Damping of machine tool structures with riveted joints

Abstract

Light weight structures typically have low inherent structural damping. The damping mechanism of jointed and riveted structures can be explained by considering the energy loss due to friction and the dynamic slip produced at the interfaces. The frictional damping is evaluated from the relative slip between the jointed interfaces and is considered to be the most useful method for investigating the structural damping. The damping characteristics in jointed structures are influenced by the intensity of pressure distribution, micro-slip and kinematic coefficient of friction at the interfaces and the effects of all these parameters on the mechanism of damping have been extensively studied. All the above vital parameters are largely influenced by the thickness ratio of the beam and thereby affect the damping capacity of the structures. In addition to this, number of layers, beam length and diameter of connecting rivet also play key roles on the damping capacity of the jointed structures quantitatively. The effects of all these parameters are studied vividly in the present investigation. It is established that the damping capacity can be enhanced appreciably using larger beam length and rivet diameters as well as lower thickness ratio of the beams. Further improvement in damping is possible with the use of more number of layers compared to its equivalent solid one. This design concept of using layered structures with riveted joints can be effectively utilized in trusses and frames, aircraft and aerospace structures, bridges, machine members, robots and many other applications where higher damping is required. Extensive experiments have been conducted on a number of mild steel specimens under different initial conditions of excitation for establishing the authenticity of the theory developed.