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Abstract: Friction-induced stick–slip of brake friction materials was investigated by examining the correlation between contact stiffness (k n) and surface topography changed by material wear at the sliding interface. By changing the surface roughness and thickness of the friction material, friction instability during sliding at low speeds was analyzed using a scale brake dynamometer. The results showed that the intensity and frequency of stick–slip were determined by the relative magnitudes of tangential contact stiffness (k t), bulk stiffness (k b), sliding velocity, and the difference (Δμ) between the static (μ s) and kinetic coefficients (μ k) of friction and these results were supported by the contact theories proposed by Greenwood and Williamson. While Friction materials with rough surfaces showed small stick–slip amplitudes due to small tangential contact stiffness (k t), friction materials with high compressibility exhibited pronounced stick–slip because the amplitude inversely varied with the bulk stiffness (k b). The high stick–slip propensity observed from heat affected friction materials also supported the correlation of the surface condition and contact stiffness (k n). [Copyright &y& Elsevier]

Abstract: Brake-induced stick–slip, which determines the propensity of a brake system to generate noise, was investigated by analyzing the friction oscillation at different loads, speeds, and surface topographies. The friction characteristics at the sliding interface were obtained using a pad-on-disk type tribometer and a 1/5-scale brake dynamometer. Results showed that the size and stiffness of the surface contact plateaus significantly affect the propensity of stick–slip and wear. The stick–slip amplitude increased with normal load and decreased with sliding speed. Contact stiffness of the friction material, which was modified by producing shallow slots on the rubbing surface, also strongly affected the stick–slip propensity, whereas Δμ(=μ s−μ k) was not changed by the surface modification. The strong effects from the contact stiffness suggest that the height distribution of the surface plateaus can change the stick–slip propensity of a brake friction material. [Copyright &y& Elsevier]