Assessment of Integrity for Three Dimensional Cracked Members by an Influence Function Method

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An influence function method has been developed by which the stress intensity factors, K, of surface cracks subjected to arbitrarily distributed surface stresses can be calculated easily by a personal computer. In order for the abouvemethod to be effective, a series of influence coefficients, K_<ij>, have to be calculated previously by three dimensional finite element analysis. In this study the author has obtained a data base of K_<ij> for cracks such as (1) semielliptical surface crack in flat plate(2) quarter-elliptical surface crack in a flat plate(3) semielliptical surface crack in a round bar(4) semielliptical surface crack in a pipe.The data base has been stored on a floppy disc of a personal computer, and a software system has been developed to calculate K for surface cracks under arbitrarily distributed stresses such as residual stress, thermal stress, and/or stress at the notch root.Further, a simulation program to estimate the fatigue life of the surface-cracked members has been developed. The algorithm is based on the integration of the Paris' law, in which the instantaneous range of the stress intensity factor, <delta>K, can be calculated by the influence function method. A probabilistic approach has been adopted in estimating the fatigue lives by taking account of the stochastic nature about the size and shape of the surface crack and material parameters dominating the rate of fatigue crack propagation.