Inclusion induced anisotropy of short fatigue crack growth in steel

In this study, the growth behaviour of short fatigue cracks in En7A steel with a high content of elongated MnS inclusions was investigated by generating and evaluating the short crack data under different loading conditions for the six principal specimen orientations. Short cracks showed a strong anisotropic behaviour in which they grew much faster in the transverse and short transverse orientations than in the longitudinal orientations in all fatigue processes. This was due to the relatively high content of the elongated inclusions. Inclusion induced anisotropy is also observed in the percentages of fatigue life of the initiation and growth periods of short cracks which may result in inaccurate fatigue life predictions. Inclusion induced anisotropy was the result of strain intensification at the matrix/inclusion interface. (C) 1996 The Institute of Materials