Issue 52

C. Caselle et alii, Frattura ed Integrità Strutturale, 52 (2020) 247-255; DOI: 10.3221/IGF-ESIS.52.19 252 Beside the presence of a brittle deformation (explicated in form of failure surface), the sample deformed at Pc = 4 MPa shows some evidences of a plastic intra-crystalline deformation (e.g. Fig. 7b). Figure 6: Stepping failure coalescence registered with DIC analysis. Each line reports six maps of lateral strains. The position of the maps is shown by the blue dots in the stress-strain graphs a. First stress drop, with the first evidence of a crack. b. Accretion of the failure surface. c. Coalescence of two failure edges in the upper part of the sample. d. Complete coalescence of the failure on the entire surface of the sample. Figure 7: Micrographs of gypsum sample deformed with a confining pressure of 4 MPa. a. Failure surface and evidences of grain crashing at optical microscope in reflected light. b. Kinked grain, in optical microscope with crossed nicols. c. Failure surface, observed at the SEM. At Pc = 6 MPa, the brittle regime is still the principal mode of strain accommodation, with the presence of a well-defined failure surface (Fig. 8a). However, the thin section reveals the additional presence of a conjugate structure. As can be seen