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Streng.hs and Fracture mech.nisms of Al_2O_3 Short Fiber Reinforced Al-Mg Alloy Matrix Composite at Elevated Temperatures

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Journal of Materials Science & Technology 2002年第3期18卷 257-260页

作者： Guozheng.KANGDepartment of appl.ed mech.nics and eng.neering, Southwest Jiaotong University, Cheng.u 610031, ChinaChuan YANG and Jixi ZHANGDepartment of Materials eng.neering, Southwest Jiaotong University, Cheng.u 610031, China [ Manuscript received Janu dept. of appl. mech. and eng. Southwest Jiaotong Univ. Chengdu 610031 China

Using the experimental and theoretical methods, the tensile streng.hs and fracture mech.nisms of AI2O3 short fiber reinforced AI-Mg alloy matrix composite at elevated temperatures were researched. The interfacial microstructural characteristics and the fracture surfaces of the composite at different temperatures were observed by transmission electron microscope (TEM) and by scanning electron microscope (SEM), respectively. Then, from the results of microscopic observation, the fracture mech.nisms of the composite at different temperatures are discussed. Finally, the tensile streng.hs of the composite at elevated temperatures were predicted by statistical integration average (SIA) method with the consideration of various fracture mech.nisms. It was shown that the streng.hs and fracture mech.nisms of the composite at elevated temperature (300℃) were significantly different from those at room temperature due to the variations of interfacial bonding states. The tensile streng.hs predicted by the SIA method at elevated temperatures agreed well with the experimental results.

关键词： Fracture A12O3 Al-Mg alloy Composite

Experimental Study on Non-proportional Multiaxial Strain Cyclic Characteristics and Ratcheting of U71Mn Rail Steel

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Journal of Materials Science & Technology 2002年第1期18卷 13-16页

作者： Guozheng.KANG, Qing GAO, Lixun CAI, Yafang SUN and Xianjie YANGDepartment of appl.ed mech.nics and eng.neering, Southwest Jiaotong University, Cheng.u 610031, China [ Manuscript received December 4, 2000, in revised form February 20, 2001] dept. of appl. mech. and eng. Southwest Jiaotong Univ. Chengdu 610031 China

An experimental study was carried out on the strain cyclic characteristics and ratcheting of U71Mn rail steel subjected to non-proportional multiaxial cyclic loading. The strain cyclic characteristics were researched under the strain-controlled circular load path. The ratcheting was investigated for the stress-controlled multiaxial circular, elliptical and rhombic load paths with different mean stresses, stress amplitudes and their histories. The experiment shows that U71Mn rail steel features the cyclic non-hardening/softening, and its strain cyclic characteristics depend greatly on the strain amplitude but slightly on its history. However, the ratcheting of U71Mn rail steel depends greatly not only on the values of mean stress and stress amplitude, but also on their histories. In the meantime, the shape of load path and its history also apparently influence the ratcheting. The ratcheting changes with the different loading paths.

关键词： U71 Mn steel Ratcheting Cyclic plasticity Non-proportional load

A LARGE EDDY SIMULATION TURBULENCE MODEL FOR COASTAL SEAS AND SHALLOW WATER PROBLEMS

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Journal of Hydrodynamics 2001年第4期13卷 24-27页

作者： Zhan, Jie-Min Li, Yok-Sheung dept. of appl. mech. and eng. Zhongshan Univ. Guangzhou 510275 China

In large scale motions of circulations in coastal seas and shallow-water problems, different characteristics of flow in the horizontal plane and in the vertical direction are expected. A new large eddy simulation model was proposed. There are some differences between the present method and the other LES models. The philosophy of the large eddy simulation and the directional eddy viscosity method were appl.ed in the horizontal plane and in the vertical direction, respectively. Compared with the other LES models in which there is no difference between horizontal viscosity and vertical viscosity, the proposed method is reasonable.

关键词： Computational fluid dynamics Computer simulation

EFFECT OF THE OPEN CRACK ON THE PULL-IN INSTABILITY OF AN ELECTROSTATICALLY ACTUATED MICRO-BEAM

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Acta mech.nica Solida Sinica 2012年第6期25卷 627-637页

作者： Asadollah Motallebi Mohammad Fathalilou Ghader Rezazadeh mech. eng. dept. Islamic Azad University mech. eng. dept. Urmia University

In this paper, the effects of the open crack on the static and dynamic pull-in volt- ages of an electrostatically actuated fixed-fixed and cantilever micro-beam are investigated. By presenting a mathematical modeling, the governing static and dynamic equations are solved by SSLM and Galerkin-based Reduced Order Model, respectively. Then, each single-side open crack in the micro-beam is modeled by a massless rotational spring and the cracked mode shapes and corresponding natural frequencies are calculated by considering the boundary and patching con- ditions and using transfer matrix methods. Finally, the effects of the crack dept. ratio, crack position and crack number on the pull-in voltage of the micro-beams are studied. It is shown that beside the residual stresses created in the machining process, the crack（s） can be initiated, growth and consequently change the pull-in voltage of the system by decreasing the natural frequencies. The results show that the crack position is effective beside the crack dept. ratio in decreasing the pull-in voltage. Also it is shown that in the fixed-fixed micro-beam there are several points for the crack location in which, the pull-in voltage is extremum.

关键词： MEMS open crack electrostatic pull-in instability

FREE-SURFACE WAVES AND FAR WAKES GENERATED BY A FLOATING BODY IN A VISCOUS FLUID

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Journal of Hydrodynamics 2003年第4期15卷 10-16页

作者： Lu Dong-qiang Department of mech.nical eng.neering, The University of Hong Kong, Hong Kong, China Shanghai Institute of appl.ed Mathematics and mech.nics, Shanghai University, Shanghai 200072, China dept. of mech. eng. Univ. of Hong Kong Hong Kong Hong Kong Inst. of appl. Math. and mech. Shanghai Univ. Shanghai 200072 China

The free-surface waves and the flow field due to a body moving on the surfaceof an incompressible viscous fluid of infinite dept. were studied analytically. The floating bodywas modeled as a normal point pressure on the free surface. Based on the Oseen approximation forgoverning equations and the linearity assumption for boundary conditions, the exact solutions inintegral form for the free-surface elevation, the velocities and the pressure were given. Byemploying Lighthill's two-stage scheme, the asymptotic representations in far field for largeReynolds numbers were derived explicitly. The effect of viscosity on the wave profiles was expressedby an exponential decay factor, which removes the singular behavior predicted by the potentialtheory.

关键词： free-surface waves velocity distribution floating body viscosity asymptotic representation light-hill's two-stage scheme

Effects of Plastic Deformation and Stresses on Dilatation duringthe Martensitic Transformation in a B-bearing Steel

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Journal of Materials Science & Technology 2001年第2期17卷 203-206页

作者： M. C.Somani and L.P.Karjalainen dept. of mech.nical eng.neering, University of Oulu, Oulu, Finland M. Oldenburg and M.Eriksson dept. of mech.nical eng.neering, Lulea University of Technology, Lulea, Sweden dept. of mech. eng. Univ. of Oulu Oulu Finland

To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transformation in a B-bearing steel were investigated. It was found that plastic deformation of austenite at high temperatures enhances ferrite formation significantly, and consequently, the dilatation decreases markedly even at a cooling rate of 280’C/s. The created ferritic-martensitic microstructure possesses clearly lower hardness and streng.h than the martensitic structure. Elastic stresses cause the preferred orientation in martensite to be formed so that diametric dilatation can increase by nearly 200% under axial compression.

关键词： Effects of Plastic Deformation and Stresses on Dilatation duringthe Martensitic Transformation in a B-bearing Steel

Experimental Study on Uniaxial and Multiaxial Strain CyclicCharacteristics and Ratcheting of 316L Stainless Steel

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Journal of Materials Science & Technology 2001年第2期17卷 219-223页

作者： GuoZheng.KANG, Qing GAO, Lixun CAI, Xianjie YANG and Yafang SUN Department of appl.ed mech.nics and eng.neering, Southwest Jiaotong University, Cheng.u 610031, China dept. of appl. mech. Southwest Jiaotong Univ. Chengdu 610031 China

An experimental study was carried out on the strain cyclic characteristics and ratcheting of 316L stainless steel subjected to uniaxial and multiaxial cyclic loading. The strain cyclic characteristics were researched under the strain-controlled uniaxial tension-compression and multiaxial circular paths of loading. The ratcheting tests were conducted for the stress-controlled uniaxial tensioncompression and multiaxial circular, rhombic and linear paths of loading with different mean stresses, stress amplitudes and histories. The experiment results show that 316L stainless steel features the cyclic hardening, and its strain cyclic characteristics depend on the strain amplitude and its history apparently. The ratcheting of 316L stainless steel depends greatly on the values of mean stress, stress amplitude and their histories. In the meantime, the shape of load path and its history also apparently influence the ratcheting.

关键词： Experimental Study on Uniaxial and Multiaxial Strain CyclicCharacteristics and Ratcheting of 316L Stainless Steel

A Study on Numerical Simulation of Core-Shooting Process

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Journal of Materials Science & Technology 2001年第6期17卷 625-628页

作者： Junjiao WU, Yi GUI and Wenzhen LI Department of mech.nical eng.neering, Tsinghua University, Beijing 100084, China [Manuscript received July 18, 2000, in revised form August 25, 2000] dept. of mech. eng. Tsinghua Univ. Beijing 100084 China

In order to evaluate the main factors influencing the core-shooting process and to optimize the design of core boxes, the fluid-particle (air-sand) model has been built based on the two-phase flow theory. The fluid phase, air, and the particulate phase, sand granules, have been treated as a continuum. By using this model, it is possible to simulate the flow and compaction behavior of sand particles during the core-shooting process. To benchmark the calculated results, the shooting process has been recorded with a digital high speed camera, and the inlet condition of sand particles has also been achieved by using the camera. The preliminary results have showed that the calculation is in agreement with the testing results.

关键词： A Study on Numerical Simulation of Core-Shooting Process Core Simulation

3D Stochastic Modeling of Grain Structure for Aluminum Alloy Casting

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Journal of Materials Science & Technology 2003年第5期19卷 391-394页

作者： Qingyan XU, Weiming Feng.and Baicheng.LIUDepartment of mech.nical eng.neering, Tsinghua University, Beijing 100084, China dept. of mech. eng. Tsinghua Univ. Beijing 100084 China

A 3D stochastic modeling was carried out to simulate the dendritic grains during solidification of aluminum alloys, including time-dependent calculations for temperature field, solute redistribution in liquid, curvature of the dendritic tip, and growth anisotropy. The nucleation process was treated by continuous nucleation. A 3D simplified grain shape model was established to represent the equiaxed dendritic grain. Based on the Cellular Automaton method, a grain growth model was proposed to capture the neighbor cells of the nucleated cell. During growing, each grain continues to capture the nearest neighbor cells to form the final shape. When a neighbor cell was captured by other grains, the grain growth along this direction would be stopped. Three-dimensional calculations were performed to simulate the evolution of dendritic grain. In order to verify the modeling results, the predictions were compared with the observation on samples cast in the sand mold and the metal mold.

关键词： 3D stochastic modeling Nucleation Grain growth