Influência do óleo automotivo nas propriedades mecânicas e na estrutura de correias sincronizadoras

Abstract

Timing belts are elastomer-based composite components reinforced with continuous fibers and, in modern three-cylinder engines, have increasingly been operated immersed in oil (“belt-in-oil”), a solution that offers reduced noise, greater flexibility, and lower mass. However, reports of premature failures have raised concerns. This study was motivated by a real case in which a timing belt with a projected lifespan of 240,000 km failed at 110,000 km. It was considered that improper tension, pulley misalignment, shock loads, and possible interaction with engine oil could have contributed to the rupture. The investigation followed a two-stage methodology. In the first stage, a stereoscopic fractographic analysis of the failed belt was carried out to identify the dominant rupture mechanisms. In the second stage, experimental tests were conducted on samples immersed in 0W20 oil, with and without additives, for 60 days at room temperature. After aging, the samples were evaluated for dimensional changes, mass gain, Shore D hardness, and possible chemical modifications via FTIR, enabling comparison between the virgin and oil-exposed states. The fractography revealed typical mechanical failure mechanisms such as fiber pull-out, shear at the tooth root, and asymmetric wear, all consistent with overload and misalignment, with no indications of oil-induced chemical degradation. In the laboratory tests, dimensional variations remained below 2%, mass gain ranged from 1.1% to 1.4%, hardness decreased by about 2 Shore D units, and FTIR showed no structural alterations, with spectral differences attributed solely to superficial oil adsorption. The results indicate that oil exposure did not promote significant material degradation under the evaluated conditions, and that the premature failure is more strongly associated with mechanical factors rather than the “belt-in-oil” environment.