Mode Lock-in And Friction Modelling

Abstract

In this paper the phenomenon of lock-in is investigated, which occurs in structures where vibrations are excited by frictional forces. In general lock-in is defined as the process by which modes of sub-structures couple with each other. A resonant response of the assembly (mode lock-in) is the result of the latter. For studying this effect an experimental pin-disc set-up was built in collaboration with Akay [1] and a corresponding FEM model was generated. The rotational speed of the disc, beam length, and the two parameters normal force and angle of attack between pin and disc can be varied with the pin-disc apparatus. The linear FE model is updated by EMA (Experimental Modal Analysis). A number of different contact descriptions, partly based on surface roughness and material constants of the bodies in contact introduced by Willner and Gaul [4] was formulated and introduced, as user-defined subroutines, into a commercial FE solver. The friction couple considered consists of aluminium/aluminium. The time-marching solutions of the FE model were checked for system resonances and compared to the experimentally observed mode lock-in. The primary objective of this investigation is to determine which friction model and which modelling details are necessary and sufficient to simulate mode lock-in.