Abstract: Fracture mechanics is one of the basic disciplines in various industries. The semi-circular bending (SCB) test is a classic test used in the study of solid mechanics. At present, the research on SCB mainly focuses on surface cracks such as bottom notch or penetrating cracks. Whereas the internal cracks and internal defects that are the intrinsic properties of material have been seldomly researched employing the SCB test. Based on the 3D-ILC (3D-internal laser-engraved crack) method, an analysis was performed on the pure internal cracks with arbitrary parameters generated randomly given that surface had no influence on crack generation, internal cracks were created in SCB specimens and the specimens were assessed by the SCB test. Numerical simulation was performed to analyze the crack growth process, stress birefringence, I-II-III crack growth surface, failure pattern, and macro to micro fractography characteristics. Moreover, the distribution law of stress intensity factor and extension path were obtained that agreed with the physical test. The results show that: 1)The 3D-ILC method is useful for solving the problem of internal cracks in fracture mechanics. 2) Stress concentration is shown at the internal crack of stress nephogram, and significant variation occurs at the internal crack of SCB stress nephogram. 3) The compression-shear crack initiation occurs at the prefabricated crack of the SCB and develop into I-II-III mix-mode crack. The crack growth surfaces are divided into smooth zone and tear zone. The continuous growth is transformed into dynamic fracture and then failure, along with the mist zone and the hackle zone. 4) Based on the M-integral and maximum tensile-stress (MTS) theory, the numerical simulation of the specimens is carried out. The distribution of the stress intensity factor at the crack tip is given, and the crack growth path is simulated. The numerical simulation agrees with the experimental results. It provides experimental and theoretical basis for the study of SCB testing, internal cracks, I-II-III mix-mode fracture, simulation of crack propagation paths in the field of fracture mechanics.

Key words: 3D-ILC, 3D internal crack, I-II-III mix-mode crack, fracture mechanics, semi-circular bending (SCB) test, brittle solid