ICE TRIAXIAL DEFORMATION AND FRACTURE

An experimental investigation into the mechanical behaviour of polycry stalline ice in triaxial compression has been conducted using conditio ns generally favourable to brittle fracture and microcracking. Under t riaxial stresses at high strain rate, ice failure occurs by abrupt she ar fracturing, generally inclined at about 45 degrees to the maximum p rincipal stress. At -20 degrees C, such failure is suppressed by the i mposition of a small confining pressure, allowing a transition to duct ile-type flow accompanied by distributed microcracking, but at -4O deg rees C shear fracture persists under confinement of up to at least 50 MPa. For low confining pressures (< 10 MPa), brittle strength is stron gly pressure-dependent; above this it Is pressure independent. Evidenc e is presented that suggests this may reflect a change from a fracture process influenced by friction to fracture initiated by localized yie lding. Ductile yield strength is found to be little influenced by conf ining pressure despite the inhibition of cracking that leads to greatl y contrasting observed crack densities. Flow conforms to the well-know n power law for ice with Q = 69 J mol(-1) and n = 4.2 over the tempera ture range -20 degrees to -45 degrees C. Under these conditions, micro cracking in ice appears to remain remarkably stable and non-interactin g.