Wear and Corrosion in Sliding Contacts

The extrapolation of the results of accelerated wear tests to real operating conditions poses many problems and a multitude of test equipments have been developed for specific purposes. Among these, the following arrangements are most 

Pin-on-disk devices consist of a rotating disk onto which a pin or ball is pressed at a constant normal force. Measurement of the normal force and of the angular momentum permits the determination the friction coefficient. 

Crossed cylinder testing uses two perpendicular cylinders, one stationary, and the other in rotation. As in the previous case, the normal force and the angular momentum provide the information required to get the friction coefficient. 

In order to get information on wear mechanisms, it is necessary to complement the determination of wear volume by a structural characterization of the worn surface. Friction and wear cause characteristic changes of surface topography and of the microstructure in a thin zone below the rubbing surface, which can give information on prevailing wear mechanisms. Additional information is obtained by an analysis of the size and composition of the wear particles. Electron microscopy (SEM, TEM) and surface analysis methods (AES, XPS, etc) are generally used for this purpose. 

A major problem of wear studies is reproducibility. To get reproducible results, one needs first of all a mechanically well designed equipment that is sufficiently rigid to permit precise control of the mechanical variables. In addition, one needs to rigorously control the operational and environmental parameters, including humidity and temperature. 

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