单颗磨粒高速磨削45钢和20Cr钢的研究

进行单颗磨粒高速磨削45钢和20Cr钢的试验。研究塑性隆起、面积去除比率和切屑形态,以及速度、磨削截面积对单颗磨粒磨削力的影响。基于摩擦系数的数学模型和试验结果,获得单颗磨粒磨削的摩擦系数。讨论了速度、材料和磨粒对摩擦系数的影响。     

Coercive-force hysteresis of carbon steels during elastic cyclic tensile deformation

Dependences of the coercive force and mechanical stresses on cyclic tensile in the region of elastic deformation of steel samples with various carbon contents (Armco iron, 3, 8) are investigated. It is shown that the dependence of the coercive force on cyclic elastic tensile deformation is reversible for well-annealed samples. The dependence for plastically deformed steels has a hysteresis loop that is significantly determined by the carbon content and increases with an increasing degree of plastic deformation. It is assumed that the hysteresis of the coercive force as a function of elastic cyclic tensile deformations in plastically deformed carbon steels is caused generally by the appearance “free” carbon atoms, i.e., those not bound in carbide phases, which act as interstitial impurity atoms in the lattice of α-iron.     

Effective elastic constants of two-dimensional cellular materials with deep and thick cell walls

In order to analyse the elastic constants of cellular materials with deep and thick cell walls, finite element analysis using two kinds of unit cell approach (stiffness matrix method and compliance matrix method) is performed which is applicable to any orthotropic cellular materials. Comparison between results from the FEA, the theories presented in this paper and experiments of previous investigators indicate that the elastic constants of cellular materials with thick cell walls depend not only on the relative density but also on the joint stiffening effect. Approximate formulae under generalised plane strain conditions are also presented for the purpose of obtaining the effective elastic constants for cellular materials with deep and thick cell walls. A satisfactory agreement was found with experimental results obtained on a deep and thick cellular material. The results indicate that the previous models in which the wall of cellular materials is treated as a simple beam are not adequate to evaluate the effective elastic constants of cellular materials with deep and thick cell walls. In addition, considerable attention needs for the measurement of effective Young's modulus of square cellular materials in the two soft directions because it is strongly affected by misalignment errors.     

Measurement of elastic constants of limited-size piezoelectric ceramic sample by ultrasonic method

Measurement of material elastic constants for limited-size samples by ultrasonic method is described and validated. Based on acoustic microscope technology, the material elastic constants are determined by longitudinal wave and leak surface wave velocities simultaneously measured by developed ultrasonic system with a line-focus PVDF transducer. In this paper, the elastic constants of limited-size Cr₂O₃ doping on 0.2 PZN–0.8 PZT piezoelectric ceramic wafer sample are determined and the measurement errors are analyzed. The experimental results show this ultrasonic system can be used for measurement of material elastic constants for limited-size samples with high measurement precision, and the relative errors for Poisson’s ratio and Young’s module measurements are, respectively, less than 1% and 3%. It can satisfy the requirement of engineering and science research. Furthermore, it is suitable to measure elastic constants of both isotropic and anisotropic materials by ultrasonic method with help of developed ultrasonic system.     

Measurement of the hysteresis characteristics of pipe steels under elastic and plastic tensile strain

The changes in the shape and characteristics of the major and asymmetric hysteresis loops of low-carbon pipe steels under the action of elastic and plastic tensile strains were studied. The hysteresis loop segments that experienced the most considerable transformations under the tension of a material were determined. The possibilities of the inspection of tensile strains by the coercive return magnetization and the magnetic field corresponding to a fixed magnetization on the descending branch of a hysteresis loop were shown.     

An analytical study on prediction of effective elastic constants of perforated plate

In this study, the validity of the Eshelby-type model for predicting the effective Young’s modulus and in-plane Poisson’s ratio of the 2-dimensional perforated plate has been investigated in terms of the porosity size and its arrangement. The predicted results by the Eshelbytype model are compared with those by finite element analysis. Whenever the ratio of the porosity size to the specimen size becomes smaller than 0.07, the effective elastic constants predicted by finite element analysis are convergent regardless of the arrangement of the porosities. Under these conditions, the effective Young’s moduli of the perforated plate can be predicted within the accuracy of 5% by the Eshelby-type model, which overestimates and underestimates the effective Poisson’s ratios by 10% and 6% for the plates with periodically and non-periodically arranged porosities, respectively.     

磨削抛光45钢的试验研究い

针对传统抛光方式的缺点,设计了一种磨液射流磨削抛光装置。利用这种装置对45钢试件进行表面磨削抛光,获得了高的表面质量,且加工表面无加工变质层。通过正交试验证明,在加工时间不变的前提下,喷射角度是影响去除量的主要因素,而喷嘴直径对表面粗糙度影响较大,同时得出加工影响因素的主次关系及其较优水平组合。     

Measurement of the elastic constants of pressure balance materials using resonance ultrasound spectroscopy

To minimise the uncertainty in pressure measured with a pressure balance its pressure distortion coefficient should be determined with a sufficiently low uncertainty. The elastic constants of piston–cylinder assembly (PCA) materials are used in the calculation of the pressure distortion coefficient and thus are one of the uncertainty sources. In this work, the resonant ultrasound spectroscopy (RUS) is applied to determine the elastic constants of PCAs’ tungsten carbide (WC) materials. A validation of the RUS technique has been carried out by measurements on rectangular parallelepiped and cylindrical samples of fused quartz, steel D22S (30CrNiMo8) and a well-known WC material. The WC materials which are used in new 7 MPa absolute pressure balances aimed at a redetermination of the Boltzmann constant have been studied. The measurements demonstrate RUS to be suitable for determining the Young modulus (E) and the Poisson ratio (μ) with standard uncertainties as low as 0.03% and 0.05%, respectively. They show variations in E and μ of up to 4% and 2%, respectively, for different batches of nominally the same material. In a few cases, even for samples cut out of the same WC piece, material inhomogeneities have been observed in both RUS and the density measurements with variations in E and μ of up to 0.8% and 0.5%, respectively.     

小试件材料弹性常数超声测量系统的研制

本文针对小试件块体纳米材料力学性能测试的特殊需求，设计开发了一套小试件材料弹性常数超声精密测量系统。系统由线聚焦PVDF探头、四轴精密运动平台、NI PXI总线嵌入式控制器、超声脉冲产生／接收仪以及数字记忆示波器组成。系统基于声学显微镜技术，利用同时测定纵波和漏表面波波速来表征材料的弹性常数等，既适用于各向同性材料，又适用于各向异性材料。试验结果表明本测量系统工作良好，能够满足试验要求，为进一步评价小试件纳米材料制备工艺和表征纳米材料的力学性能奠定了基础。     

Macroscopic elastic constants of pure metal based on the interactions between microscopic particles

The research activities of the calculation of the elastic constants of metal are mainly focused on the elastic constants of crystal at the micro level. To the calculation of the macroscopic elastic constants of metal, although molecular dynamics method and quasicontinuum method can be used, but there are shortcomings in them, such as a large amount of computation and that the spatial scale of the study model is limited. Therefore, with a pure metal thin plate composed of a single layer of microscopic particles as research object, a new mechanical model is established after the interactions between microscopic particles of the thin plate are applied on the continuum mechanics model of the thin plate. According to this model, the calculation formulas for the microscopic elastic constants, which are the elastic constants of any triangle region in the model, are obtained. After the concept of the ideal micro structure is presented, the calculation formulas for the macroscopic elastic constants, the elastic modulus and the Poisson’s ratio of pure metal are obtained, where the Poisson’s ratio is the constant that is equal to 1?3. As an example, the elastic constants and the elastic modulus of pure copper are solved, where c11 is 175.811 GPa, c12 is 58.604 GPa, c33 is 58.604 GPa and E is 156.277 GPa, the rationality and the correctness of the model are verified. The model presented fully embodies the discreteness of the microstructure of solid, is a development to the continuum model, and is more suitable to reality, more simplified and more new to the study of the macroscopic elastic constants of pure metal.     

A new model to predict effective elastic constants of composites with spherical fillers

In this study, a new model to predict the effective elastic constants of composites with spherical fillers is proposed. The original Eshelby model is extended to a finite filler volume fraction without using Mori-Tanaka’s mean field approach. When single filler is embedded in the matrix, the effective elastic constants of the composite are computed. The composite is in turn considered as a new matrix, where new single filler is again embedded in the matrix. The predicted results by the present model with a series of embedding procedures are compared with those by Mori-Tanaka, self-consistent, and generalized self-consistent models. It is revealed through parametric studies such as stiffness ratio of the filler to the matrix and filler volume fraction that the present model gives more accurate predictions than Mori-Tanaka model without using the complicated numerical scheme used in self-consistent and generalized self-consistent models.     

Determination of elastic constants of additive manufactured Inconel 625 specimens using an ultrasonic technique

The nature of additive manufacturing (AM) processes prescribes direction-dependent properties of the final parts. The degree of material anisotropy is high     

弹性啮合与摩擦耦合离合器的实验研究

介绍弹性啮合与摩擦耦合离合器结构、测量方法以及实验数据的分析.试验表明该离合器有较好的启动性能,并介绍了一种新的弹性啮合与摩擦耦合结构离合器.     

The influence of biaxial elastic deformation on the coercive force and local remanent magnetization of construction steels

The influence of biaxial elastic tension-compression and tension-tension deformation on the coercive force and remanent magnetization of Cτ3 steel and 09Γ2C pipe steel cross-shaped specimens is studied. It is shown that coercive force grows monotonically with increasing load in the direction of compression under elastic tension-compression deformation and almost does not change under elastic tension-tension deformation. The local remanent magnetization decreases for all the considered types of biaxial elastic deformation. The possibility of using these methods for the evaluation of the stressed state of complexly deformed carbon steel products is discussed.     

45钢横向进给磨削淬硬数值模拟与试验研究

采用数值模拟与试验相结合的方法对45钢横向进给磨削淬硬进行研究,分析了磨削工件不同区域的表面淬硬效果。结果表明:在本试验条件下,淬硬层最高显微硬度为738.4HV,最大深度为0.56mm,达到了表面淬火的要求。但是切入区、中间区和切出区存在差异,且工件重叠区域在表面淬硬后随即发生了低温回火,得到回火马氏体组织。     

45调质钢切削表面粗糙度的试验研究

本文采用YT15硬质合金刀片对45调质钢的表面粗糙度进行了车削试验研究,探讨了主轴转速、切削深度、进给量对表面粗糙度的影响规律,总结出车削45调质钢的合理的切削参数。试验表明：当切削速度为200m／min左右、进给量为0．1mm／r、切深为0．3-0．5mm时,可进行高效高质的加工。     

亚温淬火温度对45钢组织和性能的试验研究

针对45钢淬透性低、淬火过程易出现开裂等缺陷,本文采用亚温淬火工艺对45钢进行试验研究.结果表明:在730～770℃亚温淬火时,随着淬火温度的提高,回火板条马氏体含量逐渐增多,分布趋于均匀,铁素体含量逐渐减少,硬度和抗拉强度逐渐增强.采用适当的亚温淬火工艺可有效提高45钢综合力学性能,拓宽其使用范围,为制作性能优异的零...     

基于双模式超声换能器的选择性激光熔化316L制件弹性常数无损表征研究

选择性激光熔化技术(SLM)可以快速成型任意结构的金属零件,但其制件的内部组织和材料性能与传统制件有着显著区别.基于双模式超声换能器对SLM 316L不锈钢制件的不同方向弹性常数及其分布进行表征研究.首先通过设计并制备高性能双模式超声换能器,搭建超声弹性常数分布测量系统.对SLM制备的316L不锈钢试样依次进行纵波和两...     

Gas sulphonitriding steels in a CS2 and NH3 atmosphere

The structure and wear resistance of steels treated in a gas sulphonitriding atmosphere, which contained NH₃ and 0.006% CS₂ in endothermically derived propane carrier gas, was investigated.The sulphonitrided layers offer favourable wear resistance relative to untreated steels.     

Experimental investigations on the microstructure and mechanical properties of sinter-forged Cu and Mo-alloyed low alloy steels

The present investigation pertains to the study of the mechanical properties and fracture behavior of sinter-forged low alloy steels containing copper (Cu) and molybdenum (Mo) as alloying elements. Elemental powders of atomized iron, graphite, molybdenum, and copper were mixed in suitable proportions using a ball mill, compacted in a 1,000 kN hydraulic press using suitable cylindrical die–punch combination and sintered at 1,000 ± 10°C in a muffle furnace for a period of 120 min in order to yield the alloy compositions (by weight) such as Fe–0.5% C, Fe–0.5% C–1% Cu, Fe–0.5% C–2% Cu, Fe–0.5% C–1% Mo, and Fe–0.5% C–2% Mo. The sintered cylindrical preforms were then subjected to hot upset forging to near theoretical density and subsequently machined off to standard size in order to carry out the mechanical tests such as hardness, tensile, and impact tests. Addition of Cu and Mo to the plain carbon steel has been observed to enhance the tensile strength as well as hardness of the sinter-forged alloys. The presence of Mo carbides in the microstructure of the alloys further reinforces this observation. The impact strength of this alloy has been observed to be reduced considerably due to the addition of the alloying elements.