压力容器声发射信号人工神经网络模式识别方法的研究

采用人工神经网络模式识别技术对现场压力容器各种声发射源信号特征参数进行了模式识别分析,提出了采用人工神经网络分类方法对压力容器声发射源信号进行定量分析的概念,从而找到了评价声发射源严重程度的方法,设计和培训的人工神经网络可以给出一个多种因素产生的复合声发射源中裂纹扩展、氧化夹渣断裂、残余应力释放和机械摩擦信号所占的百分比,这一结果使声发射技术对压力容器安全状态的无损评价成为可能。     

厚壁压力容器声发射技术声源定位误差分析

声发射技术（AE）已经被广泛应用到压力容器、压力管道等检验中。声源定位在整个声发射检验与评定结果过程中起重要作用,目前这方面的研究热点是如何提高定位精度。声发射技术通常采用时差定位法来检测压力容器和压力管道的缺陷,通过检测声波到达不同传感器的时间来确定声源位置。对于厚壁压力容器来说,若声源位于容器的内表面或内部,显然容器壁厚会对声源的精确定位产生一定的影响。针对此问题,详细推导并得出厚壁压力容器中声发射检测的定位误差的解析解,分析和讨论了声源定位误差的变化规律。分析结果表明,定位误差的试验值和理论分析符合良好,计算数据与试验值之间的最大误差为7．12％。当容器壁厚小于600mm的情况下,建议实际声发射检测中对声源位置200nm以内区域采用其他常规无损检测方法进行复验以确定实际声源位置。     

泄漏声发射传感器的标定研究

介绍了声发射传感器标定原理及几种常用标定方法的模拟声源的特性。提出了将比较法应用于管道泄漏检测的声发射传感器的标定。建立了基于脉冲表面波声场的声发射传感器标定系统，对商用和自制的几种声发射传感器进行了标定。标定结果和探头使用效果证明，比较法标定声发射传感器是可行的。     

Acoustic emission source location considering refraction in layered media with cylindrical surface

To solve the problem that the existing acoustic emission (AE) source location algorithms cannot always obtain accurate results for multilayer cylindrical media, a new acoustic emission source location method considering refraction was proposed. AE source coordinates were solved by the complex method. Pencil-lead-break experiments were used to verify this method. The absolute distance errors of location results are less than 3 mm, much less than those by the traditional method. The numerical experiments were used to further analyze factors that affect location accuracy. The results of numerical experiments show that the location accuracy of the proposed method is not affected by the ratio of wave velocities but affected by the measurement accuracy of wave velocity. These results show that new method can obtain accurate AE source location in the two-layered cylindrical surface media such as the triaxial compression test.     

基于声发射信号的铝合金LSP弹塑性波传播规律探究

目的 为提高激光冲击强化(LSP)的声发射(AE)监测精度,结合AE监测技术与LSP弹塑性波理论,探究LSP过程中弹塑性波传播规律。方法 首先,基于弹塑性波理论设计LSP试验,采用AE监测技术实时获取冲击信号,并测量冲击后铝合金7075的塑性变形程度。然后,基于AE信号的时域波形,提出包络欧式距离法,确定对加工质量敏感的感兴趣片段(FOI)。进一步基于FOI,结合实际加工条件,定义了新的累积AE波形熵特征。最后,基于AE信号的多模态和非平稳信息,定义瞬时峰值能量曲线(IPEC),并进一步提取相关特征,从而探究弹塑性波传播规律、衡量传感器优劣。结果 仅包含弹性波的AE信号波形明显区别于弹塑性双波,塑性波传播速度明显落后于弹性波。包络欧式距离法确定的FOI能很好地定位弹塑性波。相较于AE波形熵,累积AE波形熵特征能很好地区分不同程度的弹塑性波。对比弹性波,塑性波主要集中在中低频段(200 kHz以下)。IPEC曲线精准确定31 kHz模态为塑性波的主要成分。进一步提取的峰值变化量 和峰值延迟时间 表明:相较于谐振传感器,宽频传感器对塑性波更加敏感。结论 所提方法和特征分别从时域和时频域上探究了弹塑性波的传播规律,所得的结论为规范和提高LSP的AE监测技术提供了理论支持与指导。     

基于波动理论的管结构损伤检测方法

针对在役海洋平台的无损检测大都采用超声等主动检测手段,这会受到工况的影响。而声发射等被动检测手段避免了这一问题,实现了对现役海洋平台的在线监测。综述了基于瞬态波、应力波、导波和模态声发射等波动理论进行的管结构声发射检测研究成果。对基于波动理论进行复杂结构检测的前景做了展望。     

传感器阵列对岩体微震/声发射源定位精度的影响（英文）

随着开采深度增加,岩体动力灾害日益突出。微震监测已成为岩爆、顶板坍塌等岩体动力灾害监测的重要技术手段。传感器阵列布设作为信号采集的第一步,严重影响信号源的定位精度。讨论和总结有关由传感器阵列布设引起的微震(MS)和声发射(AE)震源定位误差的重要研究,并分析传感器数量、传感器布设形态以及传感器与震源距离对MS/AE源定位精度的影响机制。随后,结合工程实践和实验室测试,给出传感器阵列的一些布设原则,并通过现场应用进行验证。另外,综合考虑影响传感器阵列布设数量、形状和距离的因素,找到最优布置方案,可大幅度改善信号采集效果,提高信号源定位精度。最后,对提高MS/AE源定位精度所面临的挑战和传感器阵列方面相应的应对策略进行展望。     

基于HHT变换的声发射源平面定位方法

为了应对空间碎片的威胁,研制了一种基于声发射技术的用于实时监测空间碎片撞击航天器的在轨感知系统。对平面声发射源精确定位技术提出了需求。声发射信号属于非平稳随机信号,传统的小波变换无法充分获得其中携带的信息。利用HHT技术分析声发射信号波形,改进了AO模态到达时刻的确定算法,提高了线定位精度。在此基础上,将平面定位问题转化为求取函数最小值的优化问题,并利用单纯形法进行求解。在铝合金板上对铅芯折断波源进行了定位试验,结果表明,相对于小波变换,HHT更适于分析声发射信号;改进后的线定位方法和双时标法可有效应用于各向同性板的定位问题。研究结果为空间碎片在轨感知系统的研制提供了参考。     

The effect of depth-dependent residual stresses on the propagation of surface acoustic waves in thin Ag films on Si

We give detailed calculations of the acoustoelastic effect (AE) in highly textured thin silver films on silicon substrates. The AE relates the phase velocity of the surface waves to the stresses within the films. Therefore, we have investigated several stress states that were produced by annealing and measured by X-ray grazing incidence diffraction. The selected temperatures range from 25 to 700 °C. The stress profiles are modelled by a stratification of the films into different layers. Subsequently, by application of the stiffness-matrix method (SMM) for acoustic wave propagation, the corresponding AE is calculated. No measurements of the AE itself will be reported here. Our calculations show that the AE is fairly weak and becomes maximal when the wavelength is on the order of some few film thicknesses.     

A self-calibrating piezoelectric transducer with integral sensor for in situ energy calibration of acoustic emission

Piezoelectric transducers are used as both transmitters and sensors in acoustic emission (AE) testing applications. However, the transducer outputs are significantly affected by the coupling between the transducer and the structure. This means that the coupling must be very carefully controlled or assessed if reliable AE calibration sources are to be generated, and be considered in the AE system calibration if reliable AE measurements are to be made. The paper shows that by integrating a piezoelectric AE sensor to the backing of a conical piezoelectric transducer acting as the transmitter, a self-calibrating AE energy point source can be obtained. There is a negative linear relationship between the AE signal energy from the backing sensor and the coupling efficiency for a constant electrical input to the transmitter over the frequency range of interest in AE measurements (100 kHz to around 1 MHz). This should enable the strength of the simulated AE point source to be determined using the AE measurement from the backing sensor, and hence to facilitate in situ energy calibration of AEs in structures.     

换热器管板声发射在线检测及评价方法

换热器管板属于多孔结构，制造工艺复杂，容易产生缺陷，且管板与换热管连接处连接质量不易检查。针对上述问题，采用声发射检测技术，将传感器通过专用波导杆与换热管连接，根据衰减测量结果确定管板上传感器的布置阵列。通过壳程水压试验二次加载方式对其进行声发射检测。采取区域定位方法，通过对不同阶段保压信号的分析，综合考虑声发射信号的活性和强度，制定了换热器管板声发射检测及评价方法，实现了对换热器管板质量的分级评价。     

Fracture dynamics of sprayed and laser-glazed titania by an inverse processing of elastic waves

A new elastic wave (EW) or acoustic emission (AE) monitoring and signal processing system has been developed and used to elucidate the fracture behavior of sprayed and laser-glazed ceramic coatings. The system measures the minute surface displacements excited by the propagation of elastic waves. It enables elucidation of the fracture dynamics (fracture mode and kinetics) of stressed coatings. The surface displacement at the sensor position was computed by the convolution integral of an assumed source wave with the dynamic Green’s function until signals resembled the measured wave. This new signal processing method was used to determine the fracture strength and dynamics of microcracks in sprayed and laser-glazed titania subjected to four-point bending. It was found that mode II shear cracking along the interface between the coating and substrate occurred prior to mode I cleavage cracking. The fracture strength of laser-glazed titania was higher than that of as-sprayed titania in most cases; however, this depended on the coating structure. This article introduces the principle of source inversion processing of elastic waves, the monitoring system, laser glazing of sprayed titania, and experimental work on the fracture behavior of titania coatings.     

Thermal–mechanical analysis of the surface waves in laser cleaning

The work described in this paper is to investigate the particle removal mechanism by surface wave in laser cleaning. A mathematical model of laser cleaning processes was established for a flat plate to remove micro-particles from the surfaces by surface waves. The software ABAQUS, based on finite element method, was used to simulate the non-linear stress wave problem for an uncoupled thermal–mechanical system in a two-dimensional domain. The result shows that the cleaned area increases with the laser energy, which led to surface waves with large acceleration in the vertical direction, but the effective cleaned area decreases with an increase of the laser spot size.     

Thin sensitive organic membranes on selective iron-ion sensors

The organic supramolecular compound synthesized from pyrochatechol units bound in the -position of a linear dicarboxylic acid (AE6) previously used as a stable chelate iron(III) in solution is applied in this work as an ionophoric reagent on ion-sensitive field-effect transistor (ISFET) and electrolyte—insulator—semiconductor (EIS) structures for iron detection. The surface gate oxide (SiO₂) sensitization of sensors was performed, using three deposition methods: chemical grafting to obtain an AE6 monolayer, deposition by vacuum sublimation of an AE6 thin film and incorporation in a polysiloxane gel membrane. Classical electrochemical measurements were made to test the sensitivity towards iron of the AE6 membranes, in EIS and ISFET structures. A Nernstian sensitivity, a good selectivity and a long lifetime were obtained for the evaporated layer and the gel membranes.     

Multiscale study of acoustic emission during smooth and jerky flow in an AlMg alloy

The acoustic emission (AE) accompanying jerky flow in dilute alloys, the so-called Portevin–Le Chatelier effect, is usually considered to be composed of discrete bursts associated with the motion of large dislocation ensembles giving rise to stress serrations, which are superimposed on continuous AE generated during macroscopically smooth plastic flow. The data streaming technique which allows continuous AE recording is used to investigate the jerky flow of an AlMg alloy on different timescales. The apparent behavior, discrete or continuous, of AE is found to depend on the period of observation and the characteristic surveyed. However, it is proved that AE has a burst-like character during both stress serration and smooth flow. This behavior, revealed on timescales proper to the given strain rate, reflects the inherently intermittent, avalanche-like nature of collective dislocation dynamics, and unifies the concept generally applied to jerky flow with the similar approach to macroscopically uniform deformation flow, based on recent studies of AE during plastic deformation of pure materials.     

齿轮表层疲劳裂纹扩展的声发射模型

齿轮表面的疲劳磨损是齿轮故障的主要形式之一。从弹性力学的能量理论角度,推导出了齿轮齿表疲劳裂纹在扩展时的能量关系,并根据声发射信号的特征,构造出齿表疲劳裂纹在扩展时产生的声发射信号的理论模型,说明了影响声发射信号能量强度的主要因素为裂纹扩展时间、形变体积及载荷和弹性模量的变化率,从理论上证明了声发射技术用于检测疲劳磨损的可行性。     

基于声发射与关键帧选择的LSP表面硬度监测

目的 提高激光冲击强化(Laser Shock Peening,LSP)表面硬度的在线检测能力,探究声发射信号关键帧对LSP表面硬度分类识别性能的影响。方法 在LSP处理期间声发射弹性波(Acoustic Emission,AE)具有与材料内部晶格位错和塑性变形密切相关的动态信息,是激光冲击强化在线监测的一种极具潜力的手段。但其高采样频率导致大量的实时计算,对在线监测技术的工业应用提出了巨大的挑战。为解决这一问题,提出了注意力权重统计方法获取激光冲击强化过程中声发射信号的关键帧。结果 四通道传感器各自的关键帧信号长度相比原始信号的有效长度均大幅度减少,最大可减少83.74%,相比原始数据每一轮测试(350个冲击样本),最大可减少57.37%的测试时间。关键帧信号的模型识别准确率最高可达到97.04%,相比原始数据集提升了2.93%。结论 与原始声发射信号相比,关键帧信号得到了更高的测试准确率,同时有效地减少了数据量。基于关键帧数据集的最高准确率和最短测试时间,评价了4种不同传感器中信号采集的最佳传感器,其结果可作为LSP质量监测领域的参考。     

A new method for waveform analysis for estimating AE wave arrival times using wavelet decomposition

Here we describe a new method for determination of Acoustic Emission (AE) wave arrival times for source location purposes. In complex structures or structures of small dimension, an AE source can rapidly become distorted by the presence of several modes travelling at different speeds, and through contamination by reflections and mode conversions.Using a simple geometry of carbon-fibre reinforced plastic, the responses acquired from two-sensor and four-sensor arrays have been analysed using a variety of techniques, which are variants on identification of first arrival time and/or the arrival of the maximum intensity of the wave. The methods are compared in terms of the consistency of the velocity which is indicated at different points in the arrays, and a method based on wavelet decomposition, filtering and threshold-crossing is recommended as the most consistent and accurate method of determining arrival time.     

Evaluation of the wafer polishing pad capacity and lifetime in the machining of reliable elevations

The purpose of the wafer polishing process is to ensure wide planarization, uniformity, a precise surface finish and a non-defective surface. Its significance is increasing with the trend toward large-diameter wafers. The polishing pad used in these processes is an important factor that influences the wafer surface finish. Maintenance of the pad capacity plays a key role in the machining of reliable elevations. If the machining time increases, the pad capacity decreases, creating the need for a suitable shift time. A rough pad surface condition can contain microscopic holes that serve as an exhaust pathway for minute chip particles. Such particles become reaction materials on the pad surface.In this study, a dressing effect on the machining capacity, deformation degree and pad lifetime are investigated. A 300 mm silicon wafer was polished and the dressing defect and control condition were compared and analyzed with no change of the other machining conditions. The pad capacity and lifetime were evaluated in terms of the pad deformation degree, pad surface variation and silicon wafer surface finish under various pad deformation conditions. The AE (Acoustic Emission) signal of various pad surface conditions was detected using a AE sensor during the silicon wafer polishing process. The polishing process was monitored and analyzed using the AE raw signal, RMS (Root Mean Square) conversion data and FFT (Fast Fourier Transformation) analyses. The AE signal is a spontaneous elastic wave signal caused by a change in the stress condition of each material. Using a loadcell with the wafer head fixture, variations in the applied pressure signal were detected and compared while varying the condition of the pad surface and final wafer surface finish.The silicon wafer polishing process has sensitive machining characteristics due to the interaction between various complex process factors. These can include the pad, slurry, applied pressure, rotation speed, dressing condition and the machining temperature. Among these important machining factors, the pad capacity and lifetime evaluation as they pertain to the dressing control were assessed. These characteristics were investigated through an analysis of the deformation of the pad, the wafer surface finish, the detected sensor signal and the signal process.     

声发射检测中的压电换能器

在声发射检测中，传感器是获取信息的关键部件之一。目前绝大部分声发射传感器都是压电换能器。就采用压电原理的声发射传感器的发展及其校准问题作概述，对声发射传感器中的特殊问题孔径效应及其对传感器设计、性能和校准的影响进行讨论。