仪器化压入硬度与维氏硬度的关系研究

对理想Berkovich压头和维氏压头几何形状的分析表明,名义硬度Hn与维氏硬度Hv间存在如下近似函数关系：Hv=Hn/1.08。以37种碳钢材料的单轴拉伸实验数据为例,利用非线性有限元分析软件ABAQUS,模拟分析了这组碳钢材料的仪器化压入响应,将得出的名义硬度除以1.08,并与这些碳钢材料维氏硬度的实验数据相比较,两者吻合较好,以上关系的正确性得到了验证。这一关系使仪器化压入硬度与传统硬度间的直接比较成为可能。同时,为薄膜材料、纳米材料等小尺度材料传统硬度的预测提供了可行性方法。     

Hardness estimation for pile-up materials by strain gradient plasticity incorporating the geometrically necessary dislocation density

A plastic strain gradient theory incorporating the geometrically necessary dislocation density based on the low order displacement finite element method is proposed for calculation of the hardness value by Berkovich indentation. The obtained analysis results by this work are found to be in good agreement with the experimental data. Three-dimensional modeling technique of Berkovich indentation is also suggested. An empirical coefficient that includes the strain gradient effect into the yield stress formula is introduced and determined by reviewing area factors and hardness curves generated from the analyses. As pile-up occurs, classical plasticity theory gives a higher area factor and lower hardness value than those from experiment. However the strain gradient plasticity theory used in this work gives corrected area factor and hardness values. Dislocation density plots are generated that can explain the size effect during indentation and the availability of the three-dimensional modeling of Berkovich indentation.     

金属材料维氏硬度试验测量不确定度的评定

根据测量不确定度原理及国家计量技术规范JJF1059-1999测量不确定度评定与表示方法,对金属材料维氏硬度试验测量结果的不确定度进行详细的评定,评定方法适用于检测实验室的维氏硬度测量领域。     

Vibration effect on hardness measurement

In this paper, the effect of ground vibration on hardness measurement, Rockwell scale C hardness, Vickers scale HV1 hardness and Leeb hardness is studied. The hardness machines were placed on the vibration table. The vibration signal is single frequency sinusoidal wave, which frequency and amplitude of vibration can be controlled. The hardness value at free from vibration state is used as a reference to calculate the error of each hardness measurement at certain frequency and amplitude. Two Rockwell hardness testing machines are used to measure hardness blocks: 20, 40, and 60 HRC. Both machines give the same tendency. Significant negative errors occur around frequency 5–15 Hz. Moreover, ground vibration has more impact on the soft range of hardness than hard range. The result from this paper can be used as guideline for laboratory to control environmental vibration amplitude to be less than 0.01 m/s² for frequency (10 ± 5) Hz and 0.05 m/s² for other in Rockwell scale C hardness measurement. Effect of vibration on Vickers and Leeb hardness measurement is preliminarily studied. Results on 200 HV1 and 900 HV1 measurement show that vibration creates peak of error at frequency 20 Hz of amplitude more than 0.01 m/s² and the effect can be observable at all frequency for amplitude of 0.04 m/s². Different from Rockwell and Vickers, Leeb hardness measurement is not influenced by vibration in this experiment.     

钝化压头纳米压入测试硬度的变化及校正

文中通过量纲分析和有限元数值计算，分别对弹塑性材料在Berkovich理想压头和钝化压头作用下的压入响应进行了分析，揭示了理想压头Oliver＆Pharr压入硬度与钝化压头压入硬度的关系，据此，可以把钝化压头作用下的压入硬度校正至理想压头下的测试硬度。     

Quantitative measurement of the hardness profile on carbo-nitriding steel by the hole drilling method

The thrust measured during a drilling test is related to the hardness of the material being tested. When the test is performed on a superficially heat-treated specimen, the results do not correspond exactly to the hardness profile obtained by the standard Vickers micro hardness technique.Because of the extreme hardness of the surface tested and the small diameter required to minimise material damage, a drill is more suitable than a milling cutter. The thrust measured during testing thus integrates heterogeneous resistance along the cutting edge of the drill. Consequently, correspondence between the hardness profile and the measured signal is shown to be non-linear. By discretising the thickness drilled, we have developed an algorithm which yields the hardness of each elemental thickness. Results for carbo-nitriding steel are very close to those obtained by the Vickers technique and the accuracy is also very similar for both methods.     

Influential factors on hardness uniformity of Vickers hardness blocks for high hardness range

Reference Vickers hardness blocks for high hardness range were developed from WC 9–Co and WC 6–Co mixtures by two different processes of powder metallurgy, conventional liquid phase sintering in hydrogen and vacuum-sintering with subsequent hot isostatic pressing in one cycle, sinter-HIP, in order to analyse the appropriateness of the manufacturing process and the influence of starting characteristics of the mixtures on hardness uniformity and overall metrological characteristics. WC powder of 150 nm grain size and 2.5 m²/g specific surface area with the addition of grain grow inhibitors was used as starting material. The emphasis of the research was placed on hardness uniformity of the test surface as it is the most important property placed on hardness blocks. For that purpose the surface of the blocks was divided into radial and circumferential divisions, forming different sections on the block surface. Hardness measurements were performed in each section with HV1 measuring method. A total of 40 indentations were performed, based on which the conclusions about hardness uniformity of Vickers hardness blocks were drawn. Hardness measurements and uniformity were tested by analysis of variance, ANOVA, for single factor in order to determine if significant hardness variations across the block surface were present. From the research conducted it was concluded that hardness distribution across test surfaces of Vickers hardness blocks had a trend according to a process of manufacturing and the amount of binder in the WC–Co mixture. The best material and metrological characteristics were obtained on the block manufactured by sinter-HIP with 9 wt.% Co.     

On the electromechanical effect in Si and Ge

An extensive study has been carried out of the effect of electrical current on the room-temperature indentation hardness and indentation damage area of Si and Ge. It is found that the spread of results is such that sample numbers of less than about 50–100 can give misleading conclusions. This explains the large variations in results in the literature. It is concluded that if any electromechanical effect exists, it is slight. The measured Vickers hardness has a range of at least 9.2 to 13.7 GPa for Ge and at least 10.4 to 15.3 GPa for Si.     

Tip bluntness transition measured with atomic force microscopy and the effect on hardness variation with depth in silicon dioxide nanoindentation

Depth-sensing indentation measurements of surfaces and structures with indentation depths less than 100 nm necessitate the use of accurate area functions for correct property evaluation. Here, the effect of a blunt nanoindenter tip geometry is characterized using atomic force microscopy to measure the direct tip geometry and modeled by a power law profile shape. Direct measurement of tip geometry is a method to observe changes in the tip curvature and transition from the blunt tip region to an ideal tip geometry. The tip shape, curvature, and transition to ideal geometry is found to correspond with the increase in hardness observed experimentally in SiO2 using a self-similar contact model. For a Berkovich indenter, tip bluntness was found to have a power law degree of 1.5 near the tip apex with a continuously varying degree of bluntness until an ideal pyramidal shape was reached at a depth of 160 nm.     

基于增量式旋转编码器的维氏硬度数据采集的研究

依据维氏硬度测量原理,通过测量试样表面压痕对角线的长度,从而计算出试样的硬度值。传统测量压痕对角线长度的方法是用测微目镜测量,然后肉眼读取目镜刻度尺上的刻度值,得到相应数据。鉴于测微目镜的刻度尺上刻度的不规则性、不精确性和肉眼观察的视差性,得到的刻度值绝对误差和相对误差都相当大,从而使测量的硬度不准确,因此提出了一种基于增量式旋转编码器的测量压痕对角线的方法,可以完全消除因刻度尺所引起的绝对误差和减小因肉眼视差引起的相对误差。     

Fretting of Hardened Steel in Oil

To determine the effect of hardness on fretting wear, tests of AISI 4340 steel were made in an oil bath using a new machine designed to make fretting corrosion tests with a wide range of parameters. Hardness values from 258 to 743 Vickers were tested, the hardest specimen having a nitrided surface. The fretting action used, 0.005 in. reciprocating motion at pressures from 430 psi to 5840 psi, produced much less fretting than similar tests in air, with little or no oxide products resulting. The galled areas were measured for depth of pit and height of deposit with the results indicating some small effects due to hardness up to 460 Vickers. The nitrided specimens, however, produced smaller fretted areas and the roughening of their surfaces was shallow.     

On the workpiece setup optimization for five-axis machining with RTCP function

Nonlinear errors in five-axis machining process are caused due to the nonlinear motions of the rotational axes, which are inevitable. For the RT-type machine tool, the workpiece setup location on the working table has a direct effect on the nonlinear errors, thus there must be an optimal setup position which can reduce the nonlinear errors. Today’s five-axis machine tools are mostly equipped the with the RTCP (rotational tool center point) function, with which the NC program becomes independent from the workpiece setup. In this paper, we have focused on finding the optimal workpiece setup for the RT-type machine tool with RTCP function, more specifically, the Mikron UCP 600 five-axis machine tool in our lab. The kinematics of the machine tool is briefly analyzed. Based on that, the nonlinear error evaluation method with RTCP interpolation is derived. With this method, nonlinear errors can actually be considered as a function of the workpiece setup position. Then, the particle swarm optimization (PSO) is applied to find the optimal workpiece setup, in which a mutation operation is used since PSO traps into local optimum easily. The proposed optimal workpiece setup method is implemented and tested. Example results show that the optimal setup with least nonlinear errors can be found. Some interesting results also show that the nonlinear errors are not sensitive with the z component of the workpiece setup vector. The proposed optimization is nearly zero-cost and easy to both understand and implement, yet has a potential to reduce the nonlinear errors and thus to improve the accuracy of five-axis machining.     

维氏硬度试验压痕图的小波分析与自动计算硬度

介绍了维氏硬度测试原理；分析了采用经典的数字图像处理技术边缘分割算法对试验压痕边缘提取存在的局限，进而提出运用小波多分辨率理论分析试验压痕的取样信号，用最小二乘法拟合压痕边缘直线，从而提取显微硬度压痕边缘的新方法。研究表明，该方法实现了对显微组织维氏硬度试验压痕区域快速而准确地提取，并自动计算维氏硬度，所测得的硬度值和传统方法的测量值吻合。     

Influence of Tip Geometry on Nanoscratching

Using molecular dynamics simulation, we study the influence of the tip geometry on indentation and scratching. We focus on the specific case of an Fe (100) surface scratched in \([0{\bar{1}}{\bar{1}}]\) direction. Three indenter shapes—spherical, conical and Berkovich—are investigated; for the cone, the semi-apex angle \(\beta\) is varied systematically. For conical indenters, we find a clear dependence on the semi-apex angle \(\beta\): The friction coefficient decreases strongly with \(\beta\) in agreement with a simple analytical theory, while the hardness increases. For wider cones, the dislocation network under the groove increases in complexity. The pile-up produced outside the groove changes from a frontal to a lateral rim. The results for the Berkovich pyramid line up excellently with the cones if the traditional concept of an ‘equivalent cone angle’ is used. For the spherical indenter, however, we find deviations; it is not well described by its ‘equivalent cone angle.’ The sphere shows a smaller hardness and a higher friction coefficient than an equivalent cone. This finding quantifies the difference between blunt and sharp indenters in scratching.     

金属布氏硬度试验测量结果不确定度的评定

以碳钢硬度试验为例,对金属材料布氏硬度试验中的测量不确定度来源进行了分析,并对测量结果的不确定度进行了详细的评定。另外,着重研究了测量数学模型里的灵敏系数对各不确定度的影响。评定不确定度时,应考虑硬度计复现性所引入的不确定度。     

基于自适应模糊神经网络辨识的电液伺服系统L2增益设计

为克服电液伺服系统不确定性、非线性、估计误差和干扰等因素对系统稳定性和精度的影响，提出了基于自适应模糊神经网络辨识的电液伺服系统L2增益设计方法。用自适应模糊神经网络在线估计包括系统不确定性和非线性在内的未知动态特性，同时用增益自适应变结构补偿自适应模糊神经网络的估计误差，用系统L2增益设计方法抑制干扰对系统的影响，以期使系统对不确定性和非线性具有鲁棒性，而且从干扰到描述系统跟踪误差的评价函数的L2增益小于指定值。     

Machine tool calibration: Geometric test uncertainty depends on machine tool performance

In order to show a sufficient geometric performance, every machine tool has to be calibrated geometrically before it may come into operation. The geometric machine errors have to be identified. They can afterwards be compensated either mechanically or numerically in the machine control.Machine tools are usually calibrated geometrically by performing a sequence of different measurements to identify single errors such as squareness errors between linear axes, straightness errors, positioning errors etc.The uncertainty of such measurements is of course affected by the uncertainty of the measuring device under the given environmental conditions. Methods to describe such influences are widely known and applied.Other effects having an impact on the error parameters to be determined (e.g. squareness errors) are dependent on the performance of the machine tool under test. Neglected geometric errors, hysteresis and thermal drift affect the measurement result. Such effects may be much more important contributors to the overall test uncertainty than the measurement uncertainty of the measuring device.In this paper the problem of error interdependencies leading to a worse test uncertainty is explained. The occurrence of such effects is shown with exemplary measuring results. A method for estimating the overall test uncertainty even for complex measurements is introduced. The dependence of the test uncertainty on the geometric machine performance is explained.     

Stick–Slip Motion and Static Friction in a Nonlinear Deformable Substrate Potential

Nano-scale adhesive contact mediated by intermolecular van der Waals forces has become a typical fundamental problem in many areas. Interpretation and control of the strength and efficiency of the nano-scale adhesive contacts require a proper modeling considering the actual interfacial forces, the varying contact area, and clearance. In this article, the finite-element (FE) method is developed to model the nano-scale adhesive contact of elastic bodies with an adhesive pressure derived from the interatomic interaction Lennard-Jones potential, which permits numerical solutions for a variety of interface geometries. Compared with the analytical results from conventional Hertz, JKR, and DMT models, the validity of the FE model is verified. For nano-scale contact, the assumption of equivalent radius adopted in the Hertz model is initially investigated and proved to be improper for nano-scale adhesive contact due to the distribution variations of interfacial force caused by local contact geometry. Then adhesive contact behaviors of four typical nano-scale contact geometries inspired by tip shapes of bio-adhesive pads are investigated in detail, which are flat punch tip, sphere tip, mushroom tip, and empty cup tip. The simulation results indicate that the nano-scale tip geometry plays a dominant role on the pull-off strength. Within the investigated geometries, cup tip results in a highest adhesion efficiency followed by flat punch tip, sphere tip, and mushroom tip, respectively, which are highly geometry dependent and verified by former experimental results. The dominant effect is found coming from the contact area ratio of the adhesive area to the sticking area or the whole contact area. The FE modeling can serve a useful purpose in revealing the nano-scale geometry-based adhesion contact for surface topography design in MEMS to avoid stiction failure and for the artificial sticky feet in bionics to increase adhesion strength.     

三坐标测量机动态误差的建模方法

为了提高三坐标测量机的测量速度,缩短测量周期,分析了影响给定的三坐标测量机动态误差的因素。对三坐标测量机的具体和了分析,用电感测微仪进行了动态偏转角的测量,并推导出由动态偏转误差得到测头处的动态位移误差的方法。同时,对由导轨的直线度造成的误差进行了讨论。指出动态误差主要是由各构件绕气浮导轨连接处的偏转和各运动构件本身的弯曲变形造成挫理论上可以证明,在气浮导轨力矩刚度和横梁弯曲刚度已知的情况下,只要