Features of strain localization in sylvinite under tension

This work is devoted to investigation of spatio-temporal localization of deformation at the direct uniaxial tensile of sylvinite with using of digital image correlation method and acoustic emission technique. For the implementation of direct tension there was used a special reversing device allowing to convert compressive force into tensile. Samples are concreted into the device before the experiment. Sequentially photographed images of side surfaces of specimens were used to reconstruct the distribution of components of displacement vector field and strain tensor on the side of sylvinite samples under uniaxial quasi-static tension. As result of obtained data analysis it is found that the deformation process occurs as two consistently following forms of spatiotemporal localization: a system of equidistantly located stationary foci of localized deformation and a single stationary dissipative localized structure. Areas of specimen outside the localization zones are in the undeformed state, also as result of uniaxial quasistatic tension of specimen it is established that the zones of localized deformation can be tensile as well as compressive. The transition from one localization form to another occurs in the maximum stress vicinity and is accompanied by a sharp decrease in the concentration parameter. Concentration parameter characterizes the degree of interaction between defects of different scale levels through their elastic fields and can be estimated from the acoustic emission data. Analysis of dependence of the spatial period of localized deformation bands on the size of computational cell showed that localized deformation bands are self-similar structures and process of deformation is localized at the grain boundaries minerals composing the sample.