A Survey of Contact Hysteresis Measurement Techniques

One of the limiting factors in our capability to predict the dynamics of structures formed by the assembly of several components has been the difficulty of including suitable models for the joints and interfaces that are an integral part of such structural assemblies. These interfaces often contain surfaces that have a degree of slipping, even if only microslipping, and this influences both the stiffness and the damping properties of the structure. Attempts have been made to include a simple representation of these interface phenomena, encouraged by the empirical observation that often inclusion of an extra stiffness and damping parameter can result in much improved predictions compared with those which assume a perfectly rigid connection at the interface. A common basis for such preliminary models is the presumption that the underlying physics of many interfaces can be represented to a reasonable degree by a cyclic load-deflection curve, referred to throughout this chapter as a “hysteresis characteristic.” In gas turbine applications, hysteresis data are required for different materials, and different material combinations, over a wide range of temperatures, normal loading, amplitudes of slipping regimes, and running time considerations of wear and other time-dependent properties. In all these applications, it was decided to develop rigs on which to measure the hysteresis properties of a nominal contact zone or area that could then be incorporated into a finite element type modeling of specific applications, or joints. This chapter summarizes the developments of hysteresis measurement rigs in four research groups over the past 15 years. These groups are based at Imperial College London, the University of Oxford, Politecnico di Torino, and the University of Cambridge, listed here in chronological sequence of an in-service capability.