Subcritical crack growth of rocks using the double torsion method with consideration of the crack length

The double torsion (DT) load relaxation test method has been widely used to study the subcritical crack growth (SCG) of rocks because the determination of the stress intensity factor KIis independent of the crack length. However, such disregard of the crack length may affect the results of SCG parameters obtained from the typical double torsion test seriously. Based on the analytical method with consideration of the crack length, the experimental results of this paper show that the stress corrosion index n and the logarithm of SCG parameter ν0are adjusted up to a factor of 2.2 and 2.0 respectively when the crack length is considered. As such influence on SCG parameters will affect the prediction of the long-term subcritical cracking of materials, it is concluded that DT data should be analyzed with consideration of the crack length. However, the corrective method of Ciccotti et al. (2001) requires complicated interpolations when analyzing double torsion test data. This paper simplifies the corrective method to predict the SCG parameters of rocks with suggested specimen sizes by developing charts and tables.