Application of DIC analysis method to the study of failure initiation in gypsum rocks

Abstract

The measure of local strains of geomaterials under the application of an external load is significant to the study of mechanical properties of rocks. The application of image analysis methods (i.e. digital image correlation analysis) offers the possibility to have pointwise measures of local strains on the entire surface of the samples. Strain contributions in the different areas of the samples can be highlighted and diversified. In this study the methodology was tested on gypsum rock. Image analysis was conducted by means of Ncorr, an open-source two-dimensional digital image correlation Matlab software. The processing of consecutive images acquired during the execution of uniaxial compression tests allows for the identification of strain distributions and concentrations. The test was repeated for different angles of orientation of the anisotropy. If properly calibrated, the method may be used to highlight the influence of textural features of the rock materials, such as – in this case − anisotropy, on the mechanical behaviour. Features such as the localisation of the strain, the load thresholds that lead to the opening of the first microcracks and the way they reorganise to create the failure surface may be intensively investigated.