Laboratory tests show that various splitting lines along the loading direction have been observed in Brazilian test. This is mainly due to the fact that the majority of rock materials are normally not homogeneous materials. In most laboratory tests, the main features of macro-fracture patterns within heterogeneous rock materials may vary from specimen to specimen owing to the differences of local heterogeneity. Thus, numerical simulation is conducted to study the heterogeneities of rock material under Brazilian tests in this paper. This is achieved through a well-developed distinct lattice spring model (DLSM). One of the main features of DLSM is that it can explicitly represent the microstructure of rock materials, which enable DLSM to model mechanical fracturing problems and to study the effects of heterogeneity on rock samples under Brazilian test. Numerical study demonstrates that, porosity and the distribution of pores and fractures contribute to the divergence of tensile strength and the final failure mode. Rock samples with lower porosities are featured with higher tensile strength and more brittle behaviors, and vice versa.
Generally, rock materials show different mechanical behaviors under compressive and tensile conditions owing to their different strength parameters: elastic compressive modulus Ec and elastic tensile modulus Et. The elastic compressive modulus Ec can be easily obtained through conventional uniaxial compressive test, while the tensile strength of rock material is generally obtained through the indirect approach-Brazilian test . Laboratory tests show that various splitting lines along the loading direction have been observed in Brazilian tests. This is mainly due to the fact that the majority of rock materials encountered in Civil and Mining Engineering are normally not homogeneous materials . In most laboratory tests, the main features of macro-fracture patterns within heterogeneous rock materials may vary from specimen to specimen due to the differences of local heterogeneity . Also, it is found that the same rock material with low porosities behave more brittle than those with high porosity, being regarded as hard rock . However, these experimental work normally can only demonstrate the macro-scale behaviors of heterogeneous rock. Fundamentally, when a Brazilian disc is loaded predominantly in compression, large compressive stresses may concentrate on the contact area between sub-grains in microscopic view. Meanwhile, macro failure eventually occurs when some substantial tensile stresses are generated within the disc, and it is characterized by disc splitting along a plane/planes that parallel to the loading direction . Obviously, these fundamental mechanisms of splitting failure of the Brazilian discs cannot be investigated well through macroscopic laboratory test.