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Five years ago, during the 1961 Annual Meeting, ASTM held its first Symposium on Erosion and Cavitation, the proceedings of which were published as STP 307. As a direct result of the interest stimulated by that Symposium, Technical Committee G-2 was established, and the 1966 Symposium was the first to be held under its sponsorship. In 1961 six papers were presented; the 1966 Symposium heard eighteen presentations, including six from abroad. Of these ten are contained in this volume; some of the others will eventually appear in other ASTM publications. There have been many symposia dealing with cavitation as a fluid flow phenomenon as well as a damage-producing phenomenon. Curiously though, there had been a notable lack of communication in this country (though not in Europe) between those concerned with cavitation damage and those concerned with liquid impingement damage. The two ASTM Symposia are, to the best of my knowledge, the first in this country to focus on the damage mechanism and the material response to it, and thus on the common aspect of cavitation and impingement attack—for it is now widely (though not universally) accepted that the principal direct cause of damage in both instances is the mechanical stressing due to the high-speed impact of a liquid surface upon a solid surface, though corrosion can, certainly, enter the picture under appropriate conditions and mechanical and chemical effects can reinforce each other. The mechanical stress theory was proposed by Cook in 1928, but over the years there have been many who doubted the possibility of sufficiently high mechanical stresses and postulated principally chemical mechanisms or a variety of other more fanciful mechanisms. I believe that the days of wild conjecture are over and that investigators today at least talk the same language and agree on the kind of quesions to ask. This is not to say that all stimulating disputes have vanished: such still exist, as for instance concerning the exact nature of the interaction between mechanical and corrosive effects, and the exact meaning of the various phases observed in erosion rate-time histories. ASTM is interested in the properties of materials and the ways of defining, testing, prescribing, and controlling these properties. Thus, naturally, we are interested not only in the mechanism of erosion, but in how the resistance of materials to erosion can be objectively defined, how it can best be tested, and how test results should be interpreted, and whether this property can be correlated with other known material properties. Also of interest is the influence of the physical as well as chemical properties of the impinging liquid. All of these points are still in need of further enlightenment, even though the literature of the past forty years is replete with comparative erosion test data, some of which are valuable but few of which can be quantitatively compared with one another. Here, again, the right questions are finally being asked, and some of these questions and proposed answers are discussed in these papers.
Heymann, Frank J.
Senior Engineersymposium chairman, Westinghouse Electric Corp., Lester, Pa.