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

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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.