A thermally controlled fretting wear tribometer — a step towards standardization of test equipment and methods

Abstract

A system approach to the fretting wear process indicates that besides the material, the contact temperature is the only other factor which directly influences all tribological reactions that take place at the interface. Therefore, to improve the applicability of the laboratory fretting wear tests to actual in-service conditions, it is imperative to ensure that the contact temperatures of the model (fretting specimens) and the original component (prototype) are kept as nearly identical as possible. The present paper addresses the thermal control aspect in simulative fretting tests. The approach adopted allows the contact temperature to be controlled, independent of the load and relative speed, by externally changing the temperature level and/or gradient in the bulk of the specimens. To achieve this objective a thermally controlled fretting tribometer has been developed to conduct fretting experiments in controlled environment at up to 200 °C. It is instrumented with two heat flow meters connected in series with the fretting specimens and an external heat source/sink combination. In addition to the provision of a means for adjusting the relative strength of the body and frictional heat sources, the system allows also for measuring the change in the thermal contact resistance with fretting. The method devised to qualify and adjust the thermal characteristics of the tribometer is presented. Results pertaining to the change in the thermal contact resistance with fretting wear over a period of 265 h indicate the process nonlinearity which affects the contact temperature on a closed-loop fashion. To the author's best knowledge, such data has never been published in the literature.