Elastic Tensile Stresses Research Articles

К вопросу о влиянии температуры закалки и уровня одноосных напряжений растяжения на параметры гамма-альфа превращения в мартенситно-стареющей стали при переохлаждении в интервал минусовых температур

Based on the constructed diagrams of the isothermal decomposition of quenched retained austenite, the kinetics of martensitic gamma-alpha-transformation under mechanical load at sub-zero temperatures in maraging steel 08H15N5D2T (rus) was studied. An analysis was made of the changes in the retained austenite resistance to overcooling, isothermal decomposition and resistance to uniaxial tensile stresses in the temperature range from 0 to -100 °C. It has been shown that without load, the stability of retained austenite in the sub-zero temperature range depends on the quenching temperature. After quenching from 1050 °C residual austenite has the highest resistance to overcooling. The resistance of retained austenite to isothermal decomposition is more complex and depends on the quenching temperature. Applied elastic tensile stresses in the range from 20 to 450 MPa significantly and ambiguously changed the nature of the martensitic gamma-alpha-transformation. The instability of the pre-martensitic state and the low shear stability of the retained austenite in the surface layer predetermined the formation of two types of martensite in the structure of the steel under study and the wave-like (stage-by-stage) nature of the resistance of austenite to elastic loads.

Влияние остаточных напряжений в стали У8 с грубопластинчатым перлитом на магнитную проницаемость

The physical reasons for the formation of peaks of that part of the magnetic permeability, which is caused by transitions of only 90-degree domain boundaries µ90(H0) in deformed steel U8 with coarse-plate perlite when the field changes along the back of the hysteresis loop, are considered. It is shown that the orientation relations of the Patch-Pitch between single-crystal ferrite and cementite plates in U8 steel lead to the appearance of a constant angle between the magnetic moments of these plates and, consequently, to the appearance of corresponding local scattering fields. The latter can significantly affect the values of the peak fields of the curve µ90(H0). Theoretical expressions for these fields containing contributions of scattering fields that should be taken into account when determining residual compressive stresses are obtained. It is also shown that to determine the residual stresses, two expressions for peak fields are not enough, and additional experiments are needed, as which it is proposed to use the dependences of the coercive force on elastic tensile stresses. This leads to a complication of the algorithm for determining residual compressive stresses in comparison with the case of low-carbon steels. A method for estimating the values of local scattering fields in the ferrite parts of U8 steel grains with residual compressive stresses is proposed.

Estimation of residual compressive stresses in deformed U8 steels with coarse-plate perlite by field dependences of magnetic permeability

The physical reasons for the formation of peaks of that part of the magnetic permeability, which is caused by transitions of only 90-degree domain boundaries μ90(H0) in deformed steel U8 with coarse-plate perlite when the field changes along the back of the hysteresis loop, are considered. It is shown that the orientation relations of the Patch-Pitch between single-crystal ferrite and cementite plates in U8 steel lead to the appearance of a constant angle between the magnetic moments of these plates and, consequently, to the appearance of corresponding local scattering fields. The latter can significantly affect the values of the peak fields of the curve μ90(H0). Theoretical expressions for these fields containing contributions of scattering fields that should be taken into account when determining residual compressive stresses are obtained. It is also shown that to determine the residual stresses, two expressions for peak fields are not enough, and additional experiments are needed, as which it is proposed to use the dependences of the coercive force on elastic tensile stresses. This leads to a complication of the algorithm for determining residual compressive stresses in comparison with the case of low-carbon steels. A method for estimating the values of local scattering fields in the ferrite parts of U8 steel grains with residual compressive stresses is proposed. Keywords: residual compressive stresses, deformed steel U8 with coarse-plate perlite, magnetic field, magnetization, magnetic permeability, 90-degree domain boundaries (DB), large-angle vicinity(LAV) and small-angle (SAV) grain boundaries of steel, orientation relations of the Patch-Pitch.

Study on pitting corrosion behavior and semi in-situ pitting corrosion growth model of 304 L SS with elastic stress in NaCl corrosion environment

The passive film characterization and pitting corrosion behavior of 304 L SS with various elastic tensile and compressive stresses are investigated by electrochemical measurements, acoustic emission, X-ray photoelectron spectroscopy and scanning electron microscope. The elastic tensile stress could decrease the pitting corrosion sensitivity of 304 L SS at 16.63%σ0.2. As the elastic tensile stress further increases, the pitting corrosion sensitivity of 304 L SS increases. The compressive stress has the opposite effect on 304 L SS localized corrosion behavior. X-ray computed tomography is employed to construct the four-dimensional space-time model of pitting corrosion growth of 304 L SS under the 63.24%σ0.2 elastic tensile stress.

The effect of direct current in a steel rod on the switching field dependence of magnetic permeability

It is theoretically shown that in cases where the process of irreversible magnetization reversal of ferromagnetic steels is determined by displacements of only 180° domain boundaries, the dependences of reversible permeability on the switching field in low-carbon steels when a direct current is passed along a rod sample should have two maxima instead of the usual one that occurs in the absence of this current. The distances between the maxima of these peaks linearly depend on the value of the constant component of the current and, consequently, on the constant circular magnetic field caused by it, perpendicular to the switching field. This phenomenon should occur both for undeformed steel samples in the state after annealing and for samples after plastic stretching. In the latter case, elastic tensile stresses of such magnitude should act to compensate for internal residual compressive stresses. The fields of both peaks of magnetic permeability in these two cases are close to each other.

Self-Organization of the Composition of AlxGa1 – xN Films Grown on Hybrid SiC/Si Substrates

The phenomenon of self-organized change in the composition of epitaxial layers of the AlxGa1 ‒ xN solid solution during their growth by chloride-hydride epitaxy on SiC/Si(111) hybrid substrates is discovered using spectral ellipsometry, Raman spectroscopy, and scanning microscopy with an X-ray spectrometer. It is found that interlayers or domains consisting of AlGaN of stoichiometric composition appear during the growth of AlxGa1 – xN layers with a low (about 11–24%) content of Al. A qualitative model is proposed, according to which self-organization in composition occurs due to the effect of two processes on the growth kinetics of the AlxGa1 – xN film. The first process is associated with the competition of two chemical reactions proceeding at different rates. One of these reactions is the formation of AlN; the second reaction is the formation of GaN. The second process, closely related to the first one, is the appearance of elastic compressive and tensile stresses during the growth of AlxGa1 – xN films on SiC/Si(111). Both processes influence each other, which leads to a complex pattern of aperiodic variation of the composition over the thickness of the film layer.

Tension stiffening model for lightly confined reinforced concrete elements

Reinforced concrete (RC) walls subject to in-plane lateral loads are essentially subject to axial compression and tension forces in the respective end regions of the wall. The tension forces initially result in elastic tensile stresses in both the concrete and longitudinal reinforcement. Cracking occurs after the maximum tensile stress of the concrete has been exceeded and results in the reinforcement providing the sole tensile resistance at each crack location. The mechanical interlock between the reinforcement and concrete means that a portion of the tensile stress in the reinforcement at each crack is transferred back into the concrete between adjacent cracks. This mechanism stiffens the concrete in tension and is referred to as tension stiffening. This paper presents a generalised tension stiffening model developed for limited ductile (i.e. lightly confined) RC walls. However, it is also applicable for lightly confined RC elements generally. The model was validated against 14 boundary element prism specimens subject to cyclic loading, with very good correlation observed between the theoretical model and the experimental results. This model can easily be adopted into a sectional analysis procedure to account for tension stiffening in both the elastic and inelastic regions of response in an RC wall.

Самоорганизация состава пленок Al-=SUB=-x-=/SUB=-Ga-=SUB=-1-x-=/SUB=-N, выращенных на гибридных подложках SiC/Si

Using spectral ellipsometry, Raman spectroscopy, and scanning microscopy with an X-ray spectrometer (EDS), the phenomenon of self-organized change in the composition of AlxGa1-xN epitaxial layers during their growth by chloride-hydride epitaxy (EDX) on SiC / Si (111) hybrid substrates was revealed. It was found that during the growth of AlxGa1-xN layers with a low, about 11-24% Al content, interlayers (domains) appear, consisting of AlGaN stoichiometric composition. A qualitative model has been proposed, according to which self-organization in composition arises due to the effect of two processes on the growth kinetics of the AlxGa1-xN film. The first process is associated with the competition of two chemical reactions proceeding at different rates. One of these reactions is the AlN formation reaction; the second is the reaction of GaN formation. The second process, closely related to the first, is the appearance of elastic compressive and tensile stresses during the growth of AlxGa1-xN films by the CGE method on SiC / Si (111). Both processes influence each other, which leads to a complex pattern of aperiodic changes in the composition over the thickness of the film layer. Keywords: A3B5 compounds, wide-gap semiconductors, AlGaN, AlN, GaN, silicon carbide on silicon, self-organization of the composition, HVPE method, solid solutions, heterostructures.

Effect of Heat Treatment on the Magnetoimpedance of Soft Magnetic Co68.5Fe4Si15B12.5 Amorphous Ribbons

Abstract—This work studies the effect of heat treatment on the magnetoimpedance (MI) effect of soft magnetic Co68.5Fe4Si15B12.5 amorphous ribbons prepared by melt quenching on a rotating wheel. It was found that after heat treatments at temperatures of 100°C and higher there occur irreversible changes of MI over a wide range of excitation ac frequencies. A change in the magnetoimpedance response to the action of elastic tensile stresses is shown to be related to the change in the sign of saturation magnetostriction coefficient (λS), which results from the heat treatment.

The effect of a constant tensile load on the hydrogen diffusivity in dual phase steel by electrochemical permeation experiments

This work considers the effect of a constant load on the hydrogen diffusion characteristics studied by electrochemical permeation experiments. Dual phase steel and Armco iron are used for this purpose. Different degrees of load, both in the elastic and plastic regime, are applied on the sample during the permeation experiment when hydrogen is migrating through the material. The resulting transients show that applied elastic tensile stresses increase the hydrogen diffusion coefficient of both materials. Due to the elastic stress, the crystallographic lattice expands which increases hydrogen diffusivity. From an applied constant load of 100% of the yield strength and higher, the diffusivity decreases again. This is associated to the formation of lattice defects such as vacancies, vacancy clusters and dislocations. The strain state of the specimen in the constant loading device at different loading conditions is obtained by digital image correlation. This revealed that the in-situ instrumentation is key and confirmed that a homogeneous strain distribution is present in the zone of interest for the permeation experiments.

Application of Magnetic Noise Method to Control the Mechanical Anisotropy of Ferromagnetic Materials

Presence of anisotropy of the ferromagnetic materials' properties determines the need for its research and control, since it has a significant impact on the basic physicomechanical characteristics of details, products and constructions. The aim of the work was to experimentally investigate the possibility of using the magnetic noise method for non-destructive testing of mechanical properties of ferromagnetic materials particularly value of the coefficient of normal anisotropy Rn of sheet metal, mechanical stresses under elastic deformation of electrical steel and the anisotropy of the physical and mechanical properties of ferromagnetic materials.Since the mechanical anisotropy is related to the magnetic anisotropy, the magnetic method of the Barkhausen effect (MBE) was used in its study, the informative parameters of which belong to the group of magnetic anisotropy. Comparison of the results of anisotropy evaluation on a set of samples of stamped sheet steel using the MBE with values Rn measured by the manufacturer showed their close match. This revealed the possibility of Rn level evaluation using the MBE. Device for circular rotation of the Barkhausen transducer on the sample surface and device for forming of elastic bending stresses in the sample were constructed. To study the magnetic anisotropy in various materials and the impact of elastic tensile and compressive stresses by bending on it using the MBE.It has been found that the elastic deformation in samples of electrical steel leads to dramatic change of the magnetic noise level and the shape of the circular diagrams, taking into account the sign of the stresses generated in the sample. It was established that as a result of cold rolling in the production process, electrical steel samples have a pronounced texture due to the direction of rolled sheet. The created elastic stresses in the considered range practically do not change the texture (induced crystallographic anisotropy) after the material rolling.The results can be useful for studying, monitoring and testing of anisotropy, crystallographic texture, structural heterogeneity of ferromagnetic materials in the form of sheet metal, sheet steel and coil steel, sheet metal forming and for solving other problems using the magnetic noise method in aboratory and workshop conditions.

Effect of Elastic Stresses on Pitting Behavior of Stainless Steel 304

Stress/deformation-induced accelerated corrosion has been reported for many alloys used in structural and functional applications. To understand the effect of applied elastic stresses on corrosion behavior of alloys, samples of stainless steel (SS) 304 were subjected to different levels of elastic tensile stresses and their corrosion behavior was studied. The applied elastic stress is believed to alter materials’ pitting behavior in chloride-containing environments. Results from this study show that applied tensile stresses hinder pitting resistance of SS304. Stress and stress concentration around pit vicinity accelerate salt-film repair, thereby impeding repassivation. Through this mechanism, pit growth is stabilized. Results from electrochemical tests on samples at different elastic stress levels are discussed in this paper.

Parametric study of the distribution of the tensile stresses in pavilion structures constituted by four sectors of barrel shells

A semi-analytical approach is followed in order to obtain an approximate solution for an analytical model describing the static behaviour of pavilion shells. With the aim to parametrically investigate the distribution of the linear elastic tensile stresses, a linear elastic isotropic behaviour of the material is considered. Inside the pavilion shell, a family of arches and a family of straight beams can be recognized. This assumption justifies the separation of the variables which is at the basis of the proposed semi-analytical approach. The sensitivity of the behaviour of the shells to the values of the mechanical and geometrical parameters characterizing the system is investigated. Comparisons with results obtained by finite element models are performed to confirm both the validity of the semi-analytical approach and the provided results. Since only a linear elastic isotropic material has been taken into account, the results do not claim to describe the behaviour of masonry pavilion vaults.

Numerical Modeling of Fracture-Resistant Sn Micropillars as Anode for Lithium Ion Batteries

Sn possesses three times higher capacity in comparison to graphite anode (372 mAhg–1) that makes it a promising candidate for enhanced performance Li ion batteries. Contrary to Si, Sn is compliant and ductile in nature and thus is expected to readily relax the Li diffusion-induced stresses. The low melting point of Sn additionally allows for stress relaxations from time-dependent or creep deformations even at room temperature. In this study, numerical modeling is used to reveal the significance of plasticity and creep-based stress relaxations in the Sn working electrode. The maximum elastic tensile hoop stresses for 1 μm micropillar size with 1C charging rate conditions reduces down from ∼1 GPa to ∼200 MPa when Sn is allowed to plastically deform at a yield strength of ∼150 MPa. After experimentally determining the creep response of Sn micropillars, creep deformations are incorporated in numerical modeling to show that the maximum tensile hoop stress is further reduced to ∼0.45 MPa under the same conditio...

Magnetoimpedance of cobalt-based amorphous ribbons/polymer composites

The combined influence of the temperature, the elastic tensile stress and the external magnetic field on the total impedance and impedance components were studied for rapidly quenched amorphous Co75Fe5Si4B16 ribbons. Both as-cast amorphous ribbons and Co75Fe5Si4B16/polymer amorphous ribbon based composites were considered. Following polymer coverings were studied: modified rubber solution in o-xylene, solution of butyl methacrylate and methacrylic acid copolymer in isopropanol and solution of polymethylphenylsiloxane resin in toluene. All selected composites showed very good adhesion of the coverings and allowed to provide temperature measurements from 163K up to 383K under the applied deforming tensile force up to 30N. The dependence of the modulus of the impedance and its components on the external magnetic field was influenced by the elastic tensile stresses and was affected by the temperature of the samples. It was shown that maximal sensitivity of the impedance and its components to the external magnetic field was observed at minimal temperature and maximal deforming force depended on the frequency of an alternating current.

Mechanical Characterization of an Additively Manufactured Inconel 718 Theta-Shaped Specimen

Two sets of “theta”-shaped specimens were additively manufactured with Inconel 718 powders using an electron beam melting technique with two distinct scan strategies. Light optical microscopy, mechanical testing coupled with a digital image correlation (DIC) technique, finite element modeling, and neutron diffraction with in situ loading characterizations were conducted. The cross-members of the specimens were the focus. Light optical micrographs revealed that different microstructures were formed with different scan strategies. Ex situ mechanical testing revealed each build to be stable under load until ductility was observed on the cross-members before failure. The elastic moduli were determined by forming a correlation between the elastic tensile stresses determined from FEM, and the elastic strains obtained from DIC. The lattice strains were mapped with neutron diffraction during in situ elastic loading; and a good correlation between the average axial lattice strains on the cross-member and those determined from the DIC analysis was found. The spatially resolved stresses in the elastic deformation regime are derived from the lattice strains and increased with applied load, showing a consistent distribution along the cross-member.

Component analysis of the impedance of a CoFeNbSiB magnetically soft conductor with a nonuniform magnetic structure

The influence of an external magnetic field and elastic tensile stresses on the real and imaginary components of the impedance of a magnetically soft amorphous conductor with a low positive magnetostriction constant is studied. The difference is found between the frequencies at which the circular permeabilities of conductor’s parts with different types of magnetic anisotropy do not have a dominant influence on the real and imaginary components of the impedance any longer. It is shown that the sensitivity of the imaginary part of the impedance to a change in the magnetic structure of the conductor exceeds the sensitivity of the real component in a wide frequency interval. The variation of the impedance components under the influence of external actions is analyzed. This analysis may greatly expand the potential of magnetoimpedance spectroscopy, and the detection of the impedance’s imaginary component in magnetically soft and stress-impedance transducers will raise their sensitivity.

Magnetoimpedance of Amorphous Ferromagnetic CoFeSiB Ribbons in the Wide Temperature Range

The influence of the temperature, elastic tensile stresses and external magnetic field on the impedance of amorphous Co75Fe5Si4B16 ribbons was studied. It was observed that the character of the elastic tensile stresses influences the impedance and its changes in the external magnetic field are determined by a temperature of the ribbons. It was shown that changes of the stressimpedance character and magnetoimpedance temperature dependences were caused by a change in the sign of a magnetostriction constant with the temperature.

Mechanical Analysis and Numerical Simulation of Steel-Ring and Rigid-Frame Restrained Concrete

The complicated counterbalance system of steel ring and concrete-ring，rigid-frame and concrete-plate was analyzed and simplified under the restrain deformation and strains. The material parameters of early-age concrete are measured. Based on these work, the corresponding mechanical models were established and a special tool was employed for the meshing of model, and then, internal stress and strain induced by shrinkage of early-age concrete on restrained conditions were studied by FEM. The self-induced tensile stresses and strains in the restrain concrete can be calibrated，on the basis of which the elastic strains and tensile stresses would be calculated. So, the results of the numerical simulation reveal the law of the stress and strain distribution perfectly. It is significant to contrast the restraint characters of steel-ring and rigid-frame. The early-age shrinkage behaviors can be studied in depth.

Insulating-coating flaws formed during laser processing of an electric anisotropic steel and their effects on magnetic properties

The effects of flaws in the insulating coating of an electric anisotropic steel, which are formed during its laser processing in accordance with the optimal technology used in industry, on the elastic tensile stresses induced in the metal by the coating and magnetic properties were investigated. It was shown that discontinuity of insulating coating at the location of laser-beam action does not lead to a decrease in elastic tensile stresses and deterioration of magnetic properties of steel.