砂轮磨损状态的声发射检测及其误差补偿方法的研究

砂轮磨损会破坏砂轮型面,对加工精度有重要影响。利用声发射方法检测砂轮的磨损状态以及修整过程,并提出了实现砂轮磨损误差在线补偿的方法。     

A Study on Incipient Damage Monitoring in Rolling Contact Fatigue Process Using Acoustic Emission

Acoustic emissions (AE) technique was applied to rolling contact fatigue tests of two radially loaded rollers running under constant load and velocity to detect the incipient damage and damage location. Signals detected from contacts were processed using signal conditioning and enhancement techniques by an AE source locator to bring out the difference between the signals from the sound and damaged rollers. It was found that AE hit count pulse observations by the AE source locator can provide an indication of the damage at its initial stage. The conventional AE parameters and the AE signal features were studied and correlated with the AE source locator counts. The results demonstrated the successful use of the combination of the AE monitoring and the AE source locator as a new technique for detecting the incipient damage and forecasting the position of the damage in the roller, and this technique could allow the user to monitor the rate of deterioration of the rolling elements.     

应用PC和80C196KC单片机的刀具磨损状态监测系统

设计一种融合声发射(AE)、主轴电动机电流和Z向进给电动机电流多特征参数检测方法的、以PC机为上位机、以80C196KC单片机为下位机的刀具磨损监测系统。主要介绍系统的硬件结构,阐述系统中多路信号采集装置硬、软件工作原理与设计中的关键技术,以及具有辨识功能的上位数据处理计算机的软件工作流程。     

探测精密零部件加工裂纹的声发射实时监测仪

为了提高航天航空精密零部件加工设备的可靠性、安全性,缩短研制周期,提出了一种实时监测精密零部件加工过程产生裂纹的方法,并根据此方法,研制了一台基于TI公司最新浮点数字信号处理器-TMS320F28335的精密零部件裂纹实时监测仪的样机.考虑在线实时监测的需要,采用了基于声发射(AE)技术的方案.介绍了裂纹实时监测方法的...     

三维编织C/SiC复合材料拉伸损伤演化

利用声发射技术,对三维编织C/SiC复合材料在拉伸过程中损伤发展、演化进行了实验研究。实验采集了三维编织C/SiC复合材料拉伸过程的声发射信号。运用多参数分析法,分析了三维编织C/SiC复合材料拉伸损伤的声发射特性,宏观上揭示了材料拉伸损伤的发展、演化过程和规律。研究结果表明三维编织C/SiC复合材料拉伸损伤演化可被分为两个主要阶段,损伤初始阶段和损伤严重阶段。     

基于光纤光栅阵列和MVDR算法的声发射定位

基于光纤光栅(FBG)传感器网络构建了声发射检测系统,并提出了最小方差无失真响应(MVDR)的声发射源定位方法。构建的系统由7个FBG传感器组成传感器线阵列,采用未经平坦的放大自发辐射(ASE)光源边缘滤波实现信号解调。利用Shannon小波变换从频散复杂的声发射信号中提取窄带信号,并基于MVDR算法扫描整个监测区域获取空间谱。根据空间谱函数计算输出值,并将计算的输出值作为像素值。最后,通过提取空间谱中的最大值的坐标确定声发射源的位置。在LY12铝合金板上进行了实验验证。结果表明,该方法在400mm×400mm的区域内,声发射定位的最大误差为9.4mm,平均误差为7.2mm,耗时小于3s。该系统具有较高的实时性和定位精度,是一种声发射源定位的新方法。     

结构疲劳损伤的声发射检测可靠性研究

针对声发射技术对金属结构损伤的检测可靠性问题,以金属疲劳裂纹检测试验为基础,利用声发射特征参数的趋势分析和关联分析法,首先根据贝叶斯理论,计算了声发射对一定长度疲劳裂纹的检测概率;其次,研究了检测结构起裂时对应声发射幅度参数的阈值及其对损伤判断的影响。该研究可为减少声发射检测中的金属疲劳损伤信号误判,提高检测效率,以及确定复杂航空结构疲劳寿命提供支持。     

基于独立分量分析的切削声发射源信号分离

针对切削声发射(Acoustic Emission,AE)信号的多目标状态源并行分离问题和同频干扰源分离问题,引入独立分量分析(Independent Component Analysis,ICA)技术作为研究工具,用刀具破损、切屑折断和环境噪声三个AE源的线性混合模拟切削AE信号,尝试用FastICA算法分离目标状态...     

基于声发射信号的铣削加工表面粗糙度预测技术研究

使用声发射技术对铣削过程进行监测,通过对声发射信号进行频域分析,比较不同频段的能量比来在线预测加工后的表面粗糙度.     

Evaluation of tribological properties of bearing materials for marine diesel engines utilizing acoustic emission technique

Acoustic Emission (AE) technique, which has detection capability for minute failures, has been tried to monitor the condition of a plain bearing under the laboratory conditions. In this paper, the bearing materials for marine diesel engines - tin alloy as known as “white metal”, aluminum alloy of 40% tin mass and aluminum alloy 40% tin mass with resin overlay - were tested using a sleeve-to-plate tribo-tester. The frictional force and back temperature were measured as well as the AE signals. The possibility of AE technique to monitor the bearing condition was also assessed by evaluating tribological properties under different operating conditions such as start-stop simulating the crankshaft turning during engine assembly and seizure tests. These results indicate that AE is useful for monitoring the lubricated condition of the sliding surfaces and evaluating tribological properties of the bearing.     

表面弹性波OPCM传感器的标定

标定了一种被称为正交异性压电复合材料(OPCM)的声发射(AE)传感器.利用断铅信号作为声源,SR-15型AE传感器作为标准传感器,以比较法研究了OPCM的脉冲响应.在玻璃纤维板上重点研究了OPCM的正交异性特性--陶瓷项数量的影响及响应规律的描述.实验结果表明,该传感器适于探测表面弹性波,陶瓷项数达到30,正交异性显著,能够很好地减小噪声、边界回弹波等信号对诊断信号的干扰,有助于板类结构健康监测.     

BK7光学玻璃金刚石划刻声发射信号的特征提取

以金刚石压头划刻BK7光学玻璃为研究对象,分析了脆性材料脆性去除过程中的声发射机制,研究了声发射信号的特征提取技术。多种切深实验显示:BK7光学玻璃发生脆性去除的特征主要集中在[100,200]kHz、[300,400]kHz两个频段,对应不同的声发射机制,其中[100,200]kHz频带的滤波信号呈现明显的、时间间歇的突发式声发射现象,与脆性材料裂纹的生成与扩展密切相关。基于上述实验结果,提出了以突发式声发射事件为单位的特征监测方法。针对该带通滤波信号的均方根值(RMS),研究了基于凸优化理论的声发射事件识别算法,得到了脆性材料裂纹扩展的时刻及能量信息。得到的结果表明:以声发射事件为单位的特征监测具有明确的物理意义,能够更加客观地表征脆性材料的去除过程。     

A study on gas-liquid two-phase flow metering: Identification of flow dynamics that influence the performance of CMFs

Metering on gas-liquid two-phase flow is challenging even though the Coriolis Mass Flowmeters (CMFs) outperform most of other flow measurement technologies owing to their ability to directly measure the fluid mass flowrates. This is due to complexity of the dynamics of the gas-liquid two-phase flow. Thus, Coriolis Mass Flowmeters have been undergoing modifications to improve their accuracy on measuring complex flows but still the variation of error due to bubble entrainment and the mechanisms responsible of these errors remain less understood. Hence there is a strong need to conduct further characterization on the performance of CMFs on measurement on gas-liquid two-phase flow.This study aims to analyse the performance of a U-shape CMF on metering gas-liquid two-phase flow via both CFD simulation and experimental measurements. For simulation, a two-way coupling of Fluid-Structure Interaction was used to minimize the inaccuracy in simulation results. It has the ability to count on influences of fluid forces on the tube deformation and the reaction of the oscillating-fluid conveying tube to the overall dynamics of the system.The results show that at low nominal flowrates (NFRs), the flow/phases separation occurs and dominates the previously identified factors of errors such as bubble theory effect/friction damping effect and cause positive errors. The error associated with bubble theory effect or friction damping is negative i.e. the CMFs under-estimate the mass flowrates of the mixture. Our study, however, found negative errors only at high nominal mass flowrates. In addition, it is to be noted also that even though the theoretically predicted error due to mixture compressibility in some literatures could be positive, it is important to carry out further experimental and computational studies for analysis. In this study, it is observed that the oscillations of separated fluid phases amplify the amplitude of tube oscillation and hence leading to distortion of the displacements of the CMF tube. This could lead to up to 14.9% of positive error in CMFs’ measurements at the low nominal mass flowrates.It is believed that these results can serve as baselines for future studies on corrections and compensations of CMFs’ errors on measurement on gas entraining fluid flow encountered in fuel bunkering and LNG metering processes.     

On-line measurement of the size distribution of particles in a gas–solid two-phase flow through acoustic sensing and advanced signal analysis

Acoustic emission (AE) technology is a promising approach to non-intrusively measure the size distribution of particles in a pneumatic suspension. This paper presents an experimental study of the AE sensing technology coupled with signal processing algorithms for on-line particle sizing. The frequency characteristics of the AE signals under different experimental conditions are studied and compared. Initially, the characteristics of the background noise and AE signals are compared in the frequency domain for different air velocities and particle feeding rates. Through short-term energy analysis the working features of the suction unit and the vibration feeder are revealed. To find the effective characteristic frequency band of the AE signals, a multiple scanning and accumulation method assisted with a Savitzky–Golay smoothing filter is used to denoise the power spectra of the signals. Wavelet analysis is also deployed to denoise the signals. The denoising performance of different wavelet parameters (wavelet function, decomposition level and thresholding) is compared in terms of signal-to-noise ratio and signal smoothness. Finally, particle size is predicted through a neural network with energy fraction extracted through wavelet analysis. Experimental results demonstrate that the relative error of the particle sizing system is no greater than 23%.     

Investigation on the effect of EDM process variables and environments on acoustic emission signals

Abstract

The performance of electrical discharge machining (EDM) primarily depends on the spark quality generated in the inter-electrode gap (IEG) between the tool and workpiece. A method for obtaining accurate information about the spark gap is required to effectively monitor the EDM process. The rise and fall of thermal energy in the discharge zone at a rapid rate during the dielectric breakdown produces high-pressure shock waves. This work explores the suitability of using acoustic emission (AE) generated from these shock waves and the elastic AE waves released on the workpiece due to the induced stress to monitor the performance and spark gap in EDM. The information content of the AE signals acquired at various machining conditions was extracted using AE RMS, spectral energy and peak amplitude. These features were able to well discriminate the machining condition, tool material, workpiece material, flushing pressure, current density, the initial surface roughness of the tool. Additionally, the AE signal features had a good and consistent correlation with the performance parameters, including material removal rate, surface roughness (Ra and Rq) and tool wear. The findings lay the groundwork to develop an effective, non-intrusive in-situ AE-monitoring system for performance and IEG condition in EDM.     

A study on the usability of biodiesel fuel derived from rice bran oil as an alternative fuel for IDI diesel engine

The world is faced with a problem of air pollution due to the exhaust emissions from automobile. Recently, lots of researchers have been attracted to develope various alternative fuels and to use renewable fuels as a solution of these problems. There are many alternative fuels studied in place of diesel fuel made from petroleum. Biodiesel fuel (BDF) is a domestically produced, renewable fuel that can be manufactured from vegetable oils, used vegetable oils, or animal fats. In this study, the usability of BDF, one of the oxygenated fuels as an alternative fuel for diesel engines was investigated in an IDI diesel engine. Emissions were characterized with a neat BDF and with a blend of BDF and conventional diesel fuel. Since the BDF includes oxygen of about 11%, it could influence the combustion process strongly. Therefore, the use of BDF resulted in lower emissions of carbon monoxide and smoke emissions with some increase in emissions of oxides of nitrogen. It is concluded that BDF can be utilized effectively as a renewable fuel for IDI diesel engines.     

A novel measurement method for transient detection based in wavelets entropy and the spectral kurtosis: An application to vibrations and acoustic emission signals from termite activity

This paper presents a novel non-destructive method for termite detection that uses the entropy of the continuous wavelet transform of the acoustic emission signals as an uncertainty measurement, to achieve selective frequency separation in complex impulsive-like noisy scenarios, with the aid of the spectral kurtosis as a validating tool. The goal consists of detecting relevant frequencies, by looking up the minima in the curve associated to the entropy of the difference between the raw data and the wavelet-based reconstructed version. By measuring the signal’s uncertainty, the scales corresponding to the entropy minima, or pseudo-frequencies, manage to target three main types of emissions generated by termites: the modulating components (enveloping curve), the carrier signals (activity, feeding and excavating), and the communicating impulses bursts (alarms). The spectral kurtosis corroborates the location of the entropy minima (optimum uncertainty) matching them to its maxima, associated to frequencies with the highest amplitude variability, and consequently minimizing the measurement uncertainty. The method is primarily conceived to cover the acoustic-range, in order to acquire signals via standard sound cards; a broaden high-frequency study is developed for the assessment, and with the added value of discovering new and higher frequency components of the species emissions. The potential of the method makes it useful for myriads of applications in the frame of nondestructive transient detection.     

基于声发射理论的安全阀气体内漏信号特征研究

基于声发射理论,研究安全阀气体内漏情况下的信号特征。设计搭建了安全阀内漏模拟试验台和安全阀内漏声发射信号检测系统,通过理论分析和试验研究的方法,模拟了安全阀密封面划伤、密封面出现单个漏孔、密封面出现多个漏孔等内漏情况,研究了这些情况下声发射信号的频谱特征,泄漏率对于声发射信号特征参数平均信号电平(ASL)的影响,以及泄漏率与平均信号电平之间的量化关系,为实现安全阀内漏在线监测奠定基础。     

A study on the flow characteristics between two circular cylinders in cross flow by ldv and holographic interferometry

Experimental investigation of the fluid flow and thermal flow pattern around two circular cylinders in cross flow has been carried out. Reynolds number was varied in the range of 100≦Re≦1000 and the distance between the two cylinders in the interval of 2≦L/D≦4. Velocity and turbulence intensity distributions in the isothermal distribution in the whole x−y thermal flow field was obtained by double-exposure holographic interferometry. The influences of Reynolds number and the gap spacing between the two cylinders were investigated. The characteristic flow pattern was found to depend on the distance between the two cylinders. WhenL≦3D, the wake region between the two cylinders became quasi-stationary.