Mechanical Engineering Associate Professor Mohsen Asle Zaeem was awarded over $390,000 by the Mechanics of Materials and Structures program of the National Science Foundation for a three-year project to study the multiscale mechanisms of fatigue and fracture in shape memory ceramics.

Shape memory ceramics are known for stability and corrosion resistance at extreme temperatures and would be ideal materials for actuators, jet engine components, or applications in energy conversion and storage systems. Their development for these uses is limited, however, because they fracture in these types of high-cycle fatigue scenarios.

(a) Comparison of the stress-strain curves of three samples with different size defects, and (b) distributions of equivalent plastic strain and monoclinic phase therein at maximum stress (point L).

Asle Zaeem explains that the team’s first objective is to understand the mechanisms of nanoscale fracture along interfaces and grain boundaries. To this end, they will perform nanoscale simulations of dynamic fracture during phase transformation. “Starting with single crystals, we will insert nanovoids and observe how they mitigate interface fracture that results from grain expansion during phase transformation,” said Asle Zaeem. “Then we’ll move on to more complex simulations on bicrystal models, and finally we’ll perform petascale molecular dynamics simulations to help us understand fatigue behavior of polycrystalline Z-SMCs with nanoscale voids.”

The next objective is to study the high-cycle fatigue behavior of Z-SMCs with engineered defects at microscale. To do this, the team will develop an atomistic-informed microscale modeling framework to predict and study the high-cycle fatigue behavior of Z-SMCs.

Atomistic informed phaser-field modeling of deformation of a shape memory ceramic; (a) a snapshot during deformation of a nanopillar by atomistic simulations, and (b) stress-strain curve of a deformed polycrystalline shape memory ceramic by phase-field simulations

Ultimately, the team will use these nanoscale and microscale simulations to propose new fatigue lifetime prediction functions that account for the volume fraction and size of defects and other nano- and microstructural features.

Asle Zaeem is excited about the implications of this research. “If we’re successful, this approach could significantly enhance the structural integrity of shape memory ceramics in high-cycle fatigue.” After this project, the team’s next steps would be to secure follow-on funding to computationally simulate and optimize the processing steps to achieve the desired nanostructures and microstructures. “With these models, we would be able to guide the experiments in producing SMCs with engineered defects and actually test them in high fatigue cycles.”