Reserch On The Effect Of The Prefab Crack Shape On The Rock Fracture Toughness Tested Using Disc Specimen

Rock fracture toughness is used to describe the capability of resisting the fracture because of the crack extension in the rock material, which is an inherent property. It produced a great impact on rock fracture toughness determined by laboratory tests when the man-made crack owned different shape. This paper studys the effect of man-made crack shape on testing fracture toughness of rock for disc specimen, based on the method that the experimental research was combined with the numerical computation.The effect was compared and analyzed that the different crack width and shape at crack tip resulted in the change on stress intensity factor for disc specimens, through numerical computation of finite element software ANSYS. With the increase of rectangular-shaped crack width in the range of 0.55～2.02mm for disc specimen, stress concentration at crack tip decreased gradually, and the maximum dimensionless stress intensity factor increased. As ellipticity increased in the crack tip which was in the range of 0～1.6 and fixed crack width lmm, stress concentration at the crack tip increased, and the tendency of maximum dimensionless stress intensity factor appears first decrease, then increase, finally decrease.Produced cracked flattened disc specimens with a center hole by using homogeneous white marble, which owned three shapes at the crack tip and crack width of 0.55mm,0.64mm,1.08mm,1.3mm,1.42mm,1.94mm,2.02mm, the paper studys the effect of the crack tip and width of disc specimen on rock fracture toughness tested by using experiment and numerical computation. In the overall trend, with the crack width of disc specimen increasing, the fracture toughness of rock increased, and the average value of rock fracture toughness was 1.369MPa·m1/2. Under the same shape in crack tip, the rate of increase was the smallest in the determination of rock fracture toughness through cusp-shaped cracked disc specimens, and that of rectangular-shaped cracked disc specimen was the largest. If the fracture toughness of rock was determined by the first peak load and without considering the crack width, when man-made crack width were less than 0.64mm, the result was very close to the average fracture toughness determined by using loal minimum load.