Physics

Geology

Finite element method

Tension (geology)

Strain energy

Mechanics

Structural engineering

Operating system

Ultimate tensile strength

Optics

Computer graphics (images)

Engineering

Planar

Composite material

Materials science

Computer science

Mode (computer interface)

Anisotropy

Plane stress

Fracture (geology)

Fracture mechanics

Shear (geology)

Fracture toughness

Toughness

Theoretical and Applied Fracture Mechanics

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

On the anisotropy of shear fracture toughness in rocks