Narrow Results

Fretting occurs at the contact area between two materials under load and in the presence of minute relative surface motion by vibration or external force. Bearings, clutches, riveted and bolted lap joints are subjected to fretting damage. Friction coefficient, materials of the specimen, contact surface pressure, relative slip amplitudes, temperatures and environment have an effect on the fretting. In this study, fretting wear test is conducted with SCM415 (Cr–Mo alloy steel) which are much used for making gears and shafts because of its excellent machinability, good mechanical properties and low cost, compared with those of the existing machine structural steels. In order to determine the fretting wear type, fretting wear fixture which can be attached to the servo hydraulic fatigue testing machine is made. And then, specimens and fretting pad with a constant curvature are made of SCM415 materials. Different normal forces and displacement amplitudes are applied to the fretting pad and diamond-like carbon (DLC) is coated on the fretting pad for fretting wear test.

The performance of electroless (EL) Ni–B coated brass contacts under fretting conditions was evaluated. The contact resistance of EL Ni–B coated brass contact was measured as a function of fretting cycles. The surface profile and wear depth of the fretted zone were measured using laser scanning microscope. The study reveals that EL Ni–B coated contacts exhibit better performance under fretting conditions. However, at conditions which are prone for severe oxidation such as, low frequency (3 Hz) or high temperature (155°C), EL Ni–B coated contacts fail to exhibit a better stability. The quick removal of the oxide film by fretting motion, rapid oxidation of the fresh metallic particles and trapping of the oxidation products in the remaining coating, cause the contact resistance to increase to unacceptable levels at such conditions. The study concludes that EL Ni–B coating is not a suitable choice for connector contacts that could experience fretting under highly oxidizing conditions.

Two transversely isotropics elastically similar semi-infinite solids in partial slip tangential contact are considered in the framework of the Cattaneo–Mindlin theory. The problem of limiting shape of the contacting surfaces due to wear in the slip zone is solved under the assumption of constant normal force and oscillating tangential force with a constant amplitude. It has been shown that both the stick zone and the limiting shape do not depend on the orientation of the tangential force. The novelty of the present study is not only in finding an exact analytical solution to the problem of limiting shape in fretting but also in extending the Cattaneo–Mindlin theory of local tangential contact to transversely isotropic, elastically similar solids.

A two-dimensional wear contact problem with a stick zone is considered for a Hertzian cylindrical contact configuration and Archard’s equation of wear. A one-free-parameter simple model for the wear volume accumulation during the reciprocating wear process, which occurs in two symmetric variable slip zones, is developed and validated against numerical solutions available in the literature. The developed model takes into account the observed effect of non-monotonic evolution of the friction dissipated energy. The presented analytical modeling framework does not make use of any fitting parameters to be evaluated from experiments. The only free dimensionless parameter is suggested to be fixed based on numerical simulations for the maximum of the frictional damage that is proportional to the cumulative wear rate.