Abstract
A hybrid finite-discrete element method (FDEM) is proposed to model rock fracture initiation and propagation during a three-point bending test under quasistatic and dynamic loading conditions. Three fracture models have been implemented in the FDEM to model the transition from continuum to discontinuum through fracture and fragmentation. The loading rate effect on rock behaviour has been taken into account by the implementation of the relationship between the static and dynamic rock strengths derived from dynamic rock fracture experiments. The Brazilian tensile strength test has been modelled to calibrate the FDEM. The FDEM can well model the stress and fracture propagation and well show the stress distribution along the vertical diameter of the disc during the Brazilian tensile strength test. Then, FDEM is implemented to study the rock fracture process during three-point bending tests under quasistatic and dynamic loading conditions. The FDEM has well modelled the stress and fracture propagation and can obtain reasonable fracture toughness. After that, the effects of the loading rate on the rock strength and rock fracture toughness are discussed, and the mesh size and mesh orientation on the fracture patterns are also discussed. It is concluded that the FDEM can well model the rock fracture process by the implementation of the three fracture models. The FDEM can capture the loading rate effect on rock strength and rock fracture toughness. The FDEM is a valuable tool for studying the rock behaviour on the dynamic loading although the proposed method is sensitive to the mesh size and mesh orientation.
Highlights
It is concluded that the finite-discrete element method (FDEM) can well model the rock fracture process by the implementation of the three fracture models. e FDEM can capture the loading rate effect on rock strength and rock fracture toughness. e FDEM is a valuable tool for studying the rock behaviour on the dynamic loading the proposed method is sensitive to the mesh size and mesh orientation
A relationship between the static strength and the dynamic strength obtained through experimental tests has been implemented in the FDEM to characterize the loading rate effect on rock behaviours. e loading rate effect is considered through the implementation of a relationship between the static strength and the dynamic strength for modelling the dynamic rock fracture process. e purpose of this study is to illustrate the abilities of the proposed method in modelling the transition from continuum to discontinuum through fracture and fragmentation and to demonstrate the capabilities of the proposed method in capturing the effect of loading rate on rock behaviour
Conclusion e hybrid finite-discrete element method (FDEM) is proposed to model the rock fracture initiation and propagation process during a three-point bending test under quasistatic and dynamic loading conditions. ree fracture modes are implemented in the FDEM to model the transition from continuum to discontinuum through fracture and fragmentation, which make the FDEM superior to the traditional continuum-based finite element method and discontinuum-based discrete element method. e FDEM takes advantage of finite element method in describing elastic deformations and the capabilities of the discrete element method in capturing interactions and fracturing processes of solids
Summary
The FDEM is employed to model the Brazilian tensile strength (BTS) test. e modelled results are compared with the experiential result to calibrate the proposed method. To better calibrate the hybrid finite-discrete element method, the modelled BTS result (Figure 9(a)) is compared with the experimental result (Figure 9(b)) and the typical rock failure pattern in literature (Figure 9(c)) [27, 28]. It has a long fracture along the vertical diameter and two main damage areas on the top and bottom loading vicinities. A typical fracture propagation in the BTS test includes primary tensile cracking along the loading diameter, secondary cracking from the sides parallel to the primary cracks, and tertiary cracking due to shear failure at the contact areas between the loading plates and disc.
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