On the anisotropy of shear fracture toughness in rocks

Experimental and theoretical analyses are presented that assess true mode II fracture toughness, KIIc, energy, GIIc, associated process zone (FPZ) in anisotropic rocks. The term signifies the type of crack grows a self-planar manner as result shear stresses, thus differentiates it from generic often extends by forming tension-induced kink. We give basis for sinusoidal variation present simplified relations direction dependence GIIc an plane. Our experimental data on Grimsel Granite validate this model, thereby providing supporting evidence KIIc rock indeed follows sinusoid function. This model takes only two principal values to characterise toughness energy any within also show noticeably higher than ones I, one must distinguish between these when formulating growth criteria Lastly, thorough analysis strain localisation obtained digital image correlation gives insight nature FPZ, demonstrates FPZ is semi-elliptical shape has comparable size with I crack.