Experimental characterization of sliding and impact friction coefficients between steam generator tubes and avb supports

Abstract

Experiments are described that were designed to determine the sliding and the impact friction coefficients between steam generator tubes and anti-vibration bar supports. The test environments were air and water at ambient conditions, in order to allow bracketing of actual steam generator conditions. Two tube/AVB combinations were tested. The first combination consisted of materials used in a recent flow test program on a 5 X 12 U-tube bundle during which the turbulence and fluid-elastic responses of that tube bundle were characterized with different AVB clearances. The said flow test program was also successful in the experimental determination of “work rates” between tubes and AVBs with different boundary conditions, while the tubes were excited by different flow dependent forcing mechanisms. The second combination of materials consisted of an Inconel 600 tube matched with an AVB sample retrieved from an operating steam generator. Results of the present tests on the two material combinations show some differences in the dry friction coefficients, but relatively good agreement between the wet friction coefficients. In addition, friction coefficients were determined to be mostly independent of normal force and sliding velocity. Finally, friction coefficients for oblique impacts were quite similar to those for sliding motion under preload. Interpretation of the test results for normal or near normal impacts justifies use of a single friction coefficient for all combinations of tube to AVB interactions (possibly excluding rocking and rotation) in non-linear finite element, time-domain computer simulations of the tube/AVB dynamics under turbulence and/or fluid-elastic excitations.