Monitoring tool wear during wood machining with acoustic emission

The purpose of this study was to determine the degree of change in acoustic emission (AE) during cutting as a cutter tool was worn. AE is defined as the stress or pressure waves generated during dynamic processes in materials and is generated during fracture, delamination, deformation and distortion of wood during cutting. Previous work has shown that AE is sensitive to changes in the chip formation process and therefore could be used to monitor continuously the state of the cutting process. For this study a single-point cutting tool was worn by turning a green-white fir (Abies concolor (Gord. and Glend.) Lindl.) log on an engine lathe equipped with an automatic feed. The relationship between the AE output and the amount of wood cut was close to linear in the initial stages of the blade wear. As the blade became severely worn, the AE levels dropped dramatically and an asymptotic relationship between the two variables became evident.     

声发射信号处理在轮轴故障检测中的应用研究

声发射（Acoustic Emission）可以定义为物体或材料内部迅速释放能量而产生瞬态弹性波的一种物理现象,是材料或结构受内力或外力作用产生变形或断裂,以弹性波的形式释放出应变能的结果。在基于虚拟仪器的轮轴故障检测分析平台中,可实现对声发射信号的时域分析、频谱分析、参数分析、小波去噪等主要功能。通过该平台,对具有典型状态的滚动轴承的声发射信号进行了试验研究。试验研究结果表明,对于不同状态的轴承,所测取的声发射信号包络频率特征有着明显的不同,并且和理论特征频率有着一定的关系。     

Characterization of nugget nucleation quality based on the structure-borne acoustic emission signals detected during resistance spot welding process

Acoustic emission signals detected during the resistance spot welding of aluminum alloy were studied in order to assess the characterizations of welding process, the characterizations of the effect of welding parameters to nugget nucleation and the characterizations of the nugget quality by the analysis to acoustic emission signals. The results showed that the physical phases of nugget nucleation can be characterized by the acoustic emission signals detected during the resistance spot welding process. The effects of welding current and current duration to nugget nucleation can be characterized by the characteristic parameters of acoustic emission signals. The characteristic parameters of acoustic emission signals had a better relevance to nugget dimensions and weld strength, which made it possible to measure or predict the weld strength by the characteristic parameters of acoustic emission signals detected during the resistance spot welding process.     

Use of microprocessor acoustic emission systems during aircraft endurance testing

In this article, the results of endurance testing of aircraft using the acoustic-emission method (AE) are given. Measurement information was recorded by certified distributed and combined systems. A total of 62 loading blocks were performed; each included nonflight, take-off, and flight modes. Arrival of recorded AE signals was combined with the onset of the program cycle. Examples of the localization of AE signals were given from the zones under study with the development of fatigue fractures along the left and right sides of the aircraft. The results of comparative testing on an aircraft panel with a size of 1500 × 1800 mm were analyzed using distributed and combined AE systems.     

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.     

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.     

Lead-free acoustic emission sensors

Acoustic emission (AE) sensors have been fabricated using both soft- and hard-type lead-free (Na0.5K0.5)NbO3-based ceramics. The acoustic and electromechanical properties of the ceramics have been determined using the resonance technique. The lead-free AE sensors were calibrated using a laser source and compared to a commercial sensor. A lead zirconate titanate (PZT) 5H ceramics AE sensor has also been fabricated and calibrated for comparison. It was found that the sensitivity of lead-free AE sensors is comparable to that of the lead-based PZT sensor. To evaluate the sensors for potential application, they have been used in the detection of AE in an impact test. The lead-free sensors can reproduce AE signals accurately without giving artifacts and have potential use in commercial AE systems.     

声发射技术在起重机无损检测中的现状

对起重机械常规无损检测技术(目视检测、磁粉检测、超声检测、应力测试、振动测试等)和声发射技术进行了比较,归纳了声发射技术在起重机械无损检测中的研究现状,提出了研究的基本思路,讨论了起重机械声发射技术中的几个关键问题,即典型声发射源信号的获取、声发射信号处理技术、声发射源的模式识别。最后,对起重机械声发射检测技术的研究前景进行了展望。     

STFT在AE信号特征提取中的应用

机械故障或损伤引发的声发射信号南高频突发脉冲信号和长周期准平稳噪声信号组成,适宜用短时傅里叶变换(sTFT)描述其时频特征.本文通过分析典型AE信号及其特征提取,首次将STFT引入声发射故障诊断领域,并提出了AE信号的STFT分析法.通过理论分析和仿真,确定了AE信号STFT的理想窗函数及其参数选择,有效地克服了STFT只用一个同定窗分析多尺度信号的缺陷.将STFT用于声发射检测的滚动轴承损伤类型及部件的识别,诊断结果十分准确、清晰和直观.仿真分析和实验研究均表明了STFT能有效提取AE信号的特征,为AE信号的波形分析开辟了一条有效的途径.     

无须测量声速的声发射源定位方法研究

为消除声速测量偏差给声发射系统带来的定位误差，本文提出一种多探头定位方法。从理论上导出了该方法的线定位和平面定位计算公式，并用AE21C型四通道声发射仪在碳钢管道和平板上以铅笔芯折断产生信号为模拟源进行了实验验证，结果表明用这种新的方法具有较高的定位精度，且定位时只要利用原系统的门槛跨越技术测量各探头接收到信号的时差即可，不必测量传声媒质的声速。     

基于小波的声发射信号参数提取方法

介绍小波分析方法在声发射信号处理中的应用,提出一套基于声发射信号小波分析的小波基选取的规则方法,并通过实验和仿真证明此方法的有效性.     

声发射检漏仪在阀门密封性检验中的应用

提出了利用声发射技术检验电厂阀门密封性的方法，该方法具有准确快速的特点,而且可以确定阀门的内漏程度，为检修工作提供了依据。利用该方法可以减少浪费，缩短检修工期，提高电厂的经济性与安全性。     

Improving the accuracy of electromagnetic emission method for measuring concrete strength

A method for improving the accuracy of the electromagnetic emission method of measuring concrete strength has been suggested and tested in experiments.     

Variations in several acoustic emission parameters during testing of low-carbon steel specimens

The acoustic emissions that are formed during tension of specimens made from low-carbon steels is investigated. Interpretation of the experimental data is made from the point of view of real tests of engineering objects made from low-carbon steels in order to analyze the correlation of informative parameters with the deflected mode of a metal.     

A multichannel multiplicative method for acoustic testing of large-size compact concrete building constructions

A new multichannel acoustic method for testing large-size concrete building constructions is considered. The method is based on the use of a method of free vibrations (the resonance and impactecho methods) with the subsequent multiplication of partial spectral characteristics. The multichannel multiplicative method allows performance of acoustic testing of large-size compact concrete building constructions (blocks, beams, columns, supports, and other standard articles).     

声发射技术在大型装卸设备安全评定中的应用

采用了声发射技术对2种港口装卸设备的关键部件进行缺陷检测研究,结果表明,通过适当的设置能够有效地屏蔽运动部件的共振和噪声,获得良好的检测效果,此次研究为声发射技术在大型起重设备关键部件缺陷检测中的应用提供了成功的经验,其检测结果为检测设备后续的复查和寿命计算以及安全评定提供了重要依据。     

Powder size measurement by acoustic emission

Acoustic emission was used to measure particle size properties of steel, cast iron, and alumina powders. Many powder samples with different weight and size distribution were prepared by sieving and their size distribution was measured by means of optical techniques. Acoustic emission measurements were carried out by dropping the powder on a metal plate to which an acoustic emission transducer was fixed, and results were expressed in terms of number of counts of four channels for data acquisition. The measurement set-up and procedure were original and never investigated before. Very good results were obtained for steel and cast iron samples, as measurement curves showed a clear linear trend as a function of the particle mean diameter and were vertically shifted in dependence of the sample weight. Alumina powders showed similar trends only for large particles and high weight differences.     

Wear studies using acoustic emission techniques

This paper describes measurements of acoustic emission RMS signals obtained from sliding metallic contacts. The results show that RMS measurements are able to differentiate between different wear mechanisms occurring in both dry and lubricated contacts. Further, for the test conditions studied there is a direct empirical relationship between the integrated RMS signal and the wear volume removed from the test ball.