High Temperature Loading Research Articles

Створення та обробки мідних сплавів, легованих хромом, цирконієм та ванадієм

The rapid development of mechanical engineering and electrical engineering requires alloys that have high electrical conductivity and a high level of mechanical properties, including strength at elevated temperatures. Pure and low-alloyed copper are ductile, but low-strength materials, which prevents their application in many areas. The solution of such problem can be in alloying with metals that would increase strength characteristics while maintaining electrical conductivity as much as possible, including at high current and temperature loads. The main alloying elements analyzed in this work as effective strengthening components were Cr, Zr, and V. It is shown that the increase in strength while maintaining electrical conductivity depends to a greater extent on the chromium content, the concentration of which in alloys can reach 5-10 wt. %. It was established that to achieve optimal characteristics of strength and electrical conductivity, the concentration of chromium can be close to 0,1 wt. %, and zirconium - up to 0,2 wt. %. At the same time, both for alloys with a high chromium content and in low-alloyed compositions, the characteristics of strength and electrical conductivity can differ by only 10-20%. In the vast majority of cases, copper alloys with chromium and zirconium undergo a specific, sometimes compositional and multi-stage, deformation treatment, after which a fine crystalline structure with nano-sized allocations of strengthening dispersoid phases can be formed. All considered alloys show similar technological features of obtaining a high level of final properties - homogenization and tempering from temperatures of 900-1000 °С and aging at 500 °С for 2 hours or more. At the same time, the higher the content of chromium and zirconium, the more difficult the deformation and heat treatments will be. Additional microalloying with vanadium in the amount of up to 0.2 wt. % may increase strength without a noticeable decrease in electrical conductivity and without the need for the complication of deformation and heat treatments. Keywords: alloying of copper alloys, Cu-Cr-Zr, Cu-Cr-Zr-V, heat treatment, deformation, electrical conductivity.

Composite soldering materials for high-temperature stable solder joints

The thermal load on electronic assemblies is constantly increasing. The reasons for this increase are, on the one hand, the integration of power electronic components in an ever smaller space and thus an increasing power density and, on the other hand, the increasingly harsh environmental conditions with high temperature load. In addition to electronic components and substrate materials, the soldered connections are also exposed to this stress and must withstand it. The thermal stability is primarily determined by the melting temperature of the solder material or by the remelting temperature of the final solder interconnection. The remelting temperature can be purposefully increased through diffusion soldering. The advantage of diffusion soldering is that the operating temperature of the final solder joint can exceed the joining process temperatures. By using the composite soldering materials and diffusion soldering process it is possible to produce the solder interconnections that can withstand the high thermal and thermomechanical stress [1]. In this work, the composite solder material, consisting of the base solder alloy BiSnAg in eutectic composition with a melting point of 139 °C and added copper particles, was examined. The added copper particles have a direct influence on the dynamics of the diffusion process. Diffusion can also be influenced by adjusting the soldering process parameters, such as maximum temperature and time above liquidus of the base solder alloy, with the aim of achieving isothermal solidification. The solidification can take place through the parallel reactions: the reaction between tin and copper with the formation of high-melting intermetallic phases Cu3Sn and Cu6Sn5 and the growth of bismuth crystals through coarsening of the structure and tin depletion in the original eutectic solder alloy [2].

Recycling of glass waste and spent alkaline batteries cathodes into insulation materials

Expanded glass with thermal and acoustic insulation properties are obtained from a foaming blend composed of 97% glass waste and 3% expanding agent. This latter is a blend of carbon and manganese oxides, recovered from exhausted alkaline batteries. The samples are produced after heating the mixture in a ventilated furnace at temperatures between 850 and 950 °C, for times between 15 and 60 min. Mechanical, thermal and acoustic properties are characterized as a function of process parameters. The glass foam samples have densities in the range of 290–350 kg/m3, porosity of 86–90%, thermal conductivity values of 107–120 mW m−1 K−1, noise reducing factors of 0.2–0.3 and compressive strengths up to 4.6 MPa. Although the resulting insulating performances are not as outstanding as those of polymer foams or mineral wool, these materials can emerge as competitive candidates for applications requiring low weight and moderate thermal and acoustic insulation properties, in combination with non-flammability and high temperature load bearing-capacity. Moreover, the use of 100% recycled raw materials limits the energy and the resource required for their production, if compared to those needed for the extraction, transportation, and processing of primary raw materials, making these foams attractive also in terms of environmental impact.

High−molecular weight poly(2-substituted 1,3-diene)s using iminopyridine iron precatalysts at high polymerization temperature and low iron loading

The synthesis of a series of iron(II) dichloride complexes bearing iminopyridine (ImPy) ligands, differing in the substituents at the pyridine, bridging carbon and N−aryl ring is described (1-LHPh−7-LHS). The X-ray structures of some of them are presented. All the iron compounds and, for comparison, the already reported 8-LHPhP, that features bulky ortho isopropyl N−aryl substituents, have been investigated as precatalysts for the polymerization of 2-substituted 1,3-dienes, i.e., isoprene and β-myrcene, using a low excess of methylaluminoxane (MAO) as alkylating reagent, iron loading as low as 0.025 mol% and variable temperature up to 100 °C. The goal is to have insights into ligand effects on catalyst reactivity and selectivity and to recognize the most robust iron precatalysts to access high-molecular weight (MW) polymers using low iron loading and high polymerization temperature, which meets current demands of mild, operationally simple approach. Particularly, the ketimine 4-LMePh and 5-LPhPh are more stable and least prone to chain termination than all the aldimine parents. 4-LMePh and 5-LPhPh produce cis-1,4/3,4 ultra-high-MW poly(isoprene)s and solid high-MW poly(β-myrcene)s, while maintaining narrow and unimodal molecular weight distribution. In this study we intentionally kept the monomer conversion low to provide a valuable assessment of catalyst stability, uncorrupted by mass or heat transport limitations. Furthermore, the synthesis of the unsubstituted aminopyridine (AmPy) iron(II) dichloride complex 9-LAPh, analogue to 1-LHPh, is described. 9-LAPh has been demonstrated to be a valuable probe for stability studies. Given the variety of catalytic transformations and substrates for which (ImPy)FeCl2 precatalysts have promising reactivity and selectivity, those developed in this study offer promising applications also beyond the polymerization of 1,3-dienes.

Experimental study on the thermal performance of a liquid-cooled heat sink integrating heat pipes for dual CPU servers

The increasing power consumption of server CPUs poses a challenge for data center cooling. In this work, a liquid-cooled heat pipe heat sink (LHPHS) with compactly arranged heat pipes is designed and fabricated for CPU cooling in dual CPU servers. Water is selected as the working fluid in the heat pipes. Experiments are conducted to explore the heat dissipation potential of LHPHS under high inlet coolant temperature and high heat load conditions, and to investigate the operational stability of LHPHS under the conditions of uneven heat generation between two CPUs. Furthermore, a one-dimensional thermal resistance network and numerical model of the LHPHS are established to quantitatively analyze the thermal resistance distribution of LHPHS and the variation of thermal resistance with coolant flow rate. The results show that, firstly, the LHPHS operates stably under high inlet coolant temperature and high heat load conditions, meeting the heat dissipation requirements of up to 37.5 W/cm2 with a coolant flow rate of 1 L/min and inlet coolant temperature of 35℃. Secondly, the LHPHS exhibits excellent performance in controlling temperature difference between CPUs and even when there is discrepant heat generation between them. Thirdly, the LHPHS performs a low thermal resistance, measuring 0.044 ℃/W at a coolant flow rate of 0.5 L/min, and this resistance further decreases as the flow rate increases. Additionally, it is observed that the thermal resistance of the liquid-cooled plate decreases with the increasing flow rate, and heat transfer within the heat pipes becomes a critical aspect under high coolant flow rates. Therefore, reducing the thermal resistance of the heat pipe is crucial for the thermal performance improvement of the LHPHS.

Research on Representative Volume Element Fex-Cy High-Temperature Mechanical Model Based on Response Surface Analysis

In this research, a multi-scale representative volume element method is introduced that combines the temperature and stress fields to analyze the force field distribution around microcracks in low-carbon steel using a combination of molecular dynamics and finite element analysis. Initially, an orthogonal experimental design was used to design the molecular dynamics simulation experiments. Next, a nano-level uniaxial tensile test model for mild steel was established based on the experimental design, and the uniaxial tensile behavior of low-carbon steel was investigated using molecular dynamics. Lastly, mathematical models of the modulus of elasticity E and yield strength Q of mild steel at a high temperature were obtained statistically using the response surface methodology. Meanwhile, a finite element model with a coupled temperature–stress field was established to investigate the force field distribution around the microscopic defects, and the microscopic crack stress concentration coefficient K was revised. The results indicate that regardless of the location of microcracks within the structure, the stress distribution due to size effects should be considered under high-temperature loading.

Ballastless track arching recognition based on one-dimensional residual convolutional neural network and vehicle response

In the long-term service process, high-temperature load will lead to ballastless track arching. The ballastless track arching will reduce the structural integrity, affect the smoothness of the line, and even endanger the safety of driving. Existing detection methods are costly, complex and not suitable for large-scale. This study proposes a low-cost, simple detection method based on one-dimensional residual convolutional neural network and vehicle response to recognize the arching. The vehicle responses in the simulation model are used as inputs to compare the recognition accuracies of different algorithms for the arching, and the vehicle response features extracted by the optimal algorithm are visualized in 3D using t-Distributed Stochastic Neighbor Embedding. The results show that the vehicle vertical acceleration is sensitive to the arching amplitude, and the influence of the arching on the vehicle vertical acceleration ranges from about 40 m, and, the vehicle vertical acceleration in the range of 40 m is chosen as the input. The Network 2–2 containing two residual blocks 2 has the highest recognition accuracy. The accuracy at different vehicle speeds ranged from 96.5 % to 97.5 %, and the average accuracy at a single arching magnitude ranged from 95.0 % to 100 %. The original vehicle response features under different arching magnitudes are very complexly distributed in 3D space with more overlapping. After Network 2–2 processing, the vehicle response features corresponding to different arching magnitudes are basically separated in 3D space, and only very few features overlap. It shows that Network 2–2 has strong robustness and vehicle response feature extraction capability.

Creep of un-doped and Cr-doped WC-Co at high temperature and high load

Un-doped and Cr-doped WC-10 vol% Co cemented carbides with a WC grain size of 1.4 μm have been investigated before and after hot compressive creep tests under an applied load of 900 MPa at 1000 °C and 300 MPa at 1100 °C. The Cr-doped material showed a much higher creep resistance at 1000 °C and a somewhat higher creep resistance at 1100 °C than the un-doped material. Quantitative microscopy showed that WC grain growth occurred in the plane perpendicular to the load axis during creep deformation and that the growth process was slower in the Cr-doped material. In addition, binder phase redistributed and a number of WC grain boundaries were infiltrated with binder phase. This suggests that accommodated WC grain boundary sliding occurred during creep deformation. The formation of intergranular cavities implies that also unaccommodated grain boundary sliding occurred, especially at 1000 °C. It is suggested that WC grain growth perpendicular to the load axis is rate limiting in the creep deformation process, and that Cr segregation to WC/binder phase boundaries hinders grain growth. The weak effect of Cr on creep resistance at 1100 °C at 300 MPa is explained by Cr giving a larger volume fraction of binder phase and therefore a larger number of infiltrated grain boundaries, facilitating grain growth.

Study on the Aerothermoelastic Characteristics of a Body Flap Considering the Nozzle–Jet Interference

A body flap/RCS-integrated configuration is often used to achieve pitch trimming and controlled flight in near space for hypersonic vehicles. Under the high temperature and pressure load induced by the expansion wave at the nozzle exit, the body flap is prone to significant structural deformation, which leads to a change in the resulting moment, even comparable to the control ability, and bring additional challenges to the control system. Based on the CFD/CTD/CSD coupling method, the aerothermoelastic effect on the aerodynamic characteristics and structural deformation of the body flap under jet interaction is systematically studied. Numerical results indicate that the pitching moment coefficients show an increasing trend for all the models, rigid, elastic and thermoelastic, while the increment significantly decreases with the increase in trajectory altitudes. With the increase in deflection angle, the pitching moment coefficients of the three models decrease nonlinearly at high altitude, and the aerothermoelastic effect significantly decreases. At a middle-lower altitudes, the pitching moment coefficient is reversed at a lager deflection angle, and the trailing edge of the body flap presents the deformation characteristics of upward bending, which makes the aerothermoelastic phenomenon degenerate into an aeroelastic problem. From the station along the chord and spanwise direction, the change in displacement increment of the thermoelastic model reflects the competitive relationship between normal stress and thermal stress imposed by jet interaction.

Modeling of environmentally assisted intergranular crack propagation in polycrystals

AbstractPolycrystalline nickel‐based superalloys experience accelerated intergranular crack growth when exposed to dwell times in oxygen‐rich environments and a combination of high temperature and tensile mechanical loading. Increasing crack growth rates are observed for increasing amounts of environmental oxygen in a certain oxygen concentration range, while below and above that range crack growth rates remain approximately constant. A fully coupled chemo‐mechanical modeling framework accounting for the degradation of grain boundaries by oxygen has been presented by the authors. In this work, we expand the framework by a moving boundary condition to capture a realistic oxygen flux in grain boundary cracks for both edge cracks connected to the environment and interior cracks. In numerical simulation results, the behavior of the moving boundary condition is shown for intergranular crack propagation through a polycrystal subjected to cyclic loading. Finally, the capabilities of the modeling framework to qualitatively predict the dependence of the average crack growth rate on the environmental oxygen content, load level, and dwell time are evaluated and it is shown that predictions qualitatively agree with experimental observations for intergranular fracture.

Hot temperature tribological behavior of Mg-Zn-Gd alloy under graphite surfactant functionalized SN500

The effect of SN500 and SN500 +G lubricants on the wear behavior of Mg-Zn-Gd alloy was studied. For this purpose, Mg-Zn-Gd alloy was produced by the stir casting method. The wear test was performed under 20, 40, and 80 N with a velocity of 0.5 m/s for 1000 m at different temperatures (25, 100, 150, 200, and 250 °C) under SN500 and SN500 +G lubricants. The results showed that in the presence of precipitates weight loss and wear rate were reduced. With the increasing load in all samples, weight loss and wear rate increased. The lowest wear rate was obtained at 250 under 20 N and was equal to 0.036 and 0.030 m3/m, and with an increase in the load to 80 N, it reached 0.044 and 0.042 m3/m for samples under SN500 and SN500 +G, respectively. It was also observed that lubrication of SN500 +G in all samples created better properties than SN500. The addition of graphite to SN500 also reduced the coefficient of friction. So that the friction coefficient of the tested sample under 80 N at 250 °C under SN500 has decreased by 15% compared to SN500 +G. The worn surfaces SEM micrographs of samples under SN500 +G lubricant show the presence of the mechanically mixed layer (MML) with the adhesive wear mechanism. With increasing load, the abrasion, delamination, and MML mechanisms were dominant, and a significant reduction of COF and wear rate were observed. At the high temperature and high loads, the crushing of precipitates and their orientation in the wear sliding was caused to dwindle applied load and prevented the activation of other wear mechanisms.

Surface treatments and substrate-coating interface effects on damage accumulation kinetics in hard-coated WC-Co hardmetals under cyclic multi-axial high-temperature loading

Coated hardmetals are commonly used tool materials for metal cutting applications. For these applications, the substrate- and the coating surface qualities are improved by grinding, polishing, or blasting. The focus of the current work was to study the influence of different combinations of substrate-coating surface processing techniques on the induced damage in Al2O3/TiCN hard-coated WC-12 wt% hardmetal substrates and the depth to which the damage reaches into the substrate. The substrate and coating surfaces were prepared by grinding, polishing, dry blasting, wet blasting, or remaining in the deposited state. Investigations were performed using cyclic indentation with a novel ball-in-cone test method in a vacuum at 700 °C, under conditions that imitate the combined shear-compression loads that occur at the cutting edges of metal cutting tools. Additionally, finite element simulations were performed to characterize the stress state arising during ball-in-cone testing. The kinetics of defect formation and accumulation in the hardmetal substrate as a function of the loading situation during the ball-in-cone test will also be discussed. The defects that formed in the substrate during cyclic loading were studied using scanning electron microscopy in cross-sections prepared by focused ion beam milling. A larger increase in defect frequency was observed for rougher coating surfaces and substrate-coating interfaces than for smoother ones. Furthermore, 6 μm thick coatings exhibited a higher defect frequency after cyclic loading than 15 μm thick coatings. Most of the observed defects were in the nm-size range close to the substrate-coating interfaces and tended to have increased in size after cyclic loading. The ball-in-cone test set-up enables the study of the damage mechanisms in coated hardmetal substrates with different treatments prior to and after deposition under tunable milling-like stress and temperature conditions.

Behavior and properties of ultra-lightweight concrete with foamed glass aggregate and cellulose fibres under high temperature loading

Behavior and properties of ultra-lightweight concrete with foamed glass aggregate and cellulose fibres under high temperature loading

Aluminium oxide grid blasting: grid size and blasting pressure influence on the substrate surface contamination, roughness and ceramic plasma spray coating adhesion strength

This paper concerns influence of grit blasting parameters (grid blast media size and blasting pressure) on blasted surface contamination by entrapped grid blast particles and roughness of a blasted mild steel surface and a subsequent influence of given surface specifications on a thermal spray coating adhesion strength. Main goal of an experiment presented in this paper is basic optimization of grid size of alumina oxide blasting medium and blasting pressure in order to reduce surface contamination by grid residues trapped on the surface. Those residues are known to cause reduction in adherent forces between coating and blasted substrate, functioning as major stress concentrators especially under high mechanical and/or temperature loads. Mutual relations between grid size and blasting pressure as input parameters, and surface contamination, surface roughness and adhesion of an atmospheric plasma sprayed ceramic coating is evaluated. It was found that higher surface roughness does not necessarily lead to higher adhesion of thermally sprayed coating. The resulting adhesion strength seems to be determined by the synergistic effect of the suitable roughness profile, residual blasting particles and feedstock particle size of the deposited coating. This is supported by the observed highest adhesions (around 22 MPa) of ceramic alumina-titania APS coating to the surface with lowest measured roughness (as low as Ra 2.7) but also the lowest contamination level by blasting residues (4.6 to 6.7 %).

Effect of elevated temperature on the low-velocity impact performances of GFRP reinforced concrete slabs

The objective of the present study is to study the impact resistance of GFRP reinforced concrete slabs under elevated temperature. Considering the high temperature softening effect and strain rate enhancement effect of FRP bars and concrete materials, the numerical model for the study of fire and impact resistance of GFRP reinforced concrete slabs were established and compared with the fire resistance test and drop hammer impact test respectively, which verified the rationality of the numerical model. The failure mechanism of GFRP reinforced concrete slabs under the combined action of high temperature and impact loading was analyzed. The influence of fire scenario (at high temperature or after natural cooling) and fire time on GFRP reinforced concrete slabs was revealed. Eventually, the residual bearing capacity of damaged slabs after high temperature and impact loading was obtained. The results show that high temperature significantly degrades the impact resistance of GFRP reinforced concrete slabs. The slab at high temperature shows worse impact resistance than the slab after cooling down. With the increase of fire time, the punching failure of GFRP reinforced concrete slabs become more serious while the central displacement of the slabs and the impact duration increase, accompanied by decreased impact force. Compared with RC slabs, the deformation and impact force of GFRP reinforced concrete slabs under impact loading are more affected by high temperature, while the residual bearing capacity is less affected. Under the combined action of fire and impact loading, the slab is mainly local damage while energy dissipated by concrete accounts for most of the impact energy absorbed by the slabs.

Dynamic tensile mechanical properties of thermally damaged sandstone under impact loads and the influence mechanism of composition

The stability of surrounding rock in the combustion void is the key to continuous, safe, and efficient gas production in an underground coal gasification project. The key factors influencing the stability of surrounding rock in the combustion void are high temperature and impact dynamic load. At the same time, rock structure failure mainly depends on the rock materials’ tensile strength. Therefore, it is fundamental to study the dynamic tensile mechanical properties of thermally damaged rocks to control the surrounding rock stability of the combustion void in UCG projects. This paper used the coal measures as the research object. The dynamic direct tensile test of thermally damaged sandstone was carried out using a high-temperature load system and split Hopkinson tension bar (SHTB) test system. The test results showed that the dynamic tensile strength of sandstone increased linearly with the increase in strain rate. In contrast, it increased first and then decreased with temperature. In addition, the nonlinear regression method was applied to establish the prediction model of dynamic tensile properties of thermally damaged sandstone. XRD analyzed the composition and mass fractions of sandstone. From the standpoint of composition change, the change mechanism of the mechanical properties of thermally damaged coal measured in sandstone was illustrated.

Permanent Deformation Monitoring and Remaining Life Prediction of Asphalt Pavement Combining Full-Scale Accelerated Pavement Testing and FEM

Permanent deformation (rutting) is one of the typical failure modes of asphalt pavement with a semirigid base in high-temperature areas. To address issues of pavement structure deformation and remaining life prediction, a method of combining accelerated pavement testing and finite element (FE) simulation was proposed. A modified Burgers model considering creep parameter damage was obtained using strain monitoring data and laboratory test values, which was performed in the FE model to analyze rutting development. The results showed that high temperature and heavy axle loads greatly influenced rutting development: the tested road was loaded 360,000 times at high temperature, contributing 50% to accumulated rutting; rutting increased by 90.7% under the condition of 50% overload under high-temperature seasons from the simulated results. Then, the ratio of the bulge area to the depression area (KR) was proposed to define the rutting deformation mechanism. The KR analysis results illustrated that rutting development was a transition process from compaction rutting to flow rutting. Finally, the relationship between the action times of axle load in the tested and in-service roads was established based on the rutting equivalence principle. When the action times of axle load reach approximately 25 million times (insufficient remaining life) for the investigated Hu-Ning highway, necessary maintenance measures should be taken to treat rutting deformation.

A research on excavation compensation theory for large deformation disaster control and a review on the multiphysical–multiscale responses of salt rock for underground gas storage

A research on excavation compensation theory for large deformation disaster control and a review on the multiphysical–multiscale responses of salt rock for underground gas storage

Critical role of dynamic precipitation on enhanced creep resistance in Mg–Zn alloy by Mn substitution for Zr

Mg alloys with excellent creep resistance are able to withstand fatigue and damage under high temperature and complex load. Adding alloying elements rather than rare earth elements, such as Mn, can further reduce the cost and thus facilities the widespread applications of Mg alloys. In this paper, the individual effect of Mn and Zr elements on the dynamic microstructural evolution of Mg–Zn alloys during creep is evaluated, on the basis of identical initial microstructure before creep. And the essential origin of Mn substitution for Zr improving the creep resistance of Mg–Zn alloys by one order of magnitude is revealed. Experimental investigations and first principle calculations reveal that prior-precipitation of α-Mn particles serve as the heterogeneous nucleation sites for the precipitation of β1′ phases, and Mn partitioning in MgZn2 phases promote the nucleation and thermal stability of β1′ precipitates during creep. High number density of fine precipitates can effectively inhibit the occurrence of continuous dynamical recrystallization (CDRX), pin dislocations and impede the activation of cross-slip, which are the main reasons for the enhanced creep resistance in ZM60 alloy. As Zr does not participate in the formation of precipitates in ZK60 alloy, the MgZn2 phases with low thermal stability are prone to growth and coarsening during long-term creep. Large number of fine CDRXed grains and sparse coarse precipitates in ZK60 alloy cannot effectively impede the dislocation movement, which contributes to the occurrence of cross-slip and deteriorate the creep resistance. This work provides new insights for designing and fabricating outstanding heat-resistance Mg alloys.

A Multi-Scale Attention Mechanism Based Domain Adversarial Neural Network Strategy for Bearing Fault Diagnosis

There are a large number of bearings in aircraft engines that are subjected to extreme operating conditions, such as high temperature, high speed, and heavy load, and their fatigue, wear, and other failure problems seriously affect the reliability of the engine. The complex and variable bearing operating conditions can lead to differences in the distribution of data between the source and target operating conditions, as well as insufficient labels. To solve the above challenges, a multi-scale attention mechanism-based domain adversarial neural network strategy for bearing fault diagnosis (MADANN) is proposed and verified using Case Western Reserve University bearing data and PT500mini mechanical bearing data in this paper. First, a multi-scale feature extractor with an attention mechanism is proposed to extract more discriminative multi-scale features of the input signal. Subsequently, the maximum mean discrepancy (MMD) is introduced to measure the difference between the distribution of the target domain and the source domain. Finally, the fault diagnosis process of the rolling is realized by minimizing the loss of the feature classifier, the loss of the MMD distance, and maximizing the loss of the domain discriminator. The verification results indicate that the proposed strategy has stronger learning ability and better diagnosis performance than shallow network, deep network, and commonly used domain adaptive models.