The plastic deformation of metal alloys localizes in the Portevin–Le Chatelier effect in bands of different types, including propagating, or type “A” bands, usually characterized by their width and a typical propagation velocity. This plastic instability arises from collective dynamics of dislocations interacting with mobile solute atoms, but the resulting sensitivity to the strain rate lacks fundamental understanding. In our recent joint study with researchers from Aalto University, published in Science Advances, we show that the band velocities in an aluminium alloy exhibit large fluctuations. Each band produces a velocity signal reminiscent of crackling noise bursts observed in numerous driven avalanching systems from propagating cracks in fracture to the Barkhausen effect in ferromagnets. The statistical features of these velocity bursts including their average shapes and size distributions obey predictions of a simple mean-field model of critical avalanche dynamics. Our results thus reveal a previously unknown paradigm of criticality in the localization of deformation.
T. Mäkinen, P. Karppinen, M. Ovaska, L. Laurson, and M. J. Alava, Propagating bands of plastic deformation in a metal alloy as critical avalanches, Science Advances 6, eabc7350 (2020).
See also the news story on the web page of Tampere University:
Ultranopea kamera paljastaa kuinka kuinka metallit murtuvat (in Finnish)
High-speed photos shine a light on how metals fail (in English)