Visual and Acoustic Emission Observations of Fracture in Barre Granite Bing Q. Li PhD Candidate, Department of Civil and Environmental Engineering In collaboration with Prof. Herbert H. Einstein MIT Earth Resources Laboratory 2017 Annual Founding Members Meeting 01 June, 2017
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Visual and Acoustic Emission Observations of Fracture in Barre GraniteBing Q. LiPhD Candidate,Department of Civil and Environmental EngineeringIn collaboration with Prof. Herbert H. Einstein
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting01 June, 2017
IntroductionMain research goal: Relate visual observations to acoustic emissions (laboratory analogue to microseismicity), given that fractures are not directly accessible in the field.
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting
Slide 2
High speed video Microscopic images Specimen-scale1cm 250μm 5mm
Acoustic Emissions
Four Point Bending: Experimental Setup
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting
Slide 3
Front (macro) camera
Back (micro) camera
Loading machine
Specimen
Loading Geometry
8 AE sensors (150-‐400 kHz peak)5 MHz acquisitionMagnitude calibrated with ball drop
Load-displacement Data
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting
Slide 4
Digital Image Correlation (DIC) Results
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting
Slide 5
1
2
3 4
Microstructural Changes
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting
Slide 6
Opening Strain Oblique Strain
AE Results
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting
Slide 7
Focal Mechanisms
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting
Slide 8
Double CoupleNon-‐Double Couple
Microstructural Changes Compared to AE
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting
Slide 9
General Visual Data Compared to AE
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting
Slide 10
Other Work on Hydraulic Fracture
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting
Slide 11
Conclusions
MIT Earth Resources Laboratory2017 Annual Founding Members Meeting
Slide 12
• At a specimen scale, changes detected by visual techniques match well to AE and load-‐displacement data
• On a microstructural scale, most of the damage occurs prior to the initiation of fracture considered at a specimen scale• For a tensile stress field, microstructural damage appears to be mostly shear
• For the beam bending stress condition, it appears that non double couple hypocenters are more closely related in space to the fracture than double couple events
• The process zone detected by the visual techniques corresponds well to the majority of AE hypocenter locations
• Ongoing work on experiments with hydraulic fracture boundary conditions indicate that the above observations also apply
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