Miguel M C, Vespignani A, Zapperi S, Weiss J, Grasso J R
The Abdus Salam International Centre for Theoretical Physics, PO Box 586, 34100 Trieste, Italy.
Nature. 2001 Apr 5;410(6829):667-71. doi: 10.1038/35070524.
The viscoplastic deformation (creep) of crystalline materials under constant stress involves the motion of a large number of interacting dislocations. Analytical methods and sophisticated 'dislocation dynamics' simulations have proved very effective in the study of dislocation patterning, and have led to macroscopic constitutive laws of plastic deformation. Yet, a statistical analysis of the dynamics of an assembly of interacting dislocations has not hitherto been performed. Here we report acoustic emission measurements on stressed ice single crystals, the results of which indicate that dislocations move in a scale-free intermittent fashion. This result is confirmed by numerical simulations of a model of interacting dislocations that successfully reproduces the main features of the experiment. We find that dislocations generate a slowly evolving configuration landscape which coexists with rapid collective rearrangements. These rearrangements involve a comparatively small fraction of the dislocations and lead to an intermittent behaviour of the net plastic response. This basic dynamical picture appears to be a generic feature in the deformation of many other materials. Moreover, it should provide a framework for discussing fundamental aspects of plasticity that goes beyond standard mean-field approaches that see plastic deformation as a smooth laminar flow.
晶体材料在恒定应力下的粘塑性变形（蠕变）涉及大量相互作用位错的运动。分析方法和复杂的“位错动力学”模拟在研究位错图案化方面已证明非常有效，并导致了塑性变形的宏观本构定律。然而，迄今为止尚未对相互作用位错集合的动力学进行统计分析。在此，我们报告了对应力作用下冰单晶的声发射测量结果，这些结果表明位错以无标度间歇方式移动。通过相互作用位错模型的数值模拟证实了这一结果，该模拟成功再现了实验的主要特征。我们发现位错产生了一个缓慢演化的构型景观，它与快速的集体重排共存。这些重排涉及相对较小比例的位错，并导致净塑性响应的间歇行为。这种基本的动力学图景似乎是许多其他材料变形中的一个普遍特征。此外，它应该为讨论塑性的基本方面提供一个框架，该框架超越了将塑性变形视为平滑层流的标准平均场方法。
