Intermittent dislocation flow in viscoplastic deformation

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 behavior 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

STRUCTURAL MODELS OF THE YIELD STRESS ANISOTROPY OF AMORPHOUS-ALLOYS RIBBONS

Two alternative quantitative mathematical descriptions of the yield stress anisotropy in the plane of amorphous alloys ribbons are proposed that are based on two models: model of the plane stress state and model of the oriented anisotropic polyatomic clusters. These descriptions give adequate approximations of the experimental angular dependences of the yield stress for some amorphous alloys

Low temperature mechanical properties of metallic glasses - Connection with structure

Available data on plasticity and strength of metallic glasses below the room temperature (down to 0.5 K) are considered and explained on the basis of the polycluster model of amorphous solids especially with taking into consideration possible atomic structure of clusters and defects of intercluster boundaries. (C) 1997 Elsevier Science S.A