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Otimização de tribo revestimentos multifuncionais: uma abordagem experimental/computacional / Optimization of multifunctional coatings: experimental and computational approachLara, Luciano de Oliveira Castro 11 June 2012 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Lately, we have witnessed a growing concern about determining energy consumption and
pollutant emissions. Large part of the energy spent is directly related to the friction and wear.
Likewise, there a growing demand for production of mechanical systems of high efficiency.
To develop systems that are more economical, noiseless and not harmful to the environment,
there is a limit imposed by materials and conventional surface treatment. Thus, critical
tribological contacts and possible new materials have been intensively investigated. Solid
lubrication and solid lubricants are emerging as a promising alternative to control friction and
wear in mechanical systems modern. The use of multifunctional coatings have been studied
and used in modern mechanical systems, so that the final properties depend on the system
composed of substrate - coating - environment. This study aims to optimize the thickness of
multifunctional coatings with potential for use in mechanical systems of high efficiency,
particularly on soft substrates. The aim is an optimization using the principles of contact
mechanics, together with strength criteria to analyse stress and strain. Efficient techniques to
characterize the coatings, and powerful simulation tools in the stress analysis of
multifunctional coatings were used. The results showed that the thickness of the coating plays
an important role on coating properties. / Ultimamente, tem-se presenciado uma preocupação cada vez mais determinante quanto ao
consumo energético e emissões de poluentes. Grande parte da energia gasta está relacionada
diretamente com o atrito e o desgaste. Há igualmente uma demanda crescente por produção de
sistemas mecânicos de alta eficiência, mas, também, para desenvolver sistemas cada vez mais
econômicos, silenciosos e não prejudiciais ao meio ambiente, havendo um limite imposto por
materiais e tratamento de superfícies convencionais. Assim, a tribologia de contatos críticos e
possíveis novos materiais estão sendo amplamente pesquisados. A lubrificação sólida e
lubrificantes sólidos estão aparecendo como uma alternativa promissora para controlar o atrito
e o desgaste nos sistemas mecânicos modernos. A utilização de revestimentos multifuncionais
tem sido estudada e aplicada nos sistemas mecânicos modernos, de modo que as propriedades
finais resultantes sejam dependentes do sistema substrato-revestimento-ambiente. O presente
trabalho busca a otimização de tribo revestimentos multifuncionais com potencial para a
aplicação em sistemas mecânicos de alta eficiência, particularmente sobre substratos macios.
Busca-se essa otimização por meio da análise de tensões e deformações, as quais são
compreendidas através do princípio da mecânica do contato, juntamente com os critérios de
resistência. Usam-se técnicas de caracterização de revestimentos amplamente usadas e
eficientes, como também ferramentas de simulação poderosas na análise de tensões de
revestimentos multifuncionais. Os resultados demonstram que a espessura do revestimento
tem um papel importante na origem das propriedades do revestimento. / Doutor em Engenharia Mecânica
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Modélisation expérimentale de phénomènes électrostatiques et tribologiques aux interfaces solide/solide / Experimental and numerical modeling of electrostatic and tribological phenomena at solid/solid interfacesNeagoe, Marian-Bogdan 05 December 2017 (has links)
L'objectif de cette thèse a été d'explorer la possibilité d'utiliser la charge électrostatique pour améliorer les conditions de contact glissant sec ou lubrifié (deux huiles avec viscosités différentes et de l’eau distillée) entre matériaux polymériques (PP, PE, PS, ABS et deux types de PVC). Trois nouvelles installations expérimentales ont été conçues et réalisées. La première installation est un tribomètre linéaire qui permet le réglage de quatre variables de contrôle du processus de charge (la force normale, la vitesse, la durée et l’amplitude du mouvement de glissement) et la mesure de trois caractéristiques du régime de frottement (la force tangentielle, la variation de la force normale et le déplacement relatif entre les éprouvettes). La deuxième installation est un dispositif pour mesurer la distribution de la charge électrique de surface et la corréler avec des cartographies de température. Une troisième installation est destinée à l'étude de l’influence de la charge électrique sur l’angle de contact de gouttelettes déposées en surface. Les expériences réalisées ont montré que le niveau de la charge généré par frottement sec dépend du temps de frottement, de l’usure, de la pression de contact et de la rugosité des surfaces. Une charge générée par effet triboélectrique ou par décharge couronne peut augmenter le frottement à sec. En revanche, la présence d’une charge électrique à la surface du polymère améliore le frottement lubrifié. Les mesures d’angles de contact ont mis en évidence que celui-ci dépend de la nature du liquide et du polymère étudiés, ainsi que de l’état de charge électrique des échantillons. / The approach undertaken in this thesis is to explore the possibility of using the electrostatic charge to improve the dry or lubricated (two oils with different viscosity and distilled water) sliding contacts between polymeric materials (PP, PE, PS, and ABS, two types of PVC). Three experimental benches were designed and built. The first installation is a linear tribometer designed to study the sliding contacts between solids with dry or lubricated friction. It allows the adjustment to four control variables of the tribocharging process: normal force, sliding speed, time and stroke, and the measurement of three characteristics of the friction regime: the tangential force, the variation of the normal force and the relative displacement between the specimens. The second installation is a device for measuring the distribution of the surface electrical charge, and for correlating it with the temperature mappings. A third installation is designed to study the influence of the electric charge on the contact angle of droplets deposited on the surface. The experiments showed that the level of the charge generated by dry friction depends on the friction time, the wear, the contact pressure and the roughness. A charge generated by friction or by corona discharge can increase dry friction. On the other hand, the presence of electric charge on the surface of polymers can improve a lubricated contact. The contact angle measurements pointed out the influence of the nature of both solid and liquid materials involved in the contact, as well as of the electric charge of the samples.
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