Plan

Chargement...

Figures

Chargement...
Couverture fascicule

Creep and recrystallization of polycrystalline ice

[article]

Fait partie d'un numéro thématique : Mécanismes de déformation des minéraux et des roches
doc-ctrl/global/pdfdoc-ctrl/global/pdf
doc-ctrl/global/textdoc-ctrl/global/textdoc-ctrl/global/imagedoc-ctrl/global/imagedoc-ctrl/global/zoom-indoc-ctrl/global/zoom-indoc-ctrl/global/zoom-outdoc-ctrl/global/zoom-outdoc-ctrl/global/bookmarkdoc-ctrl/global/bookmarkdoc-ctrl/global/resetdoc-ctrl/global/reset
doc-ctrl/page/rotate-ccwdoc-ctrl/page/rotate-ccw doc-ctrl/page/rotate-cwdoc-ctrl/page/rotate-cw
Page 80

Bull. Minéral. (1979), 102, 80-85.

Creep and recrystallization of polycrystalline ice

by Paul DUVAL,

Laboratoire de Glaciologie, CNRS, 2, rue Très-Cloitres, 38031 Grenoble Cedex.

Fluage et recristallisation de la glace poly cristalline.

Introduction

The plastic behaviour of polycrystalline ice has principally been studied by creep tests under a given load (Glen, 1955 ; Steinemann, 1958 ; Kamb, 1972). On the macroscopic scale, polycrystalline ice affords at first a transient creep or primary creep which dimi¬ nishes with time, then a steady or secondary creep. If the load is applied for a long time, in order that deformation exceeds 2-3 %, the creep rate starts to accelerate and a new steady state (tertiary creep) can be attained, which is up to one order of magnitude faster than secondary creep (Steinemann, 1958).

In addition to the so-called Andrade's creep, the transient creep includes an important anelastic contri¬ bution, probably produced by the dislocation motion comprising the sub-boundaries or the dislocation piled-ups (Duval, 1978).

For secondary creep, the strain-rate ii} vary with the deviatoric stresses x'itj with the relationship :

i,,i = ~ = B/2 t"_1 t'(„-(I)

2 7]

when y] is the viscosity, B a parameter which depends principally on temperature and t the effective shear stress defined by t2 = 1/2 �

The equation (1) has been verified by Duval (1976 b ) with creep tests performed in torsion, compression and torsion-compression. Equation (1) states that the strain rates depend on the current values of the deviatoric stress state. It also implies that the prin¬ cipal axes of stress and of plastic strain-rates tensors coincide.

For stresses greater than one bar, the exponant n is about three and creep rate is controlled by recovery processes (Duval, 1976 b). But for small stresses, the creep rate of fine grained polycrystalline ice (grain size smaller than one millimeter) is controlled by diffusional processes (Duval, 1973). The increase of strain rate during tertiary creep is generally attri¬ buted to the formation of fabrics by recrystallization (Kamb, 1972). Indeed, the plastic anisotropy of ice monocrystals is very important. The deformation of single crystals of ice occurs almost exclusively by

doc-ctrl/page/rotate-ccwdoc-ctrl/page/rotate-ccw doc-ctrl/page/rotate-cwdoc-ctrl/page/rotate-cw
doc-ctrl/page/rotate-ccwdoc-ctrl/page/rotate-ccw doc-ctrl/page/rotate-cwdoc-ctrl/page/rotate-cw
doc-ctrl/page/rotate-ccwdoc-ctrl/page/rotate-ccw doc-ctrl/page/rotate-cwdoc-ctrl/page/rotate-cw
doc-ctrl/page/rotate-ccwdoc-ctrl/page/rotate-ccw doc-ctrl/page/rotate-cwdoc-ctrl/page/rotate-cw
doc-ctrl/page/rotate-ccwdoc-ctrl/page/rotate-ccw doc-ctrl/page/rotate-cwdoc-ctrl/page/rotate-cw