Improved division of cyclic loading method for MSD fatigue crack growth in engineering

In view of the characteristics of multiple site damage (MSD) crack growth, two influencing factors related with the speed of crack growth are presented. Based on Pairs equation, the recursion relation of crack growth length has been deduced. Subsequently, an approximate equation derived from the recursion relation is used to compute the length of crack growth under cyclic loading. Through comparison with the constant spacing division of cyclic loading method, a variable spacing method is presented, its detailed approach is given, and its merit is discussed. One type of MSD crack configuration, that of the collinear fastener holes in rimmed thin panel, is analyzed through combining the two improvements of the approximate equation and the variable spacing method. The computed results are compared with those which made use of the constant spacing division of cyclic loading method and experiment values. These results indicate that this improved method can greatly enhance computation precision. For problems of large-scale multi-crack and long fatigue life, the proposed method can give a precise and conservative solution as well as a reduced scale of computation.