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Methodology for Evaluation of Thermal Degradation of Friction Materials in Bench Tests
ISSN: 0148-7191, e-ISSN: 2688-3627
Published February 10, 2022 by SAE International in United States
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Friction materials for automotive brakes are composites specially designed for attending various requirements, such as stable friction coefficient, low wear rate, high performance, low fade sensibility, thermal diffusivity, stiffness, strength, etc., in wide temperature ranges. For this reason, several raw materials are combined and processed so that all these requirements are met. Among the characterization tests performed for assessing the mechanical behavior of such materials, uniaxial compression, three-point bending, and internal shear tests are typically preferred. However, properties evaluated at ambient temperature and in a freshly manufactured product are only referential, as these properties tend to vary with temperature and after being subjected to the application. In order to evaluate the magnitude of the variation of mechanical properties of friction materials with temperature, different commercial linings applied to bus drum brakes were chosen, and mechanical characterization was performed at ambient temperature, at 250 oC, and after thermal cycles of heating and cooling. Variations were compared to the ones observed in a friction material, which run for 10000 km on field application. It was registered variations in mechanical properties between 1 % and 74 %, depending on the material, temperature, and the test considered, showing that significant changes can be found between a new and used product. When comparing the results of linings subjected to heating and cooling cycles to the ones obtained from used linings, very similar reductions in the properties were obtained. This shows that it is possible to estimate with reasonable accuracy the real degradation that can be expected in field through fast and straightforward laboratory procedures, which can potentially enhance material development and failure analyses. A Finite Element Structural Analysis was performed on a drum brake considering the variations found in mechanical properties, showing the strong influence of thermal degradation on the structural safety of such materials.
CitationLazzari, M., Webber, J., Matté, D., Pereira, C. et al., "Methodology for Evaluation of Thermal Degradation of Friction Materials in Bench Tests," SAE Technical Paper 2021-36-0422, 2022, https://doi.org/10.4271/2021-36-0422.
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