Date of Award
Master of Science
Interaction of brakes with external environment can considerably influence their performance which could relate to friction instabilities. Humidity can alter the chemistry of friction surfaces that could relate to unwanted phenomena which increase the cost of product. In addition to the chemical phenomena leading to unwanted reactions, there are physical effects related to adsorption of humidity and to modification of adhesion, accompanied with changes in contact surfaces and contact mechanics. The goal of this paper is to address these chemical and physical phenomena occurring at friction interfaces of model friction materials and to relate them to their performance. Friction tests were performed by using the environmental (equipped with humidity and temperature chambers) bench-top UMT TriboLab friction tester (Bruker) with scaled-down parameters derived from adopted real vehicle braking scenario. Wear surfaces/mechanisms were studied by using scanning electron microscopy (Quanta FEG 450 by FEI) equipped with the energy dispersive X-ray microanalysis (Inca System), and 3D optical microscope (NPFLEX by Bruker). Vibrational response was monitored by triaxial ICP Accelerometer (PCB Piezotronics, Model=356A45) and Oscilloscope (Agilent Technologies, Model= MSOX2024A). The data were analyzed by use of Matlab (MathWorks, Version= R2015A). The physical adsorption is dependent strongly on the surface topography; nevertheless, the chemical species/products generated at the friction surfaces are dominant factor dictating the quantity of absorbed humidity/species. Their chemistry differs from the chemistry of bulk and a complex correlation must be further studied. Adsorption considerably influences the friction performance (friction and its stability, wear, noise and environmental response/pollution capacity) of brake pads. Further studies addressing these phenomena are recommended. Keywords – humidity, friction, scanning electron microscopy, brake pads and X-ray microanalysis.
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