Analysis of Friction-Induced Instabilities in a Simplified Aircraft Brake

The stability and dynamic characteristics of frictioninduced vibrations in a simplified aircraft brake model are investigated. A finite element model equipped with nonlinear frictional contact algorithm is used. The constitutive model of the interface is based on an extended version of the Oden-Martins law [1]. The interface material constants are obtained via asperity-based homogenization methodology from the profilometric information on the surface. Initial uncoupled analyses are performed to identify the basic dynamic modes of the model. Frequencies of normal vibrations of the model are found to be dependent on the interface stiffness and the piston pressure. To study the dynamic behavior of the system, its transient response is computed after a perturbation of the steadystate sliding position. It is found that, while the vibrations are subdued in some cases categorized as stable, they grow in other, unstable cases. It is also shown that the triggering mechanism of instability can be either the velocity-dependent coefficient of friction or the dynamic coupling of certain vibration modes of the system (even without velocity-dependent friction). These two unstable modes exhibit different dynamic characteristics.