The relationship between microcracking and ice Strength has been examined using triaxial apparatus in which track damage can be inhibited by the imposition of confining pressure. Shear fracture in ice is observed to be a rapid, unstable process with no apparent indication of tensile crack localisation or interaction prior to failure and no accompanying large-scale volumetric changes, at least to within 1 ms of the occurrence of macroscopic failure. Shear fracture strength displays little or no dependence on confinement at moderate pressures (P = 5–20MPa), and there is no evidence of significant crack sliding before macroscopic fracture under these conditions. Where flow with distributed microcracking occurs, yield strength can also remain remarkably unaffected by confining pressure, despite reduced crack damage. Particularly under conditions where microcracks are induced by predominantly elastic strains, they may remain stable and non-interacting even at high volumetric densities.

Low-cycle fatigue behavior of Hastelloy X at elevated temperature is presented. We studied the effects of test temperature, cycle frequency, and stress temperature arrangement with special attention given to the minimum ductility (short-time tension test) at or near 1300 F. Isothermal fatigue data at 800, 1300, 1500, and 1800 F are presented along with strain controlled thermal fatigue data for temperature ranges of 600 to 1800, 800 to 1300, and 1800 to 1300 F. The method of universal slopes can be used to describe the fatigue behavior under elevated isothermal and cyclic thermal fatigue conditions. The thermal fatigue behavior determined from controlled strain tests can be applied to the thermal cycle behavior of bundles of thin tubes joined to a rigid plate.

ABSTRACT. Th e rela ti o nship betwee n mi erocrae king a nd ice streng th has bee n exa mined usin g tri axial a ppa ra tu s in whi ch c rac k d a m age can be inhibited by th e impositi o n of co nfining press ure. Sh ea r fr ac ture in ice is o bse ryed to be a rapid , unstable process with no a ppare nt indi ca ti o n of tensile c rac k locali sati o n or interac tion prior to failure a nd no a cco mpa n ying la rge-sc al e volum e tri c cha nges, at leas t to within lms of th e occ urrence of m acrosco pi c fa ilure. Sh ea r fr ac ture stre ng th displays littl e o r no d ep end ence o n confin em e nt a t m od era te press ures (P = j 20 :"IPa ), a nd th ere is no evidence of signili ca nt c rack sliding befo re m ac rosco pi c fr ac ture und er th ese co nditio ns. Wh ere Oo w with di stributed mi c roc rac king occ urs, yield stre ng th ca n a lso remain rem a rk a bl y unaITec ted b y confinin g press ure, d es pite redu ced c rac k dam age . Pa rtic ularl y und er conditi o ns wh ere mi crocrac ks a re indu ced b y pred o min a ntly el as ti c stra ins, th ey m ay re m a in sta bl e a nd no n-interac ting even a t high \'olum e tri c d ensiti es.

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Uniaxial compression tests were carried out on fresh-water, isotropic, granular ice at a strain rate of 6 × 10−4s−1. We investigated the effect of temperature (between −2 and −39°C) and grain-size (1 mm–8 mm) on the critical stress and strain at the initial crack nucleation. The amount of non-elastic strain at this event was estimated. The critical stress for initial crack nucleation increased strongly with decreasing temperature, following an Arrhenius law. It also exhibited a linear increase withdg−1/2(wheredgis the average grain-size). It is shown that the results cannot be explained by the purely brittle model of Sunder and Wu (1990). The results are interpreted in terms of grain-boundary sliding, controlled by the intrinsic viscosity of the boundary.