Abstract:The interaction between cracks is an important research content of fracture mechanics. However, there are few studies on the internal cracks interactions. Based on 3D-ILC, parallel internal cracks in the brittle solids have been generated. Experimental research were performed on the Brazilian discs with the cracks. The process of crack propagation was recorded, the law of the stress birefringence, the failure load and the fracture characteristics were analyzed. Based on the M integral and strain energy density factor theory, the distribution of K_Ⅰ, K_Ⅱ, K_Ⅲ was revealed and the crack propagation were simulated as well. The results showed that: 1) The applicability of the technique 3D-ILC was proved in the research of multi-internal crack interactions. 2) The failure morphology included symmetric sphincter crack, upper wing crack, lower wing crack, secondary crack, vertical crack and penetrating crack. The smooth region of the wing crack fracture was type Ⅰ-Ⅱ crack, the side was type Ⅰ-Ⅱ-Ⅲ crack with lances-like surface; 3) The failure load of the sample with internal cracks was 17.73% of that of intact sample. The relationship between internal crack growth rate and loading force followed a nonlinear rule. 4) There was shieling interaction between the two internal cracks. 5) Based on the M-integral and strain energy density factor theory, the numerical simulation results were in accordance with that of the experiment. The results provide a physical test and numerical simulation reference for the study of three-dimensional internal crack Ⅰ-Ⅱ-Ⅲ composite fracture and multi-crack interaction.