CAREER: An Experimentally-Informed Multi-Level Framework for Modeling Fracture of Hexagonal Metals

具有六方密排结构的金属和合金作为轻量化结构材料具有潜在的应用前景，特别是在未来的汽车应用中。通过在空中和地面运输中引入抗断裂轻型结构来提高燃油效率，将降低操作温度，延长部件寿命，并减少温室气体排放。这些金属也解决了设计挑战，有助于更轻、更薄的消费电子产品。限制这些材料广泛采用的一个因素是它们在加工过程中容易断裂。关于这种断裂是如何发生的，为什么会发生，以及如何减轻这种断裂，以使这些材料在制造过程中具有成本效益和节能性，还有很多有待研究。更好地了解断裂机制，并创建可靠的计算工具集来预测断裂，可以有效地设计耐损伤金属和材料认证，以及使用计算方法而不是反复试验的新工艺。该学院早期职业发展（Career）计划奖支持研究，以促进对六边形紧密堆积金属断裂的理解，并推进基于微结构的预测建模。对工业相关轻量化钛和镁合金的行为将产生新的认识。本科生和研究生将接受材料表征、测试、分析、建模和仿真方法的培训，以推进材料科学和力学领域的发展。这些技能将为学生从事有助于美国竞争力的职业做好准备。与连续断裂力学不同的是，连续断裂力学假设最初存在空洞，而这里创建的模型将对断裂发生的时间和地点非常敏感，特别是在晶界处。纯六角形金属将用于在塑性变形过程中建立晶界对成核空洞的阻力。通过聚焦离子束扫描电子显微镜的原位加载，结合电子背散射衍射成像，近场高能x射线衍射显微镜的原位测试和成像，以及微x射线计算机断层扫描，将空洞成核位置与3D结构特征联系起来。编制的结构和空洞成核事件的综合统计数据库将为表征微观组织的晶体学和空间物理状态以及晶界内聚强度的中观尺度晶体塑性模型提供信息，以预测塑性和断裂。最后，将创建一个新的多级工具集，将变形和空洞演化的中观物理联系起来，以一种易于计算的方式在宏观尺度上预测断裂，从而促进材料在制造和使用条件下的行为模拟。该工具集将为基于规定性能设计材料的长期愿景提供物理基础和途径。

Metals and alloys with a hexagonal close-packed structure have potential applications as lightweight structural materials, particularly in future automobile applications. Improving fuel efficiency by introducing fracture-resistant lightweight structures in air and ground transportation will lower operating temperatures, lengthen component life, and reduce greenhouse gas emissions. These metals also address design challenges instrumental to lighter and thinner consumer electronics. One factor limiting wide adoption of these materials is their tendency to fracture during processing. Much remains to be learned about how and why this fracture takes place, and how to mitigate it to allow cost- and energy-efficient use of these materials for manufacturing. A better understanding of the fracture mechanisms, and the creation of a reliable computational toolset for predicting fracture, can enable effective design of damage-tolerant metals and the certification of materials as well as new processes using computational methods rather than trial-and-error experimental approaches. This Faculty Early Career Development (CAREER) Program award supports research to advance the understanding of fracture in hexagonal close-packed metals and to advance microstructure-based predictive modeling. New understanding about the behavior of industry-relevant lightweight titanium and magnesium alloys will result. Undergraduate and graduate students will be trained in materials characterization, testing, analytics, modeling, and simulation methods to advance the fields of materials science and mechanics. The skills will prepare the students to pursue careers that contribute to U.S. competitiveness. Unlike continuum fracture mechanics, which assumes that a void initially exists, the models created here will be sensitive to when and where fracture originates, particularly at grain boundaries. Pure hexagonal metals will be used to establish resistance of grain boundaries to nucleate voids during plastic deformation. Void nucleation sites will be linked to 3D structural features via in-situ loading within a focused ion beam scanning electron microscope in combination with electron backscattered diffraction imaging, in-situ testing and imaging using near-field high-energy X-ray diffraction microscopy, and micro X-ray computed tomography. The compiled comprehensive statistical database of structures and void nucleation events will inform meso-scale crystal plasticity models that can represent the crystallography and spatial physical state of microstructure and the cohesive strength of grain boundaries to predict plasticity and fracture. Finally, a novel multi-level toolset will be created to link the meso-scale physics of deformation and void evolution for predicting fracture at the macro-scale in a computationally tractable manner to facilitate simulations of material behavior during manufacturing and in service conditions. The toolset will provide the physical basis and pathway towards a longer-term vision of designing materials based on prescribed performances.