Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session B58: Stick, Slip, and Interfacial Dynamics in Soft SystemsInvited
|
Hide Abstracts |
Sponsoring Units: GSOFT Chair: Justin Burton, Emory Univ Room: LACC Petree Hall C |
Monday, March 5, 2018 11:15AM - 11:51AM |
B58.00001: Scale Dependence of Friction: How Elasticity Destroys Superlubricity Invited Speaker: Mark Robbins The talk will discuss friction in single-asperity contacts as a function of contact radius a, substrate stiffness, atomic structure and adhesive strength. The friction between bare, rigid surfaces can be obtained by a simple sum over atomic forces. When surfaces are aligned and have the same periodicity, the forces add in phase and the friction force F rises linearly with area A. When the two surfaces are misaligned or disordered, so that there is no common periodicity, forces add out of phase and F∝Ax with x≤0.5. This is known as structural superubricity and implies that friction vanishes in the limit of large contact sizes. Most surfaces do not share a common period but friction is almost always observed at macroscopic scales. We use an efficient Greens function technique to study contacts with dimensions of micrometers while resolving atomistic interactions at the surface. For small tips and high loads the contact area follows predictions for contact of rigid surfaces, x=1 for identical aligned surfaces, x=1/2 for random surfaces and x=1/4 for incommensurate crystals. Elasticity becomes important when a exceeds the core width bcore of interfacial dislocations. For a>bcore parts of the contact can advance independently. The friction for identical aligned surfaces drops as a power law and then saturates at the Peierls stress for moving edge dislocations. The friction on large incommensurate1 and disordered surfaces saturates at nearly the same value. Thus for all geometries x=1 in large contacts. While this means that elasticity destroys superlubricity, the friction drops exponentially with the ratio of substrate stiffness to local interfacial shear stress. This ratio is expected to be particularly large for common solid lubricants that have weak interfacial interactions and large in-plane stiffness. |
Monday, March 5, 2018 11:51AM - 12:27PM |
B58.00002: Rate-and-State Effects in Nanoscale Contacts: How Chemical Bonding Induces Frictional Instabilities Invited Speaker: Robert Carpick Recent atomic force microscope (AFM) experiments and simulations have found that nanoscale silica-silica contacts exhibit logarithmic ageing for times ranging from 0.1 s to 100 s, consistent with the conventional, empirical rate and state friction (RSF) laws [1-3]. Evidence strongly supports that this nanoscale ageing results from the progressive formation of interfacial siloxane bonds through condensation reactions of surface silanol groups. Here, we discuss the effects of varying the normal pressure [4], the lateral loading rate (pulling speed), and the hold time for small times. We observe the existence of a nanoscale memory distance [5], but with a wide scatter that we attribute to the varying areal density of sites that act to passivate interfacial chemical bonds. We also observe a non-logarithmic tail at short ageing times attributed to the manner in which energy barriers for the chemical reactions are distributed. Related to this, we observe highly regular stick-slip events with distinct load and pulling speed characteristics, and power law scaling between amplitude and slip period. The emerging picture for these contacts is of rate and state behavior, but with significant differences compared to macroscopic systems. |
Monday, March 5, 2018 12:27PM - 1:03PM |
B58.00003: Quasi-dynamic Stick-Slip Frictional Sliding and The Mechanics of Slow Earthquakes Invited Speaker: Chris Marone Our understanding of earthquake physics and frictional slip on tectonic faults has been challenged by recent discoveries of seismic tremor, low frequency earthquakes and other modes of fault slip known collectively as slow earthquakes. These phenomena represent modes of failure that were thought to be theoretically impossible. Despite the growing number of observations of slow earthquakes and the fact that they can trigger catastrophic large earthquakes their origin remains unresolved. Basic questions remain regarding how slow ruptures can propagate quasi-dynamically, at speeds below the Rayleigh wave speed, and how tectonic faults can host both slow and dynamic earthquake rupture. I focus on laboratory results that illuminate the transition from stable sliding to repetitive, slow stick-slip and provide clues about the mechanics of slow earthquakes. Slow slip occurs near the threshold between stable and unstable failure, controlled by the interplay of frictional properties, including rate dependence of the critical rheologic friction parameter Kc, and elastic stiffness of the surrounding rock. The results suggest that slow stick-slip and transient, quasi-dynamic acceleration can arise from the same governing frictional dynamics as typical, fast stick-slip motions. As applied to tectonic faults, they imply that slow earthquakes may share similar mechanics with typical earthquakes governed by elastodynamics, contrary to other suggested models. However, the micromechanical origin of slip rate modulation during frictional stick-slip is still in question. I show that quasi-dynamic motion can be attributed to a dependence of Kc on slip rate, such that acceleration is quashed above a threshold slip rate, and discuss other possible mechanisms for slow earthquakes. |
Monday, March 5, 2018 1:03PM - 1:39PM |
B58.00004: Interfacial slip and flows in nanotubes Invited Speaker: Lyderic Bocquet The question of the hydrodynamic boundary condition of fluids at solid surfaces has entertained the field of fluid transport for most than 20 years. The debate has been quite intense among experimental groups reporting strongly contrasted results. This culminated notably with the measurement of ultra-fast flows in carbon nanotube (CNT) membranes by several groups ten years ago, which pointed to considerable surface slippage and nearly frictionless transport in CNT [1]. |
Monday, March 5, 2018 1:39PM - 2:15PM |
B58.00005: Classical shear cracks drive the onset of frictional motion Invited Speaker: Ilya Svetlizky A system of two bodies in contact, subject to shear loading, is prone to lose stability and generate frictional slip. The onset of this motion is mediated by dynamically propagating fronts that rupture the discrete contacts forming the frictional interface and separate the sticking and sliding regions. A wide range of rupture front velocities, have been observed. These span from slow ruptures propagating at a small fraction of the Rayleigh wave speed to ruptures that asymptotically approach the Rayleigh wave speed. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700