High Temperature Loading Research Articles

High strength and high electrical conductivity Cu composites reinforced by SiO2 aerogel particles

For high-performance metal matrix composites, maintaining the uniform distribution of the small-sized reinforcement phase in the matrix is the key to fully exploiting the advantages of the reinforcement phase, but it is also a technical difficulty. In this work, a new type of reinforcement phase—SiO2 aerogel particles, was selected to be added into the Cu matrix. Utilizing the characteristics of easy dispersion of the nanoporous structure in its original state and then densification under a high temperature load, its uniform distribution in the Cu matrix can be achieved by a simple powder metallurgy method. The composites have excellent electrical conductivity and high strength, which is mainly attributed to the unique distribution of silica aerogel particles: larger particles are distributed on the grain boundary, and smaller particles are distributed in the grain, which can greatly refine the grain. Quantifying the contribution of various strengthening mechanisms to yield strength increases, the results revealed that the grain refinement strengthening mechanism plays a leading role. Moreover, this work provides a new strategy for preparing high-performance copper matrix composites.

A study of electrothermomechanical converter for technological purposes with nonlinear changes in the loading and cooling medium

Heavy temperature processes with high-temperature loads require optimisation of technological processes, ensuring high reliability and combining rotating parts of electric machines with actuators to achieve greater efficiency of electromechanical converters. The research aims to provide a theoretical justification and experimental confirmation of the effect of higher harmonics in the air gap under nonlinear changes in the temperature of the medium. The research is based on the basic principles of electrodynamics, heat and mass transfer, mathematical modelling by the finite element method, and experimental verification of multi-physical parameters. Based on the analysis of the differential equation for determining the increase in the surface temperature of a ferromagnetic rotor under conditions of nonlinear temperature changes in the environment surrounding the electromechanical converter, the regularities of the formation of the free and forced components of the instantaneous temperature values of the massive rotor are established. Depending on the mode of interaction between the load-cooling medium and the electromechanical part of the screw units, kinematic diagrams of single-mass and two-mass systems with variable or constant moments of inertia and stiffness were formed. According to the size of the electromagnetic system of the experimental sample, a mathematical model for studying thermal and electromagnetic processes was built. The regularities of the spatial distribution of the temperature of the screw electromechanical unit are determined. The spectra of higher harmonics of voltage and current in the frequency range from 0 to 50 kHz have been experimentally determined, which confirms the presence of the effect of generating higher harmonics when the temperature of the medium surrounding the rotor screw changes. The detected harmonic spectrum affects both the formation of the dynamics of the rotating system and additional thermal power while increasing the overall efficiency of the screw electromechanical converter. The practical value of the obtained results lies in the possibility of predicting the optimal indicators of interrelated electromagnetic and heat exchange processes in screw electromechanical converters for technological purposes

Critical Evaluation of a Novel Analysis Technique for Assessment of Printed Circuit Heat Exchangers in High-Temperature Nuclear Service

AbstractApplication of printed circuit heat exchangers (PCHEs) to very high-temperature reactors (VHTRs) requires mechanical performance assessment methodologies. The PCHE morphology consists of thousands of millimeter-scale channels, for enhanced thermal efficiency, enclosed in a meter-scale PCHE core. PCHE geometry under thermomechanical creep-fatigue transients results in multi-axial interactions between its different segments, such as channeled core, walls, and headers. These global-level interactions influence the local channel-level responses. Hence, developing a PCHE performance assessment methodology, following the ASME Code, Section III, Division 5 provisions, is a critical gap to be filled. There is no analysis or design methodology available in ASME Code to assess a PCHE for its global and local level performances under high temperature and pressure loadings. This paper critically evaluates a recently proposed two-step analysis technique to estimate global interactions and local channel-level responses of PCHEs. In this novel analysis technique, the channeled PCHE core is replaced with orthotropic solid blocks of representative stiffness properties for the global thermomechanical analysis. Subsequent channel scale submodel analysis with detailed channel geometry, loading, and elastic-perfectly plastic (EPP) material model estimates the local responses for PCHE performance assessment. This paper critically evaluates this novel technique for its effectiveness in PCHE performance assessment. Finite element (FE) models imitating various analysis issues are developed, and FE analysis results are scrutinized. An important outcome of this study is the validation of the novel two-step PCHE analysis technique for application to the performance assessment of PCHEs in VHTRs.

Improving properties of h-BN/GH4169 self-lubricating composites prepared using nickel coated h-BN powders

ABSTRACT The service conditions of high temperature and heavy load of aero-engine require high-temperature self-lubricating composites with high strength, low wear and long life. Hence, the high-level objective of this study is to regulate the interface between the substrate and hexagonal boron nitride (h-BN) lubricant in GH4169 nickel-based high-temperature self-lubricating composites to improve the interfacial bonding strength and the overall performance. Electroless plating method was adopted to coat nickel on h-BN, and the dense high-temperature self-lubricating composites were fabricated through hot-pressing sintering. The effects of nickel coating on h-BN on the microstructure, mechanical properties and high-temperature tribological behaviors of composites were analyzed in detail, and the lubrication mechanism was also elucidated. The results illustrate the Ni@h-BN/GH4169 composites with addition of chemically modified lubricant particles have excellent mechanical properties and lubrication and wear reduction properties, compared to h-BN/GH4169 composites. This is mainly due to the introduction of nickel coating contributed to the distribution uniformity of h-BN in the matrix, and the wettability between h-BN and the substrate together with interfacial bonding strength were enhanced as well. This work provides an insight to overcome the challenges facing the technology when using GH4169 nickel-based self-lubricating composites in manufacturing of mechanical components in aerospace.

The characterization of plastic behavior and mechanical properties in the gradient nanostructured copper

Due to their individual plastic deformation behavior and mechanistic performances, gradient nano-grained (GNG) metals have been identified as promising materials for application in advanced engineering applications. However, their plasticity mechanism has not been thoroughly investigated. Hence, in this work, molecular dynamics simulation was employed to characterize the atomistic behavior of copper GNG structures under tensile loading with different grain sizes (2–9 nm) at varied temperatures (100, 300, and 600 K). The results indicated that there existed a critical grain size value (6 nm) for the Hall–Petch and inverse Hall–Petch relationship. Besides, it was found that the high-temperature loading (600 K) negatively affected the plasticity-induced strengthening, while low-temperature loading induced outstanding plasticity-induced strengthening owing to the excessive strain hardening events. The details of plastic deformation from the perspective of grain boundary, deformation twining, stacking faults, and dislocations were analyzed and a thorough discussion was presented to elucidate the grain size and temperature effects on the plasticity mechanism.

Solvent-free covalent MXene nanofluid: A new lubricant combining the characteristics of solid and liquid lubricants

A sole liquid lubricant or solid lubricant cannot cater to the demands of high-efficiency lubrication performance. From the standpoint of fusion of solid and liquid lubrication, solvent-free nanofluids are expected to be promising lubricants. In this work, solvent-free covalent MXene nanofluids were synthesized by grafting MXene with organosilane (KH560) and polyether amine oligomer (M2070) via covalent linkage. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, thermogravimetric analysis and rheological characterizations demonstrated that the MXene nanofluids were successfully synthesized and presented macroscopic fluidity at room temperature. Importantly, when used as a lubricant, the nanofluids perform well in friction-reduction and anti-wear properties even at high velocity (50 Hz), elevated temperature (100 °C), and heavy load (1100 N). The excellent tribological properties are ascribed to the nanofluids integrating the advantages of significantly improved load-bearing capacity and lubrication performance of the core nanomaterials, as well as liquid-like fluidity and self-healing characteristics of the organic shell. Moreover, the formation of 120–180 nm thick tribofilm on the worn steel surface was identified, which is significant in improving the lubrication performance. The above results suggest that the solvent-free MXene nanofluids should be a quite excellent candidate lubricant for integrating the advantages of solid and liquid lubricants and provide theoretical guidance for structural design of high-performance solvent-free nanofluid lubricants.

Test Method and Application of High-Temperature Operating Life of Automobile Chips

The high temperature operating life (HTOL) test is an important item in the reliability test of automobile chips. The goal of the HTOL test is to evaluate the durability of automobile chip products under high-temperature loads. Based on the common-used standards, calculation models, and related research experience of evaluating the reliability of electron devices at home and abroad, this paper focuses on the model of the high-temperature durability test model of automobile chips and analyzes different factors affecting the high-temperature operating life test. The general calculation and analysis model and method of the high-temperature operating life test of automobile chips are presented in this paper, which provides a reference for determining the indicators of the high-temperature operating life test of automobile chips.

Structure evolution and mechanical properties of Al-alloyed tantalum diboride films prepared by magnetron sputtering co-deposition

Alloying of transition metal diborides with other metals seems to be a suitable way to maintain their excellent mechanical properties under high-temperature loads. Here, we focus on the perspective tantalum diboride (TaB2) hard film, where we investigate the effect of aluminum alloying on the thermally induced structural evolution and mechanical properties of α-Ta1−xAlxB2 using a combination of density functional theory and experiments. Ab initio calculations predict a strong tendency toward the spinodal phase decomposition of the α-TaAlB2 solid solution into isostructural binaries in the entire concentration range at T = 0 K. However, an increase in temperature (T > 773 K) leads to stabilization of the α-Ta1−xAlxB2 solid solution at x < 0.5. The experimental results of magnetron co-sputtered Ta0.75Al0.25B2.14 and Ta0.69Al0.31B2.16 films with aluminum concentrations of 8 and 12.5 at. %, respectively, confirm the insolubility of aluminum in the TaB2 phase. The structure has a nanocomposite character formed by α-TaB2 nanofilaments surrounded by an Al-rich tissue phase. The films are structurally stable up to 1200 °C, but Al atoms already begin to diffuse from the boundary regions when the temperature exceeds 1000 °C. Al alloying causes a decrease in hardness, since the hardness of the reference as-deposited TaB1.21, Ta0.75Al0.25B2.14, and Ta0.69Al0.31B2.16 films is 34, 28, and 27 GPa, respectively. Exposing the films to high temperatures does not lead to a hardening effect; the hardness of Al-depleted films annealed at a temperature of 1200 °C decreased by approximately 10%. The decrease in Young's modulus from 420 GPa (TaB1.21) to 370 GPa (Ta0.69Al0.31B2.16) indicates a tendency toward the ductile behavior of Al alloyed films under mechanical load.

Expanded Glass for Thermal and Acoustic Insulation from Recycled Post-Consumer Glass and Textile Industry Process Waste

The production of glass foams obtained by recycling post-consumer glass and textile industry processing waste is presented. The mechanical, thermal and acoustic properties were characterized as a function of process temperature and time. The results showed that it is possible to produce glass foams with thermal and acoustic insulation properties from a mixture consisting of 96.5% of glass waste, 1% of textile waste and 2.5% of manganese dioxide, processed at temperatures between 800 and 900 °C for a time between 30 and 90 min. The samples had density in the range of 200-300 kg m-3, porosity of 87-92%, thermal conductivity of 85-105 mW m-1 K-1, noise-reducing factors of 0.15-0.40 and compressive strength of 1.2-3.0 MPa. Although their insulation performance was not as outstanding as that of polymer foams, these materials can emerge as competitive candidates for applications requiring non-flammability and high-temperature load bearing capacity in combination with low weight, mechanical strength, and thermal and acoustic insulation properties. The use of secondary raw materials (which accounted for 97.5% by weight of the synthetic blend) limits the energy required compared to that needed for the extraction, transportation and processing of primary raw materials, making these foams attractive also in terms of environmental footprint.

Study on the VCRplus Back-Up Roll Contour of 1500 mm CVC Mill

The back-up rolls of hot strip mills wear considerably under the conditions of high temperature and heavy load, which affects the roll service period and the stability of strip profile control. Serious uneven wear, short service periods, and spalling problems occurred on conventional back-up rolls of upstream stand CVC mills in 1500 mm continuous hot rolling production lines. Through finite element simulations, the problems are determined to be caused by the configuration of a flat roll contour of the back-up roll and the CVC roll contour of the work roll, which leads to uneven contact pressure between the rolls. The wear distribution form is ‘anti-CVC’ shape, and there is peak contact pressure between the rolls on both sides of the roll body. In particular, the long-term negative shifting of CVC on site further increases the peak contact pressure between the rolls, resulting in uneven wear and spalling accident. Based on the design technology of VCR back-up roll contours with variable contact lengths, and considering the cooperation between the middle of the back-up roll and the CVC work roll contour, the roll contour of the back-up roll has been improved. The designed VCRplus roll contour was analyzed and evaluated by finite element simulation, including the distribution of contact pressure between rolls, the control effect of bending force, and the transverse stiffness of the roll gap. The simulation results show that the VCRplus roll contour can effectively improve the uneven distribution of contact pressure between the rolls, and effectively improve the control effect of bending force and the transverse stiffness of the roll gap. Industrial tests demonstrate that VCRplus back-up roll contours have the advantages of uniform back-up roll wear, enhanced self-sustaining of the roll contour, and further extension of the back-up roll service life. The roll contour has now stably been put into industrial production, and the rolling capacity during the back-up roll service period has been extended from 150,000,000 kg to 250,000,000 kg.

Fatigue crack growth under large scale yielding condition: a tool based on explicit crack growth

Fatigue crack growth under large-scale yielding condition is studied for high-temperature loading. The applied strains are so important that diffuse damage phenomena are visible as a network of micro-cracks in front of the major crack. The survey of a macroscopic cracked surface is nevertheless possible, and numerical simulations with explicit representation of this crack are carried out to evaluate crack driving forces. The proposed numerical scheme takes into account plastic wake in the course of crack growth in a 3D model. A non-local model of fatigue crack growth rate, based on partition of strain energy density into elastic and plastic terms, yields improved results as compared to classical assessment of ∆J by numerical methods.

Hybrid surface modification for improved tribological performance of IC engine components – a review

The worldwide increase in demand for automotive sectors requires improved components life cycle, fuel economy and emission control. However, the occurrence of high temperature and variable loading on contact surfaces of internal combustion (IC) engine causes excessive friction results into reduced component life cycle, degrades emission level and fuel economy too. A small improvement in tribological performance and oil sealing through surface modification can able to enhance the functional performance of IC engine components significantly. Hence, in this work, a detailed discussion on the comparison of different hybrid surface modification techniques such as coatings, textures, and nanoparticles can work synergistically to improve the tribological performance of IC engine components. The process capabilities, limitations, and their effect on tribological performances of IC engine components are also presented. An analysis of surface texture parameters such as geometry, dimension, motion parameters, surface roughness, and oil transport mechanism is done to know the effects on the performance of the IC Engine. Further, the hybridization of different processes with nanoparticles (metallic, metallic oxides, carbon nanoparticles) is briefly presented. Finally, the effect of modified surface chemistry and characterization such as asperity, topography, microhardness, residual stress, and adhesive strength characteristics is also related to the tribological performances of IC engine components.

Tribotechnical properties of high-entropic coatings for metal-cutting tools

The paper presents the results of experimental studies of tribotechnical properties of high-entropic wear-resistant coatings on cutting tools for their subsequent application in high-speed turning of heat-resistant and heat-resistant steels and alloys. High-entropic alloys and coatings represent a separate group of materials with unique properties which application under conditions of high-temperature loading and action of alternating stresses on a cutting wedge would allow significantly increasing the efficiency of blade machining by cutting. High-entropic coatings on the basis of aluminum have essentially better tribotechnical characteristics and can be used in tool production.

Investigations on the long-term skid resistance of epoxy asphalt mixture based on accelerated loading test

Under long-term vehicle loads and large attenuation degrees, asphalt pavements are expected to have reduced slip resistance that does not meet the code requirements, thus impacting driving safety. Epoxy asphalt mixture has been widely used in road construction throughout recent years. Accordingly, it is necessary to explore the long-term skid resistance of epoxy asphalt mixture. Therefore, based on the indoor accelerated loading testing methodology, this paper investigates the anti-skidding performance attenuation of epoxy asphalt and SBS-modified asphalt mixtures at room and high temperatures. The rule of skidding resistance of asphalt mixture with loading times is analyzed, and the feasibility of epoxy asphalt in improving the long-term skid resistance of asphalt pavement is also explored. In general, the study results have shown that the decay rates of British Pendulum Number (BPN), the mean texture depth (MTD), and mean profile depth (MPD) epoxy asphalt mixtures are lower than those of SBS-modified asphalt ones under normal and high temperature loading conditions. Moreover, the fractal dimension of the epoxy asphalt mixture is larger and decays more slowly, and its section texture can be preserved to a greater extent during the loading process. Besides, it is observed that epoxy asphalt mixtures have better long-term skid resistance and greater retention of section texture than the SBS-modified asphalt ones.

The latest progress on neutron texture diffractometer at China Advanced Research Reactor

The first neutron texture diffractometer in China was built at the China Advanced Research Reactor (CARR). This neutron texture diffractometer has a high neutron intensity, moderate resolution and a neutron wavelength of 1.48 Å, which is suitable for studying the bulk textures in commonly used metals or alloys. The neutron texture diffractometer is now equipped with a two-dimensional position-sensitive detector, high temperature furnace and loading device after several upgrades. Now in-situ texture measurements can be performed on the texture diffractometer. A detailed description of the instrument and its performance characteristics are presented in this paper.

Mechanical properties of steel reinforced concrete T-shaped column after high temperature

The mechanical properties of 9 steel reinforced concrete T-shaped column specimens after high temperature were studied in this paper. The investigated factors included high temperature duration, loading eccentricity, loading angle and steel content. The test results showed that: (1) The failure mode of axial compression specimen was shear failure, and eccentric compression specimen was bending failure. (2) The stiffness of the specimen decreased with the increase of high temperature duration, loading eccentricity, loading angle and the decrease of steel content. (3) The ductility was quantitatively analyzed, and loading eccentricity and steel content had a more significant influence on the ductility than high temperature duration and loading angle. (4) With the increase of high temperature duration, loading eccentricity, loading angle and the decrease of steel content, the bearing capacity was reduced by 15.63 % ∼ 24.65 %, 8.87 % ∼ 14.76 %, 3.17 % ∼ 5.16 % and 18.71 % respectively. Finally, the simplified bearing capacity calculation method of steel reinforced concrete T-shaped column after high temperature was put forward, which provided a reference for post-disaster structural evaluation and reinforcement.

In-Situ Characterization of Microstructural Changes in Alloy 718 during High-Temperature Low-Cycle Fatigue

Components made of nickel-based alloys are typically used for high-temperature applications because of their high corrosion resistance and very good creep and fatigue strength, even at temperatures around 1000 °C. Corrosive damage can significantly reduce the mechanical properties and the expected remaining service life of components. In the present study, a new method was introduced to continuously determine the change in microstructure occurring as a result of exposure to high temperature and cyclic mechanical loading. For this purpose, the conventional low-cycle fatigue test procedure was modified and a non-destructive, electromagnetic testing technique was integrated into a servohydraulic test rig to monitor the microstructural changes. The measured values correlate with the magnetic material properties of the specimen, allowing the microstructural changes in the specimen’s subsurface zone to be analyzed upon high-temperature fatigue. Specifically, it was possible to show how different loading parameters affect the maximum chromium depletion as well as the depth of chromium depletion, which influences the magnetic properties of the nickel-based material. It was also observed that specimen failure is preceded by a certain degree of microstructural change in the subsurface zone. Thus, the integration of the testing technology into a test rig opens up new possibilities for improved prediction of fatigue failure via the continuous recording of the microstructural changes.

Improvement of surface properties of alloy constructional steel with ultrasonic composite strengthening modification

The key components of the automatic gun are subjected to the severe working condition of high temperature, transient state and continuous strong impact load in the shooting process, the surface of which using the alloy constructional steel is prone to fatigue cracks and gradual expansion, resulting in the fracture of the key components and the fault of the automatic gun. To improve the lifespan of the automatic gun, ultrasonic composite strengthening modification treatment (UCSM) was employed to improve the surface properties of alloy constructional steel in the present work. The three aspects of surface roughness, surface hardness and friction-wear properties, in comparison with those of the traditional dry cutting and advanced ultrasonic-rolling surface modification (AURSM), were characterized. The results show that the surface roughness of the samples after the ultrasonic composite strengthening modification fluctuates by about 0.31 μm, and the surface hardness increases by about 23.5% when compared with the cutting hardness, and the friction-wear properties of the samples has been increased by more than 75%. Ultrasonic composite strengthening modification can increases the local residual compressive stress on the material surface, which endows the material with better surface properties.

Tribological Behaviors of Inconel 718–Tungsten Carbide Friction Pair with Sulfur Additive Lubrication

This work investigated the lubricating and anti-wear properties of several sulfur additives for a nickel-based superalloy–tungsten carbide friction pair. Compared with PAO40 without any active chemical compounds, the three kinds of sulfur additives could decrease the friction coefficient from 0.2 to 0.1 and the wear volume by 90%. Sulfurized fatty acid ester had the best performance under high temperature and heavy load with COF below 0.1 and the smallest wear volume. Furthermore, the lubricating mechanism was investigated by XPS. The physical adsorptive film and the tribochemical film together enhanced the friction-reducing and anti-wear performances of the lubricants. This effective lubricant for Inconel 718 can be applied to the machining of nickel-based alloy.

Mechanical Characteristics of Sandstone under High Temperature and Cyclic Loading in Underground Coal Gasification

In the process of underground gasification of coal, the top rock of coal seam will experience a certain high temperature action and be in a complex stress environment. Therefore, it is of great theoretical and engineering significance to study the effect of cyclic unloading and loading on mechanical properties of rocks under high temperature action. In this thesis, the stress–strain curves of sandstone under different high-temperature treatments are obtained by conducting graded loading and unloading tests on sandstone treated at room temperature and at 200 °C, 400 °C, 600 °C, and 800 °C, respectively. The research content of this paper is as follows: the peak stress, peak strain, elastic modulus, Poisson’s ratio, internal friction angle, and cohesion of sandstone in the destruction stage of sandstone. The results show that the peak strain and cohesion of sandstone show an increasing trend with the increase of temperature from room temperature to 800 °C; the peak stress shows a decreasing trend with the increase of temperature from room temperature to 800 °C; the modulus of elasticity tends to increase from 200 °C to 400 °C and to decrease with temperature in the rest of the period; the Poisson’s ratio tends to increase from 600 °C to 800 °C and to decrease with temperature in the rest of the period; the internal friction angle increases sharply within room temperature to 200 °C, decreases slowly within 200–600 °C, and decreases sharply when the temperature exceeds 600 °C. The results of the study will provide important reference significance for the design and engineering application of the gasifier of a coal-bed underground gasification project.