Characterization of surface morphology and its correlation with friction performance of brake pads

Abstract

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...

The analysis of the influential parameters that cause particles formation during the braking process: A review

“…The above is possible, bearing in mind that the irregularities can be several tens of microtones, and particles are deposited there, which are later released. 15,134,150,151 According to Hagino et al, 34 Figure 3. Influence of sliding speed on brake wear and particle formation.…”

“…The above is possible, bearing in mind that the irregularities can be several tens of microtones, and particles are deposited there, which are later released. 15,134,150,151 According to Hagino et al, 34 drum brakes are more environmentally friendly, bearing in mind that particles collect in the drum and are not released into the atmosphere. When it comes to disc and drum brakes according to Laguna-Camacho et al, 152 it was found that the wear mechanism differs in both types of brakes.…”

“…The type of braking event has a significant effect on the wear rate and the particles' formation. Full stop braking significantly increases particle emission Neis et al 151 Laboratory-scale tribometer The wear rate is the highest at the very beginning of the braking process, that is in the first braking operations when the brakes are new Laguna-Camacho et al 152 Real service There is a difference in the wear mechanism of the disc (abrasion wear) and drum brakes (fatigue cracking on the surfaces) of research by Blau and McLaughlin, 155 it was concluded that the wear rate increases with increasing humidity. So it is necessary to take into account the materials that are applied and used as friction elements in different catches of vehicle exploitation.…”

A comparative analysis of original and aftermarkets brake pads sold in the Brazilian market

“…A bedding-in, also known as running-in, is characterized by a transitory increase in the friction magnitude when the sample wears out locally to conform to the disc surface [15,19]. So, in a bedding-in section is possible to evaluate how long this transitory period lasts.…”

Numerical Simulation and Accuracy Verification of Surface Morphology of Metal Materials Based on Fractal Theory

“…The surface characteristic parameters obtained by this method are obviously limited by the resolution and sampling length of the instrument, and do not have objective uniqueness, so it is difficult to fully reflect the random behavior and detailed characteristics of rough surfaces, giving rise to many inconveniences in practical application [4]. In the early days, research on surface structure was limited to surface roughness, which was used to study the relationship between the surface morphology and the contact performance of parts in order to provide accurate quantitative descriptions of surface structures [5]. Since the appearance of the first surface morphology measuring instrument in the 1920s, a great deal of quantitative research on the evaluation parameters of surface morphologies has been undertaken [6].…”