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.     

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.     

Application acoustic emission method during concrete frost resistance

Frost resistance is one of the most frequent characteristics of concrete. It is a very complex subject and the test methods themselves are still in development and the international consensus on methodology is still sought, too. The determination concrete frost resistance takes several weeks, months or even more than a year. However micro-structural changes as micro-cracks have not been described sufficiently. Acoustic Emission Method as unusual Non-Destructive Methods can help to monitor structural changes during common frost resistance measuring. Note the Acoustic Emission Method detects only active “defects” into monitored structure. Thus when e.g. crack grows some acoustic waves spread from crack place, i. e. from acoustic emission source. The method does not detect geometric discontinuities and “passive” defects. Selected Non-Destructive Methods as Ultrasound, Non-Linear Ultrasonic Spectroscopy, Impact Echo etc. are used to confirm micro-structural changes. The article describes the first experiment with its imperfections, difficulties and possibilities.     

基于声发射的阀门泄漏检测及标定方法的研究

基于阀门泄漏产生声发射信号的原理,建立了可用于测试阀门泄漏率低于0.1Pa.m3/s的微小泄漏状态的声发射检测系统,采用气泡法对阀门微小泄漏进行标定。针对声发射信号在检测中易受环境噪声干扰的问题,设计了信号调理电路来降低各种噪声,并编制了LabVIEW程序对采集的声发射信号进行分析和处理。以手动球阀为被测对象,在建立的系统上进行了大量泄漏检测实验,结果表明,该系统能快速方便地对阀门微小泄漏做出定性分析。     

Effect of traffic volume on acoustic structural noises in rails

Pre- and post-operation levels of acoustic structural noise has been studied in rail segments. The effect of the service life and let-through tonnage on the acoustic parameters of rails has been demonstrated as compared to idle rails.     

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.     

Spatial scanning for anomaly detection in acoustic emission testing of an aerospace structure

Acoustic emission (AE) monitoring of engineering structures potentially provides a convenient, cost-effective means of performing structural health monitoring. Networks of AE sensors can be easily and unobtrusively installed upon structures, giving the ability to detect and locate damage-related strain releases (‘events’) in the structure. Use of the technique is not widespread due to the lack of a simple and effective method for detecting abnormal activity levels: the sensitivity of AE sensor networks is such that events unrelated to damage are prevalent in most applications. In this publication, we propose to monitor AE activity in a structure using a spatial scanning statistic, developed and used effectively in the field of epidemiology. The technique is demonstrated on an aerospace structure - an Airbus A320 main landing gear fitting - undergoing fatigue loading, and the method is compared to existing techniques. Despite its simplicity, the scanning statistic proves to be an extremely effective tool in detecting the onset of damage in the structure: it requires little to no user intervention or expertise, is inexpensive to compute and has an easily interpretable output. Furthermore, the generic nature of the method allows the technique to be used in a variety of monitoring scenarios, to detect damage in a wide range of structures.     

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.     

基于声发射和神经网络的木材受力损伤过程检测

对受力木材的声发射信号进行检测与分析,实现木材损伤过程的检测和监控;研究过程中采用时间序列结合神经网络建模方法,对声发射信号的累积能量时间序列和载荷时间序列进行仿真和预测.利用神经网络建模对声发射信号的累积能量时间序列进行预测,模型对44个样本进行检验的最大误差为5.6%,而且误差较大的样本对应声发射振幅参数值的局部极大值,而振铃计数与声发射率则对应局部极小值.对相应载荷时间序列预测分析中,模型输出与目标输出的最大误差不到0.1%.结构为5×5×1的网络能很好地根据序列前5个值准确预测即将发生的声发射累积能量值;结构为6×5×1的网络能很好地根据序列前6个值精确预测木材即将承受的载荷.     

Field emission,developments and possibilities

The overall performance of any electron microscope is to a great extent determined by the electron source. For example, the current acceptance of the STEM concept is due to the stimulation provided by field emission sources, which made it possible to image single atoms in the STEM. The field emission source remains the electron source with the highest brightness and the lowest energy spread. As a consequence, considerable research and engineering work has been and is still being conducted in a number of important areas. These areas include: (i) the mechanisms which determine the beam current stability; (ii) the electron-electron interactions which lead to beam spreading and an increase of the energy spread; (iii) various types of emitters such as bare tungsten tips, oxygen processed tips, zirconium coated tips, carbon emitters, carbon coated tungsten emitters and even solid state emitters; (iv) the lifetime limiting factors, e.g. inclusions, ion bombardment and flashovers effects; (v) different types of optical systems for field emission guns, e.g. choice of magnetic and/or electrostatic lenses at high voltage potential in UHV systems, and special magnetic lenses just below the anode; (vi) field emission guns operating at higher kV's, up to 1·6 MeV. Because analytical work in the smallest possible volumes is a growing area of scientific interest, the demand for field emission sources which are reliable, easy to operate and stable will continue.     

网络化CAD测试系统开发研究

这里针对网络化、标准化、无纸化和智能化的综合性CAD测试技术进行了研究,目的是为CAD技术人才培训和考核提供科学的测试系统,为准确的评价CAD人才技术水平提供科学可靠的依据。     

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.     

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.     

The acoustic path in the method of multiple reflections during nondestructive testing of linearly extended objects

An approach is presented to the construction of the acoustic path for the waveguide method of testing using multiple reflections during nondestructive testing of linearly extended objects. The results of the studies on the method’s sensitivity, which depend on the test parameters, are given.     

Characterisation of fiber failure mode in T-700 carbon fiber reinforced epoxy composites by acoustic emission testing

Acoustic emissions generated by a structure under stressed condition provide an insight in to the dynamic behaviour of flaws in the structure for characterization of failure modes. Fiber failure mechanism in T-700 carbon epoxy composites is characterized by testing unidirectional specimens in longitudinal mode. Acoustic emission parameters like amplitude, energy, duration, and signal strength have been recorded and studied with respect to the applied load to assess the fiber failure characteristics. The AE data is analyzed with different correlation plots for visual pattern recognition. Significant fiber breakage is observed at above 70% of the load. Bi-linear trend of the cumulative amplitude distribution curve indicates distinctively matrix and fiber failures. Matrix cracking failure mechanism dominated the entire loading cycle and is represented by AE hits of up to 85 to 90 dB amplitude and the peak amplitude distribution is 58 to 75 dB. The wave forms of matrix cracking hits with less than 90 dB and 100 units of energy are having up to 273 kHz frequency with a peak around 100 kHz. The wave forms of fiber breakage hits with more than 90 dB and 100 units of energy have up to 448 kHz frequency and with a peak from 168 to 437 kHz. From the low amplitude filtering technique the border line for fiber breakage is observed from 89 to 92 dB.     

Automatic detection of depth of cut during end milling operation using acoustic emission sensor

Any shortfall in the required depth during milling machining can affect the dimensional accuracy of the part produced and can cause a catastrophic failure to the machine. Corrective remedies to fix the dimensions inaccuracy will increase the machining time and costs. In this work, a depth-of-cut monitoring system was proposed to detect depth of cut in real time using an acoustic emission sensor and prediction model. The characteristics of the sensor signal obtained in machining processes can be complex in terms of both nonlinearity and nonstationarity. To overcome this complexity, a regression model and an artificial neural network model were used to represent the relationship between the acoustic emission signal and the depth of cut. The model was tested under different machining cases and found to be efficient in predicting the depth of cut.     

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.