On Friction and Surface Cracking During Sliding of Ice on Ice

As a complement to earlier measurements on the friction of both granular fresh-water ice and S2 columnar salt-water ice, new experiments were performed on the friction of S2 columnar fresh-water ice sliding against itself at low velocities (5 × 10−7 to 5 × 10−1 m s−1) and at −10°C, using the same double-shear device as was used earlier. The results showed that under a given set of experimental conditions the kinetic coefficient of friction of S2 fresh-water ice compares favorably with that of the other two variants.The experiments also revealed friction-induced surface cracks and recrystallized grains.These deformation features are explained, respectively, in terms of fracture mechanics and an earlier model of dynamic recrystallization in ice

A Notch-Strengthening Effect in Fresh-Water Ice

Tensile tests have been performed onnotched and unnotched cylindrical samples of randomlyoriented polycrystalline ice of controlled grain-size (between2.2 and 7.3mm) at a loading rate of lOOPaS-l and at a temperature of -10 0c. In the notched samples, the notch-root diameter was 80% of the base diameter. Anotch-strengthening effect was observed in the large-grained ice, with fracture stresses being up to 50% higher than that for unnotched samples of the same grain-size. This notch-strengthening effect diminished as grain-size decreased, disappearing at a grain-size of \u273 mm. The notch-strengthening effect is explained in terms of the triaxial stress constraint at the notch root. This triaxialconstraint results in a change in the controlling mechanismof fracture from crack propagation in the unnotchedsamples to crack initiation in the notched samples

Does the Normal Stress Parallel to the Sliding Plane Affect the Friction of Ice upon Ice?

Sliding experiments were performed at –10 degrees C on smooth surfaces of freshwater columnar-grained S2 ice sliding against itself at a velocity of 8X10 –4 ms –1, with the purpose of examining whether normal stress parallel to the sliding plane affects frictional resistance. This component of the stress tensor was varied (0.20–1.83 MPa) using a loading system operated under biaxial compression, by orienting the sliding plane at two different angles, 26 degrees and 64 degrees, with respect to the principal loading direction. Under these conditions, no evidence was found to indicate that the normal stress in the direction of sliding affects the friction coefficient

The Role of Damage and Recrystallization in the Elastic Properties of Columnar Ice

Effects of damage on elastic properties were studied in columnar-grained specimens of freshwater and saline ice, subjected, at −10°C, to varying levels of inelastic strain. The ice was compressed uniaxially at constant strain rates up to 0.20 strain, which caused localized recrystallization and imparted damage in the form of non-propagating cracks. Damage was quantified in terms of dimensionless crack density, which, along with recrystallized area fraction, was determined from thin sections. The change in porosity due to stress-induced cracks served as another indicator of damage. Elastic properties were derived using P-wave and S-wave ultrasonic transmission velocities measured in across-column directions through the damaged ice, either parallel (x 1) or perpendicular (x 2) to the initial loading direction. In general, as damage increased with greater strain, the ice became more compliant and (particularly freshwater ice) more anisotropic. Furthermore, with increasing strain rate, the magnitude of these effects and crack density tended to increase, in contrast to the recrystallized area fraction, which tended to decrease. We observed compliance to correspond closely with porosity and with dimensionless crack density, for strains up to 0.10. At greater levels of strain these correspondences became less clear due, in part, to the different character of the damage

Effects of prestrain on the ductile-to-brittle transition of ice

AbstractThe ductile-to-brittle transition was investigated in prestrained columnar ice at −10 °C. Laboratory-grown specimens of freshwater and saline ice were prestrained under uniaxial across-column compression (to levels from εp = 0.003 to εp = 0.20, at constant strain rates in the ductile regime) and likewise reloaded (at rates from 1 × 10−6s−1 to 3 × 10−2s−1). Prestrain caused solid-state recrystallization as well as damage in the form of non-propagating microcracks. The ductile-to-brittle transition strain rate ε˙D/B increased by a factor of 3–10 after prestrain of εp = 0.035 in both freshwater and saline ice, compared to that of initially undamaged ice of the same type. Additional prestrain had little further effect on ε˙D/B. The results are interpreted within the framework of a model (proposed by Schulson, 1990, and Renshaw and Schulson, 2001) that predicts the transition strain rate based on the micromechanical boundary between creep and fracture processes. Model parameters primarily affected by prestrain were the power-law creep coefficient B (more so than the creep exponent n), Young's modulus E and, by extension, the fracture toughness KIc

Plastic Faulting in Saltwater Ice

Compression experiments on laboratory-grown columnar S2 saltwater ice loaded triaxially through proportional loading at T = –20°C at applied strain rates of ε = 10–5–10–1 s–1 demonstrate that plastic (P) faulting is a mode of failure in saltwater ice when rapidly loaded under a high degree of confinement. In terms of microstructure, mechanical behavior and strength, saltwater ice that fails via P-faulting is almost indistinguishable from columnar S2 freshwater ice that fails via P-faulting loaded under the same conditions. The results also demonstrate that saltwater ice loaded rapidly may exhibit yet another mode of failure, in addition to P-faulting, through what appears to be a mechanism of pore collapse

The fracture of water ice Ih: A short overview

From the proceedings of the Workshop on the Role of Volatiles and Atmospheres on Martian Impact Craters held on July 11-14, 2005, at the Johns Hopkins University Applied Physics Laboratory.This paper presents a short overview of the fracture of water ice Ih. Topics include the ductile-to-brittle transition, tensile and compressive strength, compressive failure under multiaxial loading, compressive failure modes, and brittle failure on the geophysical scale (Arctic sea ice cover, Europa's icy crust). Emphasis is placed on the underlying physical mechanisms. Where appropriate, comment is made on the formation of high-latitude impact craters on Mars.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Creep and Fracture of Ice

ISBN-13: 9780521806206 ; http://www.cambridge.org/catalogue/catalogue.asp?isbn=9780521806206This is the first complete account of the physics of the creep and fracture of ice, and their interconnectivity. It investigates the deformation of low-pressure ice, which is fundamental to glaciers, polar ice sheets and the uppermost region of icy moons of the outer Solar System. The book discusses ice structure and its defects, and describes the relationship between structure and mechanical properties. It reviews observations and measurements, and then interprets them in terms of physical mechanisms. The book provides a road-map to future studies of ice mechanics, such as the behaviour of glaciers and ice sheets in relation to climate change and the dating of deep ice cores. It also highlights how this knowledge is transferable into an understanding of other crystalline materials. Written by experts in the field, it is ideal for graduate students, engineers and scientists in Earth and planetary science, and materials science