Thermal Stress Failure Research Articles

Performance and Thermal Stress Evaluation of Full-Scale SOEC Stack Using Multi-Physics Modeling Method

A three-dimensional computational fluid dynamics (CFD) method coupled with multi-physics phenomena is developed and applied for a 10-cell full-scale SOEC stack in this study. Effects of gas flow patterns, operating temperature, and manifold configurations are simulated and analyzed for stack performance and thermal stress. It is demonstrated the hydrogen production and thermal stress obtained in cross-flow mode stack are about 8% and 36 MPa higher compared to that in other flow cases. Furthermore, it is found the temperature gradient is the predominant factor affecting the thermal stress distribution and failure probability. Lastly, a stack arrangement with 2-inlet and 1-outlet is proposed and analyzed to enhance gas distribution uniformity within the cell channels. The findings of this study hold significance as a reference for investigating the impact on the SOEC stack performance and thermal stress distribution.

A high-performance solar simulator pursuing high flux and fine uniformity: Modelling, optimization, and experiment

The high flux solar simulator is a significant experimental tool in concentrated solar power applications. For a simulator, the uniformity of its light spot is as vital as high flux, since uneven light spots may result in the thermal-stress failure of the solar receiver. However, most constructed simulators have only pursued extremely high flux but ignored uniformity, thus degrading the simulator’s overall performance. Considering that improving uniformity comes at the expense of decreasing the flux, a high-performance solar simulator must meet a reasonable compromise between high flux and fine uniformity. In this paper, a simulator whose input power reached 30 kWe was designed and optimized using an in-house Monte Carlo Ray Tracing (MCRT) model, and corresponding processes were demonstrated to provide universal guidelines. To improve the uniformity while maintaining satisfying high flux, a non-coaxial reflector with optimized parameters was implemented. Based on the design and optimization results, a realistic solar simulator was manufactured and calibrated through experimental methods. The results demonstrate that the manufactured simulator achieved an about 10% reduction in non-uniformity while reaching a peak flux of 8.6 × 106 W·m−2, meeting the design expectation for a high-performance simulator.

Degradation Behavior of High Power Semiconductor Modules by Low-Temperature Sintering Technology

This paper presents a degradation behavior of high-power semiconductor modules, i.e., IGBT, with sintered silver by power cycle test and thermal cycle test. The electrical characteristics, such as on-state voltage drop, thermal resistance and leakage current, were studied. For power cycle test, the IGBT module still has an acceptable electrical performance after the 30 K power cycles. No noticeable changes can be found in the die-attach layer, while the DBC-attach layer begins to fail after 30 K power cycles. For the thermal cycling test, the electrical characteristics of the IGBT module were only tested within the first 300 cycles because the Al2O3 DBC substrate failed first before the failure of the bonding layers. Finally, finite element methods (FEM) were used to analyze thermal and mechanical stress distribution and failure mechanism of the bonding layers.

A generalized thermal deviation factor to evaluate the comprehensive stress of tubes under non-uniform heating

The heaters working with supercritical fluids normally suffer from high temperature, high pressure and non-uniform heating, which would lead to thermal fragile and stress failure in practical engineering. However, efficient and accurate methods to predict the comprehensive stress in non-uniformly heating tubes are missing. Besides, to reduce the comprehensive stress, a criterion is required to provide optimization guidance of non-uniformly heating tubes. In present study, the thermal and mechanical performances of three typical non-uniformly heating tubes are numerically investigated using the FVM-FEM method. A generalized thermal deviation factor (GTDF) is then proposed. The results showed that the GTDF can accurately predict the ratio of comprehensive stress to yield strength and GTDF > 1 indicates the plastic deformation, which is much more convenient and efficient than the conventional structural analysis. Based on the GTDF, two methods of reducing heat flux non-uniformity and enhancing tube-inside heat transfer are proposed to reduce the comprehensive stress. The results show that the unilaterally elliptic dimpled tube reduces the maximum comprehensive stress by 30.8% compared with the smooth tube and also prevents the stress concentration in the dimple zone, which can be employed to reduce the comprehensive stress in various tubes under non-uniformly heating conditions.

Deep Learning Applied to Defect Detection in Powder Spreading Process of Magnetic Material Additive Manufacturing.

Due to its advantages of high customization and rapid production, metal laser melting manufacturing (MAM) has been widely applied in the medical industry, manufacturing, aerospace and boutique industries in recent years. However, defects during the selective laser melting (SLM) manufacturing process can result from thermal stress or hardware failure during the selective laser melting (SLM) manufacturing process. To improve the product’s quality, the use of defect detection during manufacturing is necessary. This study uses the process images recorded by powder bed fusion equipment to develop a detection method, which is based on the convolutional neural network. This uses three powder-spreading defect types: powder uneven, powder uncovered and recoater scratches. This study uses a two-stage convolutional neural network (CNN) model to finish the detection and segmentation of defects. The first stage uses the EfficientNet B7 to classify the images with/without defects, and then to locate the defects by evaluating three different instance segmentation networks in second stage. Experimental results show that the accuracy and Dice measurement of Mask-R-CNN network with ResNet 152 backbone can reach 0.9272 and 0.9438. The computational time of an image only takes approximately 0.2197 sec. The used CNN model meets the requirements of the early detected defects, regarding the SLM manufacturing process.

Heat transfer characteristics and compatibility of molten salt/ceramic porous composite phase change material

Molten salts are popular energy storage materials for medium- and high-temperature thermal energy storage. However, current methods for heat transfer enhancement do not apply due to the high corrosivity of molten salts and extreme high-temperature environment. Herein, porous silicon carbide (SiC) ceramic and solar salt are formed into a composite phase change material (PCM). The ceramic skeleton is fabricated to an open-cell structure with high porosity and a large pore configuration. The SiC ceramic is wetted by the solar salt, so that the impregnation of salt into ceramic achieves a high loading at atmospheric pressure. The result of visual inspection shows that the temperature distribution in the composite PCM is more uniform compared with pure solar salt. The maximum temperature difference is reduced from 148 ℃ to 130 ℃ and the overall phase change rate is increased by up to 42.9 %. The SiC ceramics show excellent corrosion resistance during the cycles of thermal charging and discharging as compared to copper and aluminium which are the widely used thermal promoters for low-temperature PCMs. The results obtained from reactive molecular dynamics (MD) simulation are consistent with the corrosion behaviours of SiC ceramic in solar salt from aspects of physical dissolution, chemical reaction, and thermal stress failure. The composite PCM has advantages of simple preparation, low cost, and easy maintenance, therefore it has a great potential for large-scale applications.

Study on High Temperature Resistant Packaging of Ultra High Temperature Fabry–Perot Optical Fibre Vibration Sensor

Thermal stress failure is the bottleneck that is restricting the development of ultra-high temperature sensors, and reliable packaging is crucial in their development process. In this paper, a two-step packaging structure was proposed for the high temperature resistant failure packaging challenges of the ultra-high temperature Fabry–Perot optical fibre vibration sensor. First, a high temperature resistant AlN base was selected according to thermal simulation. A reliable bond between the AlN base and the 6H-SiC vibration-sensitive element was designed, which could effectively avoid the failure of thermomechanical stress adaptation during drastic temperature change. In addition, a high temperature resistant ZrO2 support tube with a length of 20 cm, an outer diameter of 16 mm, and an inner diameter of 12 mm was designed as the optical fibre lead-out support structure by using finite element simulation and optimisation. Moreover, the influence of fastening fixtures on the sensor mode was analysed. The simulated first-order resonance frequency of the sensor was 2644.9 Hz, while the actual measurement was 2620 Hz. The difference was only 0.9%. Finally, the validity of the design was verified by experiments, and the sensor achieved reliable operation at 1200 °C.

High speed processing of NiFe2O4 spinel using a laser furnace

The Laser Furnace (LF) method has been applied to directionally solidify NiFe2O4 spinel disks from a mixture of Fe and Ni oxides in order to obtain uniform, dense targets for controlled synthesis of spinel nanoparticles via Laser Ablation. Application of a CO2 laser in Line Scan mode onto a sample with the desired stoichiometry, enabled melt processing above 1580 °C at its outer surface layer. This process was carried out inside a continuous roller furnace at a maximum volume temperature of 1000 °C. Such combination helps avoid excessive thermal stress, crack formation and catastrophic failure of these magnetic ceramic monoliths. Higher energy incubation values yield increased molten volumes and a thicker resolidified surface layer with a dense microstructure. Despite the high solidification rates imposed, NiFe2O4 spinel is the main phase obtained according to X-Ray Diffraction (XRD) and magnetization studies. LF processed samples exhibit a reduction of the coercive fields and an increase of the saturation magnetization values, evidence for soft ferromagnetism and characteristic of the magnetic behaviour associated with this spinel. This work demonstrates the convenience of the LF method for preparation of uniform, dense targets for Laser Ablation and other evaporation based techniques used in the fabrication of nanoparticles.

Inspection of thermal stress parameters of high temperature ceramics and energy absorber materials

Thermal stress of ceramics and high temperature materials have gained much attentions in the recent years due to their involving and increasing interest in highly advanced and severe applications. However, ceramic materials experience a high degree of brittleness and sensitivity to mechanical damage under thermal and mechanical loadings. This in turn promote the generation of thermal stresses of high magnitude. Catastrophic thermal stress failure of ceramic materials affects mainly on their successful implementation in high temperature and energy applications. Concept of thermal stress, its causes, consequences and ways to prevent its distressing failure should be inclusively studied and introduced. Moreover, due to the increased importance of solar radiation and its great role in solving the global energy deficiency problem, much efforts and studies should be exerted in overcoming the thermal stress generated among its components. So that, this article will handle several aspects concerning the thermal stress of high temperature ceramic materials. Besides, its causes and different ways to enhance thermal stress durability and resistance will be included. In addition, for the first time we will discuss the direct relationship between the thermal stress, thermoelectricity and solar energy absorption. Finally, inclusive studies on thermal stress of laminated and multilayer composites will be covered and investigated.

On the Role of Thermal Stresses during Hydraulic Stimulation of Geothermal Reservoirs

Massive quantities of fluid are injected into the subsurface during the creation of an engineered geothermal system (EGS) to induce shear fracture for enhanced reservoir permeability. In this numerical thermoelasticity study, we analyze the effect of cold fluid injection on the reservoir and the resulting thermal stress change on potential shear failure in the reservoir. We developed an efficient methodology for the coupled simulation of fluid flow, heat transport, and thermoelastic stress changes in a fractured reservoir. We performed a series of numerical experiments to investigate the effects of fracture and matrix permeability and fracture orientation on thermal stress changes and failure potential. Finally, we analyzed thermal stress propagation in a hypothetical reservoir for the spatial and temporal evolution of possible thermohydraulic induced shear failure. We observe a strong influence of the hydraulic reservoir properties on thermal stress propagation. Further, we find that thermal stress change can lead to induced shear failure on nonoptimally oriented fractures. Our results suggest that thermal stress changes should be taken into account in all models for long-term fluid injections in fractured reservoirs.

커튼월 스팬드럴용 진공유리의 열파손에 대한 비교실험

커튼월 스팬드럴용 진공유리의 열파손에 대한 비교실험

Initial damage induced by thermal residual stress and microscopic failure analysis of carbon-fiber reinforced composite under shear loading

In order to study the mechanical properties and the progressive failure process of composite under shear loading, a representative volume element (RVE) of fiber random distribution was established, with two dominant damage mechanisms – matrix plastic deformation and interfacial debonding – included in the simulation by the extended Drucker–Prager model and cohesive zone model, respectively. Also, a temperature-dependent RVE has been set up to analyze the influence of thermal residual stress. The simulation results clearly reveal the damage process of the composites and the interactions of different damage mechanisms. It can be concluded that the in-plane shear fracture initiates as interfacial debonding and evolves as a result of interactions between interfacial debonding and matrix plastic deformation. The progressive damage process and final failure mode of in-plane shear model which are based on constitute are very consistent with the observed result under scanning electron microscopy of V-notched rail shear test. Also, a transverse shear model was established as contrast in order to comprehensively understand the mechanical properties of composite materials under shear loading, and the progressive damage process and final failure mode of composite under transverse shear loading were researched. Thermal residual stress changes the damage initiation locations and damage evolution path and causes significant decreases in the strength and fracture strain.

Development of low-temperature performance specifications for asphalt mixtures using the bending beam rheometer

Thermal cracking due to stress at low temperature is a major factor in roadway degradation. The purpose of this study was to measure low-temperature response of asphalt mixtures from field cores, assess the practicality of using the bending beam rheometer (BBR) to test field mixtures, compare test results to observed field performance, determine whether a specification value can be obtained to evaluate low-temperature pavement performance, and determine if samples constructed in the laboratory using the same mix design reflect field performance. In this study, the BBR was used to test multiple field and laboratory asphalt mixtures. Field samples were obtained from cores located in the Salt Lake Valley in Utah. The response of field cores showed that although the same binder grade is used in the region, the resulting mixtures have significant differences in creep moduli and m-values. This indicates that binder testing alone might not be enough to control the material's creep modulus. The combination of BBR test results and field surveys indicates that both creep modulus and m-value play a significant role in low-temperature performance of asphalt pavements. Pavements with high creep moduli and low m-values are more susceptible to low-temperature thermal distress. From field observations, the field performance of each section was known; by plotting the test results of the field samples on a Black Space diagram, it can be observed that a thermal stress failure envelope might exist. However, more research will be necessary to further define a specific value for this specification.

Nuclear Power Plants Safety and Maintenance

With growing concerns about global warming, building more nuclear power plants is becoming one of the inevitable options to provide the world’s electricity. This is mainly because nuclear power is considered as the major source of “carbon-free” energy. Currently, extensive preventive maintenance, inspection, andmonitoring programs are developed to ensure safe and reliable operation of nuclear power plants. These programs involve safety analysis codes, equipment health monitoring, degradation-specific inspections, and plant lifecycle management (PLM). Although extensive effort has been invested to develop such programs, nuclear power plants continue to experience problems and therefore more accurate analysis and related researchwork still receive a great attention. This is mainly because the unresolved safety problems or lack in systems monitoring often causes significant safety-related events at nuclear power plants. Therefore, the demand for applied research work continues to grow in order tomitigate such events, increase the plant capacity factor, and gain public support for nuclear power as an alternative power source. This special issue identifies and analyzes major practical problems in nuclear energy and it contains 7 articles out of 14 articles that were initially received for publication. Even with the limited number of articles presented in this special issue, a wide range of topics are covered to present different experiences from several nuclear power plants and research institutions around the world. These topics are gathered in this issue to present the best engineering analyses, research effort, and practice with as little prejudice as possible. The issue starts by the novel method for optimization of the maintenance activities presented by A. Volkanovski and L. Cizelj in the nuclear power plant in order to improve plant safety. The authors consider different constraints on the optimization of the maintenance activities in the nuclear power plants. Three severe accident sequences of nuclear plants are discussed by G. Shao et al. to show that the natural circulation phenomenon results in heat transfer from the core to the pipes in RCS and consequently may cause the creep rupture of pipes in RCS and delay the severe accident progression. Also, S. Liu et al. were able to show that thermal stress failure caused by alternating operational loads is one of the important damage mechanisms in the nuclear power plants. Furthermore, R. K. Ur et al. discuss the impact of instrumentation and control components on the architecture of reactor protection systems. On the numerical and statistical analysis side, the article of S. U.-D. Khan et al. presents a modification to the neutron kinetics code, which originally works for the cylindrical type fuel elements, to plate type fuel nuclear reactor. Moreover, the study performed by M. El Nakla et al. has stressed the importance of the local scale observation leading to better understanding of the CHF phenomena in large pipe. They were able to predict the occurrence of critical heat flux in horizontal tubes using an extra correction factor to account for flow stratification. Finally, T. H. Woo contributed to this special issue with a paper on the nuclear power plant security. He presented dynamical assessment, which helps operator to find the dangerous situation in the site and avoid possible incidents that could be a catastrophe for theNPPs.We believe that this special issue provides interesting information on the recent progress in nuclear power research.

Online Fatigue-Monitoring Models with Consideration of Temperature Dependent Properties and Varying Heat Transfer Coefficients

Thermal stress failure caused by alternating operational loads is the one of important damage mechanisms in the nuclear power plants. To evaluate the thermal stress responses, the Green’s function approach has been generally used. In this paper, a method to consider varying heat transfer coefficients when using the Green’s function method is proposed by using artificial parameter method and superposition principle. Time dependent heat transfer coefficient has been treated by using a modified fluid temperature and a constant heat transfer coefficient. Three-dimensional temperature and stress analyses reflecting entire geometry and heat transfer properties are required to obtain accurate results. An efficient and accurate method is confirmed by comparing its result with corresponding 3D finite element analysis results for a reactor pressure vessel (RPV). From the results, it is found that the temperature dependent material properties and varying heat transfer coefficients can significantly affect the peak stresses and the proposed method can reduce computational efforts with satisfactory accuracy.

Thermal Stress Distribution in CF/EP Composite in Low Earth Orbit

Thermal cycle in low earth orbit environment has a negative influence on thermal stress distribution in carbon fiber/epoxy (CF/EP) composite. In our experiment a 3D finite element analysis method was used to analyze thermal stress distribution and failure mechanism in CF/EP composite. Thermal stress distribution was characterized using Von Mises stress, composite potential failure zone was analyzed using parabolic failure criterion, and composite micro-cracking distribution was studied using birth and death technique. Results indicated that thermal stress at different parts of the composite are different: at composite free end zone, the maximum thermal stress 179.9 MPa located at fiber surface with the longest distance between two fibers; while in composite inner zone, the maximum thermal stress is 29.5 MPa located in EP matrix with the shortest distance between two fibers. Thermal stress concentration at composite free end zone induces micro-cracking between fiber and the matrix, besides as thermal cycle increase micro-cracking progress from composite free end zone to composite inner zone, which will degrade the mechanical performance.

Improved Design of a High Density 3D Multichip Module for Class I Medical Devices

Today's powerful DSP based hearing instruments demand both high density and low cost microelectronic packaging solutions. In turn, this demand drives innovation and substantial collaboration among design and manufacturing personnel and suppliers. Conventional design and process envelopes are challenged and new problems arise. Rapid failure analysis and root cause identification are essential in this global, fast-paced development arena. Here we introduce a novel high density multichip module designed for placement onto a flexible, folded hearing aid SMD assembly and discuss the challenges faced by the design team. Delamination, electrochemical migration, and thermal stress failure mechanisms identified during design verification testing are examined, along with the techniques and tools of failure analysis and problem solutions.

Evaluation of Thermal Stress Failure of Square Type SMD in Mounting Process on Metal Base PWB.

Thermal stress failure of square type surface mount device (SMD) such as ceramic capacitor has been evaluated in surface mounting process on metal base printed wiring board (PWB). For the evaluation, a series of transient thermal stress analyses with FEM model and thermal stress failure experiments for the surface mount assembly were carried out with complementary relation. As a result, thermal stress failure probability of the capacitor is estimated by utilizing the distribution function of three-point bending strength and the maximum value of major principal stress in the vicinity of failure initiation point. Additionally, influence of deformation properties of solder and insulation layer, which is formed on the surface of the PWB, on the failure probability is also evaluated quantitatively by introducing two parameters Etg and σys. Etg is related to glass transition temperature and Young's modulus of the layer and σys indicates yield stress of the solder at ambient temperature. Consequently, the present evaluation has led us to appropriate choice of the solder and the layer in order to prevent the capacitor from the thermal stress failure in the surface mounting process of square type SMD on metal base PWB.

Thermal Stress Failure of Water-Cooled Zinc Fuming Furnace Jackets

The failure of zinc slag fuming furnace jackets is a common industrial problem that has received little attention in the literature. During service the water-cooled jackets develop cracks in the working panel that initiate on the slag face and propagate towards the water cavity. In-plant measurements revealed the presence of large thermal transients or temperature “spikes” in the panel approximately 20 cm above the tuyere line. The transients were observed during charging and tapping of the furnace and are associated with slag fall-off due to surface wave action and gas injection effects when the bath level is low. Temperatures at the panel mid-thickness were seen to rise by as much as 180°C above the steady-state level. A mathematical modelling analysis of the transient freezing phenomena has been coupled with an elastic thermal stress model. The experimental and modelling results indicate that the temperature spikes are associated with the sudden removal of patches of the frozen slag layer and molten slag coming into contact with the jacket. The temperature increases are large enough to generate compressive stresses that cause yielding of the material in the exposed area which upon cooling results in tensile stresses. It is postulated that cycling between compressive and tensile stress states leads to failure by low-cycle fatigue. Examination of the crack surfaces reveals features that support this mechanism. Résumé La rupture du chemisage des fours à scories de zinc fumants est un problème industriel commun, peu étudié jusqu'à présent. Pendant l'utilisation de chemisage refroidi par eau, on voit se développer des fissures dans les panneaux en cours de fonctionnement, e1les débutent à la surface des scories et se propagent vers les cavités remplies d'eau. Des mesures effectuées en usine révèlent la présence de transferts thermiques importants, ou pics de température, dans un panneau situé approximativement à 20 cm au-des sus de la ligne des tuyères. On a observé des états transitoires pendant le chargement et le déchargement des fours, on les a associées à des chutes de scories causées par des ondes de surface et l'injection de gaz lorsque le niveau du bain est bas. On a pu observer, à mi-épaisseur des panneaux, une augmentation de température de 180°C au-dessus du niveau de l'état stable. Une analyse de modélisation mathématique du phénomène transitoire de solidification a été couplé à un modèle de contrainte thermique élastique. Les résultats expérimentaux ainsi que ceux de la modélisation indiquent que les pics de température sont associés au retrait brutal de morceaux de scories en couches solides, mettant ainsi en contact scories en fusion et chemisage. L'augmentation de température est suffisamment importante pour être cause de contraintes de compression, à l' origine de déformations plastiques du matériau dans la surface exposée et par conséquence des contraintes de tension, lors du refroidissement. On postule que le cycle contraintes en compression, contraintes en tension, conduit à des ruptures par fatigue sous cycle lent. L'examen de surfaces fissurées montre des caractéristiques qui appuient ce mécanisme.

Thermal Stress Failure of Water-Cooled Zinc Fuming Furnace Jackets

Thermal Stress Failure of Water-Cooled Zinc Fuming Furnace Jackets