Desgaste de polímeros estruturais de engenharia em contato de deslizamento com cilindro metálico

Present work proposed to map and features the wear mechanisms of structural polymers of engineering derived of the sliding contact with a metallic cylindrical spindle submitted to eccentricity due to fluctuations in it is mass and geometric centers. For this it was projected and makes an experimental apparatus from balancing machine where the cylindrical counterbody was supported in two bearings and the polymeric coupon was situated in a holder with freedom of displacement along counterbody. Thus, the experimental tests were standardized using two position of the two bearings (Fixed or Free) and seven different positions along the counterbody, that permit print different conditions to the stiffness from system. Others parameters as applied normal load, sliding velocity and distance were fixed. In this investigation it was used as coupon two structural polymers of wide quotidian use, PTFE (polytetrafluroethylene) and PEEK (poly-ether-ether-ketone) and the AISI 4140 alloy steel as counterbody. Polymeric materials were characterized by thermal analysis (thermogravimetric, differential scanning calorimetry and dynamic-mechanical), hardness and rays-X diffractometry. While the metallic material was submitted at hardness, mechanical resistance tests and metallographic analysis. During the tribological tests were recorded the heating response with thermometers, yonder overall velocity vibration (VGV) and the acceleration using accelerometers. After tests the wear surface of the coupons were analyzed using a Scanning Electronic Microscopy (SEM) to morphological analysis and spectroscopy EDS to microanalysis. Moreover the roughness of the counterbody was characterized before and after the tribological tests. It was observed that the tribological response of the polymers were different in function of their distinct molecular structure. It were identified the predominant wear mechanisms in each polymer. The VGV of the PTFE was smaller than PEEK, in the condition of minimum stiffness, in function of the higher loss coefficient of that polymer. Wear rate of the PTFE was more of a magnitude order higher than PEEK. With the results was possible developed a correlation between the wear rate and parameter (E/ρ)1/2 (Young modulus, E, density, ρ), proportional at longitudinal elastic wave velocity in the material.

Avaliação tribológica dos polímeros NBR, PTFE e PTFE gravitado em contato com aço AISI 52100

Low cost seals are made of NBR, Nitrile Butadiene Rubber, a family of unsaturated copolymers that is higher resistant to oils the more content of nitrile have in its composition, although lower its flexibility. In Petroleum Engineering, NBR seal wear can cause fluid leakage and environmental damages, promoting an increasing demand for academic knowledge about polymeric materials candidate to seals submitted to sliding contacts to metal surfaces. This investigation aimed to evaluate tribological responses of a commercial NBR, hardness 73 ± 5 Sh A, polytetrafluoroethylene (PTFE), hardness 60 ± 4 HRE and PTFE with graphite, 68 ± 6 HRE. The testings were performed on a sliding tribometer conceived to explore the tribological performance of stationary polymer plane coupons submitted to rotational cylinder contact surface of steel AISI 52100, 20 ± 1 HRC Hardness, under dry and lubricated (oil SAE 15W40) conditions. After screening testings, the normal load, relative velocity and sliding distance were 3.15 N, 0.8 m/s and 3.2 km, respectively. The temperatures were collected over distances of 3.0±0.5 mm and 750±50 mm far from the contact to evaluate the heating in this referential zone due to contact sliding friction by two thermocouples K type. The polymers were characterized through Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). The wear mechanisms of the polymer surfaces were analyzed by Scanning Electron Microscopy (SEM) and EDS (Energy-Dispersive X-ray Spectroscopy). NBR referred to the higher values of heating, suggesting higher sliding friction. PTFE and PTFE with graphite showed lower heating, attributed to the delamination mechanism

Estudo das propriedades críticas do processo de contato por par para diferentes atualizações

We study the critical behavior of the one-dimensional pair contact process (PCP), using the Monte Carlo method for several lattice sizes and three different updating: random, sequential and parallel. We also added a small modification to the model, called Monte Carlo com Ressucitamento" (MCR), which consists of resuscitating one particle when the order parameter goes to zero. This was done because it is difficult to accurately determine the critical point of the model, since the order parameter(particle pair density) rapidly goes to zero using the traditional approach. With the MCR, the order parameter becomes null in a softer way, allowing us to use finite-size scaling to determine the critical point and the critical exponents β, ν and z. Our results are consistent with the ones already found in literature for this model, showing that not only the process of resuscitating one particle does not change the critical behavior of the system, it also makes it easier to determine the critical point and critical exponents of the model. This extension to the Monte Carlo method has already been used in other contact process models, leading us to believe its usefulness to study several others non-equilibrium models

Estudos de modelos Estocásticos: processo de contato, séries aleatórias e processos difusivos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

O contato em um click: ser-com em um mundo supervirtualizado

O presente estudo tem como objetivo compreender os sentidos da experiência de jovens e adultos com a interação social virtual, partindo de suas narrativas. Inspiradas nas ideias de Martin Heidegger, especialmente em seu seminário A Questão da Técnica , refletiremos sobre os modos de ser-com, em tempos de tecnologia, internet, consumo e hipermodernidade, contexto deste estudo, onde as coisas são vivenciadas em seu extremo (hiperconsumo, hipercorpo, hipermercado, hipercartões). Neste cenário, a Internet e as Tecnologias de Informação e Comunicação estão mediando, cada vez mais o contato do homem com o mundo, reconfigurando a vida em sociedade. Diante disso, apresentamos A Era do Click , em que são possibilitados novos meios de estar com os outros. Este é um estudo qualitativo, baseado na fenomenologia de Heidegger, por ser favorecedora da compreensão dos sentidos da experiência em relação à questão problematizada. Como estratégias de pesquisa foram utilizadas sondagem de campo e entrevistas individuais, inspiradas nas narrativas de Walter Benjamin. Cinco colaboradores relataram suas experiências de ser-com no mundo virtual. A partir de seus relatos foi possível compreender que o espaço virtual se revela como mais um lócus, dentre tantos, no cotidiano do ser do homem, em que emergem diferentes modos de ser-com. Dependendo de sua abertura, a proximidade ou o distanciamento tornam-se relativos, do mesmo modo que o pessoal e o impessoal, o próprio e o impróprio. Além disso, tornou-se claro que, a virtualidade pode ajudar a lidar com a solidão e a angústia temporariamente, da mesma forma que pode tornar-se uma barreira para um contato mais aprofundado e autêntico com os outros. Os colaboradores demonstraram uma atitude de serenidade, um poder dizer sim e não simultaneamente à técnica moderna, além de uma postura de meditar sobre os modos como se conectam. Questionamos as implicações em longo prazo da virtualização do contato, estimulando novos estudos, sob a luz da fenomenologia heideggeriana

Análise comparativa na influência da técnica de moldagem funcional em arcos parcialmente edêntulos sobre os pontos de contato oclusais, a integridade da fibromucosa e a extensão da base da prótese

There is a lack of clinical studies evaluating techniques of functional impression for partially edentulous arches. The aim of this double-blind non-randomized controlled clinical trial was to compare the efficacy of altered cast impression (ACI) and direct functional impression (DFI) techniques. The efficacy was evaluated regarding the number of occlusal units on denture teeth, mucosa integrity at 24-hour follow-up and denture base extension. The sample included 51 patients (female and male) with mean age of 58.96 years treated at Dental Department of UFRN. The patients, exhibiting edentulous maxilla and mandibular Kennedy class I, were divided into two groups (group ACI, n=29; group DFI, n=22). Clinical evaluation was based on the number of occlusal units on natural and/or artificial teeth, mucosa integrity at 24-hour follow-up, and denture base extension. Statistical analysis was conducted using the software SPSS 17.0® (SPSS Inc., Chicago, Illinois). Student T-test was used to reveal association between number of occlusal units and impression technique while chi-square test showed association between mucosa integrity and impression technique. Fischer s exact test was applied for association between denture base extension and impression technique at 95% level of significance. No significant difference was observed between the groups regarding number of occlusal units, mucosa integrity and denture base extension. The altered cast technique did not provide significant improvement in comparison to the direct technique when the number of occlusal units, mucosa integrity and denture base extension