Paper contribution

Tensile fracturing in granite and gneiss investigated by DIC and thin sections

Lars Jacobsson; Linus Brander; Johan Sandström; Mathias Flansbjer

Proceedings
EUROCK 2026
Pages
535-540
Submitted
28 January 2026
Accepted
15 June 2026
Published
12 August 2026

Summary

Abstract

The fracture mechanics properties in crystalline rocks depend on the microstructure, and presence of microcracks and pores. The aim was to visualize and quantify tensile fracturing properties during and after experiments. Wedge splitting tests were conducted on two quasi-brittle rock types, a medium- to coarse-grained granite and a finely medium-grained gneiss, to study the fracture processes and to determine fracture mechanics data under tensile loading. The propagating crack was followed during loading by displacement field measurements obtained from digital image correlation analysis. The propagating crack was meandering and branching in the granite, whereas the crack was straighter and smoother with almost no branching in the gneiss. The crack opening displacement was determined from the displacement field in a small band enclosing the crack path and was used to determine fracture process zone data. A fully developed crack, i.e. no cohesive force, was obtained when the crack opening displacement was about 6.5–20 μm in the granite and ≤ 6.5 μm in the gneiss. The length of the process zone was 10 mm initially and increasing to 15 mm when the crack length was 30–40 mm in the granite and 2–3 mm in the gneiss. The results on granite are in line with the few existing results in literature, whereas no previous results on gneiss were found. The onset of crack initiation was determined by the change of the crack mouth opening stiffness and compared with crack opening displacements yielding the same result. The thin section analyses confirmed mentioned observations on the crack path and showed occasionally several parallel crack paths in the granite, but a single crack path in the gneiss with a small amplitude and long wavelength. Intragranular fractures are mainly found in feldspar and large quartz grains. Several of the used methods are novel.

Contributors

Authors

  1. Lars Jacobsson RISE Research Institutes of Sweden, Sweden ORCID 0000-0003-4526-4061
  2. Linus Brander Swerock AB, Sweden
  3. Johan Sandström Saab Naval, Sweden
  4. Mathias Flansbjer RISE Research Institutes of Sweden, Sweden

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References

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