2007 Volume 79 Issue 2 Pages 90-94
Fatigue cracks are often generated in aluminum alloy die castings subject to repeated cyclic load as casting defects, which propagate and causes final fracture. This process can be formulated by the properties of fatigue crack propagation, the position of defect and cyclic load, because fatigue cracks propagate following the relation between stress intensity factor range ΔK and crack propagation rate da/dN, especially Paris equation which can be obtained by a fatigue crack propagation test using CT specimens.
The authors have already proposed a prediction method of fatigue life based on the cross section of casting defect, tensile stress at the origin, and ΔK-da/dN relation.
In the paper, the effectiveness of the prediction method was examined, focusing on the initiation process in the fatigue phenomenon of aluminum alloy die castings using artificial cracks instead of natural casting defects.
First the influence of crack, processing method on the cyclic number initiation was examined and it was found out that cracks induced by the electric discharged wire machining has the minimum number of initiations due to less residual stress at the crack tip.
Next the fatigue life of the actual suspension part of aluminum alloy AC4CH die casting with artificial crack was examined under several conditions.
Based on the results, a new correction method is proposed which takes the initiation process from artificial defect to fatigue crack into account.
