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.

International audiencePlasticity, a key property in the mechanical behavior and processing of crystalline solids, has been traditionally viewed as a smooth and homogeneous flow. However, using two experimental methods, acoustic emission and high-resolution extensometry, to probe the collective dislocation dynamics in various single crystals, we show that its intermittent critical-like character appears as a rule rather than an exception. Such intermittent, apparently scale-free plastic activity is observed in single-slip as well as multislip conditions and is not significantly influenced by forest hardening. Strain bursts resulting from dislocation avalanches are limited in size by a nontrivial finite size effect resulting from the lamellar character of avalanches. This cutoff explains why strain curves of macroscopic samples are smooth, whereas fluctuations of plastic activity are outstanding in submillimetric structures

Tensile and compression tests were conducted for AZ31, AZ61 and AZ80 alloys. The distinctive tension/compression asymmetry in the yield behaviour was analysed for textured samples from extruded bars with various grain sizes. Parallel measurements of the acoustic emission were carried out to gather information about the relative activity of twinning and dislocation glide during deformation. The acoustic emission data are used to elaborate on the possible roles of grain size and aluminium content on the deformation behaviour.

No abstract

No abstract

No abstract

No abstract

No abstract