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

这个教师早期职业发展计划（CAREER）项目将在多个长度尺度上整合变形力学，以发现金属的微观结构如何影响局部应力（标称面积上的力）的分布，从而在循环载荷下驱动失效。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中的主要挑战之一。至关重要的是，施加的机械载荷在微观结构中称为晶粒的区域之间分布的机制尚未完全理解。在这个项目中使用的计算方法的新奇是明确的目标晶界，这将内在地连接多个尺度相关的疲劳裂纹的成核和生长。微观结构和疲劳裂纹驱动力之间的相关性的知识将使定制的材料设计。增材制造技术的最新进展使得能够在材料沉积期间控制微结构。这项研究将产生一个理论和计算框架，用于设计结构部件，以利用这种灵活的制造技术。因此，这项研究将促进国家健康、繁荣、福利和国防，同时推动科学进步。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联活动相结合，并支持病媒教育的基础研究。使物理概念更容易将使学生取得成功，并为他们未来的STEM职业带来新的视角。课程的改进将直接影响到11年级到研究生水平的课程;更广泛的影响是通过向教育工作者教授新的知识来实现的。本研究的目标是通过了解在体积尺度上施加的应力如何在晶粒尺度上重新分布来促进对多晶材料疲劳行为的微观结构和纹理影响的理解。主要的研究目标是发现晶粒间的相互作用，称为邻域效应，如何影响驱动疲劳裂纹形核和生长的局部应力分布。新的方法涉及到分解的平衡力和位移跳跃沿着晶界的贡献颗粒均匀场（中尺度）和波动场（微观）。多分辨率间断Galerkin方法的开发，以衡量的邻域效应，是理想的适合捕捉沿沿着晶界的不连续性，允许从中尺度和微尺度的贡献被区分，但不必被分离。追求的假设，以揭示相对区域的影响，中尺度与微尺度的应力分量，从而提升的经验性质的疲劳阈值设计，以占微观结构和纹理的功能，增加抵抗小裂纹扩展。深入了解这些局部效应如何通过微观结构传播并影响材料疲劳，将更好地理解为什么有些缺陷会成核裂纹，而另一些则不会。该项目启动了PI，旨在成为多晶结构材料工程规模疲劳性能预测的国家领导者。该奖项反映了NSF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.