Compositional effects of the brake friction material on creep groan phenomena

Creep groan (low frequency frictional vibration in the range of 200-500 Hz during braking at a very low vehicle speed) was studied by changing the rel ative amounts of ingredients in a brake friction material containing 12 ing redients. Twenty-nine friction material specimens with different relative a mounts of the ingredients were manufactured according to a constrained mixt ure design. The difference (Delta mu) between kinetic (mu (k)) and static ( mu (s)) coefficients of friction for each formulation was measured to inves tigate creep groan propensity of each friction material since the creep gro an is caused by stick-slip phenomena. Results showed that zircon (zirconium silicate), steel wool, and phenolic resin showed a tendency to increase De lta mu. On the other hand, antimony trisulfide, cashew particles, and rockw ool tended to reduce Delta mu. Based on the results of this work, the initi al formulation was modified to reduce Delta mu. The modified friction mater ial showed a smaller Delta mu value than the initial friction material impl ying low propensity of creep groan phenomena during braking. The velocity d ependence of the friction coefficient was also examined using the initial a nd the modified friction materials. The modified formulation exhibited a le ss negative mu -V relation than the initial formulation. (C) 2001 Elsevier Science B.V. All rights reserved.