Study of subcritical crack growth in andesite using the Double Torsion test

Subcritical crack growth is one of the main causes of time-dependent behavior in rocks. Double torsion (DT) tests have often been used to study subcritical crack growth in rocks. There are three methods used for the DT test, each with different loading conditions: the constant load (CL) method, the constant displacement (CDR) method, and the load relaxation (RLX) method. The RLX method is convenient, because the wide range of data of subcritical crack growth can be obtained with a single experimental run. In this study, subcritical crack growth in andesite was investigated using RLX method of the DT test. To determine the appropriate shape for the guide groove in DT specimens, tests were performed using rectangular, semi-circular, and triangular section grooves. The level of reproducibility of the test results was highest for specimens with a rectangular groove. Hence, this is an appropriate guide groove shape for DT specimens. DT tests were also performed for different water vapor pressures to investigate the effects on subcritical crack growth. The results showed that crack growth was facilitated at higher water vapor pressures. Additionally, the activation energy for subcritical crack growth in andesite was determined from the experimental results, and the crack velocity values for various temperature, humidity, and stress conditions were calculated theoretically. The crack velocity can be predicted from theory for various environmental and stress conditions. (c) 2005 Elsevier Ltd. All rights reserved.