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

该奖项支持基础研究，以进行小规模测试，量化晶粒内金属的裂纹增长率和可比空间分辨率的计算模拟，从而产生前所未有的集成水平。构件和结构的结构健康评估通常需要了解它们在周期性重复载荷下的力学响应。在这些条件下，所谓的疲劳裂纹开始并扩展，并且它们可能导致灾难性故障。对防止疲劳失效的成本效益研究的需求推动了综合计算材料工程方法作为提高国家竞争力的手段。裂纹和材料结构之间的相互作用的理解，提高响应预测的信心，减少不必要的保守性，提高了结构部件的安全评估。此外，计划中的外展活动旨在为高中生创造独特的机会，以促进他们在STEM领域的动机，学习和学术成功。该研究将揭示影响晶粒内裂纹增长率形状和强度的参数。我们的研究将遵循一种真正集成的镍微观结构敏感疲劳方法，该方法结合了三维晶体塑性模型和一种新的基于原位扫描电子显微镜微谐振器的实验技术。实验将表征镍微梁中微结构小裂纹的早期生长，产生关键结果，如成核裂纹的晶粒形态、裂纹生长速率和微结构小裂纹的三维形貌。测量的初始裂纹扩展速率将被用来校准计算疲劳模型，在真空和空气中。校准模拟将提供洞察主导裂纹生长的参数，包括次表面微观结构属性。由于高通量的实验技术，统计上显着的分析将进行比较大量的实验和计算实现（裂纹长度与循环数），这将确定来源的认识不确定性。这些结果有可能重塑目前对裂纹和微观结构之间协同作用的理解。

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.