Papers by Keyword: Stress State

Abstract: The paper proposes an approach to studying the influence of changes in the mechanical characteristics of the material under the influence of plastic deformations in foam materials on changes in their mechanical behaviour. The research was conducted for the case of unsteady multi-cycle loading, which caused plastic deformations, but did not cause material failure. The modelling was carried out in a general unsteady formulation within the framework of Cosserat elasticity, which made it possible to take into account the influence of the heterogeneity of the structure of materials. The proposed methodology is based on the combined use of the method of integral transformations and the indirect boundary element approach. To solve the unsteady problem within the framework of couple elasticity, the time integral and discrete Fourier transform were used in the paper. The assessment of the change in the mechanical, physical and microstructural characteristics of foams under the action of loads causing plastic deformations was carried out on the basis of experimental studies of a series of polyurethane foam samples. Using experimental data based on developed analytical-numerical method [4], the change in the distribution of normalized radial stresses in the internal layers of foam media was investigated, taking into account changes in mechanical, physical, and microstructural characteristics. The use of the approach proposed in the paper makes it possible to assess the change in the residual resource of bodies made of foam materials in the case of short-term loads that cause plastic deformations of the medium.

Abstract: Elastomer-cable ropes (ECR) can be used as tractive and transporting elements in mine hoisting installations, powerful conveyors, or as stay ropes in permanent structures. The operating conditions and design of such ropes may differ in various conditions; however, the composite structure of ropes has its unique advantages in industrial applications. Article purpose is determining the influence of cable design on a stress state of elastic shell in a elastomer-cable rope. Article methodology is in numerical calculation using CAD and an analytical method used in strength of materials. Dependency of a stress-strain state is established for a elastomer-cable rope (belt) shell, which is loaded by a force evenly distributed among the cables, considering helical strand shape and periodical placement of cables with opposite twisting directions in a rope (belt). Energy loss values due to cable and elastomer-cable rope design are established. The scientific novelty of the article is in establishing that a helical strand shape of cables causes a twisting moment (torque) that is proportional to a part of an internal loading force on cables, which is transmitted by strands, a sine of inclination angle of helical strands and a distance between centers of strands cross-sections and cable axis. Stresses in the elastic shell decrease when cable placement spacing increases and does not exceed 1.7 cable diameters. Practical significance of the article is in establishing the dependency of a stress state of elastic shell in a elastomer-cable rope on rope and cable design, which allows taking into account this phenomenon during the rope design phase, increase of accuracy of determining its stress-strain state and reliability during operation in mine hoisting installations, powerful conveyors or permanent structures.

Abstract: Medium-Mn steel (MMnS) is a promising candidate of the third generation of advanced high strength steels (AHSS), which can provide superior tensile properties. To consider the edge crack issues, the local formability, as an indicator of fracture resistance, of the MMnS needs to be quantitatively evaluated for their potential application to industries. Thus, the local formability of two different MMnS is evaluated by the forming limits at fracture using the damage mechanics approaches and compared with a DP1000 steel in this study. Despite the superior tensile properties, the local formability of the investigated MMnS is worse than the DP1000, which is characterized by the fracture strain under different stress states. Therefore, for the assessment of their potential application in automotive industries, it is recommended that more attention should be paid to the local formability and fracture resistance of these advanced high strength steels.

Abstract: Both experimental method and numerical method are used to analyze the large variation in the material ductility of high pressure die casting (HPDC) Aural-2 alloy in the present work. The X-ray tomography (XRT) technique is used to characterize and reveal the significant variation of the internal porosity for the investigated material. The Mises plasticity model in conjunction with a mixed Swift-Voce hardening law, and a stress state dependent fracture initiation criterion are used to accurately describe the deformation response of the material. Very good agreement with the experimental results is obtained in the predicted average force-displacement responses for the calibrated stress states. A probabilistic damage mechanics model is put forward to depict the apparent stochastic ductile fracture behavior over a wide range of stress states. The 5^th and 95^th percentiles of the fracture initiation locus are recalibrated based on the proposed probabilistic ductile fracture model, which could provide an almost perfect prediction of the maximum and minimum bounds of force-displacement curves.

Abstract: The research purpose is to develop an approach for determining the stress concentration near the holes in composite structure elements reinforced with carbon fibres. The research is performed on the basis of a numerical-analytic approach using the method of singular integral equations. The paper studies the stress concentration near the holes in composite plate elements of the structures, which are reinforced with carbon fibres. The stresses are determined based on the singular integral equations. The integral equations are solved numerically using the mechanical quadrature method. The stress in the strip is studied at: longitudinal tension; pure bending; three-point bending; with periodically spaced holes. An approach to calculating the stresses in composite strips weakened by holes of different shapes, based on the method of integral equations, has been developed. The equation kernels are formulated on the basis of Green's functions, under which the boundary conditions on straight-line boundaries are satisfied identically. A methodology for calculating the stress concentration near the holes of arbitrary shape in plate elements of the structures has been developed. The results obtained can be used when calculating the strength of composite materials reinforced with carbon fibres.

Abstract: Taking the standard sand of Fujian as the test material, this paper concentrates on studying the influence of different stress increment directions on the direction of plastic strain increment of sand materials under different stress states and the underlying mechanism. The test results show that the plastic strain increment angle rotates counterclockwise with the increase of stress increment direction angle, but the two angles do not coincide; the higher the stress state parameters is, the larger the stress increment direction angle range corresponding to sand dilatation is, the smaller the plastic strain increment direction angle range is, and the plastic volumetric strain still increases in critical state.The plastic flow mechanism of sand is explained from the average stress increment, generalized shear stress increment and stress state, which may provide theoretical reference and numerical support for the related research of plastic strain increment direction of sand.

Abstract: The Stress and strain state of building structures in zones with bird's mouths and cuts of the boundary is characterized by stress concentration zones emergence and requires an evaluation of strength and reliability of objects, which is the engineering practice actual task. Theoretical analysis of stress and strain state of bird's mouth areas of the region boundary is confined to the study of singular solutions of the elasticity problem with power singularities. In this case, the concept of stress or strain concentration at an irregular point of the region boundary becomes meaningless. In the present article, stress and strain state is considered in the neighborhood of the bird's mouth vertex of the boundary of a plane region, which is written with the help of the intensity factors. Two approaches are given to obtaining the expressions for displacements, stresses in the neighborhoods of an irregular point of the boundary of a plane region by means of stress intensity factors and strain intensity factors. The difference in the expressions for stresses and displacements obtained for the limiting values of stresses and strains determines the practical significance of the work during the experiments and the determination of the critical values of stresses and strains.

Abstract: Wood cells are composed of cellulose, hemicellulose, and lignin. Geometrically we can idealize them as a set of hollow cylinders touching each other on the cylinder surface. The continuous displacements and stress state transmission are assumed on the cylinder surfaces. The article investigates stress development which is influenced by the wood cell axial elongation. Material properties of individual constituents are generally described by nine parameters characterizing orthotropic elastic material. Transversely isotropic constitutive model of was chosen for simplification. The analytical solution of the stress state was driven by the ideas of displacement method. Material parameters have been estimated according to available literature. The main task of our investigation was focused on the effect of transversal contraction. The actual calculation results are surprising and lead to reflection. These considerations and conclusions are summarized at the end of the paper.

Abstract: At present, hard-to-machine materials such as structural alloy steels with various chemical element additives – tungsten, chromium, etc. - are most widely used in engineering. When conventional finish methods are used for the treatment of hard-to-machine materials, the most important problems are the difficulty of obtaining work surfaces of a required quality in terms of accuracy, roughness and the physicochemical composition, and the low output. In the present paper, a finish method for metal treatment– grinding – is discussed. Zones of the formation of the surface stress state due to heating have been revealed: the zone of an insignificant increase in temperature in the contour of the contact of a grinding wheel and a work surface; the zone of the temperature intensive growth; and the zone of the temperature abrupt drop. The investigation has been conducted of the surface layer structure of high-strength and high-chromium steels during high-speed heating – grinding. The peculiarities of the change of the surface layer state of the above steels have been revealed after grinding with the use of conventional grinding wheels with a continuous cutting surface and a discontinuous cutting surface. Some recommendations are given for grinding of the high-strength ₁₂Cr₁₈Ni₉ and high-chromium Cr₁₂, Cr₁₂Mo and Cr₁₂V steels, taking into account the specific features of different technological situation characteristic of a specific grinding tool, a grinding tool grade, and conditions of grinding and cutting.

Abstract: ANNOTATIONThis article proposes an approach to the prediction of stress state and assessing the strength of a circular tunnel lining and the surrounding rock mass under construction near the production used by the micro-tunneling technology of pipe ramming. The basis of this method is an analytical solution of the corresponding plane problem of elasticity theory.