Time-Dependent Damage and Creep of Brittle Rock

摘要

Results of a combined analytical-experimental study of the relationship between subcritical microcrack growth due to stress corrosion and the time-dependent deformation and failure of brittle rock are reported. An analysis of creep and failure under uniaxial stress was performed using a continuum damage model. The model includes evolutionary equations which describe the growth of microcracks due to stress corrosion as well as incremental increases in applied stress. Also, the effect of interaction between neighboring cracks on the rate of crack growth is included. The model was used to predict the relationship between strain rate and failure stress for uniaxial compression at constant strain rate. These results are compared to the results of uniaxial compression experiments on Tennessee marble. A further implication of the analytical results is that if the material is stressed below a threshold stress level and allowed to creep, the creep rate should decay to zero over time and no failure will occur. However, if the threshold stress level is exceeded, the damage level will continue to evolve, resulting in an eventual acceleration of the creep rate (tertiary creep) and failure. To test this result, creep experiments at stress levels above and below the threshold stress level determined from the constant strain rate tests were performed. The results tend to confirm the model prediction; however, because only relatively short term tests could be performed (10 to 15 days maximum), we were not able to observe a complete decay of the creep rate at stresses below the threshold. (ERA citation 10:047459)