Fatigue Testing. Fatigue Curve Construction and Fatigue Limit Assessment

At the base of fatigue design there is the Wöhler’s curve S–N that is obtained through fatigue tests. Giving a stress amplitude S or strain amplitude εa to a series of specimens it is possible to derive the corresponding cycles to failure N or life. Considering the importance of such a curve and, therefore, of laboratory tests in general, it is convenient to spend some arguments on the matter just to evidence the most important features and the limits that may be associated, too often forgotten.