Browsing by Author "Rizo, Zakhar"

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    Comparison of the Reliability of Strength Limit Calculation Methods for Prismatic Samples with Different Spreading of Normal Contact Stresses in Their Wedge Failure Shape
    (IOP Publishing Ltd, 2024) Vasyliev, Leonid; Vasyliev, Dmytro; Malich, Mykola H.; Rizo, Zakhar; Kress, Denys
    ENG: This article explores methods for calculating the strength limits of solid objects subjected to compression. Traditionally, two stress distribution patterns are used: the exponential pattern by E.P. Unksov and the linear pattern by L. Prandtl. The authors introduce an enhanced stress distribution method. They compare the accuracy of these methods in calculating strength limits and constructing "normal stress - longitudinal strain" diagrams for wedge-shaped failures in rock samples. Four properties are considered: shear strength, coefficients of internal and external friction, and elasticity modulus. The results show that, with an external friction coefficient up to 0.3, all methods yield similar accuracy in strength limit calculations and ultimate stress-strain curves. Some curves exhibit stress drops, explained by a transition from convex to concave slip lines during failure. Additionally, there are hardening curves in the ultimate curves without theoretical justification. The comparison of calculated strength limits with experimental data confirms the method's accuracy: 13.7% error for the exponential method, 11.4% for the linear method, and 8.1% for the enhanced distribution, especially for low contact friction values (up to fc=0.3).
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    Spall Fracture Forms of High Rock Samples under Uniaxial Compression
    (IOP Publishing Ltd, 2023) Vasyliev, Leonid; Bulich, Yurii; Vasyliev, Dmytro; Malich, Mykola G.; Rizo, Zakhar; Polishchuk, Alla; Kress, Denis; Kuttiubaev, Aidar
    ENG: Prof. L.I. Baron identified five forms of destruction during uniaxial compression of samples of regular geometry of rocks including truncated wedge, wedge, diagonal, longitudinal, and explosive forms. All of them are commonly characterized by the destruction of samples in their central parts showing two or more cracks, while the trajectories of crack development align with the corner points of the samples. Recently, was unexpectedly discovered a spall fracture in the form of a single crack emerged from the side wall of the specimen and propagating into it under uniaxial compression. Based on the discovery, the method for creating stress-strain diagrams for high rock samples was developed using four rock properties such as rock shear resistance limit, contact friction ratio, internal friction ratio, and modulus of elasticity. The stress-strain diagram of the spall fracture of high samples is described by a descending curve, which is typical for the diagrams of fracture created by two adjacent cracks of regular geometry samples. The maximum stresses required for the destruction of high rock samples are lower than those for the destruction of regular geometry samples of rocks with similar physical and mechanical properties.