Ultrasonic Backscattering in Cubic Polycrystals with Ellipsoidal Grains and Texture

An ultrasonic model for backscattering from polycrystalline microstructure is developed for polycrystals with uniaxial texture and elongated cubic crystallites. The uniaxial texture or crystallographic orientation of the grains is described by a modified Gaussian orientation distribution function (ODF) with a texture parameter. Macroscopically such a textured polycrystalline medium exhibits hexagonal symmetry. The preferred texture direction and elongation are independently defined in a global system. The dependence of backscattering coefficients and their directional ratios on both texture and grain anisotropy are discussed. Attenuation coefficients in the high frequency range for arbitrary wave propagation direction are obtained and then the ratios in the three axis directions are studied. The model is compared with experimental data available in the literature for Al rolled alloys and shows good agreement when accounting for both texture and grain anisotropy effects.     

应力波在基桩中的传播特性

将基桩简化为一维弹性杆，研究了位移波和应力波在不同类型的基桩中的传播特性。同时，本文分析了位移波和应力波在固定端、自由端和弹性支承端的反射特点。在固定端，位移为零而应力加倍；在自由端，应力为零而位移加倍。通过对应力波在基桩中的传播特性的分析，不仅有利于提高基桩动测的理性认识，而且为实测响应的解释和参数的估计提供了较为严格的理论依据。     

Texture Analysis for Flaw Detection in Ultrasonic Images

In this paper, we present two approaches for flaw detection in TOFD (Time of Flight Diffraction) images based on texture features. Texture is one of the most important features used in recognizing patterns in an image. The paper describes texture features by two methods: Multiresolution analysis such as wavelet transforms and Gabor filters bank. The two-dimensional wavelet transform is used to decompose the input image into a multiresolution framework. The textural statistical parameters are used to allow the choice of the decomposition channel. The Gabor filter is a Gaussian kernel function modulated by a sinusoidal plane wave. All Gabor filters can be generated from one mother wavelet by dilation and rotation. These filters represent an appropriate choice for tasks requiring simultaneous measurement in both space and frequency domains. The most relevant features are optimized by Principal Components Analysis (PCA) and used as input data on a Fuzzy C-Mean clustering classifier. We use two classes: ‘defects’ or ‘no defects’. The proposed approach is tested on the TOFD image achieved in an industrial field.     

Optimization of SAW-type Surface Wave Ultrasonic Sensors for Ultrasonic SHM

Surface acoustic waves (SAW) are particularly suited for effectively monitoring and characterizing a structure’s surfaces (condition of the surface, coating, thin layer, micro-cracks, etc.), and in some cases it is necessary to permanently keep the sensors on the structures to enable continuous monitoring. This article focuses on the optimization of SAW-type interdigital sensors (or IDT sensors for InterDigital Transducer) because they can largely address this issue. Initially, the ability of piezoelectric materials (lead zirconate titanate [PZT] and Niobate de lithium) to generate SAW is studied by modeling. Then a design of an IDT sensor is defined and optimized for the generation of SAW on a substrate. Parameters such as electrode’s periodicity, thickness of piezoelectric plate, and type of contact between the plate and the substrate, are studied. Finally, experimental results are compared with those obtained by modeling.     

钢锻件的超声波纵波手动检测工艺的优化

钢锻件超声波手动检测时,其工艺类似钢板纵波检测,但锻件厚度较大,不易确定其缺陷位置,也不易确定其当量。本文对此工艺进行了优化：包括对超声波检测仪器、试块、探头的选择、直探头偏离的测定、检测时机和表面准备、方向、灵敏度的确定校准和复核、手动扫查方法、灵敏度补偿、缺陷当量确定、记录和评级等。     

拉深中织构系数对立方晶粒正交板材制耳的影响

板材在冲深过程中由于材料本身的各向异性而引起制耳,这种情况使得材料加工中多一道工序,而且造成材料的浪费,增加成品的造价.引入取向分布函数和织构系数,说明正交板材的各向异性仅与织构系数c004、c204、c404有关,建立正交板材冲深过程中相对径向应变与织构系数的关系式,定量说明制耳与织构间的关系.计算了几种典型织构的相对径向应变,并通过调整各织构组分的比例,达到最小制耳的比例.     

Ultrasonic Guided Wave NDT for Hidden Corrosion Detection

An experimental study of hidden corrosion detection by using ultrasonic guided waves is presented combined with a BEM numerical simulation. Both corrosion simulation specimens by machine cutting and real corrosion specimens by electrochemical processing were used in the investigation, with a range of corrosion depths from 0.02 to 0.4 mm (1.5 to 20% of the original plate thickness). Various wave modes were subsequently generated on these specimens to examine the implications of thinning on mode cutoff, group velocity, and transmission and reflection amplitudes. The transmission and reflection of guided waves upon entering the corrosion zone were simulated by a hybrid BEM calculation that combines a normal mode expansion technique of Lamb waves for far fields with the boundary element representation for the scattered near fields. A quantitative technique for hidden corrosion depth with guided waves is developed based on a frequency compensation concept. The estimated depth of the real corrosion by this method shows good agreement with that by an optical microscope.     

反向泵浦光纤喇曼放大器中双重瑞利散射噪声的抑制

研究了反向泵浦光纤喇曼放大器中泵浦和信号和求解方法，并且分析了双重瑞利散射噪声的特性，提出了在考虑反向喇曼光放大作用时，双重瑞利散射噪声的表达式。给出了在加入光隔离器进行抑制后，双重瑞利散射噪声的计算方法，并进行了模拟分析，得出了放置光隔离器的最佳位置。     

Study of Shear Ultrasonic Waves Propagating in Materials under Static Uniaxial Loadings

Abstract: Non‐destructive evaluation of applied loadings level in mechanical components and structures constitutes a versatile tool to predict the behaviour of their materials in engineering industries and check services. Ultrasonic non‐destructive techniques stand advantageously to allow predictions and diagnosis where other measurement methods are difficult or not possible. For analysing the effects of static uniaxial loads, the present work relates to the modification of waveforms of ultrasonic shear waves propagating in statically loaded materials. To predict the behaviour of waveforms of shear ultrasonic waves propagating in media under stress, an analytical method is proposed. The simulated waveforms are reconstructed by using parameters from an experimental signal measured on specimens free of any loading. Assuming the hypothesis of progressive ultrasonic plane waves and taking into account the elastic deformation and the stressed ultrasonic velocity, the time of flight calculation allowed the simulation of shear waveforms for each applied stress. To validate this method, some ultrasonic measurements have been carried out. A linearly polarised shear wave transducer is used for probing C35 steel and 2017A (AU4G) alloy samples of known macroscopic properties. Simulated and measured ultrasonic waveforms are partially in good agreement, in particular for the extra delay effect induced under compressive and tensile elastic loads.     

一种用于化纤丝饼包装的超声波封膜系统

目的完成塑料薄膜在包裹丝饼前的焊接工作。方法设计一种超声波封膜系统,阐述系统结构及工作原理,并分析塑料薄膜焊接质量的影响因素。结果针对化纤行业的特殊使用环境,结合了理论分析,确定了系统的焊接条件。结论该系统经实际应用,运转良好,具有推广价值。     

An Assessment of Joint Rigidity with Ultrasonic Wave Energy

A modular satellite design has been proposed in order to enable rapid deployment of satellites. The design would allow panels with common functions to be manufactured and tested long before a new satellite is needed. Once the satellite is assembled, a quality assessment of the connections between panels would need to be performed before the craft is deemed flight worthy. This paper reports on an investigation on the feasibility of using transmitted wave energy for joint rigidity assessment. The experimental setup and methods will be presented. Experiments were conducted on a joint between two aluminum plates consisting of a dry aluminum-to-aluminum connection, similar to possible panel-to-panel connections that could be used as part of a modular satellite design. Comparisons were made between wave energy transmission and a mechanical assessment of the joint rigidity. Results show excellent correlation between joint rigidity and energy transmission, demonstrating the feasibility of the using wave energy transmission amplitudes to inspect metal-to-metal dry connections.     

双向行波式声光驻波调制器

提出了一种新型的声光驻波调制器，即双向行波式声光驻波调制器，建立了数学模型，进行了模拟计算，并从理论上证明了其衍射光的振幅和光强的表达式安全等效于反射式的声光驻波调制器，利用中心频率为５０ＭＨｚ的器件，测得其对衍射光强的调制频率两倍于声频，并随时间做周期的变化，其带宽Δω＝７ＭＨｚ，远远大于驻波器件；而且从对调制光的调制度的测试结果来看，较易获得对光强具有大的调制度的调制器件。     

Ultrasonic Beam Models for Angle Beam Surface Wave Transducers

ABSTRACT

Explicit three-dimensional (3D) point source and multi-Gaussian beam models are obtained for the Rayleigh waves generated by a surface wave angle beam transducer using an angular plane wave spectrum approach. Simulations show that the multi-Gaussian surface wave beam model agrees well with the point source model while being computationally more efficient. The theoretical predictions obtained with the models are also compared to the experimental measurement results where good agreement with the models is found for both on-axis and off-axis field comparisons.     

弹性波主动控制中LMS算法的最佳收敛系数问题研究

对扭转弹性波的主动控制系统以及LMS算法进行了描述。通过对直轴中扭转弹性波主动控制的仿真计算，讨论了LMS算法中的收敛系数对控制系统收敛时间的影响。重点讨论了弹性波控制中误差传递途径相对于主激励源的时间延迟与收敛系数以及收敛时间的关系，并回归出最佳收敛系数与延迟时间之间的倒数关系。同时通过对期望信号和误差信号当量传递函数的研究，从理论上确定了最佳收敛系数与延迟时间的关系，两者的研究结果是一致的。     

A Method for Accurately Measuring the Vertical Electric Field Strength of a Propagating VLF Wave

Ideally, the vertical electric field strength of a propagating VLF wave can be measured by observing the terminal voltage of a short dipole antenna placed in the field; but, in applying this principle a number of practical difficulties are encountered. Methods of overcoming these difficulties have been studied using a working-model field-strength meter of convenient dimensions. Such a device can be calibrated with reference to standards of voltage and length and, hence, offers a fundamental advantage over the use of vertical antennas and ground screens. It also provides an alternative to the common practice of estimating the electric field by measuring the associated magnetic field and applying a conversion factor. Evidence is presented to indicate that this latter method may sometimes be subject to experimental or interpretational difficulties. Error analysis shows the present working model is capable of measuring VLF field strengths to an accuracy of about 5 per cent.     

仿金镀中超声波的作用

超声波在化学镀尤其是仿金镀方面对操作参数、镀层质量作用很大,但其应用报道甚少.为了找出超声波在化学镀中的一般规律,揭示其对仿金电镀中化学镀镍及Cu2+,Zn2+和Sn2+的沉积机理,考察了超声波对仿金镀活化、化学镀镍、仿金镀电镀过程等各阶段多种因素的影响,包括活化工艺、pH值、电流密度、还原剂用量、配位剂用量等;优化了试验条件.结果显示,仿金镀工艺中引入超声波,降低了施镀的温度,提高了仿金镀的沉积速率.最后详细研究了超声波所产生的超声空化等对沉积速率、镀层质量以及仿金镀其他过程的作用机理.     

脉冲波声场的数值计算与测试研究

针对超声检测中影响缺陷定量准确性的声场问题进行了深入讨论,研究了脉冲波声场的计算方法,设计了相应的计算软件并绘制出实用换能器声轴线上的声压分布曲线,分析了不同材料和厚度的采样回波对频谱的影响,比较了连续波声场和脉冲波声场的分布特性及异同点。对脉冲波声场的测试结果表明,数值计算和实测结果有较好的一致性。本研究结果为提高超声检测中缺陷定量的准确性和科学性提供了依据。     

超声波辅助扩孔对氧化铝模板结构的影响

在0.3mol/dm3的草酸溶液中,采用二次阳极氧化法制备多孔氧化铝模板,研究了阳极氧化后的扩孔处理对多孔膜形貌和结构的影响.SEM和FE-SEM结果表明,经20min超声波扩孔处理后,多孔氧化铝模板纳米孔的结构更加趋于规则,表观孔径从30nm增大到70nm,其扩孔效果较常规扩孔方法更为明显.超声波扩孔时间增加到40min后,多孔膜孔径扩大至100nm,但某些区域的纳米孔壁已被部分溶解.在一定的电压范围内,随着电压增加,经超声波扩孔后的多孔氧化铝膜孔径增大,有序度有较大提高.     

可测速的智能超声波液位仪

利用一对超声波传感器，一个安置在封闭罐外的底部，用来测量罐内液体的液位，一个安置在罐外的侧壁上，用来测定罐内液体中超声波的传播速度，这样对任何液体且不论温度如何变化，都能准确测出超声波在液体中的传播速度，并根据这一速度准确测出液位的高度。由于是直接测速方式，提高了测量精度，避免了采用热敏电阻测温补偿方式带来的滞后现象。