Wear mechanism in automotive brake materials, wear debris and its potential environmental impact

Abstract

A model semi-metallic brake lining was subjected to full scale automotive brake dynamometer tests. The structural properties and surface topography of brake linings were analyzed at different stages of wear testing and correlated to frictional performance. Characteristics of released wear particles were also addressed. A combination of abrasive and adhesive wear with oxidative processes dominated the friction process. Formation of a friction layer adhering to the friction surfaces of pads and discs is the major feature responsible for friction performance. Characteristics of the friction layer depend mostly on surface temperature, normal pressure, and sliding speed. It is a newly formed sintered composite matter consisting of a mixture of wear particulates. Wear rates and friction levels depend on chemistry, structure and hardness of the friction layer covering the surface of a pad or a disc; however, there is no simple Archard-type relationship between wear and measured hardness.Wear debris generated during the dynamometer tests was collected from containers placed under the brake inside dynamometer chamber. The collected debris was compared with ball-milled particles from identical brake lining. It is necessary to combine several analytical methods to characterize wear particles properly. The presence of copper and iron oxides as well as carbonaceous components is typical for all collected debris samples. Chemistry of wear debris resembles chemistry of the friction layer. Composition, mutagenic potency and pulmonary toxicity of wear debris and ball-milled particles were also analyzed. Mutagenic potency of initial friction composite and wear particles was evaluated by two in vitro bacterial microbioassays (SOS Chromotest, Ames test). Obtained results show potency of wear particles for interacting with DNA after metabolic activation, which indicates the presence of indirect mutagens. The pulmonary toxicity test on rats revealed an acute response of the lung tissue to the ball-milled particles. Further research is necessary to address the role of brake wear particles and potential impact of sub-chronic exposure to wear debris.

A study of the wear mechanisms of disk and shoe brake pads

“…The study was supported by SEM images, which presented the wear modes caused on disk pads due to the constant sliding and abrasion actions that affect considerably the constituents used to formulate this type of brake pads [2][3][4][20][21][22][23]. It is important to mention that more SEM micrographs were taken to analyse the wear damage on disk pads.…”

“…The delamination wear is one of the main wear mechanisms in this type of mechanical elements because as the sliding and abrasion actions are higher and longer, different surfaces can appear and new constituents used for the formulations are shown. In addition, the working temperature during breaking has an effect since it can lead to oxidation process, which accelerates the deterioration or degradation of the disk pads [20][21][22][23]. For that reason, EDS was important in this study because of the surface modifications produced in different zones of the inhomogeneous pads.…”

Detection of nano- and micro-sized particles in routine biopsy material - pilot study

“…Copper was also detected in tissues in children and adults living near busy roads as well as in tissues of several drivers and traffic police officers. This may be among others due to environmental and occupational exposure to particles generated by the braking of automobiles 7 . Surprisingly, the elemental composition of particles detected in tissues with tonsillitis was comparable to elements detected in tissues with squamous cell carcinoma.…”

“…Various metals are abundant components of particulate air pollution, e.g. wear of automotive brake pad releases Fe, Cu, Ba, and Sb into the environment 7 . Various anthropogenic processes, such as cigarette smoking, may produce these metal-containing particles where the smoke may contain metals such as Al, Cd, Ni, Pb, and Cu in the form of very fine particles 1 .…”

Efeito do cobre como adição interfacial no sistema tribológico pino X disco.

“…O conhecimento tribológico chegou muito longe baseado nesses estudos pós-fenômeno (ERIKSSON et al, 2001, tradução nossa CHO et al, 2003, OSTERMEYER, 2003, KATO et al, 2003, ÖSTERLE et. al 2004, 2006, 2010, 2011, 2012, HINRICHS et al 2011, KUKUTSCHOVÁ et al, 2009, 2010, WAHLSTRÖM, 2011, DMITRIEV et al, 2008, 2010, não são raras as inferências à formação de uma dita camada protetora oxidada sem de fato observá-la ou mostrá-la. Em trabalho do próprio Kato (2003), a transição do regime severo para o moderado com a adição de partículas óxidas ou metálicas é atribuída à formação de uma camada de transferência sem mostrá-la, utilizando-se da citação dos resultados de Jiang et al (1998) Figura 7 Apresentação esquemática dos resultados obtidos na investigação do corte transversal na interface pastilha/disco.…”