Hysteretic response of frictional joints

The importance of surface topography for normally and tangentially loaded contacts between rough bodies is well known and widely investigated in the literature. The purpose of this paper is to shed light on the link which exists between the behaviour of assemblies subjected to dynamic loadings and roughness and frictional characteristics of their mating surfaces. The results obtained using both theoretical and experimental analyses are reported, with particular emphasis placed on the implications that topographical features have on joints normal and tangential stiffness. In this article, the effect of surface topography on the overall frictional and damping performance of macroscopic contacts is studied using advanced experimental and theoretical methodologies. After discussing the general implications of the results obtained so far by the investigators, attention is also focussed on aspects related to the evolution of surface topography and structure as a function of the number of oscillating loading cycles to which the coupling is subjected. Experimental and numerical techniques Stiffness characteristics and frictional energy dissipated during the interaction between surfaces undergoing relative motion is characterised by the area included in load-displacement (hysteresis) loops. These curves are obtained experimentally either by loading the contact pair under investigation via alternating tangential forces (load control) or by imposing controlled tangential displacements (displacement control) while subjecting the specimens to a constant normal load. The hysteretic response of a number of contact pairs characterised by different materials and surface finishes has been investigated using and ad hoc experimental apparatus in which two specimens undergo reciprocating motion in a cross-sliding trajectory. The test configuration is characterised by a nominal contact area on 1 mm 2 . Advanced theoretical investigations have been performed to complement the experimental studies. Preliminary work on the effect of surface topography on frictional loops shape and energy dissipation response (3) prompted the development of an asperity-scale model of frictional contacts. The proposed methodology, based on a fast multi-level multi-integration technique for the solution of rough contact problems, has been demonstrated to apply to contact problems down to the nanoscale (4) and successfully used to predict normal and tangential stiffness and frictional loops for various geometries and loading scenarios. Results and discussion Examples of the evolution of coefficient of friction (μ) and tangential stiffness (kt measured in N/m) as