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.

Broadband, variable, and random excitations are often suppressed using active vibration absorbers (AVAs). While AVAs can be effective, they also are expensive and subject to instability when the disturbance is ill defined. A state-switched absorber (SSA) can be used for these same vibration classes while reducing the expense and instability because an SSA is only allowed to be active at discrete instances. SSAs are spring-mass-damper devices in which at least one element is controllably variable. The work presented in this dissertation evaluates the properties of magnetorheological elastomers (MREs) to assess their use in SSAs as variable springs. MREs are elastomers doped with magnetically permeable material, generally iron. They are modeled as lossy springs, and have stiffness and loss factor components. Natural frequency and stiffness behavior, and their relationships to static displacement, iron content, and forcing frequency and amplitude were determined. Loss factors were found to be independent of MRE content, configuration, and static displacement. This was confirmation that MREs are in fact controllable springs. Natural frequencies changed in the presence of magnetic fields by as much as 360%. The corresponding change in static displacement could not account for this frequency change. Transient data was found by determining the length of time it took for an MRE to achieve quasi-steady state oscillation behavior when subjected to a harmonic excitation. This time was referred to as the characteristic response time. The characteristic response time correlated to the ratio of the forcing frequency to the zero-field natural frequency. When a magnetic field was turned on, the characteristic response time on average was found to be consistently longer than when the magnetic field was turned off, regardless of iron content or configuration. The difference between these two characteristic response times is caused by the particles' mechanics. To form a chain, a magnetic field must both be set up, and particles must move to join together. When a chain is broken, the magnetic field must merely be removed. However, this difference gives opportunities for future research to be conducted on controlling MREs' transient responses.

Thesis (M.S.)--University of Michigan, 1983.

Thesis (M.S.)--University of Michigan, 1983.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-04-10T19:06:53Z No. of bitstreams: 1 LEANDRO RODRIGUES PEREIRA - DISSERTAÇÃO PPG-CEMat 2014..pdf: 3148791 bytes, checksum: 14fe302e950234a170c84cd8636b58ad (MD5) / Made available in DSpace on 2018-04-10T19:06:53Z (GMT). No. of bitstreams: 1 LEANDRO RODRIGUES PEREIRA - DISSERTAÇÃO PPG-CEMat 2014..pdf: 3148791 bytes, checksum: 14fe302e950234a170c84cd8636b58ad (MD5) Previous issue date: 2014-07-17 / Desde o final do século XIX, foram utilizados vários materiais para o aumento da mama. Como exemplos, citam-se espumas de poliuretano e polietileno, bolas de vidro, gutta percha, entre outros. O uso de silicone para fins de aumento de mama se iniciou em 1961 e, partir de então, as empresas desenvolveram inovações ao processo de fabricação de implantes mamários incluindo a inserção de camadas de barreiras para evitar a migração de gel. Em 2012, foi publicada a Resolução ANVISA RDC nº 16 que estabeleceu os requisitos mínimos de identidade e qualidade para os implantes mamários de silicone. Desta forma, este trabalho propõe a avaliar os implantes mamários regularizados no Brasil e realizar a caracterização morfológica, estrutural e mecânica de implantes mamários de silicone comercializados no Brasil em conformidade com as Normas Vigentes, por meio de caracterizações: Microscopia Ótica – MO, Microscopia Eletrônica de Varredura – MEV com espectroscopia de Energia Dispersiva- EDS e avaliação do comportamento mecânico quando submetidos ao Ensaio de Tração, sendo avaliados os quesitos estabelecidos na norma ISO 14607:2007. Com base nos resultados obtidos neste trabalho pode-se concluir que todas as membranas de implantes mamários avaliadas apresentaram-se adequadas para uso como biomaterial. Verificou-se também a oportunidade de melhoria normativa, com estabelecimento de parâmetro mínimo de desempenho para o ensaio de resistência ao rasgo, estabelecido na norma ISO 14607:2007. / Since the late nineteenth century, various materials were used for breast augmentation. Polyurethane, polyethylene, glass balls, gutta percha, among others materials were used. The use of silicone for breast augmentation purposes began in 1961 and, since then, companies have developed innovations to the manufacturing process of breast implants including the insertion of barrier layers to prevent migration of silicone gel. In 2012 was published the ANVISA Resolution RDC No. 16 which established minimum requirements for identity and quality for silicone breast implants. Thus, this study aims to evaluate six brands of regularized breast implants in Brazil and perform morphological, structural and mechanical caracterization in accordance with current standards. Optical Microscopy - MO, Electron Microscopy Scanning - SEM with Energy Dispersive Spectroscopy- EDS and evaluation of the mechanical behavior when subjected to tensile test according to ISO 14607:2007 standard. Based on the results obtained in this study, it can be concluded that all the membranes of breast implants had to be suitable for use as a biomaterial, complying with regulatory requirements. There is also an opportunity to improve the ISO 14607:2007 standard, establishing a minimum performance requirement for testing elastomer shell tear resistance.

Cette thèse traite la préparation et l'application d’élastomères bio-sourcés et leurs nanocomposites qui sont les suivants : (1) des nanocomposites basés sur le 3,9 - bis [ethyl-2-à 1,1 terne {b-(3-tertbutyle-4-hydroxy-5-méthylephényle) propionyloxy} éthyle]-2,4,8,10-tetraoxaspiro-[5,5]-undécane (AO-80) et le poly(itaconate de diisoamyle-co-isoprène) (PDII), (2) le poly(itaconate de dibutyle-co-isoprène-co-acide méthacrylique) (PDIM), un élastomère carboxylique bio-sourcé, et des nanocomposites basés sur cet élastomère et la silice ou les nanotubes de halloysite, (3) le poly(itaconate de dibutyle-co-butadiène) (PDIB), un nouvel élastomère bio-sourcé, et des nanocomposites basés sur cet élastomère et la silice. Des pneus verts bio ont été fabriqués en utilisant les nanocomposites PDIB/silice dans une formulation de bande de roulement de pneu. En plus de la préparation de ces dits élastomères bio et leurs nanocomposites, cette thèse donne aussi une revue sur les travaux sur des liaisons sacrificielles bio-inspirées qui sont introduites dans des matériaux polymères. Cette revue servira d'un guide pour incorporer des liaisons sacrificielles dans des élastomères à base d’itaconate ayant une grande rigidité et résistance / This thesis deals with the preparation and application of itaconate based engineering elastomers and their nanocomposites. The following elastomers or nanocomposites were prepared: (1) nanocomposites based on 3,9-bis[1,1-dim ethyl-2-{b-(3-tertbutyl-4-hydroxy-5-methylphenyl)propionyloxy}ethyl]-2,4,8,10-tetraoxaspiro-[5,5]-undecane (AO-80) and poly(diisoamyl itaconate-co-isoprene) (PDII), (2) a bio-based carboxylic elastomer, poly(dibutyl itaconate-co-isoprene-co-methacrylic acid) (PDIM), and nanocomposites based on it and silica or halloysite nanotubes, (3) a novel bio-based elastomer, poly(dibutyl itaconate-co-butadiene) (PDIB), and nanocomposites based on it and silica. Bio-based green tires were manufactured by using PDIB/silica nanocomposite in a tire tread formulation. In addition to the preparation of the above bio-based elastomers and their nanocomposites, this thesis also gives a review on the progresses on bio-inspired sacrificial bonds in polymeric materials. This review will serve as a guide to engineer sacrificial bonds into itaconate based elastomers with high strength and toughness

Análises numéricas confiáveis do comportamento mecânico de materiais como borrachas, dependem muito de uma calibração precisa do modelo constitutivo hiperelástico utilizado. Estes modelos são calibrados ajustando as curvas teóricas aos dados experimentais, obtidos por meio de ensaios usuais. Em muitos casos as amostras de matéria prima desses elastômeros já não se encontram disponíveis ou é impossível fabricar os corpos de prova requeridos. O objetivo deste trabalho é verificar a possibilidade de encontrar constantes constitutivas testando o próprio componente, ao invés dos usuais ensaios de tração, compressão e cisalhamento. A abordagem proposta consiste em criar uma rotina de programação associada a uma função custo onde, a partir de uma estimativa inicial de constantes constitutivas, sejam realizados processos iterativos de otimização buscando aproximar as curvas de força × deslocamento teórica e experimental. Um componente automotivo será utilizado nos estudos e dois modelos constitutivos hiperelásticos serão testados. As equações de tensões nominais dos modelos hiperelásticos serão utilizadas para predizer o comportamento teórico dos ensaios usuais, de forma a verificar a qualidade das constantes obtidas. Conclui-se que é possível utilizar o ensaio da própria peça para caracterizar o material hiperelástico, com resultados comparáveis aos que seriam obtidos com os ensaios típicos para esta aplicação. / The reliable numerical analysis of the mechanical behavior of rubber-like materials depends strongly on accurately calibrated hyperelastic constitutive models. Such models are calibrated by fitting theoretical curves against experimental data obtained in well known tests. In many cases samples of the original elastomer are no longer available or it is impossible to manufacture the specimens required by the standard tests. The aim of this work is verify the possibility of finding the constitutive constants by testing the actual component instead of the usual tensile, compression and shear tests. The proposed approach consists in creating a programming routine with a cost function that, starting from an initial estimate of the constitutive constants, iterate through an optimization algorithm in order to fit the theoretical force × displacement curves to the experimental ones. An automotive component will be used during the studies and two hyperelastic constitutive models will be tested. The nominal stress equations for the hyperelastic models are used to predict the standard tests behavior, to assess the quality of the constants obtained. The results shown that is possible to characterize an hyperelastic material by testing the actual component, with results comparable to those which would be obtained with standard tests.

O presente trabalho trata da modelagem da condução de calor transiente com geração de calor em meios heterogêneos, e tem o objetivo de desenvolver um modelo multiescala adequado a esse fenômeno. Já existem modelos multiescala na literatura relacionados ao problema proposto, e que são válidos para os seguintes casos: (a) o elemento de volume representativo tem tamanho desprezível quando comparado ao comprimento característico macroscópico (e como consequência, a microescala tem inércia térmica desprezível); ou (b) a geração de calor é homogênea na microescala. Por outro lado, o modelo proposto nesta tese, o qual é desenvolvido utilizando uma descrição variacional do problema, pode ser aplicado a elementos de volume representativos finitos e em condições em que a geração de calor é heterogênea na microescala. A discretização temporal (diferenças finitas) e as discretizações espaciais na microescala e na macroescala (método dos elementos finitos) são apresentadas em detalhes, juntamente com os algoritmos necessários para implementar a solução do problema. Nesta tese são apresentados casos numéricos simples, procurando verificar não só o modelo teórico multiescala desenvolvido, mas também a implementação feita. Para tanto, são analisados, por exemplo, (a) casos em que considera-se a microescala um material homogêneo, tornando possível a comparação da solução multiescala com a solução convencional (uma única escala) pelo método dos elementos finitos, e (b) um caso em um material heterogêneo para o qual a solução completa, isto é, modelando diretamente os constituintes no corpo macroscópico, é obtida, tornando possível a comparação com a solução multiescala. A solução na microescala para vários casos analisados nesta tese sofre grande influência da inércia térmica da microescala. Para demonstrar o potencial de aplicação do modelo multiescala, simula-se a cura de um elastômero carregado com negro de fumo. Embora a simulação demonstre que a inércia térmica não precise ser considerada para esse caso em particular, a aplicação da presente metodologia torna possível modelar a cura do elastômero diretamente sobre a microescala, uma abordagem até então não utilizada no contexto de métodos multiescala. Essa metodologia abre a possibilidade para futuros aperfeiçoamentos da modelagem do estado de cura. / This work deals with the modeling of transient heat conduction with heat generation in heterogeneous media, and its objective is to develop a proper multiscale model for this phenomenon. There already exist multiscale models in the literature related to this proposed problem, and which are valid for the following cases: (a) the representative volume element has a negligible size when compared to the characteristic macroscopic size (and, as a consequence, the microscale has a negligible thermal inertia); or (b) the heat generation is homogeneous at the microscale. On the other hand, the model proposed in this thesis, which is developed using a variational description of the problem, can be applied to finite representative volume elements and in conditions in which the heat generation is heterogeneous at the microscale. The time discretization (finite difference) and the space discretizations at both the microscale and the macroscale (finite element method) are presented in details, together with the algorithms needed for implementing the solution of the problem. In this thesis, simple numerical cases are presented, aiming to verify not only the theoretical multiscale model developed, but also its implementation. For this, it is analyzed, for instance, (a) cases in which the microscale is taken as a homogeneous material, making it possible the comparison of the multiscale solution with the conventional solution (one single scale) by the finite element method, and (b) a case in a heterogeneous material for which the full solution, that is, modeling all constituents directly on the macroscale, is obtained, making it possible the comparison with the multiscale solution. The solution at the microscale for several cases analyzed in this thesis suffers a large influence of the microscale thermal inertia. To demonstrate the application potential of the multiscale model, the cure of a carbon black loaded elastomer is simulated. Although the simulation shows that the thermal inertia does not have to be considered for this case in particular, the application of the present methodology makes it possible to model the cure of the elastomer directly at the microscale, an approach not used in multiscale methods context until now. This methodology opens the possibility for future improvements of the state of cure modeling.

Les élastomères siloxanes sont des thermodurcissables, réticulés chimiquement, qui ne peuvent être ni remis en forme, ni transférés sur un support autre que celui d'origine, ni recyclés. Afin d'apporter une réponse à ces limitations, nous avons cherché à développer des élastomères siloxanes vitrimères, les vitrimères étant des matériaux capables d'être remis en forme, réparés et soudés grâce à des réactions d'échange associatives catalysées se produisant dans le réseau et activées par élévation de la température. Dans la première approche, nous avons étudié la trans-siloxanation, réaction d'échange intrinsèque aux siloxanes vivants, catalysée par les anions silanolates SiO- présents dans le réseau. Cependant, le caractère vivant induit un équilibre entre le réseau et des cycles, ces derniers très volatils peuvent s'évaporer lors du chauffage, ce qui favorise alors la dépolymérisation du réseau par trans-siloxanation intramoléculaire. Il en résulte que ces élastomères vivants ne sont pas vitrimères, leur connectivité étant continument modifiée. Néanmoins, nous avons montré que l'ajout de carbonate de césium accélère la réaction d'échange et permet la soudure de deux joints d'élastomères dont au moins un est vivant. Dans la seconde approche, le caractère vitrimère repose sur des liens dynamiques imines au sein d'un réseau siloxane non vivant. L'avantage de ce lien étant d'être non seulement échangeable mais aussi dissociable dans certaines conditions douces, ces élastomères siloxanes ont pu être remis en forme et recyclés. Enfin, l'introduction de charges de silice a permis d'améliorer leurs propriétés mécaniques sans toutefois altérer leurs propriétés vitrimères. / The polysiloxane elastomers are thermosets, chemically cross-linked, that can neither be reshaped, transferred on a support different from their original one nor recyclable. In order to overcome these limitations, siloxane elastomer vitrimers have been developed, the vitrimers being materials able to be reshaped, repaired and welded thanks to catalyzed and thermo-activated associative exchange reactions occurring within the network. In a first approach, we studied the trans-siloxanation, the intrinsic exchange reaction of living siloxanes, catalyzed by the silanolate anion SiO-. Nevertheless, this living nature leads to equilibrium between the network and cycles, that can evaporate upon heating and cause the depolymerisation of the network by intramolecular trans-siloxanation. The living elastomers are thus not vitrimer since their connectivity is continuously modified. However, we have shown that the addition of caesium carbonate accelerates the exchange reaction and allows the welding of two joints with at least one living. In the second approach, the vitrimer behaviour relies on imine dynamic bonds introduced into a non living network (no silanolate anion). As this bond is exchangeable but also dissociable under soft conditions, imine siloxane elastomers can not only be reshaped and but also recycled. Finally, the introduction of silica charges improves the mechanical properties without altering the vitrimer properties.