共查询到20条相似文献,搜索用时 15 毫秒
1.
Open-celled metal foams fabricated through metal sintering offers novel mechanical, thermal and acoustic properties. Previously,
polymer foams were used as a means of absorbing acoustic energy. However, the structural applications of these foams are inherently
limited. The metal sintering approach provides a cost-effective means for the mass-production of open-cell foams from a range
of materials, including high-temperature steel alloys. The low Reynolds number fluid properties of sintered steel alloy (FeCrAlY)
foams were investigated in a previous study. The static flow resistance of the foams was modeled based on a cylinder and a
sphere arranged in a periodic lattice at general incidence to the flow, with the resulting predictions correlating well to
measurements. The application of the flow resistance in an acoustic model is the primary focus of the present study. The predictions
for the static flow resistance of the sintered foams are first used in a theoretical model to determine the characteristic
impedances, as well as the propagation constants of the foams. Subsequently, the predicted acoustic performance of the foams
is compared to experimental results. Finally, the design space for a simple acoustic absorber incorporating sintered foams
is examined, with the effects of absorber size, foam selection, and foam spacing explored.
Supported by the National Basic Research Program of China (Grant Nos. 2006CB601202, 2006CB601204), the National 111 Project
of China (Grant No. B06024), US Office of Naval Research (Grant No. N000140210117), the National Natural Science Foundation
of China (Grant Nos. 10572111, 10632060), and the National H-Tech Research and Development Program of China (Grant No. 2006AA03Z519) 相似文献
2.
KIM Tongbeum 《中国科学E辑(英文版)》2009,52(6):1688-1697
The solidification behavior of two-phase heterogeneous materials such as close-celled aluminum foams was analytically studied.
The proposed analytical model can precisely predict the location of solidification front as well as the full solidification
time for a two-phase heterogeneous material composed of aluminum melt and non-conducting air pores. Experiments using distilled
water simulating the aluminum melt to be solidified (frozen) were subsequently conducted to validate the analytical model
for two selected porosities (ɛ), ɛ=0 and 0.5. Full numerical simulations with the method of finite difference were also performed to examine the influence of
pore shape on solidification. The remarkable agreement between theory and experiment suggests that the delay of solidification
in the two-phase heterogeneous material is mainly caused by the reduction of bulk thermal conductivity due to the presence
of pores, as this is the sole mechanism accounted for by the analytical model for solidification in a porous medium.
Supported by the National Basic Research Program of China (“973” Project) (Grant Nos. 2006CB601202, 2006CB601203), the National
Natural Science Foundation of China (Grant Nos. 10572111, 10632060), the National 111 Project of China (Grant No. B06024)
and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519). 相似文献
3.
The methods of homogenization and finite elements are employed to predict the effective elastic constants and stress-strain
responses of a new type of lattice structure, the X-structure proposed by the authors in a companion paper. It is shown that
in most cases the predictions by the equivalent homogenization theory agree well with the experimental and 3-dimensional finite
element calculated results. The theoretical and numerical study supports the argument that the X-structure is superior to
the pyramid lattice structure in terms of mechanical strength.
Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB601202), the National Natural Science
Foundation of China (Grant Nos. 10632060, 10825210), the National “111” Project of China (Grant No. B06024) and the National
High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519) 相似文献
4.
The mechanical oscillatory behaviors of multiwall carbon nanotube oscillators in gaseous environment are investigated using
the molecular dynamics method. The effects of ambient gas and temperature on intertube frictional force and oscillation frequency
are analyzed. It is found that the intertube frictional force increases with the ambient gas density and temperature. Higher
gas density and higher temperature cause a more rapid decay in the oscillation amplitude and an increase of the oscillation
frequency. Compared to the vacuum environmental condition, the collision between gas atoms and the nanotube walls is a main
ingredient leading to the increase of the energy dissipation. Gas damping may be the main reason for the failure of carbon
nanotube oscillators working in gas environment. The ambient temperature also has an important effect on oscillations and
low temperature is advantageous to sustain oscillations.
Supported by the National Basic Research Program of China (“973”) (Grant No. 2006CB300404), the National Natural Science Foundation
of China (Grant Nos. 50676019, 50775017), the Jiangsu Province Natural Science Foundation (Grant Nos. BK2006510, BK2007113),
and the Research Funding for the Doctor Program from Chinese Educational Ministry (Grant No. 20050286019) 相似文献
5.
Ultralight X-type lattice sandwich structure (I): Concept,fabrication and experimental characterization 总被引:1,自引:1,他引:0
ZHANG QianCheng HAN YunJie CHEN ChangQing & LU TianJian State Key Laboratory for Mechanical Behavior of Materials School of Material Science Engineering Xi’an Jiaotong University Xi’an China MOE Key Laboratory for Strength Vibration School of Aerospace Department of Engineering Mechanics AML Tsinghua University Beijing 《中国科学E辑(英文版)》2009,52(8):2147-2154
A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure
was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal
sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form
sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated
experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the
2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under
both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear
peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same
relative density.
Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB601202), the National Natural Science
Foundation of China (Grant Nos. 10632060,10825210), the National “111” Project of China (Grant No. B06024) and the National
High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519) 相似文献
6.
WeiWei Ji Ning Cai Ying Zhao XiaoDan Zhang Jian Sun ChangChun Wei CunDa Yuan Yuan Li Yan Su ShaoZhen Xiong 《中国科学E辑(英文版)》2009,52(7):1923-1927
A new type counter electrode for dye-sensitized solar cells (DSCs) was proposed which consists of substrate, aluminum film
and platinum film. The new type counter electrode can obviously improve the photoelectric conversion efficiency of DSCs from
3.46% to 7.07% under the standard AM1.5 irradiation condition. Advantages and shortcomings of this new type counter electrode
in terms of electrical properties, optical properties and anti-corrosive properties were analyzed. As a result, some improvements
were proposed.
Supported by the Key Foundation for Fundamental Research of Tianjin Municipal Science & Technology Commission in China ( Grant
No. 06YFJZJC01700) and the National Basic Research Program of China (“973“ Project) (Grant Nos. 2006CB20260, 2006CB202603) 相似文献
7.
Pin-reinforced foam is a novel type of sandwich core materials formed by inserting pins (trusses) into a foam matrix to create
a truss-like network reinforced foam core. Upon loading, the pins deform predominantly by local stretching whilst the deformation
of foam is governed by local bending. This paper presents a theoretical study on the thermoelasticity of pin-reinforced foam
sandwich cores. To calculate the effective thermoelastic properties of pin-reinforced foam cores, the energy-based homogenization
approach is employed to develop a micromechanicsbased model, calibrated by the existing experimental data. It is found that
the stiffness of the sandwich core is mainly governed by pin reinforcements: the foam matrix contributes little to sandwich
stiffness. Compared with traditional foam cores without pin reinforcements, the changes in in-plane thermal expansion coefficients
are not vigorous as a result of pin reinforcements, while the throughthickness thermal expansion coefficient changes significantly.
It is also demonstrated that it is possible to design materials with zero or negative thermal expansion coefficients under
such a context.
Supported by the National Basic Research Program of China (Grant No. 2006CB601202), the National Natural Science Foundation
of China (Grant Nos. 10572111, 10632060), the National 111 Project of China (Grant No. B06024), the National High Technology
Research Development Program (Grant No. 2006AA03Z519), the NPU Foundation for Fundamental Research, the Open Foundation of
State Key Laboratory of Structural Analysis of Industrial Equipment (Grant No. GZ0701), and the NPU Foundation for Scientific
Innovation 相似文献
8.
With the rapid development of functional magnetic resonance imaging (fMRI) technology, the spatial resolution of fMRI data
is continuously growing. This provides us the possibility to detect the fine-scale patterns of brain activities. The established
univariate and multivariate methods to analyze fMRI data mostly focus on detecting the activation blobs without considering
the distributed fine-scale patterns within the blobs. To improve the sensitivity of the activation detection, in this paper,
multivariate statistical method and univariate statistical method are combined to discover the fine-grained activity patterns.
For one voxel in the brain, a local homogenous region is constructed. Then, time courses from the local homogenous region
are integrated with multivariate statistical method. Univariate statistical method is finally used to construct the interests
of statistic for that voxel. The approach has explicitly taken into account the structures of both activity patterns and existing
noise of local brain regions. Therefore, it could highlight the fine-scale activity patterns of the local regions. Experiments
with simulated and real fMRI data demonstrate that the proposed method dramatically increases the sensitivity of detection
of fine-scale brain activity patterns which contain the subtle information about experimental conditions.
Supported by Chair Professors of Changjiang Scholars Program and CAS Hundred Talents Program, National Program on Key Basic
Research Projects (Grant No. 2006CB705700), National High-Tech R&D Program of China (Grant No.2006AA04Z216), National Key
Technology R&D Program (Grant No. 2006BAH02A25), Joint Research Fund for Overseas Chinese Young Scholars (Grant No.30528027),
National Natural Science Foundation of China (Grant Nos.30600151, 30500131 and 60532050), and Natural Science Foundation of
Beijing (Grant Nos. 4051002 and 4071003) 相似文献
9.
The development of Hydro-Informatic Modelling System (HIMS) provides an integrated platform for hydrological simulation. To
extend the application of HIMS, an ecohydrological modeling system named ecohydrological assessment tool (EcoHAT) has been
developed. Integrating parameter-management tools, RS (remote sensing) inversion tools, module-design tools and GIS analysis
tools, the EcoHAT provides an integrated tool to simulate ecohydrological processes on regional scale, which develops a new
method on sustainable use of water. EcoHAT has been applied to several case studies, such as, the Yellow River Basin, the
acid deposition area in Guizhou province and the riparian catchment of Guanting reservoir in Beijing. Results prove that EcoHAT
can efficiently simulate and analysis the ecohydrological processes on regional scale and provide technical support to integrated
water resources management on basin scale.
Supported by the National Key Technology R&D Program in the 11th Five-year Plan of China (Grant No. 2006BAB06B07), the National
Natural Science Foundation of China (Grant No. 40671123), the National Basic Research Program of China (“973” Project) (Grant
Nos. 2005CB422207, G19990436), and the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No.
2006AA12Z145) 相似文献
10.
Micro powder injection molding (μPIM), a miniaturized variant of powder injection molding, has advantages of shape complexity,
applicability to many materials and good mechanical properties. Co-injection molding has been realized between metals and
ceramics on micro components, which become the first breakthrough within the PIM field. Combined with the prominent characteristics
of high features/cost ratio, micro powder injection molding becomes a potential technique for large scale production of intricate
and three-dimensional micro components or microstructured components in microsystems technology (MST) field.
Supported by National Basic Research Program of China (Grant No. 2004CB719802) and Hi-Tech Research and Development Program
of China (Grant No. 2006AA03Z113) 相似文献
11.
The microstructure and mechanical properties of Cu-12wt%Al alloy wires which are composed of continuous columnar crystals after dieless drawing forming at drawing speed of 1.0―1.4 mm/s and deformation temperature of 600―900℃ were analyzed, and deformation behavior of the alloy during dieless drawing forming was experimentally investigated. The results showed that in the abovemen-tioned conditions, recrystallization phenomenon was not found during dieless drawing forming. When a drawing speed of 1.0 mm/s was... 相似文献
12.
A new transient stability margin is proposed based on a new expression of dynamic security region (DSR) which is developed
from the existing expression of DSR. Applications of the DSR based transient stability margin to contingency ranking and screening
are discussed. Simulations in the 10-machine 39-bus New England system are performed to show the effectiveness of the proposed
DSR based transient stability margin.
Supported by Chinese National Basic Research Program (Grant No. 2004CB217900), the National Natural Science Foundation of
China (Grant Nos. 50525721, 50595411, 50707035) and China Postdoctoral Science Foundation (Grant No. 20060400518) 相似文献
13.
Based on the relationships between the Hvorslev envelope, the current yield surface and the reference yield surface, a new
constitutive model for overconsolidated clays is proposed. It adopts the unified hardening parameter, to which the potential
failure stress ratio and the characteristic state stress ratio are introduced. The model can describe many characteristics
of overconsolidated clays, including stress-strain relationships, strain hardening and softening, stress dilatancy, and stress
path dependency. Compared with the Cam-clay model, the model only requires one additional soil parameter which is the slope
of the Hvorslev envelope. Comparisons with data from triaxial drained compression tests for Fujinomori clay show that the
proposed model can rationally describe overconsolidated properties. In addition, the model is also used to predict the stress-strain
relationship in the isotropic consolidation condition and the stress paths in the undrained triaxial compression tests.
Supported by the National Natural Science Foundation of China (Grant Nos. 50479001 and 10672010), the National Science and
Technology Supporting Item (Grant No. 2006BAK12B12), and the National Basic Research Program of China (Grant No. 2007CB714203) 相似文献
14.
ZiLi Xie Rong Zhang RuoLian Jiang Bin Liu HaiMei Gong XiangQian Xiu Peng Chen Hai Lu Ping Han Yi Shi YouDou Zheng 《中国科学E辑(英文版)》2009,52(2):332-335
AlN/Al0.3Ga0.7N superlattices were grown on (0001) sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The superlattice
period varies from 6 to 30. The layer thickness of different period stack was designed. GaN or AlGaN template was employed
for growing AlN/AlGaN superlattices. Reflectivity, SEM, AFM and XRD data of the Al
x
Ga1-x
N/AlN superlattices are presented. It is found that the templates used have an intensive impact on surface roughness and interfacial
properties of following AlN/AlGaN superlattices. The result of atomic force microscopy indicates that AlN/AlGaN superlattices
grown on GaN template exhibit quasi-two-dimensional growth mode. The resulting superlattice has a smooth surface morphology
and distinct interface. No crack is observed in the area of a 2-inch wafer.
Supported by the Special Funds for Major State Basic Research Project (973 Project) (Grant No. 2006CB6049), the Hi-tech Research
Project (Grant Nos. 2006AA03A103, 2006AA03A118, and 2006AA03A142), the National Natural Science Foundation of China (Grant
No. 60676057), and the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050284004) 相似文献
15.
Molecular dynamics (MD) simulations were performed to do the test of sin-gle-walled carbon nanotubes (SWCNT) under tensile loading with the use of Bren-ner potential to describe the interactions of atoms in SWCNTs. The Young’s modulus and tensile strength for SWCNTs were calculated and the values found are 4.2 TPa and 1.40―1.77 TPa, respectively. During the simulation, it was found that if the SWCNTs are unloaded prior to the maximum stress, the stress-strain curve for unloading process overlaps with the loading one, showing that the SWCNT’s de-formation up to its fracture point is completely elastic. The MD simulation also demonstrates the fracture process for several types of SWCNT and the breaking mechanisms for SWCNTs were analyzed based on the energy and structure be-havior. 相似文献
16.
Research on cohesive sediment erosion by flow: An overview 总被引:1,自引:0,他引:1
YongHui Zhu JinYou Lu HongZhi Liao JiaSheng Wang BeiLin Fan ShiMing Yao 《中国科学E辑(英文版)》2008,51(11):2001-2012
Erosion of cohesive sediment by flow is a very complicated phenomenon occurring worldwide. Understanding and modeling of the
erosion process are important for many issues such as the breaching of embankments, riverbank stability, siltation of harbors
and navigation channels, service life of reservoirs, distribution of (heavy metal) pollutants and water quality problems.
In the last few decades, numerous studies have been done on the erosion of cohesive sediment by flow. Nevertheless, the factors
affecting the erosion resistance of cohesive sediment are still not fully understood and the knowledge of the physics of cohesive
sediment erosion is inadequate, as a result the mathematical modeling of this erosion is far from satisfactory. In this paper
an overview of the studies on the erosion resistance, erosion threshold and the erosion rate of cohesive sediment by flow
is presented. The outcomes achieved so far from the studies and the existing problems have been analyzed and summarized, based
on which recommendations are proposed for future research.
Supported by the National Key Technology R&D Program of China (Grant Nos. 2006BAC14B02 and 2006BAB05B03) and the National
Basic Research Program (973 Program) of China (Grant No. 2007CB714106) 相似文献
17.
The understanding of hydrological cycle is the core of hydrology and the scientific base of water resources management. Meanwhile,
simulation of hydrological cycle has long been regarded as an important tool for the assessment, utilization and protection
of water resources. In this paper, a new tool named Hydro-Informatic Modelling System (HIMS) has been developed and introduced
with case studies in the Yellow River Basin in China and 331 catchments in Australia. The case studies showed that HIMS can
be employed as an integrated platform for hydrological simulation in different regions. HIMS is a modular based framework
of hydrological model designed for different utilization such as flood forecasting, water resources planning and evaluating
hydrological impacts of climate change and human activities. The unique of HIMS is its flexibility in providing alternative
modules in the simulation of hydrological cycle, which successfully overcome the difficulties in the availability of input
data, the uncertainty of parameters, and the difference of rainfall-runoff processes. The modular based structure of HIMS
makes it possible for developing new hydrological models by the users.
Supported by the National Natural Science Foundation of China (Grant No. 40671031), National Key Basic Research Development
Program of China (Grant Nos. G1999043601 and 2006CB403407) and National Key Technology R&D Program (Grant No. 2006BAB06N07) 相似文献
18.
Numerical modeling of concrete hydraulic fracturing with extended finite element method 总被引:2,自引:0,他引:2
The extended finite element method (XFEM) is a new numerical method for modeling discontinuity. Research about numerical modeling for concrete hydraulic fracturing by XFEM is explored. By building the virtual work principle of the fracture problem considering water pressure on the crack surface, the governing equations of XFEM for hydraulic fracture modeling are derived. Implementation of the XFEM for hydraulic fracturing is presented. Finally, the method is verified by two examples and the advan- tages of ... 相似文献
19.
Several imidazole phosphate ionic liquids with varying carbon chain length have been synthesized at room temperature. Corrosion
characteristics and tribological properties of these synthesized ionic liquids were studied using four-ball friction and wear
testing machine. Its lubrication mechanism was also investigated by means of electron microscopy and X-ray photoelectron spectroscopy.
The experimental results showed that no corrosion was generated when the imidazole phosphate ionic liquid was applied to steel-steel
pair. Meanwhile, the imidazole phosphate showed excellent anti-wear and lubricating performances, its frictional performance
was related to the polarity of ionic liquids. It is suggested that the ionic liquids react with friction surface to form a
protective film of iron phosphate and result in reduction in friction and wear.
Supported by the National Natural Science Foundation of China (Grant Nos. 50721062 and 20533080) and the National Basic Research
Program of China (973 Program) (Grant No. 2007CB607606) 相似文献
20.
Flexible, large area electronics using various organic and inorganic materials are beginning to show great promise. During
manufacture and service, large deformation of these hybrid materials will pose significant challenges in terms of high performance
and reliability. A deep understanding of the ductility or flexibility of macroelectronics becomes one of the major issues
that must be addressed urgently. This paper describes the current level of understanding on the thin-film ductility, both
free-standing and substrate-supported, and relevant influencing factors.
Supported by the National Basic Research Program of China (Grant No. 2004CB619303), the 111 Project of China (Grant No. B06025),
and the Science and Technology Key Project from Ministry of Education of China (Grant Nos. 02182, 03182) 相似文献