Published: Jan 1970
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There still exists no objective measurement of the erosion resistance of a material, nor a theory for predicting the material loss to be expected under given service conditions, based on any generally accepted hypotheses concerning the erosion damage mechanisms. This paper presents an approach which does not presuppose any specific mechanisms but rather is based on empirical data and dimensional considerations.
First, a “normalized erosion resistance” (Ne) of a material is defined which allows direct comparison of many different test results, including cavitation tests, and provides a quantitative measure of erosion resistance even though that is not yet a physically understood property. One finds that the values of Ne for metals vary from about 0.03 for soft aluminum to about 60 for some stellites and hard tool steels; total range of about 2000:1. Neither hardness nor strain energy or other independent parameters prove to be reliable indexes to erosion resistance.
In order to develop a quantitative formula for predicting impingement erosion, the “rationalized erosion rate” (Re) is defined as the ratio of volumetric material loss rate to the volume rate of liquid impingement. Previous studies have suggested that this quantity should be proportional approximately to the fifth power of impact velocity.
Plotting NeRe for a number of experimental results versus normal impact velocity Vo (m/s) confirms the power law and yields two approximate relationships: NeRe = (Vo/2550)5.05 for impact against droplets, and NeRe = (Vo/2920)4.37 for impact against cylindrical jets.
Some of the physical hypotheses which have been proposed for the prediction of erosion damage, particularly those based upon the concept of energy transfer from the impinging liquid to the eroding surface, are examined for consistency with these findings, and tests with different liquids are found to be necessary to resolve this question.
water impingement, erosion, impingement, impact, water erosion, cavitation erosion, correlations, mechanical properties, velocity, time dependence, predictions, evaluation, tests
Senior engineerPersonal member ASTM, Westinghouse Electric Corp., Lester, Pa.