Quantitative analysis of grain size effect on tensile mechanical behavior of granite based on multi-level force chain networks

A three-dimensional grain-based model based on the discrete element method is proposed for reconstructing the filling and grouping of minerals in granite, then a batch of numerical disc specimens with different grain sizes R_G are subjected to the Brazilian splitting test. In addition, the force chain networks in the numerical samples are subjected to multi-level classification and quantitative analysis, and the grain size effect on the tensile mechanical behavior of granite is discussed from the perspective of force chain networks. The results show that the mechanical properties and micro-cracking behavior of fine- and coarse-grained samples obtained experimentally and from simulation are consistent, including the load–displacement curve, the peak load, the failure displacement, and the proportion of intergranular/transgranular cracks. Therefore, the reliability of the model is verified. As R_G increases, the number of intragranular contacts increases, while the number of intergranular contacts decreases. The bearing capacity and deformation resistance of the samples increase. As R_G increases, both the number and sum of force chains for intragranular structures increase gradually, while these two parameters for intergranular structures decrease; meanwhile, the average values for intragranular and intergranular structures increase with increasing R_G. As R_G continues to increase, the number of contacts within mineral grains capable of withstanding external loads increases, forming a robust force chain network to bear external loads. It becomes challenging for a low-level load to break the contacts within the mineral, leading to an increase in the sample’s load-bearing capacity.