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Multiple defect distributions on weibull statistical analysis of fatigue life of cast aluminium alloys

C Nyahumwa


From an engineering point of view, the fatigue strength variability of cast aluminium alloy components requires a detailed understanding of the inconsistency of cast defect distribution. Cast aluminium alloys are not generally homogeneous; they may contain two or more types of
common casting defects, which are gas and shrinkage porosities, oxide films, and inclusions. Each defect type has its own distribution of sizes; and multiple cast components of presumably the same material may have different histories and therefore different cast defect populations. A number of statistical analyses of fatigue data assume that a single distribution of casting defect is present uniformly throughout the cast aluminium alloys. As a result, fatigue data are statistically not
correctly described. By relaxing the assumptions of a single cast defect distribution, of uniformity throughout the material and of uniformity from specimen to specimen, Weibull statistical analysis for multiple defect distributions have been applied to correctly describe the fatigue life data of aluminium alloy castings having multiple cast defects competing to initiate fatigue cracks.