Development of a crack growth predictor for geomaterials using detrended fluctuation analysis and optical flow method

Several conventional methods like seismic, microseismic, acoustic, electromagnetic etc. have been proposed to investigate the crack initiation and growth in rocks during static and dynamic loading conditions. These conventional sensors are prone to acquire noise and moreover these methods do not provide comprehensive knowledge about failure process since data are collected at a few points attached to a rock sample. This paper presents the application of detrended fluctuation analysis method and optical flow method of image analysis for analyzing failure mechanism of rock specimen under uniaxial loading condition. Two predictors, normalized cumulative fluctuation coefficient (NCFC) and normalized cumulative standard deviation of strain (NCSS) have been developed for forecasting the same. Both the predictors are developed by analyzing consecutive image frames under incremental loading conditions and are found to be powerful markers for categorizing the crack initiation period, stable crack growth period and collapse period in the rock failure process. It is also obtained that NCFC and NCSS produce almost similar results even if they are derived using different image analysis concepts. Numerous laboratory experiments have been conducted to check the applicability of the both the predictors. Based on the experimental data, it is envisaged that both the predictors can be used as precursors for monitoring rock failure mechanism.