Diagnostics of critical points of the friction coefficient of a multilayer nanomodified antifriction coating by an acoustic emission technique

The dynamics of the changing parameter of the acoustic emission (AE) in the course of tests of a multilayer nanomodified antifriction coating are considered. The results of investigating the shape and the spectra of AE pulses in different regions of the experimental curve of the dependence of the friction coefficient on the test time are reported. A method is proposed for establishing the transition points from the steady-state stage to the failure and friction-without-coating stages according to the intensity of the restored AE event stream, the spectral distribution, and the amplitude of the concurrent acoustic emission in the ultrasonic-frequency range.     

大型立式储罐在线声发射检测与安全性评估

通过30余台大型立式储罐在线声发射检测以及部分储罐的开罐检测对比，讨论了储罐底板在线声发射检测和安全性评估的有关问题。     

Acoustic emission during orthogonal metal cutting

The theory of acoustic emission and the analysis of emission signals is reviewed as it applies to generation of acoustic emission in metal cutting. Based upon the mechanics of the orthogonal cutting operation a relationship is developed between the root mean square (RMS) voltage of the acoustic emission and fundamental cutting parameters. The validity of this relationship is evaluated by a series of tests varying cutting speed, feed and rake angle for orthogonal machining. Strong dependence of the RMS voltage of the emission on both strain rate and cutting velocity was observed. The sources of acoustic emission in metal cutting are discussed and areas of additional work in the study of acoustic emission from metal cutting are identified.     

基于声发射和神经网络的风机叶片裂纹识别研究

提出一种对风力机叶片裂纹声发射信号进行模式识别的方法。该方法以叶片无裂纹、萌生裂纹、扩展裂纹和断裂四个阶段为声发射源的四个模式,基于声发射信号含有丰富的发射源信息的特点,通过大量采样获得叶片裂纹声发射信号参数,并依照叶片裂纹声发射参数分析的数值特点确定BP神经网络,用选定的网络对叶片裂纹阶段进行模式识别,以判断裂纹的危害程度。仿真结果表明,利用BP神经网络可以对声发射信号进行有效识别,识别准确率达到90%以上。     

Use of rayleigh waves in testing stress-corrosion breaks in pipelines by the acoustic emission method

Four models describing emission of Rayleigh waves by cracks with normal breaking have been suggested for testing various stages of development of stress-corrosion cracking in pipelines by the acoustic emission (AE) method. Parameters of AE pulses for identifying stages of stress-corrosion breaking of pipelines have been determined in the process of investigation.     

Acoustic emission used for detection of crack generation in propellers of turbine-pump units

The problem of applying acoustic emission (AE) for detection of crack generation in heavily loaded elements of rotor systems, in particular, in propellers of turbine-pump units, in which breakdown of propellers during the operation is possible because of fatigue-crack generation, is studied. The data on AE signals radiated from some materials of the propellers exposed to monotonic and cyclic loading are presented, and the possibilities of emission and detection of AE signals with setups built in the rotor system construction are determined. Two developed setups are compared, one of which is characterized by high reliability, sufficient sensitivity to crack generation, and the absence of electronic amplifiers and power supply units. The design and results of the tests performed with this setup for AE-technique-based monitoring of the crack formation are presented.     

Analysis of boiler-tube erosion by the technique of acoustic emission Part I. Mechanical erosion

This paper investigates the mechanical erosion of the metal tubes in bagasse-fired boilers with the aid of the acoustic emission technique. By studying the material removal under various collision conditions, the paper analyzes the dependence of the erosion wear upon the impact angle, velocity, size and concentration of the particles. It was found that the material removal mechanisms were mainly dependent on the particle collision angle and fell into four regimes characterized by rubbing and scratching, cutting and cracking, forging and extrusion as well as sputtering and adhesion. The highest wear rate took place with the cutting and cracking mechanism when the particle collision angle was in the range of 20–30°. The variation of the acoustic emission energy confirmed the conclusions. Finally, three simple formulae were developed to show the dependence of the erosion wear upon the main erosion parameters.     

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)     

压力容器用钢氢致开裂的声发射试验研究

氢致开裂是在役压力容器一种常见的失效形式。声发射技术是监测动态破坏过程的有效手段。为了研究压力容器用钢氢致开裂过程的声发射特征,对电解充氢过程中的20R钢进行了监测。试验结果表明,碳钢表面电解充氢并腐蚀的过程和内部氢致裂纹的产生均会对材料的声发射活动产生影响。氢致裂纹的发展过程可分为孕育期和扩展期两个阶段,随着裂纹的生长,高幅声发射信号的数量明显增多。试验结果为压力容器现场检验提供了参考。     

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.     

Developing and testing a laboratory system for recording and analysis of acoustic emission

A laboratory system for recording and analyzing acoustic emission was designed and experimentally investigated (tested). A block diagram and the operation algorithm of the system are presented. The relationship between the results of low-frequency, high-frequency, and statistical processing of recorded data and the physical features of input signals is shown using as an example simulated acoustic signals in the various units of the designed system. The system was tested on real test objects in the case of three-point bending of nitrided steel specimens with various thicknesses of the hardened surface layer. It is shown that crack formation leads to emission of signals with an amplitudes of up to 4 V, whereas during deformation in the absence of pronounced cracking, the amplitude of the amplified signal does not exceed 0.5 V.     

Characteristics of elastic waves generated by fatigue crack penetration and growth in an aluminum plate

The characteristics of elastic waves emanated from crack initiation in 6061 aluminum alloy subjected to fatigue loading are investigated through experiments. The objective of the study is to determine the differences in the properties of the signals generated from fatigue test and also to examine if the sources of the waves could be identified from the temporal and spectral characteristics of the acoustic emission (AE) waveforms. The signals are recorded using nonresonant, flat, broadband transducers attached to the surface of the alloy specimens. The time dependence and power spectra of the signals recorded during the tests were examined and classified according to their special features. Six distinct types of signals were observed. The waveforms and their power spectra were found to be dependent on the crack propagation stage and the type of fracture associated with the signals. The potential application of the approach in health monitoring of structural components using a network of surface mounted broadband sensors is discussed.     

Hydrogen degradation of steel 12X1MΦ and its estimation by the acoustic emission method

The acoustic emission method for estimating damage to specimens made of thermally resistant steel is described as applied in air and in a gaseous hydrogen medium. Acoustic diagrams (AD) of steel cracking and their interpretation are presented. It is shown that thermal cycling of the steel in air and in a hydrogen medium leads to an increase in bulk damage to the steel. It is shown that the exploited material is more subject to micro- and macrocracking under the influence of temperature and the working environment.     

An analysis of the comparative reliability of acoustic testing methods of bar stock from spring steels

The results of comparative tests of the electromagnetic-acoustic mirror through transmission method of multiple reflections and alternative (visual, acoustic waveguide, and eddy current) methods during rod testing under factory conditions at various plants are given and their comparative reliability is calculated.     

声发射技术在冷库压力容器在线动态检验中的应用

通过对山东省冷库压力容器现状及冷库工作原理的了解，详细介绍了冷库压力容器利用声发射在线动态检验及评价的特点及目前的研究成果，并对声发射在线动态检测的原理进行了分析，指出利用声发射技术冷库压力容器罐体中的腐蚀、咬边、埋藏缺陷、应力集中、特别是钢板缺陷等均能检出，检验结果的可靠性及完整性与常规方法的开罐全面检验结果相符。     

基于Lab VIEW的声发射信号小波阈值去噪研究

虚拟仪器代表着目前测试仪器领域的发展方向,LabVIEW语言是一种功能强大的仪器开发平台。对淹没在噪声中声发射信号的有效提取（去噪）是声发射信号处理技术的第一步,也是声发射信号处理的关键所在。本文介绍了基于小波变换的阈值去噪方法。在LabVIEW平台上,通过仿真试验,对声发射信号的几种阈值法的去噪结果进行比较,选出一种适合声发射信号去噪的阈值准则。     

Advanced-reliability acoustic-emission transducers

A design of an advanced-reliability piezoelectric transducer of acoustic emission (AE) is suggested. The advanced reliability is achieved by eliminating the main reasons that lead to failures; duplicating/backing the main operating systems; and imparting redundant or extended technical capabilities to the transducer design that make it possible to compensate for partial or complete performance loss of the antenna group. It is shown that given such a design approach, it is feasible to achieve technical characteristics that are stipulated for industrial acoustic-emission transducers. Theoretical estimates of transducer reliability are presented that show that a combination of backing of AE registration channels with different versions of their connection gives ample opportunities for governing the reliability of sensors during their usage/service life.     

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.

     

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.     

Differentiation of leakage and corrosion signals in acoustic emission testing of aboveground storage tank floors with artificial neural networks

The acoustic emission method is a well-recognized procedure of floor inspection for aboveground storage tanks as well as a preventive tool for the improvement of maintenance service time. The high importance of this method is better realized when it is used in sensitive structures while they are in operation. A laboratory-based smaller-scale tank was made and all operating conditions were simulated. This provided a databank for recognition of acoustic waves. More experiments were conducted to simulate corrosion in a tank. Data were then collected from acoustic emission measurements for several aboveground storage tanks in a refinery. The data gathered from laboratory tests and the real data were combined in order to differentiate between leakage and corrosion signals. An artificial neural network (ANN) system was used to categorize the tested aboveground storage tanks. The text was submitted by the authors in English.