Recognition of texture types of wear particles

Microscopic wear particles are produced in all machines containing moving parts in contact. The particles, transported by a lubricant from wear sites; carry important information relating to the condition of the machinery. This information is classified by compositional and six morphological attributes of particle size, shape, edge details, color, thickness ratio, and surface texture. This article describes an automated system for surface texture identification of wear particles by using artificial neural networks. The aim is to classify these particles according to their morphological attributes and by using the information obtained, to predict wear failure modes in engines and other machinery. This approach will enable the manufacturing industry to improve quality, productivity and economy. The procedure reported in this article is based on gray level co-occurrence matrices which are used to train a feed-forward neural network classifier in order to distinguish among seven different patterns which can aid in the identification of wear particles. The investigated patterns are: smooth, rough, striations, holes, pitted, cracked, and serrated. An accuracy classification rate of 94.64% has been achieved and is shown by a confusion matrix.     

Micron-Scale Friction and Sliding Wear of Polycrystalline Silicon Thin Structural Films in Ambient Air

Micron-scale static friction and wear coefficients, surface roughness, and resulting wear debris have been studied for sliding wear in polycrystalline silicon in ambient air at micro- Newton normal loads using on-chip sidewall test specimens, fabricated with the Sandia SUMMiT V^TM process. With increasing number of wear cycles friction coefficients increased by a factor of two up to a steady-state regime, concomitant with a decay (after an initial sharp increase) in the wear coefficients and roughness. Wear coefficients were orders of magnitude smaller than reported macroscale values, suggesting that the wear resistance is higher at micrometer dimensions. Based on our observations, a sequence of micron-scale wear mechanisms is proposed involving: 1) a short adhesive wear regime (< 10⁴ cycles), where the oxide is worn away and the first silicon debris particles form and 2) a regime dominated by abrasive wear, where silicon particles (50-100 nm) are created by fracture through the grains (~500 nm). These particles subsequently oxidize and agglomerate into larger debris clusters, while "ploughing" by this debris leads to abrasive grooves associated with local cracking events rather than plastic deformation.     

Submicron coatings for micro-tribological applications

The miniaturisation of mechanical components and machines enables innovative future products. However, for the improvement of functionality, reliability and lifetime of those micro systems, micro tribological coatings with thicknesses in the sub-micron range are needed. To cover these needs, we investigated different submicron coatings with the aim to develop wear and friction optimized thin films for this application. The basis of this work has been the state of the art know how of well established macroscopic coatings which in general are in a thickness range of a few micrometers. It turned out, that particularly the surface topography and the substrate material influence the properties of very thin films. For investigations with single asperity contact, the coefficient of friction (COF) was reduced by lowering the tip radius and the hardness of the substrate material. In contrast, for larger contact radii (pin-on-disc), an increase of the COF with decreasing substrate Youngs modulus was found. With respect to wear, it turned out that the wear depth increased dramatically with increasing initial surface roughness (R_a).The authors gratefully acknowledge the financial support of the German Research Foundation by grant SFB 516. We also thank T. Staedler and A. Wortmann for their contributions through their respective PhD Theses on this topic.     

抛光过程游离单颗磨粒与光学元件间滚动摩擦接触分析

针对游离单颗磨粒与光学元件滚动接触过程中摩擦、磨损机理分析的不足及如何 有效控制滚动单颗磨粒对光学元件亚表面损伤的影响等问题,基于滚动接触理论,提出了一种 具有分形特征表面的单颗磨粒与光学元件双粗糙面间的摩擦、磨损接触模型,并运用有限元仿 真分析微观动态滚动的接触过程。通过对不同剪切强度下接触力、接触应力、磨粒角度及其对 亚表面损伤的影响等分析,发现随着剪切强度的增强,磨粒与光学元件表面接触界面间的摩擦 系数将减小,最佳的磨粒角度为105°~120°,并且分形特征的单颗磨粒对亚表面损伤的影响要 大于球形特征单颗磨粒,这说明了研究分形特征游离单颗磨粒滚动接触的必要性和重要性,为 更加深刻了解滚动接触过程的摩擦机理提供了借鉴意义。     

Insight into the micro scale dynamics of a micro fluidic wetting-based conveying system by particle based simulation

We simulate a microfluidic conveying system using the many-body dissipative particle dynamics method (MDPD). The conveying system can transport micro parts to a specified spot on a surface by letting them float inside or on top of a droplet, which is pumped by changing the wetting behaviour of the substrate, e.g., with electrowetting on dielectrics. Subsequent evaporation removes the fluid; the micro part remains on its final position, where a second substrate can pick it up. In this way, the wetting control can be separate from the final device substrate. The MDPD method represents a fluid by particles, which are interpreted as a coarse graining of the fluid’s molecules. The choice of interaction forces allows for free surfaces. To introduce a contact angle model, non-moving particles beyond the substrate interact with the fluid particles by MDPD forces such that the required contact angle emerges. The micro part is simulated by particles with spring-type interaction forces.     

Transient analysis of sliding contact of layered elastic/plastic solids with rough surfaces

 Based on the boundary element method (BEM) and a variational principle, a numerical model is developed to analyze the time – transient sliding contact of two layered elastic/plastic solids. Two cases are considered: one is the loading/sliding/unloading of a rough surface on a smooth surface, and the other is of two rough surfaces. Contact statistics, contact pressure profile and stress distribution are predicted at each time step with updated surface roughness. The results are used to study the effect of surface roughness, physical properties of the layer and the substrate, and lubricant film thickness on friction, stiction, and wear. Discussion on the integration of this contact model into advanced tribological models, e.g., wear model, is also presented. Received: 28 June 2002/Accepted: 23 October 2002 Currently at: Seagate Technology, Pittsburgh, PA Paper presented at the 13th Annual Symposium on Information Storage and Processing Systems, Santa Clara, CA, USA, 17–18 June, 2002     

Strategic developments to improve the optimization performance with efficient optimum solution and produce high wear resistance aluminum–copper alloy matrix composites

The aim of the present study was to find better developments to improve the performance of population optimization, especially from the angle of keeping the population diversity, to enhance the global search in the early part of the optimization and to encourage the particles to converge toward the global optima at the end of the search. The results were used to optimize the fabrication process conditions of the high wear resistance boron carbide-reinforced Al matrix composites. An experimental investigation was then carried out on the abrasive wear behavior of Al alloy matrix composites in terms of abrasive particle size, weight fraction and applied load in pin-on-disk type of wear machine.     

Narrow Band FLIP for Liquid Simulations

The Fluid Implicit Particle method (FLIP) for liquid simulations uses particles to reduce numerical dissipation and provide important visual cues for events like complex splashes and small‐scale features near the liquid surface. Unfortunately, FLIP simulations can be computationally expensive, because they require a dense sampling of particles to fill the entire liquid volume. Furthermore, the vast majority of these FLIP particles contribute nothing to the fluid's visual appearance, especially for larger volumes of liquid. We present a method that only uses FLIP particles within a narrow band of the liquid surface, while efficiently representing the remaining inner volume on a regular grid. We show that a naïve realization of this idea introduces unstable and uncontrollable energy fluctuations, and we propose a novel coupling scheme between FLIP particles and regular grid which overcomes this problem. Our method drastically reduces the particle count and simulation times while yielding results that are nearly indistinguishable from regular FLIP simulations. Our approach is easy to integrate into any existing FLIP implementation.     

SDECAY: a Fortran code for the decays of the supersymmetric particles in the MSSM

We present the Fortran code SDECAY, which calculates the decay widths and branching ratios of all the supersymmetric particles in the Minimal Supersymmetric Standard Model, including higher order effects. Besides the usual two-body decays of sfermions and gauginos and the three-body decays of charginos, neutralinos and gluinos, we have also implemented the three-body decays of stops and sbottoms, and even the four-body decays of the stop; the important loop-induced decay modes are also included. The QCD corrections to the two-body decays involving strongly interacting particles and the dominant components of the electroweak corrections to all decay modes are implemented.

Program summary

Title of program: SDECAY Version 1.1a (March 2005)Catalogue identifier: ADVJProgram summary URL:http://cpc.cs.qub.ac.uk/summaries/ADVJProgram obtainable: CPC Program Library, Queen's University of Belfast, N. IrelandLicensing provisions: noneComputer for which the program is designed: Any with a Fortran77 systemOperating systems under which the program has been tested: Linux, UnixTypical running time: A few seconds on modern personal computers and workstationsProgramming language used: Fortran77No. of lines in distributed program, including test data, etc.: 59 621No. of bytes in distributed program, including test data, etc.: 338 478Distribution format: tar.gzMemory required to execute (with test data): 7.3 MBDistribution format: ASCIINature of physical problem: Numerical calculation of the decay widths and branching ratios of supersymmetric particles in the Minimal Supersymmetric Standard Model (MSSM). The program calculates two-, three- and four-body decays and loop decays. It includes the SUSY-QCD corrections to two-body decays involving strongly interacting particles. The top-quark decays within the MSSM are evaluated as well.Method of solution: Two-dimensional numerical integration of the analytic formulae for the double differential decay widths of the three-body decays. The other decay widths are calculated analytically.Restrictions on the complexity of the problem: In the higher order decay modes the total decay widths of the virtually exchanged (s)particles are not included in their respective propagators. The higher order decays are calculated when the two-body decays are kinematically closed.     

Introducing a level-set based shape and topology optimization method for the wear of composite materials with geometric constraints

The wear of materials continues to be a limiting factor in the lifetime and performance of mechanical systems with sliding surfaces. As the demand for low wear materials grows so does the need for models and methods to systematically optimize tribological systems. Elastic foundation models offer a simplified framework to study the wear of multimaterial composites subject to abrasive sliding. Previously, the evolving wear profile has been shown to converge to a steady-state that is characterized by a time-independent elliptic equation. In this article, the steady-state formulation is generalized and integrated with shape optimization to improve the wear performance of bi-material composites. Both macroscopic structures and periodic material microstructures are considered. Several common tribological objectives for systems undergoing wear are identified and mathematically formalized with shape derivatives. These include (i) achieving a planar wear surface from multimaterial composites and (ii) minimizing the run-in volume of material lost before steady-state wear is achieved. A level-set based topology optimization algorithm that incorporates a novel constraint on the level-set function is presented. In particular, a new scheme is developed to update material interfaces; the scheme (i) conveniently enforces volume constraints at each iteration, (ii) controls the complexity of design features using perimeter penalization, and (iii) nucleates holes or inclusions with the topological gradient. The broad applicability of the proposed formulation for problems beyond wear is discussed, especially for problems where convenient control of the complexity of geometric features is desired.     

Influence of surface condition on wear behavior of ��PIM mould inserts made of tool steel and cemented carbide

Mould inserts made of low alloyed tool steel and cemented carbide were tested using a laboratory tribometer simulating micro powder injection moulding (μPIM) to characterize the influence of surface condition due to different machining (micro milling or electrical discharge machining) and finishing (ultrasonic wet peening or abrasive micro peening) processes on wear in contact with ceramic feedstocks of different composition. Results show that abrasive micro peening is a suitable finishing process to ensure an excellent wear resistance of EDM processed mould inserts made from ultrafine cemented carbide even in contact with alumina feedstock of high abrasiveness. Ultrasonic wet peening on the other hand allows effective deburring and smoothing of relatively soft steel surfaces after micro milling.     

Analysis of thermo-mechanical wear problems for reciprocal punch sliding

The relative sliding motion of two elastic bodies in contact induces wear process and contact shape evolution. In the case of a punch sliding on a substrate the transient process tends to a steady state for which the fixed contact stress and strain distribution develops in the contact zone. This state usually corresponds to a minimum of the wear dissipation power. The optimality conditions of the wear dissipation functional provide the contact stress distribution and the wear rate compatible with the rigid body punch motion. The present paper is aimed to extend the previous analyses [1], [2], [3], [4], [5] of steady state conditions to cases of periodic sliding of punch, assuming cyclic steady state conditions for both mechanical and thermal fields.     

Comparison of Au and Au–Ni Alloys as Contact Materials for MEMS Switches

This paper reports on a comparison of gold and gold-nickel alloys as contact materials for microelectromechanical systems (MEMS) switches. Pure gold is commonly used as the contact material in low-force metal-contact MEMS switches. The top two failure mechanisms of these switches are wear and stiction, which may be related to the material softness and the relatively high surface adhesion, respectively. Alloying gold with another metal introduces new processing options to strengthen the material against wear and reduce surface adhesion. In this paper, the properties of Au-Ni alloys were investigated as the lower contact electrode was controlled by adjusting the nickel content and thermal processing conditions. A unique and efficient switching degradation test was conducted on the alloy samples, using pure gold upper microcontacts. Solid-solution Au-Ni samples showed reduced wear rate but increased contact resistance, while two-phase Au-Ni (20 at.% Ni) showed a substantial improvement of switching reliability with only a small increase of contact resistance. Discussion of the effects of phase separation, surface topography, hardness, and electrical resistivity on contact resistance and switch degradation is also included.     

Tribology of microsystems

In this work the possibilities for the reduction of friction and wear in micro electro-mechanical systems (MEMS) are investigated. An improvement of the tribological behaviour of microsystems can be realized by optimizing the contact condition and by application of special coatings with low friction and low wear rates. For optimizing the contact condition a defined topography and surface profile is generated by photolithography. Furthermore tribological coatings with low friction and low wear rates are developed and investigated using nanoindentation and micro scratch experiments. Also novel results on micro structured surfaces coated with a-C:H and a-C films will be discussed. The results show the great potential of carbon-based coatings in combination with an optimized geometrical surface design.     

Measurement and mechanism of pole tip recession with advanced metal evaporated tape at low tension in a linear tape drive

Increased head-to-tape spacing in a magnetic tape drive causes signal loss. Pole tip recession (PTR) is a type of differential wear that occurs with tape heads and increases the effective head-to-tape spacing. The extent and mechanism of PTR that occurs when using metal particle (MP) tape has been examined by various authors and is well documented. To achieve higher recording density, tape manufacturers are developing thin-film tapes, such as advanced metal evaporated (AME) tape, for use in linear tape drives. The structure of AME tape is fundamentally different from MP tape and AME tape must be run at lower tension. The goals of this study are to determine the amount of PTR that occurs and to investigate the mechanism by which PTR proceeds when AME and MP tapes are rubbed against a commercial head in a linear tape drive at low tension. Atomic force microscopy (AFM) was used to measure PTR after interval sliding distances. It is shown that use of AME tape led to lower PTR than use of MP tape, and the probable mechanism of PTR growth is three-body abrasion, with different types of abrasive debris from the two tapes.     

基于磨损机理的磨粒图像识别仿真

机械设备磨损过程中产生的磨粒,可以利用智能识别技术进行识别。通过对切削磨粒、球状磨粒、疲劳磨粒以及严重滑动磨粒的磨损机理的研究,提出了能够识别各类磨粒的显著特征,将特征参数进行量化表征,并以特征参数为输入向量,建立支持向量机分类器模型,运用层次法对分类器进行训练,优化分类器的参数,最后利用分类器模型对磨粒图像进行识别以验证识别方法的可行性。实验结果表明,支持向量机分类器识别磨粒类型准确率较高,可以用于磨粒图像的识别。     

Mesoscale simulations of particulate flows with parallel distributed Lagrange multiplier technique

Fluid particulate flows are common phenomena in nature and industry. Modeling of such flows at micro and macro levels as well establishing relationships between these approaches are needed to understand properties of the particulate matter. We propose a computational technique based on the direct numerical simulation of the particulate flows. The numerical method is based on the distributed Lagrange multiplier technique following the ideas of Glowinski et al. [16] and Patankar [30]. Each particle is explicitly resolved on an Eulerian grid as a separate domain, using solid volume fractions. The fluid equations are solved through the entire computational domain, however, Lagrange multiplier constrains are applied inside the particle domain such that the fluid within any volume associated with a solid particle moves as an incompressible rigid body. Mutual forces for the fluid-particle interactions are internal to the system. Particles interact with the fluid via fluid dynamic equations, resulting in implicit fluid-rigid body coupling relations that produce realistic fluid flow around the particles (i.e., no-slip boundary conditions). The particle-particle interactions are implemented using explicit force-displacement interactions for frictional inelastic particles similar to the DEM method of Cundall et al. [10] with some modifications using a volume of an overlapping region as an input to the contact forces. The method is flexible enough to handle arbitrary particle shapes and size distributions. A parallel implementation of the method is based on the SAMRAI (Structured Adaptive Mesh Refinement Application Infrastructure) library, which allows handling of large amounts of rigid particles and enables local grid refinement. Accuracy and convergence of the presented method has been tested against known solutions for a falling particle as well as by examining fluid flows through stationary particle beds (periodic and cubic packing). To evaluate code performance and validate particle contact physics algorithm, we performed simulations of a representative experiment conducted at the U.C. Berkeley Thermal Hydraulic Lab for pebble flow through a narrow opening.     

基于透视网格的自适应窄带表面粒子提取方法

为了提升基于粒子的流体表面重建效率,提出了一种基于透视网格的自适应窄带表面粒子提取方法。与基于物体空间的方法相比,该方案根据粒子密度、离散系数等信息自适应提取视锥范围内最靠近视点的表面粒子,使表面粒子数、内存消耗仅与可见的表面区域相关,而不是整个流体表面或模拟域。此外,利用透视网格沿视线排布的优势,提出了基于粒子密度的自适应厚度估计方法。实验结果表明,该方案有效减少了40%～76%的表面粒子和30%～50%的内存开销,解决了表面粒子冗余和空洞问题,并以较低的代价获取了厚度信息。该方案为后续的表面重建和渲染带来了明显的性能提升,可以更好地处理大规模粒子集的重建和渲染。     

Adaptive particles for incompressible fluid simulation

We propose a particle-based technique for simulating incompressible fluid that includes adaptive refinement of particle sampling. Each particle represents a mass of fluid in its local region. Particles are split into several particles for finer sampling in regions of complex flow. In regions of smooth flow, neighboring particles can be merged. Depth below the surface and Reynolds number are exploited as our criteria for determining whether splitting or merging should take place. For the fluid dynamics calculations, we use the hybrid FLIP method, which is computationally simple and efficient. Since the fluid is incompressible, each particle has a volume proportional to its mass. A kernel function, whose effective range is based on this volume, is used for transferring and updating the particle’s physical properties such as mass and velocity. Our adaptive particle-based simulation is demonstrated in several scenarios that show its effectiveness in capturing fine detail of the flow, where needed, while efficiently sampling regions where less detail is required.