Admal aims to predict material behavior
New MechSE Assistant Professor Nikhil Chandra Admal wants to predict material failures. In particular, he focuses on modeling grain boundaries in small-scale crystalline materials and how they evolve in the presence of thermo-mechanical loads. An ideal material would be able to withstand shock, a characteristic of ductile materials, while still maintaining strength, a property associated with brittle materials. The toughness (shock-resistance) or strength of a material depends on its microstructure, which includes the configurations of all possible defects, including grain boundaries, in a material. Moreover, the microstructure itself evolves in the presence of external loads.
“This is like having a big playground and figuring out how to arrange grains in a system that will give you the right mixture of ductility and strength. At the same time, you need to predict how these grains evolve in the presence of thermal and mechanical loads,” said Admal.
To predict the behavior of materials under different loads, Admal studies mesoscale models that can accurately describe the microstructure and that can be numerically solved. In his research, the physics of his current models have been analyzed, and now the main focus is to make the models computationally feasible. His group is currently working on making their models predictive, by using realistic grain boundary energies obtained from molecular dynamics.
The grain boundary energy landscape is quite complex, as it is described in five-dimensions. According to Admal, a system with high grain boundaries is frustrated, so a material will try to decrease that energy by either grain boundary coarsening sliding. The underlying mechanism is a result of collective phenomena that can only be understood by simulations of a large systems of grains. The models and methods developed by Admal’s research group enable them to explore the hidden mechanisms and pave the way for a virtual materials processing paradigm.
He is also interested in exploring how strain gradients play an important role at the nanoscale. In classical elasticity, the energy density of a material is assumed to depend on the extent of strain, while in systems at the nanoscale, energy not only depends on the strain but also its gradients. For instance, higher order strain gradients play an important role in describing the core of a dislocation and surface energies. In particular, Admal is interested in establishing relationships between the gradient elastic material properties and crystal structures.
With all of these models, he is seeking to validate his predictions with experiments. In future collaborations, the microstructure of polycrystals under load will be studied, and then compared with the models he has created.
Admal earned a PhD in aerospace engineering from the University of Minnesota, and was a postdoctoral researcher in the Materials Science and Engineering Department at UCLA prior to joining MechSE in January 2019. In addition to his work in material modeling, he is currently teaching TAM 574, Advanced Finite Element Methods, a graduate-level course based in part on his own PhD studies in element analysis.