All the tests described above were done in compression
These features are visible in the post peak regime of the stress–strain curves in Fig. 8 as multiple minor peaks. The characteristics of the post-failure behaviour cover an essential part of brittleness and its impact on the properties of the failed rock, but are not fully caught by any of the brittleness index parameters defined in Table 1.
Fig. 9. Failure pattern after Brazilian tests on 2 samples of Mancos Shale.