The influence of humidity on the sliding friction of brake friction material

Effects of humidity on the friction coefficients of brake friction materials at slow sliding speeds were studied. By measuring the static and dynamic coefficients of friction (COF) at high and low humidity levels, the mechanism of humidity-induced friction instability was investigated as functions o...

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Bibliographic Details
Published in:Wear 2013-04, Vol.302 (1-2), p.1397-1403
Main Authors: Lee, Wan Kyu, Shin, Min Wook, Kim, Sung Hwan, Jang, Ho, Cho, Min Hyung
Format: Article
Language:English
Subjects:
Adhesion
Applied sciences
Brakes
Contact
Contact junctions
Creep groan
Drives
Exact sciences and technology
Exposure
Friction
Friction coefficient
Friction instability
Humidity
Instability
Mechanical engineering. Machine design
Shafts, couplings, clutches, brakes
Sliding
Stability
Stick-slip
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Summary:Effects of humidity on the friction coefficients of brake friction materials at slow sliding speeds were studied. By measuring the static and dynamic coefficients of friction (COF) at high and low humidity levels, the mechanism of humidity-induced friction instability was investigated as functions of exposure time, applied pressure, and sliding speed. Tribological properties were examined using a pad-on-disk type tribometer and a 1/5 scale brake dynamometer. Results showed that the kinetic and static COFs were significantly affected by the exposure time in the humid air, showing saturation of the static COF within 2s. The static COF increased in humid air due to the increased adhesion by water menisci produced at the contact junctions. On the other hand, the static and kinetic COFs increased as a function of pressure in dry air due to the increased real contact area at high pressure, while they were not affected by applied pressure at high humidity levels. The test results also showed that the humidity increased the amplitude of stick-slip and its critical speed, which explains high propensity of friction instability at slow speeds such as creep groan at humid weather conditions.
ISSN:0043-1648
1873-2577
DOI:10.1016/j.wear.2013.01.014