CONSIDERATIONS OF GRAIN-ORIENTATION AND WORK-HARDENING ON SHORT-FATIGUE-CRACK MODELING

Methods which consider the effect of grain orientation and work hardening on short-fatigue-crack growth are examined. Fatigue cracks are assumed to form in the most favourably oriented grains on the surface of the specimen and propagate through less well oriented grains. A method of deriving the sequence of orientation factors as the crack front traverses an increasing number of grains is presented. Grain boundaries act as barriers to plastic flow in the zone ahead of the crack tip. This has the effect of hindering dislocation movement in the plastic zone, which can be expressed in terms of an increase in the frictional stress. A method of calculating this work-hardening rate is proposed. The condition for transition from short to long fatigue cracks is established. © 1990 Taylor & Francis Group, LLC.