根据压痕深度计算布氏硬度值的方法初探

指出了目前在许多关于硬度试验方法的标准和经典著作中都没有区分"压痕深度"和"装有压头的压杆位移"这两个不同的长度量。把装有压头的压杆位移当作压痕深度,对于洛氏硬度试验不会造成错误的结果;但把装有压头的压杆位移当作压痕深度计算压痕直径和布氏硬度值,则会造成明显的错误。提出了采用从压杆最大位移中扣除硬度计弹性变形得到的压痕深度计算压痕直径和布氏硬度值的方法,试验结果表明:这种方法计算得到的布氏硬度试验结果与采用光学系统测量压痕直径方法得到的结果相吻合;该方法兼具布氏硬度试验和快速布氏硬度试验的优点,可以既快速又准确地得到布氏硬度试验结果。     

较浅压入下针尖曲率半径对纳米压入硬度影响的比较研究

基于3种不同曲率半径压头针尖对熔融石英进行纳米压入,用原子力显微镜（AFM）直接法测得压头针尖的面积函数及针尖曲率半径。研究表明,在极浅压入条件下,压头曲率半径的变化会导致硬度值的测量误差,曲率半径越小的压头针尖随接触深度的变化会更快得到真实值;相同的压入深度,曲率半径小的压头针尖测得的压入硬度值比曲率半径大的测得的压入硬度值更接近其真实值。     

较浅压入下针尖曲率半径对纳米压入硬度影响研究

基于3种不同曲率半径压头针尖对熔融石英进行纳米压入,用原子力显微镜(AFM)直接法测得压头针尖的面积函数及针尖曲率半径。研究表明,在极浅压入条件下,压头曲率半径的变化会导致硬度值的测量误差,曲率半径越小的压头针尖随接触深度的变化会更快得到真实值;相同的压入深度,曲率半径小的压头针尖测得的压入硬度值比曲率半径大的测得的压入硬度值更接近其真实值。     

布氏硬度值与维氏硬度值之间的关系

大家知道,维氏硬度试验法中之所以规定采用正四棱锥体,两相对面夹角为136°的金刚石压头,主要是为了使维氏硬度值尽量接近布氏硬度值。用维氏压头以任何载荷压人试件表面其压人角~*均为44°,即保持几何相似。因此,在这种情况下.不同材料的维氏硬度值可相互比较,同种材料的维氏硬度值相同。依 GB 231—63《金属布氏硬度试验法》规定,“试验后压痕直径的大小应在0.25D相似文献   

硅橡胶压磁复合材料力学性能纳米压痕实验研究

通过纳米压痕测试技术对非晶Fe73.5Cu1Nb3Si13.5B9/硅橡胶压磁复合材料薄膜的力学性能进行了研究,讨论了加载速率、保载时间、峰值载荷等试验参数对模量和硬度测试结果的影响.进一步分析了纳米压痕实验表征非晶Fe73.5Cu1Nb3Si13.5B9/硅橡胶压磁复合材料薄膜蠕变行为的可行性,通过合理确定压痕蠕变实验参数,获得该材料的蠕变应力指数.结果表明:相对峰值载荷,加载速率对测试结果影响更为显著,而保载时间对硬度和模量测试结果几乎没有影响.     

金属布氏硬度试验的测量不确定度评定

金属布氏硬度试验是用较大直径球体压出较大的压痕 ,用压痕表面面积与试验力之比计算出硬度值。该方法测出的硬度值比较稳定、精度高、操作简单。试件的制备较其他力学试样和硬度试样容易。试验误差来源于试验力、压头、压痕测量装置、试样、试验力保持时间等 ,评定测量不确定度以知晓试验结果的可信度。1　试验方法1 1　原理将一定直径球体压入试样表面 ,保持一定时间后卸除试验力 ,用压痕表面面积与试验力之比计算出硬度值 ,即 :ＨＢ =ＦＳ =ＦπＤｈ=2ＦπＤ(Ｄ -Ｄ2 -ｄ2 )式中　Ｆ为试验力 ,Ｎ ;Ｓ为压痕表面积 ,ｍｍ2 ;Ｄ为球体压头…     

壁厚小于等于3mm薄壁管的布氏硬度测定

在对壁厚小于等于3mm的薄壁管进行布氏硬度测试时发现测试值波动较大。通过硬度试验得到了薄壁管外壁不同深度的布氏硬度值,通过金相检验得出测量深度对布氏硬度有较大的影响,造成该影响的主要原因在于钢管外壁存在脱碳层。     

Li_2O-Al_2O_3-SiO_2微晶玻璃超光滑表面纳米硬度实验研究

介绍了纳米压痕技术的原理和方法.采用三角锥形Berkovich金刚石压头对Li2O-Al2O3-SiO2微晶玻璃的超光滑表面(Ra=0.079 nm)进行了纳米压痕实验.结果表明,当载荷低于300 mN时,微晶玻璃表现出延性特性.此外,在不同的载荷条件(20 mN~300 mN)下微晶玻璃的硬度和弹性模量存在较大的差异,分析其原因分别是纳米压痕的尺寸效应和材料发生了塑形变形.通过将实验得到的微晶玻璃的纳米硬度值与传统计算方法得到的硬度值进行比较,发现传统方法得到的硬度值较大,其原因是传统硬度计算方法忽略了材料的弹性恢复.     

基于声卡及LabVIEW软件的蠕变特性测试系统设计

设计了一种新型包装材料蠕变试验测试系统,采用声卡作为数据采集设备,厚度变化量即位移,通过位移传感器输入给V/F转换器,可得到一系列的频率值。声卡将这些频率值采集到计算机中,通过LabVIEW编程,就可得到材料的应变-时间曲线。这种新的测试系统可使得包装材料蠕变特性的测试更加智能化和信息化。     

硅橡胶压磁复合材料力学性能纳米压痕实验研究

通过纳米压痕测试技术对非晶Fe_73.5Cu₁Nb₃Si_13.5B₉/硅橡胶压磁复合材料薄膜的力学性能进行了研究, 讨论了加载速率、 保载时间、 峰值载荷等试验参数对模量和硬度测试结果的影响。进一步分析了纳米压痕实验表征非晶Fe_73.5Cu₁Nb₃Si_13.5B₉/硅橡胶压磁复合材料薄膜蠕变行为的可行性, 通过合理确定压痕蠕变实验参数, 获得该材料的蠕变应力指数。结果表明: 相对峰值载荷, 加载速率对测试结果影响更为显著, 而保载时间对硬度和模量测试结果几乎没有影响。     

Determination of creep parameters from indentation creep experiments: a parametric finite element study for single phase materials

Abstract

This paper explores the possibilities of determining creep parameters for a simple Norton law material from indentation creep testing. Using creep finite element analysis the creep indentation test technique is analysed in terms of indentation rates at constant loads. Emphasis is placed on the evolving stress distribution in front of the indenter during indentation creep. Moreover the role of indenter geometry, size effects and of macroscopic constraints is explicitly considered. A simple procedure is proposed to translate indentation creep results into constitutive creep equations for cases where the dimensions of the tested material are significantly larger than the indenter. The influence of macroscopic constraints becomes important when the size of the indenter is of the same order of magnitude as the size of the testing material. As a striking example for size effects and for macroscopic constraints the indentation creep process in a thin film is analyzed. The results contribute to a better mechanical understanding of indentation creep testing.     

Indentation creep

Abstract

From the hot hardness test, information can be obtained concerning the time dependent flow, or creep, of the material beneath the indenter. Analysis of these data for selfsimilar indentation (i.e. indentation using a pyramid or cone) leads to equations from which the power law creep exponent and activation energy for creep can be derived, within limits imposed by the approximations of the method. The technique is used to analyse hot hardness data for metals and ceramics, drawn from a number of sources.

MST/1484     

Self-Similarity Simplification Approaches for the Modeling and Analysis of Rockwell Hardness Indentation

The indentation process of pressing a Rockwell diamond indenter into inelastic material has been studied to provide a means for the analysis, simulation and prediction of Rockwell hardness tests. The geometrical characteristics of the spheroconical-shaped Rockwell indenter are discussed and fit to a general function in a self-similar way. The complicated moving boundary problem in Rockwell hardness tests is simplified to an intermediate stationary one for a flat die indenter using principle of similarity and cumulative superposition approach. This method is applied to both strain hardening and strain rate dependent materials. The effects of different material properties and indenter geometries on the indentation depth are discussed.     

Nanotribologie: Messung von mechanischen Eigenschaften im Sub-Mikrometer-Bereich

Hardness of a material describes the resistance of a material under indentation by a solid body. The vickers hardness [1] is determined by loading a diamond pyramid with a known force that is in contact with a specimen. The length of the diagonal of the remaining indent is used to calculate the contact area. The ratio of force and contact area is the vickers hardness. The abilities of modern technique of measurement replace the optical analysis of each indent by calculating the hardness from force and displacement recorded during the indent. Nano-hardness measurements now can be used to determine the mechanical properties of thin films and structures in the range from less than 10 nm to 1μm. Hardness can be measured with very small indentations, which could not be analyzed according to vickers. Time dependent properties as creep and viscose flux of material can be checked on sub-micron scale. The technique of nano-hardness measurements is comparable to the universal hardness test [2] for metals, whose minimum indentation depth of h = 0.2 μm still is too big for many applications. Combined with an atomic force microscope (AFM) the presented technique is capable image the area of interest before and after testing. Mechanical properties like friction-constants and wear can be measured quantitatively. The indenter can be used as a micro-machining tool with high precision as well.     

基于纳米压痕测试的超细晶Si_2N_2O-Si_3N_4陶瓷室温蠕变特性

目的陶瓷材料由于其固有硬脆性,难以利用传统单轴拉伸与压缩实验测试其蠕变性能,而纳米压痕测试技术对试样形状尺寸没有特殊要求,因此利用纳米压痕测试技术研究Si2N2O-Si3N4超细晶陶瓷的室温蠕变性能。方法针对1600,1650,1700℃条件下烧结制备的Si2N2O-Si3N4超细晶陶瓷,采用纳米压痕技术测试材料在最大载荷分别为5000,6000和7000μN条件下的载荷-位移曲线,并通过拟合计算获得了3种材料室温蠕变应力指数。结果 3种材料均呈现明显的加载效应。结论研究表明,在相同载荷下,压入深度和蠕变位移都随着材料烧结温度的升高而增大,且相同材料的蠕变应力指数,随着保压载荷的增大而减小。对比分析发现,在1600℃条件下烧结制备的Si2N2O-Si3N4超细晶陶瓷,晶粒细小均匀,晶界数多,室温下表现出较强的蠕变性能。     

Dynamic nanoindentation testing for studying thermally activated processes from single to nanocrystalline metals

Nanoindentation experiments are widely used for assessing the local mechanical properties of materials. In recent years some new exciting developments have been performed for also analyzing thermally activated processes using indentation based techniques. This paper focuses on how thermally activated dislocation mechanisms can be assessed by indentation strain rate jump as well as creep testing. Therefore, a small overview is given on thermally activated dislocation mechanism and how indentation data from pointed indenters can be interpreted in terms of uniaxial macroscopic testing. This requires the use of the indentation strain rate as introduced by Lucas and Oliver as well as the concepts of Taylor hardening together with Johnson expanding cavity model.These concepts are then translated to nanoindentation strain rate jump tests as well as nanoindentation long term creep test, where the control of the indenter tip movement as well as the determination of the contact are quite important for reliable data. It is furthermore discussed, that for a steady state hardness test, the interpretation of the hardness data is straightforward and comparable to macroscopic testing. For other conditions where size effects play a major role, hardness data need to be interpreted with consideration for the microstructural length scale with respect to the contact radius.Finally strain rate jump testing and long term creep testings are used to assess different thermally activated mechanisms in single to nanocrystalline metals such as: Motion of dislocation kink pairs in bcc sx-W, Grain boundary processes in nc-Ni and ufg-Al, and the Portevin-le Chatelier effect in ufg-AA6014.     

Indentation creep measurements using a Rockwell hardness tester

A Rockwell superficial hardness tester has been used to continuously monitor hardness under load with time. An analysis of the Rockwell test, that showed the relationship between the measured parameters and the on-load hardness and elastic recovery has been quantitatively verified.Low homologous temperature, high stress, indentation creep in the macrohardness range has been measured for aluminium, copper and mild steel, but was not detectable for brass and silver steel. The stress relaxation was no more than 10% and appeared to follow an exponential decay to an equilibrium value. The difference between normal uniform tensile creep and indentation creep, and explanations for the latter, have been discussed, and the measured relaxation time has been related to a ratio of elastic and creep indentation material constants.Bearing in mind the world-wide availability of Rockwell hardness testers, it is suggested that this extension to creep testing, and possibly fatigue testing, may be a useful development for industrial non-destructive quality control and specification checking of materials and components.     

Step by step building of a model for the Berkovich indentation cycle

The indentation cycle obtained from hardness testing of material has two singular points. The first one is the right end of the definition interval of loading/unloading curves; it corresponds to the cycle tip and poses no difficulties for mathematical analysis. The second one is the latest contact point between the material and the indenter tip in phase of withdrawal, it is located inside the interval of definition, more towards the left- or the right-hand side depending on the elasticity degree of the material. This second point is impractical for the analytical modelling of the cycle as the unloading curve loses there all mathematical properties of derivability and differentiability.This difficulty induced a tendency for empirical models built from experimental results that are, like any empirical laws, affected by some lack of precision. It also led to an intense focusing on the unloading curve to which main nanomechanical and structural properties have been connected, forgetting sometimes the loading curve and the valuable information it can provides.In this article, we work out an analytical model to represent the two curves of the indentation cycle as accurately as possible. In this step by step modeling we use functional analysis and force the modelling curves to fit the interval of definition, the concavity direction and the materials energetic properties.     

A comparison of three microindentation hardness scales at low and ultralow loads

Indentation hardness tests were performed on thick, fine-grained, electro-formed deposits of copper and nickel using Knoop, Vickers, and Berkovich indenters. The latter type of indenter was used for shallow penetrations (85–1750nm), and results are reported in terms of nanoscale hardness (NH) numbers. Knoop and Vickers indenters were used with applied loads of between 0.15 and 0.98 N, and at the lowest load, produced indentation depths comparable to the larger ones obtained with the Berkovich indenter. The NH numbers became very sensitive to penetration depth when the penetration depth was less than certain critical values. NH numbers for Cu and Ni were higher than those for Knoop and Vickers testing at comparable penetration depths. Applying indenter area function corrections to calculate hardness numbers (i.e., considering projected area versus facet contact area) resulted in a closer correlation between microhardness and nanohardness scales; however, changes in the tip shape because of wear or other imperfections can lead to inaccurate calculation of NH numbers at the lowest loads. Results also suggest that the interconversion of lowload hardness numbers from one scale to another can be material-dependent.     

Microhardness studies of chain-extended PE: II. Creep behaviour and temperature dependence

The variation of hardness with indentation time has been investigated for chain-extended polyethylene (PE), other PE samples crystallised under different conditions and paraffins. Hardness is shown to decrease with indentation time for all the samples investigated according to a power-law. Chain-extended PE, produced by high pressure crystallization or annealing, flows at the lowest rate under the indenter of all the PE samples considered. On the other hand, paraffins creep at the highest rate. Creep behaviour depends markedly on the crystal thickness of the material. The mechanical properties at long indentation times seem to be determined primarily by the deformation modes of the crystals. The temperature dependence of hardness and that of the creep behaviour has also been investigated. In chain-extended PE, the softening of the sample and the higher rate of creep with increasing temperature are discussed in terms of the thermal expansion of the unit cell.