Experiments on the Effect of an Impact Damper on a Multiple-Degree-of-Freedom System

An impact damper is a freely moving mass, constrained by stops, located on the structural system to be controlled. As the system is excited dynamically, the impact mass moves relative to the structure, resulting in impacts between the mass and the stops, dissipating energy as heat, noise and high frequency vibrations. Whilst the use of impact dampers for single-degree-of-freedom (SDOF) systems has received a significant amount of attention, investigations into their interaction with multiple-degree-of-freedom (MDOF) systems is rare. This paper presents results of a series of experimental investigations into the effect of an impact damper on a MDOF primary system. The effects of the size of the impact mass, clearance between the impact mass and the stops, excitation type and excitation location are considered. The results in some instances do not correspond with those found for control of SDOF systems in particular, increased size of impact mass does not necessarily lead to an increase in damping for all modes. Also, the effect of clearance is unpredictable, particularly for higher modes. The paper raises these and other issues which require consideration if impact dampers are to be used to control the dynamic response of MDOF systems.