The growth rate of the relatively benign shell type defects such as horizontal cracks found in the head of railroad rails is calculated. The effect of the residual stresses acting in the vicinity of the shell on the growth rate is significant. The results can be combined with a stability analysis of the tendency of the horizontal defects to turn into a vertical detail fracture to determine the time required for such a transition. Load reversals can cause the shell defect to grow to a length where it has lost its tendency to grow out of the plane. For this case the time required for the horizontal crack to reach the fast fatigue growth rate regime is calculated. The results allow the effect of the shell growth behavior on rail service life to be discussed.

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