Numerical investigation on the dynamic progressive fracture mechanism of cracked chevron notched semi-circular bend specimens in split Hopkinson pressure bar tests

The cracked chevron notched semi-circular bend (CCNSCB) method has been utilized in split Hopkinson pressure bar (SHPB) tests to measure the rock dynamic mode I fracture toughness. However, the measuring principle has never been thoroughly evaluated. In this study, a three-dimensional discrete element method has been employed to numerically investigate the dynamic fracture mechanism of CCNSCB specimens in SHPB testing considering different loading rates and supporting spans. Our results show that, even if the dynamic force balance can be efficiently satisfied, the conventional quasi-static analysis can still be questionable. For specimens with smaller supporting spans, the developing crack fronts are rather curved during the loading process, and the critical crack length is highly dependent on the loading rates. While for specimens with a large supporting span, the crack profiles are less affected and the critical crack fronts are finely confined within the chevron ligament with few undesirable damages. Thus, the CCNSCB method with a larger supporting span appear to be sound in the SHPB tests for measuring dynamic mode I fracture toughness of rocks.