Thermal Stress Analysis Research Articles

Perovskite Solar Cells: Challenges Facing Polymeric Hole Selective Materials in p–i–n Configuration

AbstractPolymeric hole‐selective materials (P‐HSMs) offer advantages like solution processability, tunable energy levels, and improved mechanical stability, making them suitable for large‐scale and flexible substrates. Poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA) based p–i–n perovskite solar cells exhibit promising power conversion efficiency (PCE), but wettability, dopant, and cost challenges necessitate the development of advanced next‐generation P‐HSMs. To provide a clear understanding of the structural property with photovoltaic performance, this review classifies such newly developed P‐HSMs into five distinct structural categories. Specifically, this review discusses the current status, advancements, challenges, and prospects in structural design and synthetic variations, focusing on enhancing photovoltaic performance, wettability, mitigating surface defects, and stability. Notably, incorporating polar units into P‐HSMs enhances wettability and mitigates ion instabilities and uncoordinated lead defects. Promising structural designs like polymeric self‐assembled monolayers and in situ polymerized hole‐selective materials are examined. Despite performance advancements, emerging, P‐HSMs face significant challenges such as limited thermal stress analysis (55–85 °C) and scalability restricted to small‐scale devices. To bridge this gap, this review emphasizes the urgent need for prioritizing thermal stability testing and large‐scale device fabrication in future research, paving the way for commercial viability of P‐HSMs in p–i–n perovskite photovoltaics.

Fire performance of CFRP-strengthened piloti-type columns with fire-resistant materials during standard fire exposure

This paper presents a numerical investigation into the fire endurance of carbon fiber reinforced polymer (CFRP)-strengthened columns, shielded with fire-resistant materials, in piloti-type reinforced concrete buildings. The strengthened column, equipped with a fire protection system, underwent exposure to the ASTM E119 standard time-temperature curve for a duration of 4 h. To comprehensively evaluate the thermal and structural performance of the strengthened column at elevated temperatures and substantiate the effectiveness of the fire protection system, a fully coupled thermal-stress analysis was conducted. The numerical modeling approach employed in this study was rigorously validated through previous experimental studies in conjunction with adherence to the ACI design guideline, specifically ACI 440.2R-17. Using the validated structural fire model, the thermal and structural behaviors of the RC column with an insulated CFRP strengthening system were investigated based on four key performance criteria: glass transition temperature, ignition temperature of polymer matrix, critical temperature of reinforcing bars, and the design axial load capacity at elevated temperatures. Furthermore, a comparative assessment of fire endurance was performed using diverse fire-resistant materials, including Sprayed Fire-Resistive Material (SFRM) and Sikacrete®-213 F, with insulation thicknesses ranging from 10 to 30 mm, during the 4-hour fire exposure period.

Numerical simulation and experimental analysis of thermal conduction and stress in laser cladding repair of thin-walled parts

To minimize the deformation of thin-walled parts during the laser cladding process and enhance the quality of the repaired parts, the Finite Element Abaqus software was used to develop a thermal conduction and 3D stress model, the heat source used in the experiments was a double ellipsoid heat source model. This model simulates the thermal process and the deformation resulting from residual stresses in the laser cladding process on a titanium alloy substrate with a thickness of 2 mm. Through the simulation, the temperature field of the substrate at the end of each pass was obtained, and the cladding sequence with the smallest temperature gradient during the multi-pass laser melting process was determined. By combining simulation and practice, the multilayer stacking pattern was optimized to achieve deformation control. Analog simulation experiments indicate that the optimized single-layer multi-pass laser cladding method results in less heat accumulation and thermal stress compared to the unidirectional sequential scanning method. The flatness test results show that the specimens have less deformation with the optimized multilayer stacking method. In addition, the metallographic organisation of the two cladding specimens is analysed in this paper, and the results show that the optimised specimens exhibit excellent microstructures and properties.

Adaptability analysis of flow and heat transfer multi-scale numerical method for printed circuit heat exchanger

The printed circuit heat exchanger (PCHE) is a high-efficiency and compact mini-channel heat exchanger. Due to the large number of fine channels, it is difficult to conduct the flow and heat transfer numerical simulation of the entire heat exchanger based on the actual channels, which requires a lot of computational resource and time. In this paper, a simplified multi-scale numerical method with a non-equilibrium porous media model (NOPM) is proposed to study the flow and heat transfer performance of PCHE at high temperature and pressure. The pressure field, velocity field and temperature field of NOPM and actual multi-channel model (MC) under different working conditions are compared to study the adaptability of NOPM for the PCHE. The results indicate that the NOPM can accurately predict the flow and heat transfer performance under PCHE configurations with a large number of channels. However, as the channel number decreases, the relative errors in the temperature and pressure prediction significantly increase due to the increased flow maldistribution. Similarly, the NOPM can well predict the overall temperature distribution of the PCHE solid when the channel number is numerous. This work could support accurate thermal design, and provide accurate temperature field for the thermal stress analysis of PCHE.

Failure analysis in pyrolysis furnaces: Impact of carburization and thermal cycles on tube properties

The dominant failure mechanism in radiation coil tubes in pyrolysis furnaces is the detrimental interaction between carburization and reduced material ductility. This combination results in localized deformations, significant ovalization, and cracking in the tubes. At the same time, a second critical failure mechanism emerges during emergency furnace shutdowns, characterized by brittle fractures that can generate extensive longitudinal cracks in multiple tubes. This work presents a case study on the occurrence of failures that resulted in brittle fracture rupture of several tubes in a pyrolysis furnace that accumulated 43,720 h of operation. This highlights the practical importance of monitoring and managing the integrity of coil tubes. The tube samples were analyzed using optical and scanning electron microscopy, evaluation of carburization through magnetic permeability and NACE Test TM498, identification of carbides by X-ray diffraction (XRD), and dilatometry. Additionally, thermal stress analyses were performed using the finite element method, along with tensile tests at different temperatures. It was found that the tubes of the coil that operated at lower temperatures in their operational cycle did not rupture during the emergency shutdown, unlike other coils whose tubes experienced significant failures. An important contribution from this study is the demonstration of optimized operational cycle management and thermal control are essential in preserving protective oxide layers, minimizing coke formation and the effects of carburization and creep. This can reduce shutdown frequency and maintenance costs, improving the cost-effectiveness of the cracking process.

Development of a Novel Transonic Fan Casing Making Use of Rapid Prototyping and Additive Manufacturing

Additive manufacturing (AM) presents significant cost savings and lead time reductions because of features inherent to the manufacturing process. The technology lends itself to rapid prototyping due to the streamlined workflow of quickly implementing design changes. Compared to traditional machining, AM techniques are simpler in execution for design engineers because they do not require detailed engineering drawings and they typically make use of the nominal geometry in computer models. A novel transonic fan casing assembly has been developed that makes use of AM inserts surrounding the rotor to provide an opportunity to cost-effectively change the corresponding flowpath. The rapid prototyping design philosophy developed from this work will allow for numerous experimental studies into the effects that different design parameters of casing geometries have on fan aerodynamic performance. A fan stage representative of a small turbofan engine was successfully tested with smooth-walled, additively manufactured inserts as a baseline case for future configurations. Before installing the 3D printed casing assembly, computational thermal stress analysis was performed to reduce the risk in implementation due to the demanding environment associated with the rotor. AM components and materials typically have nonlinear mechanical properties, adding to the complexity of the structural analysis. As part of the research, steady aerodynamic performance was measured over the entire relevant operating range of the fan.

Thermal-mechanical coupling characteristics of large-scale molten salt storage tanks under stable operating conditions with varying liquid levels

The large-scale molten salt storage tank is a critical component of the thermal storage system employed in concentrating solar power (CSP) plants. The storage tank is subjected to complex conditions, including high temperature, fluctuating hydrostatic pressure, and thermal stress. Therefore, it is imperative to investigate the thermal-mechanical coupling characteristics of the tank during stable operation under varying liquid levels to comprehensively understand its behavior. The study commences by establishing thermal and stress analysis models for the tank, laying the foundation for subsequent investigation. Subsequently, a comprehensive thermal-mechanical coupling model is constructed using a sequential coupling approach, enabling a more accurate representation of the system's behavior. Finally, an in-depth study is conducted to explore the thermal-mechanical coupling characteristics of storage tanks at various liquid levels. The results indicate that radiation emitted by high-temperature air, confined in the top space of the tank, induces a temperature differential of approximately 5 °C between the tank's roof and the molten salt confined within it. Furthermore, heat loss from the roof accounts for 53 % of the overall heat loss. Thermal stress analysis of each weld seam connecting the tank into an integration reveals that the inner surface experiences tensile stress, while the outer surface undergoes compressive stress, primarily influenced by radial stress. Under the influence of thermal-mechanical, the coupling effect leads to compressive stress in the form of thermal stress, resulting in a decreasing trend in stress on the inner surface of the weld seam. The radial compressive stress on the outer surface reaches approximately 140 MPa, while the tank wall is primarily subjected to circumferential forces. The temperature exerts a negligible impact on the stress of the tank wall, yet it significantly affects its deformation. The stress evaluation of hydrostatic pressure and thermodynamic coupling under different liquid levels is carried out, and the results meet the strength requirements.

Thermal Stress Analysis of Compact Heat Exchanger Produced by Additive Manufacturing

Abstract Compact heat exchangers are renowned for their high heat transfer rates and efficiency, achieved by incorporating mini and micro-channels in their core design. However, operating under conditions of high-pressure fluctuations and significant temperature differences between hot and cold streams can potentially induce fatigue failure. To the best of our knowledge, this study represents the first investigation into the thermal stresses experienced by heat exchanger samples manufactured by selective laser melting technology, focusing on circular channels. Experiments were conducted using hot water in the inner channel, while the remaining channels and the sample surface were subjected to natural convection in ambient air. Strain gauges, thermocouples, and RTDs were employed to measure strain and temperature variations over time. These data were utilized as inputs for a numerical model based on finite element method. The strain measurements were compared with those obtained from the numerical model, revealing an average difference of approximately 20%. Lastly, a thermal fatigue analysis based on the maximum equivalent stresses predicted by the numerical model is presented. The evaluation considered both S-N curves: outlined in the ASME standard and the one obtained with specimens produced through selective laser melting. In the case of circular channels manufactured through additive manufacturing evaluated in this work, thermal stresses alone are insufficient to cause component failure due to fatigue. However, significant pressure cycles superimposed on the model can reverse this situation, making the combined effect of thermal and mechanical stresses influential in determining the component's fatigue behavior.

An attention-based architecture for predicting thermal stress on turbine blade film hole surface using partial temperature data

The thermal stress of film holes is crucial for the life of turbine blades with double-wall cooling systems. Finite Element Analysis (FEA) is widely used for thermal stress analysis, which requires the entire temperature field as input. However, only partial temperature data can be measured in engineering experiments, which is insufficient for FEA. This study proposed an attention-based deep learning architecture to map partial temperature data to film hole surface thermal stress. A thermal stress dataset with 300 samples of double-wall cooling units was constructed using conjugate heat transfer and FEA simulations and the thermal stress prediction model was trained using this dataset. Compared with the simulation results, the mean relative error (MRE) of the predicted results on the test dataset is 7.43%, and the MRE of peak thermal stress is 2.16%. The impact of the model input composed of different surface groups and sampling schemes on prediction performance was analyzed, and a reference for temperature measurement arrangement that balances accuracy and cost-effectiveness was proposed. Additionally, The impact of input noise on model performance was explored and the results demonstrate that the model trained with noise demonstrated significantly enhanced resistance to noise, and the MRE was about 8%.

Temperature Field Distribution and Thermal Stress Analysis of Pumped Storage Electric Motors

Abstract With the increasingly important role of pumped storage in energy systems, new and higher requirements have been put forward for the operation, safety, and economy of pumped storage power plants. The article takes a three-phase salient pole synchronous pumped storage motor as the research object, by using ANSYS finite element analysis software, a finite element model of a three-phase synchronous generator motor was established to analyze the internal temperature field distribution and thermal stress distribution of the motor. The results show that the higher temperature region of the entire system was concentrated at the winding, followed by the stator and rotor. Therefore, when optimizing the design of the motor in the future, the first step should be to start from the winding. The analysis of the thermal stress situation of the stator shows that the thermal stress and strain were mainly distributed at the inner diameter of the stator core, which was consistent with the distribution of the temperature field at the stator. The results of this study can provide theoretical guidance for the key maintenance areas and maintenance time of pumped storage power generation motors.

Residual Stress and Warping Analysis of the Nano-Silver Pressureless Sintering Process in SiC Power Device Packaging.

Chip bonding, an essential process in power semiconductor device packaging, commonly includes welding and nano-silver sintering. Currently, most of the research on chip bonding technology focuses on the thermal stress analysis of tin-lead solder and nano-silver pressure-assisted sintering, whereas research on the thermal stress analysis of the nano-silver pressureless sintering process is more limited. In this study, the pressureless sintering process of nano-silver was studied using finite element software, with nano-silver as an interconnect material. Using the control variable method, we analyzed the influences of sintering temperature, cooling rate, solder paste thickness, and solder paste area on the residual stress and warping deformation of power devices. In addition, orthogonal experiments were designed to optimize the parameters and determine the optimal combination of the process parameters. The results showed that the maximum residual stress of the module appeared on the connection surface between the power chip and the nano-silver solder paste layer. The module warping deformation was convex warping. The residual stress of the solder layer increased with the increase in sintering temperature and cooling rate. It decreased with the increase in coating thickness. With the increase in the coating area, it showed a wave change. Each parameter influenced the stress of the solder layer in this descending order: sintering temperature, cooling rate, solder paste area, and solder paste thickness. The residual stress of the nano-silver layer was 24.83 MPa under the optimal combination of the process parameters and was reduced by 29.38% compared with the original value of 35.162 MPa.

Development of Low-Pressure Die-Cast Al-Zn-Mg-Cu Alloy Propellers Part II: Simulations for Process Optimization.

With the increasing demand for high-performance leisure boat propellers, this study explores the development of high-strength aluminum alloy propellers using the low-pressure die-casting (LPDC) process. In Part I of the study, we identified the optimal alloy compositions for Al-6Zn-2Mg-1.5Cu propellers and highlighted the challenges of hot tearing at the junction between the hub and blades. In this continuation, we developed a coupled thermal fluid stress analysis model using ProCAST software to optimize the LPDC process. By adjusting casting parameters such as the melt supply temperature, initial mold temperature, and curvature radius between the hub and blades, we minimized hot tearing and other casting defects. The results were validated through simulations and practical applications, showing significant improvements in the quality and structural integrity of the propellers. Non-destructive testing using X-ray CT confirmed the reduction in internal defects, demonstrating the effectiveness of the simulation-based approach for alloy design and process optimization.

Thermal mechanical fatigue cracking of a bladed disk in a turbo engine

After 1221 h of bench testing, linear fluorescent displays were observed on the transition arcs between the blade and the edge plate. Macroscopic and microscopic inspections revealed fatigue cracks originating from cracked grain boundaries on the surface. Metallographic examinations indicated severe oxidation of the crack flank and blunting tip. Finite element thermal stress analysis aligns with the crack distribution. The nature of the cracking is identified as thermal mechanical fatigue, and the elevated temperature gradient induced by the exhaust gas purification device is the main promoter for cracking. Comparative analysis suggests that the root cause lies in the low thermal impact resistance of the material, ultimately resulting in reduced thermal mechanical fatigue resistance. Corresponding remedial methods are proposed to enhance service life and safety.

Energy efficiency and thermal stress analysis of hexahedron and tetrahedron nanoparticles in annular fin with ternary nanofluid

Energy efficiency and thermal stress analysis of hexahedron and tetrahedron nanoparticles in annular fin with ternary nanofluid

Optimization design and performance improvement of ther-mal barrier coating (TBC) system

Thermal Barrier Coatings (TBC) technology has become one of the key technologies to improve the performance and prolong the service life of gas turbine and other high temperature equipment. In this study, the selection of materials, coating methods, the influence of environmental factors on the performance of TBC system and the thermal stress analysis and optimization strategy are discussed, improve the overall performance and stability of TBC system. TBC coatings were efficiently prepared by the use of Nikolay bonding layer and stabilized zirconia as top ceramic materials, combined with electron beam Physical vapor deposition (EB-PVD) and plasma spraying (APS) techniques. In addition, the thermal stress model was established by FEA, and the thermal stress distribution of TBC system under extreme operating conditions was analyzed in detail, to reduce thermal stress concentration and improve the thermal barrier effect of the coating. Finally, through the establishment of TBC system life prediction model and in-depth analysis of the failure mechanism, a series of preventive measures and performance improvement strategies are proposed, it provides theoretical basis and practical guidance for coating design of gas turbine and other high temperature equipment.

POD–ANN as digital twins for surge line thermal stratification

This paper describes a hybrid proper orthogonal decomposition (POD) and artificial neural network (ANN) strategy to construct digital twins of a pressurizer surge line under thermal stratification conditions. The one-way coupled conjugate heat transfer and thermal stress analysis was conducted by use of parametric modeling and the introduction of the inverse distance weighted interpolation for the grid mapping, which allows for the mapped grids to have the same number of nodes regardless of variations of surge line geometries. A snapshot-based POD was utilized to obtain truncated lower-order modes and the full-order system response was projected onto these modes with reduced state coefficients. Then the ANN was employed to establish a surrogate model between the five chosen design variables of interest and the reduced state coefficients, resulting in a surrogate-assisted digital twin for a pressurizer surge line. Prediction of fluid–structure interface temperature and thermal stress distribution was thus achieved in an in-line real-time manner for a wide range of parameter variations. We publicly share all code implementations, and we believe that our efforts open a door for the digital twining of thermo–fluid–structure interaction problems

Conceptual design of coolant circuits and thermal stress analysis for JA-DEMO divertor

Engineering design of the JA-DEMO divertor concept, i.e. double-coolant circuits of 200°C coolant (5MPa) for high heat load targets (CuCrZr-pipe) and 290°C coolant (15MPa) for high neutron load Plasma Facing Units (F82H-pipe) and cassette body (CB), has been developed. Computational fluid dynamics (CFD) calculation of the coolant distributions to targets, baffles, reflectors, dome and to CB was performed in order to determine the feasibility of the key concepts. (i) All PFU support designs for the coolant distribution to PFUs were optimized to reduce variation of the flow velocity (Vcool) at the inlet of PFUs less than 5 – 6 %. Parallel coolant circuit design for the dome and reflectors was also developed, and mass flows were adjusted by orifices and the main mass flow rate. (ii) A new cooling concept with two layers of puddles and fins at the side routes was proposed for CB. The design provided Vcool = 0.55 – 1.27 m⋅s−1 and average Vcool = 1.04 m⋅s−1 with the fin transparent ratio of 0.1. It was enough to exhaust the nuclear heat, and the design issues were identified under the coolant condition. (iii) Heat exhaust on fish-scale surface target and stress-strain of the CuCrZr pipe were investigated under assuming a DEMO divertor condition. Steady-state heat load at wet region by plasma (qtwet) was restricted below 13.5 MWm−2 to avoid W-recrystallization. In the stress-strain cycle of higher qtwet ∼15.3 MWm−2, maximum tensile σ (120 – 200 MPa) and total change in strain during the heat load cycle (Δε ∼0.25 %) were relatively small. These evaluations suggested that such high heat load cycle may not be a critical lifetime issue, but reduction in Tcool is preferable to handle ITER-like slow transients such as 15 – 20 MWm−2.

Multiscale modeling and thermal conductivity evaluation of nano-reinforced composite materials with pore defect

The performance of resin-based composite materials often exhibits diversity due to the designability of various components. Thermal conductivity, an important thermal parameter of the composite, plays a significant role in thermal-chemical reactions, thermal stress analysis, temperature conduction, etc. However, it is relatively difficult to experimentally explore the thermal conduction mechanism of hybrid composite materials, mainly due to the relatively difficult control of various components. Therefore, this paper proposes a sequentially coupled cross-scale numerical method to characterize the thermal conductivity of nano-reinforced composite materials with pores by a multiscale periodic Representative Volume Element model generated by an improved Random Sequential Absorption algorithm. Firstly, periodic temperature boundary conditions are described, and the thermal conductivity performances of nano-reinforced matrix and composite with pores are investigated based on the finite element homogenization theory. Then, the proposed modes are validated and grid sensitivity analysis is conducted, indicating that the optimal grid sizes for the RVE models are 1.9 nm for the nano-reinforced matrix and 0.14 μm for the composite with pores based on a comprehensive comparison of four pore characterization methods, respectively. Furthermore, the study explored the effect of multiple parameters including nanoparticle content, pore content, and pore shape on thermal conductivity. Numerical findings reveal that the thermal conductivity of the nanocomposite matrix exhibits a linear increase with higher particle content. Specifically, compared to 0 % particle content, the thermal conductivity rises by 141.92 % at 12 % particle content. While the composite material's transverse thermal conductivity is sensitive to porosity content, it is less influenced by pore shape. The method proposed in this paper provides an effective approach for studying the thermal conduction of nano-reinforced composite materials with pores, and the research findings also offer theoretical guidance for process engineers.

Analysis and verification of electrodynamic force, thermal stress and current sharing for CRAFT converter structure design

In the design realm of fusion power supplies, structural components play a pivotal role in ensuring the safety of fusion devices. To verify the reliability of the converter structure design at the Comprehensive Research Facility for Fusion Technology (CRAFT), meticulous analysis of the converter's dynamic impact is carefully performed based on the worst fault current (400 kA), firstly. Subsequently, the thermal stress analysis based on the maximum allowable steady-state temperature is finished, and the equivalent thermal stress, thermal deformation, maximum shear stress of a single bridge arm and the whole converter are studied. Furthermore, a simple research method involving the current-sharing characteristics of a bridge arm with multi-thyristor parallel connection is proposed using a combination of Simplorer with Q3D in ANSYS. The results show that the current-sharing characteristics are excellent. Finally, the structural design has been meticulously tailored to meet the established requirements.

Thermal Stress Analysis for Functionally Graded Plates with Modulus Gradation, Part II

BackgroundThe gradation of thermal expansion coefficient was analyzed in the earlier study. The analytical formulation derived here, which is quite different, should be validated to understand the thermal stress distribution in a laminated composite and functionally graded material. Besides this solution, a validated numerical model can also be used to optimize the material gradation of plates in terms of sustainability.ObjectiveTo validate the analytical formulation derived here, an experimental model is presented to understand the thermal stress concentration for functionally graded and laminated composite plates. A numerical model is also validated to extend to understand the effects of the number of layers, the thickness of a layer, the gradation function, the ratio of elastic moduli, and the coating.MethodsThe experimental problems in the production of the experimental models with layers of different elastic moduli are discussed here. In the experimental analysis, a three-dimensional photoelastic stress analysis of two- and four-layer composite plate was used to mechanically model the thermal expansion. The analytical solution for the thermal stress in a free plate was derived by the strain suppression method based on the principle of superposition. The numerical models were analyzed using finite element software. The step variation in the experiment was used as a reference point for a continuous or multi-layer (> 2) step variation of material coefficients in the models.ResultsThe variation of stress concentration is shown for various cases of laminated and continuous gradations of elastic modulus. The four-layer experimental model provides the difference in thermal stress distribution as a result of a layered coating. The validated analytical and numerical models provide reasonable results. An empirical formula to optimize the material gradation in terms of elastic modulus is derived.ConclusionsThe experimental model can be used to analyze thermal stress in functionally graded materials. The gradations of the material in the plate or the coating of the plates can be optimized by the validated analytical and numerical models. The empirical formula can be used to determine the elastic modulus of the coating to minimize the stress concentration.