## Research

Our research interests include a wide variety of current challenges in the field of mechanics of materials and multiscale modeling.### Computational Bicrystallography

### Grain Boundary Energy

Interfaces between grains (grain boundaries) are material defects that are responsible
for a wide range of material behavior. At large scales, GB energy can
often be safely ignored due to its relatively low energy in comparison to
volumetric energy. However, volumetric energy scales as x^3 whereas interface
energy scales as x^2--so at small enough scales, interface phenomena dominates.

The covariance interface energy model is a robust, general, efficient model of crystalline interfaces for use in analysis of micromechanical systems, optimal manufacturing of composites, and integration into multiscale computations.

* Runnels et al, "An analytical model of interfacial energy based on a lattice-matching interatomic energy" JMPS 2016*

### Microstructural Evolution

While materials tend to behave isotropically and uniformly on the macroscopic scale, they exhibit significant anisotropy on the microscopic scale due to microstructural heterogeneity. The evolution of microstructure can significantly impact bulk material behavior, and is coupled with the mechanical and thermodynamic state of the material.

We use various techniques to computationally model the evolution of microstructure in materials. Continuum-type simulations are given multifunctionality by exchanging information between the macroscopic stress state and atomistic-based material point calculations.

### Interface Morphology

Interfaces demonstrate a wide range of behavior, and can demonstrate exceedingly complex morphologies. While some interfaces are hopelessly disordered, many demonstrate highly ordered faceted structure that is conducive to analysis. Because morphology is linked to many other phenomena such as grain boundary sliding, twinning, and stability, it is of interest to understand and model this behavior.

The relaxation method used with the covariance interface energy model is able to predictively determine the morphology of interfaces with arbitrary character, and to compute the relaxed energy. The results are used to understand grain boundary mechanics, to integrate into multiscale simulations, and to predict optimal manufacturing techniques for composites.

* Runnels et al, "A relaxation method for the energy and morphology of grain boundaries and interfaces" JMPS 2015*

### Atomistic Simulations

To validate multiscale models, it is frequently necessary to perform simulations that account for atomistic degrees of freedom. Molecular statics/dynamics provides a framework for estimating atomic-level behavior in response to external loading conditions.

We use molecular dynamics to generate data for comparison with theoretical multiscale models, and perform analysis to determine the effect of interatomic potential on material properties.

### GPU-Accelerated Multiscale Modeling

- Improve methods for computational crystal plasticity
- Implement plasticity with phase transformation and twinning models
- Integrate interface energy with continuum-based multiscale polycrystalline simulations.

### Other Interests / Applications / Ongoing Projects

- Additive manufacturing
- Large-deformation continuum mechanics and mechanics of soft matter and membranes
- Rolling contact fatigue for predicting failure on railroad wheels

### Relevant Links

Crystallography and defects- Defects in Crystals by Prof. Dr. Helmut Föll
- Lectures on grain boundary engineering
- Research group at the University of Cambridge