弱正交异性材料残余应力测量的声弹性方法

为了适应工程材料的残余应力无损测量的要求,本文将横波和纵波声弹性相结合,建立适用於弱正交异性材料的平面声弹性残余应力测量方法,并应用该方法及自行研制的横波换能器对焊接试件的二维残余应力进行了测试。     

DAC加载下材料高压声速的激光超声测量技术

 设计并建立了可测量金刚石压砧（DAC）加载下材料高压声速的激光超声系统。该系统采用脉宽为6.3 ns的调Q激光器作为超声波激发光源,使用光纤位移干涉仪和速度干涉仪混合系统进行超声位移探测,不需要借助其它任何参数即可直接测量样品的高压声速和原位厚度。利用该系统,测量了2.6 GPa压力下铜样品的高压纵波声速和原位厚度,并给出了测量结果。     

应力波的激光产生和检测

应力波的激光产生和检测，是一个受到各领域专家关注的、在无损检测和应用力学等方面有着极大应用潜力和研究兴趣的新兴领域。针对其力学方面、实验技术和应用前景等，本文对有关原理、方法、技术和实用进行了简要的归纳与总结。     

Influence Of Zro2 on The Physicochemical Properties of Phosphate-Based Glasses and Glass Ceramics

Abstract

Phosphate-based bioactive glasses and their glass ceramics for 47P₂O₅– (30.5)CaO–(22.5 ? x)Na₂O–xZrO₂ for different ZrO₂ contents (x = 0, 1.5, 3.0, 4.5, and 6.0 mol%) were prepared through melt quenching and controlled heat treatment procedures. The amorphous nature of glasses and the presence of crystalline phases in glass ceramics were studied by means of X-ray diffraction (XRD) studies. The density, molar volume, ultrasonic velocities, attenuation, elastic constants, and microhardness of glass and glass ceramics were used to study the structural changes. The formation of hydroxyapatite layer on the surface of glasses and glass ceramics after immersion in simulated body fluid (SBF) was explored through XRD, Fourier transform infrared (FTIR), and scanning electron microscopy (SEM) analyses. The results indicate that the added ZrO₂ increases the crosslink density of glasses, resulting in network stability, and also induces the formation of an apatite layer on the surface of glasses.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Noise Shielding Using Acoustic Metamaterials

We exploit theoretically a class of rectangular cylindrical devices for noise shielding by using acoustic metamateriais. The function of noise shielding is justified by both the far-field and near-field full-wave simulations based on the finite element method. The enlargement of equivalent acoustic scattering cross sections is revealed to be the physical mechanism for this function. This work makes it possible to design a window with both noise shielding and air flow.     

Low frequency in situ metrology of absorption and dispersion of sound absorbing porous materials based on high power ultrasonic non-linearly demodulated waves

The present work is related to acoustic in situ free-field measurements of sound absorption in porous materials, such as cellular plastic foams, glass-wool or recycled felt materials. The emphasis is given towards fine metrology of absorption in view of potential industrial applications. A powerful ultrasonic array working at 40 kHz is used. It enables to measure absorption acoustical data down to 100 Hz due to the exploitation of the non-linear ultrasonic demodulation phenomenon in air. Fine measurements of acoustic absorption are compared to numerical predictions based on the “equivalent-fluid” model (when the squeleton frame is motionless), and to some measurements performed on a Brüel and Kjaer impedance tube. Dispersion curves are also measured and compared to the numerical predictions for some automotive felt materials which are compressed at various ratios. Data obtained with a dedicated portable instrument are also discussed for the same type of materials and configurations.     

Experimental investigation of reflection coefficients for lossy liquid-solid-liquid systems

The reflection coefficient for a bounded ultrasonic beam incident on a liquid-solid-liquid system (LSL) is studied. Systematic measurements were carried out to investigate the variations of the amplitude of the reflection modulus ∣R_LSL∣ with incident angle and parameter Fd (frequency-thickness of the plate). The experimental plots confirm the theoretical works of Claeys et al¹ and Bogy and Gracewski². It is shown that the attenuation of the media has a great influence on the variations of this coefficient as has been already mentioned in the literature, for liquid-solid configurations.     

Mechanical measurement of the parameters in a pseudo-stationary ultrasonic field in liquids

After recalling the formulae relating the energy density of a progressive wave with the sonic field parameters, the problem of deducing these parameters in a pseudo-stationary field is discussed. This field is produced in a ‘fixed force interferometer’ by two torsion balances; it is shown how to deduce from the radiation pressure, measured simultaneously at transducer and at reflector, the local pressure and velocity amplitudes, discussing the errors involved in treating pseudo-stationary fields as purely stationary.     

Residual stress determination in aluminium using electromagnetic acoustic transducers

The residual stresses in a shrink-fit specimen were measured ultrasonically, using shear-horizonal (SH) waves transmitted and received by noncontacting electromagnetic acoustic transducers. The presence of stress induces a small change in the velocity of the SH-waves. The difference in velocities of orthogonally polarized SH-waves (acoustic birefringence) was measured with a simple time-interval averaging system; this velocity difference can be related to the difference of principal stresses. The presence of material anisotropy (texture) in the specimen also causes relative velocity changes comparable to stress-induced changes. A simple method was used to remove the anisotropy-dependent component of the total relative velocity change, thereby allowing a determination of residual stress. This method consisted of measuring the birefringence in unstressed reference specimens and subtracting it from the birefringence measured at stressed locations. For the specimen used here, good agreement between theoretical and experimental values of stress was obtained.