Analysis of friction-induced vibration leading to brake squeal using a three degree-of-freedom model

Friction-induced vibration is a common phenomenon in nature and thus has attracted many researchers’ attention. Many of the mathematical models that have been proposed on the basis of mode coupling principle, however, cannot be utilized directly to analyse the generation of friction-induced vibration that occurs between two bodies because of a difficulty relating model parameters to definite physical meaning for real friction pairs. In this paper, a brake squeal experiment is firstly carried out by using a simple beam-on-disc laboratory apparatus. Experimental results show that brake squeal correlates with the bending mode of the beam and the nodal diameter out-ofplane mode of the disc as well as the cantilever length of the beam. Then, a specific three degree-of-freedom dynamic model is developed of the beam-on-disc system and the vibration behaviour is simulated by using the complex eigenvalue analysis method and a transient response analysis. Numerical simulation shows that the bending mode frequency of the beam a little greater than the frequency of the nodal diameter out-of-plane mode and a specific incline angle of the leading area to the normal line of the disc as well as a certain friction coefficient, are necessary conditions for the mode coupling of a frictional system. Results also show that when the frictional system is transited from a steady state to an unstable state for the variation of parameters, its kinetic and potential energy increase with time due to continuous feed-in energy from the friction force while the dynamic responses of the system change from the beating oscillation to the divergent, which leads to the friction-induced vibration and squeal noise.