AN ANALYTICAL MASTER CURVE FOR GOODMAN DIAGRAM DATA

Estimation of the remaining safe life of structural parts which are no t easily inspectable continues to be a problem. Even when load histori es are available, laborious interpolation of Goodman diagram data is r equired in order to determine the remaining fatigue life of such parts . An analytical formulation of Goodman diagram data would expedite the life check. It is shown in this paper that, for many engineering mate rials at room temperature, the entire range of Goodman diagram data co llapses on to a single master curve when presented as the ratio of lif etime with mean stress to lifetime at R = -1 for a given stress amplit ude, as a function of a non-dimensional load parameter consisting of s tress amplitude, mean stress, and material strength. The master curve is conveniently expressed in terms of two easily determined Weibull co nstants. Stress-concentration factor influences the value of the const ants, as does the strain-rate sensitivity of some materials. By use of the master curve formula in an algorithm together with the Manson-Cof fin life relation and Miner cumulative damage rule, computed fatigue l ives lay within a factor of 2 of results obtained in tests under aircr aft spectrum loads.