Experimental and Computational Statistical Investigation of Microstructurally Small Fatigue Crack Growth in Nickel Microbeams

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This award supports fundamental research to perform small scale tests that quantify the crack growth rate in metals within grains and computational simulations of comparable spatial resolutions, yielding unprecedented level of integration. The assessment of the structural health of components and structures usually requires understanding their mechanical response under periodic repetitive loads. Under these conditions, the so-called fatigue cracks initiate and propagate, and they may lead to catastrophic failures. The need for cost-efficient research that prevent fatigue failures has pushed towards integrated computational materials engineering approaches as a means to improve national competitiveness. The understanding of the interaction between cracks and material structure improves the safety assessments of structural components by increasing confidence on response predictions and reducing unnecessary conservatism. In addition, planned outreach activities are designed to create unique opportunities to promote motivation, learning and academic success in the STEM fields for high school students.The research will unravel the parameters that influence the shape and intensity of the crack growth rates within grains. We research will follow a truly integrated microstructure-sensitive fatigue approach for nickel that combines 3-dimensional crystal plasticity models and a novel in situ scanning electron microscope microresonator-based experimental technique. The experiments will characterize the early growth of microstructural small cracks in nickel microbeams, yielding critical results such as the morphology of grains that nucleate cracks, crack growth rates, and 3-dimensional topography of the microstructural small cracks. The measured initial crack growth rates will be employed to calibrate the computational fatigue model, both in vacuum and air. The calibrated simulations will provide insight into the parameters that dominate crack growth, including sub-surface microstructural attributes. Thanks to the high throughput experimental technique, a statistically significant analysis will be carried by comparing a large number of experimental and computational realizations (crack length vs number of cycles), which will identify sources of epistemic uncertainty. The results have the potential to reshape the current understanding of the synergy between cracks and microstructure.