Fatigue Strength Evaluation of Castings with Defects

Recently, fracture mechanics has been applied to the fatigue strength evaluation of components with casting defects. Such defects are usually equated with cracks, while actual defects have various shapes from spherical to needle. Consequently this equating with cracks is not always valid.

This paper shows that the test results for three casting alloys do not agree with the estimated strength based on the above replacement. Then a new method is investigated, in which the following points are considered.

1. 1.
   Calculating K-value with a 3-dimensional model.
2. 2.
   Correcting the stress range according to the mean stress level.
3. 3.
   Using the effective defect size.
4. 4.
   Correcting the Kth-value according to the defect end curvature.

The estimated strength by the new method agrees well with the test results.