Quasiperiodic Strain Bursts and Self-Organization in Crystal Microplasticity (PREPRINT)

Abstract : When external stresses in a system - physical, social or virtual - are relieved through impulsive events, it is natural to focus on the attributes of separate avalanches. However, during the quiescent periods in between, stresses may be relieved through competing processes, such as slowly flowing water between earthquakes or thermally activated dislocation flow between plastic bursts. Such unassuming, smooth responses can have dramatic effects on the avalanche properties. Our thorough experimental investigation of slowly compressed Ni microcrystals, covering three orders of magnitude in nominal strain-rate, exhibits unconventional quasi-periodic avalanche bursts and higher critical exponents as the strain rate is decreased. Our analytic and computational study, naturally extending dislocation avalanche modeling to incorporate competing processes, reveals the emergence of avalanche oscillator scaling behavior, a novel critical state manifesting through self-organized oscillatory approaches toward a critical depinning point. We demonstrate that the predictions of our theory are consistently manifested in our experiments.