A calibration approach to acoustic emission energy measurement

An approximate method for the quantitative characterization of acoustic emission sources whose signals are recorded with traditional instrumentation has been developed to evaluate the emission from a Fe-Ni alloy undergoing martensitic transformations. The calibration principle is based upon using pseudo sources of known elastic strain energy to produce a calibration curve relating a parameter of the acoustic emission signal measured (envelope strength) to the strain energy of the source. The curve can then be used to determine the strain energy of naturally occurring sources during martensitic transformations.     

Nature of acoustic emission during phase transformations and adequacy of the Stefan condition

The kinetics of phase transformations of water and associated acoustic effects have been considered. The contribution of the energy of acoustic emission is estimated in relation to the latent energy of crystallization.St. Petersburg Institute of Civil Engineering, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 1–2, pp. 23–26, July–August, 1994.     

Inversion of acoustic emission asymmetry accompanying martensitic transformations in titanium nickelide alloys

Asymmetry of the acoustic emission indicates that the processes of nonchemical energy scattering differ in the direct and reverse martensitic transformations. An analysis of the inversion of the emission asymmetry with increasing nickel concentration in binary Ti-Ni alloys and in the course of multiple transformation cycles suggests that in a direct transformation nonchemical energy is dissipated by plastic relaxation whereas in a reverse transformation it is dissipated by dynamic relaxation. Significantly plastic relaxation degrades to saturation and dynamic relaxation begins to appear exclusively. Pis’ma Zh. Tekh. Fiz. 25, 41–49 (December 26, 1999)     

An acoustic emission energy analysis and its use to study damage in laminated composites

A new technique which uses the output of a true RMS voltmeter to measure the acoustic emission energy output of a transducer is presented. To demonstrate its use in a typical case, this procedure is used to measure acoustic emission energy during tensile tests on [0°/±30°/90°]_s glass-epoxy laminate uniaxial and 10° off-axis tensile coupons. The test results were compared with numerical predictions of laminate response and acoustic emission energy. The experiments indicate that acoustic emission energy can be used to indicate the onset of ply and interlaminar failure.     

碎片云撞击声发射信号能量特征小波包分析

利用小波包分析技术对碎片云撞击载荷作用下铝合金板声发射信号的能量分布特征进行了研究。首先,介绍了碎片云撞击信号的获取方案及撞击引起的损伤情况;其次,对获取的声发射信号进行小波包分析,得到了信号在频率带上能量分布特征图。最后,讨论了碎片云撞击损伤特征与声发射信号能量分布的关系。分析结果发现,对于相同质量的弹丸,随着其破碎程度的提高,形成的碎片云对后板的损伤程度减少;弹丸具有的初始速度越大,弹丸破碎越完全,碎片云撞击声发射信号中的能量越小;当弹丸破碎程度低时,碎片云撞击引起的声发射信号能量集中在约488kHz以下;弹丸破碎程度越高,信号中488kHz以上的能量所占总能量的比例越大。     

Effect of transient stress on acoustic emission behaviour during firing of dental porcelain

Acoustic emission activity was measured in the glass transition range of dental porcelain during firing. Transient and residual stresses in porcelain during cooling from a temperature higher than porcelain sag point and during re-heating of the tempered porcelain were calculated by computer simulation using a viscoelastic stress analysis. The detected acoustic emission event was discussed with the relative rules of the simulated transient stresses. High acoustic emission activity was detected at the temperature where the internal stress faded away for heating and build up for cooling. The low-level acoustic emission pulses were only detected in the following conditions: (1) in the temperature range where porcelain behaved like an elastic solid; (2) at temperatures higher than the deformation point of porcelain; (3) with a re-heating process of the porcelain without tempered stress. From these results, it was concluded that elastic energy is released related to transient stress in porcelain during viscoelastic deformation and can be detected by the acoustic emission method. The acoustic emission method is considered to be helpful in non-destructive testing in order to understand transient stress due to viscoelastic deformation of glassy materials in heat treatment.     

岩石声发射信号能量分布特征的EMD分析

冲击荷载作用下岩石声发射信号具有瞬态性和多样性的特点,属于典型的非平稳信号。利用EMD方法对岩石声发射信号进行分解,得到一系列具有不同特征时间尺度的IMF分量,对每一个平稳的IMF分量提取能量特征。分析结果表明：冲击荷载作用下岩石声发射信号能量主要分布在前4个IMF分量内,且分布不均匀;岩石声发射信号各IMF分量的频谱与原始信号的频谱基本一致;随着岩石的密度、纵波波速、弹性模量的降低,冲击荷载作用下岩石声发射信号的优势频率越来越集中,且其优势频率有往低频发展的趋势;相比小波包分析,EMD分析法对于非平稳信号而言更具适应性。     

Acoustic emission in dislocation-containing silicon exposed to current and thermal influences

An investigation was made of acoustic emission in silicon single crystals during passage of an electric current. It was observed that in the temperature range studied (T=300−450K) acoustic emission signals whose intensity increases with increasing dislocation density are excited in a static electric field. The acoustic emission of silicon single crystals with and without dislocations is compared. It is assumed that the acoustic emission in silicon is caused by the unpinning and migration of dislocations under the influence of the direct electric current and thermoelastic stresses. The activation energy of this process is estimated as E=0.53±0.05 eV during passage of a direct current of density j=2.8×10⁵ A/m². Pis’ma Zh. Tekh. Fiz. 25, 28–32 (February 12, 1999)     

基于小波包分析的拉索损伤声发射信号特征提取

结合显式有限元和小波包分析技术开展了拉索损伤声发射信号特征提取的仿真分析。采用ANSYS/LS-DYNA模拟得到拉索损伤声发射信号的仿真信号,基于小波包能量谱对拉索声发射的有限元仿真信号进行了特征提取,从小波包分解层次、特征频带数量的选择及特征参数的噪声鲁棒性三个方面开展了讨论分析。结果表明:(1)通过选择适当的小波包分解层次,小波包能量谱可以精细地反映信号的特征;(2)选取少数特征频带就能使得小波包能量谱反映声发射信号的特征信息;(3)基于小波包能量谱的特征参数具有良好的损伤敏感性及噪声鲁棒性,能在强噪声影响下实现对拉索不同损伤类型的判别。     

基于声发射信号的钢桶泄漏检测

目的研究基于声发射信号的钢桶泄漏检测方法。方法利用声发射传感器、前置放大器、采集卡和计算机搭建采集系统,分析漏孔直径为0.2 mm和无泄漏状况下泄漏频率特点。对采集的声发射信号采用小波包分解,提取了泄漏信号的3个特征频段(16~30 kHz,33~47 kHz,95~102 kHz)的能量特征,将其作为支持向量机的输入特征向量,对已经训练好的支持向量机进行测试,判断钢桶是否泄漏。结果经试验测试,判断准确率达100%。结论通过小波包能量与支持向量机相结合的方法,可以成功地对直径0.2mm及以上漏孔的钢桶泄漏进行检测。     

基于声发射的钢筋混凝土梁承载能力评估

在钢筋混凝土断裂过程中能量平衡基础上,结合声发射与断裂力学参数的耦合关系,得到裂纹稳定拓展过程中,声发射振铃数与钢筋混凝土梁抗弯刚度间的关系,并通过钢筋混凝土梁静、动态弯曲破坏试验进行验证。结果表明：在能量平衡原理基础上建立声发射参数与钢筋混凝土梁承载能力的关系是可行的。在宏观裂纹稳定拓展阶段,通过声发射传感器实时监测获得破坏过程的声发射信号,能准确评估钢筋混凝土梁的抗弯刚度。     

Modeling of explosive acoustic emission accompanying martensitic transformations in alloys

The acoustic emission accompanying the stimulation of macroexplosive martensitic transformation kinetics in Ti-51.0 at. % Ni alloy has been confirmed. The macroexplosive kinetics were stimulated both by repeated cycling and by incomplete quasicycling of martensitic transformations. Pis’ma Zh. Tekh. Fiz. 24, 31–38 (January 12, 1998)     

SPCC钢滑动摩擦与拉伸声发射信号比较分析

为了将声发射技术应用在金属塑性加工中的摩擦监测中,以SPCC钢在拉伸过程与相对运动速度为100mm/min、正压力为7.5kg的摩擦过程产生的声发射信号特征为研究对象,分别用数据统计、平均值等方法对比分析了两种声发射信号的能量、振铃计数、幅度等参数。实验结果表明:SPCC钢拉伸的声发射能量值要远小于摩擦声发射能量值;拉伸的声发射振铃计数分布范围要略大于摩擦声发射振铃计数分布范围;拉伸的声发射幅度要小于摩擦声发射的幅度。最后对出现该现象的原因进行了探讨。     

Cooling rate effects on acoustic emission-microstructure relationships in ferritic steels

The study reported here systematically investigates the nature of the relationship between defect dynamics and acoustic emission in specially prepared low alloy steels containing 3.25 wt% Ni, 1 wt% Mn with carbon contents between 0.06 to 0.49 wt% as the rate of cooling from the austenitic state is varied. During plastic flow, the strongest acoustic emissions are generated from slowly cooled microstructures with a 10 m ferrite dimension, a low initial dislocation density and very widely spaced precipitates. This emission is believed to originate from the propagation of high velocity (>100 ms^–1) dislocation groups in the ferrite phase. It is consistent with an emission model in which the product of the dislocation glide distance and velocity (which are both controlled by microstructure) determines the amplitude of the acoustic emission. In air cooled samples containing retained austenite, additional emission is seen and suggests that stress-induced martensitic transformations are a second emission source. During subcritical microfracture, intergranular and alternating shear modes of microcracking occur in high strength conditions and generate strong signals. Both mechanisms involve the rapid propagation of cracks over distances of 10–100 m and the resulting emission is consistent with the model predictions. The ductile dimple mode of fracture is found to generate no detectable signals regardless of dimple spacing and fracture stress, which is consistent with the view that such fracture occurs under essentially quasistatic conditions with little or no mechanical instability.     

Q235焊接钢板受剪声发射时频特性分析

Q235钢板在工程中应用广泛,为了研究焊接对于Q235钢板性能的影响,开展了焊接试样和完整试样的受剪实验,利用数字声发射系统对实验过程的声发射信号进行实时采集。根据声发射计数率划分不同阶段,采用魏格纳-维尔分布,平滑伪魏格纳-维尔分布,对信号进行时频分析。实验结果表明:受剪实验中,焊接试样与完整试样的声发射特性明显不同,主要表现在受剪过程的各阶段中声发射信号能量集中的频带不同,弹性变形阶段信号时频带主要集中在80~100 k Hz附近;钢板塑性变形阶段时频带集中在100~140 k Hz范围内;焊缝塑性变形阶段,时频能量主要集中的频带范围在300~350 k Hz之间,部分能量较弱的信号分布在100 k Hz附近频段。     

Acoustic emission analysis and small-angle X-ray scattering from microcracks during deformation of ETFE composites

During the deformation of an unfilled matrix of ethylene-tetrafluoroethylene (ETFE), microcracking was observed by small-angle X-ray scattering (SAXS), although it does not cause significant acoustic emission because the released energy is too small to be detected (size of microcrackssize of fibres). Fibres induce local stress maxima and increase the formation of microcracks. Fibre delamination processes were monitored by acoustic emission analysis. The use of coupling agents improves the fibre-matrix adhesion and increases the mechanical yield stress and decreases delamination processes. A simple model for estimating the energy released by fibre delamination processes was suggested. The predicted difference in peak amplitude between the two extreme processes agrees well with the results of the experiments. The characteristic values of the peak amplitude distributions, however, do not show any significant dependence on fibre coating or testing temperature. Further investigations by SAXS and acoustic emission analysis, especially at low strain, will be necessary to obtain more detailed information about the initial formation of microcracks and fibre delamination.     

疲劳荷载对橡胶混凝土损伤和断裂性能的影响

虽然橡胶混凝土塑性和疲劳性能较好,但由于掺入橡胶,其在疲劳荷载下离散性增大,损伤过程及最终的断裂机制均不明确。为研究橡胶混凝土在疲劳荷载下的损伤和断裂性能,基于声发射开展了不同橡胶掺量的混凝土在疲劳荷载下的三点弯曲疲劳断裂试验。计算有效裂缝长度,分析疲劳荷载下不同橡胶掺量的混凝土裂缝长度a的变化规律,并利用裂缝长度a和声发射累积能量E_AE分别定义了损伤变量D_a和D_AE;分析疲劳荷载下不同橡胶掺量的混凝土断裂能G_F的变化规律;利用声发射中的信号持续时间分析疲劳荷载下橡胶混凝土中裂缝出现和扩展的规律。结果表明,混凝土的断裂能随橡胶掺量的增加呈线性增加;在疲劳荷载下,裂缝长度a和D_a均呈倒S型规律变化,而D_AE呈正S型规律变化;声发射信号持续时间表明,在疲劳荷载下,橡胶混凝土中的裂缝总在荷载较小时出现或发生扩展。      

钢纤维增强粉煤灰地质聚合物单轴受压过程的声发射特性

为探索纤维增强地质聚合物宏观力学行为与细观损伤演化特征之间的关联,对不同纤维体积掺量(纤维与拌合物的体积比)的钢纤维增强粉煤灰地质聚合物复合材料进行了单轴压缩试验.基于声发射技术,对试样压缩过程的声发射行为进行监测,研究了纤维体积掺量对地质聚合物单轴受压破坏行为及声发射特性的影响.结果表明:地质聚合物的强度、延性、声发射波形的上升斜率及平均频率均随纤维掺量的提高而增大,试件破坏形态由脆性灾变逐渐向延性破坏转变;在破坏前期,纤维体积掺量为0及0.5%的试件的声发射撞击率及能量释放率(简称能量率)都保持在较高水平,最终导致试件出现灾变破坏;而2.0%的纤维体积掺量使得声发射撞击率及能量率在应力-时间曲线的拐点处达到峰值,随后缓慢下降,最终导致试件呈现延性破坏;因此,仅依据声发射撞击率及能量率的快速上升来预测灾变破坏的发生,有时可能会出现谎报的情况.     

Acoustic emission location on aluminum alloy structure by using FBG sensors and PSO method

Acoustic emission location is important for finding the structural crack and ensuring the structural safety. In this paper, an acoustic emission location method by using fiber Bragg grating (FBG) sensors and particle swarm optimization (PSO) algorithm were investigated. Four FBG sensors were used to form a sensing network to detect the acoustic emission signals. According to the signals, the quadrilateral array location equations were established. By analyzing the acoustic emission signal propagation characteristics, the solution of location equations was converted to an optimization problem. Thus, acoustic emission location can be achieved by using an improved PSO algorithm, which was realized by using the information fusion of multiple standards PSO, to solve the optimization problem. Finally, acoustic emission location system was established and verified on an aluminum alloy plate. The experimental results showed that the average location error was 0.010 m. This paper provided a reliable method for aluminum alloy structural acoustic emission location.     

一种声发射源的新型平面定位方法研究

声发射现象中产生的弹性波在传播时声压遵从指数衰减规律,文中提出一种利用声衰减特性对声发射源进行平面定位的能量定位新方法。从理论上导出了该方法的定位计算公式,并用AE21C型声发射仪在高分子合成纤维平板上以铅笔芯折断产生信号为模拟源进行了实验测量,证明这种新的源定位方法可行,并具有无须测量传声媒质的声衰减和声速等优点。