ON FATIGUE-CRACK PATHS

The main features of the path taken by a propagating fatigue crack are discussed. It is assumed that a material is homogeneous and isotropic on a macroscopic scale, that behaviour is essentially elastic, and that the initial crack is 'long'. Under these conditions the path taken by a propagating fatigue crack is reasonably well understood in a qualitative sense. There is a strong tendency for crack propagation to be in Mode I; the main exception is the slant crack propagation sometimes observed in thin sheets. A crack path is influenced by the precise characteristics of the crack tip plastic zone, by microstructural irregularities, and by the line tension of the crack front. The application of chaos theory to crack paths is explored briefly, and it is found that the concept of attractor helps in qualitative descriptions.