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This dissertation aims to contribute towards the understanding and modeling of tribological phenomena of contact, friction, and wear in viscoelastic materials with application in rubber compounds. Tribiological properties of rubber compounds are important for many applications such as tires, shoe heels and soles, wiper blades, artificial joints, O-ring seals, and so on. In all these applications, the objective is to maximize the friction coefficient to avoid slipping and reduce the wear rate to improve the life expectancy and performance of the products. The first topic in this study focuses on a novel multiscale contact theory proposed by Persson and explains the advantages of this theory over other classical contact theories. The shortcomings of this theory are also investigated, and three methods are proposed to improve Persson's original contact model by correcting the approximation of deformation in the contact area. The first method is based on the original Greenwood and Williamson (GW) contact theory, which neglects the effect of elastic coupling between asperities. The second method is based on an improved version of GW theory, which considers the elastic coupling effect of asperities in an approximate way. The third method is based on the distribution of local peaks of asperities, which is particularly suitable to determine the fraction of a skewed height profile involved in tribological processes. This method can be implemented within the framework of other proposed methods. Since the height profiles of rough surfaces studied in this dissertation are approximately normally distributed, the second correction method is applied to the original contact model to calculate the real contact area and friction coefficient. The second topic addresses the theoretical model of hysteresis friction in viscoelastic materials. The multiscale temperature rise of the rubber surface due to hysteresis friction is also modeled and the effect of flash temperature on the real contact area and friction coefficient is studied. Since the hysteresis friction is not the only mechanism involved in the rubber friction, a semi-empirical model is added to the hysteresis model to include the contribution of adhesion and other processes on the real contact area. Based on the improved multiscale contact theory, a pressure-dependent friction model is also developed for viscoelastic materials, which is in good agreement with experimental results. The third topic deals with the theory of stationary crack propagation in viscoelastic materials and the effect of crack tip flash temperature on the instability of crack propagation observed in some experimental results in the literature. Initially, a theoretical model is developed to calculate the tearing energy vs crack tip velocity in a Kelvin-Voigt rubber model. Besides, two coupled iterative algorithms are developed to calculate the temperature field around the crack tip in addition to the tearing energy as a function of crack tip velocity. In this model, the effect of crack tip flash temperature on the tearing energy is considered to update the relation between tearing energy vs crack tip velocity, which also affects the flash temperature. A theoretical model is also developed to calculate the contribution of the hysteresis effect to the tearing energy vs crack tip velocity using the dynamic modulus master curve of a rubber compound. Then, the low-frequency fatigue test results are compared with the theoretical predictions and used in the framework of powdery rubber wear theory to calculate the stationary rubber wear rate due to fatigue crack propagation. Moreover, a sliding friction and wear test set-up, with both indoor and outdoor testing capability, is developed to validate the theoretical models. The experimental results confirm that the theoretical model can successfully predict the friction coefficient when there is no trace of thermochemical degradation on the rubber surface. Investigating the wear mechanism of rubber samples on three different surfaces reveals that the contribution of fatigue wear rate is less important than other wear mechanisms such as abrasive wear due to sharp asperities or thermochemical degradation due to a significant rise of temperature on the contact area. Finally, the correlation between friction coefficient and wear rate on different surfaces is studied, and it is found that the relation between friction and wear rate strongly depends on the dominant wear mechanism, which is determined by the surface characteristics, sliding velocity, normal load, and contact flash temperature. / PHD / The objective of this dissertation is to understand and develop models for contact, friction, and wear in rubber-like materials. Friction and wear of rubber-like materials are important in many applications such as tires, shoe heels and soles, wiper blades, artificial joints, O-ring seals, and so on. In all these applications, it is desired to maximize the friction to avoid slipping and reduce the mass loss due to abrasion to improve the life expectancy of the products. The first topic in this dissertation focuses on a novel multiscale contact theory proposed by Persson and different approaches proposed in this work to improve this theory. Then, the real contact area is calculated using an improved version of the contact model. The second topic addresses the theoretical model of rubber friction due to hysteresis energy dissipation and the effect of frictional heating on the real contact area. Since the hysteresis friction is not the only mechanism involved in the rubber friction, a semi-empirical model is also used to include the contribution of adhesion and other processes on the real contact area. Based on the improved contact theory, a pressure-dependent friction model is also developed for rubber-like materials, which is in good agreement with the experimental results. The third topic deals with the theory of stationary crack propagation in rubberlike materials and the effect of crack tip temperature rise on the instability of crack propagation observed in some experimental results in the literature. The low-frequency fatigue test results are compared with the theoretical predictions, and the results are used in the framework of powdery rubber wear theory to calculate the rubber wear rate due to slow crack propagation. A sliding friction and wear test set-up is also developed to validate the theoretical models. The theoretical model of the friction coefficient is successfully validated by experimental results. Investigating the rubber wear on different surfaces reveals that the contribution of fatigue wear rate is less important than the other wear mechanisms. The correlation between friction coefficient and wear rate on different surfaces reveals that relation between friction and wear rate strongly depends on the dominant wear mechanism, which is determined by the surface characteristics, sliding velocity, normal load, and temperature rise on the contact surface.

Objetivando-se estudar o efeito de métodos químicos de indução de copa no desenvolvimento da seringueira, realizou-se experimento em condições de campo, em Casa Branca-SP, aplicando-se reguladores vegetais de crescimento em plantas enxertadas do cultivar RRIM 600 com 20 meses de idade, com 1,70 a 3,00 m de altura e último lançamento foliar maduro. O experimento foi delineado em Blocos ao Acaso com quatro repetições, utilizando-se como tratamentos, a aplicação de hidrazida maléica a 500, 750 e 1. 000 ppm, chlormequat a 1.000, 1.500 e 2.000 ppm, daminozide a 2.000, 3.000 e 4.000 ppm e a testemunha. Durante a realização do experimento efetuaram-se avaliações das seguintes variáveis: perímetro do tronco, espessura de casca, altura da árvore, altura do tronco, comprimento da copa, diâmetro da copa, número e porcentual de árvores ramificadas, número de ramos, concentração de ramos, ângulo de inserção dos ramos, índice de área foliar, coeficiente de absorção de radiação e danos por vento. Estudos de correlação foram feitos para analisar a influência das características da copa sobre o desenvolvimento das árvores. Nas condições em que foi conduzido o experimento, os resultados obtidos permitiam concluir que a indução de copa por métodos químicos pode incrementar o crescimento do perímetro do tronco, reduzindo o período de imaturidade da seringueira e que a injúria ou morte da gema apical aumentam a susceptibilidade das copas a danos por vento. O melhor tratamento foi com daminozide a 2.000 ppm, que apresentou ganho de 25% no perímetro relativo do tronco em relação à testemunha. Os tratamentos com daminozide apresentaram ganhos em perímetro do tronco sem comprometer a resistência das copas a danos por vento. Os tratamentos com chlormequat e hidraliza maléica não apresentaram ganhos em perímetro do tronco sendo que o último comprometeu a resistência das copas a danos por vento. O perímetro do tronco está positivamente correlacionado com a altura da árvore, o comprimento da copa, o diâmetro médio da copa e a espessura de casca; e negativamente relacionado com a altura do tronco. / This study describes the influences of chemical methods of branch induction on growth of Hevea brasiliensis. The experiment was situated in Casa Branca-SP, Brazil, where growth regulators were sprayed on buddings of cultivar RRIM 600, 20 months after planting. The experiment was delineated in randon blocks with 4 repetitions with the following treatments: maleic hydrazide at 500, 750 and 1,000 ppm; chlormequat at 1,000, 1,500 and 2,000 ppm; daminozide at. 2,000, 3,000 and 4,000 ppm, and control. Tree girth, bark thickness, tree and crown height, crown length, crown width, branch number and concentration, branch slope, leaf area index, canopy light absorption and wind damage measurements were carried out at regular intervals, during experiment period. Correlation studies were made to explain the relationships between canopy characters and tree growth. Under the prevailing experimental conditions we may derive the following conclusions: branch induction by chemical methods may increase the tree girth, reducing immature period of rubber; injury to the terminal apex increases susceptibility to wind damage; the best treatment was daminozide at 2,000 ppm presenting 25% gain on tree girth compared to control; daminozide treatments enhanced tree girth without changing the wind damage susceptibility; chlormequat and maleic hydrazide treatments did not increase tree girth, and the latest reduced the crowns wind damage resistance; tree girth is positive correlated with tree height, crown length, crown width and bark thickness, and negative correlated with crotch height.

Objetivando-se estudar o efeito de métodos químicos de indução de copa no desenvolvimento da seringueira, realizou-se experimento em condições de campo, em Casa Branca-SP, aplicando-se reguladores vegetais de crescimento em plantas enxertadas do cultivar RRIM 600 com 20 meses de idade, com 1,70 a 3,00 m de altura e último lançamento foliar maduro. O experimento foi delineado em Blocos ao Acaso com quatro repetições, utilizando-se como tratamentos, a aplicação de hidrazida maléica a 500, 750 e 1. 000 ppm, chlormequat a 1.000, 1.500 e 2.000 ppm, daminozide a 2.000, 3.000 e 4.000 ppm e a testemunha. Durante a realização do experimento efetuaram-se avaliações das seguintes variáveis: perímetro do tronco, espessura de casca, altura da árvore, altura do tronco, comprimento da copa, diâmetro da copa, número e porcentual de árvores ramificadas, número de ramos, concentração de ramos, ângulo de inserção dos ramos, índice de área foliar, coeficiente de absorção de radiação e danos por vento. Estudos de correlação foram feitos para analisar a influência das características da copa sobre o desenvolvimento das árvores. Nas condições em que foi conduzido o experimento, os resultados obtidos permitiam concluir que a indução de copa por métodos químicos pode incrementar o crescimento do perímetro do tronco, reduzindo o período de imaturidade da seringueira e que a injúria ou morte da gema apical aumentam a susceptibilidade das copas a danos por vento. O melhor tratamento foi com daminozide a 2.000 ppm, que apresentou ganho de 25% no perímetro relativo do tronco em relação à testemunha. Os tratamentos com daminozide apresentaram ganhos em perímetro do tronco sem comprometer a resistência das copas a danos por vento. Os tratamentos com chlormequat e hidraliza maléica não apresentaram ganhos em perímetro do tronco sendo que o último comprometeu a resistência das copas a danos por vento. O perímetro do tronco está positivamente correlacionado com a altura da árvore, o comprimento da copa, o diâmetro médio da copa e a espessura de casca; e negativamente relacionado com a altura do tronco. / This study describes the influences of chemical methods of branch induction on growth of Hevea brasiliensis. The experiment was situated in Casa Branca-SP, Brazil, where growth regulators were sprayed on buddings of cultivar RRIM 600, 20 months after planting. The experiment was delineated in randon blocks with 4 repetitions with the following treatments: maleic hydrazide at 500, 750 and 1,000 ppm; chlormequat at 1,000, 1,500 and 2,000 ppm; daminozide at. 2,000, 3,000 and 4,000 ppm, and control. Tree girth, bark thickness, tree and crown height, crown length, crown width, branch number and concentration, branch slope, leaf area index, canopy light absorption and wind damage measurements were carried out at regular intervals, during experiment period. Correlation studies were made to explain the relationships between canopy characters and tree growth. Under the prevailing experimental conditions we may derive the following conclusions: branch induction by chemical methods may increase the tree girth, reducing immature period of rubber; injury to the terminal apex increases susceptibility to wind damage; the best treatment was daminozide at 2,000 ppm presenting 25% gain on tree girth compared to control; daminozide treatments enhanced tree girth without changing the wind damage susceptibility; chlormequat and maleic hydrazide treatments did not increase tree girth, and the latest reduced the crowns wind damage resistance; tree girth is positive correlated with tree height, crown length, crown width and bark thickness, and negative correlated with crotch height.

Orientador: Mauro William Barbosa de Almeida / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Filosofia e Ciências Humanas / Made available in DSpace on 2018-08-16T01:51:04Z (GMT). No. of bitstreams: 1 Rezende_RobertoSanches_M.pdf: 6639396 bytes, checksum: d25b86eb91bb2408af1c27f85d7756ed (MD5) Previous issue date: 2010 / Resumo: Este é um estudo sobre as transformações ocorridas nos seringais da Reserva Extrativista do Alto Juruá, no Acre, ao longo das décadas de 1990 e 2000, tendo como foco empírico a comunidade Restauração, localizada no Rio Tejo. A criação da Reserva no início dos anos de 1990 coincide com o momento histórico em que a produção de borracha deixa de ser a principal atividade econômica dos moradores da região. Desde então, uma série de mudanças organizacionais ocorreram: as formas de ocupação do território e de sociabilidade se transformaram e levaram a um novo modo de viver na floresta. Desejos e planos de vida de moradores e políticas públicas específicas criaram, nesse contexto, a possibilidade de ocupação do território em uma vila, onde mais de cem famílias, que antes estavam espalhadas por diversas localidades, passaram a morar em um mesmo espaço. Esse novo modo de ocupação é muito distinto do padrão disperso de colocações, antes preponderante nos seringais, e levanta questões sobre como lidar com as antigas regras de propriedade e sobre a gestão da unidade de conservação e o manejo dos recursos naturais, já que o surgimento de uma vila significa também o surgimento de um padrão urbano de ocupação territorial que aumenta a pressão sobre esses recursos e modifica as relações sociais entre os moradores / Abstract: This is a research about the transformations in the rubber states of the Upper Tejo River, located at the Extractive Reserve of the Upper Juruá River, in the last twenty years. Since the Reserve was created the rubber activity continuously declined and a new pattern of territorial occupation has emerged, transforming the way rubber tappers live in that portion of the rainforest. Public policies, wishes and desires of the habitants lead to the creation of a town inside the Reserve and the occupation pattern, that earlier was based in houses dispersed by the forest, now is of houses and habitants living close to each other in a same location in the river bank. This growth of a location puts a problem to the conservational policies, due to the fact that a Reserve is a place for nature's conservation and social development. There are other conceptual problems in the transformations in the territory occupation: the ownership rules and the social relations also change in a urban context / Mestrado / Antropologia Rural / Mestre em Antropologia Social

Element Materials Technology in Linköping is an independent material testing company that performs testing of materials to several big sectors, such as the Swedish Armed Forces and the aerospace industry. There is of great importance to characterize aging of materials to ensure material performance. Element Materials Technology recently invested in a handheld FTIR equipment and it was of interest to see if this equipment might be an additional analysis technique to characterize aging of rubber materials. A nitrile butadiene rubber and two natural rubbers were thermally aged in 50°C and 70°C for six weeks. The hardness of the rubbers increased when the rubbers were thermally aged. The compression set decreased for the aged samples as well as the tensile strength and the elongation at break. An investigation of possible methods for collecting migrated additives on the rubber surface was performed, using two different solvents and a stationary FTIR equipment. More research needs to be performed to exclude the possibility that the solvents affect the material. Universal Attenuated Total Reflectance – Fourier Transform Infrared Spectroscopy, UATR-FTIR onto the rubber surface showed in some cases changes in the spectrums between unaged and aged samples. However, it could not be concluded weather the changes occurred due to migrating additives or due to changes in the backbone polymer. Four interfaces to the handheld FTIR equipment were investigated and an ATR interface gave best results. An analysis method was developed for the handheld FTIR equipment and the spectrums from the handheld FTIR were similar to spectrums from UATR-FTIR (stationary). It could be concluded from Micro Chamber analysis that volatile organic matters were emitted at elevated temperature. Thermogravimetric analysis could detect the relative composition of the rubbers. Further it could be concluded that the mechanical properties were affected by the thermal treatment. This study could however not establish a correlation between FTIR signals and the results seen from the other analysis. The fact that differences could be detected in the FTIR spectrums before and after aging could indicate that the FTIR analysis technique can possibly be used as an analysis method. However, a more thoroughly investigation needs to be performed before using this technique. / Element Materials Technology i Linköping utför materialutredningar åt en mängd olika typer av företag, där en stor sektor är den svenska Försvarsmakten och flygindustrin. Materialutredningar är essentiella för att säkerställa att rätt material används för rätt applikation. Element Materials Technology investerade nyligen i en handhållen FTIR utrustning. Det finns förhoppningar om att den nya utrustningen kan användas som ett komplement för att ålderskarakterisera gummimaterial. Ett nitril-butadien-gummi och två stycken naturgummin var termiskt åldrade i 50°C och 70°C i sex veckor. Hårdheten på provkroppar ökade efter den termiska åldringen. Sättningen, draghållfastheten och töjningen minskade för proverna åldrade i värme. En metod för att samla upp migrerade additiv från gummiytan utvecklades och undersöktes, genom att använda två olika lösningsmedel och en stationär FTIR utrustning. Ytterligare utredningar behöver däremot genomföras för att utesluta ifall de två lösningsmedel påverkar gummimaterialet och inte bara samlar upp additiv från gummiytan. UATR-FTIR visade på skillnader i spektrum mellan icke-åldrade och åldrade gummimaterial. Däremot kunde det inte avgöras om skillnaderna i spektrumen berodde på migration av additiv till gummiytan eller på förändring i huvudpolymeren. Fyra stycken olika tillbehör till den handhållna FTIR utrustningen prövades, där ATR-tillbehöret gav bra spektrum. En analyseringsmetod utvecklades för den handhållna FTIR-utrustningen och spektrum från dessa analyser gav liknande spektrum som spektrum från UATR-FTIR (stationär). Analys med Micro Chamber visade att flyktiga organiska ämnen lämnade gummimaterialet vid förhöjd temperatur. Termogravimetrisk analys, TGA visade förhållandet mellan gummimaterialets komponenter både före och efter åldring. Studien visade också att de mekaniska egenskaperna påverkades av den termiska åldringen. Analysmetoden FTIR kunde detekterad skillnad i spektrum före och efter åldring av gummimaterialen. Studien kunde däremot inte etablera ett samband mellan dessa FTIR-signaler och de övriga analysresultaten. Det kan däremot inte uteslutas att ett sådant samband finns. Ytterligare studier behöver utföras för att undersöka detta.

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The thesis presents novel formulations of hereditary cohesive zone models able to capture rate-dependent crack propagation along a defined interface. The formulations rely on the assumption that the measured fracture energy is the sum of an intrinsic fracture energy, related to the rupture of primary bonds at the atomic or molecular level, and an additional dissipation caused by any irreversible mechanisms present in the material and occurring simultaneously to fracture. The first contribution can be accounted for by introducing damage-type internal variables, which are to be driven by a rateindependent evolution law in order to be coherent with the definition as intrinsic energy. It is then proposed that the additional dissipation can be satisfactorily characterised by the same continuum-type material constitutive law obeyed by the interface material considered as a continuum: it is postulated that the dimensional reduction whereby a three-dimensional thin layer is idealized as a surface does not qualitatively alter the functional description of the free energy. The specific application considered is mode-I crack propagation along a rubber interface. After focusing on viscoelasticity as a suitable candidate to reproduce rubber’s behaviour, firstly the most common relaxation function, namely a single exponential term, is considerd after which the attention is turned to the use of fractional calculus and the related fractional integral kernel. A comparison with experimental results is presented. A shortcoming of the proposed approach is then noted, in that certain features of experimentally measured responses (i.e.the non-monotonicity of the critical energy-release rate with respect to crack speed) will be shown to be out of reach for the described modelling paradigm. A novel micromechanical formulation is then sketched in an attempt to qualitatively understand the phenomenon. An additional interface damaging mode is introduced, physically inspired by the desire to reproduce the formation of fibrils in a neighbourhood of the crack tip. Fibril formation is then driven by a variational argument applied to the whole of the interface, yielding its non-local character. Upon the introduction of an anisotropic fracture energy, motivated by experimental considerations, it is noted how the model can predict a non-monotonic energy-release rate vs crack speed behaviour, at least for a simple loading mode.