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Results of experimental investigation of mechanical characteristics of ULTEM 9085 thermoplastic, produced by additive manufacturing, i.e., the method of layer-by-layer application of a molten polymer thread, are presented. Flat specimens were tensile tested within the temperature range of (–40) –150°C. Temperature dependencies of ultimate strength, relative elongation at break, elastic modulus, and Poisson’s ratio are obtained. At a temperature of –40°C, the linear sections of diagrams obtained for various specimens coincide; in the area of elastoplastic deformations, their discrepancy is noted. This caused small variations in elastic characteristics and significant ones in strength and relative elongation at break. Similar features of deformation diagrams were also obtained at a temperature of 50°C. However, at 150°C, tensile diagrams do not coincide even in the area of small elastic deformations; their specific bends are noted. Specimens are fractured by the normal separation mechanism at all temperatures. When the temperature changes from –40 to 150°C, thermoplastic ultimate strength almost linearly decreases; at 150°C it is 26% of the initial value at –40 °C. As temperature increases within the specified range, the relative elongation at break monotonously decreases more than twice (2.9–1.3%). The elastic modulus changes insignificantly within a temperature range of (–40)–20°C; when the temperature rises to 150°C, it decreases to 64% of the value at –40 °C. Poisson’s ratio virtually does not change and is in the range of 0.36–0.37.

The paper presents fatigue test results for 2219 aluminum alloy specimens, cut from a plate 40 mm in thickness, under symmetric and pulsating loading cycle. It is shown that at stresses for above the endurance limit, the fracture of specimens has a multi-site nature and starts from their surface. At stresses close to the endurance limit, the fatigue crack in the specimens fractured at a smaller number of loading cycles is initiated from their surface and at longer lives, from subsurface fracture initiation sites. This accounts for the significant scatter of data on the life of specimens near the endurance limit. Fatigue tests under zero-to-tension loading cycle showed that under the same heat treatment conditions, the endurance limit value of specimens made by resistance butt welding is close to that of specimens without weld and much higher than that of specimens with argon-arc weld. The fractographic investigations of the fracture of specimens with weld show that in both types of welding, the fatigue cracks propagate through pores in the weld or in the heat-affected zone.

The paper considers the processes related to the specimens and loading device in the tensile testing of metals in strain-controlled mode, including under the conditions of cryogenic temperatures up to 4.2 K. It is demonstrated how the potential elastic energy accumulation and its subsequent relaxation in the development of the specimen strain affect the process of kinetics. The strain rate dependencies on the strain value and stiffness factor (relation between the values of stiffness of the specimen and the machine) are obtained. Noteworthy is that the values of initial and nominal strain rates can differ by an order of magnitude in case of the machine compliance. To obtain the strain rates that are similar for different machines at the initial stage of the process, the formula is proposed allowing one to calculate the required nominal rate. At the temperatures lower than 30 K there is a dramatic increase of the influence of the machine stiffness, dimensions and shape of the specimens on the obtained characteristics, which requires the special measures in the process of testing. Some international and national standards are considered. It is shown that, at present, the process of standardization for tensile testing of metals is inadequate, and the requirements of the current regulatory documents are the minimum, which are not in agreement with the development paces of testing equipment. To significantly enhance the level of accuracy of the obtained mechanical characteristics, it is required to employ the urgent measures as the machine compliance limitation, as well as the decrease of the dimensions range for the specimens together with the standardization of the permissible range of the stiffness factor, and the required selection of the nominal strain rate considering the latter.

In this study, the stress concentration effect on the low-temperature strain-hardening of 12Kh18N10T and 03Kh20N16AG6 steels is investigated. It is shown that cooling of notched specimens from these steels to the temperature of liquid helium results in the increase of their ultimate strength values by 165 u 240%, respectively, whereas the structural factor contribution is significantly reduced for the former steel and remains unchanged for the latter one.

A particularly strong hardening of the specimens made of austenitic steels with notches of a large radius of bending has been detected at the temperature of 4.2 K. This phenomenon is attributed to special conditions of realization of the low-temperature discontinuous flow effect. The correlation between the strength characteristic and the number of strain jumps in the zone of stress concentration has been revealed.

The paper addresses the temperature and thermoelastic states of a single-crystal blade with a complex vortex cooling system and passages for cooling air outflow. The problem of determination of stress-strain state of the blade at hand under the action of temperature fields and centrifugal forces is solved by the finite element method. The authors study the influence of azimuth orientation of crystallographic axes on the distribution and magnitude of thermoelastic stresses in the blade volume.

The influence of machine compliance on the standard mechanical characteristics of metallic materials is investigated. It is shown that with an increase of compliance percent elongation and reduction of area after fracture decrease by several times. At cryogenic temperatures ultimate strength can decrease to the level of yield strength due to the effect of jumplike deformation of metals.

Tensile tests of titanium alloy and austenitic steel specimens have been conducted in the range of temperatures 300–4 K. Under deep-freezing conditions, there occurs a new type of scale effect – variation of low-temperature jumplike deformation, which causes a sharp variation of the plasticity characteristic (the relative elongation). The difference between jumplike deformation values in the maximum and minimum cross-sectional areas of standard cylindrical specimens is introduced as the scale effect measure. Via mathematical modeling performed for 03Kh20N16AG6 steel, we have obtained dependencies of the scale effect on the most critical factors – the trigger stress of deformation jump and specimen–test machine system stiffness. The scale effect nature is studied, and options of its minimization, in reference to the standardization of mechanical tests, are discussed.

Force, deformation, velocity, energy, and other criteria of limiting states at low-temperature serrated yield of metals are examined. The feasibility of their use for setting norms and standards of strength and mechanical tests is demonstrated.

The regularities of repeated necking have been studies on flat specimens of alloys for cryogenic engineering in the case of effect of low-temperature discontinuous yield. It has been shown that in contrast to cylindrical specimens, in this particular case there is a considerable deviation of the stressed state from linear stress, which affects greatly the mechanical characteristics determined and does not allow flat specimens to be recommended for standard mechanical tensile tests of metals at temperatures below 30 K.

In relation to the problem of determining reliable values of mechanical characteristics of metallic materials at temperatures below 30 K, the peculiarities of repeated neck fomation have been studied on cylindrical specimens of structural alloys for cryogenic engineering in the case of occurrence of the effect of low-temperature discontinuous yield. The evaluation performed of the rigidity and inhomogeneity of the three-dimensional stressed state of typical necks showed that it differs only slightly from linear stress, and that the use of such specimens for standard mechanical testing under deep freezing conditions is reasonable.

Based on 3D finite-element models, a procedure for analyzing a spatial stress-strain state in the stator-scroll assembly of hydroturbine units has been developed. It allows determination of stresses and their localization zones in structures that contain not only identical but also similar components. The output data visualization makes it possible to identify the places of stress localization in the system and in its components.

The paper presents the results of an investigation into the low-temperature jumplike deformation of BrKh08Tsr bronze and the effect of pulsed magnetic cycling on its regularities. The authors established the regularities of build-up of strain with increasing magnetic field strength and applied load. The possibility of experimental modeling of the phenomenon of intermittent yielding by the method of superposition of magnetic field pulses was demonstrated and a corresponding mathematical model of the deformation process was developed.

The effect of stress concentration on the mechanical behavior of 03KH20N16AG6 steel over a temperature range of 293–4.2 K is studied. The flow discontinuity effect under cryogenic cooling is shown to appear with a decrease in theoretical stress concentration factors, which gives rise to anomalous changes in strength and plasticity characteristics of the material.

We present the results of investigations into the deformability and strength of conical and tubular specimens of 03Kh20N16AG6 and 12Kh18N10O steels in uniaxial tension over a temperature range of 293–4.2 K. It is demonstrated that the deformability of the above steels is related to the geometry of the test object, whereas the character of this relation is determined by the test temperature and class of steel. At a temperature of 4.2 K, a qualitative change in the deformation mechanisms occurs, as a result of which the influence of the design factors changes significantly. A drop in the plasticity for both types of the specimens and a considerable hardening of the 03Kh20N16AG6 steel thin-walled tubular specimens are noted.

The given study shows that, in subzero cooling, relatively small changes in specimen dimensions can have a considerable influence on the mechanical properties and intermittent yielding by changing qualitatively the low-temperature deformation mechanism. The authors propose a new criterion of energy similarity of mechanical test conditions to study the size-scale effect manifestations and to obtain comparable characteristics of various materials.

The process of kinematic braze-welding of thin-walled tube plates and tubular elements in making heat exchangers is considered. The process is simulated by the high-velocity contact interaction of coaxial cylinders with a thin layer of high-strength amorphous solder between them. The inner cylinder expands by the action of explosive pulse load. When solving the thermoelastoplasticity problem, the dynamic properties of the material are taken into account. This process has been experimentally investigated using test specimens.

Crack resistance test results for plastic steel specimens cut from the pipe of the linear section of an oil pipeline are discussed. For studying anisotropy of properties, the crack in the specimen was oriented in the axial and circumferential pipe directions. Cyclic crack resistance values for examined steel after long-term service are cited.

We analyze the results of experimental investigations of the complex effect of various modes of prestraining and deep cooling and the strain rate on the mechanical characteristics of alloys used in cryogenic equipment. It is demonstrated that the strength characteristics of some materials can be significantly improved by strain and low-temperature hardening while preserving rather high levels of plasticity. The changes in the mechanism of deformation of metals at a temperature of 4.2 K caused by the phenomenon of intermittent yield are responsible for the anomaly of the Bauschinger effect.

The results of investigating the effect of loading system stiffness on the parameters of low-temperature intermittent yield and the mechanical characteristics of the steels 03Kh20N16AG6 and 12Kh18N10T and the titanium alloy 3M at 4.2 K at different development stages of plastic strain instability are presented. Criteria of fracture by the adiabatic-shear mechanism are considered. An analysis of the stiffness components of an electrohydraulically driven testing machine is given. The necessity of laying down stiffness regulations for conventional mechanical tests of materials has been shown.

The results of investigating the effect of deformation rate and loading conditions in the presence of a prestrain on the parameters of low-temperature intermittent yield and the mechanical properties of the steels 03Kh20N16AG6 and 12Kh18N10T and the titanium alloy 3M have been considered, taking into account the stepwise development of jumplike deformation. Kinetic criteria of the loss of plastic-deformation stability are given, and the fracture conditions during deformation jump and after its end have been formulated. The necessity of improving the standards for testing materials under deep chilling conditions has been shown.

The paper presents the results of fatigue tests of specimens cut from 630-mm-diameter 018GS2 steel pipes from the "Druzhba" oil pipeline prior to and after a long period of operation. We have found that the fatigue strength of the base and weld metal decreased upon long operation by 14.9% and 9.5%, respectively. Analysis has demonstrated that in the course of operation of linear sections of oil pipelines the material properties of the inner pipe surface deteriorate steadily and substantially, and it is this deterioration which constrains the operating reliability of the pipeline.

We propose an approach to determination of allowable stresses by a static-strength criterion for materials of structures that operate at very low temperatures (T≤20 K). This approach takes into account the qualitative change in the nature of deformation of the material, which has a significant effect on the mechanical characteristics and the specific work of deformation. The choice of critical stresses for these conditions is substantiated. The calculations are performed by introducing corrections for low-temperature hardening of the material in the presence of the intermittent-flow effect. We discuss the possibility of taking into account the influence of strong magnetic fields on the magnitude of allowable stresses.

We propose a mathematical model of jumpwise deformation under conditions of deep cooling based on an analysis of the localized adiabatic heat release, inertial properties, and accumulated elastic energy of loading forces. The model enables one to give a qualitative description of the kinetics of intermittent flow of metals and establish quantitative estimates of the parameters of the jumps of strains, which are in reasonably good agreement with the experimental data and adequately describe the mechanical behavior of the material depending on the conditions of loading and deformation. We also consider the influence of various factors on the possibility of suppressing of the effect of mechanical instability of metals, which is of significant practical interest.

The investigation results for the effect of stress concentration on the mechanical behavior of titanium alloy 3M and aluminum alloy AMg5 within the temperature range of 293 to 4.2 K Under conditions of deep cooling, its character is shown to change considerably due to a manifestation of the effect of low-temperature jumplike deformation.

On the basis of the proposed method of additional pulse loading of static preloaded specimens at temperatures of 293 and 77 K, we theoretically and experimentally established the possibility of effects similar to the effects of low-temperature discontinuous yield. The obtained effects are caused by operating-technological factors and can be observed only in the process of deep cooling. In particular, by using 03Kh20N16AG6 steel as an example, we show that as the loading rate, the level of preliminarily inclused strains in the material, or the amount of accumulated elastic energy of the loaded system increase, the jumplike development of strains results in a sharp decrease in strain resistance.

The theoretical fundamentals of the operations for freeing a drill column and a bit from stickages were formulated on the basis of an analysis of pulsed loading of the stuck elements of a drill tool. Three variations of explosive loading of a drill tool by successive detonation of charges located within the drill column in the zone of stickage and containing the amount of energy necessary for breaking of the bonds of the column with the soil causing stickage are given.

Results are considered of an experimental study of the combined effect of various factors (prior strain, loading system stiffness, and strain rate) on features of low-temperature serrated yielding of austenitic steels 03Kh20N16AG6 and 12Kh18N10T. It is shown that with high (quasistatic) loading rates r quite high accumulated elastic energy the presence of prior strain causes a quite sharp reduction in material strain resistance. This effect should be considered in evaluating the operating capacity of the rod structural elements under low-temperature conditions.

The article presents the results of the theoretical and experimental investigation of low-temperature intermittent yield for the state of uniaxial stress. It describes the mechanisms of appearance and the kinetics of stress jumps upon loss of thermal and plastic stability. It deals with the role of strain-hardening of material at the appearance and development of intermittent yield. It formulates the conditions of realization of intermittent yield and failure of a rod upon a jump of strain and stress.

We examine the application of the static condensation method in reducing the dimension of the resolving equations in calculating the natural frequencies and modes of turbine blades of complex geometric configuration on the basis of three-dimensional finite element models. We show the influence of the number of active nodes on the calculation accuracy and time for examples of the solution of test and real problems.

Separation of structural components is considered as a high-speed directed local destruction of an object in the area of a specially applied concentrator. Elements in the form of plates and shells of arbitrary curvature have been taken as destruction objects. Calculations have been made by explicit finite-element methods. Results of the investigation performed have found practical applications.

A nonlinear model of the process of low-temperature discontinuous yielding of metals has been constructed, which allows the totality of strain jumps to be described as a function of the mechanical properties of material and dynamic characteristics of the loading system. The adequacy of the model has been experimentally verified for austenitic steel and an aluminum alloy.

Results are provided for a theoretical and experimental study of the features of low-temperature interrupted yield of structural alloys taking account of loading system stiffness, deformation rate, and loading regime. Associated thermal effects are evaluated and criteria are considered for heat loss and the plastic stability of deformation.