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(CALEAR)项目将整合多个长度尺度上的变形力学，以发现金属的微观结构如何影响在循环载荷下驱动失效的局部应力(名义面积上的力)的分布。结构材料的疲劳失效--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。重要的是，所施加的机械载荷在微结构内称为颗粒的区域之间分布的机制还没有完全了解。该计算方法的新颖之处在于明确地确定了晶界，这将内在地将与疲劳裂纹形核和扩展相关的多个尺度联系起来。了解显微组织和疲劳裂纹驱动力之间的相关性将使定制材料设计成为可能。添加剂制造技术的最新进展使材料沉积过程中的微观结构得以控制。这项研究将为设计结构部件提供一个理论和计算框架，以利用这种灵活的制造技术。因此，这项研究将在促进科学进步的同时，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群体外联活动相结合，并支持病媒教育的基础研究。让物理概念变得更简单将使学生能够取得成功，并为他们未来的STEM职业生涯带来新的视角。课程的改进将直接影响11年级到研究生水平的课程；通过向教育者教授新的教学方法实现更广泛的影响。本研究的目标是通过了解施加在体积尺度上的应力如何在颗粒尺度上重新分布来促进对微观结构和织构对多晶材料疲劳行为的影响的理解。主要的研究目标是发现被称为邻域效应的颗粒相互作用如何影响驱动疲劳裂纹形核和扩展的局部应力的分布。这种新的方法包括将晶界上的力平衡和位移跳跃分解为颗粒均匀场(中尺度)和涨落场(微观尺度)的贡献。发展了一种多分辨率不连续Galerkin方法来测量邻域效应，这种邻域效应非常适合于捕捉沿晶界的不连续，允许区分来自细观尺度和微观尺度的贡献，但不必分离。假设揭示了中、微观尺度应力分量的相对影响区域，从而提高了疲劳门槛设计的经验性，以考虑到增加对小裂纹扩展阻力的微观结构和织构特征。洞察这些局部效应如何通过微观结构传播并影响材料疲劳，将有助于更好地理解为什么一些缺陷会形成裂纹，而另一些则不会。该项目启动了PI，旨在成为预测多晶结构材料工程规模疲劳性能的全国领先者。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.