A micro-cell model of the effect of microstructure and defects on fatigue resistance in cast aluminum alloys

Six different, industrially important, casting situations containing an array of typical microstructure and defects were investigated. Porosity, secondary dendrite arm spacing, Al-matrix, Si-particles, and Fe-rich intermetallics were experimentally identified as the major factors affecting the alloy's resistance to fatigue. A micro-cell model was developed to quantitatively investigate the effect of these factors on fatigue resistance. The micro-cell captures the key microstructural features and is embedded into a macro material element at the specimen surface. A nonlinear isotropic/kinematic hardening law was used to describe the cyclic plastic behavior of the Al-matrix. This model enables the quantification of the accumulation and concentration of the microscale plastic deformation induced during fatigue loading by microstructural heterogeneities. The simulation results demonstrate that microscale plastic damage could occur even when the maximum far-field stress is below the nominal yield stress of the alloy. The degree of fatigue damage, in terms of the accumulation of plastic damage dissipation energy, was found to be sensitive to the microstructural features. Fatigue strength was estimated using the model and found to be in good agreement with experimental results. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.