Fracture of brittle solid material containing a single internal crack of different depths under three-point bending based on 3D-ILC

Abstract

3D internal cracks are commonly distributed in rock masses, and their initiation and subsequent growth are believed to be responsible for the brittle fracture of materials under external loading conditions. This paper presents an experimental and numerical research on the fracture behaviours of brittle solid materials containing 3D internal cracks under a three-point bending test. We tested a series of cuboid glass samples including intact samples (group A) and samples with a pre-existing 3D internal crack at different depths (group B). The 3D internal laser-engraved crack (3D-ILC) method was applied to the fabrication of the 3D internal crack in the glass without any damage to the surface of the sample. We used the visualisation method of the stress field on the transparent samples during the test and performed a qualitative analysis. The experimental results indicate that the existence of a 3D internal crack drastically degrades the mechanical properties of glass and the characteristic loads, for example, crack initiation and failure loads, are positively correlated with the depth of the internal crack. The internal crack located in the central cross-section of the sample generally grows in the plane and finally reaches the sample end, causing splitting, a mainly mode I fracture. Wallner lines and dynamic fracture features are observed on the fracture surface of samples with a pre-existing crack under a three-point bending test, which have rarely been observed in compression tests. The 3D-ILC method was proven efficient in the experimental investigation of brittle fracture of materials containing a prefabricated 3D internal crack. The numerical simulation obtained the KI distribution at the crack tip and the crack growth path, which were consistent with those of the experimental results showing the fracture mechanical mechanism.