Vibration impact acoustic emission technique for identification and analysis of defects in carbon steel tubes: Part B Cluster analysis

Current steel tubes inspection techniques are invasive, and the interpretation and evaluation of inspection results are manually done by skilled personnel. Part A of this work details the methodology involved in the newly developed non-invasive, non-destructive tube inspection technique based on the integration of vibration impact (VI) and acoustic emission (AE) systems known as the vibration impact acoustic emission (VIAE) technique. AE signals have been introduced into a series of ASTM A179 seamless steel tubes using the impact hammer. Specifically, a good steel tube as the reference tube and four steel tubes with through-hole artificial defect at different locations were used in this study. The AEs propagation was captured using a high frequency sensor of AE systems. The present study explores the cluster analysis approach based on autoregressive (AR) coefficients to automatically interpret the AE signals. The results from the cluster analysis were graphically illustrated using a dendrogram that demonstrated the arrangement of the natural clusters of AE signals. The AR algorithm appears to be the more effective method in classifying the AE signals into natural groups. This approach has successfully classified AE signals for quick and confident interpretation of defects in carbon steel tubes.     

复合绝缘子压接质量监测仪的研制

复合绝缘子越来越广泛地应用于输电线路中，但其压接过程中的质量一直没有有效的方法进行监测。由于复合材料在变形过程中会出现声发射现象，并且随着变形或损伤的程度不同，其声发射信号的特征有所不同．分析这些特征可以对压接过程中绝缘子的压接质量进行判断根据此原理，构建了复合绝缘子的压接质量监测仪器，并且重点描述了系统软、硬件设计中的关键问题现场测试表明：基于声发射技术的监测仪在复合绝缘子压接质量判别上有着良好的效果。     

Detecting hazardous sources of acoustic-emission signals using the estimated energy of clusters

A method for detecting hazardous sources of acoustic-emission (AE) signals by the level of their energy activity using clustering by digitized signal shape was considered. The influence of the distance between a source and an AE transducer on the energy of recorded AE signals was analyzed. The energy distribution median of signals in a cluster was proposed for evaluating the hazard of an AE signal source. The application of the developed method was tested based on the example of the analysis of AE inspection data on the welding of steel specimens with incomplete fusion and a crack at the root of a weld seam. This testing confirms the results of the fractographic inspection of a defective weld seam.     

多层包扎高压氢气储罐的声发射检测技术研究

1　前言天津石化公司化工厂ＰＸ生产装置有 1 0台多层包扎式氢气储罐 ,这类储罐属Ⅲ类压力容器。根据劳动部《压力容器安全技术监察规程》的要求 ,这类储罐使用到检验周期必须实施定期检验 ,但由于多层包扎储罐的结构特点 ,一般常规无损检测方法无法对其进行全面检验 ,导致企业压力容器管理及安全生产存在隐患。声发射技术由于其实用性强 ,检测灵敏度高 ,在很多领域得到广泛应用。目前 ,在金属压力容器检验及安全评定中 ,声发射已是一种重要的无损检测方法 ,尤其是在单层金属压力容器的检验中已成功应用 ,并有相关的检测标准。通过解剖一台…     

Feature extraction of AE characteristics in offshore structure model using Hilbert-Huang transform

This paper addresses an application of recently developed signal processing tool based on the Hilbert-Huang transform (HHT) to characterize the acoustic emission (AE) signals released from the offshore structure model. The AE signals from the cracks in the welded steel nodes of the offshore structure model are collected during the tensile testing in water and the simulated AE signals are also collected in the offshore structure model. Instantaneous frequency and energy features based on local properties of the AE signals are then extracted using the Hilbert-Huang transform method. In order to demonstrate the advantage of the AE feature extraction techniques based on Hilbert-Huang transform, the conventional AE analysis is also provided side-by-side for comparison. The results verify that the method based on HHT better characterizes the AE signals than the classical AE techniques. It can be concluded that the AE signal analysis based on HHT is an effective tool to extract the features and this opens perspectives for crack recognition in offshore structures.     

基于小波分析的声发射源定位技术

声发射全波形采集技术为基于波形分析的声源定位方法提供了可能。在板状构件中声波的传播模式较为复杂,且不同模式的波到达时间和波速均不相同,从而带来了声源定位误差。将时频幅度分析方法引入声发射源定位技术：从接收到的信号中提取出某一频率的柔性波随时间变化的规律,在理论分析的基础上证明,这个分离信号的最大幅值点所对应的时间就是该频率柔性波群速度的到达时间。根据这个到达时间,以及实际测量出的群速度就可以实现声发射源更精确的定位,试验结果也证明了这种方法的可靠性。     

天然气管道球阀内漏发声机理及检测试验

球阀作为高压天然气输送管道的主要设备,其内漏时的喷流气体会产生声发射信号,通过研究该声发射信号特征规律将有助于阀门内漏流量量化检测。针对这一问题,进行了天然气输送管道球阀内漏发声机理和检测试验研究,分析了阀门内漏声发射现象产生的机理和内漏流量检测评价方法。在此基础上,应用声发射检测系统对3种不同尺寸内漏球阀进行了检测试验,通过试验分析了球阀在不同内漏流量下的声发射信号频谱特征分布规律,并采用小波包分析方法进行信号特征参数(信息熵、均方根、频域峰值)提取。拟合特征参数与内漏流量关系曲线,采用R~2(确定系数)指标对曲线拟合程度进行评价,评价结果表明,采用均方根值(root mean square,简称RMS)的曲线拟合程度最高(R2为0.979),可以用于天然气输送管道球阀内漏流量的量化检测。     

声发射监测切屑状态的可行性研究

金属切削过程中产生丰富的声发射。用声发射技术监测切屑状态是一个很有潜力的新方法。本文通过实验研究了车削时切屑状态和声发射信号间的相互关系,结果表明：1.声发射DC包络信号脉冲能准确反映断屑情况;2.声发射加权计数率波形和包络信号均值能反映切屑形状和异常切屑状态;3.不同类型切屑的形成过程具有不同的声发射信号波形。     

Excitation of acoustic emission by laser radiation for studies of structural alterations in composites and polymers

The special features of excitation of acoustic emission (AE) by laser radiation are studied. It has been found that ruby and copper-vapor lasers reliably excite AE with an amplitude high enough to be detected. It has been shown that AE parameters of polymers have a significant sensitivity to the type of laser irradiation used for initiating local thermal destruction. The results can be used for remote acoustic calibration and initiation of local thermal destruction during AE diagnostics of thermal stability of polymers and composite materials.     

Identification of fretting fatigue crack propagation mechanisms using acoustic emission

In this study, a fretting fatigue test has been equipped with an acoustic emission (AE) device in order to identify the successive crack propagation mechanisms. The fretting fatigue crack nucleation and propagation is a complicated process. Cracks initiate and propagate firstly due to shearing (mode II) and then by tension (mode I). The crack propagation generates mechanical energy emission. Elastic waves appear and can be detected through AE. A complete analysis of the AE signals (multi-parameter analysis, location of the AE in the loading cycle and a statistical analysis) led to an identification of three different steps in the crack propagation process. The evolution of the shearing and the tension influences in the crack propagation process is recognizable separately. Therefore, the three crack propagation steps have been identified as (a) crack propagation in mode II, (b) mixed mode crack propagation and (c) pure mode I crack propagation.     

Determination of the damage mechanisms in armor structural materials via self-organizing map analysis

Dynamic compression fracture behaviors together with damage mechanisms of materials subjected to a compressive load at a high strain rate were studied by using a Self-organizing map (SOM). The materials used for the analysis were Al5083, Rolled homogeneous armor (RHA) and tungsten heavy alloy (WHA). The deformation behavior and Acoustic emission (AE) signal were acquired through a Split Hopkinson pressure bar (SHPB)-AE coupled test. The self-organization map which is one of the artificial neural network technique was employed to classify the AE energy, amplitude, and peak frequency according to the characteristics of the signal. In addition, distributions of AE signals were represented in stress-strain curves. The correlation between AE characteristics and material damage mechanisms was investigated. Based on the results, it was found that cluster 1 with high AE energy, high amplitude and low frequency was the cluster of the AE signal generated near the yield point of the material. Cluster 3, which has the opposite tendency, was confirmed as a cluster of AE signals that occurred just before a fracture of the material. The change in the measured value can be seen depending on the strain rate and the material, but the overall tendency was similar.     

Ring wear monitoring in IC engines: an acoustic emission approach

Monitoring the condition of the engine compression ring in an engine operation is very important since it affects the engine performance. One of the most promising ring wear monitoring methods is based on the analysis of acoustic emission (AE) signals, which is an extremely powerful technique that can be deployed in a wide range of applications of non-destructive testing [Vallen Systeme (2000)]. This technique is already used for monitoring tool wear almost in all machining operations, but in this study, the AE signals were applied for monitoring ring wear in internal combustion (IC) engines. The AE signals generated in the ring sliding zone are very sensitive for correlation with ring wear, which in turn affects ring performance. This study was carried out with a single compression ring mounted on the piston. The AE signals were analyzed by considering signal parameters such as ring down count and RMS voltage [Krzysztof Jemielniak (2000) J Mater Process Technol 4752:1–6]. Analysis showed that the AE signal technique is applicable for ring wear monitoring in IC engines.     

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.     

A comparative experimental study on the use of acoustic emission and vibration analysis for bearing defect identification and estimation of defect size

Vibration monitoring of rolling element bearings is probably the most established diagnostic technique for rotating machinery. The application of acoustic emission (AE) for bearing diagnosis is gaining ground as a complementary diagnostic tool, however, limitations in the successful application of the AE technique have been partly due to the difficulty in processing, interpreting and classifying the acquired data. Furthermore, the extent of bearing damage has eluded the diagnostician. The experimental investigation reported in this paper was centred on the application of the AE technique for identifying the presence and size of a defect on a radially loaded bearing. An experimental test rig was designed such that defects of varying sizes could be seeded onto the outer race of a test bearing. Comparisons between AE and vibration analysis over a range of speed and load conditions are presented. In addition, the primary source of AE activity from seeded defects is investigated. It is concluded that AE offers earlier fault detection and improved identification capabilities than vibration analysis. Furthermore, the AE technique also provided an indication of the defect size, allowing the user to monitor the rate of degradation on the bearing; unachievable with vibration analysis.     

液体雾化状态的声发射检测

为检测液体雾化状态,基于声发射检测技术,通过采集雾化液体撞击挡板产生的声发射信号,结合功率谱分析、小波分析和重标极差分析,得到雾化液体撞击挡板产生声信号的机理和特征,获得表征液体雾化状态的特征声信号尺度(J1尺度)。根据特征信号尺度能量分率与液体雾化状态间的规律性变化关系,提出雾化质量的判断方法,即液体雾化质量随特征信号尺度能量分率的增大而提高,当特征信号尺度能量分率快速上升时,液体进入充分雾化状态。判断方法得到照相法的验证。利用声发射检测发现液体雾化质量随轴向距离增大而提高,与事实相符。由此获得一种快速、实时、便捷和安全的液体雾化状态检测方法,其可用于雾化机理研究、喷嘴设计选型和工业生产监控。     

Analytical verification of the results of the acoustic-emission monitoring of conditions of dangerous production objects at integral monitoring complexes

During the detection and location of active acoustic-emission sources by integral monitoring complexes it is recommended to perform an additional nondestructive inspection of corresponding zones. However, monitoring of the quality of active objects is not always possible for technical reasons. Analytical verification methods of AE inspection data for an integral monitoring complex of the condition of the large-capacity isothermal storage of liquefied ethylene are considered in this paper. Practical results are presented.     

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。     

基于声发射技术的金属高频疲劳监测

采用声发射技术监测高频疲劳条件下金属材料裂纹的扩展。介绍了如何运用软硬件处理的方法，从采集到的信号中分离出裂纹扩展的声发射信号。从处理后的声发射信号与观察得到的裂纹扩展对比来看，声发射参数的变化能够有效地反映材料疲劳裂纹扩展的过程，并且能更早地发现试样内部微小裂纹的变化。通过试验，得出了紧凑拉伸试样在裂纹稳定扩展阶段声发射信号能量率与应力强度因子幅值之间的关系式。     

钢板声发射时间反转聚焦增强定位方法

声发射检测方法具有实时动态监测优点,应用越来越广泛,但是对声源的定位始终没有更大的突破。在钢板声发射检测中,提出一种基于时间反转理论的声发射源准确定位的方法。由于声发射检测是一种被动检测技术,结合时间反转聚焦理论,推导出对声源信号实现时间反转聚焦增强处理方法,可增强检测信号中声源幅值,提高信噪比;然后根据声源信号到达时间推算出声源聚焦时刻,利用弹性波传播理论对传感器监测区域重建信号传播波动图,显示出声源位置和区域;最后通过实验测试对该方法进行验证,结果表明该方法能有效提高损伤声源信号的能量,对检测区域的信号重建和定位显示准确地给出损伤声源位置。     

A correlation analysis and invariant method of acoustic-emission signals in the diagnostics of predestruction states of materials

The results of the application of correlation analysis and invariant method of acoustic-emission (AE) signals during the mechanical loading of 95X18 steel samples are considered. The circuit of a controller that is intended for calculation of statistical characteristics of AE signals is given. A method for diagnostics of predestruction states based on the appearance of stably positive values of the amplitude-correlation coefficient and AE pulse-repetition intervals and deviations of invariant AE relationships from their stable values is proposed.