Dislocation avalanches are like earthquakes on the micron scale

Abstract

Compression experiments on micron-scale specimens and acoustic emission (AE) measurements on bulk samples revealed that the dislocation motion resembles a stick-slip process – a series of unpredictable local strain bursts with a scale-free size distribution. Here we present a unique experimental set-up, which detects weak AE waves of dislocation slip during the compression of Zn micropillars. Profound correlation is observed between the energies of deformation events and the emitted AE signals that, as we conclude, are induced by the collective dissipative motion of dislocations. The AE data also reveal a two-level structure of plastic events, which otherwise appear as a single stress drop. Hence, our experiments and simulations unravel the missing relationship between the properties of acoustic signals and the corresponding local deformation events. We further show by statistical analyses that despite fundamental differences in deformation mechanism and involved length- and time-scales, dislocation avalanches and earthquakes are essentially alike.

Multi-scale plasticity homogenization of Sn–3Ag-0.5Cu: From β-Sn micropillars to polycrystals with intermetallics

“…The reaction forces were obtained by averaging over five adjacent load data points to exclude the noise in the system. Apparent hardening behaviours are observed in both pillars, and the intermittent response of the reaction forces reflect dynamic dislocation and strain bursts [28][29][30] taking place within the pillars. A strong crystallographic orientation effect is observed, as pillar 3 shows considerably higher force required compared to that for pillar 4, influenced in addition by the anisotropy of slip strengths in β-Sn single crystals [31].…”

“…By choosing an appropriate set of slip strengths, hardening and rate-sensitivity governing parameters, the CPFE calculated stress-strain response (indicated as lines) captures the experimental results (indicated as scatter data) for the single slip activation cases. It is noted that there are errors at certain strain levels that result from the dislocation dynamic burst [30] events during compression, but the modelled behaviour reflects the overall stress-strain behaviour of the β-Sn single crystals. The resulting properties are listed in Table 3.…”

Microstructural Black Swans

“…For example, Jha et al found that the rarest and most extreme life-limiting features in a titanium alloy involved not just one microstructural feature, but a 'neighbourhood' of collaboratively-weak features [34]. Or, other researchers have revealed that the initial onset of plasticity occurs via dislocation avalanches that can be described through weakest link statistics [35]. Regardless of the examples chosen, these cases elucidate the benefits of robust statistical sampling of outlier events through high-throughput testing and characterization as well as stochastic modelling.…”

Study of Anodic Film’s Surface and Hardness on A356 Aluminum Alloys, Using Scanning Electron Microscope and In-Situ Nanoindentation

“…Microhardness tests were carried out using an UMIS indentation device with a Berkovich indenter and applying a maximum load of 500 mN. In-situ nanohardness measurements were performed using a recently developed mobile nanoindenter [23,24] that can be integrated into an SEM machine. A schematic diagram of the device is shown in Figure 3.…”