Numerical simulation of rock failure under static and dynamic loading by splitting test of circular ring

Tensile and shear fracture are the two main failure modes for rock and rock-like materials. Since its discovery, the Brazilian test has been extensively used to obtain tensile strength and also measure the toughness of brittle material such as rocks despite the various shortcomings inherent to it. Over the years, the fracture process of brittle materials has been a critical issue in fracture mechanics. As a consequence, this topic has been widely researched where experimental, analytical, and numerical approaches have all been employed to study the failure processes of rocks and rock like materials. Generally, it has been noted that numerical based methods better capture the transition from continuum to a dis-continuum state. Even better, several of these techniques can be integrated into a single tool hence offering a more profound solution to the fracture problem, for example, the integration of finite element method and discrete element method. Therefore, this provides the opportunity to integrate other techniques and observe the suitability of the generated results.

Central South University researchers in China, Professor Xibing Li and Fan Feng (PhD Student) and Professor Diyuan Li investigated the failure mode and strength characteristics of brittle hard rocks under static and dynamic loading by the simulation scheme. They choose to adopt the approach combining the finite element method and the discrete element method, named ELFEN, to simulate and investigate the failure process of a typical hard rock under static and dynamic splitting ring tests. Their work is currently published in the research journal, Engineering Fracture Mechanics.

They commenced their research work by first validating the FDEM software through simulations of Brazilian disk test under static loading. Next, they studied the failure of circular ring specimens under static and dynamic loading, with the ratio of internal to external diameter of the specimen groups varying from 0.1 to 0.6, with increments of 0.1. Afterwards, they introduced a rational load value so as to calculate the tensile strength of circular rock ring specimens under the splitting ring test. Lastly, they compared the numerical results obtained from their technique to previous experimental data, and found a good agreement between the numerical and experimental results.

They commenced their research work by first validating the FDEM software through simulations of Brazilian disk test under static loading. Next, they studied the failure of circular ring specimens under static and dynamic loading, with the ratio of internal to external diameter of the specimen groups varying from 0.1 to 0.6, with increments of 0.1. Afterwards, they introduced a rational load value so as to calculate the tensile strength of circular rock ring specimens under the splitting ring test. Lastly, they compared the numerical results obtained from their technique to previous experimental data, and found a good agreement between the numerical and experimental results.

The authors observed that under the static loading, with the increase in internal diameter, the failure mode was transformed from diametrical splitting to four-fan-shaped failure. The researchers also noted that under the dynamic loading, four-fan-shaped failure also occurred from geometric axial symmetry to axial asymmetry, which meant that, with increasing internal diameter, the tensile cracks along the horizontal diametrical direction gradually deviated toward the top loading platen. Overall, it was seen that the peak load of the circular ring had a descending trend with the increase in internal diameter under both loading conditions.

The study successfully employed the FDEM approach (ELFEN) to model the fracture process and failure characteristics of Carrara marble specimens by the splitting ring test, including both static and dynamic loading conditions. Generally, the numerical results obtained showed that the ratio of internal to external diameters and loading conditions were the main factors that affected the final failure modes and tensile strengths of the circular rock ring specimens. Altogether, the FDEM approach is an effective and convenient way to study the failure processes of rocks or rock-like materials.