Ultrasonic measurements as a probe of3He/4He phase separation in aerogels

We have used ultrasonic velocity and attenuation measurements to study the phase separation of³He/⁴He mixtures confined in a silica aerogel with a porosity of 87%. We used both shear and longitudinal sound and varied the frequency between 4 and 20 MHz. The superfluid transition is accompanied by a velocity increase due to decoupling and by a critical attenuation peak which increases with frequency. At the phase separation there are changes in the velocity and attenuation, and hysteresis on thermal cycling. We show some recent results and discuss how they relate to the phase diagram inferred from torsional oscillator and heat capacity measurements on helium mixtures in aerogels.     

The attenuation and phase velocity of ultrasonic third sound for optically smooth and roughened substrates

The attenuation and phase velocity of third sound have been measured for propagation on optically smooth and roughened substrates and for ultrasonic frequencies in the 20–200 kHz range. The attenuation for both kinds of substrates is found to be proportional to the frequency and have a magnitude that increases with the amount of roughening. The data are found to be inconsistent with a number of proposed attenuation mechanisms. The phase velocity is nearly independent of the frequency. Pulse wave shapes change substantially as the third sound propagates along a substrate surface.     

Ultrasonic Velocity and Attenuation in Epoxy Resin/Granite (Marble) Powder Composite

In this research, gamma radiation has been used to graft styrene and acrylic acid monomers onto marble (M) and granite (G) powder, with irradiation doses 30, 10 kGy, respectively. The grafted marble and granite powders were used as filler of epoxy composites. They added to an epoxy resin at 20, 60, and 100 wt% and then cured at room temperature. Ultrasonic velocities and attenuation measurements in epoxy composites at 4 MHz in the 25–300°C temperature range in addition to Fourier Transform Infrared (FTIR) analysis had been investigated. The ultrasonic compression wave velocity and the shear wave velocity measurements were performed using the pulse-echo technique, and then wecalculated elastic modulus, Young’s modulus, longitudinal and shear moduli, and Poisson’s ratio. In addition to attenuation at different temperatures of epoxy/granite composites, ultrasonic results indicated that the ultrasonic wave’s velocities V_L and V_s increased with the increase of (M, G) content and a linear relation was observed. Also, the attenuation of epoxy was stable and appeared to increase at temperature 385°C, while the addition M or G to epoxy composites increased the attenuation.     

High resolution ultrasound studies of UPt3 at very low temperatures

We have performed longitudinal sound velocity and attenuation measurements on a single crystal of UPt₃ between 5 mK and 700 mK. The very low temperatures reached in this experiment allow a better comparison to the theoretical predictions of the longitudinal sound attenuation for different gap states. We have also observed for the first time a significant dispersion of sound associated with the superconducting transition. Within the resolution of our ultrasonic measurements on this sample, we did not observe any manifestation of the recently reported specific heat anomaly around 18 mK¹.     

Nondestructive Characterization and Evaluation of Embrittlement Kinetics and Elastic Constants of Duplex Stainless Steel SAF 2205 for Different Aging Times at 425°C and 475°C

In this work, an experimental study was carried out to evaluate the potential of the ultrasonic technique, with ultrasonic velocity and attenuation measurements, to assess the heat aging effects on duplex stainless steel SAF 2205, at temperatures of 425°C and 475°C for time periods of 12 h, 24 h, 50 h, 100 h and 200 h, as well as in the as received state of the material. Velocity measurements were calculated for both longitudinal and transversal waves. The elastic constants, Young’s modulus and shear modulus, of the material were computed from the relationship between longitudinal and transversal velocities. For the ultrasonic attenuation, only longitudinal waves were considered. Despite the large scatter measurements, both ultrasonic velocity and attenuation increased with the heat aging time, particularly at 475°C. Thus, it may be concluded that the technique used is promising and provides relevant contributions to an accurate characterization of materials and evaluation of their mechanical properties in a non-destructive manner.     

Evaluation of grain refiners influence on the mechanical properties in a CuAlBe shape memory alloy by ultrasonic and mechanical tensile testing

This work carried out a non-destructive evaluation of grain size influence on the mechanical properties of a CuAlBe shape memory alloy with and without grain refiners. Ultrasonic signal processing, considering only the longitudinal velocity, was used for the non-destructive evaluation. Therefore, the average modulus of elasticity values found for the CuAlBe shape memory alloy was 45.7 GPa and 57.3 GPa with and without grain refiners, respectively. The corresponding values obtained by conventional mechanical tensile testing were equal to 43.2 GPa and 52.6 GPa, respectively. Additionally the mechanical tensile testing verified that the addition of grain refiners increases the stress of the alloy but has a slight effect on the alloy’s ductility. Thus, the modulus of elasticity and consequently the ultrasonic velocity, as well as the stress and strain values of CuAlBe alloy are fully dependent on its grain size. The ultrasonic analysis shows that this alloy is an excellent sound, vibration and mechanical wave absorber, presenting a high attenuation coefficient related to the wave scattering through the grains. In addition, the ultrasonic signal processing method used here confirms its main advantages of fastness and reliability.     

Characterization of solutionizing behavior in VT14 titanium alloy using ultrasonic velocity and attenuation measurements

VT14 titanium alloy (Ti–4.5Al–3Mo–1V) was subjected to a series of heat treatments consisting of solutionizing for 1 h at the selected temperatures in range of 923–1323 K at an interval of 50 K, followed by water quenching. Hardness and optical microscopy results are correlated with ultrasonic longitudinal and shear wave velocities and attenuation in these specimens. Ultrasonic velocities and hardness decrease with solution annealing temperature (SAT) in the 923–1123 K range. Beyond 1123 up to 1223 K, they increase slightly. Beyond 1223 K, ultrasonic velocities become constant, whereas hardness increases up to 1323 K. Ultrasonic attenuation exhibits an opposite behavior to velocity and hardness. Further, for the first time, authors have shown that ultrasonic velocity can be used to identify the β-transus temperature in this alloy. Because of non-monotonous variation of velocity and attenuation with solutionizing temperature, it was not possible to identify the SAT using any one of these parameters. Hence, a new parameter, ratio of normalized differential of ultrasonic attenuation to normalized differential of ultrasonic velocity (RNDAV) has been used, which is found to increase monotonously with SAT and hence enabling unambiguous characterization of SAT in solution annealed VT14 alloy.     

Broadband Laser-Ultrasonic Spectroscopy for Quantitative Characterization of Porosity Effect on Acoustic Attenuation and Phase Velocity in CFRP Laminates

This work aims at applying the method of broadband laser-ultrasonic spectroscopy for quantitative evaluation of the effect of isolated dispersed voids and additional extended interply delaminations on the acoustic attenuation and on the phase velocity in CFRP laminates. This method is based on the laser thermoelastic generation of broadband reference pulses of longitudinal ultrasonic waves in the specially designed source of ultrasound. The high-sensitivity piezoelectric transducer is used to detect these pulses propagating normal to the fiber plies in composite specimens. The laminate specimens investigated have different total porosity levels up to 10.5 % determined by the X-ray computer tomography. The resonance peak of the attenuation coefficient and the corresponding jump of the phase velocity are observed governed by the periodic layered structure of the specimens. The absolute maximum and the frequency bandwidth of the resonance attenuation peak depend on the total porosity level formed by the predominant type of imperfections, either of isolated spheroidal voids entrapped in epoxy layers or of extended interply delaminations. With an increase of the specimen’s total porosity dispersion of the phase velocity becomes noticeable in the low-frequency band before the resonance jump. The derived empirical relations between the total porosity level and the parameters of the frequency dependencies of the ultrasonic attenuation coefficient and of the phase velocity can be used for rapid quantitative characterization of the structure of CFRP laminates subject to different fabrication conditions.     

A nondestructive integrity test for membrane filters based on air-coupled ultrasonic spectroscopy

This work describes the application of an ultrasonic air-coupled characterization technique to membrane filters. Coefficient of transmission of sound at normal incidence through each membrane in the frequency range 0.55 MHz-2.4 MHz was measured. For all cases, at least one thickness resonance was observed. From these measurements density, velocity, and attenuation of ultrasonic longitudinal waves are calculated and compared to available filtration data such as water flux measurements and bubble point data, both provided by manufacturers. Results show that velocity of ultrasonic waves in membrane filters depends on the membrane grade and can be correlated to filtration properties; attenuation per wavelength is independent of membrane grade but sensitive to moisture content. Advantages of this technique over other conventional membrane tests are pointed out.     

纵波脉冲回波法和兰姆波法在表征薄层结构中的应用比较

介绍了两种常用的材料薄层超声表征方法——纵波脉冲回波法和兰姆波法。阐述了其基本原理，并结合实例比较了它们的应用情况、优缺点和适用条件等。纵波脉冲回波法简单易行，能够获得薄层厚度、声速和衰减等信息。但实验结果受薄层介质的声衰减和表面粗糙度影响较大，对探头的性能要求较高。兰姆波法主要用于表征薄板类材料，无需较高检测频率，可以测得板中纵波和横波的声速、板厚和板与板之间的结合特性等，检测精度较高。缺点是发射和接收探头之间的距离和倾斜角度需要严格控制，影响因素较多。     

An ultrasonic prospecting of shape-memory alloy behaviour under thermal charges

Thermomechanical models may be produced to describe the macroscopic deformations of shape-memory alloys educated to be deformed with special shapes as a function of temperature. To be accurate, these models need to take into account evolution of the microstructure via homogenization theories. So, the aim of this work was to provide all available information about phase transformations occurring in the grain structures from an investigation close to the microscopic scale. In this work, we have visualized grain structures of Cu–Zn–Al duplex alloys using acoustic microscopy. Evolution of phase transformations as a function of temperature has also been followed on these acoustic images with a spatial accuracy up to few micrometres. This observation of sample surface has also enabled estimation of grain baring due to phase transformations. Using the same experimental device, acoustic signatures have been taken on samples in complete austenic or martensitic forms to measure the speed of Rayleigh surface waves. Despite the use of a wide ultrasonic frequency range from 15–600 MHz, it seems that wave attenuation due to viscosity is important and disables velocity measurements by this method. Finally, using an acoustic echographic technique, we have correlated attenuation and velocity of longitudinal waves to the global phase transformation of heated samples. © 1998 Kluwer Academic Publishers     

仿生皮肤等效材料超声波测试方法的研究

为评定汽车安全碰撞实验模拟人的皮肤肌肉等效复合材料的力学特性,提出仿生皮肤等效材料的超声检测方法。通过测试仿生皮肤等效材料对超声波声速、衰减、散射和吸收率的变化,建立仿生皮肤等效材料力学性质与超声回波信号频率之间的关系模型,对仿生皮肤等效材料的弹性模量、组织特性、粘弹性和松弛模量进行等效性的分析与评定。对3种不同密度的仿生皮肤等效材料的声速、弹性模量和声衰减等参数进行了测算,结果表明:该测试方法正确可行,测试数据为仿生皮肤等效材料的设计合成、制备提供力学参数依据,对仿生材料的力学等效性能评定有着重要的参考价值。     

超声水浸法高精度测量玻璃材料声速的研究

材料的声速与其杨氏模量和密度有关,通过测量材料的声速可以评价材料的特性。相关研究表明,超低膨胀玻璃的声速是评价其热膨胀系数的关键参数,通过测量声速可以实现对超低膨胀玻璃热膨胀系数的间接无损测量。针对市售的超声声速测量仪器存在系统复杂且不易集成化的问题,结合高精度的数据采集卡设计了超声信号采集显示软件,并基于超声水浸脉冲反射法搭建了高精度的声速测量系统,系统结构简单,操作方便且较易集成化。采用该测量系统对制备的超低膨胀玻璃样品的声速进行了测量,结果表明该系统具有较高的声速测量分辨率,声速分辨率可达为0.2 m.s^-1,为使用超声声速法高精度测量超低膨胀玻璃的热膨胀系数奠定了研究基础。     

Ultrasonic velocity and attenuation measurements at the metamagnetic transition in UPt3

The longitudinal ultrasonic attenuation and velocity were measured on a single crystal of UPt₃ in a high magnetic field of up to 23T. Earlier ultrasonic measurements had seen a softening of the lattice as evidenced by a huge drop in the velocity at a field of 20T. Both the attenuation and velocity have been measured in field sweeps. Accompanying the large dip in the velocity is a large attenuation peak at this metamagnetic transition. Measurements were also done at several frequencies.     

Mechanical relaxation in simple molecular liquids from the liquid to the supercooled state

Attenuation and velocity of acoustic waves have been revealed at ultrasonic frequencies (2, 5 and 10 MHz) in some glass-forming liquids. The mechanical response has been studied following continuously the materials from the liquid to the supercooled state, using an experimental set-up developed to this purpose. A peak in the attenuation of longitudinal acoustic waves has been observed in a temperature region in which the liquids are supercooled. Correspondingly, the sound velocity shows a dispersion, increasing from liquid-like to solid-like values for decreasing temperatures. Both features develop above the calorimetric glass transition temperature (T_g). In the deeply supercooled liquids, nearly 10 K above their calorimetric T_g, also the propagation of transverse wave sound (which is a characteristic behaviour of solid-like materials) has been experimentally detected. Shear and longitudinal relaxation times are not decoupled in the time–temperature region investigated. Compared to the mechanical one, the dielectric relaxation studied as a function of temperature at the same frequency of the ultrasonic experiments shows a loss peak centred at the same temperature. Depending on the liquid investigated, the mechanical relaxation spectrum can be broader than the dielectric one, specially in the low temperature flank, suggesting that some dissipative processes at lower energies can contribute to the mechanical loss, even though they do not couple to the electric probe field.     

Ultrasonic attenuation in hcp 4He

The ultrasonic attenuation was measured for longitudinal sound waves in solid hcp ⁴He at frequencies of 5, 15, and 25 MHz from 0.25 to 3.5 K. Near melting, the attenuation is very small and in agreement with theoretical predictions. In most samples the attenuation rises gradually with falling temperature until a point is reached which approximately corresponds to the onset of a previously observed velocity anomaly. Then the attenuation rises more quickly and remains very large to the lowest temperatures measured. Two samples exhibit neither a steep rise in attenuation nor a velocity anomaly. A number of explanations for the large attenuation are considered.Research supported by grants from the National Research Council of Canada.     

Ultrasonic determination of the particle concentration in model suspensions and ice slurry

The development of ice slurry for refrigeration systems and the enhancement of its efficiency depend on an accurate control of the ice concentration. We present here an ultrasonic method capable to measure precisely the particle concentration in ice slurry. To calibrate the ultrasonic measurement, we first determine the sound velocity and attenuation in two model suspensions (glass beads/polyethylene glycol and polyethylene beads/vaseline oil) for different particle volume fractions. The experimental results show a good agreement with the predictions of the two-component models in the long-wavelength limit. Additionally, the sound attenuation reveals a clear signature of the aggregate formation in the nearly iso-dense suspension. We next conduct the measurement of the sound velocity in the polypropylene glycol ice slurry where the ice concentration changes with temperature. The ice concentrations extracted from our sound velocity measurements are well consistent with the values determined from the binary phase diagram.     

A novel ultrasonic transducer backing from porous epoxy resin–titanium–silane coupling agent and plasticizer composites

In this paper, a new composite for ultrasonic attenuation backing has been successfully fabricated from porous epoxy resin containing titanium (Ti), silane coupling agent and plasticizer composites. The effect of Ti particles on the network structure and mechanical properties of epoxy resin has been analyzed in detail. The ultrasonic parameters in epoxy composites have been measured by a conventional pulse-echo-overlap technique at a frequency of 1–5 MHz. The effect of Ti content and temperature on the longitudinal sound velocity and attenuation of epoxy resin composites were investigated. Precise in situ observations of the acoustic properties such as attenuation and acoustic impedance of epoxy composites are expected to be useful for ultrasonic transducer systems for new as well as for backing application with high attenuation.     

基于声发射技术的陶瓷基复合材料声速特性

基于Christoffel方程,运用复合材料刚度矩阵与弹性常数间的关系,将正交各向异性模型运用于2D-C/SiC复合材料的声学特性中,得到材料声速的表达式。通过循环加卸载试验测量了2D-C/SiC复合材料整个拉伸过程中不同应力水平处的声速变化,研究了声速对2D-C/SiC复合材料的损伤表征。研究发现,随着应力水平的不断增加,声速逐渐下降,2D-C/SiC复合材料损伤程度对声波在材料中的传播速度有较大影响;引入卸载模量和再加载模量,代替声速理论计算切线模量,理论结果与试验结果吻合良好,误差随载荷增加而增大;声波速度随2D-C/SiC复合材料损伤而发生衰减的关系,根据此衰减关系建立了基于声速的损伤表征量。      

(Nd0.75Na0.25)1-x(Nd0.5Ca0.5)xMnO3中电荷有序稳定性关系的超声研究

系统研究了（Nd0.75Na0.25）1-x（Nd0.5Ca0.5）xMnO3（x=0、0．25、0．5、0．75、1）单相多晶样品在低温下的电磁输运性质和超声特性．电阻和磁化率的测量表明所有样品均发生了电荷有序相变．随着钠掺杂量的增加，电荷有序相变温度（Tco）向低温移动同时低温端磁化强度增大，并且电荷有序态趋向于不稳定和短程化．超声纵波声速从室温开始随着温度的降低逐渐减小，在Tco之后声速急剧硬化．这种超声异常表明体系中存在着强烈的电-声子相互作用，该电-声子耦合来源于Mn^3＋的Jahn-Teller效应．对纵波模量软化部分的拟合显示，随着钠的掺入，反映Jahn-Teller效应大小的Jahn-Teller耦合能EJT变小．分析认为电荷失配效应是导致电荷有序被抑制和Jahn-Teller耦合能EJT变小的主要因素．