Parameters Of Stress-strain State Research Articles

GAS TURBINE ENGINES IMPELLERS FORCED VIBRATION AND STRESS-STRAIN STATE INVESTIGATION

The method of the gas turbine engine impeller forced vibration and stress-strain state parameters calculation is given. Using the finite element method, a refined mathematical model was developed for the several types of impellers most widespread in the practice of gas turbine engines building. The developed mathematical model takes into consideration the impeller blades geometric parameters and the construction of blades connectors. The results of its forced vibration frequencies calculation, caused by the influence of non-stationary gas flow are given for different types of the blades connectors. The dependencies of the impeller blades stress-strain state from the value its feather geometric perameters have been studied too.

Computer Simulation and Study of the New Forging Technology of Billets in a Step-Wedge Dies

The paper presents the results of a computer simulation of the drawing process in the step-wedge dies of two configurations: with wedge-shaped protrusions in the first and second sections of the top and bottom dies, and with a wedge-shaped protrusion in the first and second sections of the top die and wedge-shaped cavity in the first and second sections of the bottom die. A comparative analysis of the stress-strain state and energy-power parameters is carried out. Based on the analysis conclusions about the feasibility of choosing a specific configuration of step-wedge dies depending on the set aim were made.

Research of opening reliability of blast easily disposable systems with honeycomb polycarbonate sheets by finite elements method

In the article, the author presents results of mathematical modeling of operation of the venting relief structures made of honeycomb polycarbonate sheets and fixed in the standard window profiles, under the effect of explosion. In order to reproduce the explosion effect on venting relief structures, an approach to modeling dynamic systems was applied, which used a finite element method to approximate the basic general equations of dynamics added by the equations of the stress-strain state of a solid body. The applied approach differs by reproduction of the explosion process impact on the venting relief structures of this type by using equations which describe the motion of the dynamic system with accounting a contact interaction with the friction of honeycomb polycarbonate sheets and corresponding surfaces of the standard window profile locks. The honeycomb structure of the polycarbonate sheet was modeled by appropriate finite elements with considering the polycarbonate elastic properties. In order to implement numerical algorithms of this approach, a program code of the LS-DYNA computer system was used. The conducted numerical experiment on reproducing the explosion effect on the relief elements of this type of the venting relief structures made it possible to trace all stages of the honeycomb polycarbonate sheets deforming and moving under the action of explosion up to the exit of their edges from the window profile locks with the study of the corresponding stress-strain state parameters. By using this approach, reliably disclosure of the venting relief structures based on honeycomb polycarbonate sheets was investigated, and conditions for their reliable disclosure were identified with considering geometrical parameters of such type of venting relief structures opening and thickness of the honeycomb polycarbonate sheets. Results of the research have shown that reliable disclosure of the honeycomb polycarbonate sheets occurs within the range of the explosion overpressure, hence, confirming the effectiveness of such type of the venting relief structures used for protecting buildings against the explosion action.

The T-stress influence on the plastic zone size around the crack tip under the thermal load

A review of the fracture mechanics problems for estimating the safety of constructions with the crack-like defects is carried out. The need to develop a new methodology that combines the advantages of calculation and instrumental methods was revealed. The correlations between the most important fracture mechanics parameters and the characteristics of acoustic-emission signals proposed to use for estimating the parameters of stress-strain state. It is noted that considerable attention should be paid to the size and shape of the plastic zone in order to establish a theoretical relationship between the characteristics of acoustic signals and the fracture mechanics parameters. It is assumed that T-stresses are the cause of differences in the coefficients of the power dependence of the parameters of acoustic signals for the same values of the stress intensity factor. The task of finding the influence of T-stresses on the size of the plastic zone at the crack tip is set. A numerical modeling of thermal loading of a steel sheet with a central crack by the finite element method is carried out in order to determine the dependence of the crack tip plastic zone size on the stress intensity factor for several values of T-stress. Multiple calculations of the stress intensity factor and the T-stresses were performed for the several values of the cooling zone, using the parametric design language ANSYS APDL. By substituting the yield point of the material into the equations of linear elastic fracture mechanics, the specific volume and linear plastic zone size along the crack line were determined for the previously found values of the stress intensity factor and T-stress. A relationship between the fracture mechanics parameters and the plastic zone size at the crack tip was established using numerical methods. The assumptions that the T-stress influence to the plastic zone size are qualitatively confirmed. It is shown, that the negative values of T-stresses decrease the plastic zone size for a same value of the stress intensity factor.

Determination of the flow curve based on the torsion of conical specimen

The paper describes the existing methods for constructing hardening curves based on the torsion of continuous cylindrical and tubular samples. The advantages and disadvantages of the known methods are observed. It resulted in the development of an approach to determine the hardening curve based on the torsion of a conical specimen. The specific feature of the approach is that a conical specimen of definite shape as well as sizes is applied. The experimental tests and numerical simulations were performed. A model of the torsion of conical specimen was adopted to commercial finite-element code QFORM 9.0. It allowed to investigate numerically a problem of metal forming connected to the torsion of the specimen clamped between the rotated and fixed tools. The paper shows the results of experimental studies of conical samples made of steel 20H (analogue of AISI 5120H, DIN 20CrS4) in accordance with the proposed and traditional methods. The analysis of the results of experimental studies has also been done and presented here. The numerical model of the torsion of conical specimen allowed to investigate stress-strain state parameters distribution during the process.

The study of the complex thread knurling process

The study carried out to research a manufacturing process of long products for mining industry by a method of cold knurling, in particular, on a stud of a self-drilling bolt used for strengthening of mountain rocks. The solution of the task was obtained by mathematical simulation of the knurling process in the FE software package that allows establishing stress-strain state parameters necessary to analyze forming and loading of the process. According to the R&D carried out on a basis of the two-rolled screw thread rolling machine was developed a technological process for which the knurling rollers were design and created. The manufactured pilot batch of items that’s meeting the requirements for such type of anchors speaks of capability to maintain low-series production of self-drilling fasteners based on the complex profile cold knurling method of a long billet.

Stress-Strain State of the Bottom of the Casing String in the Horizontal Well

The purpose of the work is to develop the method for calculating the stress-strain state parameters of the bottom of the casing which is lowered into a horizontal well during its construction. When pushed into a well, a long casing string on the supports experiences cross bendings and bucklings which are caused by its own gravity and frictional forces created by axial forces of string compression. The latter are variables in length and depend on the reactions at the supports. The problem is solved by integrating the differential equation of the long rod buckling caused by its own gravity. In a first approximation, the reactions at the supports are found out disregard-ing the axial forces of friction. The author finds the general solution of the basic differential equation of horizontal pipe column deformations taking into account friction and axial forces acting during its lowering. It forms the basis for calculating bucklings and bendings, angles of rod rotation, its inner bending moments and cross forces at the sections between the supports. Geometric and power parameters of pipe deformations at the sections between the supports can be determined using the system of equations of the compatibleness of the angles of rotation and the support moments equilibrium. These equations contain axial force parameters, which can also be derived using the suggested system of algebraic equations. The solution of the problem becomes possible due to adding the transverse force equations to this system. These equations are obtained on the basis of the established relation between transverse and axial forces in the column and reactions and friction at the supports. It allows determining the axial compressive forces simultaneously. The method of linearization of the algebraic equations system and its iterative solution with high accuracy is developed. Due to the value of axial forces, calculated in a first approxi-mation, the system becomes linear, and its iterative solution allows finding the desired parameters with high accu-racy. The obtained results take into account the requirements to the construction technology of a horizontal well. The author considers the deviations of the well direction from the horizontal on the change of the stress-strain state of the casing. The paper offers the formulae to calculate the optimal distance between the casing centralizers as well as solves the problem of its reverse motion. The author takes into consideration additional moments of frictional forces affecting the casing centralizers. The obtained results might serve for the analysis of the stress-strain state of the casing column in the technological process of the horizontal well construction which makes it possible to increase its reliability and lifelength.

Numerical analysis of mechanical safety parameters of Congress Hall building in Chelyabinsk

Aims of research. The article is devoted to actual problems of computational analysis of stress-strain state, strength and stability of load-bearing structures with allowance for the main and special combinations of loads and impacts, comparison of the results of alternative structural analysis of unique cultural and business complex “Congress Hall” in Chelyabinsk. The natural conditions of the area of location of this object and main load-bearing structures of the object are described. Besides, characteristic and design loads, their combinations, formulation of objectives of computational research and methods of solution are presented. Methods. Space discretization and solution of the corresponding problems of mathematical (numerical) and computer modelling of the considering unique building were carried out with the use of finite element method. Detailed finite element models of the coupled system “combined foundation - loadbearing structures” and its fragments (subsystems) were developed and verified. They adequately reflect geometric-stiffness, inertial and load parameters of the object and the resulting stress-strain state. Progressive collapse analysis are under consideration as well. Licensed, certified and verified (by the Russian Academy of Architecture and Construction Sciences) finite element software package “ANSYS Mechanical” was used. Results. The resulting parameters of stress-strain state, strength and dynamics of load-bearing structures of the building with allowance for design (in accordance with design codes) combinations of vertical and wind loads are considered. Besides, information about results of progressive collapse analysis is presented. Thus, a reasonable conclusion is made about the reliability of the criterion parameters of strength, stability and dynamics of the load-bearing structures of the object.

Effect of fixing the pass-through turning tool in the tool holder on the roughness and surface macro deviations during turning

A study of the effect of the tool overhang length from the tool holder and cutting forces corresponding to different sizes of the removed layer on the formation of the quality of the surface layer of parts during turning is presented. Linear displacements arising in a stress-strain state and roughness parameters were used as estimated parameters. It is revealed that the quality of the surface layer improves with a decrease in vibration in the zone of contact between the workpiece and the tool.

Forming Features and Properties of Titanium Alloy Billets After Radial-Shear Rolling.

Radial-shear rolling (RSR) of titanium alloy billets was realized in a three-high rolling mill. Experimental rolling was simulated using DEFORM software. The purpose was to reveal how stress-strain state parameters, grain structure and hardness vary along the billet’s radius in the stationary stage of the RSR process. It was also the goal to establish a relation between stress state parameters, hardness and grain structure. Changes in the accumulated strain and the stress triaxiality were established by computer simulation. Hardness and grain size changes were obtained after experimental rolling. The novelty aspect is that both computer simulation and experimental rolling showed that there is a ring-shape area with lowered strength in the billet’s cross-section. The radius of the ring-shape area was predicted as a result of the research.

Расчет напряженно-деформированного состояния заготовки при вытяжке с утонением стенки через матрицу с малым углом конусности

The paper considers computing the stress-strain state of a workpiece during drawing with wall thinning through a die with a small taper angle. A manufacturing process for a sleeve usually includes several drawing operations, whereas recommendations for the final drawing operation are a low extent of deformation and using dies with a small taper angle of (2°--4°). We present a diagram for drawing with wall thinning, delineating all deformation stages recorded on the chart showing force as a function of tool path. We computed the stress-strain state and deformation in the workpiece wall during the final operation of drawing through a die with a small taper angle α ≤ 4°. We provide equilibrium equations in toroidal coordinates and compute stress-strain state parameters and extents of deformation for the axisymmetric problem statement. No longer assuming a plane strain state, we compute the stress-strain state and extent of deformation in the workpiece wall during drawing with wall thinning through a die with a small taper angle α = 2°--4°. We show that at the stage when intermediate product walls are formed, for a small taper angle it is reasonable to consider the process of drawing with wall thinning to be monotone.

Особенности расчетного определения параметров напряженно-деформированного состояния газопроводов в сложных инженерно-геологических условиях

Особенности расчетного определения параметров напряженно-деформированного состояния газопроводов в сложных инженерно-геологических условиях

Numerical Modeling of Stress-Strain State of a Deep Beam

The article presents calculation results for model elastic problem of defining stress-strain state of a deep beam preformed in 3D and 2D statements with the use of ANSYS software package. Geometric relations are taken in the form of Cauchy equations. The purpose of the study is to assess error in the results obtained for the two statements and to draw a conclusion on the possibility of using 2D statement for the deep beam under study. Based on 3D statement calculation results one may observe a short area near the support surface of a deep beam with the maximum load across the entire thickness. In this area the concentration of maximum stress values and maximum linear and angular deformations in the structure material are observed. The area is located on the axis of symmetry of the deep beam near the inner edge of support surface. It is found that the stress intensity values obtained for the two statements have considerable differences in this area, for that reason 3D statement shall be used when performing calculations for the deep beam. This way of solving the problem is illustrative of stress-strain state parameters distribution across the thickness of the structure, which is necessary for its strength evaluation.

Probabilistic analysis and reliability evaluation of the harmonically loaded rod systems with dynamic vibration dampers, based on the use of modern software complexes

The problems of determining the probabilistic properties of the stress-strain state parameters of dynamically loaded systems with the application of modern software are considered. The advantages and possible risks of using the multifunctional ANSYS software in probabilistic analysis and reliability calculations of dynamically loaded systems are analyzed. Peculiarities of software application have been revealed taking into account the character of the changes in the probability density distribution of the stress-strain state parameters of dynamic system in the frequency intervals in the vicinity of the resonance zone. Qualitative and quantitative comparison of the results of probabilistic characteristics calculated in ANSYS software with analytical solutions has been carried out.

Study of technological factors’ effects on deforming of thin-wall tubes deformation forces in short-term creep mode

In the modern world, slow isothermal deformation, which leads to a significant increase of the deformed metal’s plasticity, have become more widely used in the manufacturing of ax-isymmetric products made of hard-to-deform light alloys. Despite a large number of works devoted to theoretical and experimental research of distribution processes, the problems of the forming theory have not been fully discussed at the present time. This paper presents the results of studies of the pipe workpiece expansion under isothermal conditions, performed in the QFORM 3D software. The workpiece was made of high-strength alloys AMg6 and BT6. It was assumed that the behavior of the workpiece material during deformation corresponds to the following equation, which characterizes the transition of the workpiece material from viscous to viscoplastic state. The study reveals the influence of a wide range of technological factors on the stress-strain state and operational force parameters. The results can be used to create scientifically based methodologies for the design of high technology processes for manufacturing of axisymmetric geometrically-complex parts using isothermal deformation methods.

Block Based Finite Element Model for Layer Analysis of Stress Strain State of Three-Layered Shells with Irregular Structure

Ablock based finite element approach is proposed for layer-by-layer analysis of the stress strain state (SSS) of three-layer shells with an irregular structure. The shell aggregate can be modeled by the required number of finite elements over its thickness, which allows to take into account the change in the geometric and physico-mechanical properties of the material and the SSS parameters in all three coordinates to which the shell is related. According to the developed algorithm for constructing the finite elements (FE) of the aggregate, the inner and outer surfaces of the shell are accepted as datum surfaces and in the aggregate elements joined to the bearing layers, the same number of nodes is accepted as in the elements of the bearing layers. The same generalized displacements and approximations as for the elements of the bearing layers are taken as the nodal unknowns and the approximating functions of the aggregate, which allows to avoid errors caused by the breakdown of the generalized displacements on the interfaces between the layers. The algorithm for constructing a block-based finite element model for the layer-by-layer SSS analysis is considered using the example of irregular three-layer conical shells with moment-carrying layers and three-dimensional aggregate.

Continuum mathematical modelling of pathological growth of blood vessels

The present study is devoted to the mathematical modelling of a human blood vessel pathological growth. The vessels are simulated as the thin-walled circular tube. The boundary value problem of the surface growth of an elastic thin-walled cylinder is solved. The analytical solution is obtained in terms of velocities of stress strain state parameters. The condition of thinness allows us to study finite displacements of cylinder surfaces by means of infinitesimal deformations. The stress-strain state characteristics, which depend on the mechanical parameters of the biological processes, are numerically computed and graphically analysed.

Modeling of storage tank settlement based on the United States standards

Up to 60% of storage tanks in operation have uneven settlement of the outer bottom contour, which often leads to accidents. Russian and foreign regulatory documents have different requirements for strain limits of metal structures. There is an increasing need for harmonizing regulatory documents. The aim of this study is to theoretically justify and to assess the possibility of applying the U.S. standards for specifying the allowable settlement of storage tanks used in Russia. The allowable uneven settlement was calculated for a vertical steel tank (VST-20000) according to API-653, a standard of the American Petroleum Institute. The calculated allowable settlement levels were compared with those established by Russian standards. Based on the finite element method, the uneven settlement development process of a storage tank was modeled. Stress-strain state parameters of tank structures were obtained at the critical levels established in API-653. Relationships of maximum equivalent stresses in VST metal structures to the vertical settlement component for settlement zones of 6 to 72 m in length were determined. When the uneven settlement zone is 6 m in length, the limit state is found to be caused by 30-mm vertical settlement, while stresses in the wall exceed 330 MPa. When the uneven settlement zone is 36 m in length, stresses reach the yield point only at 100-mm vertical settlement.

Modeling of storage tank settlement based on the United States standards

Up to 60% of storage tanks in operation have uneven settlement of the outer bottom contour, which often leads to accidents. Russian and foreign regulatory documents have different requirements for strain limits of metal structures. There is an increasing need for harmonizing regulatory documents. The aim of this study is to theoretically justify and to assess the possibility of applying the U.S. standards for specifying the allowable settlement of storage tanks used in Russia. The allowable uneven settlement was calculated for a vertical steel tank (VST-20000) according to API-653, a standard of the American Petroleum Institute. The calculated allowable settlement levels were compared with those established by Russian standards. Based on the finite element method, the uneven settlement development process of a storage tank was modeled. Stress-strain state parameters of tank structures were obtained at the critical levels established in API-653. Relationships of maximum equivalent stresses in VST metal structures to the vertical settlement component for settlement zones of 6 to 72 m in length were determined. When the uneven settlement zone is 6 m in length, the limit state is found to be caused by 30-mm vertical settlement, while stresses in the wall exceed 330 MPa. When the uneven settlement zone is 36 m in length, stresses reach the yield point only at 100-mm vertical settlement.

ОРГАНІЗАЦІЯ ВИРІШЕННЯ ОБЕРНЕНИХ ЗАДАЧ ТЕРМОПРУЖНОСТІ ДЛЯ ТОНКОГО КІЛЬЦЯ

The research of stress-strained conditions of aviation and power industrial facilities refers to the problems of mechanics of a solid deformed body. In this case the ultimate goal of the research may be different: determination of the stress-strain state of specific objects; identification of mechanical characteristics of materials. But if we assume that the study of the stress-strain state of a body with known all other initial data is the subject of a direct problem, then the definition of any parameter of the system by known characteristics stress-strain state can be attributed to the class of inverse problems of the mechanics of a deformed solid. New inverse thermoelasticity problems for thin ring have been formulated in which unknown thermal loading (temperature of boundary surface and intensity of frictional heat flux) has been determined using additionally given vertical displacements of one of the outer boundary surfaces. The functional spaces, for which the problems are well-posed, have been found. The method for solving the problems has been suggested and numerically verified with the use of the solution of the direct problem. This paper deals with the determination of heating temperatures and temperature distributions on the upper surface of a thin ring. The expressions of the heating temperatures and temperature distributions have been obtained in series form, involving Bessel’s functions with the help of the integral transform technique. Thermoelastic deformations have been discussed and illustrated numerically with the help of temperature and determined. In the framework of the nonlinear theory of thin rings on the basis of the inverse problem method was formulated a model of deformation of the observed thin-walled ring with loads, boundary conditions, geometric parameters to be determined. The basis of the model is the parametrization of a direct problem of nonlinear theory thin-walled elements using the boundary elements method г and the variational formulation of the identification problem, which provides for minimization of the residual functional reflecting the deviation of stress-strain state parameters obtained as a result of observationfrom those calculated on the basis of an approximate solution.