Fracture of brittle solid with an internal penny-shaped crack: Semi-circular bending test and numerical simulation

Abstract

Semi-circular bending (SCB) tests are usually performed on samples with a bottom notch to investigate the mechanical properties of certain materials. Few studies have been conducted on the propagation of internal cracks in SCB tests despite the fact that the existence of internal defects is inevitable in most materials. When using the three-dimensional internal laser-engraved crack method, internal cracks are generated without causing any damage to the surfaces of the sample. Here, SCB tests are performed on samples with internal cracks at different depths. The crack growth process, failure mode, and macro- and micro-fractography are analyzed. Numerical simulations are carried out, revealing the distribution of the stress intensity factors around the crack tip and the internal crack growth path. The simulation results are consistent with those of the SCB tests. The results show that: (1) The propagation mode of internal cracks is mixed in the SCB tests; (2) The existence of internal cracks significantly reduces the failure load of the samples; (3) Dynamic fracture occurs in the intact samples of groups A and B1 (depth: 30 mm), while the failure of the samples of groups B2–B5 is due to the internal crack propagation. (4) Based on the J-integral and the maximum tensile stress criterion, the distribution of the stress intensity factors around the crack tip and the fracture path are in agreement with the test results.