The cracked chevron notched semi-circular bending (CCNSCB) method falls into a significant testing category of chevron notched specimens for measuring the mode I fracture toughness, of which the progressive fracture mechanism deserves to be further assessed. In this study, the discrete element method (DEM) is adopted to depict the fracture processes of the CCNSCB specimens considering different supporting spans and heterogeneity. Our results demonstrate that the crack front of the CCNSCB specimen with any loading condition is prominently curved, which violates the straight-through crack propagation assumption and may induce some errors in the fracture toughness measurements. The peak force of the CCNSCB specimens evidently increase with decreased supporting span. For a relatively large span, the crack grows restrictively in the notched ligament, which conforms to the ideal assumption of the fracture process and contributes to an accurate measurement of the mode I fracture toughness. Thus, a large supporting span is suggested for the semi-circular bend tests. In addition, the tanglesome weak elements distribution in the heterogeneous specimen can disturb stress distribution, and the more heterogeneous specimen corresponds to the lower peak force. This study calls for more attention on how to accurately determine the fracture toughness via chevron notched samples.

1. Introduction
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