Finite element analysis of anti-plane shear (Mode III) fracture mechanism of brittle rock

Finite element method is used to calculate the crack-tip stresses of rock specimens under anti-plane compression-shear loading in order to study the mechanism of anti-plane shear(Mode III) fracture.Numerical results show that both the tensile and shear stresses exist at the crack tip and the ratio of maximum shear stress to maximum tensile stress,τmax/σ1,is about 3~6.Since the additional compressive can restrain tensile stresses at the crack-tip,τmax can easily reach its limited value before σ1 and cause anti-plane shear(Mode III)fracture.Anti-plane shear-box test is a potential method for obtaining Mode III fracture of rock and determining Mode III fracture toughness KIIIC of rock.