Abstract
Aim of this study is to unravel the effect of macroscopic casting defects on fatigue life of pressure die cast aluminium alloy. Macroscopic casting defects are highly dependent on the product shape or casting process. Therefore, a methodology of fatigue design is strongly demanded to take account of casting defects specific to the product. In this study, observation of casting defects by X-ray CT and tension-compression fatigue test are carried out. Three-dimensional image processing visualizes actual shape and configuration of casting defects, such as porosities, in the specimen before fatigue test. Visualization of porosities during fatigue test or after failure can also be used to investigate the fracture process. We found that crack initiation is almost restricted to from surface or near-surface defects, and shrinkage porosities can accelerate the crack propagation and reduce the failure life. Moreover, a plane defect, which was hardly observed by the X-ray CT, extremely decreased the fatigue life notwithstanding its location.
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