Wavelet packet analysis for the propagation of acoustic emission signals across turbine runners

Acoustic emission (AE) signals propagated across turbine runners incur attenuation due to propagation distance and structure interface. Wavelet packet transform (WPT) was used to analyze the attenuation characteristics of AE signals. A series of experiments had been carried out on an HLA286a-LJ-800 Francis turbine runner and AE signals were obtained from standard pencil lead break sources. The experimental results indicate that the WPT technique is an effective tool in extracting the attenuation characteristics. The feature packet can reflect the attenuation characteristics of signals across the runner. As a result, the pressure on data transmission and storage can be decreased by extracting feature packet coefficients using the wavelet packet technique, which indicates the feasibility to apply the AE technique to monitor the running state of turbine runners on site.     

基于时序灰度图和分组ResNet的回转支承故障诊断北大核心

为解决大型回转支承转速低、背景噪声大、常规的声发射诊断方法难以适用的问题,提出一种基于灰度图和ResNet模型相结合的声发射信号处理方法。将声发射信号编码为二维灰度图像,并通过ResNet模型识别声发射信号编码得到的灰度图,通过训练模型实现对大型回转支承的故障诊断。对某型号大型回转支承进行试验,结果表明:以时序二维化后的灰度图作为故障诊断依据,可以显著提高回转支承的故障诊断准确率;相比于传统方法,所提方法泛化性能和鲁棒性能更好,可以很好地应用在实际工况中的大型回转支承故障诊断。     

滚动轴承故障的声发射检测技术

介绍声发射信号技术的机理,研究用声发射检测滚动轴承故障的方法。把声发射信号与振动信号作对比,通过高通滤波后再进行包络解调,结果表明声发射信号可以较早地诊断出故障,抗干扰性好。而且经过信号处理之后,声发射信号分析的频率比较单纯,能够很简单地判断出故障部位。     

Study of oxygen reduction on stainless steel surfaces and its contribution to acoustic emission recorded during corrosion processes

Acoustic emission technique is often used to monitor corrosion processes. Yet, among the potential sources of AE associated to corrosion phenomena, the emissivity of oxygen reduction on metallic surfaces has never been studied up to now. In that context, dissolved oxygen reduction was monitored by acoustic emission (AE) on as polished, pre-reduced, electrochemically or chemically passivated surfaces of AISI 316L austenitic stainless steel. The influence of the composition of the passive film on the oxygen reduction reaction has been confirmed. Moreover, in our experimental configuration, it has been demonstrated that proton reduction or iron oxide reduction were not at the origin of AE signals recorded during cathodic polarization of the specimens. On the other hand, oxygen reduction involving O–O bond rupture and/or atomic oxygen desorption from metallic surface appears to be the source of detected acoustic emission. However, these mechanisms generally occur too slowly during free corrosion processes, such as crevice corrosion, to promote any significant acoustic emission when developing naturally on metallic surfaces.     

飞机蜂窝复合材料板压缩过程的声发射定位研究

声发射检测的主要目的是发现声发射源和有关源的信息,声发射源定位是声发射检测中至关重要的指标,其准确程度反映了声源的检测位置与实际缺陷源位置的符合程度。本研究针对复合材料的特性,结合实际情况进行了声速和衰减测量实验,并通过断铅实验对复合板进行声发射定位。通过对复合材料板压缩实验的在线监测,基于声发射信号参数的提取及关联图分析,给出了各损伤阶段的参数特征,以及声发射监测区域内的裂纹萌生扩展断裂的时间和位置。研究结果表明,复合板实际断裂位置与声发射监测得出的位置相吻合。     

Analytical modeling of acoustic emission for monitoring of peripheral milling process

This paper presents the development of an analytical model relating the acoustic emission (AE) energy content to the cutting process parameters in peripheral milling and the experimental verification of the effects of the cutting parameters on the AE energy measurement to assess the applicability of AE sensing to the monitoring of peripheral milling. The model consists of an oblique cutting component and a rubbing component. It includes the contribution from both the AE attributed to plastic deformation in the primary shear zone and the AE resulting from interfaces between chips and the rake faces of the cutting teeth, between the workpiece and the cutter periphery as well as between the cutter flank and the machined workpiece surface. The adoption of an effective shear angle and a mean fraction angle in the model formulation provides insight into the fundamental mechanism of the cutting process responsible for the generation of the acoustic emission. A numerical example following the model development and a series of peripheral milling tests show that the true mean square voltage of the AE signal from peripheral milling increases with the primary cutting parameters (cutter rotating speed, feedrate, axial and radial depths of cut). The result of this work suggests that the energy measurement of the AE signal can be effectively used for the monitoring of peripheral milling processes.     

Detection of breakaway oxidation and spalling in the oxide scales of 2 1/4Cr-1Mo steel using acoustic emission technique

The onset of breakaway oxidation and in-situ cracking and spalling of the oxide layer formed on 2 1/4Cr-1Mo steel have been detected by the use of the acoustic emission (AE) technique. Various AE parameters, viz., acoustic emission event counts vs time, acoustic emission counts vs time, and voltage level vs time have been used to detect these phenomena. It has been found that variations in AE parameters are marginal during heating at 600, 700, and 800°C, and a sudden rise in these parameters occurs during cooling. Increase in AE activity during cooling has been related to spalling of the oxide layers. At 900 and 950°C, a considerable increase in AE parameters (except voltage level) has been detected after certain times at the respective temperatures. By comparing with corresponding thermogravimetric curves, this increase in AE parameters has been attributed to the onset of breakaway oxidation. A very large increase in AE parameters during cooling from these temperatures has been related to in-situ cracking.     

大型观览车主轴系统的声发射信号特征

大型观览车不仅是游乐园的标志,而且是城市的标志。针对大型观览车主轴系统难以拆卸的特点,通过试验模型,模拟了主轴运行过程,采用声发射仪器获取了主轴系统运行过程中的声发射信号。通过分析声发射信号,初步得出了主轴运行过程中声发射信号的规律特征,包括参数特征和波形频谱特征。     

管道声发射泄漏检测技术研究进展

声发射检测的目的是获得声发射源的有关信息(如声发射源的特征和位置等)。管道泄漏声发射信号既携带结构的某些特征信息(泄漏孔大小和位置等)，同时又有很大的随机性和不确定性，属于一种非平稳随机信号。在分析管道泄漏声发射信号特点基础上，着重对管道声发射泄漏检测技术及信号处理方法的最新研究进展进行了回顾。模态声发射能够解决常规声发射技术发展中的问题，是一种潜在的能够实现管道泄漏定量检测的方法。     

压力容器声发射信号人工神经网络模式识别方法的研究

采用人工神经网络模式识别技术对现场压力容器各种声发射源信号特征参数进行了模式识别分析,提出了采用人工神经网络分类方法对压力容器声发射源信号进行定量分析的概念,从而找到了评价声发射源严重程度的方法,设计和培训的人工神经网络可以给出一个多种因素产生的复合声发射源中裂纹扩展、氧化夹渣断裂、残余应力释放和机械摩擦信号所占的百分比,这一结果使声发射技术对压力容器安全状态的无损评价成为可能。     

Observations of acoustic emission activity during gear defect diagnosis

It is widely recognised that acoustic emission (AE) is gaining ground as a non-destructive technique (NDT) for health diagnosis on rotating machinery. The source of AE is attributed to the release of stored elastic energy that manifests itself in the form of elastic waves that propagate in all directions on the surface of a material. These detectable AE waves can provide useful information about the health condition of a machine. This paper reports on part of an ongoing experimental investigation on the application of AE for gear defect diagnosis. Furthermore, the possibility of monitoring gear defects from the bearing casing is examined. It is concluded that AE offers a complimentary tool for health monitoring of gears.     

热障涂层无损检测技术研究进展

为提高发动机的涡轮前温度和热端部件服役寿命,热障涂层（TBCs）被广泛应用于燃气涡轮发动机。热障涂层具有多相、多界面和非均质特性,且其服役工况恶劣复杂。寻找一种可以表征涂层显微组织、缺陷、热物性、应力等反映涂层质量和剩余寿命的无损检测方法,对发动机的热端部件安全性和可靠性至关重要。文中综述了超声检测技术（UT）、声发射技术（AE）、红外热成像技术（IRT）、阻抗谱技术（IS）和光激发荧光压电光谱技术（PLPS）的原理以及其在热障涂层无损检测中的研究应用,并详细介绍了太赫兹时域光谱（THz-TDS）技术及其在热障涂层中的应用。最后总结了上述无损检测方法的检测能力,并对热障涂层无损检测方法进行展望。     

复合材料损伤过程的声发射研究方法

对声发射（ＡＥ）研究的基本方法作了简介,采用参数分析和波形分析方法对金属基和陶瓷基复合材料在变形损伤过程中的ＡＥ特征进行了研究,结果表明,通过记录声发射特征参数可以有效地判断复合材料各阶段的变形损伤机制。因此,利用这一手段可以更全面、更深入地了解复合材料伤破坏过程。     

Investigation of acoustic emission signals under a simulative environment of grinding burn

Grinding burn is a common phenomenon of thermal damage that has been one of the main constraints in grinding in respect of high efficiency and quality. An acoustic emission (AE) technique was tried in an attempt to identify grinding burn on-line. However, the AE features of grinding burn are relatively weak and are easily obscured by other AE sources. This paper presents an investigation of the AE features of the thermal expansion induced by laser irradiation, which was designed to simulate grinding thermal behaviour. By using wavelet packet transforms, AE features at the grinding burn temperature can successfully be extracted without other mechanical interferential factors. Such thermal AE features provide a firm foundation for analysing and monitoring the AE features of grinding burn.     

On-line monitoring of depth of cut in AWJ cutting

Monitoring of the abrasive waterjet (AWJ) cutting process has become increasingly important. The present paper proposes a model for on-line depth of cut monitoring based on the acoustic emission (AE) response to the variation in AWJ depth of cut, instead of the expensive and impractical vertical cutting force monitoring. The main objective is to use the AE technique in order to predict the actual depth of cut in AWJ cutting under normal cutting conditions. It was found that the root mean square of the acoustic emission energy (AErms) increases linearly with an increase in the depth of cut and could be used for its on-line monitoring. The results show that the AE is the most suitable technique for AWJ monitoring, as the AE signal has high sensitivity to the variation in the depth of cut.     

硬质合金PA30高速深磨过程中声发射信号特征的变化研究

在硬脆难加工材料硬质合金PA30高速深磨声发射实验中,随着工件速度和磨削切削深度增加,声发射信号特征参数均方根（AE_RMS）和磨削力变大;随着砂轮速度增大,AE_RMS和磨削力减小。磨削力和AE_RMS有相同的变化趋势。硬质合金PA30高速深磨AE频谱的能量在100~600kHz的频段比较集中,其AE信号频谱的能量与频率范围明显高于低速浅切磨削。      

Monitoring extremely slow rolling element bearings: part II

The most established technique for monitoring the integrity of rolling element bearings is vibration analysis. However, at extremely slow rotational speeds monitoring the health of rolling element bearings is fraught with difficulty. Part I of this work details difficulties with monitoring rolling element bearings rotating at speeds of less than 2 rpm. Furthermore, it presents a study of the high frequency acoustic emission (AE) technique as a means of monitoring low-speed rolling element bearings. The application of AEs to monitor operational slow-speed bearings with bore diameters of 120 mm is presented. It is concluded that the mechanism of AE generation was the relative movement between bearing elements experiencing loss of mechanical integrity, for example, the rolling/sliding action of a roller on a defective outer race.     

模态声发射——声发射信号处理的得力工具

模态声发射是声发射信号处理技术的得力工具。介绍它在声发射源定位、复合材料损伤源识别、疲劳裂纹萌生和扩展的声发射监测以及日历损伤声发射评价等工程实践中的应用。     

Failure Behavior of Plasma-Sprayed Yttria-Stabilized Zirconia Thermal Barrier Coatings Under Three-Point Bending Test via Acoustic Emission Technique

In this paper, the failure behavior of plasma-sprayed yttria-stabilized zirconia thermal barrier coatings fabricated by atmospheric plasma spraying (APS-TBCs) under three-point bending (3PB) test has been characterized via acoustic emission (AE) technique. Linear positioning method has been adopted to monitor dynamic failure process of the APS-TBCs under 3PB test. The investigation results indicate that the variation of AE parameters (AE event counts, amplitudes and AE energy) corresponds well with the change of stress–strain curve of the loading processes. The failure mechanism was analyzed based on the characteristics of AE parameters. The distribution of frequency of crack propagation has been obtained. The AE signals came from two aspects: i.e., plastic deformation of substrates, initiation and propagation of the cracks in the coatings. The AE analysis combined with cross-sectional observation has indicated that many critical cracks initiate at the surface of the top-coat. And some main cracks tend to propagate toward the substrate/bond-coat interface. The actual failure mechanism of the APS-TBCs under 3PB test is attributed to the debonding of metallic coating from the substrates and the propagation of the horizontal crack along the substrate/bond-coat interface under the action of flexural moment.     

基于声发射和振动信号的振动钻削钻头故障诊断试验研究

针对钻削过程中钻头状态监测问题,基于声发射采集系统和振动采集系统设计超声轴向振动钻削钻头故障监测装置,分别应用完整钻头和故障钻头进行45钢板的超声振动钻削对比试验,采集不同钻头状态的AE和振动信号,通过时域分析、频域分析和小波分解,分析故障钻头对AE和振动信号的影响。试验结果表明：通过AE和振动信号判别钻头状态,判别结果与实际一致,能够实现钻头的故障诊断。