Creep and Fabrics of Polycrystalline Ice Under Shear and Compression

Abstract

ABSTRACT. Creep tests were performed in torsion and torsion-compression on polycrystalline ice at temperatures near the melting point. Syntectonic recrystallization occurs at strains of the order of 2-3%, leading to a rapid increase in strain-rate. It is shown that the increase of creep-rate during tertiary creep arises from the development of fabrics favouring the glide on basal planes but also from the softening processes associated with recrystallization. The c-axis fabric of recrystallized ice developed in simple shear consists of two-maxima, one at the pole of the permanent shear plane and the other between the normal of the second plane of maximum shearing stress and the principal direction of compression. In torsion-compression, a three-or four-maximum fabric is formed according to the intensity of different components of the stress tensor. The maxima are clustered around the principal direction of compression. Processes of fabric formation are discussed. The experimentally developed fabrics are probably produced by the strain-induced recrystallization, for which the driving force is provided by differences in stored plastic strain energy. However the degree of preferred orientation of ice c-axes must be a function of the total strain when syntectonic recrystallization becomes less important. In this case, fabrics are principally formed by plastic flow and a steady state is obtained for very high strains. RESUME. Fluage et recristallisation de la glace polycristalline soumise au cisaillement et la compression. Des experiences de fluage ont ete realisees en torsion et torsion-compression sur de la glace polycristalline pres du point de fusion. La recristallisation syntectonique debute pour des deformations de l'ordre de 2 a 3%, entrain ant une augmentation rapide de la vitesse de deformation. On montre que I'augmentation de la vitesse du fluage durant le fluage tertiaire provient de la formation de fabriques qui favorise le glissement basal, mais aussi des processus d'adoucissement associes a la recristallisation. En cisaillement simple, les fabriques de la glace recristallisee consistent en deux maximums, dont l'un est confondu avec le pole du plan de cisaillement permanent et I'autre est situe entre la normale au deuxieme plan de cisaillement maximum et la direction principale de compression. En torsion-compression, des fabriques a trois ou quatre maximums sont formees suivant I'intensite des differentes composantes du tenseur des contraintes. Les maximums entourent dans to us les cas la direction principale de compression. On discute des processus de formation des fabriques. Les fabriques obtenues dans ces experiences sont probablement produites par la recristallization dont le moteur est I'energie de la deformation pia tique. L'orientation preferentielle des axes c des cristaux de glace doit etre une fonction de la deformation totale atteinte lorsque la recristallization syntectonique devient moins importante. Dans ce cas, les fabriques sont principalement formees par la deformation plastique et un eta...

The effect of particles on dynamic recrystallization and fabric development of granular ice during creep

“…Actually, during the compressive creep tests, the slip direction rotates away from the compression axis if one considers each crystal individually. Compared with some previous data, which show a strong girdle-shaped orientation at strains above 15% (Duval, 1981;Azuma and Higashi, 1985), the $10% strain is rather small to generate such a girdle-shaped fabric in our tests. The reason for this phenomenon is not clear at this stage.…”

“…There are a number of studies (Duval, 1981;Jacka, 1984a;Jacka and Maccagnan, 1984;Azuma and Higashi, 1985;Wilson and Sim, 2002) concerning fabric development in laboratory-prepared and glacier ice. These studies examined fabric development under compression and shear.…”

A new laboratory device for study of subglacial processes: first results on ice–bed separation during sliding

“…12) have been observed in previous experiments (Kamb, 1972;Duval, 1981) but are poorly understood. However, there seems to be consensus that such fabrics are indicative of recrystallization of ice at or near its pressure-melting temperature under simple shear and compression normal to the plane of shear (Hooke, 2005;Cuffey and Paterson, 2010).…”

Fault geometries on Uranus’ satellite Miranda: Implications for internal structure and heat flow

“…Results of laboratory experiments have indicated that strain-softening, particularly with added impurities such as HF (Jones, 1967;Jones and Glen, 1969) and HCl (Nakamura and Jones, 1970), can occur in H 2 O ice. In some cases, this softening has been attributed to the development of preferred orientations favoring basil slip (Steinemann, 1954;Kamb, 1972;Duval, 1979Duval, , 1981. Strain-softening has also been found to occur during laboratory strength experiments of cryogenic ice, and was attributed to dislocation multiplication and velocity-limited dislocation glide (Weertman, 1983;Durham et al, 1983Durham et al, , 1992.…”