Key Engineering Materials Vol. 743

Abstract: Problems of wave propagation in poroelastic bodies and media are considered. The behavior of the poroelastic medium is described by Biot theory for partially saturated material. Mathematical model is written in term of five basic functions – elastic skeleton displacements, pore water pressure and pore air pressure. Boundary element method (BEM) is used with step method of numerical inversion of Laplace transform to obtain the solution. Research is based on direct boundary integral equation of three-dimensional isotropic linear theory of poroelasticity. Green’s matrices and, based on it, boundary integral equations are written for basic differential equations in partial derivatives. Discrete analogue are obtained by applying the collocation method to a regularized boundary integral equation. To approximate the boundary consider its decomposition to a set of quadrangular and triangular 8-node biquadratic elements, where triangular elements are treated as singular quadrangular. Every element is mapped to a reference one. Interpolation nodes for boundary unknowns are a subset of geometrical boundary-element grid nodes. Local approximation follows the Goldshteyn’s generalized displacement-stress matched model: generalized boundary displacements are approximated by bilinear elements whereas generalized tractions are approximated by constant. Integrals in discretized boundary integral equations are calculated using Gaussian quadrature in combination with singularity decreasing and eliminating algorithms.

Abstract: The paper studies the stress-strain state of a surface longitudinally oriented crack in the wall of a vertical steel tank with specified volume of 20,000 m³. Surface non-through cracks are one of the main causes of tank failure. The prognostication of the crack critical dimensions requires analytical expression for the K-calibration function. K-calibration function is the dependence taking into account the change in dimensions, location of a defect and geometrical peculiarities of the structure as well. The calculation of the stress-intensity factor (SIF) of a surface longitudinally oriented crack located in the tank wall was performed using ANSYS Mechanical software. The cracks with various dimensions were studied by generating global finite-element model of the tank and a sub-model of the tank ring with a crack. MATLAB software was implemented to derive analytical expressions for K-calibration function of cracks with different shape located in the wall of vertical steel tank. All expressions for the K-calibration function are described by a polynominal function that allows estimating the critical size of a defect. The work results could be interesting for oil industry engineers.

Abstract: Mechanics of advanced materials, such as poro-, visco-or poroviscoelastic materials, is relevant to such disciplines as geophysics, geo-and biomechanics, seismology, constricting. Because of the complexity of the inertial viscosity and mechanical phases coupling in porous media most transient response problems can only be solved via numerical methods. The present work is dedicated to numerical modelling of a problem of a Heaviside-type impact load acting on a brittle slab situated above a fluid saturated foundation. Slab is treated as elastic or poroelastic rock. Fluid saturated foundation is a soil and modeled as a poroviscoelastic media. Poroviscoelastic formulation is based on Biot’s theory of poroelasticity in combination with elastic-viscoelastic correspondence principle. Classical models of viscoelasticity are employed, such as Kelvin-Voight model, standard linear solid model and model with weakly singular kernel. The problem is treated in Laplace domain. Direct boundary integral method approach is used to obtain solution. Modified Durbin’s algorithm of numerical inversion of Laplace transform is applied to perform solution in time domain. A problem of Heaviside-type vertical load acting on a slab bonded on a poroviscoelastic halfspace is considered. The comparison of dynamic responses when poroviscoelastic halfspace is described by different viscoelactic models is presented.

Abstract: The numerical simulation of biocomposites consisting of zirconia-based ceramics and cortical bone was performed with the use of a multilevel approach. The mechanical properties of the ceramic biocomposite were determined. The evolution of mesoscopic stress distributions in the biocomposite components during the process of its deformation was investigated, taking into account damage accumulation up to the fulfillment of the macro strength criterion. It is shown that damage accumulation has an impact on the stress distribution laws at the mesoscopic level, which is manifested through the appearance of a threshold for the stress distribution, as well as through a significant decrease in the distribution amplitude.

Abstract: 3D finite element simulation of behavior of composite VT6-AD1-D20 with the intermetallic layer at axial compression was carried out. The properties of the intermetallic interlayer were described using the model of Johnson-Holmquist. The effect of the aluminum layer thickness on failure deformation was defined.

Abstract: This article considers the issues related to the correct description of the internal structure of grain boundaries in metals. We offered a mathematical model describing grain boundaries formation as a result of two-sided crystallization by applying molecular dynamics method with third-type boundary conditions for heat extraction (Newton-Richman law). In the construction of the interatomic potential, the embedded atom method (EAM) is used. The work offers an algorithm for generation of initial conditions for two adjacent grains with different crystal lattices orientation and melt between them. To detect defects and defective areas we use a central symmetry parameter. The system energy before and after the crystallization process is estimated.

Abstract: In this article, the effect of a severe plastic deformation (SPD) achieved by groove pressing (GP) on the grain structure and mechanical properties of a rolled sheet Al-Mg alloy was investigated. The study of the microstructure of the samples before and after processing was carried out by means of electron backscattered diffraction (EBSD). The mechanical properties of the samples were experimentally studied under uniaxial tension in quasi-static conditions, and microhardness testing was implemented. It was found that the conventional yield strength and ultimate tensile strength increase by the factor of 1.4 and 1.5, respectively; and the microhardness increases by approximately 2.7 times after four machining sequences of the rolled sheet alloy. A bimodal grain structure, consisting of two grain types with particular features, is formed in the samples after four machining sequences of GP.

Abstract: The paper considers the features of the manifestation of dynamic strain aging (DSA) effect during severe plastic deformation processing via equal-channel angular pressing of low-carbon steel 10 and during the deformation processing via rolling of steel 20Kh. The deformation mechanisms under different regimes of deformation processing are analyzed. The temperature ranges for the manifestation of the DSA effect during the deformation by rolling of steel 20Kh and by equal-channel angular pressing of steel 10 are established. It is demonstrated that the deformation of low-carbon steels in the temperature range of DSA leads to further structure refinement and, as a consequence, to the enhancement in strength properties.

Abstract: Various contributions to the overall strength of the Cu-1Cu-0.7Al-0.2Zr alloy after the combined severe plastic deformation treatment have been calculated and compared with those after the standard industrial processing. Contrary to the common viewpoint, the SPD increases the strength not only due to the structure refinement, but also because of greater contribution of the dispersion strengthening. It is argued that this effect is linked to the deformation-induced phase transitions upon the SPD.

Abstract: This study examines the effect of severe plastic deformation on the physical and mechanical properties of a light structural Al-Mg alloy. Severe plastic deformation has been performed by equal channel angular pressing through a die with an angle of 90° between the channels to produce ultrafine-grained structure in specimens of studied alloy. A complex investigation of the physical and mechanical properties of the processed alloy has been carried out to examine the microstructure and texture, and to measure microhardness, yield stress and ultimate tensile strength. The obtained results demonstrate high efficiency of the chosen treatment method and mode of producing a light ultrafine-grained alloy.