Method for determination of dynamic fracture toughness of rock using holed-cracked flattened disk specimen

There is no standard for the determination of dynamic fracture toughness of rock because of the difficulty to make a rock specimen with ideal initial crack and the complexity to study the dynamic fracture problem. A flattened marble disk specimen having a centre hole and initial cracks with width less than 1 mm was made for the dynamic test. The dynamic fracture tests were performed with the split Hopkinson pressure bar equipment, and the dynamic toughness was determined by the experiment combined with numerical analysis. Based on the one-dimensional stress wave theory, the loading P(t) on the specimen was got from the strain gauge on the Hopkinson bar and the fracture time tf was got from the strain gauge on the sample. The dynamic fracture toughness KId was determined by the corresponding fracture time tf, and the dynamic stress intensity factor history KI(t) was calculated using the loading P(t) as input for the finite element analysis.