On the critical character of plasticity in metallic single crystals

Abstract

Abstract:Previous acoustic emission (AE) experiments on ice single crystals, as well as numerical simulations, called for the possible occurrence of self-organized criticality (SOC) in collective dislocation dynamics during plastic deformation. Here, we report AE experiments on hcp metallic single crystals. Dislocation avalanches in relation with slip and twinning a re identified with the only sources of AE. Both types of processes exhibit a strong intermittent character. The AE waveforms of slip and twinning events seem to be different, but from the point of view of the AE event energy distributions, no distinction i s possible. The distributions always follow a power law given by P(E)~E -τ E , with τ Ε = 1.5±0.1, even when multi-slip and forest hardening occur. The exponent τ Ε is in perfect agreement with those previously found in ice single crystals. Along with observed time clustering and interactions between avalanches, these results are new and strong arguments in favour of a general, SOCtype, framework for crystalline plasticity.

Statistics of Dislocation Slip Avalanches in Nanosized Single Crystals Show Tuned Critical Behavior Predicted by a Simple Mean Field Model

“…In this case, the effective stress distance from criticality remains constant [1], and the experiment effectively measures rather than þ . In this case the SOC assumption [5,6,8] with the measured value of ¼ 1:5 is valid and agrees with the MFT predictions [1,2,27,31].…”

“…Introduction.-Sheared small-scale crystals deform via a sequence of discrete slips, measurable either as steps in stress-strain curves or as acoustic emission pulses [1][2][3][4][5][6][7][8][9][10][11][12][13]. We show that the statistical distributions of the slip sizes and their stress dependence (i) reflect tuned criticality, (ii) agree with the predictions of a simple mean-field theory (MFT) model, down to 75-nm-diameter samples, and (iii) reflect the same scaling behavior (universality) for a wide variety of materials, crystal structures, size scales, and experimental parameters.…”

“…(i) Tuned criticality.-Previous experimental studies focused on fitting exponents k to power-law distributions DðSÞ $ S À , similar to self-organized criticality (SOC) [5,6,8]. SOC assumes that the (''cutoff'') size S max of the largest observed avalanche exclusively depends on the system size and not on other experimental parameters.…”

Slip statistics of dislocation avalanches under different loading modes

“…Yet another example of a discretely evolving system is a plastically flowing crystal, where the underlying dislocation structure reorganizes from one critical state to another. While early stress-strain evidence exists that plastic flow is intermittent [2], acoustic emission (AE) is readily used to record the crackling noise from deforming crystals [3][4][5][6][7][8]. In such experiments, the AE amplitude reveals power-law scaling indicative of the scale-free nature of plastic deformation.…”

The probability distribution of internal stresses in externally loaded 2D dislocation systems

“…This feature and the fact that dislocation movement is often constrained to single glide plane result in dynamics exhibiting very high spatiotemporal complexity. This is indicated, for instance, by the multitude of observed dislocation patterns or by the recently revealed fact that plastic deformation is characterised by intermittent strain bursts with scale-free size distribution [1,2,3,4].…”