Scale-dependent pop-ins in nanoindentation and scale-free plastic fluctuations in microcompression

Abstract

Abstract

Microstructural signatures of dislocation avalanches in a high-entropy alloy

“…This can be in the subnanometer per second regime, which is much lower than typically considered. Despite the increasing complexity regarding the scaling behavior of plastic fluctuations, this recent development points toward nonuniversal intermittent microplasticity [14,25,[27][28][29], which would be in good agreement with the classical material physics approach that relies on microstructural-specific processes and scales.…”

“…Such homogenization schemes are fundamentally based on Gaussian-like statistics with well-defined mean values and stand in stark contrast to a few selected bulk * robert.maass@bam.de deformation studies that report scale-free deformation [7][8][9]. The signature of scale-free and thus non-Gaussian dislocation activity has been revealed with acoustic-emission sensing on bulk hexagonal closest packed (hcp) crystals [10,11] and a plethora of recent small-scale deformation experiments across numerous material systems [12][13][14][15][16][17][18][19][20][21]. One of the dominant findings was that a lot of experimental data showed agreement with analytical statistical physics frameworks, notably a pinning-depinning model for avalanches near the depinning transition [22].…”

“…This approach is motivated by our desire to understand if certain parts of the event-size distribution are statistically favoring a particular slip morphology and therefore spatial localization. In the view of our earlier results demonstrating nontrivial and nonuniversal scaling exponents [12][13][14]25,27,33], it furthermore became of interest what statistical scaling particular types of slip morphologies, if they are definable, may have. These considerations emerged out of our observation that postmortem visualized slip patterns across different types of single crystals can be dramatically different while exhibiting statistical scaling that was practically identical.…”

Chemomechanical weakening of muscovite quantified with in situ liquid nanoindentation

“…As such, the self-similar or scale-free behavior is described via a scaling exponent a, enabling features at one scale to depict features at another scale across two or more orders of magnitude. Several small-scale mechanical phenomena demonstrate SOC behavior, including microfracture in disordered materials [50], shear-induced rearrangements in two-dimensional foams [51], dislocation motion in Ni [35] and Cu microcrystals [52], and structural transitions in self-assembled monolayers [53]. Two common themes were clear from these systems: the extracted values for a (1.3-1.8) were in agreement with those from theoretical models (1.2-2.0) [54] and the subsequent scaling behavior was used to link the nanoscale events to macroscale phenomena.…”

Intermittent microplasticity in the presence of a complex microstructure

“…Today, the spatiotemporal nature of intermittent plastic flow is an established concept and in fact is seen in a variety of bulk-scale experiments [7][8][9], and is essentially the norm in small-scale mechanical testing [10][11][12][13][14]. Progress in understanding the intermittent rearrangement of the mediating dislocation network was mainly made via a statistical assessment of either acoustic emission pulses [15] or stress-strain increments [16], revealing non-Gaussian behavior in the form of perfect power laws, P ∼ S −τ [17] or exponentially truncated power laws, P ∼ S −τ e − L / S [18,19], where S is the event size, P the probability of the event occurring, and L a material-specific length scale.…”