Name: Johnni Almeida Nascimento
Type: MSc dissertation
Publication date: 03/04/2020

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Examining board:

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FLAVIO JOSE DA SILVA External Examiner *
Temistocles de Sousa Luz External Examiner *

Summary: The objective of this work is to study the behavior of the wear of polymeric pair polypropylene (PP) and elastomeric polyurethane (PU) in environments lubricated with distilled water, synthetic seawater and without lubrication. Tests were performed on a tribometer in the alternating pin-plane configuration in conformal contact. In both lubricated environments, two normal loads and two sliding speeds were used. In the non-lubricated environment, a normal load and three sliding speeds were maintained. The average slip speeds of the tests varied between 18 and 90 mm / s. The sliding distance ranged from 108 to 1080 m. The normal applied load was 230 and 690 N. The subsurface temperature of the samples were measured during the tests, by placing a thermocouple sensor 1.5 mm from the samples surface before each test, using a specific methodology. The wear rate was calculated by measuring the mass of the samples before and after each wear test. To reduce the effects of water absorption on the measured mass, a comparative weighing method with control samples in the same environment was used. The effect of the PV condition (product of the nominal contact pressure by the sliding speed) on the heat and the wear rates of the tests was also analyzed. In the environment without lubrication, it was observed that the increase in sliding speed was responsible for the transition of the polypropylene wear rate: from moderate to severe, due to the increase in the contact temperature. The variation of the load and sliding speed in the lubricated conditions did not cause a transition in the polypropylene wear regime, always maintaining a moderate condition, and with close wear rates. In the test in distilled water with higher load and speed, there was a higher rate of polypropylene wear among the lubricated tests. The wear rate of the polyurethane was measured, but the high hygroscopicity of the material, the adhesion of polypropylene and the dispersion of the data made it impossible to identify differences in wear rates between the three environments. The superficial aspect was observed by means of an optical microscope, which indicated in the polypropylene the micro-mechanisms of abrasion wear, melt wear, superficial fatigue (microcracks), Schallamach waves and film transfer. In polyurethane, abrasion and surface fatigue micro mechanisms (microcracks) were observed.

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