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Auswahl der wissenschaftlichen Literatur zum Thema „Transformer thermal cycling“
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Zeitschriftenartikel zum Thema "Transformer thermal cycling"
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Galipeau, James, und George Slama. „Characterization and Reliability Testing on an LTCC Transformer Operable to 250 °C“. Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2012, HITEC (01.01.2012): 000354–60. http://dx.doi.org/10.4071/hitec-2012-tha24.
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Environments prone to vibration and shocks can cause premature failure in small wire-wound transformers due to cracked cores and broken wires. These problems are only exacerbated by temperatures exceeding 200 °C where the heat causes organic compounds to age rapidly. As more electronics are used in harsh, high temperature environments, high reliability, compact transformers for use in power, filtering, and isolation applications are needed. To address this need monolithic low-temperature co-fired ceramic transformers were developed. In this work transformers were made from a low-temperature, co-fire compatible, ferrite with a Curie temperature of 350 °C. The transformers were first subjected to a 2,000 hour life test at 250 °C in which the transformer was used to charge a load capacitor once every two seconds. The inductance, resistance, core loss, and saturation flux density of the transformers were measured at various temperatures. Additional testing focused on the effect of temperature on the device's frequency profile and performance changes under thermal cycling.
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Tokarev, Mikhail. „A Double-Bed Adsorptive Heat Transformer for Upgrading Ambient Heat: Design and First Tests“. Energies 12, Nr. 21 (23.10.2019): 4037. http://dx.doi.org/10.3390/en12214037.
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A full scale lab prototype of an adsorptive heat transformer (AHT), consisting of two adsorbers, an evaporator, and a condenser, was designed and tested in subsequent cycles of heat upgrading. The composite LiCl/SiO2 was used as an adsorbent with methanol as an adsorbtive substance under boundary temperatures of TL/TM/TH = −30/20/30 °C. Preliminary experiments demonstrated the feasibility of the tested AHT in continuous heat generation, with specific power output of 520 W/kg over 1–1.5 h steady-state cycling. The formal and experimental thermal efficiency of the tested rig were found to be 0.5 and 0.44, respectively. Although the low potential heat to be upgraded was available for free from a natural source, the electric efficiency of the prototype was found to be as high as 4.4, which demonstrates the promising potential of the “heat from cold” concept. Recommendations for further improvements are also outlined and discussed in this paper.
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Gaynes, Michael, Timothy Chainer, Edward Yarmchuk, John Torok, David Edwards, David Olson und Katie Pizzolato. „Using In situ Capacitance Measurements to Monitor the Stability of Thermal Interface Materials in Complex PCB Assemblies“. International Symposium on Microelectronics 2010, Nr. 1 (01.01.2010): 000450–57. http://dx.doi.org/10.4071/isom-2010-wa3-paper4.
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A thermal solution for an array of voltage transformer modules which are cooled by a large area, common aluminum heat spreader for a high end server was evaluated using an in situ, capacitive bond line thermal measurement technique. The method measures the capacitance of a non-electrically conducting thermal interface material (TIM) between the electronic module and heat spreader to quantify the TIM bond line effective thickness during assembly and operation. The thermal resistance of the TIM has the same geometric dependence as the inverse of capacitance, therefore, the capacitive technique also provided a monitor of the thermal performance of the interface. This technique was applied to measure the bond line in real time during the assembly of the heat spreader to an array of 37 modules mounted on a printed circuit board. The results showed that the target bond lines were not achieved by application of a constant force alone on the heat spreader, and guided an improved assembly process. The mechanical motion of the TIM was monitored in situ during thermal cycling and found to fluctuate systematically from the hot to cold portions of the thermal cycle, either compressing or stretching the TIM respectively. The capacitive bond line trend showed thermal interface degradation vs. cycle count for several modules which was confirmed by disassembly and visual inspection. Areas of depleted TIM ranged as high as 25% of the module area. Several design and material changes were shown to improve the TIM stability. Power cycling tests were run in parallel to the thermal cycle tests to help relate the results to field performance. The capacitance technique enabled the development and verification of a thermal solution for a complex mechanical system early in the development cycle.
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Hisada, Shota, Mitsuhiro Matsuda, Minoru Nishida, Carlo Biffi und Ausonio Tuissi. „Microstructure and Martensitic Transformation Behavior in Thermal Cycled Equiatomic CuZr Shape Memory Alloy“. Metals 9, Nr. 5 (18.05.2019): 580. http://dx.doi.org/10.3390/met9050580.
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Equiatomic CuZr alloy undergoes a martensitic transformation from the B2 parent phase to martensitic phases (P21/m and Cm) below 150 °C. We clarified the effect of the thermal cycling on the morphology and crystallography of martensite in equiatomic CuZr alloy using a transmission electron microscopy. The 10th cycled specimens consisted of different multiple structures at the maximum temperature of differential scanning calorimetry (DSC) measurement −400 °C and 500 °C, respectively. At the maximum temperature 400 °C of DSC measurement, it is composed of the fine plate-like variants, and a lamellar eutectoid structure consisting of Cu10Zr7 and CuZr2 phases on the martensitic variant. Concerning the maximum temperature of 500 °C of DSC measurement, it is observed the martensitic structure and the lamellar structure in which the martensitic phase was completely eutectoid transformed. The formation of this lamellar eutectoid structure, due to thermal cycling leads to the shift of forward and reverse transformation peaks to low and high temperature side. In addition, new forward and reverse transformation peaks indicating a new transformation appeared by thermal cycling, and the peaks remained around −20 °C. This new martensitic transformation behavior is also discussed.
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Daróczi, Lajos, Tarek El Rasasi und Dezső L. Beke. „Effect of Partial Thermal Cycles on Non-Chemical Free Energy Contributions in Polycrystalline Cu-Al-Be Shape Memory Alloy“. Materials Science Forum 738-739 (Januar 2013): 38–45. http://dx.doi.org/10.4028/www.scientific.net/msf.738-739.38.
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Abstract. Thermoelasic martensitic transformations are controlled by the local equilibrium of chemical and non-chemical free energy contributions (D and E being the dissipative and elastic energies, respectively). The derivatives of non-chemical free energies ( ) as a function of the transformed martensite fraction (ξ) can be expressed from the experimental data obtained from the temperature-elongation, temperature-resistance, etc hysteresis loops. This method, developed in our laboratory, was used for the investigation of non complete, partial thermoelastic transformation cycles. In the first set of experiments the subsequent cycles were started below the Mf temperature and the maximum temperature was decreased gradually from a value above Af (series U). In the second (L) set the cycles were started above the Af and the minimum temperature was gradually increased from a value below Mf. In the third (UL) set the minor loops were positioned into the centre of the two phase region (i.e. the cycling was made with an increasing T temperature interval with T0.5 and <0.5, respectively. On the other hand the d() functions show a maximum at about the central point of the sub-cycles, and deviate considerably from the d() function obtained from the full cycles. This is also reflected in the dependence of the integral value of the dissipative energy, D(): its value for the partial loops is lower than the dissipative energy calculated from the full cycle for the same transformed fraction interval. An opposite tendency (i.e. higher values for the partial loops) was obtained for the integral value of the elastic energy, E. The relative values of the dissipated energies, D, (calculated from the areas of the minor loops and normalized to the area of the major loop) are not very sensitive to the details of the cycling process, i.e. they are very similar for all sets.
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Sitepu, H., Heinz Günter Brokmeier, Daniel Chateigner und J. P. Wright. „Crystallographic Phase Composition and Structural Analysis of Ti-Ni-Fe Shape Memory Alloy by Synchrotron Diffraction“. Solid State Phenomena 105 (Juli 2005): 139–44. http://dx.doi.org/10.4028/www.scientific.net/ssp.105.139.
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The preferred crystallographic orientation (i.e. texture) and the non-transformed austenite can cause serious systematic errors in the structural study of the R-phase in 50.75at.%Ti- 47.75at.%Ni-1.50at.%Fe (hereafter referred to as Ti-Ni-Fe ternary) shape memory alloy. The crystal structure refinement of R-phase synchrotron high resolution powder diffraction (SRD) data using Rietveld refinement with generalized spherical harmonic (GSH) description for preferred orientation correction showed that the sample consists of minor cubic phase and the space group was 3 P [1]. The objective of the present paper is to study the crystallographic phase composition and crystal structure refinement of SRD data of trigonal R-phase martensite and monoclinic (B19¢) martensite in Ti-Ni-Fe ternary alloy during thermal cycling using the GSH description.
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Wertz, Markus, Florian Fuchs, Hieronymus Hoelzig, Julia Maria Wertz, Gert Kloess, Sebastian Hahnel, Martin Rosentritt und Andreas Koenig. „The Influence of Surface Preparation, Chewing Simulation, and Thermal Cycling on the Phase Composition of Dental Zirconia“. Materials 14, Nr. 9 (22.04.2021): 2133. http://dx.doi.org/10.3390/ma14092133.
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The effect of dental technical tools on the phase composition and roughness of 3/4/5 yttria-stabilized tetragonal zirconia polycrystalline (3y-/4y-/5y-TZP) for application in prosthetic dentistry was investigated. Additionally, the X-ray diffraction methods of Garvie-Nicholson and Rietveld were compared in a dental restoration context. Seven plates from two manufacturers, each fabricated from commercially available zirconia (3/4/5 mol%) for application as dental restorative material, were stressed by different dental technical tools used for grinding and polishing, as well as by chewing simulation and thermocycling. All specimens were examined via laser microscopy (surface roughness) and X-ray diffraction (DIN EN ISO 13356 and the Rietveld method). As a result, the monoclinic phase fraction was halved by grinding for the 3y-TZP and transformed entirely into one of the tetragonal phases by polishing/chewing for all specimens. The tetragonal phase t is preferred for an yttria content of 3 mol% and phase t″ for 5 mol%. Mechanical stress, such as polishing or grinding, does not trigger low-temperature degradation (LTD), but it fosters a phase transformation from monoclinic to tetragonal under certain conditions. This may increase the translucency and deteriorate the mechanical properties to some extent.
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Hu, Tian Qi, Hong Tao Chen und Ming Yu Li. „Fabrication of Cu@Sn Core-Shell Structured Particles and the Application in High Remelting Temperature Bonding“. Materials Science Forum 878 (November 2016): 3–7. http://dx.doi.org/10.4028/www.scientific.net/msf.878.3.
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A novel solder bonding material for high-temperature applications based on Cu@Sn core-shell structured particles was developed, and the fabricated Cu@Sn particles were compressed into preforms for die attachment. The reflow temperature for this bonding material could reached as low as 260°C due to the low melting temperature of the outer Sn layer. However, after reflow soldering, the resulting interconnections can withstand a high temperature of at least 415°C, outer Sn layer completely transformed into Cu-Sn intermetallic compounds (IMCs) with high remelting temperatures. The formed bondlines exhibit good electrical conductivity due to the low porosity and the embedded Cu particles in the interconnections. Furthermore, the interconnections also exhibit excellent reliability under thermal shock cycling from-55°C to 200°C. This die attach material is suitable for power devices operating under high temperatures or other harsh environments.
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Ren, Y., H. Zhou, X. Wang, Q. W. Liu, X. D. Hou und G. F. Zhang. „Study of the Structure and Properties of ZnS Utilized in a Fluorescence Biosensor“. Stem Cells International 2021 (28.08.2021): 1–6. http://dx.doi.org/10.1155/2021/7067146.
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ZnS materials have been widely used in fluorescence biosensors to characterize different types of stem cells due to their excellent fluorescence effect. In this study, ZnS was prepared by vulcanizing nano-Zn particles synthesized using a DC arc plasma. The composition and structure of the ZnS materials were studied by X-ray diffraction (XRD), and their functional group information and optical properties were investigated by using IR spectrophotometry and UV-vis spectrophotometry. It has been found that the synthesized materials consist of Zn, cubic ZnS, and hexagonal ZnS according to the vulcanization parameters. Crystalline ZnS was gradually transformed from a cubic to a hexagonal structure, and the cycling properties first increase, then decrease with increasing sulfurization temperature. There is an optimal curing temperature giving the best cycling performance and specific capacity: the material sulfurized thereat mainly consists of cubic β-ZnS phase with a small quantity of Zn and hexagonal α-ZnS. The cubic phase ZnS has better conductivity than hexagonal ZnS, as evinced by electrochemical impedance spectroscopy (EIS). The ZnS (as prepared) shows board absorption, which can be used in fluorescence biosensors in cell imaging systems.
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Islam, Atikul, Ally J. Su, Zih-Ming Zeng, Pin Ju Chueh und Ming-Hung Lin. „Capsaicin Targets tNOX (ENOX2) to Inhibit G1 Cyclin/CDK Complex, as Assessed by the Cellular Thermal Shift Assay (CETSA)“. Cells 8, Nr. 10 (18.10.2019): 1275. http://dx.doi.org/10.3390/cells8101275.
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Capsaicin (8-methyl-N-vanillyl-6-noneamide), which is an active component in red chili peppers, is used as a chemopreventive agent that shows favorable cytotoxicity against cancer cells. Accumulating evidence indicates that capsaicin preferentially inhibits a tumor-associated NADH oxidase (tNOX, ENOX2) that is ubiquitously expressed in cancer but not in non-transformed cells. This attenuates cancer cell growth by inducing apoptosis. The capsaicin-mediated inhibition of tNOX was recently shown to prolong the cell cycle. However, the molecular events underlying this regulation have not yet been investigated. In the present study, we used a cellular thermal shift assay (CETSA) to detect “target engagement” of capsaicin and its consequent impact on cell cycle progression. Our results indicated that capsaicin engaged with tNOX and triggered the proteasomal degradation of tNOX, which leads to the inhibition of NAD+-dependent SIRT1 deacetylase. Ultimately, the acetylation levels of c-Myc and p53 were enhanced, which suppressed the activation of G1 cyclin/Cyclin-dependent kinase complexes and triggered cell cycle arrest in cancer cells. The results obtained when tNOX was overexpressed in non-cancer cells validated its importance in cell cycle progression. These findings provide the first molecular insights into the regulatory role of tNOX and the anti-proliferative property of capsaicin in regulating the cell cycle of bladder cancer cells.
Dissertationen zum Thema "Transformer thermal cycling"
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Luedtke, Elin. „Minimizing Transformer No-Load Losses at Hydropower Plants : A Study of Effects from Transformer Switch-Off During Stand-by Operation“. Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-447635.
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Hydropower is the most important power balancing resource in the Swedish electrical power system, regulating the power supply to match the load. Consequently, several hydropower plants have periods of stand-by operation where the power production is absent but where several devices within a plant are still active. Such a device is the step-up power transformer, which during stand-by operation still generates no-load energy losses. These losses can accumulate to a considerable amount of energy and costs during the long technical lifetime of the apparatus. One option to minimize these no-load energy losses is by turning the transformer off when its generating unit is in stand-by operation. However, when this transformer operational change has been explained to experts in the field, the most common response has been that a more frequent reenergizing of a transformer leads to higher risks for errors or transformer breakdowns. This study aimed to analytically investigate three effects from this operational change. First, the potential of fatigue failure for the windings due to the increased sequences of inrush current. Secondly, the thermal cycling as a consequence of change in present losses. Lastly, the energy and economic saving potentials for hydropower plants where this operational adjustment is applied. The study used both established as well as analytical tools explicitly created for this study. These were then applied on currently active transformers in different plant categories in Fortum’s hydropower fleet. The study primarily showed three things. Firstly, risk of fatigue failure due to the increased presence of inrush currents did not affect the transformer’s technical lifetime. Secondly, the thermal cycling changes were slightly larger with absent no-load losses during stand-by operation. The average temperature for the transformer decreased, which in general is seen as a positive indicator for a longer insulation lifetime and thus the transformer’s technical lifetime. Finally, the created frameworks showed the potential of saving energy and money for all plant categories, where the potential grew with the installed production capacity and the stand-by operation timeshare. Despite the simplifications made to describe the complex reality of a transformer operating in a hydropower plant, this thesis contributes to lay a foundation for future investigation of an easy adjustment to avoid unnecessary energy losses and costs for transformers in hydropower plants.
Konferenzberichte zum Thema "Transformer thermal cycling"
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Montazeri, Mahsa, John Harris, David R. Huitink, Adithya Venkatanarayanan und Simon S. Ang. „Thermomechanical Stress and Warpage Augmentation Using Auxetic Features in Electronic Design“. In ASME 2019 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ipack2019-6424.
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Abstract One of the leading contributors to assembly and reliability issues in electronic packaging arises from warpage and interfacial stresses stemming from coefficient of thermal expansion (CTE) mismatch of the interfacing components. Trends toward miniaturizing and increasing density of the electronic packages exacerbate the assembly problems, leading to issues such as die cracking and board level assembly yield loss. One potential solution may be found in the inclusion of auxetic structures, which demonstrate negative Poisson’s ratio through re-entrant geometries, which has been investigated for use in augmented structural mechanics for impact energy absorption. Because of the unique structural design, auxetics become thicker perpendicularly under an applied tensile load, unlike typical material loading responses. This interesting behavior has opportunity for integration into electronic packages for stress mitigation under thermal cycling since the structures can disrupt the typical expansion behavior. Here, auxetic trace geometries and structures were evaluated in various packaging implementations (die and substrate level) for warpage and stress reduction under thermal cycling conditions. By replacing standard Manhattan-style layouts and power and ground plane features with re-entrant trace geometries, reductions in thermomechanically induced interfacial stresses were observed, in addition to considering heat spreading properties within a package. Herein, deformation of silicon chip with addition of raised re-entrant Evans auxetics and raised ellipse shape auxetic traces as well as deformation of direct bonded copper (DBC) substrate with and without re-entrant auxetic patterned pads are estimated and compared using Finite Element Analysis (FEA) in ANSYS software. To demonstrate the benefits of passive auxetic traces, a planar transformer with re-entrant Evans auxetic patterns on PCB layers has been examined under full-load operating condition and compared with a traditionally patterned transformers. A better thermal distribution and lower maximum temperature in the device are achieved by including auxetic patterned features. FEA simulation results also show stress reduction in windings and lower deformation in PCB layers. Inclusion of auxetic structures in passive metal deposition layers which are not part of the circuit is shown to reduce maximum stress and warp deflection, as well as improve thermal gradient distribution and reduce overall temperature for 2D planar and 3D stacked packages. Consequently, use of auxetic features may extend package reliability significantly.
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Chen, M. W., M. L. Glynn, D. Pan, K. T. Ramesh, K. J. Hemker, R. T. Ott und T. C. Hufnagel. „Influence of Martensitic Transformation on the Durability of TBC Systems (Invited)“. In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-43203.
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Microstructural evolution of bond coat with thermal cycling was characterized with transmission electron microscopy (TEM) and high temperature X-ray diffraction (HT-XRD) analysis. Before thermal cycling, the structure of asfabricated bond coat was confirmed to be a long-range ordered B2 β-phase. After thermal cycling to ∼28% of the cyclic life, the bond coat was found to transform into a Nirich L10 martensite (M) from its original B2 structure. The transformations, M ↔ B2, were demonstrated to be reversible and to occur on heating and cooling in each cycle. Quantitative high temperature XRD measurements verified the phase transformations produce about 0.7 % transformation strain. Finite element calculations incorporating the transformation strain indicate that the mertensitic transformation significantly influences the development of stresses and strains in TBC systems.
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Ahmad, Mudasir, Weidong Xie, Kuo-Chuan Liu, Jie Xue und Dave Towne. „Parametric acceleration transforms for lead-free solder joint reliability under thermal cycling conditions“. In 2009 IEEE 59th Electronic Components and Technology Conference (ECTC 2009). IEEE, 2009. http://dx.doi.org/10.1109/ectc.2009.5074087.
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Pendyala, Swetha, Prashanth Sridharan, Sarada Kuravi, Chand K. Jotshi, Manoj K. Ram, Muhammad Rahman, Elias Stefanakos und D. Yogi Goswami. „Macroencapsulation of Sodium Nitrate for Thermal Energy Storage in Solar Thermal Power“. In ASME 2012 6th International Conference on Energy Sustainability collocated with the ASME 2012 10th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/es2012-91447.
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Storage systems based on latent heat storage have high-energy storage density, which reduces the footprint of the system and the cost. However, phase change materials (PCMs) have very low thermal conductivities making them unsuitable for large-scale use without enhancing the effective thermal conductivity. In order to address the low thermal conductivity of the PCMs, macroencapsulation of PCMs is adopted as an effective technique. The macro encapsulation not only provides a self-supporting structure but also enhances the heat transfer rate. In this research, Sodium nitrate (NaNO3), a low cost PCM, was selected for thermal storage in a temperature range of 300–500°C. The PCM was encapsulated in a metal oxide cell using self-assembly reactions, hydrolysis, and simultaneous chemical oxidation at various temperatures. The metal oxide encapsulated PCM capsule was characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The cyclic stability and thermal performance of the capsules were also studied.
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Boucly, Vincent, Daniel Ne´lias und Michel Brunet. „Thermal-Elastic-Plastic Contact Analysis for Rough Bodies With a Semi-Analytical Method“. In ASME/STLE 2007 International Joint Tribology Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ijtc2007-44067.
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Nowadays, Finite Elements softwares allow the user to model efficiently the contact between two solids. It is though necessary to make numerous assumptions in order to compute a contact in a reasonable time: generally surfaces are smooth and the mesh is too coarse to accurately study transient phenomena. Moreover, friction on the surface is rarely taken into account since models are usually axi-symmetric. This paper presents a semi-analytical formulation that allows computing the contact between two elastic-plastic solids with rough surfaces. The numerical methods used, i.e. the conjugate gradient and the fast Fourier transform allow to refine the mesh drastically. The main advantage of this formulation over Finite Elements method is the much shorter computation times. This model takes into consideration the hardening of material as well as friction and frictional heating at the interface. Loading can be vertical or rolling/sliding. This formulation allows realizing cyclic loadings in order to model numerous engineering problems as running-in, fretting, asperities tugging, as well as electro-mechanical micro-contacts. A comparison is made between the vertical contact (static loading) and the rolling/sliding contact (transient loading) in the case of an adiabatic elastic sphere rotating and pressed against a rough and stationary elastic-plastic surface. The influence of the friction coefficient is underlined.
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Sakai, Shinsuke, Kei Honda, Satoshi Okajima, Satoshi Izumi und Naoto Kasahara. „Direct Damage Evaluation Method for Thermal Fatigue Based on Power Spectrum Density Functions“. In ASME 2007 Pressure Vessels and Piping Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/pvp2007-26168.
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At an incomplete mixing area of high and low temperature fluids, fluid temperature fluctuation often occurs. It induces cyclic thermal stresses in the wall, which may result in fatigue crack initiation. Kasahara et. al. proposed the thermal fatigue evaluation method based on power spectrum density (PSD) in PVP05. This method generalizes the evaluation procedure by preparing PSD charts of fluid and frequency transfer functions of stress for various kinds of plant components. From design point of view, however, this method is too complicated due to the inverse Fourier transform and wave decomposition procedures named Rain Flow Cycle Counting (RFC). In this paper, simplified damage evaluation method for thermal fatigue is proposed by directly evaluating fatigue damage from PSD of stress. Since analytical treatment for evaluation of fatigue amplitude distribution based on PSD is difficult due to complicated procedure of RFC, direct evaluation method for RFC amplitude distribution from PSD is newly proposed. This method gives fatigue damage evaluation with safety margin. This paper shows the dependency of safety margin on geometry of PSD. Finally, application to design for thermal fatigue will be shown. Since PSD of stress in the wall near temperature fluctuation can be easily evaluated using Kasahara’s method, the proposed method will make thermal fatigue damage evaluation far easier.
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Dubsky, J., B. J. Kolman und A. Buchal. „Phase Composition Changes in Plasma Sprayed Zircon-Alumina Tubes“. In ITSC 1998, herausgegeben von Christian Coddet. ASM International, 1998. http://dx.doi.org/10.31399/asm.cp.itsc1998p1613.
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Abstract Protective tubes (Ø90x1500 mm) were manufactured by spraying with a water stabilized plasma gun. Mixtures of zircon (ZrSiO4) and alumina (Al2O3) were used as feedstock powders. Products made of these powders exhibit very good properties during thermal cycling. Previous results of the phase composition and phase changes were obtained from as-sprayed and annealed samples using X-ray diffractometry (XRD) and scanning electron microscopy. During plasma spraying zircon decomposed into ZrO2 and SiO2, which on impact and after rapid quenching formed a very fine eutectic mixture of tetragonal or monoclinic ZrO2 and amorphous SiO2. During this process alumina, in feedstock as α-phase (corundum), formed the spinel γ-phase. On annealing the y-phase transformed into the a-phase, whereas amorphous SiO2 crystallized and reacted with tetragonal ZrO2 to form ZrSiO4. Mullite (3Al2O3.2SiO2) was found at the highest annealing temperature of 1500°C when alumina reacted with SiO2. High temperature XRD was used for direct observation of phase changes during heating and cooling between room temperature and 1500°C in powdered as-sprayed deposits. This method confirmed the phase changes observed at room temperature in annealed samples, in particular the partial transformation of tetragonal to monoclinic ZrO2.
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Chen, Bicheng, und Cemal Basaran. „Continuous Wavelet Transform Based Nanoscale Strain Field Measurement Using Moire´ Interferometry With Phase Shifting“. In ASME 2009 InterPACK Conference collocated with the ASME 2009 Summer Heat Transfer Conference and the ASME 2009 3rd International Conference on Energy Sustainability. ASMEDC, 2009. http://dx.doi.org/10.1115/interpack2009-89016.
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Moire´ Interferometry (MI) provides real-time full strain field measurement for the structure under the dynamic loading. It has been successfully applied to the reliability testing of the electronic packaging under different loadings (e.g. thermal cycling, electrical current stressing and etc). The miniaturization of the microelectronic packaging calls for the operation of MI at a level with higher sensitivity and better resolution. The proposed operation of MI combines two novel methods in the interferometry, phase shifting (PS) and continuous wavelet transform (CWT) to achieve a 164 nm/pixel spatial resolution. The entire operation procedure is completed automatically by computer programs. A two-level zooming system is designed and implemented in MI to give a high spatial resolution. The idea of combination of CWT and PS here is to put both spatial phase calculation and temporal phase calculation together. By introducing both the spatial and temporal redundancy, the authors show that the hybrid methods take the advantages from both of them. Furthermore, the direct calculation of the spontaneous spatial frequency of the interferogram is carried out using the property of the maximum power ridge of CWT. This method doesn’t require unwrapping and differentiation, which avoid the possible numerical noise introduced in these two steps. In the proposed system, pixel by pixel in-plane strain tensors can be calculated from the intensity map of interferograms using phase-based method for MI in contrast with the traditional fringe counting. The resulting strain tensor can be used to model constitutive relationship or compare with finite element analysis results. A thermal experiment on BGA packaging is used to demonstrate the advantages of the proposed new design.
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Kasahara, Naoto, Nobuyuki Kimura und Hideki Kamide. „Thermal Fatigue Evaluation Method Based on Power Spectrum Density Functions Against Fluid Temperature Fluctuation“. In ASME 2005 Pressure Vessels and Piping Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/pvp2005-71307.
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Fluid temperature fluctuates at an incomplete mixing area of high and low temperature fluids in nuclear components. It induces random variations of local temperature gradients in structural walls, which lead to cyclic thermal stresses. When thermal stresses and cycle numbers are large, there are possibilities of fatigue crack initiations and propagations. It is recognized that there are attenuation factors depending on fluctuation frequency in the transfer process from fluid temperature to thermal stresses. If a frequency of fluctuation is very low, whole temperature of the wall can respond to fluid temperature, because thermal diffusivity homogenizes structural temperature. Therefore, low frequency fluctuations do not induce large thermal stress due to temperature gradients in structures. On the other hand, a wall surface cannot respond to very high frequency fluctuation, since a structure has a time constant of thermal response. High frequency fluctuations do not lead to large thermal stress. Paying attention to its attenuation mechanism, Japan Nuclear Cycle Development Institute (JNC) has proposed a fatigue evaluation method related to frequencies. The first step of this method is an evaluation of Power Spectrum Density (PSD) on fluid, from design specifications such as flow rates, diameters of pipes and materials. In the next step, the PSD of fluid is converted to PSD of thermal stress by the frequency transfer function. Finally, the PSD of thermal stress is transformed to time history of stress under an assumption of random phase. Fatigue damage factors can be evaluated from stress ranges and cycles obtained by the rain flow wave count method. Proposed method was applied to evaluate fatigue damage of piping junction model tests conducted at Oarai Engineering Center. Through comparison with direct evaluation from measurements and predictions by conventional methods, the accuracy of the proposed method was validated.
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Burra, K. G., und A. K. Gupta. „Isothermal Splitting of CO2 to CO Using Cobalt-Ferrite Redox Looping“. In ASME 2020 Power Conference collocated with the 2020 International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/power2020-16960.
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Abstract Rising atmospheric CO2 levels from significant imbalance between carbon emissions from fossil fuel utilization, especially for energy and chemicals, and natural carbon sequestration rates is known to drive-up the global temperatures and associated catastrophic climate changes, such as rising mean sea level, glacial melting, and extinction of ecosystems. Carbon capture and utilization techniques are necessary for transition from fossil fuel infrastructure to renewable energy resources to help delay the dangers of reaching to the point of positive feedback between carbon emissions and climate change which can drive terrestrial conditions to uninhabitable levels. CO2 captured from the atmosphere directly or from flue gases of a power plant can be recycled and transformed to CO and syngas for use as energy and value-added chemicals. Utilizing renewable energy resources to drive CO2 conversion to CO via thermochemical redox looping can provide a carbon negative renewable energy conversion pathway for sustainable energy production as well as value-added products. Substituted ferrites such as Co-ferrite, Mnferrite were found to be promising materials to aid the conversion of CO2 to CO at lower reduction temperatures. Furthermore, the conversion of these materials in the presence of Al2O3 provided hercynite cycling, which further lowered the reduction temperature. In this paper, Co-ferrite and Co-ferrite-alumina prepared via co-precipitation were investigated to understand their potential as oxygen carriers for CO2 conversion under isothermal redox looping. Isothermal reduction looping provided improved feasibility in redox conversion since it avoids the need for temperature swinging which improves thermal efficiency. These efforts alleviates the energy losses in heat recovery while also reducing thermal stresses on both the materials and the reactor. Lab-scale testing was carried out at 1673 K on these materials for extended periods and multiple cycles to gain insights into cyclic performance and the feasibility of sintering, which is a common issue in iron-oxide-based oxygen carriers. Cobalt doping provided with lowering of reduction temperature requirement at the cost of oxidation thermodynamic spontaneity that required increased oxidation temperature. At the concentrations examined, these opposing phenomenon made isothermal redox operation feasible by providing high CO yields comparable to oxygen carriers in the literature, which were operated at different temperatures for reduction and oxidation. Significantly high CO yields (∼ 750 μmol/g) were obtained from Co-ferrite isothermal redox looping. Co-ferrite-alumina provided lower CO yields compared to Co-ferrite. The oxygen storage was similar to those reported in the literature on isothermal H2O splitting, but with improved morphological stability at high temperature, especially compared to ferrite. This pathway of oxygen carrier development is considered suitable with further requirement in optimization for scaling of renewable CO2 conversion into valuable products.