Fracture Mechanics Approach to Fatigue Analysis in Design

Abstract

Many engineering structures are subjected to cyclically varying (fatigue) loads during service. Fatigue analysis, or the estimation of fatigue lives on such structures, is therefore an essential part of engineering design. In this paper, the fracture mechanics approach to fatigue analysis is described. This approach has evolved over the last decade, and is based on the assumptions (i) that there are preexisting flaws or cracks in a structural component, or that cracks are initiated early in the life of the component, and (ii) that the fatigue life of the component is determined principally by the rate of growth of these cracks under cyclic loading. Characterization of the rate of fatigue crack growth in terms of fracture mechanics parameters is discussed. The relationship between these parameters and those commonly used in fatigue analysis is identified. A procedure for estimating fatigue lives from crack growth data is outlined. The importance of various loading and environmental variables on fatigue life prediction is considered. A number of example problems are given to illustrate the procedure and the various effects.