Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Q36: Where Applications Meet Statistical and Nonlinear PhysicsInvited
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Sponsoring Units: GSNP Chair: Dvora Perahia, Clemson University Room: Room 236 |
Wednesday, March 8, 2023 3:00PM - 3:36PM |
Q36.00001: Local Yield Surfaces in Model Amorphous Solids Invited Speaker: Michael L. L Falk It has been the aim of much recent work to connect concepts regarding the physics of plasticity in glassy and amorphous materials to plastic constitutive theories. In doing so, many "plastic descriptors" have emerged to predict irreversible response to shear in atomistic models; almost all of these are inherently scalar. The scalar nature of these predictors mirrors the state variables that have been incorporated into many rate-and-state based theories of amorphous plasticity: concepts like "free volume," "effective temperature," and "softness". However there are strong reasons to believe that scalar measures are insufficient for describing the response of the glass structure. Here we discuss our investigations of both 2D and 3D simulated glasses from which we extracted the local yield stress throughout the simulated system. The shape of the resulting yield surface and the statistics of the yield events reveal interesting aspects of the underlying physics. We will use this data as a jumping off point to discuss what should supersede scalar order parameters in next-generation constitutive theories of amorphous plasticity. |
Wednesday, March 8, 2023 3:36PM - 4:12PM |
Q36.00002: Breaking down brittle fragmentation: gaining theoretical insight through simulation Invited Speaker: Joel T Clemmer Under large stresses, brittle solids crack and fracture into granular fragments. These fragments continue breaking down with further loading in a process known as comminution that is relevant to many fields including mining, manufacturing, and geophysics. Using a minimal bonded particle model, we explore the dynamics of fragmentation and characterize the evolving distribution of granular masses and population balance statistics. We find this distribution is described by a power-law with a cutoff that increases as a power of both decreasing strain rate and increasing system size. By constructing a new scaling theory, we measure multiple exponents that characterize this behavior. Finally, we discuss extensions of the model to calibrate material properties and how these changes affect fragmentation. |
Wednesday, March 8, 2023 4:12PM - 4:48PM |
Q36.00003: Ubiquitous Stick-Slip Motions: from Tribology, Biosensing to Carbon Capture Invited Speaker: Bingquan Luan Contact and friction are omnipresent and play essential roles in the physical world, ranging from the tectonic earthquake along fault lines to the nanoscale antibody-antigen recognition. Besides the well-known steady-sliding of any two contacting objects (e.g. with lubrication), many interfacial lateral motions are in the nonequilibrium stick-slip fashion that in general can cause surface damages and thus should be avoided. Theoretically, stick-slip motions occur when the shear velocity is slow and the interfacial interaction is strong, as described in the Prandtl-Tomlinson model. In this talk, I will present molecular dynamics (MD) studies for ubiquitous stick-slip phenomena in various developed/developing nanotechnologies, such as the motion of an AFM tip on a solid surface [1], the transport of biological molecules (DNA or proteins) through nanopores [2,3], and the capture of CO2 into solid sorbents with open metal sites [4]. These works highlight the possibility of taking the advantage of stick-slip motions in development of novel nanotechnologies. |
Wednesday, March 8, 2023 4:48PM - 5:24PM |
Q36.00004: Lengthscales in avalanche dynamics in sheared granular systems Invited Speaker: M Lisa L Manning Under shear, amorphous solids fail via localized particle rearrangements that often coalesce into avalanches, but a microscopic explanation of the dynamics of avalanches has remained out of reach. I will discuss some of our recent work to develop new tools to characterize the dynamics of avalanches and relate them to microscopic structural features. We have used these techniques to quantitatively compare spatiotemporal four-point correlations in the plasticity field during avalanches in both frictionless granular simulations and simulations of coarse-grained elasto-plastic models. We find two length scales: a short "excitable" length scale associated with sites that have finite yield stresses and a large "marginal" length scale associated with sites that have vanishing yield stress. The larger length scale exhibits the same scaling with time in both elasto-plastic and granular simulations, while the short one scales differently in the two systems. |
Wednesday, March 8, 2023 5:24PM - 6:00PM |
Q36.00005: Dissipation mechanisms and the crossover from Stokes to Coulomb friction: From toy models to disordered water Invited Speaker: Martin Muser Many different mechanisms are responsible for the friction that counteracts the relative sliding motion of two solids in mechanical contact. They range from elastic instabilities via plastic deformation to the flow of non-Newtonian fluids, i.e., boundary lubricants, to name a few. Most mechanisms have in common that they can be characterized as instabilities of certain (collective) degrees of freedom: an external force pushes part of the system to a maximum of the potential energy barrier, from where it quickly slides downhill into the next valley without giving the gained kinetic energy back to the solids' center-of-mass motion. In this contribution, I demonstrate that the velocity dependence of an isolated friction mechanism appears universal, i.e., Eyring like, at first sight. However, even a simple model like Prandtl's model exhibits a rate dependence of friction obeying the Carreau Yasuda equation (CYE). The latter applies to complex fluids like highly viscous polystyrene or camel blood. Particular attention is paid to the origin of the inaccuracy of the CYE at very small shear rates. Original data for the simulated shear-rate dependence of the viscosity of amorphous and liquid TIP-4P water will also be scrutinized. |
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