Call number:
ZSP-201-86/5
In:
CRREL Report, 86-5
Description / Table of Contents:
This work presents the results of a study to examine the effects of grain 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 to the minus 2nd power at the minimum creep rate epsilon. The coarse-grained material experienced severe cracking and a drop in the strain at epsilon min to approximately 4x10 to the minus 3rd power. 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 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.
Type of Medium:
Series available for loan
Pages:
v, 79 Seiten
,
Illustrationen
Series Statement:
CRREL Report 86-5
URL:
https://apps.dtic.mil/docs/citations/ADA171571
URL:
https://hdl.handle.net/11681/9321
Language:
English
Note:
CONTENTS
Abstract
Preface
Background
Present research in perspective
Explanations of the grain-size dependency
Grain size effects on the ductile to brittle transition
Nucleation mechanisms and modeling
Characteristic size of nucleated crack
Cracking in ice
Detection of internal fracturing by acoustic emission techniques
Test methods
Specimen preparation
Creep testing apparatus
Crack length and crack density measurements
Crack healing measurements
Thin section photographs
Grain size determination
Acquisition of acoustic emission data
Presentation of results
Specimen characteristics
Microcrack measurements
Creep behavior
Crack healing
Slip plane length distribution
Acoustic emission observations
Grain orientation
Analysis and discussion
Thick section observations
The grain size vs crack size relationship
Crack nucleation condition
Crack density and specimen strain
Creep behavior
Normalized crack length
Location of cracks
Acoustic emission activity
Summary and conclusions
Suggestions for future work
Literature cited
Appendix A: Crack length histograms
Appendix B: Crystal orientations
Location:
AWI Archive
Branch Library:
AWI Library
