and Computational Methods

Rubric: "1.1.8. Mechanics of a Deformable Solid Body (Physical and Mathematical Sciences)"

doi: 10.18698/2309-3684-2022-2-2862

The problem of development a theory for calculating the stress-strain state of thin multilayer elastic plates, for which linearized slip conditions are specified at the interface between the layers, is considered. The solution of this problem is constructed using an asymptotic analysis of the general equations of the 3-dimensional theory of elasticity with the conditions of non-ideal contact of the layers. The asymptotic analysis is carried out with respect to a small geometric parameter representing the ratio of the plate thickness to its characteristic length. Recurrent formulations of local quasi-one-dimensional problems of the theory of elasticity with slip are obtained. Explicit analytical solutions are obtained for these problems. The derivation of the averaged equations of elastic equilibrium of multilayer plates is presented, taking into account the slippage of the layers. It is shown that due to the effect of slippage of layers, the system of averaged equations of the theory of multilayer plates has an increased - 5th order of derivatives, in contrast to the classical 4th order, which takes place in the theory of Kirchhoff-Love plates. It is shown that the asymptotic theory makes it possible to obtain an explicit analytical expression for all 6 components of the stress tensor in the layers of the plate. As a special case, the problem of calculating the stress-strain state of a 4-layer plate under uniform pressure bending with one slip coefficient is considered. A complete analytical solution of this problem is obtained, including explicit expressions for all non-zero components of the stress tensor. A numerical analysis of the solution of the averaged problem for a composite plate is carried out, in which the layers are unidirectional reinforced fibrous materials oriented at different angles. A comparative analysis of the influence of the fiber reinforcement angles and the slip coefficient of the layers on the displacement of the plate and the distribution of stresses in the layers was carried out. It is shown that the problem of bending a plate with slip admits the existence of a spectrum of critical values of the slip coefficient, when passing through which the displacements and stresses in the layers of the plate change significantly, and these critical values depend on the angle of reinforcement of the composite layers.

Димитриенко Ю.И., Губарева Е.А. Асимптотическая теория многослойных тонких упругих пластин с проскальзыванием слоев. Математическое моделирование и численные методы, 2022, № 2, с. 30–64

doi: 10.18698/2309-3684-2021-4-316

Since the classical hypotheses of Bernoulli for beams and Kirchhoff for thin plates contradict the additional condition of incompressibility for rubber-like (incompressible) materials (invariability of the volume during deformation), a calculation model for a bending beam is proposed, which does not lead to a serious complication of the problem in comparison with the classical solution. The invariability of the volume is manifested under the action of a power load; in the case of a temperature load, the deformation of the volume change is not zero. The absence of volumetric deformations for rubber-like materials is a consequence of Hooke's law for such materials. Summing the linear deformations expressed in terms of stresses and taking Poisson's ratio 0.5, we obtain the equality of the indicated sum to zero. Many rubber-like materials are incompressible and low-modulus, which means their weak resistance to tension and shear, but the resistance of the material to change in volume tends to infinity, therefore the physical relations of the generalized Hooke's law are transformed into the so-called "neo- Hooke " equations of the relationship between stresses and strains. Of the two independent physical characteristics (modules) for incompressible materials, only one module remains, which characterizes the resistance of the medium to change in shape. In physical relations for an incompressible material, the product of an infinitely large volumetric modulus by the deformation of a change in volume equal to zero is an uncertainty that is replaced by some force function that has the dimension of stresses and is an additional unknown. At the same time, the system of governing equations of the mechanics of incompressible media is supplemented by the equation of invariability of volume. The scheme for solving the problem in displacements for traditional structural materials turns into a mixed scheme for rubber-like materials, since for them not only displacements but also the mentioned force function act as the main unknown sought function.

Фирсанов В.В. Моделирование изгиба балок из резиноподобных материалов. Математическое моделирование и численные методы, 2021, № 4, с. 3–16.

doi: 10.18698/2309-3684-2021-2-1537

The aim of this work is to find the constitutive relations for a layered elastoplastic composite according to the flow theory using the method of asymptotic averaging. This goal is achieved by developing an algorithm for solving the problem of the theory of plastic flow for a layered composite material, taking into account various characteristics and properties of these layers of the material, followed by visualizing the result in the form of effective plasticity diagrams connecting the components of averaged stress tensors and components of averaged strain tensors.

Димитриенко Ю.И., Губарева Е.А., Черкасова М.С. Моделирование деформирования слоистых периодических композитов на основе теории пластического течения. Математическое моделирование и численные методы, 2021, № 2, с. 15–37.

doi: 10.18698/2309-3684-2021-4-1744

A model of constitutive relations for elastic-plastic composites with cubic symmetry of properties is proposed. This class includes a significant number of composite materials: dispersed-reinforced composites, which have an ordered rather than a chaotic reinforcement system, as well as some types of spatially reinforced composites. To build a model of nonlinear constitutive relations, a tensor-symmetry approach was used, based on the spectral expansions of stress and strain tensors, as well as the spectral representation of nonlinear tensor relations between these tensors. The deformation theory of plasticity is considered, for which the tensor-symmetric approach is used, and specific models are proposed for plasticity functions that depend on the spectral invariants of the strain tensor. To determine the model constants, a method is proposed in which these constants are calculated based on the approximation of deformation curves obtained by direct numerical solution of three-dimensional problems on the periodicity cell of elastic-plastic composites. These problems arise in the method of asymptotic averaging of periodic media. To solve problems on a periodicity cell, a finite element method and special software was used that implements solutions to problems on periodicity cells, developed at the Scientific and Educational Center for Supercomputer Engineering Modeling and Development of Software Packages of Bauman Moscow State Technical University. An example of calculating the constants of a composite model using the proposed method for a dispersed-reinforced composite based on a metal matrix is considered. Also, the verification of the proposed model for various ways of multiaxial loading of the composite was carried out with direct numerical simulation. It is shown that the proposed microstructural model and the algorithm for determining its constants provide a sufficiently high accuracy in predicting the elastic-plastic deformation of the composite.

Димитриенко Ю.И., Сборщиков С.В., Димитриенко А.Ю., Юрин Ю.В. Микроструктурная модель деформационной теории пластичности квази-изотропных композиционных материалов. Математическое моделирование и численные методы, 2021, № 4, с. 17–44.

doi: 10.18698/2309-3684-2022-1-6396

The article presents the result the review of works devoted to the research the properties of elastoplastic materials. The article consists of two parts. In the first part, universal single, two- and three-parametric laws describing the nonlinear dependence between the stress and deformation up to the destruction. The review includes: power laws, parabolic laws, exponential laws, harmonic law. A comparison the considered empirical curves with a sample experimental points is carried out by the standard procedure for minimizing the total quadratic deviation and using the method the gradient descent to determine the minimum function of many variables. To assess the predictive force for models on the compliance with the experiment, a representative sample used from 158 experimental points in the deformation curve of the Russian titanium alloy WT6. The analysis showed that the empirical laws of deformation containing less than four formal parameters cannot describe the universal deformation curve with the stress specified at the ends and the tangent module. Analysis of the advantages and disadvantages of existing empirical laws of deformation, made it possible to formulate certain requirements for their wording.

Головина Н.Я., Белов П.А. Анализ эмпирических моделей кривых деформирования упругопластических материалов (обзор). Часть 1. Математическое моделирование и численные методы, 2022, № 1, с. 63–96

doi: 10.18698/2309-3684-2023-1-331

This article is the third part of a review of works devoted to the study of the properties of elastic-plastic materials. The first and second parts were devoted to the analysis of universal empirical laws of deformation, which model the material properties over the entire range of deformation, up to fracture. It was concluded that in order to create a model of the material response to stress growth, the deformation law must be at least four-parametric. The empirical Ramberg-Osgood law was found to be the most qualitative, at least for the titanium alloy VT6 considered. However, despite its accuracy, it does not reflect the material properties in the zone of large plastic strains, including in the vicinity of the point of ultimate strength. This paper presents an analysis of multilink models describing the relationship between strain and stress by different laws in the elastic zone and in the plastic zone. The review includes two-link models by Nadai, Mirambell-Real, Rasmussen, Abdella, formulated for materials whose strain curve has no positive curvature section. Also considered in the review are the three-link models of Quach; Hertele; Belov-Golovina, which allow modeling of deformation curves with a positive curvature region. The evaluation of the quality of empirical laws and their correspondence to the sample of experimental points was carried out by minimizing the standard quadratic deviation and using the method of gradient descent to determine the minimum of the function of many variables. The material for the comparative analysis of empirical models is titanium alloy VT6; for the Hertele and Belov-Golovina models — steel St3sp. It is shown that the models built on the basis of multi-line splines determine the properties of elastic-plastic materials more accurately than the models built on the basis of universal laws.

Головина Н.Я. Анализ эмпирических моделей кривых деформирования упруго-пластических материалов (обзор). Часть 3. Математическое моделирование и численные методы, 2023, No 1, с. 3–31.

doi: 10.18698/2309-3684-2021-3-323

This paper presents the mathematical formulation and the results of calculations of the problem of metal deformation on a casting-forging module with modified side strikers’ drive. A complex spatial problem of determination the stress-strain state of the flow region under loading with an external load that changes over time is considered. The fundamental equations are based on flow theory. At solving the problem, a proven numerical method is used, as well as numerical schemes and the software package used earlier at solving similar problems. The software package implements a step-by-step loading algorithm considering the history of the process and the changing geometry of the flow region. A small time step is associated with a 10° rotation of the eccentric shaft. The deformation area is divided into elements by an orthogonal system of surfaces (elements have an orthogonal shape). For each element, the formulated system of equations is written in a difference form, which is solved according to the developed numerical schemes and algorithms, that consider the initial and boundary conditions. The result of the solution is the fields of stresses and velocities of displacements in the spatial area. The analysis of the obtained results is given. A comparison with the results of the current structure module solving has been made. Lead is taken as a deformed material, the physical properties of which are approximated by an analytical dependence according to the available experimental data. The physical nonlinearity of the system of equations is realized during solving by the iterative method. Local calculations of the solution of the problem were carried out on three variants of division of the area into elements. The choice of the mesh density imposed on the considered deformation region is substantiated. The solution results are presented graphically. The efficiency of the deformation process according to the improved method on a new design of the casting and forging module is shown.

Одиноков В.И., Дмитриев Э.А., Евстигнеев А.И., Потянихин Д.А., Квашнин А.Е. Математическое моделирование процесса деформации металла на литейно-ковочном модуле с измененным приводом боковых бойков. Математическое моделирование и численные методы, 2021, № 3, с. 3–23.

doi: 10.18698/2309-3684-2021-4-4557

A unified numerical method for different fatigue fracture modes from low-cycle to very-high-cycle fatigue is described on the basis of a multi-mode two-criterion model of cyclic damage. This method allows for a through calculation of the evolution of crack-like fatigue fracture zones in a material, as well as an assessment of the durability of specimens from crack nucleation to macrofracture. Fatigue fracture calculations of titanium alloy specimens under prolonged cyclic loading under three-point bending scheme with development of "quasi-cracks" in modes from multi-cycle to super-multi-cycle fatigue have been carried out. Numerical and experimental results are compared to each other.

Стратула Б.А. Математическое моделирование усталостного разрушения при высокочастотных изгибных колебаниях образцов из титановых сплавов. Математическое моделирование и численные методы, 2021, № 4, с. 45–57.

doi: 10.18698/2309-3684-2023-1-6480

At the initial stages of designing compressor blades, screws, cutting tools, it is advisable to use a finite element model based on a model of a naturally twisted beam. This model takes into account the influence of the angle of natural twist on the rigidity of the part. The torsional stiffness of a bar significantly affects the stiffness parameters of the finite element model. It is shown that the torsional stiffness correction obtained on the basis of the relations of the technical theory of naturally twisted beams makes it possible to obtain results at small angles of natural twist that are in good agreement with the three-dimensional calculation of a twisted FEM beam. At large specific angles of initial twist, the technical theory gives overestimated values of the torsional stiffness. The article proposes a modification of the relations of the technical theory to determine the torsional rigidity, taking into account large angles of initial twist.

Темис Ю.М., Зиятдинов И.З. Новый метод вычисления жесткости на кручение в модели естественно-закрученного стержня. Математическое моделирование и численные методы, 2023, No 1, с. 64–80