Abstract:The present work presents the morphology evolution of a brake material surface submitted to braking tests through a laboratory-scale tribometer. Optical microscope images of the material's surface were obtained for every 10 braking operations. These images were post-processed in appropriate computational software. By means of the image segmentation technique, morphological parameters related to the brake material surface were estimated. The wear rate and also the coefficient of friction resulting from the tests were measured. For the NAO material used in this study, the friction behaviour revealed to be strongly associated with the amount of contact plateaus. Besides, the mean area of the contact plateaus was the main factor responsible for increasing the real contact area of the friction material. The higher wear rate observed in the first braking operations can be mainly attributed to the higher surface roughness measured in this condition. As the braking operations progress, the plateaus becomes flatter and wear rate is reduced. Finally, the image segmentation technique proved adequate for investigating morphological aspects in friction material surface.Keywords: brake pad; image segmentation; real contact area
INTRODUCTIONNowadays there is an increasing number of researches devoted to study aspects related to the surface morphology of brake materials (brake pads and linings). For instance, some publications describe the mechanism of formation and destruction of the contact plateaus, which are the elements that effectively make contact between a friction pair (brake pad and disc). Yet, according to these studies, under certain circumstances the existence of large amount of small loose wear particles (also known as wear debris or third body) passing through the contact entrapped and embedded into pad interface due to the applied pressure, shear force and friction heat. Unevenly distributed wear and compaction of wear debris results in a surface characterised by flat plateaus, rising above the rest of the surface. As explained by Eriksson [1], the area of real contact is confined within the contact plateaus.On the other hand, Ostermeyer and Wilkening [4] describe the mechanism of destruction of the contact plateaus which are formed on the surface of a brake composite material. According to this study, a contact plateau might be destroyed when its size becomes too large. Third body abrasion and erosion by wear debris transported through the contact are the processes which lead to the contact plateaus destruction.Although many authors have focused on explaining the mechanism of formation and destruction of the contact plateaus, relatively few researchers have addressed the relationship between the morphology of the plateaus and performance (friction and wear) of brake materials.Thus, this work aims to correlate morphological aspects related to the brake material's surface (number of plateaus -N, mean area of plateaus -Ap, as well as the real contact area of the brake pad -Ar) with the coefficient of fric...
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