Investigation into the damage mechanism of concrete in the Brazilian test and flattened Brazilian test through the moment tensor

The acoustic emission technique and moment tensor inversion were applied to investigate and quantify the damage evolution process and intensity of microcracks in the Brazilian and flattened Brazilian concrete tests. The spatial and temporal evolution process of microcracks was monitored using the acoustic emission technique and the intensity of each AE event was computed based on the moment tensor analysis. The microcracks were classified into tensile cracks, shear cracks, and implosive cracks. The results of the Brazilian test demonstrated that microcracks gradually propagate from the zones between the loading points and center to the center and loading points. The results of the flattened Brazilian test showed that the initiation positions of microcracks were random and no crack accumulation phenomenon could be observed before the first peak of the load. Crack accumulation occurred near the center of the specimen when the first peak load was reached; cracks subsequently propagated to the platforms of the flattened Brazilian disk. The intensity of AE events induced by crack nucleation is small and the intensity of AE events caused by the propagation and coalescence of cracks is severe. The analysis results of the number and proportion of different types of cracks showed that the damage process of concrete in the Brazilian test and flattened Brazilian test are all dominated by the tensile mechanism.