Integrated computational materials engineering workflows for microstructure-sensitive fatigue of advanced alloys

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Stopka, Krzysztof S.
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The high cost and data scatter of physical fatigue experiments, particularly in the High Cycle Fatigue (HCF) regime, requires a paradigm shift to efficiently assess the fatigue criticality of metallic components. Integrated Computational Materials Engineering (ICME) presents an attractive additional pathway that employs microstructure-sensitive simulations given accessible process paths and resulting microstructures to assist and augment decision-support from experiments. In this research, multilevel scripted workflows are implemented into the open-source Python programming language to study the effects of intrinsic (e.g., crystallographic orientation distribution, grain shape, and grain size distribution) microstructure attributes, boundary conditions (e.g., fully periodic vs. traction free), strain states (e.g., uniaxial, shear, biaxial), and model sample sizes. Digital microstructure instantiations of Duplex Ti-6Al-4V and Al 7075-T6 are generated for simulation with Crystal Plasticity Finite Element Method constitutive models using the open-source Dream.3D software, with extreme value fatigue response as the primary performance requirement. Fatigue Indicator Parameters (FIPs) are used as surrogate measures of the driving force for fatigue crack formation and are volume averaged over regions within grains representative of fatigue damage process zones. These FIPs are fit to known extreme value distributions so that the effects of different microstructure attributes and boundary/strain states may be assessed. Other extreme FIP characteristics (e.g., proximity to free surface, elastic strain normal to slip plane) are examined. A major contribution of this thesis to the research community is the open-source PRISMS-Fatigue framework pursued in collaboration with researchers at the University of Michigan, which is a highly efficient, scalable, flexible, and easy-to-use community ICME platform.
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