Quantitative investigation on localized deformation process of rocks by uniaxial test and digital image correlation

Abstract

The uniaxial monotonic and cyclic loading tests were carried out. The acoustic emission (AE) events and surface deformation images in the loading process were obtained using the AE system and digital image correlation (DIC). The variance of the deformation field was introduced to reveal the formation and evolution processes of the localized deformation. The results show that the variance begins to increase significantly in the initiation of the macro-scale failure stage, and it increases sharply under cyclic loading before failure. The shape of the stress-variance hysteresis curve varies with increasing upper limit stress, and four types of stress-variance hysteresis curves were revealed. The damage variables are respectively defined by cumulative AE counts and variance, and the evolution process of damage variable can be divided into crack closure stage, initial damage stage, stable development stage, accelerated development stage and failure stage. By proposing the differentiation rate, it is found that there are apparent failure precursor points under monotonic and cyclic loading.