Discussion of the Definition for Acoustic Emission Event in the Time Series of Concrete Damage Process

Acoustic emission signals from concrete compression damage process are non-stationary and their arrival time is unknown. Therefore, the definition on the acoustic emission event in the time series is not clear. In this paper, the acoustic emission signals associated with concrete specimen under uniaxial compression are acquired by full-digital acoustic emission system. The overlapping phenomenon of acoustic emission signal is presented and discussed by the analysis of time interval between adjacent hits. Acoustic emission signals are classified into three categories according to their waveform characteristics. And the result shows that as the loading process continues, more and more amount of continuous type of acoustic emission signals appeared, indicating the acoustic emission signal does not carry the features of burst type, which will introduce obvious errors in the calculation of acoustic emission event. In contrast, the average signal level used in the analysis of continuous type of acoustic emission signal shows a good regularity with the damage process of concrete.

     

Analysis on acoustic signal characteristics of the fatigue cracks in anchor structure of cable-stayed bridge tower

The full size model fatigue test on the anchor structure of cable-stayed bridge tower was engaged in laboratory. The acoustic emission instrument was used to monitor the fatigue cracks continuously in the fillet of the anchorage, to investigate the acoustic signal characteristics. Through different ways of loading, the periodic variation of acoustic signals, and crack propagation parameters of the acoustic signals are obtained. By continuously monitoring of the acoustic signal of the fatigue cracks, it can be possible to find the location of the fatigue cracks, and the time it generates. According the active changes of the acoustic signals of the fatigue crack via continuous monitoring, the propagation tendency of the crack in the anchor structure of the cable-stayed bridge tower can be predicted. This method provides support for the crack detection and on-line real-time monitoring by acoustic emission.     

Developing a Nondestructive Method for Revealing Defective Areas in Reinforced Concrete Under Bending Conditions

We present results of studying the spatial variation of parameters of the electrical response to a weak impact under stepwise loading of concrete beams reinforced with steel rods. It is proposed to use the following diagnostic parameters to characterize the presence of a defective area in reinforced beams: the maximum coefficient of correlation between the spectrum of electrical signal after stepwise loading and the original spectrum; the frequency shift for which the maximum correlation coefficient is observed; the coefficient of correlation between the spectrum of signal at the current loading stage and the signal spectrum at the previous stage; and the center of gravity of the spectrum. The proposed method can be used to locate the defective area in reinforced concrete under bending conditions.

     

Diagnostics of fracturing of structural materials based on parameters of electromagnetic radiation signals

The methodological aspects and results of experimental studies allowing for remote evaluation of the integrity of structural materials under loading using the method of electromagnetic emission (EME) are considered. It is known that in the process of loading different materials systems of cracks that are formed in them emit acoustic and electromagnetic signals. Based on signal parameter variations, it is possible to predict an oncoming moment of disruption of their integrity. The EME is a remote method and does not require direct contact with an object under study, be it rock specimens or metal articles. It is proposed to use it for testing the integrity of metal articles. The first results of diagnostics of the integrity of metal rings made of different materials (steels, duraluminum, zirconium, and copper) using sensing devices, namely antennas of electrical and magnetic types, are presented. It is shown that when loaded different types of materials emit EME signals of different amplitudes whose level substantially exceeds the level of external disturbances and internal equipment noises. It is proposed to evaluate the integrity of different metal articles, especially those in nooks, based on increased amplitudes of EME signals.     

基于小波能谱系数的风力机疲劳裂纹特征

提出了风力机叶片裂纹扩展声发射信号的优化小波重分配尺度谱及小波能谱系数相结合的分析法。基于Shannon熵理论计算裂纹扩展声发射信号的重分配尺度谱小波基函数带宽参数,得到最适合裂纹声发射信号的Morlet小波基函数。用优化后的小波基函数计算重分配尺度谱,获得裂纹扩展特征成分在时间尺度平面的高幅值能量分布,利用特征能谱系数表征其重分配尺度谱的特征。实验结果表明,该方法有良好的时频聚集性和抗噪能力,实现了风力机叶片裂纹扩展声发射信号的时频特征提取,得到了能谱系数作为特征向量表示信号特征。该方法可用来实现风力机叶片在复杂环境中的模式识别。     

状态热图在AGC伺服缸早期振动辨识中的应用

通过对轧制自动厚度控制系统(automated gauge control,简称AGC)伺服缸分别模拟3个阶段的保载和振动加载下所收集到的声发射信号,依托前期研究,探索基于状态热图的AGC伺服缸早期振动的辨识方法。通过在迁安沪久660mm轧机的AGC伺服缸上模拟保载和早期振动状态,采集声发射信号,对所采集信号的累计概率分布进行分析,选取可表征伺服缸加载状态变化的声发射特征。基于对所选特征进行组合并施加一定的值域约束和逻辑运算条件,构建了AGC伺服缸保载和早期振动的声发射热图。对状态热图的分析结果显示,AGC伺服缸在同等加载状态下的振动和保载状态可较好地通过此类状态热图予以呈现,为AGC伺服缸的早期振动状态提供一种快速、便捷的可视化辨识方案。     

Using a probabilistic model to estimate the reliability of locating acoustic emission sources

A probabilistic model for estimating the error in determining the coordinates of acoustic emission (AE) sources based on experimental data is considered. A spherical indentor was pressed in a test object to obtain a large number of AE signals. Processing of signal parameters has made it possible to reveal the dependence of the likelihood of determining the coordinate with a prescribed accuracy on the maximum amplitude and AE-signal rise time. The possibility for choosing the method of detection of the AE-signal time of arrival at receivers depending on the signal parameters has also been examined.     

Acoustic emission method for tool condition monitoring based on wavelet analysis

It is believed that the acoustic emission (AE) signals contain potentially valuable information for tool wear and breakage monitoring and detection. However, AE stress waves produced in the cutting zone are distorted by the transmission path and the measurement systems and it is difficult to obtain an effective result by these raw acoustic emission data. In this article, a technique based on AE signal wavelet analysis is proposed for tool condition monitoring. The local characterize of frequency band, which contains the main energy of AE signals, is depicted by the wavelet multi-resolution analysis, and the singularity of the signal is represented by wavelet resolution coefficient norm. The feasibility for tool condition monitoring is demonstrated by the various cutting conditions in turning experiments.     

不同小波基在碳钢材料声发射信号分析中的应用

为研究不同小波基对同一声发射信号分析结果之间的可比性,以碳钢在塑性变形和裂纹扩展时产生的声发射信号为研究对象,用db5和sym5两种常用小波基对检测信号进行了分析对比.结果表明,对碳钢在塑性变形和裂纹扩展时产生声发射信号,2种小波变换在信号能量分布趋势上分析结果一致,在主要信号峰值对应频率上分析结果接近,平均相对偏差仅为1.53%,而在各级信号占能量比例的具体值和信号峰值上偏差较大,平均相对偏差在10%左右,可比性较差.     

金属切削中流屑角突变的实验研究

对金属切削中的一类非线性问题－切屑流屑角的突变进行了检测实验研究,得出了流屑角突变时刻的力,振动和声发射信号。多次实验表明,这3种信号中对切削过程的非线性特征以切削力信号最为灵敏。根据传感器突变信号的产生时间,可以计算出突变时的切削层厚度aW和切削层图形系数gs。     

混凝土结构中PZT传感器的多功能性分析及应用

针对混凝土结构被动监测中的压电陶瓷(也称锆钛酸铅,Pb-based lead zirconium titanate,简称PZT)传感器信号的多功能特性,提出了PZT传感器不同用途信号的提取方法。根据不同功能信号的频率范围差异,通过小波Mallat分解,得到用于反映结构整体动态信息的振动信号以及局部断裂破坏引起的声发射信号,通过与加速度传感器和声发射传感器信号比较,验证了提取方法的正确性,并将该方法应用到钢筋混凝土框剪结构模型地震破坏试验的实时监测中。试验结果表明,应用该方法提取到的振动信号能准确测得结构主频率等结构的动态信息,声发射信号部分能清楚捕捉局部损伤引起的能量释放情况。应用该方法可准确提取出结构的振动信号和声发射信号,利用同一PZT传感器能够实时评估和监测结构的整体动态特性和局部损伤状况。     

基于宽频激励电磁声谐振7075铝合金板厚检出概率

电磁超声换能器(EMAT)换能效率低、激发信号弱,而基于长周期激励信号以产生声波共振的电磁声谐振技术(EMAR)虽然可以提高接收信号的信噪比,然而可能导致主脉冲加宽并扩大超声波检测盲区,降低测量精度.本文应用一种宽频激励电磁声谐振技术(BE-EMAR)和一种Halbach阵列纵波EMAT,以单周期宽频激励作为EMAT输...     

新能源汽车油泵电机电磁力建模及其匝间故障监测方法研究

新能源汽车油泵电机出现匝间故障,无法保证燃料供给、控制压力、提供润滑和冷却等,威胁行车安全。对此,本文提出了一种基于电流和振动信号相结合的匝间故障在线监测方法。首先,根据麦克斯韦张量法构建含有故障电流谐波的电磁力模型。其次,设计了一个多传感器的电机信号采集电路。最后,采用改进的自适应经验模态分解法对经降噪后的振动信号进行自适应分解,利用相关系数法对所得的一系列本征模式函数筛选和重构。综合评估峭度与均方根值之比以及包络谱特征因子,得到故障特征指标提升52.3%,表明重构信号具备更高的敏感性,并通过电流波形分析验证了重构信号与故障特征的一致性。该研究对油泵电机故障诊断和状态预测具有重要工程意义。     

A Novel Technique of AE Signal Processing for Upgrading the Accuracy of Flaw Localization

The paper is devoted to improving the accuracy of localization of acoustic emission signals. In uence of various factors on the accuracy of the arrival times of signals has been analyzed. The paper suggests a new technique for measuring the arrival time of an AE signal at a transducer. Different localization techniques have been compared.     

A new acoustic emission source location technique based on wavelet transform and mode analysis

For wave propagation in dispersive media, the arrival time of the acoustic emission signal to the sensor is dependent on the setting of the threshold voltage, which results in the inaccuracy of the acoustic emission location. Based on the wavelet transform and the theory of modal acoustic emission, a new method is proposed to improve the accuracy of acoustic emission source location. It is believed that the acoustic emission signal propagation in the structure has the characteristics of multi-mode and dispersion, and the acoustic emission source location should use the arrival time to sensors obtained from the output signals not only at the same mode but also at the same frequency. The wavelet transform is used to resolve the problem. By utilizing the time-frequency data of the wavelet, the frequency-dependent arrival time traveling is easily obtained; by numerical computation of the wave’s propagation in structure, the group velocity of the guided mode is also obtained, therefore the accuracy source location is realized. The acoustic emission source location experiments were conducted in a thin steel plate and results show that the technique is an effective tool for acoustic emission source location. __________ Translated from Chinese Journal of Scientific Instrument, 2005, 26(3) (in Chinese)     

The possibilities of acoustic emission testing of rails during exploitation

The possibilities of acoustic emission testing of rails on a bridge are considered. The stress-strain state of a rail under conditions of train loading is analyzed. The problems of minimization of levels of mechanical and electromagnetic noises are considered. The results of field acoustic emission tests and their analysis are presented.     

Studying the influence of the scale factor on the parameters of mechoelectric transformations during elastic excitation of concrete

The results of experimental studies of the influence of the geometrical dimensions of heavy-concrete articles on the parameters of the electric response under an elastic impact excitation are presented. It is established that an increase in the length of models at a constant cross section leads to a decrease in the electrical-response magnitude and an increase in the signal attenuation factor, as well as to a shift of the main spectral maximum of electrical signals toward lower frequencies and a change in the positions and ration of significant spectral peaks. It is shown that changes in the geometric dimensions of heavy-concrete articles do not lead to appreciable changes in the maximum cross-correlation coefficient between the electrical-response spectrum and the spectrum of freely damped harmonic oscillations.     

气体管道泄漏模态声发射时频定位方法

针对声发射信号频散特性导致基于时延估计的气体管道泄漏定位误差大的问题,提出一种基于模态声发射时频分析的泄漏定位方法。该方法采用平滑伪Wigner-Ville时频分布对两泄漏信号的互相关函数进行时频分析,利用互相关函数的时频谱可同时提取泄漏信号的时间延迟和与之对应的频率;然后根据泄漏声发射信号的主导模态的频散曲线即可确定该频率对应的声速,利用实时确定的声速和时间延迟并根据两传感器之间的距离即可确定泄漏点的位置。实验结果表明,采用时频分析的气体管道泄漏定位误差与互相关相比减少了6倍。所提出的模态声发射时频定位方法能有效抑制泄漏信号的频散,提高泄漏信号的相关性,从而更适合用于声发射管道泄漏定位。     

裂纹长度和位置影响下声发射信号传播特性

针对再制造毛坯闭合裂纹检测较困难,采用声发射技术,从仿真和实验两个方面研究裂纹长度和裂纹位置对声发射信号传播特性的影响。根据裂纹中波的传输理论,采用时域有限差方法,仿真两个因素对声信号的影响,实验结果表明,裂纹长度对于信号衰减影响比裂纹位置明显;裂纹长度小于3 mm时信号的能量和幅值衰减系数(分别为-0.28和-0.15)明显大于裂纹长度大于6 mm的信号衰减系数(分别为-1.48和-0.9);裂纹长度为3 mm比裂纹长度为0.5 mm时能量和幅值相对衰减率分别大0.62 d B和0.2 d B,而其比裂纹长度为15 mm的能量和幅值相对衰减分别小14.7 d B和8 d B;裂纹位置的能量相对衰减率位于-6.4~-6.6 d B,幅值相对衰减率位于-1.4~-1.7 d B。实验研究了裂纹长度对声发射信号的影响,得出裂纹长度小于2 mm时的衰减系数明显大于裂纹长度超过6 mm的衰减系数,与仿真结果相符。因此,声发射参数与裂纹长度有明确的对应关系,声发射技术可有效检测再制造毛坯中的裂纹,尤其是长度小于3 mm的微裂纹。     

Noncontact excitation of sound in metals by a video pulse of electric field

An acoustic signal that is excited without acoustic contact by an excitation electrode in a metal sample has been studied. A constant electric voltage close to the breakdown value was applied between the electrode and the sample. A video pulse of electric field with a duration of 0.4 μs was used to excite sound in the sample. The ratio k of signals that were registered with noncontact and contact excitation proved surprisingly large (k = 0.14) when compared to the value expected from the literature data. A strong dependence of the noncontact acoustic signal on the filling frequency f of the excitation pulse has been observed. For f > 10 MHZ, the signal dropped to the level of noises. An explanation for this frequency dependence is proposed. It is based on the assumption of quasi-atomic thickness of the charged metal layer that is created by the electric field.