Application of 3D coherent processing in ultrasonic testing

A 3D variant of the coherent method of projection in the spectral space (PSS) for obtaining images of reflectors on the basis of measured echo signals is considered. Its application allows recon-struction of reflector images with a high frontal resolution in both the main plane of an ultrasonic transducer and an additional plane. The application of the PSS method is especially efficient when a reflector is far from the receiving aperture. In this case, it is possible to increase the signal-to-noise ratio by more than 12 dB and a tenfold increase in the frontal resolution can sometimes be attained as compared to the 2D layer-by-layer variant of the PSS method. Examples of the application of this method during reconstruction of reflector images in a specimen of the wall of a chemical reactor, in the case of multiple reflections from the walls of a welded T-branch with an overlaid plate (WTP), and when testing large-diameter studs and supports of the divertor, which is manufactured as part of the work on the thermonuclear reactor (ITER) project, are presented. The efficiency of applying the 3D variant of the PSS method for testing at large depths is shown.     

Sparsity enhancement for blind deconvolution of ultrasonic signals in nondestructive testing application

The received signal in ultrasonic pulse-echo inspection can be modeled as a convolution between an impulse response and the reflection sequence, which is the impulse characteristic of the inspected object. Deconvolution aims at approximately inverting this process to improve the time resolution so that the overlap between echoes from closely spaced reflectors becomes small. This paper presents a modified minimum entropy blind deconvolution algorithm for deconvolving ultrasonic signals. Enhancement of the resolution is achieved by using the presented method. In addition, the presented approach will, in many cases, lead to a faster computation. A nonlinear function is the key point to the efficiency of the modified blind deconvolution algorithm, which is used to increase the sparsity of the iteration output and to decrease the influence of the added noise by replacing each iteration output by output of the nonlinear function. Simulations showed the efficiency of the modification as compared with minimum entropy deconvolution when deconvolving synthetic ultrasonic signals. Experimental results using real ultrasonic data evaluated further that the exact solution consistently yields good performance. The thickness of a thin steel sample can be calculated by the modified blind deconvolution filter with a reasonable accuracy.     

False echo signals during ultrasonic testing of a steam generator

One important special case, namely, the ultrasonic testing of the welded joint of a steam generator was considered. The signal from a flaw is distinguished against a background of signals from technical reflectors.     

Analysis of 3D elemental mapping artefacts in biological specimens using Monte Carlo simulation

In this paper, we present Monte Carlo simulation results demonstrating the feasibility of using the focused ion beam based X-ray microanalysis technique (FIB-EDS) for the 3D elemental analysis of biological samples. In this study, we used a marine diatom Thalassiosira pseudonana as our model organism and NISTMonte for the Monte Carlo simulations. We explored several beam energies commonly used for the X-ray microanalysis to examine their effects on the resulting 3D elemental volume of the model organism. We also performed a preliminary study on the sensitivity of X-ray analysis for detecting nanoparticles in the model. For the conditions considered in this work, we show that the X-ray mapping performed using the 5 keV beam energy results in 3D elemental distributions that closely reflect the elemental distributions in the original model. At 5 keV, the depth resolution of the X-ray maps is about 250 nm for the model organism. We also show that the nanoparticles that are 50 nm in diameter or greater are easily located. Although much work is still needed in generating more accurate biological models and simulating experimental conditions relevant to these samples, our results indicate that FIB-EDS is a promising technique for the 3D elemental analysis of some biological specimens.     

复合材料曲面构件缺陷超声三维成像方法

针对目前复合材料曲面结构缺陷检测技术存在的检测结果不直观、效率低等问题,提出一种基于超声相控阵的缺陷三维成像方法。使用三维激光扫描仪获取曲面的点云模型,通过平行截面法规划检测路径,然后使用相控阵轮式探头采集超声图像数据。利用均匀三次B样条函数拟合检测路径与曲面,根据扫查步长和图像序列关系计算超声图像数据点的空间位置以生成超声点云集。最后利用体素化降采样方法对超声检测结果进行重建,实现复合材料内部缺陷的三维成像。实验结果表明,本文方法的缺陷成像结果与CT检测结果的平均误差为1.14 mm,能够快速准确地重建缺陷的位置、形状与尺寸信息,实现复合材料曲面样件内部缺陷的精确表征。     

Requirements for choosing the parameters of broadband transducers for testing objects with high damping of ultrasonic signals

The main concepts of the theory of optimal signal processing as applied to tasks of ultrasonic testing of articles with high integral damping of acoustic vibrations are considered. The conditions for ensuring the optimal transfer coefficient of the receiving section of an ultrasonic flaw detector’s electroacoustic channel are formulated. The requirements for the characteristics of broadband piezoelectric transducers aimed at the insurance of undistorted transmission of ultrasonic signals are formulated.     

A split method of ultrasonic testing

The considered new split method of ultrasonic testing is based on the optimal quasi-harmonic synthesis of echo signals and substantially extends the possibilities of designing adaptive ultrasonic testing systems. This method is highly sensitive, noise-immune, and algorithmically flexible.     

Analysis of reflected signals in testing cylindrical specimens by the multiple reflection echo-shadow method

In this paper, we present the results of correlation, spectral, and probabilistic-statistical analyses of signals in the flaw inspection of cylindrical specimens by the multiple reflection echo-shadow method, and establish new informative parameters for the purpose of their integrated use to improve the reliability of nondestructive testing results.     

Issues of ultrasonic testing of extended complexly structured items with strong attenuation of signals

These and subsequent articles present the results of the studies of interference resistant methods and devices for ultrasonic testing of extended items made of complexly structured materials. The presented results are based on the radio-engineering R &; D that have been conducted for over 30 years by the Department of Electronic Devices of the Moscow Power Engineering Institute. The studies are concurrently focused on the development of methods for separating echo signals from white and structural noise, on the application of complexly modulated signals, on the development of spatial and temporal methods for processing signals, on the development of broadband mosaic transducers, and on the design of multifunctional devices for ultrasonic testing. The necessity of such a comprehensive approach to ultrasonic testing is substantiated in this article by analysis of the problems of ultrasonic testing of complexly structured items with strong integral attenuation of ultrasound.     

Comparison of the features of composite and mosaic piezotransducers for the ultrasonic testing of products with a high attenuation level of ultrasonic signals

The problem of the creation of stacked (mosaic and composite) broadband transducers that simultaneously provide a broad band and a high electroacoustic transduction efficiency is analyzed. The mosaic technology is shown to be optimal for the practical implementation of ultrasonic broadband low-frequency electroacoustic transducers. Being functionally flexible, the mosaic technology allows the development of numerous variants of electroacoustic transducers for the solution of different ultrasonic testing problems and, first of all, for the undistorted transduction of signals.     

Sample holder for axial rotation of specimens in 3D microscopy

In common light microscopy, observation of samples is only possible from one perspective. However, especially for larger three‐dimensional specimens observation from different views is desirable. Therefore, we are presenting a sample holder permitting rotation of the specimen around an axis perpendicular to the light path of the microscope. Thus, images can be put into a defined multidimensional context, enabling reliable three‐dimensional reconstructions. The device can be easily adapted to a great variety of common light microscopes and is suitable for various applications in science, education and industry, where the observation of three‐dimensional specimens is essential. Fluorescence z‐projection images of copepods and ixodidae ticks at different rotation angles obtained by confocal laser scanning microscopy and light sheet fluorescence microscopy are reported as representative results.     

准规则生物组织超声背散射信号的仿真

超声背散射信号能提供反映组织微结构的有用信息.本文在原有的生物组织超声背散射信号仿真模型基础上,将影响平均散射元间距(MSS)估计的组织特性具体为4个主要参数,为检测各种平均散射元间距估计方法的性能提供了方便.文中用AR倒谱方法对仿真信号4个参数的合理性进行反向测试,实验结果表明,仿真信号的4个参数能表示影响平均散射元间距估计性能的组织特性.通过仿真信号与人体脾组织的背散射信号以及相关文献中组织信号的比较,证明仿真信号与具有准周期性的生物组织背散射信号基本类似.     

The possibility of using the maximum-entropy method in ultrasonic nondestructive testing for increasing the resolution of echo signals

The problem of deconvoluting echo signals via regularization according to the maximum entropy method followed by the reconstruction of 2D images via the Fourier transformation synthetic aperture focusing technique (FT-SAFT) is considered. Numerical and experimental simulations have been performed. The possibility of improving the ray resolution of echo signals and reducing the speckle-noise level is demonstrated. The results obtained are compared to the results of constructing an AR model of the spectrum of echo signals.     

Calibration blocks for ultrasonic nondestructive testing

The main parameters of calibration blocks for ultrasonic testing that must be measured during metrological certification are considered: the geometric dimensions of reflectors, the velocity and attenuation of elastic waves, etc. A method for measuring the damping factor is proposed that simplifies the measurement procedure. A form of the certificate registered officially for calibration blocks that were subjected to metrological certification is presented.     

3D spectral analysis for vibration signals by wavelet-based demodulation

In this paper, a wavelet-based demodulating function is proposed to apply in 3D spectral analysis for vibration signals. In the function, there are three parameters required to assign for adjustment and designation of the filtering passband, which are the low cut-off frequency, the high cut-off frequency and the dilation. Accordingly, it would be convenient to apply in the high-frequency resonance technique. In addition, by sweeping the filtering passband from a low-frequency band to a high-frequency band, a 3D spectrum could be constructed to describe how energy distribution between the instantaneous frequency and the filtering passband for a vibration signal. The 3D spectrum would be helpful to give a clear view of both characteristic frequencies and system resonances, and possesses the advantage of minimising the interventions by the end-user.     

Numerical simulation of ultrasonic minimum reflection for residual stress evaluation in 2D case

A number of interesting phenomena at fluid-solid interfaces can be observed when the incident angle approaches the Rayleigh angle, including Schoch displacement and leaky Rayleigh waves. Besides the experimental and theoretical research on these problems, numerical tools have been more and more widely used for these complex problems. Based on previous experimental and numerical researches, a 2D finite element model has been built to reproduce the Schoch effects. With the same model, the minimum reflection profile is investigated for the feasibility of material characterization, especially for residual stress evaluation. Residual stress is one of the important properties for structures, and its measurement is a popular research topic in nondestructive evaluation. However, it is not possible to put the residual stress into the numerical model directly. According to the relation of residual stress with mechanical properties, the material damping and wave speed have been alternatively adopted in this work. The influence of minimum reflection profile by residual stress has been shown by the change of wave speed and damping factor. Simulation results show that the minimum reflection profile is a potential method for residual stress evaluation.     

Frequency multiplexer for ultrasonic Doppler blood flow signals

An instrument is described which uses single-sideband techniques to combine two channels of Doppler flow signals into a form suitable for simultaneous processing by a single-channel real-time spectral analyzer. The maximum input frequency range is 50 Hz to 10 kHz.     

电液伺服三维加载轿车零部件疲劳试验系统设计与仿真

电液伺服三维加载轿车零部件疲劳试验台主要是针对轿车中较小零部件的一种通用疲劳寿命试验台,能从三个方位按程控波形对试件进行恒力或交变力加载,可较好地模拟轿车行驶过程中奉部件受力状态,其中电液伺服加载是试验台关键所在.对电液伺服加载液压系统进行了理论分析计算和动态性能仿真,同时介绍了试验台测控系统硬件和软件构成.利用室内试验设备能较好地模拟轿车在不平道路上行驶时状况,对轿车零部件在承受动载荷状态下的疲劳寿命进行研究.试验进程不受外界环境影响,试验周期短、投资少.     

一种编织物三维模拟的新方法

首先从编织物的结构中提取出三种基本编织结构：Knit、Tuck、Welt,并对这三种结构进行模型构造;然后分析纹理图案的bmp图片,从中得到编织物针珐数据;接着把这三种基本结构按照得到的针珐数据连接起来,生成一条条粗糙的纱线中心线,并由此得到粗略的编织物框架;再从纱线的每个结构中选取一定的点作为控制点,由这些控制点生成NURBS曲线,得到精确、平滑的纱线中心线;然后构造纱线的横截面,根据横截面生成纱线表面的三角面片;最后按照每条纱线的颜色显示这些面片,从而生成逼真的编织物模拟效果。同时,运用弹簧一质点模型,模拟了编织物受到拉力后变形的情况。     

A molecular dynamics simulation of 3D rough lubricated contact

In this paper, a molecular dynamics simulation of three dimensional rough surface contact under different lubricated conditions was carried out. At atomic scale, mixed lubrication involves nano-asperity contact where the load is supported not only by asperities but also by a sufficient amount of confined lubricant. The contact area and pressure distribution of various lubricated conditions, e.g. dry, partially lubricated and fully lubricated, were presented. It has been found that cavities were formed between upper and lower surfaces under the load, and confined lubricant molecules were able to fill the cavity and support the load, resulting in the decrease of contact area and thus the protection of surface topography.