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作者： barreira, Eduardo M. Negrão, Cezar O.R. Hermes, Christian J.L. Thermal Science Laboratory Postgraduate Program of Mechanical and Materials Engineering Federal University of Technology - Paraná Av. Sete de Setembro 3165 80230-901 Curitiba PR Brazil Center for Applied Thermodynamics Department of Mechanical Engineering Federal University of Paraná P.O. Box 19011 81531-990 Curitiba PR Brazil

A simulation-based optimization methodology for designing unitary residential air conditioners with focus on both energy performance enhancement and cost savings is presented. A steady-state system simulation model was put forward for a 2.5-ton nominal cooling capacity split-type air conditioning unit operating with R-410A as the working fluid. The model predictions for cooling capacity, sensible heat ratio (SHR) and coefficient of performance (COP) were compared with experimental data, when it was found that the model is able to predict the experimental trends within a ±6% error band. The model was then used to find out the condenser and evaporator geometries (face area, heat transfer area) that enhance the system COP for a fixed cost. On one hand, it was observed that the COP can be increased by 7% if the cost is held fixed. On the other hand, cost savings of 33% were achieved when the system COP was held constant. © 2012 Elsevier Ltd. All rights reserved.

关键词： Air conditioning

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Development and validation of a strain-rate and temperature dependent crushing model for expanded polystyrene foam applied in bicycle helmets 17

Development and validation of a strain-rate and temperature ...

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17th European Conference on Composite materials, ECCM 2016

作者： Krundaeva, A.N. De bruyne, G. Van Paepegem, W. Department of Materials Science and Engineering Faculty of Engineering and Architecture Ghent University Technologiepark 903 Zwijnaarde GentB-9052 Belgium SIM M3 Program Technologiepark 935 Zwijnaarde GentB-9052 Belgium Lazer Sport Lamorinierestraat 37 Antwerpen2018 Belgium Product Development Faculty of Design Sciences University of Antwerp Ambtmanstraat 1 Antwerp2000 Belgium

ISBN: (纸本)9783000533877

This research is aimed at developing a strain-rate and temperature dependent crushing model for expanded polystyrene foam (EPS). EPS is a closed cell foam that is mainly used in applications where energy absorption is critical such as in bicycle helmets. It has good mechanical properties and offers at the same time a reduction on material costs and weight. The main purpose of this work is to study the dynamic properties of EPS foams by deriving stress-strain curves at different strain rates and temperatures. Further objective is to study the compressive loading of EPS foam in bicycle helmets by finite element (FE) simulation and to create a model to simulate the behavior of the EPS foam. Finally, it is also aimed to establish a comparison of the FE analysis in LS-DYNA with the dynamic compression test results. The stress-strain curves for different strain rate and for different temperatures are the output of this experimental test program. During compression, no internal damage was observed in CT-scans. This result allowed the creation of a uniform foam model. The methodology in this research allows developing more accurate FE models for bicycle helmets that can be used during a design process. © 2016, European Conference on Composite materials, ECCM. All rights reserved.

关键词： Strain rate

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Lanthanum Manganite and Cobaltite-based Composite Cathodes for SOFCs

Lanthanum Manganite and Cobaltite-based Composite Cathodes f...

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2012 International Conference on Power and Energy Systems(ICPES 2012)

作者： Daniel A.Macedo Moisés R.Cesário beatriz Cela Carlos A.Paskocimas Dulce M.A.Melo Rubens M.Nascimento Antonio.E.Martinelli Materials Science and Engineering Postgraduate Program UFRN 59072-97 Natal/RN Brazil Chemistry Postgraduate Program UFRN 59072-970 Natal/RN Brazil Forschungszentrum Jülich GmbH Central Department of Technology (ZAT) Jülich Germany

The development of novel high-performance cathodes is essential to reduce Solid Oxide Fuel Cell (SOFCs) operation to low and intermediate temperatures. To that end, the performance of CeO 2 -based composite cathodes is very attractive. In the present work, LSM (La0.8 Sr0.2 MnO3 ), LSCF (La0.5Sr0.5Co0.8Fe0.2O3 ) and SDC (Ce0.8Sm0.2O1.9 ) powders were synthesized by different synthesis methods and used to prepare SOFC composite film cathodes. LSM-SDC and LSCF-SDC composite powders were obtained by milling. Composite films were deposited onto yttria stabilized zirconia (YSZ) electrolytes and characterized by scanning electron microscopy. Preliminary performance tests were carried out using a single cell having a LSCF-SDC cathode. I-V curves indicated that the cell had qualitatively good performance with maximum power density of 19 mW/cm 2 at 800℃. The preparation of LSM and LSCF composites by mixing SDC, synthesized by the method proposed herein is an innovative alternative for the production of high performance ceramic materials for SOFC cathodes.

关键词： Modified Pechini Method, Microwave-assisted Combustion, Composite materials, SOFC cathodes.

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Alkali-Aggregate Reaction and its Mineral Reactive Phases Contribution to the Microstructural Consolidation of Portland Cement and Geopolymeric Mortars with Metakaolin-based Precursors

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SSRN 2023年

作者： Valenga, Matheus Villian de Lima, Rubia Catarina Przybysz Pereira, Elias Pereira, Eduardo Farias, Marcelo Miranda Pianaro, Sidnei Antonio State University of Ponta Grossa Postgraduate Program in Engineering and Materials Science Carlos Cavalcanti Avenue 4748 Uvaranas Paraná Ponta GrossaCEP: 84030-900 Brazil

HIGHLIGHTS Metakaolin-based geopolymeric mortars are not negatively affected by *** aggregates contribute to geopolymer matrix consolidation and *** cement partial replacement by metakaolin reduces AAR effects in *** ... 详细信息

关键词： Mortar

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Patterning Colloidal Films via Evaporative Lithography

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Physical Review Letters 2007年第14期98卷 148301-148301页

作者： Daniel J. Harris Hua Hu Jacinta C. Conrad Jennifer A. Lewis Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory University of Illinois at Urbana-Champaign Urbana Illinois 61801 USA Corporate Engineering Technical Lab The Procter and Gamble Company West Chester Ohio 45069 USA INEST Group Postgraduate Program Philip Morris USA Richmond Virginia 23234 USA

We investigate evaporative lithography as a route for patterning colloidal films. Films are dried beneath a mask that induces periodic variations between regions of free and hindered evaporation. Direct imaging reveals that particles segregate laterally within the film, as fluid and entrained particles migrate towards regions of higher evaporative flux. The films exhibit remarkable pattern formation that can be regulated by tuning the initial suspension composition, separation distance between the mask and underlying film, and mask geometry.

关键词： Liquid films

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bio-inspired impact-resistant composites

Bio-inspired impact-resistant composites

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作者： Grunenfelder, L.K. Suksangpanya, N. Salinas, C. Milliron, G. Yaraghi, N. Herrera, S. Evans-Lutterodt, K. Nutt, S.R. Zavattieri, P. Kisailus, D. Department of Chemical and Environmental Engineering Bourns Hall B357 University of California Riverside Riverside CA 92521 United States School of Civil Engineering Purdue University West Lafayette IN 47907 United States Materials Science and Engineering Program University of California Riverside Riverside CA 92521 United States National Synchrotron Light Source Brookhaven National Laboratory Upton NY 11973 United States Department of Chemical Engineering and Materials Science University of Southern California Los Angeles CA 90089 United States

Through evolutionary processes, biological composites have been optimized to fulfil specific functions. This optimization is exemplified in the mineralized dactyl club of the smashing predator stomatopod (specifically, Odontodactylus scyllarus). This crustacean's club has been designed to withstand the thousands of high-velocity blows that it delivers to its prey. The endocuticle of this multiregional structure is characterized by a helicoidal arrangement of mineralized fiber layers, an architecture which results in impact resistance and energy absorbance. Here, we apply the helicoidal design strategy observed in the stomatopod club to the fabrication of high-performance carbon fiber-epoxy composites. Through experimental and computational methods, a helicoidal architecture is shown to reduce through-thickness damage propagation in a composite panel during an impact event and result in an increase in toughness. These findings have implications in the design of composite parts for aerospace, automotive and armor applications. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： biomimetics

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The effect of voids on transverse cracking in composite laminates as revealed by combined computational analysis at the micro- and meso-levels 21

The effect of voids on transverse cracking in composite lami...

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21st International Conference on Composite materials, ICCM 2017

作者： Mehdikhani, Mahoor Petrov, Nikolay Melro, António R. Lomov, Stepan V. Gorbatikh, Larissa KU Leuven Department of Materials Engineering Kasteelpark Arenberg 44 Leuven3001 Belgium SIM M3 program Technologiepark 935 ZwijnaardeB-9052 Belgium Center for Design Manufacturing and Materials Skolkovo Institute of Science and Technology Skolkovo Innovation Center Nobel St. 3 Moscow143026 Russia University of Bristol Bristol United Kingdom

An extensive amount of experimental research on voids and their effects on mechanical properties of composite materials has been performed over the years. However, fewer studies have tried to investigate these effects through computational modeling. The scale issue is one of the reasons. Intra-laminar voids are defects that have microscopic features and interact with other micro-heterogeneities like fibers, and at the same time they influence the behavior of composites at the ply and laminate levels (referred here as the meso-level). Prediction of their effects on statistically-controlled properties, such as transverse cracking, requires a multiscale modeling approach. In the present study, a methodology is proposed, in which the micro-scale effect of voids on transverse strength of fiber-reinforced composites is evaluated through computational micromechanics. The results are then transferred to a ply-level model as input parameters to investigate the influence of voids on transverse cracking of a cross-ply composite laminate. Through this methodology, the influence of void size on the evolution of crack density in function of the applied strain can be modeled in a macro-level specimen at a manageable computational cost. The results show strong influence of voids on transverse cracking. They also reveal that the developed two-level methodology is a promising technique to evaluate this influence. © 2017 International Committee on Composite materials. All rights reserved.

关键词： EXtended finite element method (XFEM) Multiscale modeling Transverse cracking Voids

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Facile Synthesis, Structure and battery-Type behavior of Graphene Oxides

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SSRN 2023年

作者： Silva, Jullyani M.D. Fenandes, Filipe P.M. Silva, Mariana de O. Maraschin, Thuany G. Ferreira, Luciena S. Macedo, Daniel A. da Silva, Lucineide b. Fim, Fabiana de C. Materials Science and Engineering Postgraduate Program UFPB João Pessoa58051-900 Brazil Department of Materials Engineering UFPB Paraíba João Pessoa58051-900 Brazil RS Porto Alegre90619-900 Brazil

Graphene oxide (GO) is one of the main precursors for the production of graphene and other graphene-based materials. In this work, we report a simple, safe and fast synthesis method for obtaining graphene oxide as a functional material for battery-type electrodes. The method provides to obtain an aqueous solution of graphene oxide suitable for drying by freeze-drying (sample GO1). Washing and freeze-drying processes are performed to assess their effects on the exfoliation and removal of functional groups from the graphene sheets (sample GO2). GO1 sample consists of a stack of 10 oxidized graphene layers without any additional exfoliation process, while the GO2 sample has 8 stacked layers, after two washing and freeze-drying processes. FTIR results indicate that bulkier groups such as carboxylic acid are most likely to be found on the edges and surfaces of the graphene sheets of both samples. The presence of point defects such as vacancies was also observed in both samples, with the GO2 sample having a higher content of vacancies. The electrochemical performance of graphene oxide-based electrodes, classified as battery-type, indicate an improved specific capacity of 10.15 C g-1 for GO1 against 4.55 C g-1 for GO2 at a specific current of 0.5 A g-1. This superior battery-type behavior of the GO1 electrode, also confirmed by electrochemical impedance spectroscopy, is most likely due to a higher degree of oxygenated groups on its surface, as shown by EDS and FTIR studies. © 2023, The Authors. All rights reserved.

关键词： Washing

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Effects of deposition and synthesis parameters on size, density, structure, and field emission properties of Pd-catalyzed carbon nanotubes synthesized by thermal chemical vapor deposition

Journal of Vacuum Science & Technology B: Microelectronics a...

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Journal of Vacuum science & Technology b: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena 2005年第2期23卷 793-799页

作者： S. Wei W. P. Kang W. H. Hofmeister J. L. Davidson Y. M. Wong J. H. Huang Interdisciplinary Program in Materials Science Vanderbilt University Nashville Tennessee 37235 USA Department of Electrical and Computer Engineering Vanderbilt University Box 1661-B Vu Station B Nashville Tennessee 37235 USA Department of Chemical Engineering Vanderbilt University Nashville Tennessee 37235 USA Department of Materials Science and Engineering National Tsing Hua University Hsinchu 300 Taiwan Republic of China

The effects of deposition parameters and NH3 pretreatment on the size and distribution of Pd catalytic particles and subsequently their effects on the characteristics of the synthesized carbon nanotubes (CNTs) were systematically investigated. It was found that the size of Pd particles decreases and the particle density (total number of Pd particles per unit area) increases as the Pd film thickness decreases. Moreover, pretreatment of Pd film in NH3 gas promotes smaller Pd particles and higher particle density which is beneficial for CNT growth. The CNTs were synthesized by thermal chemical vapor deposition at 750 °C using methane (CH4) as the carbon source, and a mixture of Ar/H2 (80 vol %: 20 vol %) as a carrier gas with NH3 serving as a processing reagent. The incorporation of NH3 in CNT synthesis, per the specific pretreatment of catalytic film, has a distinct effect on the size and morphology of CNTs produced. The interrelation between processing, structure and emission behavior of CNTs produced with different synthesis conditions was examined by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and field emission measurements.

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Nanocrystalline Rare Earth-doped Gallium Nitride Phosphor Powders

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MRS Online Proceedings Library 2005年第1期866卷 184-189页

作者： Hirata, G.A. Tao, J. Chen, P. Mishra, K.C. McKittrick, J. CCMC-UNAM Ensenada B.C. Mexico Department of Mechanical and Aerospace Engineering and Materials Science and Engineering Program University of California at San Diego La Jolla USA Osram Sylvania Central Research Beverly USA

We report on the fabrication and luminescent properties of rare earth-doped gallium nitride (GaN) phosphor powders. Single phase GaN and GaN:RE3+ powders were prepared by using a novel chemical route. In this work a new method for the synthesis of high purity, single phase doped GaN powders is reported. (Ga1-xREx)N powders are obtained by dissolving metal nitrates (Ga(NO3)3, (RE(NO3)3) in deionized water and an organic fuel (hydrazine) in order to form a gallium/RE amorphous/nanocrystalline powder. The RE-oxide powders are then reacted with heated ammonia at different temperatures and processing times producing GaN:RE phosphors. X-ray diffraction analysis showed that single phase GaN powders are formed. Preliminary results show (Ga0.95Eu0.05)N powders are luminescent, with the main emission occurring at 611 nm which is due to the 5D0→7F2 transitions in Eu3+. High-purity GaN powders are obtained according to X-ray photoelectron spectroscopy (XPS) chemical analysis. Low-temperature cathodoluminescence and photoluminescence measurements indicate that the emission at λ=611 nm is originated from energy transfer from the host to the rare earth ion and to a direct excitation to the Eu3+ electronic levels. This method can be used to obtain red-luminescence GaN:Eu3+ and other rare earth (e.g. Er, Tb, Tm)-doped GaN powders to produce green and blue luminescence as well.

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