Maps of the strain tensor component εyy and profiles of the distribution of εyy along the length of the sample plotted by the method of digital image correlation are used to study the evolution of εyy and the width bb of the nucleating center, of the band nucleus and the band itself during tension of sample 1 of steel 08G2B exhibiting a high magnitude of the strain aging effect (SAE) after heating to Th = 250°C; the results are compared to the data for sample 2 (Th = 680°C) with low SAE. The experimental data obtained are used to reconstruct at the micro- (dislocation) level the process of formation and growth of the nucleating center and of the nucleus of the localized strain band emerging from it.

The aim of this paper is to describe a methodology for determining the elastic constants and thickness of the interphase between matrix and fiber in fiberglass plastic composites from macro- and micromechanical testing. Macromechanical testing is tension of unidirectional fiberglass plastics along and across the fiber direction. Micromechanical testing is tension of glass fibers and instrumented microindentation into the matrix and the fiberglass. The interphase thickness is determined by dynamic force microscopy on thin sections without a height difference. The measured interphase thickness is 621 nm. Based on the interphase thickness, a mesomechanical finite element model of a fiberglass monolayer is constructed. As a result, it is found that the elastic modulus and Poisson’s ratio are 12.7 GPa, 0.07. It is established that the elastic properties of the interphase differ significantly from those of the matrix. The paper also explores the possibility of determining the interphase thickness through computational experiments. It turns out that by knowing the actual elastic properties of the matrix and the fiber, as well as the fiberglass monolayer, it is feasible to calculate the interphase and its elastic properties with acceptable engineering accuracy. The deviation of the calculated interphase thickness from the experimentally measured one is 6%.

По картам компоненты тензора деформации εyy и профилям распределения εyy вдоль длины образца, построенных методом корреляции цифровых изображений, изучена эволюция εyy и ширины bп зародышевого центра, зародыша полосы и самой полосы в ходе растяжения образца 1 стали 08Г2Б, имеющего большую величину эффекта деформационного старения (ЭДС), после нагрева до Тн = 250 °C, а также образца 2 (Тн = 680 °C) с низким ЭДС. На основе полученных экспериментальных данных реконструирован на микро- (дислокационном) уровне процесс образования и роста зародышевого центра и выходящего из него зародыша полосы локализованной деформации.

Представлены результаты работы, выполненной методом корреляции цифровых изображений и состоящей из трех частей: I. Формирование зародыша полосы и очагов деформации. II. Деформация на площадке текучести. III. Потеря пластичности стали при деформационном старении. Все части отражают решение общей задачи: установить основные факторы на мезо/макроуровне, ответственные за снижение пластичности сталей с эффектом деформационного старения на площадке текучести, линейной и степенной стадиях, а также в целом при растяжении образцов до уровня предела прочности. В части I изучена эволюция структурно-деформационной картины на ниспадающей ветви зуба текучести и в начале площадки текучести. В части II приведены данные о ходе пластической деформации на площадке текучести. В части III описаны особенности деформации на линейной и степенной стадиях растяжения, а также проведен анализ результатов всей работы. В части I, приведенной в настоящем номере журнала, изучены механические свойства и характеристики деформации стали 08Г2Б, проявляющей различную величину эффекта деформационного старения после термической обработки по режимам: отжиг при 250 °C, 30 мин с охлаждением на воздухе и отжиг при 680 °C, 30 мин с охлаждением в воде. Показано, что, несмотря на значительно различающиеся прочностные и пластические свойства стали после разных режимов обработки, она деформируется на площадке текучести по одинаковому механизму Людерса. Механизм включает возникновение и рост зародышевых центров, зародышей полос локализованной деформации, их пересечение, а в середине образца — с образованием очаговых центров. Рассмотрены параметры, определяющие напряжение старта источников, испускающих дислокации плоских серий, которые формируют растущий зародыш полосы, что позволило объяснить влияние различных факторов на нижний и верхний пределы текучести в районе зуба. Проанализированы условия реализации полосового механизма деформации и его сочетание с рассредоточенной деформацией, при которой дислокации одновременно распространяются в различных системах скольжения.

The paper presents the results of studying the fracture of an epoxy layer in modified Brazil-nut-sandwich specimens. The effect of the angle α between the compression direction and the plane of the epoxy-metal interface on the fracture pattern is studied. The specimens with three adhesive compositions synthesized on the basis of the ED-20 epoxy resin are tested. It has been found that the cohesive failure mechanism dominates only at the angle α = 0° for all the epoxy compositions. The failure mechanism changes to the mixed adhesive-cohesive one as the angle α increased.

The mechanical properties and deformation characteristics of steel 08Mn2Nb manifesting different magnitudes of the effect of strain aging after the heat treatments with heating at 250°C (τ = 30 min) and air cooling and heating at 680°C (τ = 30 min) and water cooling are studied. It is shown that despite the significantly different strength and ductility properties of the steel after the two treatment modes, it is deformed in the yield plateau according to the same Luders mechanism. The mechanism involves emergence and growth of nucleating centers and nuclei of localized strain bands, their intersection at the center of the sample and formation of initiating centers. Tracing of the parameters that determine the initiating stress of the sources emitting dislocations of planar series, which form the growing nucleus of the band, has made it possible to explain the influence of various factors on the top and bottom yield points in the region of the yield drop. The conditions of implementation of the band deformation mechanism and its combination with distributed deformation, in which dislocations propagate simultaneously in different slip systems, are analyzed.

The paper reports the results of Brazilian tests on aluminum alloy specimens with an epoxy interlayer. ED-20 epoxy resin cured by polyamidepolyamine and diethylenetriamine is used as the interlayer. The stress state is varied by altering the tilt angle of the adhesion plane to the applied load in the range between 0 and 20 degrees. The experiments were performed at −50, +25, and +50°, and this corresponds to the range of climatic temperatures on the Eurasian continent. The experiments show that the composition of the curing agent affects differently the strength of the joints, depending on temperature and the angle between the action of the loading force and the adhesion plane.

X-ray diffraction analysis, ellipsometry, and optical microscopy have been used to study aluminum alloy samples (of Al and Al–2.3

The effect of the stress state on the deformability of an aluminum matrix composite with 10 vol% of SiC particles is studied by using the damage criterion. Backward extrusion of a standard cup-shaped part is used as an example. The process is simulated by the finite element method to evaluate the stress-strain state and damage. It has been found that, in order to make a high-quality product, it is necessary to carry out extrusion under all-round compression at near-solidus temperatures. A laboratory die was designed and manufactured for the experimental verification of the simulation results. The die is peculiar in that the value of compressive stresses can be controlled during deformation. The extrusion process yields a defect-free product. It has been revealed that heating to near-solidus temperature breaks the initial cellular structure of the composite under external loading.

The influence of Ar+ ion beams (energy E = 20 keV, ion current density j = 200 μA/cm2) on the fatigue resistance of samples of V95 alloy (Al–Zn–Mg–Cu) 6 mm thick cut from profiles in the state of delivery, after hot pressing and subsequent artificial aging, was studied. It was found that irradiation with Ar+ ions with a fluence of 1 × 1016 cm–2 contributes to an increase in the fatigue resistance of the alloy by a factor of 6.4 at the level of load amplitudes σ/σu = 0.3.

The features of plastic flow during tensile deformation of 08G2B steel samples exhibiting the effect of strain aging are studied by means of the digital image correlation method. Standard flat samples cut out from a sheet made by controlled rolling are tested for tensile strength after heat treatment according to the following conditions: 680 °C, holding time of 30 min, air cooling. It is shown that, at the stage of macroelastic deformation, there occur both diffuse plastic flow in separate parts of the sample under tension and the emergence of a nucleus center in the near-surface region, wherefrom a localized deformation band nucleus subsequently grows.

The plastic properties of specimens of Al — 2.3% V alloy and A85 aluminum, obtained by the method of selective laser melting, have been studied. Ultimate plasticity diagrams of these materials were plotted. It was found that the ultimate plasticity of the studied materials significantly depended on the deformation conditions (the type of stress state, which is characterized by the Lode—Nadai coefficient μσ). Thus, under tensile and shear test conditions (–1 ≤ μσ ≤ 0), the ultimate plasticity of the studied materials is practically the same. In the case of tests on extrusion of the bottom of a thick-walled cup (μσ = +1), the ultimate plasticity of the Al — 2.3% V alloy is approximately twice as high as that of primary aluminum under tensile stresses and by 30% higher under compressive stresses.

X-ray diffraction analysis, ellipsometry, and optical microscopy have been used to study aluminum alloy samples (of Al and Al-2.3% V) fabricated by 3D printing using selective laser melting. The mechanical properties of the resultant products have been compared. The strength and plastic properties of parts made from pure Al and Al-2.3% V alloys have been found to be insensitive to heat treatment. The addition of vanadium to pure Al showed that the Al-2.3% V alloy has significantly improved performance properties compared to those of primary aluminum, without affecting its initial plasticity.

Rotary friction welding (RFW) is used in the production of drill pipes for solid mineral prospecting. The need for the creation of the lightened drill strings for high-speed diamond drilling of ultradeep wells dictates the necessity of a greater focus on the study of a weld zone and setting the RFW technological parameters. This paper presents the results of experimental studies of a welded joint of a drill pipe of the H standard size according to ISO 10097, made of the 30ХГСА (pipe body) and 40ХМФА (tool joint) steels under the cyclic loads. The authors evaluated the influence of the force applied to the workpieces in the process of friction of the contacting surfaces (force during heating), and postweld tempering at a temperature of 550 °С on the cyclic life of welded joints, under the conditions of alternate tension-compression at the cycle amplitude stress of ±420 MPa. The study determined that with an increase in the force during heating, the microstructure changes occur in the zone of thermomechanical influence, contributing to an increase in the fatigue strength of welded joints. The authors identified the negative effect of postweld tempering on the fatigue strength of welded joints, which is expressed in the decrease in the number of cycles before failure by 15–40 %, depending on the magnitude of the force during heating. The optimal RFW mode of the specified combination of steels is determined, which provides the largest number of cycles before failure: the force during heating (at friction) Fh=120 kN, forging force Ffor=160 kN, rotational frequency during heating n=800 Rpm, and upset during heating l=8 mm. A series of fatigue tests have been carried out at various values of the cycle amplitude stress of the welded joint produced at the optimal mode and the 30ХГСА steel base metal; limited endurance curves have been plotted. It is shown that the differences in the limited endurance curves of the pipe body material (30ХГСА steel) and the welded joint are insignificant. The obtained results are supplemented by the microhardness measurement data and fractographs of fractured samples, revealing the mechanism of crack propagation under the cyclic loads.

In order to improve non-destructive methods for assessing the stress state of metal constructions, the effect of biaxial tension on the coercive force of low-alloy steel has been studied. The experiment was performed on an original biaxial testing machine, in the working area of which there are no ferromagnetic parts. The geometry of the cruciform specimen with recess in the central zone made it possible to obtain an area for measuring magnetic properties with a uniform distribution of stress intensity. The magnetic characteristics of the material under the action of stresses were measured with U -shaped electromagnetic sensor. The greatest relative changes in the coercive force were in the uniaxial stress state in the case of magnetic measurements perpendicular to the direction of load application. Changes in the coercive force under symmetrical tension are close to the measurement error, regardless of the direction of magnetic measurements. If sensor is positioned at an angle of 45º to the load axes, the coercive force is most sensitive to uniaxial loads.

The paper studies changes in the structural state of a Ni–Fe–Cr–Ti–B–C composite after hot plastic deformation. The matrix of the composite consists of a mechanical mixture of two solid solutions: austenite and ferrite. Titanium carbide and diboride particles resulting from self-propagating high-temperature synthesis (SHS) are the strengthening phases. Additional strengthening is provided by carbide Cr23C6 and intermetallic Ni3Ti particles formed in austenite during cooling. The constituent with a ferrite matrix, which is a mixture of α-(Cr,Fe) + TiB2 + TiC + Cr23C6, is shown to have the highest ductility. The strongest constituent of the composite is represented by regions with an austenitic matrix and the most abundant TiB2 particles. These regions are characterized by the highest hardness, elastic modulus, elastic recovery Re and wear resistance ratio HIT/E. The hardness of the composite is 58 HRC. For plastic deformation of the composite, it is proposed to perform hot rolling at a heating temperature of 1000 °C under all-round compression. To do this, a composite specimen is pressed into a 10 mm steel shell, with 6 mm steel plates welded on top and from below. True plastic strain ε = 0.6 is achieved under these conditions. EBSD analysis testifies that the deformation is implemented due to dynamic polygonization and recrystallization of the austenitic and ferritic grains of the composite matrix. Dynamic recrystallization prevails in the austenitic grains, whereas dynamic polygonization predominates in the ferritic ones.

Composites with a copper matrix attract the attention of researchers due to their ability to combine high ductility, heat conductivity, and electrical conductivity of the matrix with the high hardness and strength of the reinforcing phases. In this paper, we present the results of studying the effect of thermal deformation processing of a Сu-Ti-C-B composite produced by self-propagating high-temperature synthesis (SHS) on its ability to deform plastically without failure. The composite consists of a copper matrix and reinforced particles of titanium carbide TiC (sized up to 1.0 μm) and titanium diboride TiB2 (sized up to 3.0 μm). The composite hardness is 60 HRC. Under uniaxial compression, the composite starts to deform plastically at a temperature of 700 °C and a pressure of 100 MPa. Temperatures ranging between 765 and 800 °C and an initial pressure of 150 MPa prove to be the most effective condition for composite deformation. These conditions enabled a true strain of 0.36 to be obtained without composite failure. Under higher strain, surface cracks appeared on the specimen surface. The EBSD analysis shows that dynamic recrystallization prevails at a deformation temperature of at least 765 °C; therefore, the composite can plastically deform. To increase the deformability of the composite, it is proposed to perform deformation under conditions of a favorable stress state. Based on the results of numerical modeling by the finite element method, the critical diameter of the steel shell is determined, which is sufficient for deformation of the composite with the most uniform distribution of the stress coefficient k. Composite deformation in a steel shell under a pressure of 150 MPa, at 800 °C, is experimentally implemented until a true strain of 0.53 is reached.

The mechanical properties and microstructure of an α + β VT23 titanium alloy are studied after quenching under various conditions and strengthening aging. Aging at 500°C for 8 h is shown to decrease the static fracture toughness (SFT) of the alloy quenched from 800 or 860°C by a factor of 1.4 and 2.4, respectively. The highest set of strength properties and static fracture toughness (σ 0.2 = 1130 MPa, σ u = 1252 MPa, K 1 c = 39.2 MPa m 1/2 ) at a retained sufficient structural strength reserve T = 44.4 × 10 3 MPa 2 m 1/2 is achieved after quenching from 800°C and subsequent aging at 500°C for 8 h. The regularities of the evolution of the phase composition and the structure of the alloy as a function of heat-treatment conditions are found. The peculiarities of the macro- and microstructure of the fracture surfaces of compact ST specimens after static fracture toughness tests are revealed.

Frictional treatment, as a method of surface plastic deformation, forms a gradient hardened layer. In the case of metastable steels, this hardening is due, among other things, to the formation of strain-induced α'-martensite. The most reliable information about the thickness of this hardened layer can be obtained by measuring the hardness on transverse sections. This paper compares strain distribution through the depth of the hardened layer, obtained from layer-by-layer phase analysis and finite element modeling, with the data of durametric studies for the AISI 321 metastable steel subjected to frictional treatment under various loads on the indenter. A satisfactory coincidence of the distributions of the α'-phase concentration and hardness through the depth is observed only for the specimen subjected to frictional treatment at a maximum load of 400 N on the indenter. At the other loads on the indenter, the thickness of the layer containing α'-martensite is lower than the thickness of the hardened layer estimated from the durametric studies. In contrast, it is shown that, for all the loads applied to the indenter during frictional treatment, the through-depth distributions of the calculated values of equivalent plastic strain obtained from finite element modeling agree satisfactorily with the experimental hardness values.

The regularities of the effect of a complex stress state on the strength of an AlMg5/epoxy adhesive joint are experimentally studied at −50 and +23 °C in tension+shear and compression+shear tests with different normal-to-shear stress ratios. The tests use modified Arcan specimens and Brazil-nut-sandwich specimens, with the lateral faces of the adhesive layer having a shape of a mushroom-like “ridge” aimed at reducing stress concentration at the specimen edges. An original computational model of a selected microvolume including the interface together with the adjacent substrate and adhesive layers is used to process the experimental results. The attainment of the threshold value of strain energy density in the selected microvolume, W*, is used as the failure criterion. The effect of the hardener composition, the testing temperature, and the value of the phase angle β determining the proportion of normal and shear stresses at the adhesive interface on the threshold value W* is detected. W*(β) diagrams (fracture loci) are plotted and analytically described logarithmic functions. They can be used to make strength calculations for adhesive joints in structures and metal-polymer composites.