Pavel N. Ryabov

The processes of plastic shear localization in DU-0.75Ti alloy samples subjected to high-speed shear are considered. A mathematical model describing this process in the 1D and 2D cases is formulated. A numerical algorithm for the mathematical modeling of the processes under consideration is proposed. A series of computational experiments on high-speed loading of DU samples is carried out. The localization process dynamics depending on the initial rate of plastic shear is investigated. The values of the temperature, velocity, stress, and shear fields are obtained. The influence of the problem dimension on some of the most important characteristics of the localization process is investigated.

Решение задачи балансировки нагрузки актуально при проведении высокопроизводительных вычислений. Одним из оригинальных методов решения задачи балансировки является использование диаграмм Вороного для декомпозиции области. Сильной стороной данного подхода является возможность применения такой декомпозиции на различных типах данных. Балансировка может использоваться на эйлеровых сетках, лагранжевых сетках, совместно с методикой сглаженных частиц (SPH). Метод также может использоваться для балансировки адаптивных сеток, но в этом случае проявляется его недостаток: из-за сильной неоднородности нагрузки на адаптивных сетках метод динамической балансировки может быть неустойчивым или обладать плохой сходимостью. В работе предлагается усовершенствование алгоритма балансировки за счет перехода от использования обычных диаграмм Вороного к взвешенным диаграммам. Предложенный алгоритм реализован в виде программного комплекса. Тестирование предложенного алгоритма строится на базе ряда модельных задач и задач из области механики сплошной среды. Оценка эффективности балансировки строится на базе исследования поведения величины дисбаланса с учетом балансировки и без. Показано, что предложенный алгоритм успешно справляется со своей задачей, и величина дисбаланса в случае использования взвешенной диаграммы Вороного в 10–100 раз меньше, чем при использовании обычных диаграмм Вороного.

An important task of material science is a prediction of material failure at different conditions. It especially has signifi-cance for application in nuclear, m

In this work we suggest a mathematical model of motion of the elasto-plastic materials with nonlinear plasticity constitutive law; we also propose an effective numerical method for numerical simulations of such tasks on two-dimensional eulerian meshes. Based on the method, we research formation of multiple adiabatic shear bands (ASB) at high-speed shear deformations. We test our approach on two-dimensional problem where the initial heterogeneity of temperature leads to formation of adiabatic shear band.

We consider the processes of plastic flow localization in dipolar materials undergoing high speed shear deformations. The mathematical model of the processes of plastic flow localization is formulated taking into account dipolar effect. We introduce the numerical algorithm which is based on adaptive mesh refinement technique. We show that this algorithm allows to increase performance of computations. We also studied the statistical properties of shear bands formation. We show that dipolar effect changes average characteristics of the processes considered such as average temperature, stress and etc. Moreover this effect leads to increase in initiation time, changes the widths of localization zones and distances between them.

The process of torsion deformation of a hollow cylinder is considered. The mathematical model describing this process is formulated. Numerical algorithm which allows one to simulate the fully localized plastic flow is proposed. The influence of the geometrical parameters of the problem of plastic flow localization is studied. The limiting case when the problem of torsion deformation of a hollow cylinder transforms to the plane problem of deformation of infinite slab is considered. An influence of cylinder size to the formation of adiabatic shear bands is considered. It is shown that declining of inner size of cylinder results to a significant change of solution and displacement of localization area to the inner surface of a hollow cylinder.

The process of plastic flow localization in materials undergoing shear deformations is considered. Starting from mathematical model a new numerical approach, which is based on Courant-Isaacson-Rees scheme, that allows one to simulate fully localized plastic flow is proposed. The accuracy and efficiency of the proposed algorithm was showed of three benchmark problems. Next, using the proposed method we study the features of plastic flow localization in materials under shear deformations.

We study the wave processes described by the generalized Swift-Hohenberg equation. We show that the traveling wave reduction of this equation does not pass the Kovalevskaya test. Some solitary wave solutions and kink solutions of the generalized Swift-Hohenberg equation are found. We use the pseudo-spectral algorithm to perform the numerical simulation of the wave processes described by the mixed boundary value problem for the generalized Swift-Hohenberg equation. This algorithm was tested on the obtained solutions. Some features of the nonlinear waves evolution described by the generalized Swift-Hohenberg equation are studied.

We consider the adiabatic shear banding phenomenon in composite materials undergoing the high speed shear deformations. The mathematical model of adiabatic shear banding in thermo-visco-plastic material is given. New two step numerical algorithm which is based on the Courant-Isaacson-Rees scheme that allows one to simulate fully localized plastic flow from initial stage of localization is proposed. To test this numerical algorithm we use three benchmark problems. The testing results show the accuracy and efficiency of proposed algorithm. The features of adiabatic shear bands formation in composites are studied. The existence of characteristic depth of localization in composites is shown. Influence of initial temperature distribution on the processes of adiabatic shear bands formation in composites is considered.