Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session T7: Avalanches in Condensed Matter |
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Sponsoring Units: GSNP DCMP Chair: Craig Maloney, Carnegie Mellon University Room: Portland Ballroom 254 |
Wednesday, March 17, 2010 2:30PM - 3:06PM |
T7.00001: Avalanches and universality in condensed matter Invited Speaker: An overview is given on recent progress in the study of avalanches in a number of experimental systems and in models having disorder. In particular, we show how recent studies on magnetizing avalanches (``Barkhausen noise'') in magnets (driven by a slowly increasing magnetic field) shed light on modeling damage avalanches in stressed materials, the plastic depinning of charge density waves, the statistics of earthquakes in irregularly shaped fault zones, and other systems characterized by ``crackling noise''. In particular, we focus on the universal, i.e., detail independent, effects of disorder in these cases. Unexpected connections between nonequilibrium and equilibrium ``avalanches'' reveal a surprisingly large universality class of systems that all show the same scaling behavior on long length scales. This universality class includes driven far-from-equilibrium behavior (for various histories), and the equilibrium behavior of some of these systems. The studies draw on methods from the theory of phase transitions, the renormalization group, and numerical simulations. [Preview Abstract] |
Wednesday, March 17, 2010 3:06PM - 3:42PM |
T7.00002: Physics of Earthquakes and Faults Invited Speaker: Detailed observations and theoretical results on brittle failure events in individual fault zones point to three general dynamic regimes [1]. The first is associated with broad range of heterogeneities, little dynamic weakening during failure, power law frequency-size statistics, and temporal clustering of events. The second is associated with relatively-uniform localized structures, significant dynamic weakening, and quasi-periodic occurrence of characteristic system-size events. For a range of conditions, the response can switch back and forth between the forgoing two types of behavior. These dynamic regimes, geometrical properties of slip, and observed moment rate shapes can be explained by a simple model having two tuning parameters: dynamic weakening and conservation of elastic stress transfer during failure events [2]. The model can also explain multiple aspects of deformation in volumetric regions, including stress-strain curves, acoustic emissions and related power spectra, with a continuous transition from brittle to plastic behavior, and statistics of failure events in granular media [3]. The results from the latter studies are in good agreement with experimental data [4] and simulations with other frameworks [5]. An extension of the model to include cohesion changes during failure and healing phases of deformation may account for transitions between solid and granular phases of materials [6].\\[4pt] [1] Y. Ben-Zion, \textit{Rev. Geophys.}, \textbf{46}, RG4006 (2008) and references therein. \\[0pt] [2] D.S. Fisher et al., Phys. Rev. Lett. \textbf{78, }4885 (1997); Y. Ben-Zion, and J.R. Rice, J. Geophys. Res., \textbf{98}, 14109, (1993). K.A. Dahmen et al., Phys. Rev. E 58, 1494 (1998). A.P. Mehta et al., Phys. Rev. E \textbf{73}, 056104 (2006). \\[0pt] [3] K.A. Dahmen, et al., \textit{Phys. Rev. Lett.}, \textbf{102}, 175501, 2009. K.A.Dahmen, Y. Ben-Zion and J.T. Uhl, submitted, 2009. \\[0pt] [4] K.E. Daniels and N.W. Hayman, Journal of Geophysical Research, \textbf{113} B11411 (2008). H. Jaeger, S.R. Nagel, R.P. Behringer, Revs. Mod. Phys. \textbf{66}, 1259-1273 (1996) and references therein. \\[0pt] [5] K. Chen \textit{et. al.,} Phys. Rev. A \textbf{43}, 625 (1991). M. Zaiser, Adv. Phys. \textbf{55}, 185 (2006); M.J. Alava et al., Adv. Phys. \textbf{55}, (2006). E. Aharonov and D. Sparks, Phys. Rev E, \textbf{60}, 6890-6896 (1999). E. Aharonov and D. Sparks, J. Geophys. Res, \textbf{109}, B09306 (2004). \\[0pt] [6] Y. Ben-Zion, K. A. Dahmen and J.T. Uhl, submitted, 2009. [Preview Abstract] |
Wednesday, March 17, 2010 3:42PM - 4:18PM |
T7.00003: Avalanche dynamics of imbibition fronts Invited Speaker: The spatio-temporal dynamics of interfaces driven through random media has become a subject of central importance in non-equilibrium statistical mechanics in last years. A wide variety of slowly driven physical systems - vortex lines in superconductors, dislocation lines in defective crystalline solids, fracture fronts in heterogeneous materials, magnetic domain walls in disordered ferromagnets or wetting contact lines on rough substrates - exhibit a self-affine morphology and burst-like correlated motion, that arise from the interplay between competing interactions. In this context, we address here the problem of forced-flow imbibition in a disordered medium where a fluid (oil) that preferentially wets the medium displaces a resident fluid (air) at a constant flow rate. Using a high resolution fast camera, we follow the propagation of the fluid-air interface invading a disordered Hele-Shaw cell. Measuring the local waiting time fluctuations along the front during its propagation, we show that the imbibition fronts display an intermittent behavior signature of an avalanche-like dynamics. First, we will discuss the Non-Gaussian fluctuations of the global (spatialy averaged) velocity V (t) of the interface. Then, we will focus on the various scaling behavior of the local avalanches defined as spatial clusters of large local velocity. Our experimental results underline the critical behavior of the imbibition dynamics, suggesting the existence of a critical depinning transition for this process at V=0. [Preview Abstract] |
Wednesday, March 17, 2010 4:18PM - 4:54PM |
T7.00004: Avalanches in the Plastic Deformation of Crystalline Solids Invited Speaker: Plastic avalanches and highly fluctuating stress strain relations have been reported for crystalline materials as diverse as ice or several conventional metals and alloys. The most recent theoretical interpretation of these experimental findings is based upon collective dislocation dynamics and non-equilibrium critical phenomena. Dislocation assemblies in crystalline substrates represent a new example of the broad class of systems that exhibit avalanches and a jamming (or yielding) transition. Rheology experiments carried out on this broad class of systems ranging from granular media to foams show that their dynamics becomes increasingly heterogeneous when approaching the jamming threshold. Likewise, experiments on crystal plasticity at various scales have recently emphasized the heterogeneous character of plastic flow. Here we explore further the analogy between dislocation ensembles and other jamming systems by analyzing the behavior of dynamic response functions, such as the four point dynamic susceptibility, as well as the shear stress distributions in both jammed and moving dislocation arrangements. Our results show the existence of a diverging dynamic correlation length as the jamming threshold is approached. At microscopic scales, where only a limited number of dislocations mediate the deformation process and no dislocation storage phenomena are observed, heterogeneous behavior in the mechanical properties is even more dramatic and technologically relevant. Bursts of plastic activity in microscopic colloidal crystals under compression are broadly distributed, both in strain/stress-controlled tests, but scaling exponents are anomalous, and thus the interpretation of these findings within the framework of collective dislocation phenomena and the yielding transition is no longer appropriate. Moreover, non-trivial size effects on the mechanical properties of micrometer-to nanometer scale crystals can be explained in terms of the interactions of dislocations with the boundaries of the sample. [Preview Abstract] |
Wednesday, March 17, 2010 4:54PM - 5:30PM |
T7.00005: Barkhausen avalanches in thin films Invited Speaker: The magnetization process in thin films is due to the avalanche-like motion of domain walls, that can be recorded by magneto-optical methods. Here, I discuss experimental measurements of these Barkhausen avalanches in Permalloy thin films where zigzag domain walls are formed by the competition between long-range dipolar forces and the short-range line tension of the wall. The resulting avalanche distribution is affected by the limited size of the observation window requiring an appropriate correcting scheme. Next, I present results of numerical simulations of a dipolar random-field Ising model and of a flexible domain wall model that allow to reproduce the experimental results. By studying the avalanche size distribution, we observe a cross-over from a universality class dominated by line tension to another universality class where the long-range dipolar forces become important. This crossover is accompanied with a change of the domain wall morphology from a rough to a zigzag structure. [Preview Abstract] |
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