Fretting wear of Zr-alloy pressure tubes under the combined effects of in-plane and out-of-plane flow-induced vibrations

Proper design and reliable operation of nuclear power generating plants require accurate prediction of fretting wear failure criteria, which include the volumetric wear losses, the maximum wear depth and minimum root radius of the scar. A unique three-axis fretting wear test facility was developed to simulate the in-plane and out-of-plane dynamic characteristics of the bearing pad/pressure tube tribo-system. The fretting wear of Zr-2.5% Nb alloy at 265 °C was investigated. The results showed that the specific wear rate coefficient decreases with the increase of work rate, and is not constant as it is commonly assumed. The increase in the maximum wear depth with the accumulated wear energy was shown to be approximated by a second-order polynomial function. The correlation between the maximum wear depth hmax and the minimum root radius Rr, has been established, an aspect that has never been investigated before. Examination of the fret scars showed that they can be classified into three types. When the ratio hmax/Rr was correlated to hmax, the data are contained within a well-defined bell-shaped envelope, which resembles the normal distribution curve.