期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：1
页码：49-53
DOI：10.1073/pnas.1413468112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceGranular materials are used for a wide variety of technological applications in nearly every industry and also serve as an instructive prototype for far-from-equilibrium behavior. Although they have received considerable attention, there are few general guidelines describing how they collectively organize and yield under shear, especially in physically relevant frictional grains. Using simulations, we explore the response of granular packings to slow periodic shear, systematically varying both the friction and shear. We discover a previously unidentified state in which the otherwise chaotic motion gives way to a precisely repetitive limit cycle for each individual grain. Understanding how grains self-organize into stable, periodic limit cycle configurations in this unlikely system foretells new approaches to understand yielding and memory formation in disordered materials. The disordered static structure and chaotic dynamics of frictional granular matter has occupied scientists for centuries, yet there are few organizational principles or guiding rules for this highly hysteretic, dissipative material. We show that cyclic shear of a granular material leads to dynamic self-organization into several phases with different spatial and temporal order. Using numerical simulations, we present a phase diagram in strain-friction space that shows chaotic dispersion, crystal formation, vortex patterns, and most unusually a disordered phase in which each particle precisely retraces its unique path. However, the system is not reversible. Rather, the trajectory of each particle, and the entire frictional, many-degrees-of-freedom system, organizes itself into a limit cycle absorbing state. Of particular note is that fact that the cyclic states are spatially disordered, whereas the ordered states are chaotic.
