Best wavelet basis for wavelet transforms in acoustic emission signals of concrete damage process

It is critical to select the best wavelet basis for implementing wavelet algorithms. Firstly, the mathematical characteristics of the eight kinds of wavelet basis commonly used in the field of engineering are summarized and compared based on the analysis of the features of acoustic emission signals from concrete damage process. Secondly, wavelet basis suitable for acoustic emission signals in concrete damage are given by the theoretical analysis. Finally, the best wavelet basis for wavelet transforms in acoustic emission signals of concrete damage process are obtained by calculating the energy entropy. The results show that the energy entropy can be used to select the wavelet basis for acoustic emission signals during the process of concrete damage. Among them, the wavelets of Symlets can be used as the optimum wavelet basis.     

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。     

Developing an integrated technique to evaluate crack formation in reinforced concrete under uniaxial compression

Regularities of changes in the parameters of acoustic and electromagnetic emission and of forced electric response from reinforced concrete under uniaxial compression have been studied. It has been established that the main diagnostic criteria of the onset of crack formation are the emergence of high-amplitude signals of acoustic and electromagnetic emission; considerable changes in the spectral composition of the electric signal; a decrease in the maximum coefficient of correlation between the spectra of signals registered at different stages of loading as compared with the spectrum of the signal prior to loading; and hopping shift of the frequency at which the maximum correlation coefficient is observed. On-line monitoring and periodic inspection can be used to assess the onset of crack-formation processes.     

基于小波包变换的FRP容器爆破声发射信号分析

对FRP复合材料容器进行水压爆破的力学性能实验,采集FRP复合材料容器在受压损伤和爆破过程中的声发射信号。基于小波包变换对复合材料容器爆破声发射信号进行时频对比分析,由能量在频段上的分布情况,得出爆破信号特征。     

Damage Processes of Steel Fiber Reinforced Mortar in Different Fiber Content Revealed by Acoustic Emission Behavior

The performance of the cement-based materials could be improved by the incorporation of steel fiber, but the damage processes become more complex with different content at the same time. The acoustic emission (AE) technology can achieve the global monitoring of internal damage in materials. Under the axial compression load, the AE signals of steel fiber reinforced mortar specimens with different fiber content during the whole damage process were selected. The analysis of the damage evolution process, failure mode and damage degree were conducted by AE energy, RA value, AF value and b value respectively. It is found that the cement matrix cracked on the initial stage, the cracks further developed in the medium stage as well the fiber out of shape and the fiber were pullout on the last stage. The cumulative AE energy is proportional to the ductility of the material. The damage mode and damage degree can be judged by identifying the damage stage which obtained by the analysis of the AF value. It conducted that AE parameters can describe the failure processes due to it change monotonically with the progress of damage.     

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.     

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。     

FRP复合材料容器水压爆破声发射特性分析

通过FRP复合材料容器水压爆破过程的力学性能试验研究,结合声发射技术,研究FRP复合材料容器在受压损伤及爆破过程中的声发射信号变化规律。运用参数分析法,分析了FRP复合材料容器损伤过程的声发射特性,应用费利西蒂比评价其损伤程度。研究结果,为在用FRP复合材料容器的完整性评价提供试验依据。     

港口起重机箱型梁模型声发射信号参数分析法研究

利用参数分析法的目的是为了有效准确的分析声发射信号的特性,常用的参数有振铃计数、能量、上升时间、脉冲持续时间、幅值分布、事件计数等。每个参数都可以提供与声发射信号特征相关的信息,在声发射信号分析中有着重要作用。     

A study of tool wear using statistical analysis of metal-cutting acoustic emission

Many aspects of the interactions between cutting tools, workpiece material and the chips formed during machining that affect the wear and failure of the tool are not fully understood. The analysis of acoustic emission signals generated during machining has been proposed as a technique for studying both the fundamentals of the cutting process and tool wear and as a methodology for detecting tool wear and failure on line. A brief review of the theory of acoustic emission is presented. Acoustic emission data from reduced contact length machining experiments and tool flank wear tests are analyzed using distribution moments. The analysis shows that the skew and kurtosis of an assumed β distribution for the r.m.s. acoustic emission signal are sensitive to both the stick-slip transition for chip contact along the tool rake face and progressive tool wear on the flank of the cutting tool.     

An investigation into diesel engine air-borne acoustics using continuous wavelet transform

The emitted acoustic signals from diesel engines carry useful indicators about their operating conditions and health status. Unfortunately, those signals are very complex, contain numerous numbers of sources and corrupted by subnational amount of noise. This makes it difficult to extract those condition indicators via the use of conventional time and frequency domain analysis techniques. This paper studies the characteristics of diesel engine air-borne acoustic signals using time-frequency domain techniques. One analysis technique is investigated; continuous wavelet transform (CWT). First, some of the mathematical background of the CWT is reviewed. Second, the detection capabilities of this technique are evaluated using air-borne acoustic signals collected from diesel engine in acoustically untreated laboratory. Consequently, some engine operating conditions and faults are investigated using the CWT techniques. The achieved results prove the technique’s sensitivity to engine speed and load variations. More important the CWT shows excellent capabilities in detecting engine’s injection process and lubrication related faults at early stages.     

基于小波神经网络的FRP容器爆破声发射信号研究

对FRP复合材料容器进行水压爆破的力学性能实验,利用声发射检测技术,采集FRP复合材料容器在受压损伤和爆破过程中的声发射信号。将采集到的声发射信号进行小波包特征提取,得到的前8个频带的特征向量作为小波神经网络的输入样本。据得到的数据样本库数据来预测、验证复合材料容器的破坏过程。     

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。     

基于声发射技术的金属动态塑性摩擦研究

利用声发射技术研究了凸模胀形过程中有油润滑和干摩擦2种不同摩擦条件下的动态摩擦过程，得到了凸模胀形声发射特性曲线，并对声发射特性曲线进行了分析。结果表明：凸模胀形过程中的声发射信号是由凸模胀形过程中的摩擦产生；摩擦力随胀形深度而变化，是胀形深度的函数；凸模胀形过程中的声发射信号证明凸模胀形过程中的摩擦是一个动态过程；声发射信能动态地反映这一摩擦变化过程。     

批量钻削监测信号双谱特征融合研究及应用

基于钻削工步质量波动与监测信号特征变化之间的耦合现象,提出一种基于监测信号双谱特征的高精度批量钻削工步质量一致性控制检测方法。认为正常钻削过程的声发射和三向加速度振动监测信号可视为随机过程,满足或近似高斯分布,信号偏离高斯分布的程度与各钻孔加工质量波动间存在对应关系;以各钻孔声发射和加速度振动监测信号为研究对象,提取各钻孔监测信号的双谱幅值平均值为特征,对不同钻削情况下信号偏离高斯分布的程度进行定量分析;采用基于ReliefF算法的特征加权模糊聚类分析,进行基于监测信号双谱幅值均值特征矩阵的钻孔质量分类,并与人工检测的工步质量一致性结果对比分析。计算和分析结果表明,监测信号双谱特征与各钻削工步质量之间存在有机联系,对信号双谱特征进行融合聚类可分析批量钻削工步质量的一致性。     

A Feature Extraction Method for the Wear of Milling Tools Based on the Hilbert Marginal Spectrum

Abstract

The Hilbert–Huang transform (HHT) can adaptively delineate complex non-linear, non-stationary signals when used as the Hilbert–Huang marginal spectrum through empirical mode decomposition (EMD) and the Hilbert transform, to highlight local features of signals. Characterized by high resolution, the Hilbert marginal spectrum has been widely applied in mechanical signal processing and fault diagnosis. In the research, an HHT based on the improved EMD was proposed to analyze the cutting force, vibration acceleration (AC), and acoustic emission (AE) signals during tool wear in the milling process. At first, the collected signals were subjected to range analysis, which revealed that tool wear was closely related to the signals collected during the cutting process. Then, EMD was applied to the signals, followed by variance analysis after calculating the energies of each intrinsic mode function (IMF) component. Afterwards, the IMF components significantly influenced by wear degree, while slightly influenced by the three cutting factors (cutting velocity, feed per tooth, and cutting depth), were selected as IMF sensitive to the degree of wear. The HHT was finally applied to the sensitive IMF components of signals containing major tool wear information, thus obtaining the Hilbert marginal spectra of the signals, which were able to reflect the changes in signal amplitude with frequency. On the basis of the Hilbert marginal spectrum, the method defined the feature energy function which was then used as the eigenvector for predicting tool wear in milling processes. The analysis of signals in four tool wear states indicated that the method can extract salient tool wear features.     

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。     

基于MATLABGUI的声发射信号特征参数分析平台

文章在MATLABGUI编程的基础上,设计了基于MATLAB．GUI的声发射信号特征参数分析平台。该平台用于分析混凝土构件在损伤状况下释放的有效声发射信号参数随时问或外变量变化的情况,从而得到声发射源的活动情况和发展趋势。仿真试验表明,该平台能够反映出预应力混凝土构件破坏过程中的特征信息,为实际远距离在线结构健康的监测提供了实际依据。     

声发射和小波包分析在损伤状态监测中的应用

为应用声发射技术对结构的损伤状态进行监测与识别,基于小波包分析提出了一种在线损伤监测方法。采用D-S证据理论对声发射信号的小波包能量谱进行多源信息融合得到改进的小波包能量谱,计算Mahalanobis距离构建结构损伤状态判别指标,采用t检验的概率方法考察不同损伤状态下判别指标的变化情况。旋转轴承结构的声发射信号分析结果表明,D-S证据理论能够对声发射信号的小波包能量谱识别样本抽取有效信息,结构损伤状态判别指标具有良好的结构损伤识别能力,能够准确地实现对结构不同损伤状态的识别。