The Effect of Casting Porosity on the Fatigue Life of Lost-Foam Cast Iron and Aluminum-Silicon 319
by
Anthony J. Biell IV
Frederick V. Lawrence, Jr.
Department of Materials Science and Engineering
Abstract
The fatigue and monotonic properties of a nodular cast iron, gray cast iron, and Aluminum-Silicon 319 cast using the empty-cavity and the lost-foam processes were determined. The cast iron tests were performed at room temperature while the aluminum-silicon specimens were tested at room temperature at 99% humidity and at 300°F. Fatigue cracks in the nodular coast iron and Aluminum-Silicon always initiated at the largest casting flaw. Initial flaw sizes were measured using a scanning electron microscope and used to calculate the initial stress intensity factor, ΔK0. There is a better correlation in the nodular cast iron and the aluminum-silicon alloy between the initial stress intensity factor of the initiating flaw and the fatigue life than with the maximum stress. There is a better relationship in the gray cast iron between the maximum stress (R=0.1) and the fatigue life than was observed for the nodular cast iron tests. The role of internal casting porosity was quantified using a linear-elastic fracture mechanics (LEFM) model for fatigue crack growth. The predicted lives agreed with measured values within a factor of two. The nodular cast iron predictions were increasingly conservative at long lives.
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