ANALYSIS OF DAMAGED SURFACES - PART I: CAVITATION MARK MEASUREMENTS BY 3D LASER PROFILOMETRY

摘要

A cavitation marking technique based on 3D laser profilometry was proposed. An automatic analysis software of the sample surfaces marked by cavitation was developed and used to treat several experimental results. The special software provides the distributions of mark radius, depth and volume for every single indentation. The paper describes the method used to determine the geometric characteristics of each indentations, and the approach applied to treat the overlapping marks problem. This cavitation marking technique was applied to analyze the sample surfaces damaged in the EDF Modulab test loop under different flow conditions. An experimental mechanical system was developed to improve the control of the exposure time of the sample to the cavitating flow. The study pointed out the strong influence of the test duration and the effect of the analysis cut-off parameters (related to the measurement resolution threshold) on the evaluation of the volume marking rates and of the pit number rates. In the scope of the European Research Program PROCOPE, this technique was also applied to analyze samples marked in the test rig of the Laboratory of Turbomachinery and Fluid Power of the Darmstadt University of Technology. 3D profilometry results were compared with ones obtained by 2D optical pit counting technique presented in the second part of the paper [Lohrberg et al., 1999].