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Experimental study on time-dependent stress and strain of in-plane shear (Mode Ⅱ) fracture process of rock

王志  饶秋华  谢海峰  
【摘要】:正Shear-box test with strain measurement was used to study time-dependent stress and strain of in-plane shear(Mode Ⅱ) fracture process of rock and to reveal the mechanism of Mode Ⅱ fracture.Numerical results show that the maximum shear stress τ_(max)at the crack tip is much larger than the maximum tensile stress σ_1 and the ratio of τ_(max)/σ_1 is about 5,which favors Mode Ⅱ fracture of rock.Test results indicate that the strain—time curve comprises three stages:the linear deformation stage,the micro-cracking stage and the macroscopic crack propagation.The strain in the direction of the original notch plane is negative,due to restraining effect of compressive loading applied to the original notch plane.Both σ_1.and τ_(max)are increased as the load increases,but the slope of τ_(max)is larger than that of σ_1 and the value of τ_(max)is always larger than that of σ_1.Therefore,τ_(max)reaches its limited value at peak load before σ_1 and results in Mode Ⅱ fracture of rock.Shear-box(i.e.compression-shear)test becomes a potential standard method for achieving the true Mode Ⅱ fracture and determining Mode Ⅱ fracture toughness of rock.

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