Quantification of the interaction within defect populations on fatigue behavior in an aluminum alloy

The interaction between fatigue crack evolution and porosity in A356-T6 alloys was characterized using both X-ray microtomography and finite-element analysis. The formation and propagation Of fatigue cracks are dominated by the highest local stress-strain concentration (k(g) = root k(sigma)k(epsilon)) caused by the presence of porosity adjacent to the free Surface and the crack tip, respectively. The k(g) factor proved to be a Suitable parameter to quantify the influence of porosity on fatigue cracking and to predict the fatigue crack growth rate (d(a)/d(N)). Although microporosity has a complex, tortuous morphology, a simple method for mapping the shape to an idealized sphere was proposed. It was found that using a sphere with equal projected area in the plane normal to the loading direction was a good approximation, allowing an equivalent k(g) to be calculated. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.