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I12-JEEP: Joint Engineering, Environmental and Processing	Correlative optical and X‐ray imaging of strain evolution during Double Torsion Fracture Toughness measurements in shale Michael R. Chandler , Anne-Laure Fauchille , Ho Kyeom Kim , Lin Ma , Julian Mecklenburgh , Roberto Rizzo , Mahmoud Mostafavi , Sebastian Marussi , Robert Atwood , Steven May , Mohammed Azeem , Ernie Rutter , Kevin Taylor , Peter Lee Journal Of Geophysical Research: Solid Earth DOI: 10.1029/2018JB016568 Diamond Proposal Number(s): [13824] Open Access Show Abstract ▼ Abstract: Mode‐I Fracture Toughness, KIc, was measured in six shale materials using the double torsion technique. During loading, crack propagation was imaged both using twin optical cameras, and with fast X‐Ray radiograph acquisition. Samples of Bowland, Haynesville, Kimmeridge, Mancos, Middlecliff and Whitby shales were tested in a range of orientations. The measured fracture toughness values were found to be in good agreement with existing literature values. The two imaging techniques improve our understanding of local conditions around the fracture tip, through in‐situ correlation of mechanical data, inelastic zone size and fracture‐tip velocity. The optical Digital Image Correlation (DIC) technique proved useful as a means of determining the validity of individual experiments, by identifying experiments during which strains had developed in the two "rigid" specimen halves. Strain maps determined through DIC of the optical images suggest that the scale of the inelastic zone is an order of magnitude smaller than the classically used approximation suggests. This smaller damage region suggests a narrower region of enhanced permeability around artificially generated fractures in shales. The resolvable crack‐tip was tracked using radiograph data and found to travel at a velocity around 470μm.s−1 during failure, with little variation in speed between materials and orientations. Fracture pathways in the bedding parallel orientations were observed to deviate from linearity, commonly following layer boundaries. This suggests that while a fracture travelling parallel to bedding may travel at a similar speed to a bedding perpendicular fracture, it may have a more tortuous pathway, and therefore access a larger surface area.	Dec 2018

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I12-JEEP: Joint Engineering, Environmental and Processing

Correlative optical and X‐ray imaging of strain evolution during Double Torsion Fracture Toughness measurements in shale