Vol.:(0123456789) 1 3 Tribology Letters (2020) 68:4 https://doi.org/10.1007/s11249-019-1244-x ORIGINAL PAPER Experiment to Investigate the Relationship Between the Third‑Body Layer and the Occurrence of Squeals in Dry Sliding Contact Narinder Singla 1  · Jean‑François Brunel 1  · Alexandre Mège‑Revil 1  · Haytam Kasem 2,3  · Yannick Desplanques 1 Received: 15 July 2019 / Accepted: 31 October 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract Braking is an energy dissipation mechanism used to restrict the movement of vehicles. Friction brakes may induce vibrations and noise. These efects constitute a major shortcoming related to the functioning of friction braking systems. Known as brake squeal, this phenomenon involves unstable vibrations induced by coupling modes between components in frictional contact leading to large amplitude vibrations. Despite signifcant progress in experimental techniques and numerical modeling, the origin of squeal occurrence remains misunderstood and is still a matter of debate. It is, however, commonly admitted that squeal is afected by many diferent factors on both micro and macro scales. In addition, a close correlation between wear and squeal occurrence in braking system has been reported. This study examines linking the change in the third-body layer with the occurrence of squeals in sliding dry contact. A simplifed customized test rig was used with a transparent glass disc and an artifcial alumina third-body. Results show that squeal occurrence is strongly linked to the densifcation and redistribution of the third-body, as well as internal fows in the interface. Keywords Brake squeal · Friction-induced vibrations · Tribological circuit · Third-body fows List of Symbols Q s (ext) External third-body source fow Q s (int) Internal third-body source fow Q e Particles wear-out Q r Third-body recirculation fow Q i Internal third-body fow 1 Introduction Braking is a vital function that helps to control vehicle motion and therefore ensures the safety of passengers. Among the diferent braking technologies used in transport (friction, eddy current, rheostatic, etc.), braking by fric- tion (considered the most efective, particularly in cases of emergency) is still the most commonly used. Although fric- tion brakes have been improved considerably over the years, certain fundamental problems related to their use remain unresolved. The most frequent of these problems are crack- ing within brake discs due to thermal fatigue [1], friction instabilities [2], wear [3–5] and noise emissions among them squeal [6, 7]. Indeed, vibrations lead to a wide array of noises at various frequencies. Depending upon the involved frequencies and the nature of vibrations, noises can be clas- sifed as squeal, squeak, groan, chatter, judder, moan, hum, etc. [8]. Of these, brake squeal is the most troublesome for both people as well as the environment. Since squeal is a noise with a high frequency and acoustic pressure (above 1 kHz and 80 dB), it may be associated with high frequency and large amplitude vibrations under sliding conditions [9]. Despite recent signifcant progress in processing techniques, characterization tools, and computational algorithms, the fundamental understanding of physical conditions leading to squeal is still lacking, since it is inevitably afected by many diferent factors on both micro and macro scales. Various mechanisms for the dynamic analysis for the occurrence of squeal have been proposed on the macro scale, i.e., negative friction coefcient sliding velocity slope, sprag-slip, futter instabilities, stick–slip, mode lock-in [10, 11]. Although these mechanisms can be interrelated, the * Jean-François Brunel jean-francois.brunel@polytech-lille.fr 1 Univ. Lille, CNRS, Centrale Lille, FRE 2016 – LaMcube – Laboratoire de mécanique multiphysique multiéchelle, 59000 Lille, France 2 Department of Mechanical Engineering, Technion, 32000 Haifa, Israel 3 Department of Mechanical Engineering, Azrieli College of Engineering, 9103501 Jerusalem, Israel