Large Thermal Stresses Research Articles

Phase transition suppression, thermal and electrical properties of (YNb)0.2Zr0.6P2O7

ZrP2O7 is a promising material with excellent thermal and electrical properties. However, when temperature approaches to 563 K, it undergoes a structural phase transition, which will cause large thermal stresses. When Zr is substituted by Y and Nb, a new material of (YNb)0.2Zr0.6P2O7, was successfully prepared and the phase transition of material was effectively inhibited. This new material adopts a cubic structure similar to ZrP2O7, and exhibits medium thermal expansion (α = 7.1×10-6 K-1) in the measured range of 200-1073 K. The values of thermal conductivity from RT to 973 K are between 0.4474 W·m-1·K-1 and 0.8526 W·m-1·K-1, which can be comparable to the values of traditional thermal insulation materials. The dielectric constant and dielectric loss factor at the frequencies above 1 MHz are stable and low. The electrical conductivity of the material indicates that it is electronically insulating at RT-573 K.

A novel compact supercritical CO2 solar receiver based on impinging jet: Heat transfer performance and thermal stress analysis

The compact solar receiver can withstand high temperature and high pressure, which provides promising solutions for direct supercritical CO2 (S-CO2) solar receiver applications. However, it still suffers from local high temperature and large thermal stress due to the non-uniform heating boundary condition. The impinging jet method can significantly enhance the local heat transfer coefficient, holding significant potential in reducing the local high temperature of the compact S-CO2 receiver. Inspired by this, a novel design for a compact S-CO2 receiver using the impinging jet was proposed in this work. The heat transfer performance and stress behavior of the jet channel within the receiver were numerically investigated. The results showed that the jet channel has a significantly higher heat transfer performance than the rectangular channel, and the shorter flow path of the jet channel also effectively reduces the pressure loss. Meanwhile, the jet pattern significantly enhances the temperature uniformity, thereby reducing the thermal stress. In addition, increasing the channel aspect ratio improves the thermo-hydraulic performance, but increase the stress at the same time. The increase in the number of jet holes and the jet hole diameters not only enhance the thermo-hydraulic performance, but also reduce the stress of the jet channel.

Influence of thermal fatigue cycles on concrete cold joints

Mass concrete structures in northern climates experience extreme oscillations in temperature each year. These fluctuating conditions incur large thermal stresses, which are of particular concern at cold joint locations. To better understand the behaviour of cold joints subjected to these thermal fatigue cycles, an experimental program was conducted at the University of Manitoba, focusing on the performance of concrete cylinders with concrete-to-concrete interfaces. Specimens were prepared with joints oriented either horizontally to evaluate direct tensile performance or at a 35°, 40°, or 45° angle for slant shear. These cylinders were then installed in specially designed vertical translation-restricting frames and placed in an environmental chamber, where they were subjected to temperatures cycling between −25 °C and 40 °C. Static testing after 50, 150, and 250 cycles was performed to ascertain remaining bond strength. An increase in performance of approximately 20 % was observed in direct tension after 50 cycles, followed by a subsequent decrease. In general, the thermal fatigue cycles did not appear to detrimentally impact bond strength after 250 cycles in both direct tension and slant shear. Additionally, interface friction demonstrated no meaningful trend between specimens that had experienced zero to 250 cycles, remaining relatively consistent with their corresponding roughness level defined in the Canadian Design of Concrete Structures code, and bond cohesion appeared to follow a similar trend to mean direct tensile bond strength results.

Development of a Microheater with a Large Heating Area and Low Thermal Stress in the Heating Area.

In this paper, a microheater that can absorb thermal stress and has a large heating area is demonstrated by optimizing the structure and process of the microheater. Four symmetrically distributed elongated support beam structures were machined around the microheater via deep silicon etching. This design efficiently mitigates the deformation of the heated region caused by thermal expansion and enhances the structural stability of the microheater. The updated microheater no longer converts the work area into a thin film; instead, it creates a stable heating platform that can uniformly heat a work area measuring 10 × 10 mm2. The microheater is verified to have high temperature uniformity and structural stability in finite element simulation. Finally, thorough investigations of electrical-thermal-structural characterization were conducted. The test findings show that the new microheater can achieve 350 °C with a power consumption of 6 W and a thermal reaction time of 22 s. A scan of its whole plane reveals that the surface of the working area of the new microheater is flat and does not distort in response to variations in temperature, offering good structural stability.

Influence of laser printing mode on thermal behaviors, forming characteristics, and microstructure evolutions of additive manufactured Ti6Al4V alloy

Ti6Al4V parts fabricated by laser powder bed fusion (LPBF) technology have been widely used in such fields as aerospace, automotive and medical implants. This study investigates the effect of laser scanning modes on thermal behaviors, forming characteristics, and microstructural evolutions of LPBF-fabricated Ti6Al4V parts. The numerical simulations on the temperature field provide a theoretical explanation of various surface morphologies, surface roughness values and relative densities of samples. The rotation between adjacent layers diminishes the large directional thermal stress generated by X scanning or Y scanning, the Ti6Al4V samples using XY scanning and Island scanning present smooth surface and higher relative density (> 99.0%). The observed staggered martensite within the columnar β grains is due to the epitaxial solidification across the deposited layers with 90° or 37° rotation. The martensite growth of LPBF-processed Ti6Al4V components using X scanning has a similar inclination along the building direction and presents anisotropic characteristics. These findings provide new inspirations for achieving high-performance titanium alloy components with specific microstructure by LPBF technique using a proper laser scanning mode.

Rapid 2-Dimensional prediction of supercritical CO2 heat transfer behaviors in inclined tubes based on deep learning

At present, there is a dearth of empirical correlations for the prediction of the inclined supercritical heat transfer. Considering the shortage of the rapid prediction method in the initial design stages for the supercritical fluid heat exchanger with inclined tubes or under inclined conditions, a 2-Dimensional rapid prediction method based on the numerical method combining deep learning method was proposed to reconcile the accuracy and the efficiency of the inclined supercritical heat transfer behaviors prediction. In order to train the deep learning model, 200 numerical cases with 520,000 data were conducted. After that, 7 new cases were chosen to analyze the inclined heat transfer behaviors and validate the current model. The results were indicative of a significant circumferential inner wall temperature difference in the inclined supercritical heat transfer. The temperature difference was larger when the inclined angle was closer to 90°, even though the circumferentially averaged temperature is smooth and acceptable. This potential temperature difference would not only cause large thermal stress which may accelerate fatigue failure, but also increase the risk of over-temperature. Fortunately, the current deep learning model could predict the 2D temperature distribution of these new cases with the max absolute relative error of 16.60%. Therefore, the circumferential inner wall temperature distribution of the inclined supercritical CO2 heat transfer could be evaluated during the initial heat exchanger design. Moreover, the trained model and the relative files are available at Supplementary materials.

Flux jump and mechanical response in inhomogeneous high-temperature superconductor under the pulsed-field magnetization

The high-temperature bulk superconductors with high critical current density are brittle, and can be damaged by large Lorentz forces and thermal stress during magnetization. Several studies have reported the failure of bulk superconductors during flux jumps. In this study, we analyzed the magnetization characteristics and mechanical response of the HTS bulk with inhomogeneous current density along the c-axis. The numerical simulation was consistent with the experimental results presented in the reference. Moreover, a flux jump occurred near the area of the pre-arrangement flux during the second pulsed field magnetization. The maximum temperature is lower than the critical temperature during the flux jump. In the mechanical analysis, the flux jump led to an abrupt change in the maximum stress of the bulk, and the maximum radial stress was significantly higher than the maximum hoop stress during the flux jump. The maximum radial stress increased with decreasing ambient temperature during the flux jump, and the maximum stress area was always near the seeded plane. Subsequently, the magnetization characteristics and mechanical response were studied for different locations of the seeded surface, two concentric superconducting bulks, and non-uniform fields.

Preparation and ablation behavior of a ZrB2-SiC coating-matrix integrated C/C composite

The preparation of a ZrB2-SiC coating-matrix integrated C/C composite was achieved by a slurry method and precursor infiltration and pyrolysis. The obtained composites consisted of a SiC outer layer, a ZrB2-SiC inner layer and a C/C-ZrB2-SiC substrate. Compared with a composite without the ZrB2-SiC layer, the mass ablation rates of the composite were reduced by 14.8 %, 12.0 %, and 19.4 %, and the linear ablation rates were reduced by 41.3 %, 28.2 %, and 14 %, respectively, after ablation under an oxyacetylene flame with a heat flux of 4.18 MW/m2 for 60 s, 120 s, and 300 s. During the ablation process, the SiC outer layer played a role in reducing the heating rate and surface temperature and promoting the sintering of ZrO2 so that the oxide layer avoided peeling off under large thermal stress. The ZrB2-SiC inner layer acted as an oxygen, heat and flow barrier, reducing the oxidation rate of the substrate.

Prognosis of Li-ion Batteries Under Large Load Variations Using Hybrid Physics-Informed Neural Networks

The development of new modes of transportation such as electric vertical takeoff and landing aircraft and the use of drones for package and medical delivery have increased the demand for reliable and powerful electric batteries. Therefore, accurately predicting the degradation of a battery’s state-ofhealth (SOH) and state-of-charge (SOC) is a crucial albeit still challenging task. There is a need for models that can accurately predict the SOH and SOC while taking into account the specific characteristics of a battery cell and its usage profile. While traditional physics-based and data-driven approaches are used to monitor the SOH and SOC, they both have limitations related to computational costs or that require engineers to continually update their prediction models as new battery cells are developed and put into use in battery-powered vehiclefleets.Battery capacity degradation can vary from battery to battery and can also be influenced by changes in load due to internal thermal stress. While sophisticated electrochemistry-based models can provide precise predictions of the SOC during adischarge cycle when parameters are well-tuned, using highfidelity models for prognostics purposes can be computationally expensive. Those models also require tuning to specific battery types and at times to specific specimens, thus hindering generalization. In contrast, purely data-driven approaches can learn the relationship between input and output for SOC prediction based on load input, but they require a large and diverse training dataset and lack any physical or electrochemical understanding, making far-ahead predictions challenging if test loading conditions fall outside the training distribution. To address some of the drawbacks of the aforementioned modeling approaches, in this paper, we enhance a hybrid physics-informed machine learning version of a battery SOC model we presented in previous work to predict voltage dropduring discharge. The enhanced model captures the effect of wide variation of load levels, in the form of input current,which causes large thermal stress cycles. The cell temperature build-up during a discharge cycle is used to identify temperature-sensitive model parameters. Additionally, we enhance an existing aging model built upon cumulative energy drawn by introducing the effect of the load level. We then map cumulative energy and load level to battery capacity with a Gaussian process model. To validate our approach we use a battery aging dataset collected on a self-developed testbed, where we used a wide current level range to age battery packs in accelerated fashion. Prediction results show that our model can be successfully calibrated and generalizes across all applied load levels.

Thermal fatigue crack initiation and propagation behaviors of GH3230 nickel‐based superalloy

AbstractThe drastic severe temperature cycle in an aero‐engine combustion chamber leads to large thermal fatigue stress, which may induce thermal fatigue failure of the combustion chamber. In this paper, thermal fatigue crack initiation and propagation behaviors of GH3230 nickel‐based superalloy sheet specimens with V‐notch were studied under different peak temperatures 800°C, 900°C, and 1,000°C using self‐built thermal fatigue equipment. The temperature, stress, and crack propagation driving force of the V‐notch specimen were discussed in detail. Results show that the thermal fatigue crack initiation life gradually decreases with the increase of the peak temperature. Oxidation caused by high temperature will weaken alloy's strength and accelerate its crack propagation. Higher peak temperature will make the crack propagate faster and the thermal deformation at V‐notch end easier to accumulate. At last, there is a good consistency between fitting curves from the modified Paris formula and the experiment results.

Numerical simulation of the coupled multiphysics fields and reactions during the microwave pyrolysis of wood particles

Microwave heating has gained significant attention as an alternative to conventional methods for biomass pyrolysis. To investigate the electromagnetic-thermal-hydraulic-chemical processes during biomass pyrolysis under microwave irradiation, a three-dimensional comprehensive pyrolysis model was developed. The model numerically described the physicochemical processes of the electromagnetic wave propagation in the reactor, heat transfer and fluid flow inside porous wood particles, pyrolysis reactions, and phase changes. The model was validated by comparing the temperature profiles of biomass samples under varying microwave powers against literature data. The modeling results demonstrated that there was a strong interaction between the distributions of the microwave electromagnetic fields in the cavity and that inside the wood particles; these distributions changed with the size, shape, and location of the biomass sample in the cavity. Using the model, the thermal response of wood particles to microwave radiation was determined. The predicted results showed that a millimeter-sized wood particle was large enough to straddle multiple high-energy microwave regions in the cavity, resulting in more than one intraparticle hotspots. The transient dielectric loss inside wood particles is nonuniform due to the enhancement of the local relative permittivity by the local hotspots. The maximum permeability within the wood particles increases by an order of magnitude during microwave pyrolysis at 1 kW. The hotspots have a considerable influence on the structural homogeneity and stability of biochar due to the formation of large thermal and expansion stresses around the hotspot locations. Moreover, the energy efficiency (ηe) of converting microwave electromagnetic energy into the thermal energy of wood particles is sensitive to the input microwave power and particle shape. For instance, ηe ranges from 12.44% to 36.15% under the microwave powers of 0.8–1 kW for the pyrolysis of a cylindrical wood particle with aspect ratios of 0.25–2. This work provides the fundamental technical support for the industrial application of microwave pyrolysis.

Understanding Scale-Up of High-Current Electrodes

A simple and generic model for the heat distribution in electrodes for primary metal production has been investigated. The equations have been analyzed focusing on understanding the scale-up of electrodes under both direct current (DC) and alternating current (AC) conditions. The analysis provides a theoretical foundation for Westly’s empirical scale-up rule. For graphite and small carbon electrodes, the current-carrying capacity is limited by the ohmic heating, which controls the lateral heat flux and the temperature at the electrode periphery. For these electrodes, the current capacity is higher for DC than for AC. For large carbon or Søderberg electrodes, the electrode current must be limited to avoid large thermal stresses and subsequent breakages, especially in connection with shutdowns or considerable current fluctuations. Thermally, the current capacity is then limited by the maximum temperature difference between the center and the periphery. For this case, AC electrodes can carry more current than DC.

Shape Adjustment and Experimental Study of a Shape Memory Cable (SMC) Structure.

Large deployable cable net antennas have attracted extensive attention worldwide because of their simple structure and high storage ratio. The cable net structure is affected by long exposure in a harsh space environment during satellite operation, resulting in large thermal deformation and stress relaxation, which leads to a degradation of antenna performance. To address the thermal deformation of the cable net structure, a shape memory cable (SMC) net structure model was proposed with surface accuracy as the research objective. Specifically, we aimed to utilize its phase transition characteristics to adjust the thermal deformation of cable net structure and improve its surface accuracy. A shape memory cable net structure model with a diameter of 2.2 m was built, and a normal temperature experiment and high- and low-temperature experiments were carried out. High- and low-temperature test refers to environmental simulation testing of shape memory cable net structures under high- and low-temperature conditions. This was done to determine whether the adjustment method for surface accuracy meets the requirements. The results showed that the shape memory alloy wire has a relatively stable ability to adjust the surface accuracy of the cable net structure at room temperature. During temperature cycling, the thermal deformation of the shape memory cable net structure is slight, and the surface accuracy is good. Compared with ordinary cable net structures, the shape memory cable net structure has improved surface accuracy by 44.4% and 45.2% at high and low temperatures, respectively. This proved the effectiveness of the method for adjusting surface accuracy. These experimental results offer guiding significance for engineering applications.

Thermal Stress Analysis of Blast Furnace Hearth with Typical Erosion Based on Thermal Fluid-Solid Coupling

The life of the hearth is the main limiting link of the campaign of a blast furnace. As the equipment for holding molten iron in the furnace, the high-temperature molten iron is in direct contact with the refractory, which makes the refractory have a larger temperature increase. If the temperature gradient inside the refractory is large, it generates large thermal stress and causes the refractory to crack. Blast furnace gas and molten iron intrude into the gap, which directly causes melting erosion and other chemical erosion with carbon bricks. It aggravates the erosion degree of the furnace and seriously affects the production life of the furnace. Therefore, the furnace often occurs with different types of severe depression erosion in the late service of the blast furnace. In this study, the calculation model of the thermal fluid-solid coupling considering the molten iron flow and the solidification of molten iron was established. This calculation model was applied to study thermal stresses in the furnace with severe erosion. Based on the calculation model, the effect of blast furnace production parameters and deadman condition on thermal stresses in the furnace with severe depression erosion were analyzed, including tapping productivity, tapping temperature, cooling intensity, and deadman geometry. The research results are of great significance for prolonging the safe production life of blast furnaces.

Evolution of temperature and damage in rock mass after heat shock

Heat shock is a feasible means to break rock mass in engineering duo to the large additional thermal stress caused by thermal expansion. This paper established a coupled thermal transfer and rock deformation model based on the energy conservation and the elastic deformation theory of rock. In the model, the failure and damage of rock are judged according to the Drucker-Prager criterion. A finite element method of COMSOL Multiphysics to study the characteristics of temperature, stress distribution and damage zone on a rock surface is proposed. Results show that the failure of rock mass occurs at the cusps of the heater first duo to stress concentration and then grows at both sides of the heater greatly.

Development of a new modified TSRST test to measure the thermal stress of asphalt supporting layer in the slab track system

The unique thermal stress environment of asphalt supporting layer (ASL) in the slab track system is critical to its service safety. The extra thermal load is responsible for causing large thermal stress in ASL. A new modified thermal stress restrained specimen test (TSRST) method was developed to measure the thermal stress development of ASL during the cooling process. The high density polyethylene (HDPE) blocks were assembled onto the asphalt mixture beam to provide extra thermal load automatically during the cooling process, the modified TSRST test were conducted on two types of asphalt mixture types comparing to the standard TSRST test. The tests results show that the extra thermal load accelerates the development of thermal stress in asphalt concrete and elevates the fracture temperature and transition temperature. The modified TSRST test was proved to characterize the effect of the extra thermal load effectively, and the test results have good repeatability.

A Digital Control Structure for Lissajous Frequency-Modulated Mode MEMS Gyroscope

This article proposes a digital control structure for a doubly decoupled gyroscope working in the Lissajous frequency-modulated (LFM) mode based on digital phase-locked loops (PLLs), which demodulates the angular rate signal directly from the readable digital gyroscope resonance frequency, eliminating the need for specific frequency readout circuits. The resonance frequencies of the LFM gyroscope working modes contain a mode mismatch frequency modulated by input angular rate, respectively, which are tracked by two digital PLLs followed by subsequent digital demodulation and filtering. A linearized model of the digital PLL is built to analyze noise and control characteristics for different PI parameters. The impact of different amplitude–phase extraction architectures on the extracted phase signal is also addressed in this article. Contrast experiments are carried out using the same gyroscope with large internal thermal stress due to the silicon-glass bonding process and no stress relief structure around the sensing element, working in the traditional amplitude-modulated (AM) mode and the LFM mode. Overall, the LFM working mode maintains its low-temperature sensitivity and high stability in spite of the large internal thermal stress in the gyroscope compared to AM working modes. The maximum scale factor variation over the temperature range from 10 °C to 50 °C is 1000 ppm for the LFM mode compared to 51 900 ppm for the AM closed mode. The maximum zero rate output drift over the same temperature range is 0.1248 °/s for the LFM mode and 10.7139 °/s for the AM closed mode. The scale factor nonlinearity is 329 ppm with an angular rate input range of ±50 °/s for the LFM mode compared to 1902 ppm for the AM closed mode. The LFM mode zero-bias fluctuation for ten days is less than 0.12 °/s. The angle random walk (ARW) and the bias instability (BI) of the LFM gyroscope are 0.316 °/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd \text{h}$ </tex-math></inline-formula> and 2 °/h, respectively.

Laser additive manufacturing of ductile Fe-based bulk metallic glass composite

• Fe-based BMGCs with high strength and record-breaking ductility was fabricated via LAM technique. • An appropriate amount of stainless steel can effectively ductile the Fe-based BMG without seriously sacrificing strength. • Dual-phase structure was achieved by simply transporting the second phase into laser molten pool in the form of powder during LAM process. Laser additive manufacturing (LAM) is a promising technology for processing bulk metallic glass (BMG) with freeform geometries or unlimited size. However, the inherently brittle Fe-based BMGs produced by LAM have always been plagued by the micro-cracking induced by the large thermal stresses during the LAM process. To solve this dilemma, 316L stainless steel (SS) with excellent toughness and similar elemental composition was carefully selected as the second phase to form Fe-based BMG composites (BMGCs). The obtained Fe-based BMGCs are equipped with a heterogeneous structure, i.e., the 316L SS phase is wrapped by the metallic glass and forms a unique "fishbone" structure with a micron - scale. Excitedly, the special structure nicely improves a plastic strain of the Fe-based BMGC with a strength of 2355 MPa to ∼17%, achieving a record-breaking achievement among Fe-based amorphous with critical dimensions over 1mm.

Preliminary studies on detonation sprayed W/W-steel composite coating materials on steel substrates for the first wall of blanket

The mismatch of the thermo-mechanical properties of tungsten and steel would lead to large thermal stress between detonation sprayed (DS) tungsten coatings and steel substrates. DS W-steel composite coatings were prepared on 316 L stainless steel (SS) substrates as the interlayer of DS-W coatings to solve this issue. The DS-W coatings manufactured on 316 L SS substrates without interlayers were used for comparing. The surface and cross-section morphologies showed the composite coating material was dense steel lamellas-stacked structure in which tungsten particles dispersed homogeneously. The EDS and XRD results showed the composite coating was consisted of three different textures: W, SS and W-SS compound alloy. But the tungsten content in the coating was lower than the expected 50 vol% due to the low deposition efficiency of the tungsten powders. The Vickers hardness of the composite coating was 577– 647 HV which was between that of the DS-W and the SS substrate. The bonding strengths of the DS W/W-SS/SS substrate three-layer coating samples and the DS-W/SS substrate coating samples were about 61.33 MPa and 52.45 MPa, respectively. Besides, the three-layer samples had better performance under the transient heat shock tests than that of the DS-W/SS substrate samples. All these results proved the addition of the DS W-SS composite interlayers improved the overall properties of the DS-W/SS substrate system. The relatively low tungsten content in the composite coatings should be optimized to further improve the performance of the three-layer coating system in the following.

Effects of gear structural parameters on unsteady-state temperature field of large transmission ratio gear and tooth root thermal stress

A calculation method of tooth root stress for large transmission ratio gear and rack is proposed using a broken-line section model and thermal-mechanical coupling analysis. To describe the transient meshing dynamics between the gear and the rack, a contact deformation model between the gear and the rack is fitted by using the least square method, and the meshing temperature field is calculated using the Blok flash temperature theory. The method of the broken-line section is modified based on the fatigue crack growth path at the tooth root. A new broken-line section model to calculate the tooth root stress is established, and a stress permeability factor is introduced to identify the width of the broken line. Using the meshing temperature field of gear and rack, the calculation formulas of root bending stress and root compression stress are derived by the integral-iterative method under thermal-mechanical coupling, and the correctness of the maximum tooth root stress model is validated by the finite element method (FEM). Compared with other methods for analyzing the thermal strength of gear roots, the proposed novel broken-line section method has simpler calculations and higher accuracy, and it can systematically analyze the effect of structural parameters on the dynamic strength of gear transmission mechanisms under actual working conditions.