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Characterization of Phases in an As-cast Copper-Manganese-Aluminum Alloy

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Journal of Materials Science & Technology 2006年第6期22卷 779-784页

作者： J.Iqbal f.Hasan f.Ahmad Department of Metallurgical and Materials Engineering University of Engineering and TechnologyLahorePakistan

Copper-manganese-aluminum （CMA） alloys, containing small additions of fe, Ni, and Si, exhibit good strength and remarkable corrosion resistance against sea water. The alloys are used in as-cast condition, and their microstructure can show wide variations. The morphology, crystallography and composition of the phases presented in an as-cast （CMA） alloy of nominal composition Cu-14%Mn-8%Al-3%fe-2%Ni were investigated using optical, electron optical, and microprobe analytical techniques. The as-cast microstructure consisted of the grains of fcc α and bcc β-phases alongwith intermetallic precipitates of various morphologies. The room temperature microstructure exhibited four different types of precipitates inside the α-grains： the ＇large＇ dendritic-shaped particles and the cuboid-shaped precipitates, which were rich in fe and Mn and had an fcc structure, while the ＇small＇ dendritic-shaped particles and the globular precipitates were based on feaAI and had DO3 structure. These four different morphologies of intermetallic precipitates exhibited discrete orientation-relationships with the α-matrix. The β-grains only contained very small cuboid shaped precipitates, which could only be resolved through transmission electron microscopy. These precipitates were found to be based on fe3Al and had the DO3 structure.

关键词： Orientation relationship DO3 structure Intermetallic phases

Numerical simulation of wave transformation,breaking and runup by a contravariant fully non-linear Boussinesq equations model

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Journal of Hydrodynamics 2016年第3期28卷 379-388页

作者： f.GALLERANO G.CANNATA f.LASAPONARA Department of Civil Constructional and Environmental Engineering Sapienza University of Rome

In this paper we propose a new model based on a contravariant integral form of the fully non-linear Boussinesq equations （fNBE） in order to simulate wave transformation phenomena, wave breaking, runup and nearshore currents in computational domains representing the complex morphology of real coastal regions. The above-mentioned contravariant integral form, in which Christoffel symbols are absent, is characterized by the fact that the continuity equation does not include any dispersive term. The Boussinesq equation system is numerically solved by a hybrid finite volume-f＇mite difference scheme. A high-order upwind weighted essentially non-oscillatory （WENO） finite volume scheme that involves an exact Riemann solver is implemented. The wave breaking is represented by discontinuities of the weak solution of the integral form of the non-linear shallow water equations （NSWE）. On the basis of the shock-capturing high order WENO scheme a new procedure, for the computation of the structure of the solution of a Riemann problem associated with a wet/dry front, is proposed in order to simulate the run up hydrodynamics in swash zone. The capacity of the proposed model to correctly represent wave propagation, wave breaking, run up and wave induced currents is verified against test cases present in literature. The results obtained are compared with experimental measures, analytical solutions or alternative numerical solutions. The proposed model is applied to a real case regarding the simulation of wave fields and nearshore currents in the coastal region opposite San Mauro Cilento （Italy）.

关键词： fully non-linear Boussinesq equations contravariant formulation Christoffel symbols upwind WENO scheme wet-dryfronts

formation and Microstructural Characterization of Silicon-modified Aluminide Coating on Nickel-based Superalloy IN738LC

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材料热处理学报 2004年第05B期25卷 657-660页

作者： f. Shahriari f. Ashrafizadeh A. Monshi Materials engineering department Isfahan University of Technology Isfahan IranMaterials engineering department Isfahan University of Technology Isfahan IranMaterials engineering department Isfahan University of Technology Isfahan Iran

In this investigation, aluminide coatings used to protect industrial components at high temperature and corrosive environments were modified with silicon addition and the microstructural features and formation mechanism were evaluated. The coating on the nickel-based superalloy IN738LC was carried out by a two stage process including siliconizing at first and aluminizing thereafter. Pack cementation siliconizing performed at 950C for 2, 4 and 6 hours in several powder mixtures of Si, A12O3 and NHiCl, then aluminum was diffused into the surface of the specimens by an industrial aluminizing process. The modified coatings were characterized by means of standard metallography, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction methods. The results show that Si in the coatings mainly presents in the form of secondary phases including Cr3Si, Mo5Si3 and Nii6Ti6Si7, well distributed within the NiAl matrix. The advantages of this two stage modified coating is discussed.

关键词：显微结构 IN738LC 镍超级合金扩散渗碳处理生长机制

Identification of Hammerstein-Wiener model with discontinuous input nonlinearity

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Science China(Information Sciences) 2023年第12期66卷 33-47页

作者： A.BROURI f.Z.EL MANSOURI f.Z.CHAOUI C.ABDELAALI f.GIRI ENSAM Moulay Ismail University ENSAM University Mohammed V Normandie Universite

This paper deals with the identification of Hammerstein-Wiener models with an irregular function in the input block. These models comprise a set of linear segments. The linear time invariant(LTI) block may be parametric or nonparametric. The nonlinearity of the output can be any continuous function of arbitrary shape; it is not necessarily assumed to be invertible. Subsequently, sine inputs will be used to identify the system parameters. first, the output nonlinearity is determined by filtering the system output and varying the phase of a given reference sine signal; second, the parameters of the linear block can be determined for any frequency; and finally, the input nonlinearity can be obtained by changing the offset and amplitude of the input sine signal.

关键词： nonlinear systems nonlinear systems identification Hammerstein-Wiener models discontinuous nonlinearities hard nonlinearities

Closed-form solutions for free vibration of rectangular fGM thin plates resting on elastic foundation

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Acta Mechanica Sinica 2016年第6期32卷 1088-1103页

作者： T. f. Xu Y. f. Xing Institute of Solid Mechanics Beihang UniversityBeijing 100191 China China Academy of Launch Vehicle Technology R&D Center Beijing 100076 China

This article presents closed-form solutions for the frequency analysis of rectangular functionally graded material (fGM) thin plates subjected to initially in-plane loads and with an elastic foundation. Based on classical thin plate theory, the governing differential equations are derived using Hamilton's principle. A neutral surface is used to eliminate stretching-bending coupling in fGM plates on the basis of the assumption of constant Poisson's ratio. The resulting governing equation of fGM thin plates has the same form as homogeneous thin plates. The separation-of-variables method is adopted to obtain solutions for the free vibration problems of rectangular fGM thin plates with separable boundary conditions, including, for example, clamped plates. The obtained normal modes and frequencies are in elegant closed forms, and present formulations and solutions are validated by comparing present results with those in the literature and finite element method results obtained by the authors. A parameter study reveals the effects of the power law index n and aspect ratio a/b on frequencies.

关键词： functionally graded material free vibration Rectangular plate Close form solutions Neutral surface

Determination of stress intensity factor with direct stress approach using finite element analysis

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Acta Mechanica Sinica 2017年第5期33卷 879-885页

作者： X.Ji f.Zhu P.f.He School of Aerospace Engineering and Applied Mechanics Tongji University

In this article, a direct stress approach based on finite element analysis to determine the stress intensity factor is improved. firstly, by comparing the rigorous solution against the asymptotic solution for a problem of an infinite plate embedded a central crack, we found that the stresses in a restrictive interval near the crack tip given by the rigorous solution can be used to determine the stress intensity factor, which is nearly equal to the stress intensity factor given by the asymptotic solution. Secondly, the crack problem is solved numerically by the finite element method. Depending on the modeling capability of the software, we designed an adaptive mesh model to simulate the stress singularity. Thus, the stress result in an appropriate interval near the crack tip is fairly approximated to the rigorous solution of the corresponding crack problem. Therefore, the stress intensity factor may be calculated from the stress distribution in the appropriate interval, with a high accuracy.

关键词： fracture mechanics Stress singularity Stress intensity factor finite element method Direct stress method

The role of AVDR in linear cascade testing

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航空动力学报 2007年第6期22卷 933-944页

作者： Wing f.Ng Department of Mechanical Engineering Virginia Polytechnic Instituteand State University

Linear cascade testing plays an important role in the research and development of turbomachinery and is widely used over the *** ideal cascade model of a turbomachinery blade row is *** actual linear cascade testing,the flow through the test section converges due to the development of the boundary layer and secondary flow along the sidewall surfaces of the test *** velocity density ratio(AVDR) is adopted to account for the deviation of the tested cascade flow from the ideal 2D *** numerous published cascade works,the influence of AVDR on cascade performance is seen to be complicated with many affecting factors,such as those related to cascade/blade geometry and flow ***,controlling AVDR is limited by the facility ***,real blade-to-blade flow in turbomachines is usually associated with AVDR greater than unity due to limited span of blades between the hub and shroud such that cascade testing without reducing AVDR could be favored *** these facets add complexity and diversification to the *** current paper reviews previous studies and results on *** understanding on the role of AVDR and recommendations on how to deal with it in linear cascade testing are provided.

关键词：线性叶栅试验轴向速度密度比空气流动叶栅特性

Competitive effect between roughness and mask pattern on charging phenomena during plasma etching

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Plasma Science and Technology 2022年第3期24卷 152-161页

作者： Peng ZHANG Ruvarashe f DAMBIRE School of Electronic Information Engineering Yangtze Normal UniversityChongqing 408100People's Republic of China School of Chemistry and Chemical Engineering Yangtze Normal UniversityChongqing 408100People's Republic of China

In the plasma etching process,the edge roughness and mask pattern usually play a significant role in the deformation of holes under the influence of the charging *** competitive effect between these two factors has been investigated,focusing on the surface charging in a hexagonal array,with various values of roughness parameters(amplitude(A)and wavelength(W))and distances between holes(L).A series of classical particle dynamic simulations of surface charging,surface etching and profile evolution were used to investigate the effect of roughness and pattern on *** study showed that various roughness and patterns(represented by different values of L)can significantly influence surface distributions of the electric-field(Efield)and the etching rates on the mask *** simulations also showed that(1)the shape of the pattern array influences the mask hole profile during the etching process,i.e.a hexagonal array pattern tends to deform the profile of a circular mask hole into a hexagonal hole;(2)pattern roughness is aggravated during the etching *** factors were found to be significant only at a small feature pitch and may be ignored at a large feature *** mechanisms of these results during the etching process are *** work sheds light on the ways to maintain pattern integrity and further improve the quality of the pattern transfer onto the substrate.

关键词： plasma etching pattern roughness

Experimental Investigation of Separation and Transition Processes on a High-Lift Low-Pressure Turbine Profile Under Steady and Unsteady Inflow at Low Reynolds Number

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Journal of Thermal Science 2010年第1期19卷 26-33页

作者： Satta f Simoni D Ubaldi M Zunino P Bertini f DIMSET-Università di Genova Via Montallegro 1I-16145 GenovaItaly Avio R&D V.I Maggio99 I-10040 Rivalta(TO)-Italy

The effects induced by the presence of incoming wakes on the boundary layer developing over a high-lift low-pressure turbine profile have been investigated in a linear cascade at *** tested Reynolds number is 70000,typical of the cruise operating *** results of the investigations performed under steady and unsteady inflow conditions are *** unsteady investigations have been performed at the reduced frequency of f+=0.62,representative of the real engine operating *** aerodynamic loadings as well as boundary layer velocity profiles have been measured to survey the separation and transition *** analysis has been also performed to better understand the phenomena associated with the transition process under steady *** the unsteady case,a phase-locked ensemble averaging technique has been employed to reconstruct the time-resolved boundary layer velocity distributions from the hot-wire instantaneous signal *** ensemble-averaging technique allowed a detailed analysis of the effects induced by incoming wakes-boundary layer interaction in separation ***-resolved results are presented in terms of mean velocity and unresolved unsteadiness time-space plots.

关键词： boundary layer separation boundary layer transition wake-boundary layer interaction high-liftprofile low-pressure turbine