Collaborative Research: Multiscale Modeling of Damage Tolerance in Hexagonal Materials

六方密排晶体（六方）金属广泛用于工业和生物医学领域，例如作为核电站中的燃料棒（锆合金）;医疗支架和牙科应用（钛和镁合金）;发电系统和喷气发动机中的压缩机和涡轮机盘和叶片（钛合金）以及低温燃料箱和太空望远镜反射镜（铍合金）等。然而，目前还没有材料建模框架可用于对其耐久性和损伤容限进行稳健的工程预测。该奖项支持解决这一关键差距的基础研究，重点是强度和延展性极限的预测建模。这项研究的成果不仅将推进寿命评估程序，还将避免加工和制造过程中的材料浪费。待开发的模型和仿真工具将为工程师提供在制造和使用过程中预测金属结构在复杂载荷条件下的机械响应的方法。此外，从这项研究中获得的基本理解将有助于合金和微观结构设计人员通过击败控制机制而不是遵循试错法来开发损伤容限材料。此外，PI将让本科生参与这项研究计划，并为暑期学校开发讲座和配套材料，旨在为下一代机械工程师提供计算力学和材料科学工具。对六方晶系金属中滑移和孪生机制的进一步理解，导致了其无损伤塑性本构模型的进展。然而，微观力学为基础的模型，耦合塑性与损伤仍有待开发。一个挑战是评估必须纳入损伤模型的晶体学细节的程度。另一个同样重要的问题是损害过程的表现。最近的实验已经清楚地表明，六角合金确实会因空穴成核、生长和聚结而失效。以损伤和断裂的无参数公式为目标，这项合作研究旨在通过以下方式对一般应力状态下六角材料中的韧性损伤进行基础研究：（i）使用三维晶体塑性晶胞模拟研究变形机制对微孔洞生长和合并的作用，（ii）制定一种新的，计算效率高的基于微观力学的各向异性多孔多表面模型，充分评估对单位细胞计算，及（iii）审慎评估该等-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。

Hexagonal close-packed crystalline (hexagonal) metals are widely employed in industrial and biomedical sectors, e.g. as fuel rods in nuclear power plants (zirconium alloys); medical stents and dental applications (titanium and magnesium alloys); compressor and turbine disks and blades in power generation systems and jet engines (titanium alloys) and in cryogenic fuel tanks and space telescope mirrors (beryllium alloys) among many others. Yet, there currently are no material modeling frameworks that can be used to make robust engineering projections regarding their durability and damage tolerance. This award supports fundamental research addressing this critical gap and focus is laid on predictive modeling of strength and ductility limits. The outcomes of this research will not only advance life assessment procedures but also avoid material waste in processing and manufacturing operations. The models and simulation tools to be developed will provide engineers with means of predicting the mechanical response of metallic structures under complex loading conditions, both during manufacturing and in service. In addition, fundamental understanding gained from this research will help alloy and microstructure designers develop damage-tolerant materials by defeating the controlling mechanisms rather than following trial-and-error approaches. In addition, the PIs will engage undergraduate students in this research program and develop lectures and accompanying material for a summer school aimed at empowering the next generation of mechanical engineers with computational mechanics and materials science tools. Improved understanding of the slip and twinning mechanisms in hexagonal metals has led to advances in constitutive modeling of their damage-free plasticity. However, micromechanics-based models that couple plasticity with damage remain to be developed. One challenge is to assess the extent of crystallographic detail that must be incorporated in a damage model. Another, equally important issue is one of representation of the damage process. Recent experiments have clearly shown that hexagonal alloys do fail by void nucleation, growth and coalescence. With the goal of a parameter-free formulation of damage and fracture, this collaborative research aims at fundamental investigations of ductile damage in hexagonal materials under general stress states by - (i) investigating the role of deformation mechanisms on micro-void growth and coalescence using three-dimensional crystal plasticity unit cell simulations, (ii) formulating a novel, computationally efficient micromechanics-based anisotropic porous multi-surface model, fully assessed against the unit cell calculations, and (iii) critically assessing the so-developed anisotropic damage model against existing experimental data for magnesium alloys.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.