Multistage Fatigue Modeling of Cast A356-T6 and A380-F Aluminum Alloys
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CAST aluminum alloys of various compositions and casting conditions have been developed as major structural materials for automobiles and industrial equipment. These structural components are subjected usually to cyclic loading in service. The components, in general, are designed in such a way that the stress remains in the elastic regime, except perhaps for an occasional overload. However, the stresses around microstructural discontinuities, such as hard and brittle Si- or Fe-bearing particles, oxides, casting pores, and dendrite features, may exceed the elastic limit, even if the macroscopic response is elastic. Due to the complex microstructure of Y. XUE, Assistant Research Professor, C.L. BURTON, Research Associate, and M.F. HORSTEMEYER, Chaired Professor, are with the Center for Advanced Vehicular Systems, Mississippi State University, Starkville, MS 39759, USA. Contact e-mail: axue@cavs. msstate.edu D.L. McDOWELL, Regents’ Professor and Carter N. Paden, Jr. Distinguished Chair in Metals Processing, is with the G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405, USA. J.T. BERRY, Coleman Professor of Mechanical Engineering, is with Mississippi State University, Mississippi State, MS 39762, USA. This article is based on a presentation made in the symposium entitled ‘‘Simulation of Aluminum Shape Casting Processing: From Design to Mechanical Properties,’’ which occurred March 12–16, 2006 during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the Computational Materials Science and Engineering Committee, the Process Modeling, Analysis and Control Committee, the Solidification Committee, the Mechanical Behavior of Materials Committee, and the Light Metal Division/Aluminum Committee. METALLURGICAL AND MATERIALS TRANSACTIONS B
cast aluminum alloys, the fatigue life exhibits two to four orders of variation in the high-cycle fatigue (HCF) regime, in which the fatigue life is sensitive to microstructures. Therefore, a practical fatigue life prediction model must incorporate the effects of the microstructure features on fatigue life to capture the scatter due to stochastic discontinuities in the component. A multistage fatigue (MSF) model that incorporates microstructural effects on fatigue damage incubation and growth was developed for a cast A356-T6 aluminum alloy by McDowell et al.,[2] based on micromechanics simulations[3,4] and small-scale experiments.[5–9] The MSF model and concepts of fatigue growth stages were extended to a 7075-T651 aluminum alloy for airplane frame applications[10,11] and lightweight AM50 and AE44 magnesium alloys.[12,13] A few MSF model parameters specifically developed for A356 aluminum alloy are represented by the static mechanical properties indicated by Xue et al.[10,12] In this article, we extend the MSF model developed by McDowell et al.[2] for a cast A356-T6 aluminum alloy to a die-cast A380-F aluminum alloy to obtain HCF life predictions. The two alloys have different amounts of primary alloy element Si (7 wt pct and
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