Fe—3wt—%Si合金氢损伤的X射线形貌照相法研究

采用Lange式透射X射线形貌照相法研究了电解充氢导致Fe-3wt-％Si单晶中氢损伤的规律。结果表明:在不加毒化剂的1mol/LH_2SO_4中电解充氢时,不产生氢损伤;在有毒化剂时,即使电流密度很低,也会产生氢损伤。在一定电流密度下产生的氢损伤有一极限大小,并不随充氢时间增加而无限止长大。随电流密度增加,氢损伤尺寸增大,但当电流密度较大时,这种增大不明显。外应力显著促进氢损伤。在含毒化剂时,氢渗透曲线随时间延长而下降是由于产生了氢损伤所致。     

The effect of machined topography and integrity on fatigue life

The paper reviews published data which address the effect of machining (conventional and non-conventional processes) and the resulting workpiece surface topography/integrity on fatigue performance, for a variety of workpiece materials. The effect of post-machining surface treatments, such as shot peening, are also detailed. The influence of amplitude height parameters (Ra, Rt), amplitude distribution (Rsk) and shape (Rku) parameters, as well as spatial (Std, Sal) and hybrid (Ssc) measures, are considered.There is some disagreement in the literature about the correlation between workpiece surface roughness and fatigue life. In most cases, it has been reported that lower roughness results in longer fatigue life, but that for roughness values in the range 2.5–5 μm Ra it is primarily dependent on workpiece residual stress and surface microstructure, rather than roughness. In the absence of residual stress, machined surface roughness in excess of 0.1 μm Ra has a strong influence on fatigue life. Temperatures above 400 °C reduce the effects of both residual stress and surface roughness on fatigue, due to stress relieving and the change in crack initiation from the surfaces to internal sites. The presence of inclusions an order of magnitude larger than the machined surface roughness generally overrides the effect of surface topography.     

Machining of free-form surfaces. Part I: Analytical chip load

In the machining simulations of 3D free-form surfaces with ball-end mill, determinations of instantaneously changing tool-workpiece engagement regions and chip load play very critical roles in force and surface quality predictions. Cutting force models for ball-end milling are based on the undeformed chip load. Undeformed chip load can be constructed from the boundaries of instantaneous engagement region between the ball-end mill and workpiece. In order to predict the cutting forces accurately, precise determination of the varying engagement regions is important. In the literature, there are two main engagement region constructing methods; one is the Z-mapping and the other one is using solid modeler based on Boolean operation method. Both methods construct the engagement region within accuracy limits, on the other hand the computational time for these methods are long such that it is not possible to calculate the forces at the same time of CL-point construction. This paper presents development of a new analytical method for fast and accurate determination of the instantaneous engagement regions in the 3D machining of monotonic free-form surfaces. The analytical tool is grid size independent, thus it is much faster than discretization and Boolean methods. In addition to that, the analytical tool gives the most precise and exact engagement regions.     

A Wavelet–Fractal-Based Approach for Composite Characterisation of Engineering Surfaces

Many types of engineering surfaces have been seen to have fractal characteristics. A good model of the properties can be produced using wavelet-based expansions. For multiscale analysis of surface topography, a difficulty exists in determining quantitatively the feature separation index for comprehensively characterising roughness, waviness, and form errors from a primary surface structure. In this project, we utilise the fractal dimension, which has proved to be an intrinsic parameter capable of measuring surface irregularities, to quantify the feature separation index in the wavelet transform for a composite characterisation of engineering surfaces. The effectiveness of the proposed method is validated in the computational testing of 2D and 3D surfaces. ID="A1"Correspondance and offprint requests to: Dr Y. Gao, Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. E-mail: meygao@ust.hk     

基于MATLAB仿生非光滑形态模拟

仿生学研究发现,生物体表大都相当明显地体现着各种几何非光滑形态。为了研究仿生非光滑表面形态对磨损的影响以及非光滑表面形态自身的参数变化对耐磨性的影响,本文对典型的仿生非光滑形态进行计算机模拟,并设计了优化原则,为制作具有非光滑形态试样提供了数学模型。     

The development of the modified Hurst orientation transform for the characterization of surface topography of wear particles

A modified Hurst orientation transform (HOT) method for characterization of wear particle surfaces is proposed and described in this paper. The method involves the calculation of self-affine Hurst coefficients in all directions and displays the calculated coefficient values in a form of rose plot. The calculation of individual Hurst coefficients, H, is based on the rescale range (r/s) analysis (r(d)/s∼ d ^H ). The rose plot is then used to obtain three texture surface parameters, i.e.: texture aspect ratio, texture minor axis and texture direction. The effectiveness of this modified HOT and resulting surface texture parameters was evaluated. The method was first applied to computer-generated images of isotropic and anisotropic particle fractal surfaces and then to field emission scanning electron microscope images of wear particles found in synovial joints. The ability of the surface parameters to reveal surface isotropy or anisotropy, measure roughness and determine the dominant direction of surface texture was assessed. The effects of measurement conditions such as noise, gain variations and focusing on the surface parameters were also investigated. The results demonstrate that the HOT and surface texture parameters developed can successfully be used in the characterization of wear particle surface topography. This revised version was published online in August 2006 with corrections to the Cover Date.     

准分子激光加工工艺参数与修饰表面形貌参数的关系

表面微观形貌修饰是改善和控制表面微摩擦性能的一种方法。采用准分子激光表面形貌修饰技术在A l2O3陶瓷材料表面构建微观形貌,通过改变准分子激光加工工艺参数,探讨了准分子激光加工表面形貌参数(包括粗糙度参数和分形参数)与加工工艺参数的相关关系。研究表明:准分子加工工艺参数与表面形貌参数之间存在相关性,轮廓高度算术平均值、轮廓高度均方根值、坡度均方根值和分形维数与激光能量密度成正比,承载量系数与激光能量密度成反比;随着激光能量密度的增大,表面形貌的起伏程度和致密程度增大、陡峭程度有细微的变化、承载面积比减小。     

铝合金板表面形貌模型的研究

介绍了用于测量铝合金板表面微观形貌的AF-LI型表面轮廓测量仪的基本工作原理和技术指标，并采用接触式测量法，获得了铝合金板表面形貌的详细数据，得出了形貌评定参数，在此基础上建立了基于统计学规律的铝合金板表面形貌的数学模型。     

Design and performance assessment of a Kelvin clamp for use in relocation analysis of surface topography

This article describes the design and fabrication of a low-cost relocation device. The device is suitable for relocating small specimens on a stylus roughness measuring instrument to allow observation of the changes in topography of specific surface features arising from processes such as contact, wear, or corrosion. A principal feature of the article is that it describes an indirect method of assessing the accuracy of relocation using positioning tables driven by stepper motors. The method is applied to the author's design.     

Sliding wear behaviour of an electrochemically modified austenitic high-nitrogen steel surface

Wear debris from artificial metallic implant joints is known to provoke detrimental foreign-body reactions in the surrounding human tissue. Although commonly used biotolerant metals generate only a little amount of particles, wear is still a major cause for concern. It is the aim of this work to evaluate the sliding wear resistance of a topologically modified high-nitrogen austenitic stainless steel. A disc-on-pin test in self-mating contact is performed in distilled water. Submicron particles are trapped by the structured topography and form together with the plastically deformed metal a hybrid surface which has the potential to significantly improve the tribological behaviour of the tested high-nitrogen steel.