This article considers the efficiency of the food grinding plant and appropriate methods aimed at increasing its reliability and durability. It is established that a plant’s service life is limited by the service life of its knives. It is proposed to apply surface plasma nitriding with a compressed moving plasma arc to strengthen the knives. The use of such a highly concentrated heating source allows for surface hardening of a product, though only of its wear parts, including preliminary bulk hardening of its core and thereby maintaining materials’ plastic properties. This method of heat treatment allows to increase the resistance to wear and fatigue; to provide hardness and wear resistance of the surface; to reduce the deformation of the hardened parts due to the locality and short-term interaction of plasma with the metal surface. According to the results of the preliminary experimental studies on surface temperatures close to the melting temperature of steel, the temperature distribution law is established. Based on the Gaussian law of temperature distribution in the finite element computing system ANSYS, a theoretical model is developed to study the distribution of the temperature field in the knife in depth at different speeds of the heating source and currents in order to provide optimal parameters of the heat treatment process at a given depth of tempering, hardness, etc. Further, on the basis of these data, a theoretical experiment is conducted to study the stress-strain state of the knife under the influence of a moving heating source modelling the plasma jet. The mechanical and mathematical model developed by ANSYS takes into account the temperature change in the diameter of the moving heating spot and the dependence of the physical and mechanical characteristics of the knife’s material on temperature. A plasma torch and plasma system are developed, and surface plasma nitriding of knives subject to preliminary bulk hardening is performed. The wear resistance of the blades after an extensive surface hardening and plasma nitriding is investigated. The results of the research allowed to increase the wear resistance of knives subject to preliminary bulk hardening and surface plasma nitriding by more than 2 times compared to bulk hardening.

The processes of heat transfer and diffusion in metals are characterized by different physical periods. However they are described by structurally similar equations of mathematical physics. This fact is used in the paper to adapt the well-defined mathematical principles set for heat transfer to the purposes of solving the problems of hydrogen diffusion into metals. An approach is assumed which is based on the substitution of the heat transfer equation with an equivalent variable equation utilized to calculate parameters of complexly shaped bodies and boundary conditions of various types via the finite-element method. The necessity of utilizing the numerical methods used in the research is dictated by the main direction of the algorithm applied to the determination of the interrelated influence of hydrogen and mechanical stresses on the kinematics of deformation and fracture of structural elements. The calculation of the stress-strain state of actual structural elements is carried out by means of numerical methods only. An analytical solution of the problem of heat distribution in a rod is utilized to test software based on the finite-element method. The goal of the research is to develop an approach necessary to solve a related thermodiffusion problem of hydrogen saturation in a steel shell structure and to determine the law of hydrogen concentration distribution in the body of a shell depending on temperature and the hydrogen concentration at the boundaries. As an example, a problem of hydrogen penetration into the wall of a diffusion device is solved. The solution would allow one to evaluate changes in the mechanical properties of materials and the service life of a product. The approach proposed here has allowed us to determine the kinematics of the processes of heat transfer and hydrogen saturation in steel walls of a cylindrical section of the device. The applied importance of the results obtained is based on the fact that the temperature, pressure and concentration of hydrogen over the inner surface are in correspondence with the operational conditions.

Features of deformation behavior and fracture resistance of a material of fuel element claddings are used to design and ensure their safe operation. To determine these features, JSC “Institute of Nuclear Materials” applies static eccentric tension tests of thin-walled circular specimens with a stress concentrator in the form of a single-edge-notch, which are cut from shell pipes. The tests were made in certain time intervals of fuel element cladding operation. The experiments show various dependences of the specimen loading force on the value of the test machine grip displacement. These dependences are influenced by the accumulated damage of a fuel element cladding. Loading curve behavior is explained by the test simulation. The paper presents the test scheme. We formulated the elastoplastic problem of stress-strain state simulation of a single-edge-notch circular specimen under eccentric tension. The plane strain state is considered. The finite element simulation is made using the specialized computer program for the considered type of tests. The program is developed in the Institute of Engineering Science, Ural Branch of the Russian Academy of Sciences. The load is applied gradually in small increments of the test machine grip motion. At each load step, the simulation algorithm is based on the principle of virtual power. Constitutive equations developed by the authors for the elastoplastic medium with large plastic deformations are used. The simulation results of loading processes are shown for the specimens made from the austenitic steel ChS86hd. It appears that the curve describing the dependence of tensile force in the specimen on the test machine grip displacement consists of two straight line segments with a smooth transition. The first straight segment is notoriously more inclined to horizontal axis compared to the second one. The change of the accumulated plastic strain in the region of the specimen notch in different points of the loading curve was analyzed. The features of the specimen at different points of the loading curve were explained taking into account the formation and development of a macrocrack at the top of the specimen notch. Fields of stress state indicator distributions in the region of the specimen notch are shown.

The fatigue crack growth kinetics on samples from four types of steels under constant and variable amplitude cycling loading with different asymmetry ratio is studied. The loading parameters were chosen in such a way that the resulting fatigue crack growth rate curves fit onto the middle region of the fatigue crack growth diagram. Standard compact specimens with an edge crack were used for the tests. Loading was carried out on a modern servo-hydraulic test machine, which allows you to specify different laws of stroke movement, record all parameters. The readout of the crack opening displacement gauge was recalculated into the crack length by the compliance method using software supplied with the test equipment. The available methods aimed at predicting the fatigue crack growth life with a variable amplitude cyclic loading are not capable of taking into account the peculiarities of random loading. In this study, a new approach is proposed to estimate the fatigue crack growth life with a constant and variable amplitude loading with different loading parameters, taking into account the phenomenon of a "crack closing" and nature of random loading. The "crack closing" is taken into account by the introduction of an effective stress intensity factor (SIF) into the calculation, which, unlike the well-known SIF, is calculated using the closing factor. The nature of random loading is determined by the irregularity factor of the random loading block. Calculation of the fatigue crack growth life according to the proposed model and according to the known "cycle-by-cycle" calculation method. A comparison of the calculated data with the experimental ones showed similar results. At the same time, the proposed model aimed at calculating the fatigue crack growth supposes the presence of a small number of initial parameters and requires considerably less resources for calculation.

Hydroelastic systems can be characterized by a simultaneous manifestation of elastic and hydrodynamic instabilities and their interaction. Mutual effects of pipe bending, internal and external pressures, the action of compression force and fluid with a set density flowing along the pipe are under consideration. A thin elastic pipe is fixed on clamped sliding supports. In this case the supports do not hinder the flow of fluid travelling inside the pipe along its axis. Outside the pipe there is the fluid at rest. At the supports, the pipe bending and rotation angle are equal to zero. Assumptions are made regarding the incompressibility of the pipe midline and also the ideality and incompressibility of the fluids. The pipe is subjected to longitudinal compression. The smallness of inertial forces is conditioned by a relatively slow change of disturbances under slowly changing external effects (compressive forces in the pipe, hydrostatic forces, velocity of fluid motion in the pipe). External effects can be both independent and interconnected with each other. Here, the static mutual influence between those instabilities is called the instability interaction in the pipeline. We have obtained the linearized equation of the pipe bend and the critical value of the force that squeezes the pipe, which represents a generalization of the classical critical value for the static longitudinal compressive force acting on the pipe in the Euler problem due to the action of pressures inside and outside the pipe and the fluid motion inside the pipe. The investigation is focused on static instability interactions depending on the compression force in the pipe, internal and external pressures and fluid velocity. Given the large number of input parameters, it is possible to identify a great number of particular cases being important in their own right. Some of them are considered here. The domains of change for these parameters are determined by the occurrence of stabilization and destabilization of the rectilinear shape. Bending rigidity, tensile forces and external hydrostatic pressure stabilize the pipe. By contrast, compressive forces, internal hydrostatic pressure and fluid movement inside the pipe at any velocity have a destabilizing effect.

A wide variety of metals and metal alloys can be transferred to a specific state in which materials are capable of extremely large (hundreds and thousands of percents) strains without fracture at relatively low (compared with normal plasticity) stresses. For that materials should be fine-grained (with an average grain size less than some critical size for a given class of alloys, usually less than 10 microns) and subject to deformation in a certain range of temperatures and strain rates. The property of materials to test anomalously large deformations under the specified conditions is classified as structural superplasticity and is widely used in manufacturing processes by formation methods various (in the first place - large-sized) products in many industries (aerospace, automotive and etc.). Mathematical modelling is the most effective “tool” in developing rational regimes of technological processes, which, in turn, requires the creation of constitutive models (constitutive relations) allowing to adequately describe the physics and mechanics of superplastic deformation processes. To date many dozens of constitutive relations of various classes (macrophenomenological, structural-mechanical, thermodynamic, physical) have been created. Identification and verification of such models is carried out on the basis of the experimental data which are obtained on macro-samples, as a rule. The extensive experimental material about features of structural superplasticity has been currently accumulated for various materials. In most cases the experiments are carried out on cylindrical specimens by using uniaxial tension on kinematic type machines. The proposed review pays special attention to the issue of the staged nature of “longitudinal stress - strain” dependence which is observed in experimental tests with a transition to the superplasticity regime. This review attempts to systematize data from experimental studies which can be useful to form a more complete picture of physical nature of structural superplasticity phenomenon in various materials and necessary changes in material structure for transition to this deformation regime. It considers the effect of initial temperature-velocity conditions, meso- and microstructure of materials on the form of curves. The analysis of the considered experimental data confirms that the grain-boundary sliding is a predominant mechanism of superplastic deformation, but other mechanisms and processes play an important role: intragranular dislocation sliding, grain-boundary diffusion and rotation of crystallite lattice, along with the dynamic recrystallization. The paper performs and analyzes factographic data and their descriptions about a possible action of the above mechanisms and processes, their influence on each deformation stage and effect on the change in stress-strain state and material structure.

Despite a long history of research and a large number of publications, currently there are no methods for assessing and calculating the residual life of structural elements with their multi-cycle fatigue that would meet the requirements of engineering practice. In this regard, the role of physical methods to record the features of accumulation of local fatigue damage without stopping the operation or testing of various objects for fatigue increases. In the article two laser methods are used to study the origin of fatigue crack. Earlier, after testing for high-cycle fatigue of polished steel specimen with a Charpy notch, two zones of different sizes with different roughness were found near the notch. The first zone of 50´100 µm was located directly on the top of the notch. It consisted of inhomogeneities up to 10 µm in diameter and about 100 nm in height. In the center of the zone a macro-crack was discovered. The second zone with a diameter of 500-700 microns had a form of a hole (tie) with a depth of about 1 micron. Its center was located at a distance of 250-300 microns from the top of the notch. The aim of the work was to determine the formulation of inhomogeneities in a small zone and the sequence of the two zones’ occurrence. By using Raman microscopy, it is shown that the inhomogeneities are pieces of iron carbide. By the peculiarities of speckle image changes it is shown that the formation of two zones begins almost simultaneously. After the origination of a macro crack with a length of about 100 microns, a new plasticity zone at its top begins to form. Possible formation mechanisms of two zones are discussed. The disadvantages of the speckle method and the direction of further research are considered.