LAUSR

A series of dynamic fracture experiments on semicircular bend (SCB) marble specimens were conducted to characterize the loading rate effect using the INSTRON testing machine and the modified SHPB testing system. The fracture toughness of the marble specimens was measured from a low loading rate to a high loading rate (10-3~106 MPa·m1/2s-1). The results show that the fracture toughness will increase with the loading rate. Since the fracture toughness at a magnitude of 10-3 MPa·m1/2s-1 is regarded as the static fracture toughness, the specific value of (the dynamic increase factor of fracture toughness) can be obtained at the other loading magnitudes from dynamic fracture tests. To describe the variation in from low to high loading rates, a new continuous model of was put forward to express the quantitative relation between the loading rate and rock dynamic fracture toughness. It is shown that the new model can accurately describe the loading rate effect on the dynamic fracture testing data for rock materials.