Influence of contact shape and supporting condition on tube fretting wear

The focus of this study was on the fretting wear of vibrating tubes such as those used in nuclear power plant fuel rods. Zircaloy-4 was the material of interest. The current approach to reduce wear damage was to study the effects of contact shape and to identify the wear mechanisms by optical and scanning electron microscopy (SEM). Two types of testing machines were used to simulate the support of the thin tubes by springs: (1) sliding and (2) sliding with impact. Two loads (10 and 30 N) and slip displacement ranges of 10–100 μm were used in the sliding tests. In sliding tests, the critical slip range for a transition to high wear depended on the magnitude of the normal force. It was found that the wear region could be separated even under the gross slip conditions depending on the contact shape. The contact shape also affected the debris dispersion behavior. In sling/impacting tests, the supporting condition between the tube and the spring varied (0.1 mm gap and loads of 5 and 0 N). It was found that the influence of the supporting condition on the wear evolution varied depending on the contact shape. From the SEM observation, the larger wear volume was caused by the relatively easier dispersion of debris and the less wear volume was attributed to the formation of the debris layer. Contact traction was analyzed to discuss the shape difference of the wear region.