Dynamic notched semi-circle bend (NSCB) method for measuring fracture properties of rocks: Fundamentals and applications

Rocks are increasingly used in extreme environments characterised by high loading rates and high confining pressures. Thus the fracture properties of rocks under dynamic loading and confinements are critical in various rock mechanics and rock engineering problems. Due to the transient nature of dynamic loading, the dynamic fracture tests of rocks are much more challenging than their static counterparts. Understanding the dynamic fracture behaviour of geomaterials relies significantly on suitable and reliable dynamic fracture testing methods. One of such methods is the notched semi-circle bend (NSCB) test combined with the advanced split Hopkinson pressure bar (SHPB) system, which has been recommended by the International Society for Rock Mechanics and Rock Engineering (ISRM) as the standard method for the determination of dynamic fracture toughness. The dynamic NSCB-SHPB method can provide detailed insights into dynamic fracture properties including initiation fracture toughness, fracture energy, propagation fracture toughness and fracture velocity. This review aims to fully describe the detailed principles and state-of-the-art applications of dynamic NSCB-SHPB techniques. The history and principles of dynamic NSCB-SHPB tests for rocks are outlined, and then the applications of dynamic NSCB-SHPB method (including the measurements of initiation and propagation fracture toughnesses and the limiting fracture velocity, the size effect and the digital image correlation (DIC) experiments) are discussed. Further, other applications of dynamic NSCB-SHPB techniques (i.e. the thermal, moisture and anisotropy effects on the dynamic fracture properties of geomaterials, and dynamic fracture toughness of geomaterials under pre-loading and hydrostatic pressures) are presented.