MSE Seminar: Michael Gibbons, Continuum-Scale Modeling of Shear Banding in Bulk Metallic Glass-Matrix Composites

Abstract

Bulk metallic glass matrix composites (BMGMCs) with metallic dendrite reinforcements combine the excellent strength, hardness, and elastic strain limit of amorphous metallic glass with a ductile crystalline phase to achieve extraordinary toughness with minimal degradation in strength. In order to explore the mechanical interactions between the amorphous and crystalline phases a full-field micromechanical model, which couples a free-volume based constitutive model for the matrix with crystal plasticity, and its implementation via an elastic-viscoplastic Fast-Fourier Transform (FFT) solver. The model is calibrated to macroscale stress-strain data for Ti, Zr, V, Cu, Be BMGMCs with varying composition, then exercised to study the nature and origin of shear bands in metallic glass composites. This work addresses the disconnect between the morphology and size of the precipitated dendritic reinforcement and the overall mechanical behavior of the composite. Synthetic 3D microstructures were produced using images of real BMGMCs, and then subjected to uniaxial tension deformation simulations. The findings indicate that in BMGMCs, local inhomogeneities in the glass phase are less influential on the mechanical performance than the contrast in individual phase properties and the spatial distribution of the microstructure. Due to the strong contrast in mechanical properties between the phases, highly heterogeneous stress fields develop, contributing to regionally confined free-volume generation and localized flow and softening in the glass. These softened regions can link together inducing plastic flow which then rapidly localizes into a thin shear band with planar like geometry. This work sheds light on the nature of shear banding in bulk metallic glass matrix composites and demonstrates the feasibility of using spectral continuum-based model to efficiently predict the macroscopic mechanical behavior in the search for new and better performing materials.

Bio

I received my bachelor’s degree in chemical engineering from the University of Dayton with a minor in bioengineering, then decided to broaden my knowledge/skills in the physical sciences and engineering fields by extending my education in materials science and engineering. My initial research interests were in sustainability and materials for energy related applications, where I studied ceramic membranes for separating carbon dioxide from flue gas. However, I decided to pursue a different approach which involved using a porous graphene sheet as an atomic-scale sieve to selectively separate the gases. This introduced me to computational materials modeling which immediately captured my interest and ultimately led me to joining Dr. Windl’s computational materials modeling group. In his group, my focus actually switched to modeling the deformation of bulk metallic glass-matrix composites at the continuum-scale to study the inner workings of shear bands which are ultimately responsible for failure in this group of materials. That being said, while there are numerous individual subjects within these disciplines that I’ve become very interested in, I’m most fascinated by the application of many interdisciplinary concepts towards an elegant solution to a particular problem and would like to eventually work in product and process design.

Outside of academics, I enjoy playing computer games, watching and predicting stock market trends, keeping up with politics and current world events, building small interactive electronic gadgets, skiing, and playing soccer when I have the time. I try to find the time to maintain relationships with old friends from high school and undergrad as much as possible. Lastly, what has really made me tick during my college years has been my wonderful girlfriend, Rebecca. I can be happy doing just about anything with her, and her presence and support have always given me a positive outlook on the world and motivated me to continue following my interests.