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The Relative Contributions of Particle Rearrangements and Softening to the Nonlinear Mechanical Response of Glasses

Speaker

Corey O'hern, Yale

Time

2017.06.12 10:00-11:00

Venue

601 Pao Yue-Kong Library

Abstract

Glassy materials such as metallic, polymeric, and colloidal glasses exhibit complex history-dependent mechanical response to applied deformations. For example, depending on the preparation protocol, glassy materials can display brittle or ductile mechanical response. In this study, we perform computer simulations to investigate the mechanical response of binary Lennard-Jones glasses undergoing athermal, quasistatic pure shear as a function of the rate $R_c$ used to cool them to zero temperature. The ensemble-averaged stress versus strain curve for a given system size resembles the spatially averaged curve in the large system limit. The ensemble-averaged stress versus strain relation appears smooth and displays a putative elastic regime at small strains, a peak in stress at intermediate strain whose height depends on the preparation history, and a plastic flow regime at large strains. In contrast, for each glass configuration in the ensemble, the stress versus strain curve consists of many short nearly linear segments that are punctuated by particle rearrangement-induced rapid stress drops. To develop a fundamental understanding of the ensemble-averaged stress versus strain relation, we quantified the shape of the small stress versus strain segments and the frequency and size of the stress drops for each glass configuration. We decompose the stress loss (deviation in the slope of the ensemble-averaged stress versus strain from the zero-strain behavior) in terms of the loss from particle rearrangements and the loss from softening of the shear modulus (or decrease in the slope of the small linear segments in the single-configuration stress versus strain). We also characterized the topography of the potential energy landscape along the pure shear strain direction for glasses prepared with different cooling rates $R_c$. We find that properties of the potential energy landscape change significantly near the yielding transition. We also show that the rearrangement-induced energy loss per strain can serve as an order parameter for the yielding transition, which becomes sharp in the large system limit.

Bio

Corey is an Associate Professor with Tenure in the Departments of Mechanical Engineering & Materials Science, Applied Physics, and Physics and Graduate Program in Computational Biology & Bioinformatics at Yale. Before joining the faculty at Yale, he was a postdoctoral fellow working with Prof. Andrea Liu (UPenn, Physics) who was then at UCLA and Prof. Sidney Nagel (UChicago, Physics) on computational studies of jamming transitions in frictionless granular materials and glass transitions in model glass-forming liquids. Corey recieved his Ph.D. in Physics from the University of Pennsylvania in 1999; his dissertation focused on developing elasticity theories for liquid crystalline systems with biological importance such as DNA-cationic lipid complexes. See his Ph.D. thesis. Corey was an undergraduate at Duke University and graduated in 1994 with a B.S. in Physics. He likes to point out that while at Duke, he performed experimental research on granular materials in Bob Behringer’s Lab and to his knowlege did not break anything!