Compressive shear faults in ice: plastic vs. Coulombic faults

A re-examination of the literature has revealed two kinds of compressive shear faults in terrestrial ice when rapidly loaded under triaxial states of stress. One kind, termed a Coulombic or C-fault, develops under lower degrees of confinement and (at 263 K) is typically inclined by 28-30degrees to the direction of shortening. The other kind, termed a plastic or P-fault, develops under higher confinements and is inclined by 45degrees. The C-P transition occurs when confinement becomes sufficiently large to suppress frictional crack sliding. A criterion (upper limit) is given, in terms of the coefficient of internal friction, that defines the transition in terms of the ratio of minimum to maximum principal stress at failure. Plastic faulting, it is suggested, is caused by adiabatic softening. The role of shear faulting in ice mechanics is discussed. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.