The main physical laws of thermal–plastic deformation and fatigue damage accumulation processes in polycrystalline structural alloys under various regimes of cyclic thermal–mechanical loading are considered. Within the framework of mechanics of damaged media, a mathematical model is developed that describes thermal–plastic deformation and fatigue damage accumulation processes under low-cycle loading. The model consists of three interrelated parts: relations defining plastic behavior of the material, accounting for its dependence on the failure process; evolutionary equations describing damage accumulation kinetics; a strength criterion of the damaged material. The plasticity model based on the notion of yield surface and the principle of orthogonality of the plastic strain vector to the yield surface is used as defining relations. This version of defining equations of plasticity describes the main effects of the deformation process under monotone cyclic, proportional and nonproportional loading regimes. The version of kinetic equations of damage accumulation is based on introducing a scalar parameter of damage degree and energy principles, and account for the main effects of nucleation, growth and merging of microdefects under arbitrary regimes of low-cycle loading. The strength criterion of the damaged material is based on reaching a critical value of the damage degree. The results of numerically modeling cyclic thermal–plastic deformation and fatigue damage accumulation in heat-resistant alloys (Nimonic 80A, Haynes 188) under combined thermal–mechanical loading are presented. Special attention is paid to the issues of modeling the processes of cyclic thermal–plastic deformation and fatigue damage accumulation for complex deformation processes accompanied by the rotation of the main stress and strain tensor areas. It is shown that the present damaged medium model accurately enough for engineering purposes describes the processes of cyclic isothermal and nonisothermal deformation and fatigue damage accumulation under combined thermal–mechanical loading and makes it possible to evaluate low-cycle fatigue life of heat-resistant alloys under arbitrary deformation trajectories.

EPJ Web of Conferences, open-access proceedings in physics and related sciences

A complex experimental-theoretical approach to studying the problem of high-rate strain of soft soil media is presented. This approach combines the following contemporary methods of dynamical tests:...

A 2 D nonstationary problem of an orthotropic one-component elastic layer, accounting for diffusion, is considered. A locally balanced model of elastic diffusion is used, which includes a coupled set of equations of elastic body motion and a mass-transfer equation. On the layer boundaries normal displacement, tangential stress and diffusive flow are assumed. At an initial time, the layer is in an undisturbed state. The solution is sought in an integral form, as a double convolution in time and along the space coordinate of Green functions and the right-hand sides of the boundary equations. To construct a solution of the initial problem, Laplace time transform, exponential Fourier transform along the space coordinate in the direction of the layer surface, reduction to zero boundary conditions, and expansion into incomplete Fourier series along a coordinate directed through the depth of the layer are successively used. Thus, the initial problem is reduced to a set of linear algebraic equations, from which forms of the sought functions are found. It is shown that the necessary condition of the applicability of the present algorithm is orthotropy of the medium in question. Inversion of Laplace transform of the sought functions is reduced to computing the originals of the rational functions, which is done analytically, using deductions. It is found that all Green functions are even (odd) relative to Fourier transform parameters, which makes it possible, when the right-hand sides of the boundary conditions are even (odd), to reduce the inversion of exponential Fourier transform to the inversion of sinus-, cosine-transform. In that case, quadrature formulas of medium rectangles are used to find the originals of Fourier transformants. An example is considered, where surface perturbation is modeled with Heaviside time function and a Gaussian along the space coordinate. A homogenized medium of interlaced layers of aluminum and copper is used as a model of an orthotropic medium. The computational results are presented both analytically and in the form of 3D diagrams of the diffusant concentration increment and displacement vector components.

The results of experimental and theoretical studies of steel 09G2S deformation and fracture laws in a wide range of strain rates and temperature variations are given. The dynamic deformation curves and the ultimate characteristics of plasticity in high-rate strain were determined by the Kolsky method in compression, extension, and shear tests. The elastoplastic properties and spall strength were studied by using the gaseous gun of calibre 57 mm and the interferometer VISAR according to the plane-wave experiment technique. The data obtained by the Kolsky method were used to determine the parameters of the Johnson-Cook model which, in the framework of the theory of flow, describes how the yield surface radius depends on the strain, strain rate, and temperature.