Research On Dynamic Fracture Toughness Of Rock Determined By Three-dimensional Analysis Method

Rock dynamic fracture toughness can denote the resistance capacity of crack. The research is helpful to reveal the characteristics of rock fracture failure and provide a basis for geotechnical design parameters. Determining the dynamic fracture toughness of rock is difficult and more by two-dimensinoal method. In order to obtain a more reliable and accurate test value, it's necessary to study the effect of the specimen dimension.Analyzing the propagation of different loading waveform in the bar and the stress equilibrium in the specimen. The dynamic fracture tests of the HCFBD were performed. Using three-dimensional finite element model of disc specimen to solve the dynamic fracture toughness were compared with the two-dimensional method. Investigate the influence of disc specimen thickness on dynamic fracture toughness.The results show that the half-sine plus carrier can be able to maintain the one-dimensional propagation compared with the rectangle plus carrier in different distances of different diameters and different Poisson's ratio bar. It can be used as a ideal loading waveform for the non-homogeneous brittle materials. Changing dimensions and materials of the specimens will affect the stress balance at both ends. The stress imbalance present at both ends of disc specimen which is difficult to determine the load accurately in experimental-numerical method.Dynamic stress intensity factor curve of the three-dimensional crack front points is similar to the result of the two-dimensional method. The relative error of stress intensity factor between plane crack tip and the crack front midpoint is within 5%. The dynamic fracture toughness are different when crack fractured at different points. The relative error of the dynamic fracture toughness between the three-dimensional analysis and the plane analysis consisdering the fracture time affected by the thickness is limited to 1.2%, when specimens fractured from the middle of the crack front.The analysis of experimental data show that the stress equilibrium state at both ends is not obviously affected and the dynamic fracture toughness is discrete with the increase of the specimen thickness.Three-dimensional analysis can consider the actual situlation of crack initiation and obtain a more accurate dynamic fracture toughness value of rock.