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

Micheal 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

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)
39 Downloads (Pure)


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 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 Digital Image Correlation 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 470 μm/s 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 traveling 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.
Original languageEnglish
Pages (from-to)10517-10533
Number of pages17
JournalJournal of Geophysical Research: Solid Earth
Issue number12
Early online date12 Dec 2018
Publication statusPublished - Dec 2018

ASJC Scopus subject areas

  • Computers in Earth Sciences
  • Materials Science (miscellaneous)
  • Geotechnical Engineering and Engineering Geology


Dive into the research topics of 'Correlative optical and X‐ray imaging of strain evolution during Double Torsion Fracture Toughness measurements in shale'. Together they form a unique fingerprint.

Cite this