Mäkinen Tero, Karppinen Pasi, Ovaska Markus, Laurson Lasse, Alava Mikko J
Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 Aalto, Espoo, Finland.
ProtoRhino Ltd, Betonimiehenkuja 5C, FI-02150 Espoo, Finland.
Sci Adv. 2020 Oct 7;6(41). doi: 10.1126/sciadv.abc7350. Print 2020 Oct.
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. Here, we show, by using high-resolution imaging in tensile deformation experiments of an aluminum alloy, that the band velocities 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.
金属合金的塑性变形在不同类型的带中表现出Portevin-Le Chatelier效应，包括扩展带或“A”型带，通常以其宽度和典型的传播速度为特征。这种塑性不稳定性源于位错与可移动溶质原子相互作用的集体动力学，但由此产生的对应变速率的敏感性缺乏基本认识。在这里，我们通过在铝合金的拉伸变形实验中使用高分辨率成像表明，带速表现出很大的波动。每个带产生的速度信号让人联想到在从断裂中的扩展裂纹到铁磁体中的巴克豪森效应等众多驱动雪崩系统中观察到的噼啪噪声爆发。这些速度爆发的统计特征，包括它们的平均形状和尺寸分布，符合临界雪崩动力学简单平均场模型的预测。因此，我们的结果揭示了变形局部化中一个以前未知的临界范式。
