A survey has been made of the history of fatigue since the time of Woehler and this revealed the ever-increasing number of problems caused by fatigue, ranging from complex aircraft to everyday products. Consideration of fatigue is now an essential part of design. The possibility of a fatigue failure in mechanical or structural components is usually solved by either 'ad hoc' fatigue tests or by a safety margin. Both solutions are expensive and can only be avoided by making available suitable design data based on carefully planned tests. In this research a large number of tension bolts and screwed bar specimens were tested under constant amplitude loading over a wide range of the variables. Planning of the tests made possible an analysis which allowed statistical values to be quoted for the resulting curves. The theoretical representation of fatigue data has been studied and methods are presented which allow computer production of comprehensive fatigue design S-N curves. The required data to produce the curves is limited to the tensile strength and two constants which can be determined from a small number of fatigue tests. The principles have been demonstrated for tension bolt joints and can be extended to other types of joints. The designer normally obtains data from 'Standards' which provide the statistically safe strength for materials and components. This research demonstrates that fatigue data can be presented to the designer in a similar manner by the introduction of two additional constants.
|Date of Award||1981|