Reciprocating sliding wear behavior of laser-clad small amplitude Mo2Ni3Si/NiSi metal silicide composite coatings

Mo₂Ni₃Si/NiSi metal silicide composite coatings with a fine microstructure consisting of Mo₂Ni₃Si primary dendrites and the interdendritic Mo₂Ni₃Si/NiSi eutectics were fabricated on austenitic stainless steel AISI 321 by laser cladding process. Small amplitude reciprocating sliding wear resistance of the coatings is evaluated as functions of normal load and slip amplitude and the wear mechanisms were discussed based on worn surface morphology observations. Results showed that the Mo₂Ni₃Si/NiSi coatings have excellent small amplitude reciprocating sliding wear resistance.     

Relationship between the dynamic softening transition and wet sliding friction of elastomer compounds

For properly chosen elastomer compounds, thermorheological characterization is combined with an examination of the variation of the wet sliding friction with temperature. A conceptual argument leads to the assumption that the wet sliding friction should maximize at the energy dissipation peak associated with the dynamic softening transition at a characteristic frequency determined by the sliding speed and the effective smallest surface asperity scale. The dynamic softening transition is characterized with the peak in tan δ/G′ⁿ, where tan δ is the loss tangent, G′ is the elastic modulus, and n is a constant between 0 and 1. The William–Landel–Ferry transform is uncritically applied for extrapolating the position of the peak in tan δ/G′ⁿ at high frequencies. Even based on the criterion of tan δ, the results obtained on a concrete surface indicate that the effective smallest asperity scale is of order of 100 μm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2467–2478, 2004     

Phase Separation Driven by a Fluctuating Two-Dimensional Self-Affine Potential Field

We study phase separation in a system of hard-core particles driven by a fluctuating two-dimensional self-affine potential landscape which evolves through Kardar–Parisi–Zhang (KPZ) dynamics. We find that particles tend to cluster together on a length scale which grows in time. The final phase-separated steady state is characterized by an unusual cusp singularity in the scaled correlation function and a broad distribution for the order parameter. Unlike the one-dimensional case studied earlier, the cluster-size distribution is asymmetric between particles and holes, reflecting the broken reflection symmetry of the KPZ dynamics, and has a contribution from an infinite cluster in addition to a power law part. A study of the surface in terms of coarse-grained depth variables helps understand many of these features.     

Simulation of single‐ and two‐phase flows on sliding unstructured meshes using finite volume method

The paper presents an efficient finite volume method for unstructured grids with rotating sliding parts composed of arbitrary polyhedral elements for both single‐ and two‐phase flows. Mathematical model used in computations is based on the ensemble averaged conservation equations. These equations are solved for each phase and in case of single‐phase flow reduce to the transient Reynolds‐averaged Navier–Stokes (TRANS) equations. Transient flow induced by rotating impellers is thus resolved in time. The use of unstructured grids allows an easy and flexible meshing for the entire flow domain. Polyhedral cell volumes are created on the arbitrary mesh interface placed between rotating and static parts. Cells within the rotating parts move each time step and the new faces are created on the arbitrary interfaces only, while the rest of the domain remain ‘topologically’ unchanged. Implicit discretization scheme allows a wide range of time‐step sizes, which further reduce the computational effort. Special attention is given to the interpolation practices used for the reconstruction of the face quantities. Mass fluxes are recalculated at the beginning of each time step by using an interpolation scheme, which enhances the coupling between the pressure and velocity fields. The model has been implemented into the commercially available CFD code AVL SWIFT (AVL AST, SWIFT Manual 3.1, AVL List GmbH, Graz, Austria, 2002). Single‐phase flow in a mixing vessel stirred by a six‐bladed Rushton‐type turbine and two‐phase flow in aerated stirred vessel with the four‐blade Rushton impeller are simulated. The results are compared with the available experimental data, and good agreement is observed. The proposed algorithm is proved to be both stable and accurate for single‐phase as well as for the two‐phase flows calculations. Copyright 2004 John Wiley & Sons, Ltd.     

Determination of cake thickness and porosity during cross-flow ultrafiltration on a plane ceramic membrane surface using an electrochemical method

The thickness and the porosity of a deposit during ultrafiltration experiments are determined using an electrochemical method. Twenty microelectrodes are mounted flush to a ceramic plane membrane and maps of deposit thickness are determined for three inlet/outlet distributors configurations. Combining an electrochemical method and a step transient method, the determination of the thickness and the porosity of a particles deposit is performed. These local thickness and porosity values are analyzed thanks to wall shear stress local measurements obtained in a previous work [Sep. Sci. Technol. 37 (10) (2002) 2251]. The results emphasize the heterogeneity of the deposit thickness, especially in zones of low wall shear stress. Furthermore, the porosity values of the deposit are ranged between 0.3 and 0.8 as a function of the location at the membrane surface.     

稳态双曲流场中液/液混合的粘性液滴哑铃分散模型

通过对稳态双曲流场中液／液混合体系分散相液滴所受分散作用力的分析，建立了粘性液滴的哑铃分散模型．趋于将两粘性液滴分开的分散作用力与粘度比、流场类型和强度、液滴半径、哑铃取向和尺寸有关．该模型解释了流场类型与分散作用的关系．流场类型对液滴的分散具有很大影响，在纯应变拉伸流场中分散作用力是简单剪切流场中的两倍，因而对于液滴的分散，拉伸流场较简单剪切流场更有效，这与以前的实验结论符合．当体系粘度比趋于无穷大时本模型转化为刚性哑铃分散模型     

Exact solution of plane isolated crack normal to a bimaterial interface of infinite extent

This paper presents an exact solution for the transverse interface crack in the plane strain case. The crack is perpendicular to the interface and in one material. The exact complex stress functions are first obtained with some unknown constants. The satisfactions of all boundary conditions are then checked, the condition at infinity is considered and the unknown constants are determined. Further study may focus on the case with different shear moduli and the influence of the large deformation.The English text was polished by Keren Wang.     

Nano-WC/PTFE-Ni复合电刷镀层的磨损性能研究

采用电刷镀技术在Q235钢基材上制备含纳米WC和PTFE的镍基复合镀层,采用S-2700型扫描电子显微镜观察镀层表面形貌及其显微组织,采用HX-1型显微硬度计测定镀层的显微硬度,采用WS-2005型涂层附着力自动划痕仪测定镀层与基体的结合强度,采用HT-500型销-盘高温摩擦磨损试验机测量镀层的滑动磨损性能.结果表明:镀液中同时加入纳米WC和PTFE可以得到表面形貌平整、纳米粒子分布均匀的纳米复合镍镀层;复合镀层的硬度随WC含量的增加而增大,随PTFE含量的增加而减小;含有2种纳米粒子的复合镍镀层的耐磨性比镍镀层和含单一WC或PTFE的镍镀层的耐磨性优良;当镀液中WC和PTFE含量分别为3.0 g/L和7.5 mL/L时,复合镍镀层的显微硬度较镍镀层提高约30%,耐磨性较镍镀层提高7倍.     

残余奥氏体含量对马氏体高强钢滑动磨损性能的影响

对3种不同残奥(RA)含量的马氏体高强钢进行干滑动摩擦磨损试验, 研究RA含量对其磨损性能的影响. 利用扫描电镜、透射电镜、X射线衍射仪等对试验后的磨损表面及横截面显微组织进行表征. 结果表明, RA含量越高, 磨损表面越光滑, 摩擦系数和磨损率越小, 也即马氏体高强钢的耐磨性越好. 磨损引起的大应变使RA发生应变诱导马氏体相变, 导致硬度和硬化层厚度显著增大. RA含量最高的HT3试样的硬度提高了18.3%, 硬化层厚度达70μm. 相比RA含量低的试样, HT3试样表现出很好的耐磨性. 这是因为马氏体相变使硬度逐步增加, 抗裂纹萌生能力提高; 同时由于亚表面良好的韧性, 可延缓和阻止裂纹扩展, 使得点蚀和剥落不易形成. 因此, 要提高马氏体高强钢的耐磨性, 除了硬度要求外, 还需要考虑其亚表面韧性.     

A comparison of numerical and analytical radiative-transfer solutions for plane albedo of natural waters

Several numerical and analytical solutions of the radiative transfer equation (RTE) were compared for plane albedo in a problem of solar light reflection by sea water. The study incorporated the simplest case—a semi-infinite one-dimensional plane—parallel absorbing and scattering homogeneous layer illuminated by a monodirectional light beam. Inelastic processes (such as Raman scattering and fluorescence), polarization and air-water surface refraction-reflection effects, were not considered. Algorithms were based on the invariant imbedding method and two different variants of the discrete ordinate method (DOM). Calculations were performed using parameters across all possible ranges (single-scattering albedo ω₀ and refracted solar zenith angle θ₁), but with a special emphasis on natural waters. All computations were made for two scattering phase functions, which included an almost isotropic Rayleigh phase function and strongly anisotropic double-peaked Fournier-Forand-Mobley phase function. Models were validated using quasi-single-scattering (QSSA) and exponential approximations, which represent the extreme cases of ω₀→0 and ω₀→1, respectively. All methods yielded relative differences within 1.8% for modeled natural waters. An analysis of plane albedo behavior resulted in the development of a new extended QSSA approximation, which when applied in conjunction with the extended Hapke approximation developed earlier, resulted in a maximum relative error of 2.7%. The study results demonstrated that for practical applications, the estimation of inherent optical properties from observed reflectance can best be achieved using an extended Hapke approximation.