Formation of the acoustic field of a Rayleigh-wave transducer in an object with a protrusion. Part I. Protrusion with a right angle

Attention is drawn to the possibility of using transducers of Rayleigh waves as the sources (receivers) of transverse waves for ultrasonic testing of objects with auxiliary protrusions, at which elastic modes are transformed and scattered. The acoustic section was analyzed and the influence of both the curvature of the radius junction of a protrusion and the wave frequency on the parameters of the formed field was experimentally studied. The contribution of the accompanying subsurface transverse mode and the outgoing mode, which is generated by an edge head wave, to this field was revealed. Data on the influence of the angular position of artificial reflectors inside the specimen with a protrusion on the amplitude of reflected transverse waves, whose primary source is a Rayleigh-wave transducer, are presented.     

矩阵换能器超声三维成像方法研究*

针对常规超声检测难以直观地显示被检对象缺陷的形状及走向等问题,开展矩阵换能器超声三维成像方法研究。超声三维成像技术具有直观显示被测对象内部缺陷三维特征的优点,基于矩阵换能器的超声三维成像方法具有扫查速度快、分辨率高等优点,是当前超声三维成像技术的研究热点。本文介绍了矩阵换能器体扫查原理及其控制方法;提出了矩阵换能器体扫查时三维体数据采集方法和数据融合算法;基于矩阵换能器和相控阵板卡系统对铝标样等试样进行了体扫查检测实验,采用等值面和体绘制两种算法对缺陷进行三维成像,并对单一缺陷进行了定量分析,定量精度较高。研究结果表明,矩阵换能器超声三维成像方法能够表征缺陷的三维形貌特征,在无需移动换能器的情况下便可实现缺陷三维检测,是超声三维检测的有效方法。     

Broadband electrostatic acoustic transducer for ultrasonic measurements in liquids

A broadband capacitive electrostatic acoustic transducer (ESAT) has been developed for use in a liquid environment at megahertz frequencies. The ESAT basically consists of a thin conductive membrane stretched over a metallic housing. The membrane functions as the ground plate of a parallel plate capacitor, the other plate being a dc biased electrode recessed approximately 10 mum from the electrically grounded membrane. An ultrasonic wave incident on the membrane varies the membrane-electrode gap spacing and generates an electrical signal proportional to the wave amplitude. The entire assembly is sealed for immersion in a liquid environment. Calibration of the ESAT with incident ultrasonic waves of constant displacement amplitude from 1 to 15 MHz reveals a decrease in signal response with increasing frequency independent of membrane tension. The use of the ESAT as a broadband ultrasonic transducer in liquids with a predictable frequency response is promising.     

非线性超声谐振方法及在结垢检测中的应用研究

针对压力容器和管道安全运行需要,发展了一种非线性超声谐振结垢检测方法。从理论上分析非线性细观弹性材料因迟滞效应引起的非线性弹性本构关系。研究发现,随着超声波激励幅值的增加,迟滞导致的非线性效应主要表现为超声波谐振频率向低频偏移和谐振频谱品质因数的变化。对涂有不同厚度模拟结垢的板试件进行非线性超声谐振检测试验,研究了激励电压水平对基波及二次谐波谐振频谱的影响规律,提出基于二次谐波弹性迟滞非线性系数和耗散迟滞非线性系数的结垢层厚度表征方法。在此基础上,将非线性超声谐振检测方法应用于实际工程中炉管结垢层检测,结果表明,利用二次谐波的弹性迟滞非线性系数和耗散迟滞非线性系数能较好反映炉管结垢状况。研究工作为实际工程中炉管结垢层检测提供了新的思路和方法。     

板结构裂纹兰姆波阵列复合成像方法研究

针对板结构中裂纹方向识别及定量检测问题,提出了一种板结构兰姆波阵列复合成像方法。利用超声阵列采集的单模态兰姆波全矩阵数据,分别提取其幅值信息和极性信息,进行全聚焦成像和极性一致成像,并利用极性一致成像对全聚焦成像进行了加权处理;对全阵列进行子阵列划分,计算出各子阵列的特征矢量,并进行加权合成,得到矢量全聚焦成像;利用全聚焦成像的强度信息和矢量全聚焦成像的方向信息,综合得到兰姆波阵列的复合成像,并从中提取出缺陷的方向及空间分布范围等信息。实验结果表明,提出的兰姆波阵列复合成像方法可以很好地实现板中多个裂纹方向识别,其角度测量误差在20%以内。本文工作为裂纹缺陷识别及定量检测做了有益探索。     

一种磁致伸缩式超声波激发/接收传感器的研究

以研制磁致伸缩式超声波传感器为目标，分析了磁致伸缩式超声波传感器的工作原理——磁致伸缩效应及逆效应，重点讨论传感器结构设计及线圈参数选择计算，制作了磁致伸缩式超声波传感器。本文研制的传感器在脉冲激励电流的作用下，可在细丝中激发超声波，同时还可以接收细丝中传播的超声波；该传感器既可以激发扭转波，又可以激发纵波。可用于测量液位、温度、液体密度和材料的声速、弹性模量等物理量。     

Study of ultrasonic vibrations’ effect on friction stir welding

In this paper, effect of ultrasonic vibrations on friction stir welding (FSW) is studied. Ultrasonic vibrations were employed on the tool in pin direction (perpendicular to the welding direction). To do this study, a vibration tool was designed by Abaqus software in a way to have a longitudinal frequency about 20 kHz and was then manufactured and assembled with an ultrasonic transducer and was controlled using an ultrasonic generator to oscillate ultrasonically with a peak-to-peak amplitude of 10 μm. After preparation of experimental setup, some experiments were performed on AA6061-T6 as a work material, and the effect of ultrasonic vibrations on force, temperature, tensile strength, and hardness was investigated in FSW. Based on the achieved results, ultrasonic vibrations can decrease force and increase temperature in FSW.     

Internal defect detection using laser-generated longitudinal waves in ablation regime

Laser ultrasonics could be an attractive solution for the nondestructive testing of structures in harsh environments. Longitudinal waves generated in the ablation regime are especially well suited to internal defect detection because they provide a higher signal-to-noise ratio in comparison to ultrasonic waves generated under a thermo-elastic regime, while their propagation direction normal to the surface enables the simplified interpretation processing of received signals when the defect echoes are analyzed. The internal defect detection using laser-generated longitudinal waves in the ablation regime was investigated numerically and experimentally, and a numerical model to simulate the generation and propagation of ultrasonic waves in the ablation regime was developed. This model was based on the simulation of ultrasonic generation and propagation caused by the net reaction force that was directly converted from the laser intensity absorbed onto the surface. This model was also extended as a model for internal defect detection. A steel specimen containing artificial internal defects was fabricated and inspected by using the through-transmission (T-scan) and pulse-echo (B-scan) modes. Clear amplitude reduction was observed in the transmitted waves at the defect positions in T-scan images, while B-scan images clearly showed the defect echoes arriving at different times depending on the depth location of internal defects. These results demonstrate that longitudinal waves excited in the ablation regime can be effectively used for internal defect detection.     

Estimating the Parameters of Signals Observed during Ultrasonic Testing of a Cylindrical Article with a Normal Probe on the End Surface

The first and second signals observed during ultrasonic testing of a cylindrical article with a normal probe set on the article’s end surface are studied. The amplitude of the second pulse caused by a reflection from a lateral wall with transformation of elastic waves is estimated relative to the amplitude of the first (ordinary bottom-reflected) pulse. It is ascertained that, under certain conditions, the amplitude of the second pulse can be comparable to or even exceed the amplitude of the first pulse. The effect of a change in the specimen radius-to-length ratio on the amplitude of the bottom signal is estimated.     

一种复杂结构件圆柱面扩散焊缝阵列超声检测方法

航空发动机某高温合金盘构件采用盘体与叶片环进行焊接的方式制备,由于构件结构复杂,在检测圆柱形焊接面缺陷时,采用单晶超声检测换能器检测效率不高,缺陷信号信噪比低。为提高该种结构件的检测能力,研究圆柱面焊缝的阵列超声自动检测方法,分析面积型缺陷和声源的相对位置对缺陷反射声压和波型转换的影响,提出一种基于双阵列换能器的一发一收检测方案。根据高温合金盘结构设计基于双阵列换能器的声束发射-接收方法和圆柱面焊缝全覆盖检测方案;基于时域有限差分方法建立高温合金盘的阵列超声声学响应仿真模型,对检测参数进行设计和优化。对含有人工缺陷的实际试样进行检测试验,结果表明所提出的双阵列超声换能器检测方法能有效检测到圆柱面焊缝区域? 2 mm的当量缺陷。     

A study on the ultrasonic nondestructive evaluation of carbon/carbon composite disks

It is desirable to perform nondestructive evaluation (NDE) to assess material properties and part homogeneity because the manufacturing of carbon/carbon brake disks requires complicated and costly processes. In this work several ultrasonic techniques were applied to carbon/carbon brake disks (322mmod, 135mmid) for the evaluation of spatial variations in material properties that are attributable to the manufacturing process. In a large carbon/carbon disk manufactured by chemical vapor infiltration (CVI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CVI process. Low frequency (e.g., 1-5MHz) through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. Images based on both the amplitude and the time-of-flight of the transmitted ultrasonic pulse showed significant variation in the radial direction. The radial variations in ultrasonic velocity and attenuation were attributed to a density variation caused by the more efficient densification of pitch impregnation near theid andod and by the less efficient densification away from exposed edged of the disk. Ultrasonic velocities in the edges of the disk. Ultrasonic velocities in the thickness direction were also measured as a function of location using dry-coupling transducers; the results were consistent with the densification behavior. However, velocities in the in-plane directions (circumferential and radial) seemed to be affected more by the relative contents of fabric and chopped fiber, and less by the void content.     

小尺寸材料弹性常数超声测量系统的研制及其应用

提出一种小尺寸材料弹性常数测量的新方法——利用线聚焦超声传感器和超声浸水技术同时测定纵波和漏表面波的波速，求得材料的弹性常数。基于PXI-8186嵌入式控制器构建了小尺寸材料弹性常数测控系统，利用LabVIEW软件平台开发了小尺寸材料弹性常数自动测量软件。实验结果表明，该方法可以实现小尺寸材料弹性常数的测量，测量结果具有很好的重复性。     

未焊透对铝焊缝使用性能的影响

报道了L3R焊接试板在无缺陷有焊缝余高、无缺陷无焊缝余高、有未焊透有焊缝余高、有未焊透无焊缝余高四组试样的拉伸试验结果和L3R热轧板和焊接板的裂纹张开位移试验结果。通过对四组拉伸试样抗拉强度和断裂位置的比较及热轧板和焊接板的裂纹扩展分析，对带轻微未焊透缺陷L3R焊缝对使用性能的影响进行了评价。     

Detection of an axial surface microcrack in steel wire rods with noncontact ultrasonic reverberation spectroscopy

In the manufacturing process of steel rod, a number of micro-scale defects occur along the axial direction on the surface of the rods. To prevent failures in advance, a method to detect the micro-scale cracks remaining on the surface of rod is required. This work employs an Electromagnetic acoustic transducer (EMAT) to evaluate the cracks of the wire rods with the noncontact Ultrasonic reverberation spectroscopy (URS). The resonance at the cross section of the cylindrical rods is generated by horizontally polarized shear waves driven in the circumferential direction. Through a series of URS experiments, changes in the resonant frequency, the amplitude of the resonant peak, and the attenuation of the ultrasonic reverberation were observed at intact and defected parts of specimens. The results showed that the URS technique may be one of the effective tools to detect the axial surface microcrack with its depth of a few tens of micrometers.

     

Inverse analysis of ultrasonic signals of ceramics based on ultrasonic self-compensating technique

An ultrasonic self-calibrating technique for the characterization of a ceramic which was fabricated by change pressing time during the HIP process has been applied by using the ratio of the reflection and transmission coefficients of normal incidence longitudinal waves. The ratio is self-compensated, in that it is independent of the characteristics for transmission and reception of ultrasound by the transducer and the condition of the couplant. The insensitive direction in parameter space is defined as the direction in which the variation of the ratio to changes of two parameters vanishes. For inverse problem the distribution of minima in an error surface is investigated.     

基于动态支路电流检测的功率超声振幅控制

在功率超声的应用中,精确的振幅控制是决定加工质量的重要因素。传统的检测控制结构需要复杂的外部仪器或检测电路,可能存在灵活性差及非线性等问题。针对此问题,提出了一种轻量级振幅检测与控制方案。该方案采用高速AD转换器采样换能器的工作电流和电压,实时计算可以反映振幅的动态支路电流。采用现场可编程逻辑门阵列(field-programmable gate array,简称FPGA)作为超声电源控制器,同时对换能器工作频率和动态支路电流进行闭环控制。在本设计中,超声电源工作在反谐振点以获取较高的能量传输效率。实验结果表明,该方案能够准确地控制振幅,并能在负载变化较大时稳定振幅。     

DETECTION OF DELAMINATION IN A COMPOSITE PLATE BY SEM

0 INTRODUCTIONUltrasonic waves have been successfully used todetect defects (delamination, cracks, inclusions ) instructures. It is very difficult to obtain the scatteringwave fields by such defects analytically. Numericalmethods are often used. Finite element method(FEM) is often used to investigate wave proP8gation..in comPOsite platest l,2]. A disadvant8ge of the FEM isthe need for a large memory.The Green's functions due to a line load on thesurface of a comPOsite plate were pres…     

Measurement of the contact area of a dovetail milling cutter using an ultrasonic method

Since there is no reliable mathematical model to analyze a multi-points contact simultaneously, the most effective way to know the contact area is to use experimental method directly. This study measures the contact area between a dovetail milling cutter and a steel plate by using ultrasound for regional scanning. This is a novel application for milling cutters and has not been applied before. The transducer emits an ultrasonic pulse to detect the contact surface. If contact occurs, the pulse is partially transmitted into the specimen. Therefore, the signal reflected back to the pulse receiver is reduced. The amount by which the signal amplitude is reduced is a measure of the degree of contact.     

Excitation of Elastic Waves in Half-Space with Periodic Surface Undulations

The components of the displacement of elastic waves excited by a normal transducer in half-space with periodic surface undulations is calculated by the perturbation method within the framework of the two-dimensional model. The numerical examples of the calculation results obtained for a surface described by harmonic functions are given. The phenomenon of transformation of longitudinal waves into transverse waves on periodic surface undulations, which has been revealed earlier, is confirmed. As a result of this phenomenon, transverse waves are emitted in the direction of the normal to the plane of the transducer at its center.     

基于激光测振仪的兰姆波离面和面内位移检测

激励模态和频响特性是超声导波传感器性能评估的两个重要指标,而传统的传感器,如压电传感器和电磁声传感器(Electromagnetic acoustic transducer,EMAT)等,受自身带宽和模态选择性的影响,无法有效地实现这两个参数的评估。激光测振仪可以测量结构中弹性波原始的离面和面内位移,且测量不受带宽的限制,因而是进行超声导波传感器激励模态测定和频响特性测量的理想方法之一。采用此种方法对一种周向一致激励兰姆波的EMAT进行测试,结果表明,此传感器在150～210 kHz的范围内能激励产生出单一S0模态兰姆波,在50～150 kHz范围内,A0模态与S0模态共存。利用激光测振仪检测离面和面内位移的方法,是进行传感器评估和兰姆波接收的有效方法,在超声导波的非接触测量、高温波导体检测及弹性波传播3D可视化方面也有广阔的应用前景。