早龄期荷载及低温作用下的混凝土声发射特征试验研究*

井壁混凝土由于施工与环境特殊性导致其裂缝扩展情况异常,本文通过对不同早龄期荷载、低温条件下混凝土轴压破坏过程的声发射检测,分析井壁施工环境对混凝土内部裂缝产生、发展的影响。研究表明,早龄期荷载、低温单独作用时,与标养混凝土主要差异在轴压过程中的声发射初始阶段,对混凝土内部的原有收缩裂缝有所影响。当两者耦合作用时,早龄期荷载影响比低温作用显著,并且在早龄期荷载较大时会出现声发射信号"倒置"现象。     

10.6MeV/u 84Kr+27Al碰撞中粒子发射的方位角分布和方位角关联

研究了10.6MeV/u ⁸⁴Kr+²⁷Al反应中与碎片符合的轻带电粒子发射,重点研究了用二阶傅里叶级数拟合发射粒子的方位角分布和方位角关联得出的二阶各向异性系数的性质.结果证实了一个事件中的粒子都以相同方位角分布统计独立发射.发现二阶各向异性系数同碎片的质量用微弱的信赖性,并随发射粒子质量的增加而增加.     

蒸养再生骨料混凝土断裂声发射特征*

为研究蒸汽养护对再生骨料混凝土断裂过程损伤特征的影响,开展了再生骨料混凝土三点弯断裂试验,并采用声发射技术对损伤过程进行了监测分析。结果表明,蒸养降低了再生骨料混凝土断裂峰值荷载,断裂过程中声发射信号强度低于标准养护试件。声发射振铃计数、撞击数、b值等参数能够准确反映再生骨料混凝土断裂过程损伤演变规律。加载上升阶段,声发射信号活动性很低,试件内以微裂纹的形成为主,加载至荷载峰值,声发射振铃计数累计值增长呈现平缓阶段,混凝土内微裂缝的聚合会持续一段时间。峰值后荷载迅速降低阶段声发射信号最活跃,为裂缝迅速发展的过程。峰后荷载缓慢降低的过程,声发射信号活跃性降低,裂缝扩展至试件顶部区域,主要是宏观裂缝的开展,不再产生新的裂缝。     

声表面波气体传感器研究进展*

基于声表面波技术的气体传感器包括采用敏感膜和结合气相色谱两种方式。比较而言,采用敏感膜的声表面波气体传感器体积小、功耗低,适应小型化毒气报警器的发展要求,但可检测的气体种类少、灵敏度低、存在交叉干扰问题;声表面波与气相色谱联用的气体分析仪灵敏度高、可检测气体种类多、很好地解决交叉干扰问题,特别适合于复杂大气背景条件下的气体成分分析。本文从传感器响应机理分析与物理功能结构两方面出发介绍了两类声表面波气体传感器的研究进展情况。     

基于噪声预估计的DPOAE最小二乘估计方法*

针对畸变产物耳声发射(distortion product otoacoustic emission, DPOAE)信号比较微弱,估计结果的准确性对信噪比依赖性强的特点,本文给出一种新的DPOAE信号最小二乘估计(least square estimation, LSE)方法。该方法先估计本底噪声,将本底噪声的影响体现于估计模型中,再估计DPOAE信号。记录信号经过一定的预处理后,利用频域加窗法估计本底噪声并进行噪声衰减;利用IFFT变换后的信号估计DPOAE信号的模型参数,给出DPOAE的强度和相位。仿真和实验结果表明,该方法相对于传统的最小二乘拟合(least-square-fit, LSF)法,对DPOAE的估计更加准确,抗噪声干扰能力更强。     

偶极子声波测井仪发射声系性能快速检测方法*

该文提出了一种针对偶极子声波测井仪发射声系性能进行快速检测的方法。通过实验测量方法,采用专门设计的简易装置测量偶极子声波测井仪发射声系激发的声场波形,并提取声场强度、声源主频以及空间分布对称性等特征参数。如果准确掌握了仪器处于完好状态时的这些特征参数,以此为参考依据与实验测量结果进行对比,通过设定可接受的相对偏差,就可完成对偶极子声波测井仪发射声系性能的快速评价。相对于现有的声波测井仪器检测方法,该方法具有高效、便捷的优势,便于在测井前线基地应用。     

声辐射阻测量系统设计及测量精度影响因素分析*

在噪声控制领域,声辐射阻是一个重要的声学变量,在产品的设计阶段,可以通过改变结构表面形状来改变结构的声辐射阻抗,从而达到降噪的目的。本文基于集中参数模型,设计了测量设备,搭建了实验测量系统,并通过对无限大障板上圆形活塞声源的声辐射阻的测量对影响实验测量结果的因素进行了研究,之后对消音器入口处辐射阻进行了测量。测量结果表明:该实验测量系统具有操作简单,测量方便快捷,测量结果精度高等特点,可用于确定结构表面声辐射阻矩阵。     

Al2O3陶瓷涂层尖端受载下的声发射信号参量分析

为了考察再制造零件涂层结合强度检测仪评价涂层结合强度的可行性,以Al₂O₃陶瓷涂层为研究对象,在涂层表面进行压入试验,提取并分析了试验过程中声发射信号中的幅度、计数、能量与有效值电压(RMS)特性参数的时间分布曲线,读取了声发射信号突变点的波形,观测了压痕处涂层截面微观形貌。结果表明,声发射信号出现明显突变时,涂层界面确实产生了开裂失效。采用此检测设备可以有效诱导、界定涂层界面的断裂失效,声发射信号可以作为涂层开裂的临界判据,其中幅度的时间分布更能体现出Al₂O₃陶瓷涂层在压入过程中的裂纹萌生至涂层断裂的扩展过程;能量值对涂层的失效更为敏感,最为适合评价涂层的结合强度。     

超声空化及其声流结构实验研究*

超声空化及其声流效应在医学、化工和能源等领域得到广泛应用。本文采用高速摄像和粒子图像测速系统分别研究了超声场下的空化形态和声流场结构的时空演化规律。实验研究了50W,100W,200W和250W等四种不同输入功率对18kHz的超声变幅杆附近空化及其声流场的影响。研究结果表明：（1）在变幅杆下端面处观察到由大量空化气泡均匀分布组成的倒置锥形空泡结构,并且锥形空泡结构为稳态流动结构。（2）在超声变幅杆附近产生了两种不同的声流形式,第一种是变幅杆底端的射流型声流,第二种是变幅杆两侧的回旋流。此外,通过研究空泡与声流场中最大速度点之间的空间对应关系,发现声流是因为空泡流动带动而产生的。（3）空间位置和输入功率能显著影响射流型声流的流场结构,但是对回旋流的影响十分微弱。     

高速运动目标的自适应线谱增强算法研究

本文研究了低信噪比、目标高速运动情况下,多普勒频移较大时针对线谱信号的自适应增强算法。对海试数据的分析表明,常规自适应线谱增强算法对多普勒频移下的线谱增强效果明显,但要求信噪比较高,且实时性较差;基于高阶累积量对角切片的自适应线谱增强算法对非线性高斯色噪声下的线谱增强效果显著,但对低信噪比环境下变化线谱的跟踪性能较差;频域批处理自适应线谱增强算法对低信噪比下的线谱信号具有很好的增强效果,降低了运算量。     

Using acoustic emission signals for monitoring of production processes

The systems for in-process quality assurance offer the possibility of estimating the workpiece quality during machining. Especially for finishing processes like grinding or turning of hardened steels, it is important to control the process continuously in order to avoid rejects and refinishing. This paper describes the use of on-line monitoring systems with process-integrated measurement of acoustic emission to evaluate hard turning and grinding processes. The correlation between acoustic emission signals and subsurface integrity is determined to analyse the progression of the processes and the workpiece quality.     

神经网络在声发射信号模式识别中的应用

介绍了人工神经网络中的BP网络、RBF网络、Hamming网络、BP－Hamming网络在声发射信号模式识别中的应用现状，并对这些方法的优缺点进行了比较。     

单矢量水听器估计目标方位的方法与实验

为评估基于单矢量水听器的方位估计能力,在黄海海域对矢量水听器进行实验。矢量水听器吊放于接收船尾部,采用平均声强器和复声强器方位估计方法,并提出以概率密度值最大的方位角作为目标方位估计值的具体处理准则,对恒定方向、匀速行驶的目标船方位进行估计,并求出两种方法的方位估计误差。结果表明,水听器布放深度10 m时,对正横距离为0.42 km的航速10 kn的目标船,平均声强器方法的水平方位角估计误差18°,极角估计误差为5°,可以在离目标船最远1.17 km处估计其方位;复声强法的水平方位角估计误差为13°,极角估计误差为8°,可以在离目标船最远2.35 km处估计其方位。在有接收船的噪声干扰情况下,复声强器比平均声强器方法估计的方位更准确,可以对更远处的噪声源进行方位估计。     

油罐声发射检测信号数据库研究及应用

分析了油罐声发射检测技术特点和弱点,基于对检测影响因素的分析研究提出了油罐声发射信号特征数据库系统。采用盐水腐蚀真实罐底板,模拟油罐腐蚀。以Matlab软件为基础,提取全波形文件中被识别为腐蚀类别的特定帧信号,选取合适的自适应阈值电压得到信号特征参数,将全波形信号和信号特征参数入库。根据数据库特征参数训练支持向量机分类器,应用到实际油罐检测中并与开罐检测结果作对比,达到预期油罐分类效果。     

滚动轴承声信号特征提取和诊断试验研究

为解决振动检测方法不能有效识别低速旋转机械滚动轴承故障问题,利用声发射检测方法,建立了滚动轴承低速声发射信号采集试验装置,对模拟人工缺陷滚动轴承声发射信号进行了采集,进而对滚动轴承声发射信号进行总体平均经验模式分解,结合能量矩及相关系数法综合判断分解后各模态分量的真伪,据此提取出特征信号并做出其局部Hilbert边际谱,最后对滚动轴承各种故障模式进行诊断。试验结果表明该诊断方法能准确识别滚动轴承声发射信号故障频率,依据特征频率及幅值大小可对低速滚动轴承故障进行有效诊断。     

Energy monitoring and analysis during deformation of bedded-sandstone: Use of acoustic emission

This paper investigates the mechanical behaviour and energy releasing characteristics of bedded-sandstone with bedding layers in different orientations, under uniaxial compression. Cylindrical sandstone specimens (54 mm diameter and 108 mm height) with bedding layers inclined at angles of 10°, 20°, 35°, 55°, and 83° to the minor principal stress direction, were produced to perform a series of Uniaxial Compressive Strength (UCS) tests. One of the two identical sample sets was fully-saturated with water before testing and the other set was tested under dry conditions. An acoustic emission system was employed in all the testing to monitor the acoustic energy release during the whole deformation process of specimens. From the test results, the critical joint orientation was observed as 55° for both dry and saturated samples and the peak-strength losses due to water were 15.56%, 20.06%, 13.5%, 13.2%, and 13.52% for the bedding orientations 10°, 20°, 35°, 55°, and 83°, respectively. The failure mechanisms for the specimens with bedding layers in 10°, 20° orientations showed splitting type failure, while the specimens with bedding layers in 55°, 83° orientations were failed by sliding along a weaker bedding layer. The failure mechanism for the specimens with bedding layers in 35° orientation showed a mixed failure mode of both splitting and sliding types. Analysis of the acoustic energy, captured from the acoustic emission detection system, revealed that the acoustic energy release is considerably higher in dry specimens than that of the saturated specimens at any bedding orientation. In addition, higher energy release was observed for specimens with bedding layers oriented in shallow angles (which were undergoing splitting type failures), whereas specimens with steeply oriented bedding layers (which were undergoing sliding type failures) showed a comparatively less energy release under both dry and saturated conditions. Moreover, a considerable amount of energy dissipation before the ultimate failure was observed for specimens with bedding layers oriented in shallow angles under both dry and saturated conditions. These results confirm that when rock having bedding layers inclined in shallow angles the failures could be more violent and devastative than the failures of rock with steeply oriented bedding layers.     

方位偶极声波远探测技术研究与应用

偶极横波远探测测井技术是当前缝洞型和复杂储层油气勘探开发和评价不可缺少的技术手段。常规偶极远探测技术受限于180?方位的不确定性,难以判别缝洞等地质体的真实方位。采用双偶极错位发射多分量阵列接收研究偶极方位识别方法。首先以传统正交偶极模式获得地质体方位探测结果,再以45?错位角发射偶极声波信号,通过多个邻近接收器的波形差的组合以及反射波在仪器孔径上的时间延迟来区分方位,进一步压制伪像干扰获得地质体真实的方位成像结果。针对弱反射信号,在硬件上,研究了多分量有源接收器阵列声系,有效提升了偶极声波信号信噪比,结合动态增益控制提升反射波幅度;研究了双偶极宽频发射器与多模式发射技术,提高偶极发射功率,保证了偶极声波信号在地层中的远距离传播与反射。数值仿真与实际测井数据表明,双偶极方位识别方法可行,有助于偶极横波远探测技术的进一步发展和应用。     

木塑复合材料缺陷及损伤的声发射信号特征分析及神经网络模式识别

针对木塑复合材料五种典型的缺陷及损伤机制，选择合适的木塑试样，应用三点弯曲的加载方法采集声发射信号。对主损伤区附近的声发射事件，应用小波变换提取特征参数，确定五类主要损伤机制所对应的声发射信号特征。采用B—P型反向传播神经网络构成的智能化模式分类器，对此五类声发射信号进行识别，获得了满意的效果。     

Near-field beamforming analysis for acoustic emission source localization

This paper attempts to introduce a near-field acoustic emission (AE) beamforming method to estimate the AE source locations by using a small array of sensors closely placed in a local region. The propagation characteristics of AE signals are investigated based on guided wave theory to discuss the feasibility of using beamforming techniques in AE signal processing. To validate the effectiveness of the AE beamforming method, a series of pencil lead break tests at various regions of a thin steel plate are conducted. The potential of this method for engineering applications are explored through rotor-stator rubbing tests. The experimental results demonstrate that the proposed method can effectively determine the region where rubbing occurs. It is expected that the work of this paper may provide a helpful analysis tool for near-field AE source localization.     

Shaft angular misalignment detection using acoustic emission

Shaft angular misalignment (SAM) is a common and crucial problem in rotating machinery. Misalignment can produce several shortcomings such as premature bearing failure, increase in energy consumption, excessive seal lubricant leakage and coupling failure. Vibration analysis has been traditionally used to detect SAM; however, it presents some drawbacks i.e. high influence of machine operational conditions and strong impact of the coupling type and stiffness on vibration spectra. This paper presents an extensive experimental investigation in order to evaluate the possibility of detecting SAM, using acoustic emission (AE) technique. The test rig was operated at under different operational conditions of load and speed in order to evaluate the impact on the AE and vibration signature under normal operating conditions. To the best of the author’s knowledge, this is the first attempt to use AE for the detection of SAM under varying operational conditions. A comparative study of vibration and AE was carried out to demonstrate the potentially better performance of AE. The experimental results show that AE technique can be used as a reliable technique for SAM detection, providing enhancements over vibration analysis.