Integrated Experimental, Analytical, and Computational Design for Fatigue Crack Growth Resistance in Cast Aluminum Alloys

Long and small fatigue crack growth (FCG) studies at various stress ratios have been performed on solution-strengthened A535-F and precipitation-strengthened A356-T6 cast aluminum alloys. Microstructures were altered through processing and chemistry in order to systematically investigate the individual and combined effects of materials’ characteristic microstructural features on FCG. Mechanisms of FCG at the microstructural scale of the studied alloys were identified at various growth stages, and load-microstructure-damage mechanisms design maps were created. Complementary to this work, a fracture mechanics methodology for data treatment and reduction has been developed for long-to-physically small crack growth corrections, and an original material science-based model that further compensates for the microstructurally small crack growth behavior was created and validated. A computational toolset has been constructed for microstructure-specific FCG simulations. FCG response is represented by the superposition of material's matrix and secondary phase behavior, with phase property data generated using a novel microhardness indentation technique. Actual microstructural images are used as the basis for meso-scale simulations to make numerical evaluations of the FCG response and to optimize the materials for FCG resistance. Examples on the application of these methods and tools will be given as they relate to design for FCG resistance, life predictions, and material optimization.