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In his introduction to the 1958 Symposium on Basic Mechanisms of Fatigue, Professor Dolan noted that a great deal was known about fatigue failure and the basic mechanisms of fatigue, but that it was impossible to evolve an exact design on a quantitative basis largely because of the statistical nature of the phenomenon. A review of the papers of that symposium 2 shows clearly that a great deal was indeed known at that time concerning basic fatigue mechanisms without the benefit of thin-foil transmission electron microscopy (TEM) and other sophisticated techniques which we regard today as being essential tools in such studies, but there is no question whatsoever that we are today in a position of having an understanding in detail which may be considered to be several orders of magnitude greater than that obtaining in 1958. This has come about through the many specialized studies made over the past 20 years and through the use of much more sophisticated techniques such as thin-foil TEM, scanning electron microscopy (SEM), electron channeling, and Auger spectroscopy, as have been discussed and illustrated in the papers of the present symposium. However, despite all this progress in detail we are still faced with considerable uncertainties when attempting to design a component or structure to avoid the occurrence of fatigue failure or in predicting its fatigue life. This was well brought out by Fong  and it certainly appears shocking (at first sight, at least) to be considering a scatter factor of 20 in the fatigue life or of 2 in the mean strain range for fatigue failure of pressure vessels .
Professor of Mechanical Engineering, University of Saskatchewan, Saskatoon