Influence of the shape of an inclusion on the stress distribution in rock

Abstract

In the long run, the strength of rock is determined by the strength of the bonds between atoms in the crystals and on their contacts.As is known, fracture is initially local in nature and can be associated with the rupture of the weakest bonds as well as with the nonuniformity in the stress distribution in the rocks under loading [I]. Here a different kind of defect in structure, inclusion, pore, etc. are the stress concentrators that contribute to overstressing of the bonds in such sections and facilitate rupture.Results of simulating the stress distribution around inclusions in rocks are represented in this paper.We started from the fact that the microstresses are concentrated near a phase which is less in the material independently of its density.Moreover, the magnitude of the stress is associated with different radii of curvature of the surface of the minerals [2,3] comprising this rock or being present in the form of phenocrysts.We represented the theoretical estimates of the change in the stress state of the material containing inclusions and pores.Model experiments were performed using the photoelastic properties of the material [4] in order to confirm the dependence of the stress concentration zone power and their intensity of the crystal shape (inclusion).The models were fabricated as follows: cavities were made in organic glass (polymethyl metacrylate) blocks, wherein were embedded quartz globules and quartz crystal cuts (perpendicular to the C axis) of hexagonal shape.Then the cavities were filled with methylmetacrylate and subjected to polymerization.Therefore, the quartz specimens were polymerized in the organic glass and the stresses originating therein during fabrication of the cavities in which the quartz inclusions were placed were eliminated, i.e., the stresses are associated only with the size and shape of the inclusions.The size of the specimen ready for testing was 80 x 50 x 140 mm.In this case stresses associated with the presence of the quartz inclusions occur during loading of the organic glass (compression). The difference in the magnitude of the stresses and their distribution is due to the different radii of curvature of the inclusions.The magnitude of the quartz and polymethyl metacrylate bond is determined by adhesion and the specific energy of the adhesion is ~ = i-i0 J/mm 2 [5]. The magnitude of the stresses originating in the tests was determined by the photoelastic properties of the organic glass in the unloaded specimens and under 2-12 kN loads (stresses along the greatest axis).The stress bands are seen in the photograph of an organic glass specimen with quartz inclusions