Internal Stress Values Research Articles

Grain binding derived reinforced interfacial mechanical behavior of Ni-rich layered cathode materials

The fragmentation caused by cracks spreading along grain boundaries seriously deteriorates the cycling performance of high nickel (Ni ≥ 90%) layered cathode materials for lithium-ion batteries (LIBs). In this study, heterogeneous nucleation was utilized to epitaxially grow LiNbO3 layer onto LiNi0.90Co0.05Mn0.05O2 (NCM90). Importantly, the LiNbO3 layer was compatible with the highly reactive surface of NCM90. The formation process of LiNbO3 solid embryos was calculated and discussed based on crystal solidification theory, and the distribution of solid embryos revealed thin zone crystallization and aggregation zone grain pinning. More interestingly, the surface stiffness and surface Young's modulus of the NCM90 were significantly enhanced, and the grain movement (fragmentation) caused by the non-uniform contraction of the unit cell was bound correspondingly at high cut-off voltages. Originating from the binding effect of the coating layer, the value of surface hoop internal stress of NCM90 decreased by 22.88% to inhibit the cracking and reduce the loss of NCM90 during cycling. At the potential range of 3.0–4.3 V at 50 mA g−1, the specific discharge capacity of the optimized NCM90 increased from 109.3 mAh g−1 to 147.4 mAh g−1 after 200 cycles. It is believed that this study provides a simple, convenient but effective strategy to restrain the fragmentation of high nickel layered cathode materials for LIBs.

Highly reflective Mo/Be/Si multilayer mirrors with zero stress values for 13.5 nm wavelength

This study investigates mechanical stresses in Mo/Be/Si multilayer mirrors. We determined layer thicknesses (for Si∼1.0 nm, Mo∼2.8 nm and Be∼3.2 nm) in the period that simultaneously provided high reflection coefficients (R∼66–67%) at a wavelength of 13.5 nm with zero internal stress values. At the wavelength of 13.5 nm, the reflection coefficient of a stressless Mo/Be/Si multilayer mirror deposited on a micro-electro-mechanical system of micromirrors had a value of about 23% with a reflection from the witness of 67%. An interferometric method for determining the stress values in films, which is able to provide a measurement accuracy at the level of Δs ∼ ±0.24 MPa, is described in detail.

Research of methods for determining dynamic stress of the bars in the main structure of gantry crane installed on the cap of bridge pier to serve installation of Super-T girder

The article presents briefly findings in researching methods for determining dynamic stress of the bars in the main structure of gantry crane installed on the cap of bridge pier to install and launch SUPER-T girder. In order to study the dynamic stresses in the bars of the main truss structure of the gantry, the author first had to build a dynamic model, using Matlap software to solve the problem of dynamics with two cases cargo lowering combination combines braking and moving of gantry with cargo to find out the rules and values of dynamic cable tension, dynamic inertial force ( time-varying force), then consider these forces is the external force acting on the main truss structure model of the gantry, from which the author calculates the value of internal force and stress of each bar corresponding to the value of dynamic cable tension and corresponding dynamic inertia force. with two adverse working cases of the gantry. Using Matlap software to calculate the author has obtained a graph of internal force, stress changes over time of each bar in the main truss steel structure of the gantry. The findings of the research provided methods for determining the dynamic stress of the bars in the main structure of gantry crane, pointed out values and rules of change of the dynamic stress of the bars in the main structure of gantry crane. The findings of the research may be used to calculate fatigue, life-span of the main steel structures as well as other parts of the gantry crane

СВОЙСТВА ГЛИНИСТЫХ ГРУНТОВ С ПОЗИЦИЙ ФИЗИКО-ХИМИЧЕСКОЙ ТЕОРИИ ПРОЧНОСТИ

scientific and methodological issues of studying clayey soils and determining their mechanical properties are considered on the standpoint of the physicochemical theory of effective stresses in soils. The modern theoretical base of research assumes estimate only the effect of external loads on the soil and their relationship but does not consider its internal structure. It is shown that the value of the forces of interaction between the particles of clayey soils determines their structure, properties, and character of the deformations under various conditions of external loads. A practical method of clayey soils studying is considered. This methodology makes it possible to determine the value of internal stresses between the mineral particles of the clayey soils

Stress distribution of endodontically treated mandibular molars with varying amounts of tooth structure restored with direct composite resin with or without cuspal coverage: A 3D finite element analysis.

Decision-making regarding whether cuspal coverage is required or not for the restoration of root canal-treated posterior teeth is still a matter of challenge for the dentist. Four models of endodontically treated mandibular molars with mesio-occlusal (MO) cavity were designed and simulated with direct composite resin restorations. Group 1A - cavity width <½ the intercuspal distance restored without cuspal coverage, Group 1B - same as Group 1A but with cuspal coverage, Group 2A - MO cavity width >½ but <2/3rd the intercuspal distance restored without cuspal coverage, and Group 2B - same as Group 2A but with cuspal coverage. The models received occlusal load to simulate a mastication load. Static finite element analysis (FEA) was adopted for predicting the stress distribution generated in the restored tooth by the loading condition. FEA of the models have shown that the variations in stress values were significant in bulk-fill material compared to enamel and other structures. Comparing the maximum and minimum principal stress values in the overall region demonstrated that 2A was safer, whereas 2B was found to be the worst case. The results indicate that restoration of endodontically treated mandibular molar with loss of one marginal ridge with composite resin without cuspal coverage revealed minimal internal stress values and showed the best performance overall.

Stable a-CSi:H films with a wide range of modulus of elasticity and low internal stress

Amorphous hydrogenated silicon carbide (a-CSi:H) thin films were deposited by plasma-enhanced chemical vapor deposition using tetravinylsilane as organosilicon precursor. The mechanical properties of the thin films, namely the modulus of elasticity, hardness, and elastic recovery parameter, were determined by nanoindentation, as well as the internal stresses by scanning electron microscopy and optical profilometry. It was found that the modulus of elasticity increased from 10 to 137 GPa with increasing power (2–150 W) delivered to plasma, while the hardness increased from 1.5 to 14.5 GPa. This improvement in mechanical properties with increasing energy delivered to the plasma is related to greater fragmentation of the precursor which led to an increase in the crosslinking of the material network. The compressive internal stresses in the films reached low values of −0.04 to −0.2 GPa with increasing power (2–75 W) and an acceptable −0.5 GPa for 150 W. The elastic recovery parameter decreased with increasing power from 0.86 to 0.64, i.e., the thin films behaved more plasticity with increasing power. The modulus of elasticity and hardness were investigated in terms of the aging of the films for a period of 6 years when samples were stored under ambient conditions. No significant changes in these properties were observed. However, minor changes were observed in the indentation curves obtained for the 2 W and even less for the 10 W samples. Small changes were then also observed for the elastic recovery parameter, whose value for these samples partially decreased which may be related to postdeposition oxidation. No changes in internal stress values over time were observed. The wide range of mechanical properties of stable a-CSi:H films with low internal stress increases their application potential and their wide use as materials with tailored properties from polymer-like to tough material.

Evaluation of Internal Stresses in Modified Near-Surface Layer of 20Kh13 Steel during Incubation Period of Water Droplet Impact Erosion

This study investigates the change in internal stresses of ion nitrided and Cr–CrC ion-plasma-coated 20Kh13 steel samples during the incubation period of the droplet impact erosion. To obtain internal stress values, a method based on measuring the deformation (curvature) of the sample along the surface profiles before and after its modification/coating, as well as during the subsequent droplet impact has been applied. The results suggest that the initial droplet impact on the uncoated, nitrided and coated material leads to a sharp increase in the initial internal stress values. The rate of increase in internal stress decreases with the surface damage development and accumulation. The proposed method of stress evaluation can be used in selecting a criterion for comparing the erosion resistance of a material and a method for modifying its surface.

Study of Internal Stress in Conductive and Dielectric Thick Films

This paper is focused on the study of internal stress in thick films used in hybrid microelectronics. Internal stress in thick films arises after firing and during cooling due to the differing coefficients of thermal expansion in fired film and ceramic substrates. Different thermal expansions cause deflection of the substrate and in extreme cases, the deflection can lead to damage of the substrate. Two silver pastes and two dielectric pastes, as well as their combinations, were used for the experiments, and the internal stress in the thick films was investigated using the cantilever method. Further experiments were also focused on internal stress changes during the experiment and on the influence of heat treatment (annealing) on internal stress. The results were correlated with the morphology of the fired thick films. The internal stress in the thick films was in the range of 8 to 21 MPa for metallic films and in the range from 12 to 16 MPa for dielectric films. It was verified that the cantilever method can be successfully used for the evaluation of internal stress in thick films. It was also found that the values of deflection and internal stress are not stable after firing, and they can change over time, mainly for metallic thick films.

Analysing the Generative Design of Payload Part for the 3D Metal Printing

Additive manufacturing provides the possibility to print complex generative designed bodies. The research deals with redesigning a payload part of a camera holder using generative design for selective laser melting. The possibility of replacing the original polymer component with a metal printed component of a greater strength and the effect of different parameters of generative design were investigated. By comparing the generative design results obtained in several phases, the goal was to find a solution that can be used to replace the previous part and become printable with 3D metal printing. The internal stress values for each case and the amount of weight reduction that can be achieved were determined. With the results obtained, the parts were prepared for printing. It is the key aspect of the industrial application of generative optimization.

ОЦЕНКА ТРЕЩИНОСТОЙКОСТИ ЗАЩИТНО-ДЕКОРАТИВНЫХ ПОКРЫТИЙ В ЗАВИСИМОСТИ ОТ ПОРИСТОСТИ ПОДЛОЖКИ

The issue of assessing the stress state of protective and decorative coatings, depending on the porosity in the contact zone "coating-substrate" is considered. Several schemes are considered: the absence of pores, the pores are filled with a paint composition, the pores are not filled with a paint composition. To assess the stress state of the coatings, the SCAD Office software module is used. It has been established that the presence of pores in the contact zone leads to the appearance of a more inhomogeneous stress state. When a pore is filled with a paint composition, the maximum stresses in the coating occur in the zone of contact between the coating and the substrate. In the absence of filling the pores with paint, the maximum stresses occur on the surface of the coating. The influence of the substrate on the change in the values of internal thermal stresses is revealed. Stresses in coatings on a claydite-concrete substrate are significantly lower compared to the use of heavy concrete as a substrate. The ratio of maximum thermal stresses and long-term cohesive strength is analyzed. It is established that cracking is possible in the polymer lime coating from the action of temperature stresses in the period from August to January

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ВНУТРЕННИХ НАПРЯЖЕНИЙ НА БАЛЛИСТИЧЕСКУЮ СТОЙКОСТЬ МЕЛКОЗЕРНИСТОГО ОКСИДА АЛЮМИНИЯ, ПОЛУЧЕННОГО МЕТОДОМ ЭЛЕКТРОИМПУЛЬСНОГО ПЛАЗМЕННОГО СПЕКАНИЯ

The results of tests for ballistic resistance of ceramic samples based on aluminum oxide (Al2O3 + 0.25MgO) obtained by high-speed electric pulse plasma sintering (EIPS) are presented. Samples 30 mm in diameter, 6.5 and 7 mm thick had a high relative density (more than 99%), a uniform fine-grained microstructure (average grain size ~1–1.5 mm), and increased hardness (more than 17 GPa). Using the finite element method, using the ANSYS Workbench package, it is shown that during rapid cooling at a rate of 50 °C/min, an uneven temperature field is formed in the samples and a difference in temperatures arises on two opposite sides of the ceramic samples. It has been established that non-uniform cooling during SPS leads to the formation of compressive internal stresses (up to –450 MPa), and there is a significant difference in the magnitude of internal stresses on opposite sides of ceramic samples. The differences in the parameters of the microstructure and microhardness on opposite sides of the samples are insignificant. Ballistic resistance tests were carried out at a speed of 700 m/s, using cylindrical-conical impactors made of hardened steel 52100. The ballistic resistance of the ceramics was evaluated by the anti-barrier action, i.e., the penetration depth of the striker into the aluminum witness sample located behind the tested ceramic plate. It is shown that the barrier action during testing of a ceramic plate with a large value of compressive internal stresses (from –390 to –450 MPa) is 1.5–2 times less than during ballistic testing of a ceramic plate, in the surface layer of which internal compressive stresses are small (from –60 to –90 MPa). The results obtained for the first time demonstrated the importance of the formation of compressive fields of internal stresses in ceramics, which makes it possible to further increase the ballistic resistance of protective ceramic plates.

Effect of filler particles on adhesive properties of poly (m-, p-phenylene isophtalamide) coatings

The adhesive properties of composite coatings based on poly (m-, p-phenylene isophtalamide) with widely used antifriction fillers (copper phthalocyanine, molybdenum disulfide, graphite and boron nitride) were investigated. The results of measurements of adhesive characteristics are obtained by means of cross cutting test and quantitative peel test. Introduction of fillers leads to an increase in the adhesive strength of coatings, while the type of a filler virtually does not affect the adhesive properties. When the filler content is 20 wt.% and more, the cohesive fracture of the coating occurs during the peel test. Introduction of the fillers significantly reduces the value of internal stresses that is accompanied by an increase in the adhesion strength. By way of example of graphite, we showed that an increase in the particle dispersion of the filler results in an increase in the value of adhesion strength of composite coatings, but does not cause any fundamental changes in the character of the dependence of adhesion strength on the filler concentration.

Оценка влияния дисперсности структуры стали на магнитные и механические свойства

Introduction: The control of the mechanical properties of structural steels is one of the main processes that regulate the service life of equipment. In most technical processes (pressure treatment, welding, rolling, thermal exposure), structure changes both in local areas and in the entire volume. Changes in the steel structure entail changes in its properties and as a result in local areas, at various stages of operation, the likelihood of the occurrence and development of critical defects increases. Its presence significantly affects the performance of the equipment, and leads to premature aging of the material and its failure. Precisely because the control of the mechanical properties of steel remains one of the urgent problems, new control methods are being developed. It is known that all properties of steel depend on the structure of the substance, however, studies on the effect of the dispersion of the structure under consideration on the mechanical properties are presented in an insignificant amount. Purpose: to analyze from a mathematical point of view the influence of the factor of different grain size, as a parameter reflecting the dispersity of the system, on the mechanical properties of structural steel. The paper studies a heat-treated planar samples of steels 15KhSND, 09G2S and St3. Methods of research: scanning electron and optical microscopes are used to study the grain structure and grain boundaries; SIAMS 700 software package is used for finding the boundaries and average data of the grain structure; portable X-ray fluorescence analyzer of metals and alloys X-MET 7000 is used to determine the chemical composition of the test samples in percentage; tensile testing machine IR-50 is used for measuring the tensile strength of samples; Vickers hardness tester is used to determine the hardness of samples. Results and discussion: it is found that there is a satisfactory correlation for the mechanical properties of structural steels (hardness and ultimate strength) and the grain size factor, which can be used to predict the hazardous states of structures and the operating time. The analysis of variance and regression of the detected dependencies is carried out. It is noted that the dropout of some values from the general regression dependence can most likely be associated with a decrease in the value of internal stresses as a result of a decrease in the distortions of the crystal lattice of steel occurring during heat treatment. It should be noted that the processes occurring and the degree of its influence on the properties of the structural steels under consideration can be different due to the presence of different amounts of alloying elements in the composition of the studied steels.

Increasing the uniformity of characteristics of a plastic scintillator by reducing its internal stresses

This paper presents the results of the study of internal stresses effect on the light collection uniformity in a plastic scintillator (PS) and setting conditions for obtaining long plastic scintillators with a low level of internal stresses. Plastic scintillators based on polystyrene were used as test samples, produced in an air polymerizer from styrene monomer by radical thermoinitiated polymerization in an aluminum ampoule. To reduce internal stresses in the polystyrene polymer base of the PS, scintillator samples were annealed at a temperature of 100 °С. After a 12 hours exposure, the samples were gradually cooled at a rate of 2.5 °C/h. To reduce the surface tension due to the adhesion of the PS to the walls of the polymerization mold, the inner coating of the polymerization mold with polytetrafluoroethylene was used. The values of internal stresses in the PS material before and after additional annealing of the samples, as well as in the case of using the anti-adhesive coating, were determined. The control of internal stresses was carried out using a PKS-250M circular polariscope. To calculate the internal stresses, the difference of main stresses in the flat plates of the plastic scintillator was calculated. The dimensions of scintillator plates for evaluation of internal stresses are 10×50×300 mm. To measure the uniformity of the relative light output distribution along the long plastic scintillator, samples with dimensions of ø50x1000 mm were used. The obtained data showed that additional annealing of plastic scintillator blanks and the use of anti-adhesive coating for the polymerization mold reduce the level of internal stresses in the plastic scintillator from 1.8÷2.9 MPa to 0.55÷1.0 MPa. The nonuniformity of the relative light output distribution along the long plastic scintillator with dimensions of ø50x1000mm was reduced to ΔС ≤3 %.

THE TRIBOTECHNICAL CHARACTERISTICS OF DIAMOND-LIKE COATINGS FORMED BY HYBRID TECHNOLOGY

The use of low temperatures to improve the performance of steel products is a widely used technology in mechanical engineering. Another directionof increasing the efficiency of machine parts and mechanisms is the creation of thin-layer systems using vacuum technologies. The combinationof these technological approaches made it possible to obtain antifriction vacuum superhard coatings with increased tribotechnical characteristics.The effect of increasing the wear resistance of hybrid coatings is the formation of nanodisperse structures in the steel substrate and coating, the decayof residual austenite, which leads to an increase in martensite in the structure of steel subjected to cold treatment, a significant change in the values ofinternal stresses in superhard coatings.

Theoretical and experimental study of the effect of wollastonite on the physical and mechanical properties of concrete

As part of the work, an experimental and theoretical study of the effect of adding wollastonite on the physical and mechanical characteristics of concrete was carried out. The internal stress was calculated according to Hooke’s law. The change in the specific volume was determined from the change in the volume of the hydrated phase. The calculation of the chemical interaction was carried out within the framework of thermodynamic equilibrium. According to the results of the work, it was shown that the addition of wollastonite leads to a linear decrease in the value of internal stresses, which is consistent with experimental results on the increase in compressive and bending strength.

Influence of deformation degree of austenitic steels welded joints on structural state and internal stresses felds in weld line zone

Nowadays initial assessment of welding quality is performed by testing equipment with increased loads (high pressure) at technical devices of hazardous production facilities. Test requirements are regulated by standardized documents of the Federal Service for Environmental, Technological and Nuclear Oversight of Russia (Rostekhnadzor). Recently, along with traditional tests, a “stress test” was used – the essence of which is to load pipeline section to the yield point, followed by leak test. However, in scientifc publications there is practically no information about physical processes occurring in the base metal and in welded joints during such tests. In addition, effect of preload (deformation) on the parameters of substructure and internal stresses feld in welded joints of austenitic steels and, consequently, on the further trouble­free operation of the tested equipment was not evaluated. The paper analyzes changes in structural state and values of internal stresses in the samples of austenitic steel under the action of high loads. It substantiates the use of modulated current welding with automatic control of heat input process in molten weld pool. The admissible limits values of plastic deformation are argued when testing technical devices with high pressure for this type of steel. In order to reduce the risk of damage to austenitic steels welded joints of technical devices of hazardous industrial facilities, performed by pulsed welding with small­drop transfer, and to exclude formation of microdefects in them, high pressure tests (stress test) can be performed under loads that create deformations in metal, not exceeding 5 %. For joints welded by manual arc welding, deformations should be less than 5 %. Welded joints made by pulsed welding with large­drop transfer (with and without defects) are not recommended to be tested with high pressure.

Analytical Evaluation of Strengthening, Local Internal Stresses and Microderformations in Welded Joint Metal during Wet Underwater Welding

Analysis of structural factor influence on local internal stresses and zones of deformation localization in upper and lower bainite structures in welded joints of low-alloy steel at wet underwater welding was performed. It is established that when welding joints under the water and applying an external electromagnetic field in the metal of the heat-affected zone (HAZ), a finer-grained substructure is formed with a general decrease in the dislocations density and with their uniform distribution. Estimates of the local internal stresses level considering the dislocation density distribution in the structural zones of their localization show that their maximum level is formed in the metal of the HAZ overheating region at welding without the external electromagnetic field along the upper bainite laths boundaries. The upper bainite structure is characterized by forming localized deformation zones, where the most significant dislocation density gradients are observed. This can lower the crack resistance of welded joints. Low values of local internal stresses are characteristic of welded joints obtained in the modes applying an external electromagnetic field. This is facilitated by the overall decrease in the dislocation density and their uniform distribution in the lower bainite structural components, which provides high crack resistance of welded joints.

Freezing and Thawing of D2O/Sand Mixtures Investigated by Neutron Diffraction

Evolution ice diffraction patterns in mixtures of D2O with quartz sand of three different grain coarseness (100–600, 300–800 and 600–1200 μm) were studied under various temperature regimes by means of neutron diffraction method. The studied structural parameters and characteristics involved the phase composition of specimens, Ih D2O ice lattice parameters, and crystallographic texture of the present phases. Variations in the ice crystallographic texture during the repeated freezing and thawing were observed for all tested sample types, showing an intermittent enhancement of ice and quartz texture indices accompanying the start of specimens cooling. Formation of radial internal stresses is demonstrated by the observed split of (002) and (100) diffraction maxima of ice. Estimated mean internal radial stress values are calculated.

Импульсная сушка пиломатериалов из древесины груши в конвективных сушильных камерах

A review of literary sources on the physical and mechanical properties of pearwood and its use as structural elements of furniture is given. The aerodynamic chambers, their advantages and disadvantages, as well as their modernization are considered. The use of impulse modes for drying hardwood is substantiated, including sawn timber from pear wood 50 mm thick, pilot drying of which began in the modernized URAL-72 chamber in 1999 at Intar LLC, Moscow. The moisture content of the wood samples and the value of internal stresses were controlled in accordance with GOST 16588. The process of impulse drying included from 9 to 12 steps, the temperature at the operating stage ranged from 45 °C to 72 °C. It has been proved that the use of pulse modes for drying pear timber saves up to 30% of electricity.