日本機械学會論文集. A編 = Transactions of the Japan Society of Mechanical Engineers. A

Purpose




The purpose of this paper is the proposal of fatigue-life-prediction curve for cast aluminum alloy A356-T6 with different casting defect sizes.




Design/methodology/approach




Four kinds of A356-T6 fatigue specimens were sampled from the actual large-scale cast component, where the cooling rates were different. In addition, three kinds of A356 were casted under different casting conditions to simulate different defect sizes in the actual component. Subsequently, rotating bending fatigue tests were conducted using those samples. The maximum sizes of casting defects were quantitatively evaluated through microstructural observation and extreme value statistics. The fatigue limits of all samples were predicted using hardness and defect sizes based on modified Murakami’s equation.




Findings




The modified equation for fatigue limit prediction in A356-T6 was proposed. Fatigue limits were successfully predicted using the proposed equation.




Originality/value




Fatigue limit prediction method using hardness and maximum defect size was limited to steels. This paper proposed the modified method for A356-T6 aluminum alloy with lower elastic modulus. The method was valid for A356-T6 with different defect sizes.

Fatigue limit prediction of A356-T6 cast aluminum alloys with different defect sizes sampled from an actual large-scale component

In order to clarify the effect of casting defects on the high cycle fatigue properties, rotary bending fatigue tests were carried out on a cast aluminum alloy, JIS AC4CH, with two different levels of defect size. As a result of fatigue tests, the fatigue strength decreased with increasing the defect size. The fatigue limits were estimated by the area parameter model and compared with experimental values. The maximum defect size evaluated by the extreme value statistics was used in the prediction. The predicted values of fatigue limits for specimens with the different defect sizes were not in good agreement with the experimental values. In addition, the effects of the roller burnishing process on surface conditions and fatigue properties were also investigated. Vickers’ hardness and compressive residual stress on the specimen surface were increased by the burnishing process. An improvement of fatigue property was found in the burnished specimen. It is due to the disappearance of casting defect on the specimen surface, and increase of hardness and compressive residual stress.

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T. Shimizu

Papers

Effect of casting defects and roller burnishing on fatigue properties of a cast aluminum alloy AC4CH