A UNIFIED ENGINEERING THEORY OF HIGH STRESS LEVEL FATIGUE

Abstract : A unified engineering theory of high stress level fatigue is proposed which enables one to understand and predict the various aspects of fatigue from the same basic model. This model combines cert in features of dislocation theory of metals with elasto-plastic analysis of the stress distribution near a crack, and permits an estimate of fatigue life to failure based upon estimates of the rate of crack propagation. The theory predicts the shape of the familiar stress versus number of cycles curve extending from one four h of a cycle at the ultimate static tensile strength down to several million cycles and incorporates no additional assumptions in predicting cumulative damage during fatigue. The theory also discusses the dependence of fatigue upon the several commonly observed variables as well as residual static strength in fatigue and its dependence on material properties. The inherently statistical nature of the fatigue problem is emphasized and this is attributed to an internal stress existing at the level of the lattice structure. (Author)