Estimating mode II fracture energy of rocks using the scratch test and phase field modeling

This study introduced a mode II fracture energy approximation based on scratch test results and a phase field modeling approach. Using a length-insensitive approach, an analytical solution to in-plane shear (mode II) fractures was derived based on the phase field model for quasi-brittle fractures. Thereafter, the analytical solutions were related to the experimental data collected from the scratch testing to estimate the shear fracture energy, wherein the stress–strain degradation observed during fracture formation was compared. Panoramic pictures acquired after the test and the observed acoustic emission activity aided in identifying the evolution of shear fractures. The resulting shear fracture energy predicted for the reference material was consistent with results published in the literature. Subsequently, the developed methodology was applied to the shale rock samples in which mode II fractures were identifiable. This study demonstrated a cost- and time-effective approach to evaluating fracture properties of materials from small samples, which is valuable when limited samples are available and time/cost are of constraint.