Quasi-periodic events in crystal plasticity and the self-organized avalanche oscillator

摘要

When external stresses in a system - physical, social or virtual - arerelieved through impulsive events, it is natural to focus on the attributes ofthese avalanches. However, during the quiescent periods in between, stressesmay be relieved through competing processes, such as slowly flowing waterbetween earthquakes or thermally activated dislocation flow between plasticbursts. Such unassuming, smooth responses can have dramatic effects on theavalanche properties. Here we report a thorough experimental investigation ofslowly compressed Ni microcrystals, covering three orders of magnitude innominal strain rate, that exhibits unconventional quasi-periodic avalanchebursts and higher critical exponents as the strain rate is decreased. Ouranalytic and computational study naturally extends dislocation avalanchemodeling to incorporate dislocation relaxations and reveals the emergence ofthe self-organized avalanche oscillator, a novel critical state exhibitingoscillatory approaches toward a depinning critical point. We demonstrate thatthe predictions of our theory are faithfully exhibited in our experiments.