Experimental Tools for Characterizing Fretting Contacts.

Abstract

The severe near-surface conditions associated with partial slip or fretting contact of interacting surfaces have been linked to premature and often catastrophic failure of a myriad of mechanical systems and components, including riveted aircraft structures, power generation systems and jet engines. Developing a mechanics-based characterization of these conditions through combined modeling and experimental efforts is a challenging task, confounded by factors such as an evolution of friction driven by interfacial wear and the multiaxial, non-proportional nature of the cyclic contact stress field. This paper presents results from the recent successful application of infrared thermal imaging techniques to measure near-surface temperature fields in a way that clearly discerns this change in friction coefficient. These thermal images illustrate the transition from sliding to partial slip conditions related to wear-induced increases in friction coefficient. The experimental temperature fields have also been juxtaposed with recorded histories of the requisite fretting fatigue loads and a finite element analysis of the fully coupled thermoelastic and heat conduction problems to obtain a validated model of the near-surface conditions responsible for fretting wear and fretting fatigue damage. The observed interfacial conditions have been combined with results from three-dimensional finite element modeling to assess the applicability of two-dimensional modeling approaches to contacting mechanical components of finite dimensionality. As an example, the thermography/FEM approach has been exercised to understand the influence of fretting on the fatigue failure of riveted aircraft structures.