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Fracture Mechanics Investigations on Cast AluminiumAluminium castings cannot be massproduced economically without casting pores or similar flaws. These flaws must, however, be avoided, at least in the highly stressed regions of cast safety components of automobiles by changes in design or casting procedure. In other regions flaws up to a certain size can be tolerated if it can be shown by calculation and experiment that cracks either will not propagate from these flaws or at least will not reach critical sizes during the life of the component. Cast aluminium wheels are an example of such a component. Their allowable flaw sizes were determined in the following way: -The stresses occuring in service were measured in 17 locations in a test rig in the laboratory and on a race track. -The crack propagation characteristics and the AK,,-values of the cast aluminium material were determined. -Crack propagation was calculated under the stresses measured in service; based on these measured stresses and the fracture mechanics characteristics, locations were selected in the cast aluminium wheel where no flaws can be allowed; in other locations with lower stresses the allowable flaw sizes were calculated with a large safety factor.

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