WC-Co硬质合金的弹性性能

综述了WC-Co硬质合金弹性性能的预测模型,并计算了硬质合金不同Co含量时的弹性性能参数值,并对不同的模型的预测值与文献中的测量结果进行了比较。采用引入WC晶粒邻接度C的Golovchan模型计算的WC-Co硬质合金的弹性模量值,相比Voigt-Reuss模型和Hashin-Shtrikman模型,更接近于实测值。而泊松比的值相对偏低,但可以采用Hashin-Shtrikman模型的泊松比上限确定泊松比的值。另外,给出了弹性模量的实验测定方法标准。这为硬质合金重要弹性参数值的确定提供了实验测定和理论计算的依据。  

TiB2和TiB弹性性质的理论计算

采用基于密度函数理论的赝势平面波方法和广义梯度近似对TiB2和TiB化合物的弹性性质和电子结构进行了理论计算,并用Voigt-Reuss-Hill方法计算得到多晶体的弹性模量和切变模量。结果表明：TiB2和TiB的弹性模量分别为599 GPa和443 GPa,切变模量分别为268.5 GPa和193.5 GPa,Pugh定律和泊松比等经验判据表明TiB2比TiB脆性更大;并从这两种化合物的电子结构对其弹性性质的差异进行了讨论。  

Ti-Nb合金β结构稳定性和弹性性质

采用基于密度函数理论的缀加平面波加局域轨道（APW＋lo）方法和超晶胞方法对Nb含量为6.25%～37.5%Nb（摩尔分数）的Ti-Nb二元合金的能量、电子结构以及弹性性质进行了理论计算,研究Nb含量对Ti-Nb合金的β结构稳定性和弹性性质的影响。结果表明,随着Nb含量的升高,Ti-Nb合金的β结构稳定性提高,正方剪切常数C＇以及弹性模量K、E和G呈单调增加。当Nb含量为9.87%时,正方剪切常数大于并接近于零,此时Ti-Nb合金的β结构稳定性最低,并具有最低的弹性模量。  

Mixed numerical–experimental identification of elastic properties of orthotropic metal plates

This paper compares results of three different methods to determine the in-plane elastic properties of sheet materials. Results obtained with standard resonant beam and tensile tests are used to assess a mixed numerical–experimental technique developed to determine the in-plane elastic properties of orthotropic plates from the resonance frequencies of rectangular plate samples (the so-called ‘Resonalyser’ technique). Test materials were selected on the basis of an expected low degree of elastic anisotropy in order to put the accuracy and sensitivity of the different techniques to assess anisotropic materials to a test. Therefore, aluminium alloy and stainless steel samples were prepared from hot-rolled plates, deliberately avoiding pronounced cold-rolling textures. The differences between the results obtained with the three experimental approaches are critically evaluated.In the case of very thin plates, the existing mixed numerical–experimental Resonalyser procedure succeeded in accurately identifying the elastic material properties. A slightly adapted procedure is proposed to extend the applicability of the Resonalyser procedure to thicker plates.  

Near field inversion method to measure the material properties of a layer

This study develops an in situ methodology that uses ultrasonic waves to measure the material properties of a layer. These material properties include the longitudinal and shear wave speeds, as well as the thickness of the layer. The unknown properties are determined by comparing measured experimental data with values obtained from a theoretical model. Emphasis is placed on the effectiveness of measuring both the in-plane, and the out-of-plane surface displacement components with a laser Doppler vibrometer. An inversion scheme compares (in the frequency domain) the experimentally measured data with data predicted using the theoretical model, and an error-function quantifies the difference between these values. Finally, a downhill-simplex algorithm is used to minimize this error-function and thus determine an optimum set of material properties.  

Ultrasonic non-destructive on-line estimation of the tensile stiffness of a running paper web

A new method for measuring the elastic properties of paper on-line in a paper machine by using ultrasound has been developed. The unique feature of the method is that a continuous stochastic ultrasonic signal is used for measurements, which is generated by means of a dry friction between a running paper web and a rigidly fixed friction head. The signals from the web are picked up by an array of air-coupled ultrasonic receivers, which have no mechanical contact with the paper web. The ultrasound velocity in the web is obtained by means of the correlation processing. By using advanced digital signal processing, the tensile stiffness index (TSI) of the running web is determined. From the sensor we get the TSI values both in the machine direction and the cross-machine direction.The on-line ultrasonic sensors have been installed on two different paper machines for more than two years. This paper describes the background of the method, as well as some experiences and applications from two mill installations.  

Detection of shock-wave-induced internal stresses in Cu-Al-Ni shape memory alloy by means of acoustic technique

1. The present results indicate that the stress-induced β₁→γ₁′ martensitic transformation occurs for an impact duration of 2 × 10⁻⁶ s. This time interval appears to be sufficient also for the subsequent deformation of the γ₁′ martensitic phase to occur.2. A structure memory effect has been found: Cu-Al-Ni austenitic crystals, shock-loaded at room temperature to induce γ₁′–martensite, recall during subsequent temperature-induced martensitic transformation the martensitic variant structure (elastic properties) formed under the shock loading.3. Elastic properties of quenched β₁′ and γ₁′ crystals of the Cu-Al-Ni system are extremely sensitive to the shock-wave loading. Mechanisms of these effects, as well as of the structure memory effect, include the generation of internal stresses due to the high elastic anisotropy of the martensitic phases. These internal stresses either change the distribution of martensitic variants or govern the formation of the martensitic variant structure during the temperature-induced martensitic transformation. The generation of high internal stresses by impact loading of the β₁′ martensitic phase is also detected by several anelastic phenomena.4. In contrast to elastic and anelastic properties, transformation temperatures are insensitive to the impact loading, pointing to the difference of structural elements responsible for the anelastic effects and for the interval and hysteresis of the thermoelastic martensitic transformation.  

Surface Brillouin scattering studies on vanadium carbide

Vanadium carbides in a range of carbon to metal ratio were investigated by surface Brillouin scattering (SBS) on the (100) and (110) surfaces. The surface acoustic wave (SAW) velocity varies with the crystal surface and direction and displays an approximately linear increase with the carbon to metal ratio. The tensor elastic constants of the samples were extracted and, while they vary significantly from the different carbon to metal ratio, the value of anisotropy ratio remains close to 0.8 for all samples. The directional dependence of the Young's modulus and shear modulus are obtained from the tensor elastic constants. In the directions chosen, both Young's modulus and the shear modulus reduce with decreasing carbon to metal ratio, with this behaviour being directionally dependent.  

Temperature dependence of single-crystal elastic constants of Mo(Si,Al)2

The temperature dependence of single-crystal elastic constants of Mo(Si,Al)₂ with the hexagonal C40 structure has been measured by the rectangular parallelepiped resonance method over the temperature range from room temperature to 1373 K. The silicide has the largest value of Poisson's ratio among transition-metal silicides with the C40 structure. This is interpreted in terms of the reduced directionality in atomic bonding due to the partial substitution of Al for Si atoms. The expression of the elastic constants on the basis of simple interatomic interactions cannot reproduce the elastic anisotropy of crystal with the C40 structure. The disagreement is considered to be a consequence of the occurrence of internal displacements during elastic deformation in crystals with the non-centrosymmetry.