CAREER: Towards Fatigue Behavior Prediction of Structural Materials through Computationally-Informed Textural and Microstructural Characteristics

该学院早期职业发展计划（Career）项目将整合多种长度尺度的变形力学，以发现金属的微观结构如何影响局部应力（名义面积上的力）的分布，从而导致循环载荷下的失效。结构材料的疲劳失效——在循环载荷下损伤的累积——仍然是力学和材料科学的主要挑战之一。至关重要的是，在微观结构中，施加的机械载荷在称为晶粒的区域之间分布的机制尚未完全了解。该项目中使用的计算方法的新颖之处在于明确地针对晶界，这将内在地连接与疲劳裂纹形核和扩展相关的多个尺度。了解微观结构与疲劳裂纹驱动力之间的关系将有助于定制材料设计。增材制造技术的最新进展使材料沉积过程中的微观结构控制成为可能。这项研究将产生一个理论和计算框架来设计结构部件，以利用这种柔性制造技术。因此，在科学进步的同时，研究将促进国家的健康、繁荣、福利和国防。该项目的研究成果将与具体的K-12和代表性不足的少数民族外展活动结合起来，并支持媒介教育方面的基础研究。让物理概念变得更简单将使学生获得成功，并为他们未来的STEM职业生涯带来新的视角。课程改进将直接影响11年级到研究生阶段的课程；通过向教育工作者教授新的教学法，可以产生更广泛的影响。本研究的目的是通过了解在体尺度上施加的应力如何在晶粒尺度上重新分布，来推进对多晶材料疲劳行为的微观结构和织构影响的理解。主要研究目的是发现晶粒相互作用（称为邻域效应）如何影响驱动疲劳裂纹形核和扩展的局部应力分布。该方法将沿晶界的力和位移跳跃的平衡分解为颗粒均匀场（中尺度）和波动场（微观尺度）的贡献。一种多分辨率不连续伽辽金方法被开发用于测量邻域效应，这种邻域效应非常适合捕获沿晶界的不连续，允许中尺度和微观尺度的贡献被区分，而不必被分开。假设是为了揭示中尺度与微观尺度应力分量的相对影响范围，从而提升疲劳阈值设计的经验性质，以考虑增加对小裂纹扩展阻力的微观结构和纹理特征。了解这些局部效应是如何通过微观结构传播并影响材料疲劳的，将有助于更好地理解为什么有些缺陷会形成裂纹，而另一些则不会。该项目启动了PI在多晶结构材料工程尺度疲劳性能预测方面的国家领先地位。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This Faculty Early Career Development Program (CAREER) project will integrate mechanics of deformations at multiple length scales to discover how the microstructure of a metal influences the distribution of local stress (force over nominal area) that drive failure under cyclic loading. Failure of structural materials by fatigue -- the accumulation of damage under cyclic loading -- remains one of the major challenges in mechanics and materials science. Crucially, the mechanisms through which applied mechanical loading distributes between regions called grains within the microstructure are not fully understood. The novelty of the computational approach to be used in this project is to explicitly target the grain boundaries, which will inherently connect multiple scales relevant to fatigue crack nucleation and growth. Knowledge of the correlations between the microstructure and fatigue crack driving forces will enable tailored material design. Recent advances in additive manufacturing technology have enabled control of microstructure during material deposition. This research will yield a theoretical and computational framework for designing structural components to capitalize on this flexible manufacturing technology. Thus, the research will advance national health, prosperity, welfare, and defense, while progressing science. The research outcomes of the project will be integrated with specific K-12 and underrepresented minority outreach activities as well as support foundational research in vectors education. Making physics concepts easier will empower students to succeed and bring new perspectives to their future STEM careers. Curriculum enhancements will directly impact courses at the 11th grade up to graduate level; broader impact is achieved through teaching new pedagogies to educators.The goal of this research is to advance the understanding of microstructural and textural influences on fatigue behavior of polycrystalline materials by understanding how stress applied at the bulk scale is redistributed at the grain scale. The primary research objective is to discover how grain interactions, called the neighborhood effect, influence the distribution of local stresses that drive fatigue crack nucleation and growth. The novel approach involves decomposing the balance of forces and displacement jumps along grain boundaries into contributions from the granular uniform field (mesoscale) and fluctuation field (microscale). A multi-resolution Discontinuous Galerkin method is developed to measure the neighborhood effect that is ideally-suited for capturing discontinuities along grain boundaries, allowing contributions from mesoscale and microscale to be distinguished but not having to be separated. Hypotheses are pursued to reveal the relative zone of influence of mesoscale versus microscale stress components, thereby elevating the empirical nature of fatigue threshold design to account for microstructural and textural features that increase resistance to small crack growth. Insight as to how these local effects propagate through the microstructure and affect material fatigue would provide a better understanding of why some flaws nucleate cracks while others do not. This project launches the PI towards becoming a national leader in the prediction of engineering scale fatigue properties for polycrystalline structural materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.