Abstract
Jerky flow in alloys, or the Portevin-Le Chatelier effect, presents an outstanding example of self-organization phenomena in plasticity. Recent acoustic emission investigations revealed that its microscopic dynamics is governed by scale invariance manifested as power-law statistics of intermittent events. As the macroscopic stress serrations show both scale invariance and characteristic scales, the micro-macro transition is an intricate question requiring an assessment of intermediate behaviors. The first attempt of such an investigation is undertaken in the present paper by virtue of a one-dimensional (1D) local extensometry technique and statistical analysis of time series. The data obtained complete the missing link and bear evidence to a coexistence of characteristic large events and power laws for smaller events. The scale separation is interpreted in terms of the phenomena of self-organized criticality and synchronization in complex systems. Furthermore, it is found that both the stress serrations and local strain-rate bursts agree with the so-called fluctuation scaling related to general mathematical laws and unifying various specific mechanisms proposed to explain scale invariance in diverse systems. Prospects of further investigations including the duality manifested by a wavy spatial organization of the local bursts of plastic deformation are discussed.
Highlights
Plastic flow of alloys is prone to instability caused by the interaction of mobile dislocations with solute atoms diffusing in their elastic fields, or dynamic strain aging (DSA) [1]
The propagation is explicitly demonstrated in plots (c), (b), and (d): Figure 1b shows a step-wise character of εi (t) dependences for three local extensometers (data for other extensometers, as well as raw xi (t) records, are not shown); Figure 1c presents the corresponding εi (t) curves
The analysis of deformation curves leads to a distinction of two qualitatively different cases, one corresponding to a single power-law dependence and another revealing a crossover between two power laws
Summary
Plastic flow of alloys is prone to instability caused by the interaction of mobile dislocations with solute atoms diffusing in their elastic fields, or dynamic strain aging (DSA) [1]. In tensile tests with a constant applied strain rate, εa , this nonlinearity must give rise to stress serrations caused by repetitive strain-rate jumps within localized deformation bands [2,3,4,5,6,7,8,9,10,11,12,13]. Such jerky flow is observed in various alloys and is well-known as the Portevin-Le Chatelier, or PLC, effect [14]. The intrinsic strain heterogeneity leads to complex behaviors of real materials
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