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

Abstract 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 2 s. 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.

[1]  J. Lepage,et al.  The influence of the environment on the friction and wear of graphitic carbons: I. Action of atomic hydrogen , 1989 .

[2]  Michael G. Jacko,et al.  The role of friction film in friction, wear and noise of automotive brakes , 1991 .

[3]  B. Bhushan,et al.  The micro-meniscus effect of a thin liquid film on the static friction of rough surface contact , 1996 .

[4]  David Tabor,et al.  The effect of surface roughness on the adhesion of elastic solids , 1975, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[5]  Andreas A. Polycarpou,et al.  Application of a two-dimensional model of continuous sliding friction to stick-slip , 1995 .

[6]  R. S. Sharp,et al.  INVESTIGATION OF AUTOMOTIVE CREEP GROAN NOISE WITH A DISTRIBUTED-SOURCE EXCITATION TECHNIQUE , 2002 .

[7]  E. Rabinowicz,et al.  Friction and Wear of Materials , 1966 .

[8]  E. Riedo,et al.  Kinetics of capillary condensation in nanoscopic sliding friction. , 2002, Physical review letters.

[9]  James K. Thompson.  Brake NVH: Testing and Measurements , 2011 .

[10]  F. P. Bowden,et al.  The Friction and Lubrication of Solids , 1964 .

[11]  Ho Jang,et al.  Compositional effects of the brake friction material on creep groan phenomena , 2001 .

[12]  R. T. Spurr.  A Theory of Brake Squeal , 1961 .

[13]  Doris Kuhlmann-Wilsdorf,et al.  Fundamentals of stick-slip , 1993 .

[14]  J. Israelachvili.  Intermolecular and surface forces , 1985 .

[15]  L. Sirghi.  Effect of capillary-condensed water on the dynamic friction force at nanoasperity contacts , 2003 .

[16]  Bharat Bhushan,et al.  Nanoscale tribophysics and tribomechanics , 1999 .

[17]  J. Lepage,et al.  The influence of the environment on the friction and wear of graphitic carbons: II. Gas coverage of wear debris , 1990 .

[18]  H. A. Sherif.  Investigation on effect of surface topography of pad/disc assembly on squeal generation , 2004 .

[19]  J. Frenken,et al.  Capillary condensation in atomic scale friction: how water acts like a glue. , 2006, Physical review letters.

[20]  Peter J. Blau,et al.  Effects of water films and sliding speed on the frictional behavior of truck disc brake materials , 2003 .

[21]  Yutaka Kurita,et al.  Considering the Dynamic Pad Stiffness in FEM Analysis of Disk Brake Squeal , 2010 .

[22]  Ken Nakano,et al.  Map of low-frequency stick–slip of a creep groan , 2010 .

[23]  Hartmut Hetzler,et al.  On the influence of contact tribology on brake squeal , 2012 .

[24]  Y. Wang,et al.  FRICTION-INDUCED NOISE AND VIBRATION OF DISC BRAKES , 1989 .

[25]  H. A. Sherif,et al.  Relationship between normal and tangential contact stiffness of nominally flat surfaces , 1991 .

[26]  B. Bhushan,et al.  Meniscus and viscous forces during separation of hydrophilic and hydrophobic smooth/rough surfaces with symmetric and asymmetric contact angles , 2008, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[27]  Staffan Jacobson,et al.  Wear and contact conditions of brake pads : dynamical in-situ studies of pad on glass , 2001 .

[28]  J. Lancaster.  A review of the influence of environmental humidity and water on friction, lubrication and wear , 1990 .

[29]  Harald Fuchs,et al.  Temperature dependence of atomic-scale stick-slip friction. , 2010, Physical review letters.

[30]  Jonathan R Felts,et al.  Controlling nanoscale friction through the competition between capillary adsorption and thermally activated sliding. , 2012, ACS nano.

[31]  Staffan Jacobson,et al.  Surface characterisation of brake pads after running under silent and squealing conditions , 1999 .

[32]  D. Kuhlmann-Wilsdorf,et al.  Adsorption films, humidity, stick-slip and resistance of sliding contacts , 1990, Thirty-Sixth IEEE Conference on Electrical Contacts, and the Fifteenth International Conference on Electrical Contacts.