DISLOCATION DYNAMICS AND STRAIN HETEROGENEITIES IN ICE SINGLE CRYTALS:EXPERIMENTS AND MULTISCALE SIMULATIONS
Ice single crystal has a hexagonal crystallographic structure.It is strongly anisotropic and essentially deforms by the glide of dislocations on basal planes.In such material,the plastic strain rate is very slow and caracterisation are usually performed through creep tests.Creep strain rate always reaches a steady state stage that can be related to the applied stress using a power relationship.In this presentation,torsion tests were carried out on ice single crystals machined so that the torsion axis matches with the cristallographic c axis.Thus,the applied stress is maximal at the periphery of the cylinder,the basal screw dislocations move towards the center and there is no macroscopical force to drive the dislocations along any non-basal direction.Therefore,dislocation multiplication on the three basal slip systems is not sufficient to explain the plastic flow experimentally observed.However,when dislocations pile up in the basal systems,they induce a resolved shear stress on the prismatic system that may activate these secondary systems.Moreover,X-ray diffraction analysis of strained samples showed scale invariance and a spatially long distance correlation of the basal dislocation density (Montagnat et aL,2006).Taking into account those two caracteristics,we suggest that double cross-slip of basal dislocations through prismatic planes is responsible for dislocation multiplication.This idea was tested by Discrete Dislocation Dynamics (DDD) simulations (Verdier et al.1998).When cross-slip from basal to prismatic system is accounted for,steady-state behaviour is observed.Moreover,statistical analyses of the strain localization show a scale invariance of the dislocation arrangement that denotes long range interactions of the different slip bands. Complementary simulations have been recently performed by (Varadhan et al.,2006,Taupin et al.2007) using a continuum description of the dislocation dynamics.The model is based on balance equations of excess and statistical dislocations.It involves many phenomenological equations that were fitted on the torsion experiments.In this presentation we propose to use the DDD simulations to understand the physics involved in the continuum model.Special emphasis will be put on the description of the cross slip behaviour between basal and prismatic systems.Finally,the two models will be used to simulate the hardening observed alter the inversion of the applied torque.Explanations are proposed based on the evolution of the population of mobile dislocations and their interaction with the pre-existing dislocations.
J.Chevy M.C.Fivel P.Duval
SIMaP-GPM2,Grenoble INP/CNRS,BP 46,38402 St Martin dHères cedex,France;LGGE,UJF/CNRS,54 rue Molière SIMaP-GPM2,Grenoble INP/CNRS,BP 46,38402 St Martin dHères cedex,France LGGE,UJF/CNRS,54 rue Molière,38402 St Martin dHères cedex,France
国际会议
第二届国际非均质材料力学会议(The Second International Conference on Heterogeneous Material Mechanics)
安徽黄山
英文
323-324
2008-06-03（万方平台首次上网日期，不代表论文的发表时间）