Understanding Mixed-Mode Fracture Mechanics in Additively Manufacturable Functionally Graded Microcellular Solids

在从生物医学到航空航天、民用和汽车工业的各种工程应用中，具有蜂窝结构的材料的使用正在迅速增长。如果设计准确，蜂窝结构可以既高强度又重量轻。与传统的结构中单元的统一模式不同，优化设计通常要求单元的非均匀分级，称为功能梯度结构。加法制造和计算技术的最新进展使研究人员能够精确地构建具有复杂图案的功能梯度细胞结构。然而，大多数用于优化单元图案配置的可用设计忽略了在制造过程中或由于过载而可能在印刷组件中形成的凹槽或裂缝。这项研究的主要目的是了解暴露在复杂载荷条件下的附加制造的功能梯度蜂窝结构在这些关键区域附近的断裂力学。这种基本的理解可以整合到下一代工程细胞结构的设计中，增强抗断裂能力。本研究开发的数学模型和力学将推动断裂力学、理论和计算力学、复合材料结构和添加剂制造等领域的发展。此外，通过这个项目，研究生、本科生和K-12年级的学生将参与几个专业、教育和外展活动。这个项目旨在提供对断裂行为的更多了解，以及可制造的功能分级微蜂窝结构。这项工作的科学目标是：i)证明具有不同图案功能的不同微孔结构可以通过添加制造成功地产生；ii)通过实验和计算表征其本构响应；iii)开发一种新的计算高效的多尺度方法来预测其混合模式断裂行为；以及iv)提供关于如何在应力集中附近配置细胞的图案和分布(即，拓扑和形态)的详细信息。为了实现这些目标，将通过添加制造来构建不同的空间图案微孔结构，以实验研究它们的本构响应、复合型断裂韧性和裂纹扩展机制。将开发一个协同的实验/计算框架，通过考虑由微孔图案和印刷方向引起的材料各向异性来预测和优化断裂行为。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。

The use of materials having cellular structures is rapidly growing in various engineering applications ranging from biomedical to aerospace, civil, and automotive industries. If designed accurately, cellular structures can be both high strength and light weight. In contrast to a traditional uniform pattern of cells across a structure, optimal designs usually require a non-uniform grading of cells, called a functionally graded structure. Recent advances in additive manufacturing and computational techniques have enabled researchers to precisely build functionally graded cellular structures with complex patterns. However, most available designs for optimized cell pattern configurations ignore the notches or cracks that can be formed in the printed components either during the fabrication process or due to excessive loads. The main goal of this research is to understand fracture mechanics near such critical areas in additively manufactured functionally graded cellular structures exposed to complex loading conditions. This fundamental understanding can then be integrated into next-generation design of engineered cellular structures with enhanced fracture resistance. The mathematical models and mechanics developed in this research will advance the fields of fracture mechanics, theoretical and computational mechanics, composite structures, and additive manufacturing. Additionally, through this project, graduate, undergraduate, and K-12 students will engage in several professional, educational, and outreach activities.This project aims to provide a greater understanding of fracture behavior in additively manufacturable functionally graded microcellular structures. The scientific objectives of this work are to i) demonstrate that different microcellular structures with different pattern functions can be successfully produced by additive manufacturing, ii) experimentally and computationally characterize their constitutive response, iii) develop a novel computationally efficient multiscale approach for prediction of their mixed mode fracture behavior, and iv) provide detailed information regarding how patterns and distributions of cells (i.e., topology and morphology) should be configured near the stress concentrations. To achieve these goals, different spatially pattered microcellular structures will be built by additive manufacturing to experimentally investigate their constitutive response, mixed-mode fracture toughness, and the crack propagation mechanism. A synergistic experimental/computational framework will be developed to predict and optimize fracture behavior by considering the material anisotropy induced from both the microcellular patterns and the printing orientation.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.