Action Of Internal Stresses Research Articles

Effect of Pulsed Magnetic Field on the Microstructure of QAl9-4 Aluminium Bronze and Its Mechanism.

The effect of a pulsed magnetic field on the microstructure of a QAl9-4 aluminium bronze alloy was studied in this work. It was found that the dislocation density, grain boundary angle, and microhardness of the alloy significantly changed after the magnetic field treatment with a peak magnetic induction intensity of 3T, pulse duration of about 100 us, pulse interval of 10 s, and pulse time of 360. EBSD was used to test the KAM maps of the alloy microzone. It was found that the alloy's dislocation density decreased by 10.88% after the pulsed magnetic field treatment; in particular, the dislocation in the deformed grains decreased significantly. The quantity of dislocation pile-up and the degree of distortion around the dislocation were reduced, which decreased the residual compressive stress on the alloy. Dislocation motion caused LAGB rotation, which reduced the misorientation of adjacent points inside the grain. The magnetic field induced the disappearance of deformation twins and weakened the strengthening effect of twins. The microhardness test results show that the alloy's microhardness decreased by 8.06% after pulsed magnetic field treatment. The possible reasons for the magnetic field effect on dislocation were briefly discussed. The pulsed magnetic field might have caused the transition to the electronic energy state at the site of dislocation pinning, which led to free movement of the vacancy or impurity atom. The dislocation was easier to depin under the action of internal stress in the alloy, changing the dislocation distribution and alloy microstructure.

Possibility of estimation of mechanical stresses in nickel by the magnetic ponderomotive method

The paper considers a technique for assessing mechanical stresses in coatings by the magnetic ponderomotive method, based on the use of the magnitude of the magnet breakaway force and its relation to the magnetic characteristics of nickel (magnetic susceptibility), which change under the action of internal stresses. It is shown that the existing mechanical stress measuring equipment using X-ray, magnetic or ultrasonic methods have specimen size limitations or have low measurement locality. At the same time, a magnetic ponderomotive method for controlling mechanical stresses is presented, which does not have the indicated disadvantages. The change in the magnetic breakaway force on the thickness, applied and residual stresses caused by elastic and plastic deformations in the sample is theoretically substantiated. It is shown that the presence of residual stresses in the sample changes the nature of the dependence of the magnet breakaway force on the applied stresses. A calculation algorithm has been developed that allows measuring the magnet breakaway force to obtain the ratio between the applied and residual stresses. It is shown that the ratio between residual and applied stresses can be used to assess the degree of proximity to the critical stresses levels that lead to failure. Calibration surfaces are constructed for the dependence of applied stresses on magnetic separation force and thickness, corresponding to elastic-plastic deformation, as well as leveled calibration surfaces, corresponding to elastic deformation in the presence of residual stresses in the material. Experiments have been carried out on real samples and coatings, that determine the degree of approximation of internal stresses in the material to critical levels that may lead to destruction. It is shown that when comparing the readings of calibrated gauges with a certified tool, the largest deviation occurs at low stress values due to the inverse dependence of the breakaway force on the stress level.

Failure Analysis of the Metal Hose Puncture and Leakage in a Natural Gas Reinjection Station

The metal hose in the pump room of an oilfield natural gas reinjection station has multiple punctures and leaks. In order to analyze the reasons for the failures, a macro inspection, hydrostatic pressure and blasting test were carried out on a new hose of the same specification. Phase organization analysis, macro inspection, physical and chemical inspection, scanning electron microscopy (SEM), energy spectrum analysis, metallographic analysis and composition analysis of the conveying medium were carried out on the two failed hoses. The results show that the hydrostatic pressure test of the same batch of the new hoses of this specification meets the requirements of the standard, however the burst pressure does not meet the requirements of the standard. The failure is caused by the welding quality problems at the joint connection, welding defects such as weld bead, incomplete penetration and welding slag. The existence of deformation-induced martensite is found in the metallographic structure of the failed hose corrugated tube. There is tensile stress in the service environment, and a high content of corrosive medium Cl- in the conveying medium. Under the action of internal stress, the internal corrosive medium causes corrugation, the tube undergoes stress corrosion, thus initiating corrosion cracks and propagating along the grain boundaries, leading to the cracks and failure accidents.

Computational study of the formation of aluminum-graphene nanocrystallites

The molecular dynamics method is used to study the formation of the Al/graphene nanocomposite in the structural grains of different size under the action of internal stresses. The behavior of graphene sheets inside an individual structural grain as well as in the process of two Al grains containing graphene are joined is investigated. The motion of graphene films, starting from the middle of the aluminum matrix, ends with their location at the crystallite boundaries. Graphene moves in the Al matrix along closely packed planes. In this case, graphene sheets acquire curvature. An intergrowth of graphene sheets is also observed. A contact between two Al-C nanocrystallites through a graphene interlayer is created. The self-diffusion coefficients of atoms and the partial potential energies increased with decreasing nanocrystallite size. The angular distribution of the nearest geometric neighbors and the distribution of distances to the nearest neighbors are determined using the construction of Voronoi polyhedra.

Frost Weathering as a Process of Degradation of Surface of Rocks under the Action of Internal Stresses

The article presents the results of studies of self-organization of ice inclusions in the surface layer of frozen moisture-bearing rocks. Frosty weathering of rocks is determined by the formation of inhomogeneous stresses in the surface layer. They are due to the random nature of the appearance of crystallization centers and further inhomogeneous growth of crystalline (ice) formations. They are narrow, rectangular inclusions of fixed sizes for which solutions of the theory of elasticity are known. An original model of heat and mass transfer in the surface layer of a moisture-containing rock under the influence of variable temperatures with a period of ∼ 12 hours is used. The correlated arrangement of crystalline formations is determined by the process of minimizing the total elastic energy of the ensemble of ice formations depending on the angle of their mutual orientation.

Electron-Microscopic Examination of the Surface Layer of Titanium Alloys OТ4 after Ion Implantation

The electron microscopic and diffraction analysis presented in the article showed that the structure of the surface layer of the titanium alloy OT4 after implantation at an accelerating voltage of 30 kV from the cathode Cu-Pb-Bi has a different hierarchical character. As a result of investigations of each of the levels, it was determined experimentally that the deformation mechanism under the action of internal stresses, as well as diffusion-relaxation reactions, are the main reasons for their formation, leading to the appearance of structural features in the surface layer of the OT4 alloy. In this case, penetration of alloying components to a depth of 10-25 nm is observed.

Microstructure Analysis of Laser Bonding Welding on Steel-Aluminum

Laser bonding welding test of the lap joint between steel and Al was conducted. The microstructure analysis is carried out by means of metallographic microscope, which provides an important theoretical and experimental basis for the popularization and application of laser welding of steel / aluminum dissimilar metal structures. The results showed that under the conditions of 1650W laser power, 35m/s welding speed, +3mm defocus amount and 25L/min flow rate of Ar as the protective gas, there are no cracks, pores and inclusions in the weld zone. The fusion line is smooth and smooth. Under the conditions of 1650W laser power, 38m/s welding speed, +3mm defocus amount and 25L/min flow rate of Ar as the protective gas, the overall appearance of the weld zone of the laser welding joint, there are serious cracks, pores and other defects in the weld area. In the P=1680W, V=35mm/s, f=+1mm, q=20L/min, the crystal structure appeared, in the process of cooling, the crack expands and forms a radial shape under the action of internal stress.

Analysis of TiAlSiN coatings deposited by reactive magnetron sputtering under high-current ion assistance

TiAlSiN nanocomposite coatings are obtained by the reactive magnetron sputtering of one-component targets with a widely varying (5–25) ratio of the ion current density j i to the atomic flux density j n on the sample surface. The plasma in the deposition chamber is generated by a broad (80 cm2) low-energy (100 eV) electron beam. The beam current is varied from 5 to 30 A, which makes it possible to adjust j i in the range of 1.8 to 9 mA/cm2. It is shown that an increase in the ratio j i /j n is accompanied by a nonmonotonic variation in the hardness and texture of the coatings under the action of internal stresses. It is established that exceeding the value j i /j n at which the maximum hardness of the coating is reached (43 GPa) leads to the relaxation of intrinsic stresses and a reduction in the hardness to 36 GPa.

The energy of a prolate spheroidal shell in a uniform magnetic field

The problem of the energy of a spheroidal magnetic shell, solved by methods of classical electrodynamics, arises, in particular, upon the study of thin-wall biocompatible microcapsules in connection with a pressing issue of targeted drug delivery. The drug inside a microcapsule should be released from the shell at a required instant of time by destroying the capsule’s shell. The placement inside a shell of magnetic nanoparticles sensitive to an external magnetic field theoretically makes it possible to solve both problems: to transport a capsule to the required place and to destroy its shell. In particular, the shell can be destroyed under the action of internal stress when the shape of a capsule is changed. In this paper, the analysis of the model of a magnetic microcapsule in the form of a prolate spheroidal shell is performed and formulas for the magnetostatic and magnetic free energy when the magnetic field is directed along the major axis of the spheroid are derived.

Solid-phase combustion in a plane stress state. 2. Stability to small perturbations

Stability of a plane reaction front in the solid phase to small perturbations under conditions of a generalized plane stress state is studied with allowance of the coupled character of heat transfer and deformation processes and possible changes in the reaction rate under the action of internal stresses without external mechanical loading. The problem is solved analytically by the method of perturbations. Conditions of the loss of stability of various conversion regimes in some limiting cases are studied for different technological and physical parameters.

ESR in the Earth’s magnetic field as a cause of dislocation motion in NaCl crystals

The resonance displacements of the dislocations, l ∼ 100 μm, in NaCl crystals placed in the crossed Earth’s magnetic field B Earth and the ac field \( \tilde B \) ≈ 3 μT of the variable frequency ν ∼ 106 Hz have been discovered in the absence of any other impact on the crystals. Two peaks of the mean dislocation path l(ν) with the maxima at ν1 = 1.3 MHz and ν2 = 3 MHz have been observed for the field \( \tilde B \) oriented along the vertical and horizontal components of B Earth, respectively. The effect is explained by the depinning of the dislocations from the impurity centers after their structural transformation due to the ESR in the dislocation-impurity system in the crossed fields. The subsequent motion of the dislocations proceeds under the action of internal stress in the crystals. A physical model has been proposed to explain the strong anisotropy of the effect with respect to the mutual orientation of the dislocation lines and magnetic fields.

Hydrodynamics of nanorolling

An initial stage of nanoroll formation in a hydrothermal medium is investigated - the stage of rolling of a double layer under the action of internal stresses. A critical role in the rolling process is attributed to the viscous liquid surrounding the roll. A method is proposed to calculate the liquid flow around the forming nanoroll. A calculation of the rolling process is also performed. Finally, disturbance of the liquid by the rolling nanotube is studied.

First-Principle Analyses of Stress and Strain During Li Deintercalation in LiCoO2

The stress and strain during Li-ions deintercalation processes in LiCoO2 was preliminarily calculated using the first-principles theory based on Density Functional Theory (DFT) with the Vienna ab-initio simulation package (VASP). The capacity fading mechanism of cathode material was discussed from a point of view of micomechanics. The results showed that when Li-ions are deintercalated in LiCoO2 , there exists internal stress on the O-Co-O octahedron slab, and the stress increases with the increase in the quantity of Li deintercalation. At the same time, the compressive strain increases significantly with the decrease in Li concentration. It was found that at x=0.5 the strain in the O-Co-O octahedron slab would reach 4.8%. The capacity fading in cycling processes mostly related to the stress on and strain in the O-Co-O octahedron slab.When the cathode material underwent repeated charge/discharge cycles, it is possible that the action of internal stress would ultimately induce fatigue failure.

Spontaneous growth of single crystals of various shapes in tin-fullerite films

Changes in the structure and elemental and phase compositions of tin-fullerite films after their storage in air are investigated by X-ray diffraction, scanning electronic microscopy, atomic force microscopy, X-ray spectroscopic microanalysis, and Auger electron spectroscopy. Formation of the new phase SnxC60, whisker tin and SnxC60 crystals, and petal and flowerlike fullerite crystals under the action of internal stress is established.

Precise semiconductor nanotubes and nanoshells fabricated on (1 1 0) and (1 1 1) Si and GaAs

In our previous works, we showed that ultrathin epitaxial heterofilms (down to two monolayers for the case of InGaAs/GaAs) can be controllably detatched from substrates and rolled, under the action of internal stresses, into various cylindrical micro- and nanoshells (tubes, scrolls, rings, spirals, etc.). The present review outlines the cornerstone stages in the development of this fabrication technology for semiconductor and metal nanoobjects, including: (1) directional rolling of films yielding 3D micro- and nanoshells of various shapes; (2) assembling of micro- and nanoshells in more complex architectures; (3) super-critical drying of nanoshells, and (4) formation of nanoshells whose sizes can be precisely controlled in three dimensions. With this technology new possibilities that open up for the use of strained films, selectively, grown on uncommonly used (1 1 0) and (1 1 1) surfaces, are presented. The role of mechanical anisotropy in the formation of the 3D nanoshells and the electrical and mechanical properties of formed nanotubes are discussed.

Precise semiconductor nanotubes and nanoshells fabricated on (110) and (111) Si and GaAs

In our previous works, we showed that ultrathin epitaxial heterofilms (down to two monolayers for the case of InGaAs/GaAs) can be controllably detatched from substrates and rolled, under the action of internal stresses, into various cylindrical micro- and nanoshells (tubes, scrolls, rings, spirals, etc.). The present review outlines the cornerstone stages in the development of this fabrication technology for semiconductor and metal nanoobjects, including: (1) directional rolling of films yielding 3D micro- and nanoshells of various shapes; (2) assembling of micro- and nanoshells in more complex architectures; (3) super-critical drying of nanoshells, and (4) formation of nanoshells whose sizes can be precisely controlled in three dimensions. With this technology new possibilities that open up for the use of strained films, selectively, grown on uncommonly used (1 1 0) and (1 1 1) surfaces, are presented. The role of mechanical anisotropy in the formation of the 3D nanoshells and the electrical and mechanical properties of formed nanotubes are discussed.

Nonlinear elastic constants of solids with cracks

Experimental data on a cracked medium exhibiting high acoustic nonlinearity is a commonly observed phenomenon. Here a physical model of a medium with cracks is suggested to explain the observed phenomena. The model is based on the assumption of uniform stress that is valid for a low concentration of cracks. The crack behavior is described using the model in which a crack is represented as an elastic contact of two rough surfaces, pressed one to the other under the action of internal stresses in the surrounding solid. Linear and nonlinear acoustic constants of the fractured medium are calculated. It is shown that, in this medium, negative values of the Poisson’s ratio and anomalously high values of the nonlinear constants are possible.

The model describing the higher-order elastic constants of solids with cracks

There are many experimental data showing that third-order elastic constants of solids with cracks can be anomalously high and can exceed these parameters for homogeneous solids more than a thousand times. Here a physical model of a medium with cracks is suggested to explain such high nonlinearity. The model is based on the assumption that the stress applied to a single crack is the same as that applied to the whole body, that is valid for a low concentration of cracks. The crack behavior was described using the model in which a crack can be presented as an elastic contact of two rough surfaces, pressed one to another under the action of internal stresses in the surrounding solid. The nonlinear behavior of a crack is due to the contact area changing when the crack is undergoing stress or extension. Linear and nonlinear elastic constants of the medium with cracks are calculated; it is shown that in this medium negative values of Poisson’s ratio and anomalously high values of the third-order constants are possible.

The role of mechanical phenomena during the formation of network polymers

AbstractA review of new results concerning the role of mechanical phenomena during cure of epoxy matrices has been made. The influences of various factors (temperature, nature and concentration of components, the character of adhesion interaction of matrix and filler, etc.) on the rate of structural relaxation of polymer have been examined. The problem of the mechanical degradation of network chains under the action of internal stresses has been discussed.

Melting of nascent superhigh-molecular-weight poly(ethylene oxide) obtained by means of heterogenous ion-coordinate polymerization

Abstract The melting of nascent superhigh-molecular-weight poly(ethylene oxide) (PEO) has been studied by means of differential scanning calorimetry (DSC). High values of the melting temperatures and enthalpies were established. The higher temperatures are explained by the presence of tie molecules in high concentration. The phase transition is accompanied with the absorption of heat in addition to the heat of fusion. This additional heat can be interpreted as follows: (1) a large entropy change in amorphous areas during the transition, caused by disorientation of chains with a long distance between the chain ends in the nascent crystal state, to entangled statistical coils; and/or (2) a large internal energy change in the crystal areas caused by deformation of the crystal lattice under the action of internal stresses, increasing with temperature in the range from solid-plastic crystal transition (50°C) temperature to the melting point.