“…Broadly the Andrade creep increases with grain-size. This result is in accordance with that given by Duval (1973). Fig.…”
Section: Resultssupporting
confidence: 93%
“…A constant uniaxial load was applied parallel to the long axis of samples with the apparatus used by Duval ([1977]) in a cold room kept at (– 4.6±0.1)°C or at (– 7.1 ±0.1)°C. Strain was measured as a function of time by a linear variable differential transformer transducer (L.V.D.T.)…”
Section: Experimental Methodsmentioning
confidence: 99%
“…From Baker (1978), the steady creep with fine-grained ices is controlled by diffusional processes whereas that with coarse-grained ices is controlled by the mobility of dislocations in their glide planes. If, as shown above, Nabarro–Herring diffusional creep seems to be occurring for fine-grained ices and low stresses, it is not the case for a glide-controlled creep increasing with crystal size (Duval, 1973).…”
Section: Introductionmentioning
confidence: 97%
“…For low stresses, it seems that the exponent n is smaller than 3 (Mellor and Testa, 1969; Colbeck and Evans, 1973; Duval, 1973). These results support the idea that two distinct mechanisms are controlling the deformation of ice for low and high stresses.…”
ABSTRACT. Uniaxial compression creep tests were p erformed on a rtificial and natural polycrystalline ices at tempera tures near -7°C . The grain-size range investigated was from I to 10 mm. C ontrary to previous results, the p ermanent creep-ra te was not found to in crease with crystal size. Only the transien' t creep appears to b e sensitive to variations in crystal size.R EsuME . L a vitesse du j1uage stationnaire de la glace poiyeristalline erolt elle avee la taille des eristaux? Des experiences d e fluage en compression uniaxial e o nt ete realisees sur d es glaces polycristallines artificielles et naturell es aux temperatures voisines de -7°C. L a taille des grains va ria it entre I et 10 mm. A I'oppose des resultats recemment publies, il est montre que la vitesse du fluage sta tionnaire ne croit p a s a vec la taille des crista ux. Seulement le flu age tra nsitoire appa ra it etre influence pa r d es variations de la taille des cristaux.
“…Broadly the Andrade creep increases with grain-size. This result is in accordance with that given by Duval (1973). Fig.…”
Section: Resultssupporting
confidence: 93%
“…A constant uniaxial load was applied parallel to the long axis of samples with the apparatus used by Duval ([1977]) in a cold room kept at (– 4.6±0.1)°C or at (– 7.1 ±0.1)°C. Strain was measured as a function of time by a linear variable differential transformer transducer (L.V.D.T.)…”
Section: Experimental Methodsmentioning
confidence: 99%
“…From Baker (1978), the steady creep with fine-grained ices is controlled by diffusional processes whereas that with coarse-grained ices is controlled by the mobility of dislocations in their glide planes. If, as shown above, Nabarro–Herring diffusional creep seems to be occurring for fine-grained ices and low stresses, it is not the case for a glide-controlled creep increasing with crystal size (Duval, 1973).…”
Section: Introductionmentioning
confidence: 97%
“…For low stresses, it seems that the exponent n is smaller than 3 (Mellor and Testa, 1969; Colbeck and Evans, 1973; Duval, 1973). These results support the idea that two distinct mechanisms are controlling the deformation of ice for low and high stresses.…”
ABSTRACT. Uniaxial compression creep tests were p erformed on a rtificial and natural polycrystalline ices at tempera tures near -7°C . The grain-size range investigated was from I to 10 mm. C ontrary to previous results, the p ermanent creep-ra te was not found to in crease with crystal size. Only the transien' t creep appears to b e sensitive to variations in crystal size.R EsuME . L a vitesse du j1uage stationnaire de la glace poiyeristalline erolt elle avee la taille des eristaux? Des experiences d e fluage en compression uniaxial e o nt ete realisees sur d es glaces polycristallines artificielles et naturell es aux temperatures voisines de -7°C. L a taille des grains va ria it entre I et 10 mm. A I'oppose des resultats recemment publies, il est montre que la vitesse du fluage sta tionnaire ne croit p a s a vec la taille des crista ux. Seulement le flu age tra nsitoire appa ra it etre influence pa r d es variations de la taille des cristaux.
“…For secondary creep, the strain-rates ⋵ ij vary with the deviatoric stresses τ ij ' , with the relationship where τ is the effective shear stress defined by: and B is a constant. For stresses greater than one bar, the exponent n is about three and creep-rate is controlled by recovery processes (Duval, 1977), but for small stresses the creep-rate of fine-grained poly-crystalline ice (grain size smaller than one millimeter) is controlled by diffusional processes (Duval, 1973).…”
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...
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