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.     

一种立方体监测网络的声发射源和微震源解析定位方法(英文)

通过选取合理的坐标原点及传感器位置简化声发射源定位方程, 得到声发射源或微震源三维定位方法的解析解。算例研究表明,对于传感器阵列内、外的声发射源事件, 解析方法定位结果完全与实际坐标一致;对于传感器阵列内的声发射源事件,传统方法略有误差,一般为 0.010.03m, 而对于传感器阵列外的微震源, 传统时差定位方法的定位误差很大,最大的达到 1080986 m;采用横截面为 100mm×98mm、长度为350mm 的花岗岩试样, 进行 5 次断铅定位实验,分别用传统方法和解析方法进行定位,结果发现在监测网络外的4个声发射事件, 解析定位的误差亦小于传统方法的定位误差。可见解析定位精度较传统方法有明显提高,最高可提高 17.61mm;利用解析解定位, 无需确定拟合初值和拟合迭代算法, 仅通过简单的四则运算即可定位,用常规的计算器或Microsoft Excel 即可求解。     

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。     

Study of the performance of TBC under thermal cycling conditions using an acoustic emission rig

An experimental rig based on the use of infrared quartz lamps has been developed to monitor the degradation mechanisms causing failure of thermal barrier coatings (TBC) under thermal-cycling conditions. An acoustic emission (AE) technique monitored these degradation mechanisms, and advanced signals processing identified the key parameters that classify the AE signals according to the long-term behavior of the TBC. The AE technique enabled the localization of degradation sources inside the TBC with a linear resolution of ∼5 mm by the use of two transducers fixed at both ends of the sample. Furthermore, sample zones of high AE activity showed typical vertical cracks at the surface and delaminations at the interface between the ceramic and the bond-coat layer. Vertical cracks were induced preferentially during the heating period of the thermal cycles when the ceramic coating was in a tensile-stress state, while delaminations were induced during the cooling period when the TBC was in a compressive-stress state.     

小波变换用于声发射波波达时间的研究

基于模态声发射和互相关技术,利用小波变换的方法,计算声发射波达时间,进而进行声发射源定位,提高了定位精度。     

Thermal Stress Cleaving of Brittle Materials by Laser Beam

Thermal stress cleaving is a prospective technique for separating a wafer or thin plate from brittle materials such as glasses and ceramics. In this paper, the cleaving mechanism of a silicon wafer irradiated with Nd: YAG laser is investigated. A pulsed laser is used for the purpose of investigating the mechanism of crack propagation more precisely. The temperature at the area irradiated with the laser is measured using a two-color pyrometer with an optical fiber. The AE signal is also measured to examine the mechanism of the crack propagation. The AE signal makes it possible to monitor the crack behaviour. During one pulse of the laser, crack propagation begins some milliseconds after laser heating and ceases at about the end of irradiation. The temperature at the area irradiated with the laser is an important factor in the control of the propagation of the crack to achieve high cleaving accuracy and low thermal damage.     

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。     

Acoustic emission measurements during the electrodeposition of chromium layers on steel

The formation of cracks in chromium layers during the electrodeposition process of chromium on steel specimens was studied by means of acoustic emission (AE). It was possible to detect the AE signals associated with the cracking of the chromium layer and to eliminate the weaker signals due mainly to the evolution of hydrogen. A good correlation was found between the AE response and the crack pattern observed in optical micrographs of cross-sections of the chromium layers obtained in various stages of the deposition process. The occurrence of an AE response was characterized by an incubation time. The AE signals obtained after this initial period were found to show a periodicity for certain combinations of temperature and current density.     

消除某发动机壳体旋压裂纹的工艺改进

薄壁、长形发动机壳体是弹箭类的关键零件,使用材料为D6AE高强度合金钢,对旋前毛坯进行球化退火处理,在强力旋压成形过程中筒体出现批量周向裂纹,裂纹呈鱼鳞状,由内腔沿壁厚向外表面延展而且裂纹位置集中.为解决该问题,基于强力旋压成形机理、成形工艺、热处理工艺等理论,对裂纹形貌、产生位置及旋压受力状态进行分析,获得了裂纹产生...     

飞机蜂窝复合材料板压缩过程的声发射定位研究

声发射检测的主要目的是发现声发射源和有关源的信息,声发射源定位是声发射检测中至关重要的指标,其准确程度反映了声源的检测位置与实际缺陷源位置的符合程度。本研究针对复合材料的特性,结合实际情况进行了声速和衰减测量实验,并通过断铅实验对复合板进行声发射定位。通过对复合材料板压缩实验的在线监测,基于声发射信号参数的提取及关联图分析,给出了各损伤阶段的参数特征,以及声发射监测区域内的裂纹萌生扩展断裂的时间和位置。研究结果表明,复合板实际断裂位置与声发射监测得出的位置相吻合。     

手工焊接过程声发射实时监测可行性研究

利用俄制MAES声发射系统对手工焊接过程进行实时监测,对焊接过程的不同时段采集到的声发射信号特征进行分析,以寻找出现裂纹时的声发射信号的特点,从而确定声发射实时监测手工焊接过程的可行性。     

声发射源特性的神经网络模式识别研究

提出一种对声发射源活动情况进行模式识别的方法。该方法以裂纹的形成、扩展和断裂三个阶段为声发射源,通过对声发射的参数进行采样和分析,利用不同类型的人工神经网络进行模式识别,以判断理解纹的危害程度。该方法也可用于区别噪声、泄漏、裂纹等不同声发射源的声发射信号,以判断缺陷的类别。     

裂纹参数变化对叶片低阶弯曲振动特性的影响

目的研究叶盘叶片进气及出气边萌生的横向贯穿型裂纹的分布位置及深度变化对叶片一阶弯曲振动特性的影响。方法根据叶片尺寸及工况建模,得到正常叶片在静止及不同旋转速度下的一阶振动频率,并进行拟合。在正常叶片模型的基础上,通过布尔运算建立裂纹模型,研究横向贯穿型裂纹在不同分布位置及不同深度下对一阶弯曲振动频率的影响,并进行拟合。针对裂纹深度变化采集的定时信号通过DFT变换,得到正常及含有不同深度裂纹叶片的一阶频率,对建模结论进行验证。结果一阶弯曲振动频率先减小后增大,在距离叶根4.23 mm时为最小值801.16 Hz;当裂纹距叶根的距离大于35 mm时,振动频率先接近后大于正常叶片,振幅先接近后小于正常叶片,最终将35 mm设定为位置的阈值;裂纹深度的增加使振动频率单调减小,且速率不断增大。采集的信号经DFT变换得到的一阶弯曲振动频率与建模结果的误差分别为1.9%,2.0%,1.5%,0.6%。结论当叶片进气或出气边位置阈值内出现裂纹萌生及扩展时,一阶弯曲振动频率会小于正常值,此时叶片的一阶弯曲共振区域会增大,需要对旋转机械进行严格的工况监测,同时裂纹深度的增加可提高叶尖定时监测的准确性。     

Study on source location using an acoustic emission system for various corrosion types

In this paper, four main types of corrosion: uniform, pitting, crevice and stress corrosion cracking (SCC) found in the petrochemical industry, were characterized and identified by Acoustic Emission (AE) analysis using their locations and extracted AE parameters. A novel low-cost AE location system based on a Field Programmable Gate Array PC (FPGA-PC) and a LOCAN 320 AE analyzer were utilized in this study. Specimens used in experiments were austenitic stainless-steel SS304. The pattern of AE signals from each type of corrosion was plotted using their location and correlation. Experimental results show the ability of our FPGA-PC system to determine corrosion locations. The correlations of AE parameters including amplitude, counts, hits and time were used to identify different types of corrosion. In addition, the characteristics of the corrosion process for each type are explained using the AE signals obtained corresponding to the source locations, together with experimental observation.     

机械结构在役缺陷危害性的声发射定量评价方法

水力发电厂起重机械是用于起吊转子和闸门等大型零部件的关键特种设备,主要支撑部分为金属结构,一般为非标准设计,结构庞大,利用超声或射线等常规无损检测技术很难对它们进行全面有效的定期检测。探讨了利用声发射技术对其进行检测的可行性,通过对带裂纹缺陷的金属结构加载试验,采集活性缺陷发生发展的声发射信号。应用统计参数方法分析,提出评价裂纹缺陷的活度和强度的定量指标,进而定量评定出在役裂纹缺陷的危险性,为重大机械的定检和安全评价提供理论指导和试验数据。     

The cracking behavior of anodic films on cast aluminum alloy after heating in the temperature range up to 300 °C

The cracking behavior of sealed anodic films on cast aluminum alloy after heating in the temperature range up to 300 °C was studied and the effects of anodizing temperature, heating temperature and heating rate on cracking behavior were investigated. The results showed that before heating some micro-cracks were present in sealed anodic films on the aluminum alloy tested. After heating between 100 °C and 300 °C, the initial micro-cracks became wider and deeper, and new cracks also may be initiated in the film. As anodizing temperature increased, both the crack density and the crack width increased after heating, which was attributed to increase of the porosity of the anodic films formed at higher temperatures. At higher heating temperature, the cracks obviously got wider, but the crack density remained almost unchanged. Increased heating rate resulted in more cracks in the anodic film, indicating that higher strain rate may promote initiation of the micro-cracks, while cooling rate had little influence on cracking behavior.     

Failure Behavior of Plasma-Sprayed Yttria-Stabilized Zirconia Thermal Barrier Coatings Under Three-Point Bending Test via Acoustic Emission Technique

In this paper, the failure behavior of plasma-sprayed yttria-stabilized zirconia thermal barrier coatings fabricated by atmospheric plasma spraying (APS-TBCs) under three-point bending (3PB) test has been characterized via acoustic emission (AE) technique. Linear positioning method has been adopted to monitor dynamic failure process of the APS-TBCs under 3PB test. The investigation results indicate that the variation of AE parameters (AE event counts, amplitudes and AE energy) corresponds well with the change of stress–strain curve of the loading processes. The failure mechanism was analyzed based on the characteristics of AE parameters. The distribution of frequency of crack propagation has been obtained. The AE signals came from two aspects: i.e., plastic deformation of substrates, initiation and propagation of the cracks in the coatings. The AE analysis combined with cross-sectional observation has indicated that many critical cracks initiate at the surface of the top-coat. And some main cracks tend to propagate toward the substrate/bond-coat interface. The actual failure mechanism of the APS-TBCs under 3PB test is attributed to the debonding of metallic coating from the substrates and the propagation of the horizontal crack along the substrate/bond-coat interface under the action of flexural moment.     

岩石力学试验中的声发射源定位技术

在岩石力学实验中，声发射源定位的研究方法，是实验室声发射研究的重要方面。在总结前人关于声发射源定位在实验硬件和定位算法两方面工作的基础上，从定位算法上着重分析了当前几种地震模拟岩石力学实验室声发射定位方法的利弊，指出了未来声发射定位方法可能的发展方向，并从定位算法上阐述了提高AE定位精度所必须克服的障碍。     

Non-destructive evaluation of plasma sprayed functionally graded thermal barrier coatings

Acoustic emission (AE) as a non-destructive evaluation technique has recently been used in a number of studies to investigate the performance and failure behavior of plasma sprayed thermal barrier coatings. The mechanism of coating failure is complex, especially when considering the composite nature of the coating. In the present paper, the thermal shock tests with in situ acoustic emission are used to study the cracking behavior of plasma sprayed functionally graded thermal barrier coatings. Each thermal cycle consists of 8 min heating in the furnace at 1000°C and 8 min cooling from 1000°C to the room temperature by a compressed air jet. The AE signals are recorded during the quench stage. Three, four and five layer functionally graded coatings have been tested. The results show that the five layer functionally graded coatings appear to have the best thermal shock resistance in the specimens tested, because of the gradual changes in material properties. Higher AE energy counts and cumulative counts recorded by the tests are associated with the macro-crack initiation and growth. On the other hand, micro cracking and phase transformation only give rise to lower AE signals.     

AE monitoring and data analysis for large spherical tanks

The successful assessment of structural integrity by means of AE depends on the quality of the recorded AE data and on correct post-test data analysis. AE monitoring and signal analysis of tests on two large, spherical tanks were carried out using a 32-channel AE system (Spartan, from PAC, USA). Water pressurization was used on one, whilst the other was tested on-line. The effects of both the residual and loading stresses on the surface-opening cracks produced by multiple welding passes were assessed by means of AE. AE measurements generally take a rather long time and background noise cannot always be restricted during the test period (a major problem with on-line testing). It is possible to improve the detection of AE in the field by varying the pressure of the operating medium by 10% P (P = operating pressure of tank). The relationship between the source (a crack growing with load changes) and its associated AE parameters is also discussed.