Mechanisms and Theory of Indentation of Ice Plates

Abstract

ABSTRACT. This study gives the results and interpretation of tests made in a cold room on ice pla tes held vertically in a press and indented at various speeds with a rectangular indentor. These plates, 81 cm square, were held and frozen solid to a steel frame to represent semi-infinite ice sheets. The tests were carried out at -lO o e with indentation speeds varying from 6 X 10-5 cm/s to 3 cm/so I t was found that the nominal pressure of indentation varies as a function of loading rates in a manner similar to that of the strength of 52 ice in uniaxial compression. The pressure increases rapidly with loading rates up to its maximum value at a strain-rate of 5 X 10-4 5-1 • From there on, the pressure decreases. In the ductile range and up to the point of maximum pressure, a theoretical model was proposed where the theory of Hill (1950) of indentation of an ideal plastic body can be applied to predict an indentation pressure close to three times that of the uniaxial crushing strength.The tests did not show any so-called "ratio effect" caused by the ratio of the indentor width to the plane thickness. This effect could be explained by the influence of th e geometry of the indentor on the strain-rate. 'une fa~on semblable a celle de la resistance ultime de la glace 52 en compression uniaxiale. La press ion croit rapidement avec les taux de chargement jusqu' a un maximum correspondant a un taux de deformation de 5 X 10-4 S-I. A partir d e ce point, la pression diminue. Dans le domaine ductile e t jusqu'a ce maximum, un modele theorique es t propose ou la theorie de Hill (1950) d e l'indentation d' un plastique ideal peut s'appliquer pour predire une pression d'indentation egale a pres d e trois fois la resistance en compression unia xi ale de la glace.Les essais n'ont pas montre d'effet geometrique cause par le rapport d e la largeur de l'indenteur a l'epaisseur de la glace. Cet effet peut etre explique indirectement par l'influence d e la geometrie d e l'indenteur sur le taux de deformation. Die Versuche zeigten keinen sog. "Verhaltnis-Effekt", hervorgerufen durch das Verhaltnis zwischen Breite des Pragers und Plattendicke. Dieser Effekt konnte mit dem Einfluss d er Form des Pragers auf die V erformungsra te erklart werden. ZUSAMMENFASSUNG. M echanismus und Theorie der Priigebelastwzg von

Confined compression tests: Outlining the failure envelope of columnar sea ice

“…For the latter applilowing form can be used to describe the failure cation, the reader is referred to the review article by envelope in terms of the normal stresses (o) and shear Sanderson (1 984). stresses (t) Several different formulations have been used to mathematically describe the failure envelope for ice including the von Mises (Michel and Toussaint, 1977), Tresca (Croasdale et al, 1977), n-type (Reinicke and Ralston, 1977;Ralston, 1978) and modified DruckerPrager Das, 1983a, 1983b). Of all of these methods, only the n-type yield function can represent the anisotropic nature of the ice.…”

Brittle to ductile transition during indentation of ice

“…The average diameter of pennyshaped cracks and the width of cracks in columnar-grained ice are of the same order as the grain size (Cole 1986(Cole , 1989Gold 1972b). Similar cracks are observed to form duing indentation; the first ones occurring near the edge of the indentor (Nuttall and Gold 1966;Michel and Toussaint 1977).…”

“…If the rate of indentation is sufficiently high, brittle failure occurs; and the indentation pressure appears to be relatively constant and independent of the rate. As the indentation rate decreases from a relatively critical value, the indentation pressure increases to a maximum (Michel and Toussaint 1977;Sanderson 1988). …”

“…This condition must have applied a constraint that would not be present for an indentor impressed on a long straight edge. Michel and Toussaint (1977) used ice plates of thicknesses 2.54, 5.08, and 10.16 cm, maintained at a temperature of -10°C.…”

Physical mechanism of ice/structure interaction

“…It is found and proved that ice uniaxial stress or indentation stress is a function of the strain rate as shown in Figure 2 (Blenkarn, 1970;Michel and Toussaint, 1978;Palmer and others, 1983;Sodhi and Haehnel, 2003). The strain rate is defined by v r /λD, where the dimensionless coefficient λ varies from 1 to 4 and D is the structural width (Yue and Guo, 2011).…”