Effects of Loading Rate and Notch Geometry on Dynamic Fracture Behavior of Rocks Containing Blunt V-Notched Defects.

Rock naturally contains numerous defects, and both loading rate and defect geometry affect the loading capacity of rock structures when subjected to dynamic impact loads. Understanding the rate-dependent mechanical response and characterizing geometry-related fracture parameter of defected rocks are crucial to safety assessment of rock engineering. In this paper, the effects of loading rate and notch parameter on dynamic brittle fracture behavior of Fangshan granite weakened by a blunt V-notch are experimentally studied. First, the dynamic fracture experiments on blunt V-notched semi-circular bend (BVNSCB) specimen of Fangshan granite with different notch geometries are performed using the split Hopkinson pressure bar (SHPB) system. Second, the dynamic fracture processes of blunt V-notched rocks are recorded using an ultrahigh-speed camera, and the mechanical responses to different impact loading conditions are obtained via digital image correlation (DIC) method. Third, the effects of loading rate and notch parameter on the dynamic fracture parameters including notch fracture toughness, crack propagation toughness, and crack velocity are discussed to reveal the fracture mechanism of blunt V-notched rocks subjected to impact loads. It is found that dynamic notch fracture toughness obtained from DIC method is usually larger than that measured directly from conventional maximum impact load method. The maximum tangential stress (MTS) criterion eliminating the effect of the fracture process zone (FPZ) at blunt V-notch tip is used to correct the apparent notch fracture toughness value measured from the maximum load method. The results show that corrected notch fracture toughness values are in good agreements with those obtained from the DIC method. This study is significant for dynamic fracture analyses and strength assessments of rock masses containing notches or other defects with complex geometry. Highlights: Effects of loading rate and notch geometry on dynamic fracture behavior of blunt V-notched rocks are studied. Dynamic notch fracture toughness and crack propagation toughness are simultaneously determined. DIC method is used to track the development of FPZ at blunt V-notch tip and quantify the FPZ length. [ABSTRACT FROM AUTHOR]