Bio: Michael Falk is a professor of Materials Science and Engineering at Johns Hopkins University where he also serves as the Vice Dean for Undergraduate Education. He holds a bachelor’s degree in physics and a master’s degree in Computer Science from Johns Hopkins. He completed his Ph.D. in physics at the University of California, Santa Barbara and then launched his academic career as a computational materials scientist at the University of Michigan in 2000. In 2008 he returned to Johns Hopkins as an associate professor of Materials Science and Engineering with joint appointments in Mechanical Engineering and Physics. Prof. Falk’s research focuses on utilizing computer simulation on the atomic scale to understand the processes by which materials are pushed out of equilibrium by processes such as bending, breaking, charging and undergoing frictional sliding. His research has had an abiding focus on the ways glass structures accommodate plastic flow, deformation and fracture. These investigations have involved developing new methodologies for deploying molecular dynamics simulations and the development of thermodynamically motivated constitutive theories. Prof. Falk also engages in educational research and is a strong advocate for diversity and inclusion, engaging in outreach to Baltimore City elementary schools and advocating for a welcoming climate for LGBTQ people within the engineering and physics professions.

Connecting atomistic simulations, defect-based theories and continuum plasticity in amorphous solids

Glasses, and the more general category of materials known as amorphous solids, lack crystal structure and find wide application from consumer goods to photovoltaics. Yet, issues quantifying disorder have stymied the construction of physically grounded mechanical constitutive laws for these materials suitable for failure prediction. Atomistic simulation methods can provide some insight regarding the mechanisms of plastic deformation and strain localization. Recent investigations have aimed at quantifying the defects that control plastic flow by quantifying a yield stress field at the nanometer scale. Analysis of these fields have confirmed some of the assumptions built into the shear transformation zone theory of amorphous plasticity, most notably the orientational nature of the defect and their pre-existence in the structure. I will further discuss methods for quantitatively predicting strain localization, a limiting failure process in high-strength metallic glasses and other amorphous materials by parameterizing the effective-temperature shear transformation zone theory from molecular dynamics simulations. We have directly cross-compared molecular dynamics simulations and continuum representations of these same materials in order to test and validate our constitutive theories. The role of coarse graining in the linkage of continuum and atomistic methods is crucial, and convergence only arises above a critical length scale on the order of tens of angstroms. The investigation makes clear the need to separate out the relevant fluctuations in material structure from the shorter wavelength fluctuations that serve to obscure them. It is, in the end, the interactions between these larger-scale relevant fluctuations via the material’s mechanical response that controls the failure process during strain localization.

Prof. Falk is being hosted by Prof. Yue Fan (Mechanical Engineering). If you would like to meet him during his visit please email [email protected]