s mechanical properties, that its NQR frequency shift is representative of the hydrostatic component of the elastomer inner stress field. We then investigated the ability of this method to map an heterogeneous stress field.

<p>A novel strategy for synthesising segmented poly(urethane urea) (PUU) without using a chain extender but nevertheless with the opportunity to vary the hard segment content has been developed. The strategy is based on amine formation from isocyanate upon reaction with water. By adding a dissolved soft segment to an excess of diisocyanate followed by the addition of water in the gas phase, amines are formed <i>in situ</i>. Urea linkages are then formed when these amines react with the excess of isocyanate groups. The gas phase addition facilitates addition in a slow and continuous manner. The hard segment content can easily altered by varying the diisocyanate/soft segment ratio. Even though the strategy is shown to be applicable to different diisocyanates, the focus has been on the potentially biodegradable methyl-2,6-diisocyanatehexanoate (LDI) and 1.4-butanediisocyanate (BDI) and various well known biodegradable polyesters and polycarbonates. </p><p>All the synthesised materials exhibited pronounced phase separation and hydrogen bonding within the hard domains. However, a major increase in hydrogen bonding strength was seen when a symmetric diisocyanate was used instead of an asymmetric. Based on FTIR measurements, PUUs with BDI and a polydisperse hard segment can exhibit the same degree of phase separation and hydrogen bonding as the monodisperse product.</p><p>The elastic properties of this new group of PUUs were exceptional with an elongation at break from 1600% to almost 5000% and the elastic modulus could be varied from a few MPa up to a couple of hundreds. </p><p>Hydrolytic degradation was greater in the polyester-based than in the polycarbonate-based PUUs due to the more reactive ester bonds. Low mass loss but a considerable loss in molecular weight was seen in the polyester PUUs. The tensile strength decreased dramatically due to the loss of strain hardening.</p><p>An MTT seeding assay using human fibroblasts and an in vivo biocompatibility study were performed and no signs of cytotoxicity were seen and the inflammatory response was comparable to other inert polymers.</p><p>A biodegradable PUU with properties that can be tailored through an easy synthesis is here presented. </p>

A novel strategy for synthesising segmented poly(urethane urea) (PUU) without using a chain extender but nevertheless with the opportunity to vary the hard segment content has been developed. The strategy is based on amine formation from isocyanate upon reaction with water. By adding a dissolved soft segment to an excess of diisocyanate followed by the addition of water in the gas phase, amines are formed in situ. Urea linkages are then formed when these amines react with the excess of isocyanate groups. The gas phase addition facilitates addition in a slow and continuous manner. The hard segment content can easily altered by varying the diisocyanate/soft segment ratio. Even though the strategy is shown to be applicable to different diisocyanates, the focus has been on the potentially biodegradable methyl-2,6-diisocyanatehexanoate (LDI) and 1.4-butanediisocyanate (BDI) and various well known biodegradable polyesters and polycarbonates. All the synthesised materials exhibited pronounced phase separation and hydrogen bonding within the hard domains. However, a major increase in hydrogen bonding strength was seen when a symmetric diisocyanate was used instead of an asymmetric. Based on FTIR measurements, PUUs with BDI and a polydisperse hard segment can exhibit the same degree of phase separation and hydrogen bonding as the monodisperse product. The elastic properties of this new group of PUUs were exceptional with an elongation at break from 1600% to almost 5000% and the elastic modulus could be varied from a few MPa up to a couple of hundreds. Hydrolytic degradation was greater in the polyester-based than in the polycarbonate-based PUUs due to the more reactive ester bonds. Low mass loss but a considerable loss in molecular weight was seen in the polyester PUUs. The tensile strength decreased dramatically due to the loss of strain hardening. An MTT seeding assay using human fibroblasts and an in vivo biocompatibility study were performed and no signs of cytotoxicity were seen and the inflammatory response was comparable to other inert polymers. A biodegradable PUU with properties that can be tailored through an easy synthesis is here presented.

Commonly used thermoplastic biodegradable polymers are generally brittle and lack appreciable elasticity at physiological temperature and thereby fail to mimic the elastic nature of many human soft tissues such as blood vessels. Thus, there is a need for biomaterials which exhibit elasticity. Biodegradable elastomers are promising candidates whose elasticity more closely parallels that of soft tissues. In this research, we developed hybrid biodegradable elastomers comprised of organic and inorganic polymer components in a block copolymer system: poly(e-caprolactone) (PCL) and poly(dimethylsiloxane) (PDMS), respectively. A block structure maintains the distinct properties of the PCL and PDMS components. These elastomers may be useful for the tissue engineering of soft tissues as well as for shape memory polymer (SMP) devices. Tri-block macromers of the form PCLn-block-PDMSm-block-PCLn were developed to permit systematic variations to key features including: PDMS block length, PCL block length, PDMS:PCL ratio, and crosslink density. The macromer was capped with acrylating groups (AcO) to permit their photochemical cure to form elastomers. Thus, a series of biodegradable elastomers were prepared by photocrosslinking a series of macromers in which the PCL blocks varied (n = 5, 10, 20, 30, and 40) and the PDMS block was maintained (m = 37). All elastomers displayed hydrophobic surface properties and high thermal stability. These elastomers demonstrated systematic tuning of mechanical properties as a function of PCL block length or crosslink density. Notable was strains at break as high as 814% making them suitable for elastomeric bioapplications. Elastomers with a critical PCL block length (n = 30 or 40) exhibited shape memory properties. Shape memory polymers based on an organic-inorganic, photocurable silicon-containing polymer system is a first of its kind. This SMP demonstrated strain fixity of 100% and strain recovery near 100% after the third thermomechanical cycle. Transition from temporary to permanent shape was quite rapid (2 sec) and at temperatures near body temperature (60 degrees C). Lastly, porous analogues of the biodegradable elastomers were created using a novel porogen - salt leaching technique. Resulting porous elastomers were designed for tissue engineering scaffolds or shape memory foams.

The first part of this dissertation focuses on the development, implementation and validation of models that capture the behavior of joints in a realistic manner. These models are presented within the framework of finite element based, nonlinear multibody dynamics formulations that ensure unconditional nonlinear stability of the computation for systems of arbitrary topology. The proposed approach can be divided into three parts. First, the joint configuration: this purely kinematic part deals with the description of the configuration of the joint and the evaluation of the relative distance and relative tangential velocity between the contacting bodies. Second, the contact conditions: in most cases, contact at the joint is of an intermittent nature. And finally, the contact forces: this last part deals with the evaluation of the forces that arise at the interface between contacting bodies. The advantage of the proposed approach is that the three parts of the problem can be formulated and implemented independently. Many articulated rotor helicopters use hydraulic dampers, which provide high levels of damping but are also associated with high maintenance costs and difficulties in evaluating their conditions due to the presence of seals, lubricants and numerous moving parts, all operating in a rotating frame. To avoid problems associated with hydraulic dampers, the industry is now switching to elastomeric lead-lag dampers that feature simpler mechanical design, lower part count, and result in "dry" rotors. However, the design of robust elastomeric dampers is hampered by the lack of reliable analytical tools that can predict their damping behavior in the presence of large multi-frequency motions experienced by the rotor and thus the damper. The second part of this dissertation focuses on the development of an elastomeric damper model which predicts the behavior of the elastomeric damper based on a continuum mechanics approach: the configuration of the damper is modeled using a finite element approach, and material behavior is represented by a set of nonlinear constitutive laws and material parameters. The validated finite element model of the elastomeric damper is then coupled with a comprehensive, multibody dynamics analysis code to predict the behavior of complex systems featuring elastomeric components.

Nanostructures and properties of blends of homopolymer and elastomeric block copolymer nanoparticles were studied focusing on the effect of morphology and the viscoelastic properties on blends. The cylindrical and lamellar morphology of PS-b-PI copolymer was employed to generate the morphology of elastomeric nanoparticles such as nanofiber and nanosheet. The particles were synthesized using cold vulcanization process. The vulcanization process using sulfur monochloride (S2Cl2) was used to preserve the morphologies. The crosslinking density of block copolymer was controlled by exposure time of crosslinking agent in the chamber. The blend samples for DMA and rheometer were prepared using solvent casting process. The diameter and thickness of nanofiber and nanosheet obtained by the process were ~40 nm and ~70 nm, respectively. The rheological and dynamic mechanical properties of the blends of polystyrene (PS) and elastomeric nanoparticles were studied in terms of morphology and crosslinking density. The effect of core PI size also investigated and discussed. Based on these viscoelastic results, the theoretical percolation threshold was calculated and compared with experimental results. It is demonstrated that block copolymer is a facile method to generate elastomeric nanoparticles using cold vulcanization and viscoelastic properties can be tuned with addition of nanoparticles.

Gewebeverstärkte Thermoplaste lassen sich durch Thermoformen zu räumlich gekrümmten Bauteilen verarbeiten. Durch die eingehende Analyse des Thermoformvorgangs konnte die Einsicht in die parallel verlaufenden Teilprozesse verstärkt werden. Interlaminare Scherung, der Wärmeaustausch und die Reibvorgänge zwischen Laminat und Werkzeug und die Stempeldeformationen werden eingehend experimentell untersucht. Für die Untersuchung der Reibverhältnisse zwischen Laminat und Werkzeug und des interlaminaren Gleitens werden neue Versuchsanordnungen vorgestellt. Außerdem wurden theoretische Modelle hinsichtlich ihrer Eignung zur Beschreibung dieser Effekte untersucht und gegebenenfalls angepasst. Durch die Aufteilung des Gesamtprozesses in zeitliche Phasen und die Entkopplung der physikalischen Vorgänge in der Beschreibung konnte ein Ansatz zur mathematischen Beschreibung des Gesamtprozesses gefunden werden, der für eine Implementierung in Simulationsprogrammen geeignet erscheint. Aus den gewonnenen Erkenntnissen werden praktische Schlussfolgerungen für die Gestaltung von Werkzeugen und Prozessen abgeleitet.