Ice triaxial deformation and fracture

Abstract

ABSTRACT. An experimental investigation into the mechanical behaviour of polycrystalline ice in triaxial compression has been conducted using conditions generally favourable to brittle fracture and microcracking. Under triaxial stresses at high strain rate, ice failure occurs by abrupt shear fracturing, generally inclined at about 45° to the maximum principal stress. At -20°C, such failure is suppressed by the imposition of a small confining pressure, allowing a transition to ductile-type flow accompanied by distributed microcracking, but at --40°C shear fracture persists under confinement of up to at least 50 MPa. For low confining pressures « 10 MPa), brittle strength is strongly pressure-dependent; above this it is pressure-independent. Evidence is presented that suggests this may reflect a change from a fracture process influenced by friction to fracture initiated by localized yielding. Ductile yield strength is found to be little influenced by confining pressure despite the inhibition of cracking that leads to greatly contrasting observed crack densities. Flow conforms to the well-known power law for ice with Q = 69J mol-1 and n = 4.2 over the temperature range -20° to-45° C. Under these conditions, microcracking in ice appears to remain remarkably stable and non-interacting.

Plastic faulting in saltwater ice

“…Rist and Murrell (1994) report that freshwater granular ice loaded under a high level of confining pressure at T = -408C fails by shear faulting at applied strain rates of _ " = 1 Â 10 -2 s -1 and by global ductile flow at applied strain rates of _ " = (1 Â 10 -5 ) -(1 Â 10 -3 ) s -1 . At higher temperatures (T = -208C), they report that failure under high levels of confining pressure followed global ductile flow under the range of strain rates examined ( _ " = (1 Â 10 -5 ) -(1 Â 10 -2 ) s -1 ), i.e.…”

Mixed Phase Modeling in GlennICE with Application to Engine Icing

“…Rist (Ref. 13) measured the deformation and fracture of 1.5 cm ice particles over a wide range of temperatures. He measured the strain rate at failure to the corresponding stress applied and produced the following relationship:…”

Ice internal friction: Standard theoretical perspectives on friction codified, adapted for the unusual rheology of ice, and unified

“…In Rist and Murrell's [22] expression for brittle shear strength (equation 24), there appears an explicit, local normal stress at the asperity contacts Σ. We propose that, to bear the appropriate load, it must be given by This means that, if the failure of the contact is brittle and the real contact fraction…”

“…The shear strength T may be the ductile yield stress T du [13,21], the brittle fracture stress in shear T br [13,22], or an effective shear strength T ml , representing a process whereby heat dissipated in frictional sliding melts part of the material surface, generating a fluid layer, which separates the peaks of the the analysis is the integral formulae…”