Low Linear Expansion Coefficient Research Articles

Разработка и исследование катушки Роговского для работы в условиях эксплуатации открытого распределительного устройства

The interest to use Rogowski coils (RC) as current sensors to design secondary systems increases due to application of microprocessor relay protection and automation devices, including those that support the reception and processing of information in a form of a digital code in the format of protocols defined in IEC61850, as well as the disadvantages of traditional electromagnetic current transformers. Despite the popularity of RC, there are many unstudied issues of their functioning under operating conditions of open switchgears of power facilities, especially when operating with modern relay protection and automation devices. The aim of the study is to analyze the effect of ambient temperature on the error of current conversion by Rogowski coils. Studies of Rogowski coils have been carried out using the experimental and industrial samples. During the research modern testing equipment has been used. The equipment is listed on the Unified Register of Measuring Equipment of the Russian Federation and has valid verification certificates. The analysis of the factors influencing the error of metrological channels has been carried out. The analysis is conducted based on traditional current transformers (CT). The factors influencing the measurement error of RC are systematized. Experimental data obtained as a result of the study of the RC conversion error in a wide temperature range are presented. It has been established that due to design solutions, it is possible to neutralize the influence of such factors as the position of the primary conductor, external electromagnetic fields, uneven winding, the number of layers of the secondary winding, and thermal expansion. The use of materials with a low coefficient of linear expansion to manufacture the core of the Rogowski coil makes it possible to obtain the metrological characteristics of the transducer that meet the requirements of normative technical documentation in a wide temperature range. Application of RC as a primary current sensor for relay protection and automation systems is a promising area that requires further comprehensive research, and specifically in the process of industrial operation.

セルロースナノファイバーコンポジットの高分散技術とその特徴

Cellulose Nano Fibers (CNFs) is expected to be utilized in various fields because of its attractive properties such as high strength, high rigidity, and low coefficient of linear expansion. CNFs have attracted significant attention as materials that can enhance the mechanical properties of polymers. CNFs can easily form hydrogen bonds between CNFs because of the many hydroxyl groups on the surface of a CNF. Therefore, in many cases, CNF agglomerates with diameters greater than 100 µm remain in a composite when compounded with hydrophobic polymers. Recently, we can success in preparing the dry powders of CNFs by coating of hydrophobizing agent and special drying (trial products by Sugino Machine ; 20 nm of fiber diameter, 1 and 10 µm of fiber length) . The CNFs are easily dispersed in a polypropylene (PP) matrix by melt-compounding with using a twin-screw extruder. No agglomerates of CNFs with diameters greater than 1 µm can be found in the composite by optical microscope observations and TEM observations of electron staining ultrathin section.

Powder-bed-based 3D printing with cement for sustainable casting

3D printing allows for the cost-effective fabrication of moulds and can cast complex shapes. In this study, alumina cement and fine aggregates for refractories were used as the main raw materials, and saturation was adjusted to an appropriate level to control the cement binder mixture for sand casting. For cast iron, the mould must withstand temperatures of up to 1400 °C and must exhibit sufficient strength, gas permeability, and thermochemical durability at high temperatures. To accomplish these requirements, 3D printing powder was prepared by adjusting the ratio of fine aggregate (D50: 30 μm) and an even finer cement component (D50: 4 μm). To improve the moulding quality, a green body was used to optimise the cement admixtures to increase the strength, and the saturation level of the 3D printer was adjusted for dimensional accuracy. The high-temperature durability of the mould was evaluated by measuring its strength after heat treatment, using Simultaneous Thermal Analysis (TG-DSC), and through dimensional stability assessment. In addition, the pores of the specimens were analysed through microscale X-ray tomography. The surface resolution and tolerance of the final casting were determined by a 3D image roughness test using a surface roughness scanner. The cement exhibited the shortest curing time and the highest strength when the mass ratio of CA (CaO·Al2O3) to C12A7 (12CaO·7Al2O3) was 8:2. The final mixing mass ratio of cement to the fine aggregate was 8:2, which was determined based on the relationship between flowability and powder bed surface quality. The results proved the high-temperature thermal stability of the 3D-printed mould, which showed a total mass reduction of less than 3% and a low coefficient of linear expansion up to 1300 °C. Consequently, the suitability of the 3D-printed moulded body, composed of casting sand with cement as a binder, for casting at temperatures >1400 °C was demonstrated. Additionally, the final printed porous mould de-powdered easily, and its recyclability was verified by strength testing various mass ratios of fresh and recycled powder. Therefore, through optimisation of the material combinations and adjustment of the 3D printing process parameters, optimal gas permeability and moulding resolution could be achieved without any casting defect, while maintaining handling strength. The findings of this study demonstrate the potential of expanding the scope of powder-bed-based 3D printing of cement material to the casting market.

Multiscale simulation on nonlinear mechanical properties of 3D printed cellulose composites

Polypropylene (PP), a major thermoplastic resin, is widely used in compression molding and injection molding due to its excellent mechanical properties and recyclability. In general, talc, an inorganic mineral product, is widely used as a reinforcing filler in PP. Talc has excellent chemical stability, electrical insulation, and affinity with organic materials. However, PP has a high coefficient of linear expansion, making it difficult to use with the fused deposition modeling 3D printers that have become increasingly popular in recent years because of warping of the printed structures. On the other hand, cellulose nanofiber (CNF) is a plant fiber that has been degraded to the nanoscale and is expected to be used as a reinforcing filler for composite materials because of its superior specific stiffness and specific strength. It is expected to reduce environmental impact compared to conventional reinforcing fillers due to its reduced CO2 emissions and high recyclability. In addition, the high aspect ratio and low coefficient of linear expansion of CNF can be expected to reduce thermal deformation of composite materials. In this study, the mechanical properties of PP composites reinforced by talc and CNF fillers were tested by multiscale finite element analysis. The contents of talc and CNF were changed, and the effects of adding each were clarified.

Study on mechanical and thermal properties of a modified epoxy resin

The uniaxial tensile test, linear expansion coefficient test of a modified epoxy resin in the ambient temperature range from -35℃ to 120℃, and the impact test at room temperature were carried out to explore its mechanical and thermal characteristics under temperature change environment. The constitutive model of the material suitable for temperature change environment is deduced, the numerical calculation is carried out in MATLAB, compared with the relative tested curve, and the obtained constitutive model is applied to the modeling calculation in ABAQUS and the results are verified. The results show that the modified epoxy resin has better strength, stiffness, impact toughness and lower coefficient of linear expansion than common epoxy resins such as E-44, E-51 and EPON e863. The material is suitable to be used as the matrix of spaceborne electronic component potting module. The proposed empirical constitutive model can obtain the stress-strain relationship of the material at any temperature in the range of -35℃~120℃ through interpolation, and can be directly used in relevant damage analysis and life prediction of electronic component potting module. The research method and derivation results have engineering reference value.

The Effect of Different Additives on the Hydration and Gelation Properties of Composite Dental Gypsum.

Dental mold gypsum materials require fine powder, appropriate liquidity, fast curing, and easy-to-perform clinical operations. They require low linear expansion coefficient and high strength, reflecting the master model and facilitating demolding. In this article, the suitable accelerators and reinforcing agents were selected as additives to modify dental gypsum. The main experimental methods used were to compare the trends of linear expansion coefficients of several commercially available dental gypsum products over 72 h and to observe the cross-sectional microstructure of cured bodies before and after dental gypsum modification using scanning electron microscopy. By adjusting the application of additives, the linear expansion coefficient of dental gypsum decreased from 0.26% to 0.06%, while the flexural strength increased from 6.7 MPa to 7.4 MPa at 2 h. Formulated samples showed good stability and gelation properties with linear expansion completed within 12 h. It is indicated that the performance of dental gypsum materials can be improved by adding additives and nanomaterials, which provided a good reference for clinical preparation of high-precision dental prosthesis.

Successful application of optical bench in Taiji-1 laser interferometer

As an important part of laser interferometry system, optical bench is one of the core technologies for the detection of spaceborne gravitational waves. As the first step of the space Taiji program, Taiji-1 provides the measurement accuracy of laser interferometry system better than 100 pm/Hz[Formula: see text](@10 mHz–1 Hz). Taiji-1 is required to be able to track the motion of test mass in inertial sensor. According to the requirements, four interfering optical paths were designed. By adopting an integrated satellite design and selecting the optical and mechanical materials with low linear expansion coefficient, the high stability of optical path was achieved. By using the DOE method, the alignment errors (position/attitude) of four optical paths were all reduced to below 50 [Formula: see text] m/100 [Formula: see text] rad. In the performance test, the accuracy of laser interferometry system was better than 100 pm/Hz[Formula: see text](@10 mHz–1 Hz), and the modulation signal of inertial sensor was successfully detected. The results show that all technical indexes of optical bench have met or exceeded the design requirements.

Mechanical and Thermal Properties of Harmonic Structured Composites by MM/SPS Process

Harmonic structured composites consist of a low fraction metal region like network and a dispersed another major metal region like island. The harmonic structured composites were produced via mechanical milling (MM) followed by spark plasma sintering (SPS), and its mechanical and thermal properties were investigated in detail. Microstructural observation of the MM powders and SPS compacts was achieved using scanning electron microscopy (SEM). The mechanical properties of the harmonic structured composites were evaluated using results of the Vickers hardness and the tensile tests. The thermal properties of a part of the harmonic structured composites were evaluated using results of thermo-mechanical analysis and laser flash method. High speed steel / mild steel harmonic structured composite exhibited high strength and enough ductility in spite of the trade-off relationship between strength and ductility. In addition, the high speed steel / mild steel harmonic structured composite also demonstrates a superior wear properties and low hardness simultaneously. On the other hand, molybdenum / copper harmonic structured composite demonstrate low coefficient of linear expansion and enough thermal conductivity compared to the conventional copper / molybdenum particle dispersed composite. The coefficient of linear expansion and thermal conductivity are the trade-off relation in this composite. In summary, the harmonic structure control is effective for improvement of the trade-off mechanical and thermal properties in the composite.

The modification of hypereutectic high-alloy silumins — prospects for the development of technology for producing materials with a low linear expansion coefficient

This article discusses the possibilities of using hypereutectic silumins and the problems that impede their wider distribution. The known methods of manufacturing products from hypereutectic silumins of high quality are shown. A method for producing casting blocks from hypereutectic silumins by direct chill casting is considered. The possibility of milling primary silicon crystals by introducing modifiers and master alloys of Al-Si-P, Al-Cu-P systems, inorganic carbon and phosphorus compounds is shown. The tendency of copper-doped silumins to hot shortness is shown. The technology of impact on the melt of ultrasonic cavitation is considered together with the introduction of additional active modifiers made of master alloy rods to obtain casting blocks from hypereutectic high-alloy silumins using the method of direct chill casting with a primary silicon crystal size of no more than 10 µm. Technological principles for reducing the grain size of α-solid solution, uniformly distributed over the ingot cross-section, are proposed.

A Study of the Effect of Post-Heating Pulse on Hot Cracking Susceptibility in Pulsed Laser Welding of Invar Alloy

Hot cracking is one of the major challenges in laser welding of Invar alloy. In this study, welding hot cracking susceptibility experiments are conducted with fish-bone-type Invar alloy sheets under pulsed laser welding condition. The pulse wave consists of two distinct power levels: welding pulse and post-heating pulse. The welding temperature field can be controlled by changing the duration of the post-heating pulse. The results of experimental measurements and finite element method calculation show that increasing of the post-heating pulse duration leads to a decline in the cooling rate of weld metal within the brittle temperature range, although the welding hot cracking susceptibility decreases at first and then increases. Neither the heat input nor the cooling rate is the only decisive factor for hot cracking during the welding process. 1. Introduction Invar alloy is widely applied in precision measurement devices and low-temperature-resistant structures for its low linear expansion coefficient at ambient temperature, which is less than 1.6 × 10—6 k—1, about 1/10 of the low carbon steel, and it changes very little within a large temperature range (Corbacho et al. 1998; Park et al. 2011; Zhao et al. 2015; Qiu et al. 2016). With the increase in demand for natural gas, the liquefied natural gas (LNG) carrier has been developed rapidly as a means of long-distance transport. The material of primary and secondary barriers on the containment insulation system of membrane-type LNG carrier is welded Invar alloy with a thickness of .7 mm, which directly contacts the — 163°C LNG (American Bureau of Shipping 2006; Bureau Veritas 2011; Wang et al. 2006). The total weld length of Invar alloy on an LNG carrier over 13 million cubic meters can reach up to 100 km according to statistics. Hot cracking is the major problem in the welding of Invar alloy, and currently Tungsten inert gas (TIG) arc welding is commonly used. However, the problem of hot cracking cannot be solved completely, and requires that the operator have good technical knowledge. Invar alloy has high hot cracking susceptibility during the welding process because of its single-phase austenite structure and high content of Ni (Kou 2003). Studies show that the welding hot cracking susceptibility of Invar alloy can be reduced when elements such as Ti, Mn, and Mo are added (Hirata et al. 2001), but these alloying elements will increase the linear expansion coefficient of the weld, resulting in the deterioration of mechanical properties at low temperature. Thus, laser welding and friction stir welding are proposed by researchers to solve the welding hot cracking problem of Invar alloy from the aspect of reducing welding heat input.

Study of thermal expansion anomalies of multilayer steel materials at high temperatures

The paper presents the results of a study of the anisotropy of the thermal coefficient of linear expansion (CTE), which was found in a multilayer metallic material based on steels, made by hot batch rolling. It is established that the material consisting of alternating layers of steel, has abnormally low CTE values in the direction perpendicular to the rental plane. To explain this phenomenon, a hypothesis was proposed about the relationship between normal and tangential stresses arising at the interlayer boundaries of such material. The confirmation of the hypothesis of the leading role of reactive stresses in the manifestation of the specified invar effect are the results of metallographic analysis. It is also shown that the conduct of cyclic high-temperature heating provokes recrystallization at the interlayer boundaries caused by the difference in the thermal expansion coefficient values of the adjacent layers and the effect of high temperature.

Technological features of production of copper-based composites reinforced with cast iron granules by means of casting

Increasing the operational reliability of friction units is one of the priorities for mechanical engineering, which requires the creation of effective tribotechnical materials. First of all, this applies to sliding bearings, which are used in various friction units in a wide range of operating conditions and must meet a number of requirements: low coefficient of friction, high wear resistance and fatigue resistance, as well as good thermal conductivity, workability, corrosion resistance and machinability, low coefficient of linear expansion and low cost. It is problematic to satisfy these requirements in real conditions; therefore, different friction materials that are best suited to specific conditions have been developed. In particular, cast composite materials (LCM) have been developed, which have found application in various friction units operating in severe operating conditions. Currently, the theoretical foundations of the mechanics of reinforced composite materials are well developed, and a significant progress has been achieved in their material science. However, there are still many problems associated with the choice of optimal technology ensuring the achievement in practice of the predicted composites properties by theory, control of interfacial interaction to improve the stability of the structure and properties of CM, with the development of new types of reinforcing elements that can raise the level of composite performance.In the present work results of scientific and experimental studies on the development of casting technology (solid-liquid synthesis) for obtaining composite materials with macroheterogeneous structure have been summarized. The structures of composites are studied for different methods of synthesis, as well as for different chemical composition of cast iron granules. The prospects of using white vanadium cast iron granules as a reinforcing phase are shown.

Feasibility of Magnesium Phosphate Cement (MPC) as a repair material for ballastless track slab

Ballastless tracks are becoming more popular with their lower overall lifecycle costs and increased lateral load capabilities but cracking due to cyclic vehicle loads and temperature loads have known to cause cracking which has become a major problem for this kind of construction. Based on the needs of the repair material, Magnesium Phosphate Cement has been studied in this paper as a possibility. A finite element model of a stretch of ballastless track slab has been developed to study the stress and strain properties of MPC repaired ballastless track under different temperature conditions. Results have then been compared to that for epoxy resin which is currently the industry standard for these kinds of repair. The analysis revealed that stress concentration occurred at the end of crack and that the smaller the magnitude of this stress concentration, the more obvious its effects were. The cracking resistance of MPC was found to be comparable to that of epoxy resin, though not better than epoxy resin. However, MPC was concluded to be more suitable than epoxy resin practically because of its superior compatibility with concrete, lower coefficient of linear expansion, better stability to temperature changes and lower setting times.

An overview of the computer-integrated systems and manufacturing technologies of pistons of internal combustion engines

The technological features of manufacture of pistons of internal combustion engines (ICE) taking into account the operational characteristics that form the functional requirements of the piston material are considered. It is shown that the chill casting of pistons is recommended for alloys with a low coefficient of linear expansion, and the liquid forging of pistons is preferable to the hot forging since it allows to obtain defect-free, dense billets with the fine structure of the piston material. For the heavy-loaded diesel engine pistons, chill casting is acceptable, provided the maximum possible porosity prevention in massive parts of castings.For the simulation of the casting processes of ICE pistons, it is advisable to use the LVMFlow package since it is focused on the finite-difference computation algorithms, ensuring stable operation of the computational station at a relatively low consumption of its hardware resources, ease of interface, computation speed and low cost of the software package. For the engineering simulation of the thermal and the stress-strain state of the ICE cast pistons, the ANSYS complex that has a high interaction with existing CAD and CAE systems having full interaction with WorkbenchProducts and well-known ANSYS, as well as a large number of mathematical solvers, allowing to quickly and accurately conduct computations in the WorkbenchProducts can be recommended.

Temperature-Dependent Structure of a High-k (Ba,La)(Ti,Ce)O<sub>3</sub> Ceramic

The lattice structure of a high-k BL3TC5 [(Ba1-xLax)(Ti1-x/4-yCey)O3 (x = 0.03, y = 0.05)] ceramic with cubic structure at room temperature was investigated using temperature-dependent X-ray diffraction (XRD) and Raman spectroscopy. The XRD results indicated that with increasing temperature, the cubic lattice of BL3TC5 showed a lower coefficient of linear expansion (α = 7.7 × 10-6/°C) relative to the cubic BaTiO3 (9.3 × 10-6/°C), but no abnormal change in cell volume occurred around the dielectric peak temperature Tm (= 38 °C). The peak position of the ~835 cm-1 Raman band induced by the substitution of La3+ ions for Ba sites in BL3TC5 was nearly independent of temperature on each side of Tm, whereas a slight fall (3 cm-1) in the peak position around Tm was detectable. The link between the dielectric peak with DPT and the lattice change was discussed.

Laser Bonding of Hydroxyapatite Ceramics

Orthopaedic implants have been fixed to bone tissue by other artificial materials such as bone cement or clinical screws. It is important to develop the bonding technique between bone and implant materials directly. Laser technique with high energy density is effective tool for bonding the different materials in short duration precisely. In this study, the laser technique for the bonding of bone and implant material has been proposed. The applications of laser technique were examined for the sintered (HAp), glass-added hydroxyapatite (G-HAp) and bone tissue. As a result of laser irradiation on brittle HAp, the cracks appeared near the melting region. However, on G-HAp containing cordierite-glass ceramics with a low linear expansion coefficient, crack-generation was reduced and performance of laser processing improved. The application for the bonding of bone and G-HAp showed that a sufficient bonding was achieved by the generation of melting region of HAp and bone with cavities by the evaporation of bone tissue.

Effect of preliminary plastic deformation on the structure and physicomechanical properties of aging invar alloy N30K10T3

The invar alloy N30K10T3 after water quenching from 1150°C (austenite, γ phase) has the temperature of the start of martensitic transformation M s ≈ −80°C and the Curie temperature T C ≈ 200°C. The effect of aging-induced phase decomposition in a deformed supersaturated solid solution on its hardness HV, electrical conductivity σ, magnetic permeability μ, and linear expansion coefficient β has been studied. It has been shown that cold plastic deformation of the alloy (at 20°C) to 30–50% increases its hardness, virtually does not change the conductivity, and decreases permeability. Aging of the deformed invar results in increasing HV and σ and decreasing μ. At room temperature, the deformed invar has a low linear expansion coefficient; its magnitude grows the faster, the greater the aging temperature T a. Plastic deformation increases the density of dislocations, which form a banded substructure in austenitic grains. Besides, a metastable martensitic phase has been observed, which undergoes a reverse martensitic transformation into austenite upon heating in the temperature range from 550°C to 650°C. This transformation causes a decrease in the linear expansion coefficient β(T) of the deformed material. In samples aged at T a = 700°C (after deformation), an athermal aging-induced martensite (αa phase) appears after cooling them to 20°C. The appearance of the αa phase is due to an increase in the temperature of the start of the martensitic transformation to above the room temperature caused by aging. In the samples containing the αa phase, there is observed a decrease in β in the temperature range from 350 to 670°C, which is due to the reverse transformation of the aging-induced martensite into austenite (αa → γ).

Effect of microcrystallinity on the mechanical performance of polycarbonate

Samples of polycarbonate (PC) before and after remelting and isothermal solidification treatment were characterized by wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS), microhardness, and stretching calorimetry techniques. Both PC samples could be regarded as structurally identical (X-ray amorphous); however, the isothermally solidified sample exhibited higher microhardness and Young's modulus, as well as a lower linear expansion coefficient and greatly reduced breaking strain. These results are attributed to the overlap of a network of ultramicrocrystals on the original entanglement network in the reference (untreated) PC sample.

Structural design for nonmetallic optical fiber cables made of high-modulus and low linear-expansion coefficient polymer tubes

This paper describes a design method for a simple structure nonmetallic optical fiber cable, consisting of stranded loose tubes which are made from a high Young's modulus and low linear-expansion coefficient new polymer. First, the Young's modulus and stranding pitch of the tube unit to effectively bear all laying tension have become obvious from mechanical investigation. The allowable region between the pitch and optical fiber excess length also became obvious. In the allowable region, no additional loss due to tube characteristics was observed in the wide range of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm 60\deg</tex> C. Moreover, it is shown that good performance of the cable using the new polymers is not attained using conventional cable materials.

Environmental effects on the dynamics and control of an orbiting large flexible antenna system

The environmental effects on a proposed large flexible space structure, namely, the Hoop/Column antenna system are studied. Mathematical models for the disturbances resulting from the interaction of solar radiation pressure with the vibrating and also thermally deformed antenna structure are developed. Expressions for the stabilizing gravity-gradient torques are also obtained. The uncontrolled transient response of the antenna system shows that the structure may tumble in orbit due to the expected disturbances. Linear quadratic regulator techniques are used to develop control laws for the actuators which could provide both shape and orientation control. The controlled response of the system is simulated for various initial conditions. The steady state rms pointing accuracy and the antenna surface accuracy are met in all the cases considered here. In order to reduce the control effort required to maintain the shape and orientation, the thermal deformations will have to be minimized. In the preliminary design of the system, materials should be considered which have a higher thermal conductivity and a lower coefficient of linear expansion, within cost constraints.