Significant Enhancement of Structural Integrity of Shape Memory Ceramics in High Cycle Fatigue

虽然形状记忆陶瓷在低周疲劳中表现出良好的性能，但其在高周疲劳中的显著劣化阻碍了其应用。该奖项支持基础研究，以了解形状记忆陶瓷中纳米和微米级断裂的机制，并研究工程缺陷如何阻碍高周疲劳下的断裂。这些新的科学见解对于在需要高温和耐腐蚀执行器的应用中开发和使用形状记忆陶瓷非常重要，并可能推动美国进入先进形状记忆陶瓷技术的最前沿。该奖项将提供多个层次的培训和教育：将招募一名研究生和一名博士后研究助理进行研究，由本科研究实习生提供支持，并将向K-12学生介绍高级计算研究的概念。最后，将进一步开发研究生的专业发展课程，并将研究纳入计算力学的核心研究生课程。高周疲劳断裂一直是形状记忆陶瓷的主要缺陷之一。到目前为止，大多数努力都集中在消除这些陶瓷制造中的缺陷结构，使其能够用于不利用形状记忆效应的应用。介导陶瓷的热机械形状记忆行为的基质相变与纳米级体积膨胀相关，有助于纳米级断裂。本研究将从根本上研究如何将工程缺陷引入形状记忆陶瓷的纳米和微观结构中，以适应体积膨胀并减轻界面和晶界断裂以及高周疲劳过程中不需要的非晶相的形成。在最初的几个疲劳周期的纳米级裂纹的机制将研究千万亿次原子模拟。在微观尺度上，将形状记忆行为的物理学和热力学与疲劳断裂的物理学和热力学耦合起来，在相场模型框架下研究工程缺陷对高周疲劳断裂的影响。模型和模拟数据的验证和确认沿着不确定性量化将使用文献中的实验数据进行。研究结果将用于提出新的疲劳寿命预测函数，该函数将缺陷的体积分数和尺寸以及其他纳米和微观结构特征考虑在内。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。

Although shape memory ceramics have shown good performance in low cycle fatigue, their significant deterioration in high cycle fatigue has stalled their applications. This award supports fundamental research to understand the mechanisms of nano and microscale fracture in shape memory ceramics and to study how engineered defects can impede facture under high cycle fatigue. These new scientific insights are important for the development and use of shape memory ceramics in applications requiring high-temperature and corrosion-resistant actuators and may propel the U.S. into the forefront of advanced shape memory ceramic technology. The award will provide training and education at several levels: a graduate student and a postdoctoral research associate will be recruited to perform the research, supported by undergraduate research interns, and K-12 students will be introduced to concepts in advanced computational research. Lastly, a professional development course for graduate students will be further developed and the research will be integrated in a core graduate-level course on computational mechanics.Fracture in high cycle fatigue has been one of the main drawbacks of shape memory ceramics. Until now, most efforts have focused on eliminating defect structures in the manufacturing of these ceramics to enable their use in applications that do not take advantage of the shape memory effect. Matristic phase transformation that mediates the thermo-mechanical shape memory behavior of ceramics is associated with a nanoscale volume expansion aiding the nanoscale fracture. This research will fundamentally study how engineering defects into the nano and microstructures of shape memory ceramics can accommodate the volume expansion and mitigate both interface and grain boundary fracture and unwanted amorphous phase formation during high cycle fatigue. The mechanisms of nanoscale cracking during the first few fatigue cycles will be studied by petascale atomistic simulations. And at the microscale, the effects of engineered defects on high cycle fatigue fracture will be studied by coupling the physics and thermodynamics of shape memory behavior in ceramics with those of the fatigue and fracture under a phase field modeling framework. Verification and validation of models and simulation data along with uncertainty quantification will be done with experimental data available in the literature. The findings will be used to propose new fatigue lifetime prediction functions that account for the volume fraction and size of the defects and other nano and microstructural features.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.