A Feasibility Study on the Worn Area Estimation by Measuring a Contact Resistance (I)

In order to improve the fretting wear resistance of the nuclear fuel rod with considering the effect of the contacting spring shape, it is necessary to examine the formation procedure of the worn area during the fretting wear experiments with including its shape, size and the debris removal path. This is because the wear volume and the maximum wear depth are dominantly affected by the worn area and the wear resistance of the nuclear fuel rod was dominantly affected by the spring shape rather than the test environment and the contact mode (i.e. impact, sliding, rubbing, etc.). Unfortunately, it is almost impossible to archive the size and shape of the worn area on real-time basis because the contact surfaces are always hidden. If we could measure the worn area properties during fretting wear tests, it enables us to promptly estimate the wear resistance or behavior with various contacting spring shapes. Generally, fretting wear degradation is generated by the localized plastic deformation, fracture and finally detachment of wear debris. Generally, wear debris easily oxidized by frictional heat, test environment, etc. From the previous studies, most of the wear debris was detached from the worn surface in the distilled water condition while the wear debris in the dry condition remained on or adhered to the worn surface. At this time, it is reasonable that the accumulated wear debris on the worn surface is existed in the form of oxide. If small amount of electric current was applied between the contacting surfaces, wear debris could be an obstacle to flow the electric current. This means that the variation of the contact resistance under constant electric current during the fretting wear tests has much information on the formation of the worn area even though the applying current could accelerate the oxidation of the generated wear debris. So, in this study, fretting wear tests have been performed with applying an electric current in room temperature air in order to examine the variation of contact resistance with increasing slip amplitude and fretting cycles. The objective is to verify the relationship between the variation of contact resistance and the worn area characteristics