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Center for Nonlinear Studies |
When a physical system, under slowly increasing external stress, responds through impulsive events, there is commonly a regime where avalanches cluster in time and oscillatory "stick-slip" response is observed. The traditional explanation for such phenomena has to do with a microscopic stick-slip effect due to increasing friction at material contacts. However, earthquakes deep in the Earth's crust, jammed granular matter near jamming onset, plastically deformed microcrystals, bulk metallic glasses, as well as the brain during sleep, all develop oscillatory response as collective stress relaxation channels proliferate but with no apparent connection to friction --if can be defined-- or other microscopic, "friction"-inspired effects. In this talk, I will present a novel universal mechanism for the emergence of oscillatory response in such systems, the self-organized avalanche oscillator. This is a novel critical state exhibiting oscillatory approaches toward an interface depinning critical point. While the theory is general enough to be applicable to all aforementioned I will demonstrate how its predictions are faithfully exhibited in a thorough experimental investigation of slowly compressed Ni microcrystals, where unconventional quasi-periodic plastic bursts and higher critical exponents are observed while the nominal strain rate is decreased.
Host: Cynthia Reichhardt,