Effect of sensor quantity on measurement accuracy of log inner defects by using stress wave

Wood nondestructive testing （NDT） is one of the high efficient methods in utilizing wood. This paper explained the principle of log defect testing by using stress wave, and analyzed the effects of sensor quantity on defect testing results by using stress wave in terms of image fitting degree and error rate. The results showed that for logs with diameter ranging from 20 to 40 cm, at least 12 sensors were needed to meet the requirement which ensure a high testing accuracy of roughly 90% of fitness with 0.1 of error rate. And 10 sensors were recommended to judge the possible locations of defects and 6 sensors were sufficient to decide whether there were defects or not.

WAVELET METHOD FOR CALCULATING THE DEFECT STATES OF TWO-DIMENSIONAL PHONONIC CRYSTALS

Based on the variational theory, a wavelet-based numerical method is developed to calculate the defect states of acoustic waves in two-dimensional phononic crystals with point and line defects. The supercell technique is applied. By expanding the displacement field and the material constants （mass density and elastic stiffness） in periodic wavelets, the explicit formulations of an eigenvalue problem for the plane harmonic bulk waves in such a phononic structure are derived. The point and line defect states in solid-liquid and solid-solid systems are calculated. Comparisons of the present results with those measured experimentally or those from the plane wave expansion method show that the present method can yield accurate results with faster convergence and less computing time.

Defect detection in brazed weldment with lattice structure using ultrasonic Lamb wave technique

In this paper, defects detection in brazed weldment with lattice structure is studied using ultrasonic Lamb wave. Based on the ultrasonic guided wave theory, the frequency dispersion curves for phase and group velocity of I Cr18Ni9Ti are obtained by solving the Rayleigh-Lamb equation. The incident angles of different modes are determined through theoretical calculation and experimental analyses. Artificial defects of through-wall slots with different dimensions are made and tested. Experimental scattering effects of the fundamental symmetric mode S2 and asymmetric modes A1 and A0 are analysed and compared. The results show that mode Ao is suitable for detecting artificial defect, and the amplitude of the received signals are in good agreement with the defect size. Brazed weldment specimen containing lack of brazing with certain dimensions is made. Using the same methodology, scattering effects produced by weld defects are measured. The results show that the clutter wave brought about by the filler metal will certainly disturbs the identification of defect signal. But, when the defect is 3.0 mm in width, the presented mode Ao could be used potentially.

Propagation behavior of elastic waves in one-dimensional piezoelectric/piezomagnetic phononic crystal with line defects

Using a stiffness matrix method, we in- vestigate the propagation behaviors of elastic waves in one-dimensional （1D） piezoelectric/piezomagnetic （PE/PM） phononic crystals （PCs） with line defects by calculating energy reflection/transmittion coefficients of quasi-pressure and quasi-shear waves. Line defects are created by the re- placement of PE or PM constituent layer. The defect modes existing in the first gap are considered and the influences on defect modes of the material properties and volume fraction of the defect layers, the type of incident waves, the location of defect layer and the number of structural layers are discussed in detail. Numerical results indicate that defect modes are the most obvious when the defect layers are inserted in the middle of the perfect PCs; the types of incidence wave and material properties of the defect layers have important effects on the numbers, the location of frequencies and the peaks of defect modes, and the defect modes are strongly de- pendent on volume fraction of the defect layers. We hope this paper will be found useful for the design of PE/PM acoustic filters or acoustic transducer with PCs structures.

Fano resonance and wave transmission through a chain structure with an isolated ring composed of defects

We consider a discrete model that describes a linear chain of particles coupled to an isolated ring composed of N defects. This simple system can be regarded as a generalization of the familiar Fano Anderson model. It can be used to model discrete networks of coupled defect modes in photonic crystals and simple waveguide arrays in two-dimensional lattices. The analytical result of the transmission coefficient is obtained, along with the conditions for perfect reflections and transmissions due to either destructive or constructive interferences. Using a simple example, we further investigate the relationship between the resonant frequencies and the number of defects N, and study how to affect the numbers of perfect reflections and transmissions. In addition, we demonstrate how these resonance transmissions and refections can be tuned by one nonlinear defect of the network that possesses a nonlinear Kerr-like response.

Propagation Characteristics of Ultrasonic Guided Waves in Grouted Rockbolt Systems with Bond Defects under Different Confining Conditions

A rockbolt acting in the rock mass is subjected to the combined action of the pull-out load and confining pressure, and the bond quality of the rockbolt directly affects the stability of the roadway and cavern. Therefore, in this study, confining pressure and pull-out load are applied to grouted rockbolt systems with bond defects by a numerical simulation method, and the rockbolt is detected by ultrasonic guided waves to study the propagation law of ultrasonic guided waves in defective rockbolt systems and the bond quality of rockbolts under the combined action of pull-out load and confining pressure. The numerical simulation results show that the length and location of bond defects can be detected by ultrasonic guided waves under the combined action of pull-out load and confining pressure. Under no pull-out load, with increasing confining pressure, the low-frequency part of the guided wave frequency in the rockbolt increases, the high-frequency part decreases, the weakening effect of the confining pressure on the guided wave propagation law increases, and the bond quality of the rockbolt increases. The existence of defects cannot change the strengthening effect of the confining pressure on the guided wave propagation law under the same pull-out load or the weakening effect of the pull-out load on the guided wave propagation law under the same confining pressure.

DETECTION OF LONGITUDINAL DEFECT IN PIPES USING TORSIONAL MODES

The multi-modes and disperse characteristics of torsional modes in pipes are investigated theoretically and experimentally. At all frequencies, both phase velocity and group velocity of the lowest torsional mode T（0,1） are constant and equal to shear wave velocity. T（0,1） mode at all frequencies is the fastest torsional mode. In the experiments, T（0,1） mode is excited and received in pipes using 9 thickness shear vibration mode piezoelectric ceramic elements. Furthermore, an artificial longitudinal defect of a 4 m long pipe is detected using T（0,1） mode at 50 kHz. Experimental results show that it is feasible for longitudinal defect detection in pipes using T（0,1） mode of ultrasonic guided waves.

心电图Defective T波对成人继发孔型房间隔缺损的诊断价值和形成因素分析

目的:探讨心电图Defective T波(DTW)诊断成人继发孔型房间隔缺损(ASD)的价值及主要形成因素。方法:选取经心脏超声心动图确诊的继发孔型ASD成人患者243例(ASD组)和心脏超声未见明显异常者247例(非ASD组),均描记标准十二导联心电图,观察DTW、不完全性右束支传导阻滞(IRBBB)检出情况,分析DTW对继发孔型ASD的诊断价值和形成因素,观察不同术式前后心电图的变化。结果:ASD组、非ASD组DTW检出率分别为58.02%(141/243)、5.67%(14/247),DTW合并IRBBB检出率分别为51.85%(126/243)、0.81%(2/247),ASD组均高于非ASD组(χ^(2)=155.263、165.363,P<0.001)。DTW诊断继发孔型ASD的敏感度、特异度和准确度分别为58.02%、94.33%和76.33%,DTW合并IRBBB诊断继发孔型ASD的敏感度、特异度和准确度分别为51.85%、99.19%和75.71%。右心室增大、肺动脉收缩压增高是ASD患者DTW形成的主要影响因素[OR(95%CI)分别为1.095(1.020~1.176)、1.040(1.006~1.075)];术前DTW、IRBBB和DTW合并IRBBB阳性的ASD患者经过外科手术或介入手术治疗6个月后均缓解,缓解程度在两种术式组间的差异无统计学意义(P>0.05)。结论:心电图DTW对成人继发孔型ASD的诊断具有较大指导意义,右心室增大、肺动脉收缩压增高是ASD患者DTW的主要形成因素。

Application of Laser Ultrasonic Technique for Non-contact Detection of Angled Surface Defects

Based on the finite element method,the angled surface defects have been investigated by using the laser generated surface acoustic wave(SAW).The feature of laser generated SAW interaction with the angled defect is analyzed in time and frequency domains.An increase in the amplitude of SAW at the edge of the defect is observed,and the spectral feature is angle dependent.With the angle decreasing from 120°to 30°,the maximum amplitude of frequency spectrum of SAW increases gradually.The corresponding experimental results verify the feasibility of numerical analyses and reach a good agreement with simulation results.

Crack Detection in Pipes with Different Bend Angles Based on Ultrasonic Guided Wave

Pipeline plays an indispensable role in process industries,because the progressing crack-like defects of in it may result in serious accidents and significant economic losses.Therefore,it is essential to detect the cracks occurred in pipelines.The axial crack-like defects in elbows with different angle are inspected by using the T(0,1)mode guided waves,in which different configurations including 45°,90°,135°and 180°(straight pipe)are considered respectively.Firstly,the detection sensitivity for different defect location is experimentally investigated.After that,finite element simulation is used to explore the propagation behaviors of T(0,1)mode in different bend structures.Simulation and experiment results show that the crack in different areas of the elbow can affect the detection sensitivity.It can be found that the detection sensitivity of crack in the middle area of the elbow is higher compared to the extrados and intrados of the elbow.Finally,the mode conversion is also investigated when the T(0,1)crosses the bend,and the results show that bend is a key factor to the mode conversion phenomenon which presents between the T(0,1)mode and F(1,2)mode.

Model Tests of Pile Defect Detection

The pile, as an important foundation style, is being used in engineering practice. Defects of different types and damages of different degrees easily occur during the process of pile construction. So, dietecting defects of the pile is very important. As so far, there are some difficult problems in pile defect detection. Based on stress wave theory, some of these typical difficult problems were studied through model tests. The analyses of the test results are carried out and some significant results of the low-strain method are obtained, when a pile has a gradually-decreasing crosssection part, the amplitude of the reflective signal originating from the defect is dependent on the decreasing value of the rate of crosssection β. No apparent signal reflected from the necking appeares on the velocity response curve when the value of β is less than about 3. 5 %.

Defect detection in brazed weldment with lattice structure using acoustic shadow technique

Brazed weldment with lattice structure has been widely used in aerospace industry. The non-destructive testing is often difficult because of the poor inspection accessibility. The present paper illustrates how the plane-like defect lack of brazing can be detected rapidly in this kind of structure by using ultrasonic Lamb wave. Experimental weldments are prepared and weld defect are tested using S2 mode Lamb wave. Acoustic shadow technique is employed based on Lamb wave testing method. The character of the tested D-scan image and A-scan signal is studied. The experimental results show that acoustic shadow based Lamb wave testing method is effective in detecting through-wall lack of brazing. Meanwhile, the D-scan tested data can be rapidly collected and easily interpreted compared with pulse echo bused Lamb wave testing method.

Building Wave Functions of the Outer Electron for Alkaline Atoms Theory and Wave Functions Representation

The effects of the polarization potential serve to model spectra of alkaline atoms. These effects have been known for a long time and notably explained by the physicist Max Born (1926). The experimental knowledge of these alkaline spectra enables us to specify the values of these quantum defects. A simple code is used to calculate two quantum defects for which δl can be distinguished as: δs l = 0 and δp l = 1. On the theoretical part, it is possible to have an analytical expression for these quantum defects δl. A second code gives the correct wave functions modified by the quantum defects δl with the condition for the principal number: n* = n – δl ≥ 1. It is well known that δl → 0 when the kinetic momentum l ≥ 4, and for such momenta the spectra turns out to be hydrogenic. Modern software such as Mathematica, allows us to efficiently generate the polynomes defining wave functions with fractional quantum numbers. This leads to a good theoretical representation of these wave functions. To get numerically the quantum defects, a simple code is given to obtain these quantities when the levels assigned to a transition are known. Then, the quantum defects are inserted into the arguments of the correct modified wave functions for the outer electron of an atom or ion undergoing the short range polarization potential.

Study of Surface and Subsurface Defects in Materials by Photothermal Deflection Technique: Theory and Experience

Photothermal deflection is widely used to study defects in materials. Both high spatial resolution and high sensitivity are required to detect them. In order to improve the theoretical model in the case of uniform heating (one dimensional heat treatment) we have chosen to heat the sample by a halogen lamp. The sample which contains a known surface and subsurface defects is first covered by a thin graphite layer and placed in air. The sample fixed on a vertical holder is able to move in the x and y directions thanks a two stepper motors. The measurement showed excellent agreement between experimental and simulation results.

CONSTITUTIVE EQUATION WITH ORDERED PARAMETERS FOR VISCOELASTIC MATERIAL CONTAINING DEFECTS

Based on the experimental results of local temperature field formed in the evolution period of defects, the defect field is defined by this internal temperature field. The evolutionary processes of statistically correlative meso-scopic defects are analysed with the growth rate and nucleation rate of the meso-defect, and it is deemed that the dynamic failure process of the viscoelastic material with defects can be quantitatively described by the normal method of the procedure of heat wave transmission. The defect field is regarded as a complex system of the union of the real sets and null sets, its main characteristics depending on the stratum hypothesis about the activities of the subsystems of the highest stratum described by ordered parameters. The fluctuation of ordered parameters is demonstrated by means of the projection operator method. The constitutive equation with ordered parameters for the meso-defect evolutionary state of viscoelastic material with defects is deduced from the nonlinear rheological dynamic approach, and its solution is obtained.

High Precision Ultrasonic Guided Wave Technique for Inspection of Power Transmission Line

Due to the merits of high inspection speed and long detecting distance, Ultrasonic Guided Wave（UGW） method has been commonly applied to the on-line maintenance of power transmission line. However, the guided wave propagation in this structure is very complicated, leading to the unfavorable defect localization accuracy. Aiming at this situation, a high precision UGW technique for inspection of local surface defect in power transmission line is proposed. The technique is realized by adopting a novel segmental piezoelectric ring transducer and transducer mounting scheme, combining with the comprehensive characterization of wave propagation and circumferential defect positioning with multiple piezoelectric elements. Firstly, the propagation path of guided waves in the multi-wires of transmission line under the proposed technique condition is investigated experimentally. Next, the wave velocities are calculated by dispersion curves and experiment test respectively, and from comparing of the two results, the guided wave mode propagated in transmission line is confirmed to be F（1,1） mode. Finally, the axial and circumferential positioning of local defective wires in transmission line are both achieved, by using multiple piezoelectric elements to surround the stands and send elastic waves into every single wire. The proposed research can play a role of guiding the development of highly effective UGW method and detecting system for multi-wire transmission line.

基于超声导波的车用氢瓶在线检验技术研究

在役车用氢瓶的安全性能直接影响到氢能产业交通应用场景的可行性。传统拆卸离线检验模式制约了产业发展,结合前期研究成果,创新车用气瓶定期检验策略,通过定位损伤引导判断是否应进行拆卸离线验证气瓶安全性能。本文开展超声导波技术对车用氢瓶缺陷的定位算法研究及装置开发,进而攻克金属基碳纤维复合材料制气瓶噪声干扰大、信噪比高等不利因素,有效提取损伤信号,实现高精度损伤定位,经对极端冲量损伤、表面裂纹损伤后的车用氢瓶进行试验,验证其损伤定位误差可达到5%以内,对在役车用氢瓶安全性能评估具有非常重要的应用前景。

Laser-Based Guided Wave Propagation and Mode Decomposition in Detecting the Integrity of Structural I-Beams

This paper addresses the studies carried out on an I-beam to reveal the wave propagation characteristics and tackle the multi-mode propagation of Lamb waves. The experimental setup consisted of a new 3D Scanning Laser Doppler Vibrometer manufactured by Polytec (3D-SLDV) and was used to acquire high resolution time-space Lamb waves that were propagating in the I-beam. A high power and pulsed Nd:YAG laser was used to emit the required Lamb waves. The emission and sensing of the waves were carried out simultaneously. The wave propagation data was recorded by scanning the surface of the I-beam in a sequential manner. The measured data was used to construct the wave patterns that were propagating in the I-beams at different time instants. Furthermore, as the waves in an I-Beam propagate with multiple modes even at low frequency range, filtering was carried out in the frequency-wavenum- ber domain in order to decompose the modes. The results presented thereby confirm that the new 3D-SLDV possesses tremendous capability in revealing the wave propagation characteristics and its interaction with defect. The results could be the first time that the waves propagating in a real I-beam can be visually observed, whilst in the past, it can only be visualized through simulation. The capability of using such totally laser-based 3D inspection system to reveal the characteristics of Lamb wave and its interaction with defects are substantial.

基于预测兰姆波参考信号的缺陷概率成像

针对兰姆波缺陷概率成像需要从材质相同的无缺陷结构获得参考信号的问题,提出一种基于参考信号理论预测的概率成像方法,实现兰姆波缺陷定位.该方法将初始信号和兰姆波的频散特性结合,根据拟合得到的幅值衰减系数计算概率成像路径上的参考信号.根据该方法计算得到的参考信号和对应路径上响应信号的希尔伯特谱定义缺陷表征指数,结合兰姆波椭圆概率成像方法实现缺陷定位.单一缺陷和双缺陷成像定位的实验结果表明,该方法可以得到缺陷的概率图像,对缺陷定位的误差小于7.07 mm,解决了需要测量兰姆波参考信号的问题,定位准确、实用性好.

高纯度横波蝶形线圈电磁超声换能器优化设计

蝶形线圈电磁超声换能器(EMAT)能够在铝块中同时激发出超声横波和纵波,接收信号中存在横波反射回波和纵波反射回波,纵波回波会影响缺陷检测的准确性。该文设计了一种变尺寸蝶形线圈EMAT,通过改变线圈不同位置导线的宽度与间距,改变不同位置的换能效率,以实现横波的增强和纵波的抑制。首先,考虑永磁体的空间磁场分布,分析蝶形线圈EMAT不同位置导线所受洛伦兹力与激发超声波类型的关系,结合有限元声场云图,得到EMAT接收信号中存在多个回波的原因;其次,研究线圈参数对换能效率和横波纵波幅值比的影响规律,利用有限元仿真确定变尺寸EMAT的设计参数;最后,制备常规与变尺寸蝶形线圈EMAT,采集无缺陷铝合金试块的回波,结果表明,当永磁体直径与线圈中心宽度比为1.92时,纵波幅值削弱了66.1%,横波幅值增大了36.3%,横纵波幅值比从5.8升至23.1。该文设计的变尺寸蝶形线圈EMAT实现了对纵波的削弱和横波的增强,提升了横波电磁超声内部缺陷检测的可靠性。