CORRELATION OF FATIGUE-CRACK GROWTH BY CRACK-TIP DEFORMATION-BEHAVIOR

Growth of a long mode I crack under variable fatigue loading was experimentally investigated on mild steel specimens. A dynamic elastic-plastic two-dimensional finite element program, purposely developed for the simulation of cyclic crack lip deformation, was utilised to model the transient effects on crack tip advance. The model accommodated crack tip opening displacement and both crack tip and crack edge closure. Fifty one different cycle patterns were analysed to include the application of a single overload, a single underload, a single cycle having a combined overload and underload and finally loading blocks of different sequences. Correlations of experimental fatigue crack growth rates were made from knowledge of crack tip deformation behaviour, including the use of data found in the literature. Specimens of eight materials and different geometries were analysed to determine the validity of the present approach.