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Title: Effect of grain size on the internal fracturing of polycrystalline ice
Authors: Cole, David M.
Keywords: Acoustic emissions
Ice creep
Creep tests
Ice crystals
Ice crystal structure
Fracture (mechanics)
Fracture mechanics
Grain size
Ice mechanics
Issue Date: Jul-1986
Publisher: Cold Regions Research and Engineering Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: CRREL report ; 86-5.
Description: CRREL Report
Abstract: This work presents the results of a study to examine the effects of grain size on the number and size of internal microfractures in polycrystalline ice. Laboratory-prepared specimens were tested under uniaxial, constant-load creep conditions at -5°C. Grain size ranged from 1.5 to 6.0 mm. This range of grain size, under an initial creep stress of 2.0 MPa, led to a significant change in the character of deformation. The finest-grained material displayed no internal cracking and typically experienced strains of 10^-2 at the minimum creep rate εmin. The coarse-grained material experienced severe cracking and a drop in the strain at εmin to approximately 4x10^-3. Extensive post-test optical analysis allowed estimation of the size distribution and number of microcracks in the tested material. These data led to the development of a relationship between the average crack size and the average grain size. Additionally, the crack size distribution, when normalized to the grain diameter, was very similar for all specimens tested. The results indicate that the average crack size is approximately one·half the average grain diameter over the stated grain size range. A dislocation pileup model is found to adequately predict the onset of internal cracking. The work employed acoustic emission techniques to monitor the fracturing activity. This information shed light on the time and strain at which the fracturing began and when the peak fracturing rate occurred. Other topics covered in this report include creep behavior, crack healing, the effect of stress level on fracture size and the orientation of cracked grains. Theoretical aspects of the grain size effect on material behavior are also given.
Appears in Collections:CRREL Report

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