01\Jf At:.. A TENSILE FRACTURE MODEL FOR ICE S. S. Sunder and S. Nantliikesan Massachusetts Institute of Tecnnology Department of Ci•il Engin.eering Cambridge, Massachuseru ABSTRACT The fracture of ice under tensile loading is characterized in terms of the stress versus separation behavior in the process zone. This process zone characterization can be used in numerical simulations based on discrete crack models. '!he stress-separation model is then integrated wit:. a rate-sensitive tensile stress-strain-strength model to account for strain-softening at the continuum scale. The resulting constitutive theory can be applied, in conjunction an objective energy criterion proposed here, to simulate localized fracture processes based on the blunt crack band theory. Quantitative estimates of the fracture process zone size are obtained to assess the validity of toughness measurements based on linear elastic fracture (LEFM). INTRODUCTION In oost real world applications involving ice either as\ a load bearing mediui:r. or as a load transoitting mediUJ:l, the strength of ice is licll.ted by fracture. Investigations on the fracture behavior of ice have been relatively few in -:.o the work on its continuum behavior. They bclude the works of Gold (_U, Goetze (2), Good:nan (3-5), Hamza and Muggeridge (6,7), Urabe et al. (S-lO), Timco and ?rederking (11--;-12), and Schulson-and Nixon (13,14). Hellar ("iS)has rev'_e;,·ed much of this The general ei:r.?hasis of past work has been to the mode I fracture behavior of pure and sea ice in terms of the linear elastic fracture parameter, Krc, a sequence of tes":.S conducted under varying rates of loading and varying temperature. Since for rates of greater than about 10 K?a m1/2 and below about -10°C the -:.oughness parameter Krc. tends to be;;ome i!"lsensitive to rate and tempe.r-a".:ure, it is LEFM applies under such cor.ditions. T:--.eoretical support for loading rate criterion has been proposed by Urabe et al. (9) based on Riedel and Rice's analytical study of tensile cracks in creeping solids which assumes that elastic strains dominate almost everywhere in the specimen except in a small "creep zone", which grows around the crack tip. The analysis models ice as an elastic, power law material and considers the fracture "process zone" to be of negligible size vi thin the creep zone. '):'his paper is motivated by the following three concerns: 1. Numerical models for simulating fracture processes during ice-structure may be developed on ·t.'1e basis cf t·Jo distinct theories. The first theory leads to discrete crack models U. .2.-20) "'"".ich assume that all cracking activity is loca:ized on a plane, The second theory leads to smeared or blunt crack models (i!_-24) which assume that cracking activity is distributed over a characteristic width re?resenting a material property. Ccnstitutive models describing fracture of i=e i.:.nder tensile loading suitable for use either of t.'1e two numerical approaches iacking at the present time. 2. In many practical applications, fracture in ice is accompanied by significant nonlinear deformations. For example, in the nearshore zone viscoelastic deformations a::cur:ulat:e during t..'1.e winter mont...'-1s prior to •=reai<:out" which occurs in early spring as a result of crack nucleation and propagation. The asso=iated states of stress and strain in the ice tend to be multiaxial, the strains typically tension-compression in the region where nucleate This precludes t.'1e use of fracture toughness parameters. 225
A TENSILE FRACTURE MODEL FOR ICE
May 19, 2023
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Related Documents
