Acoustic emission activities and damage evaluation of reinforced concrete beams strengthened with CFRP sheets

In this study, the applicability of acoustic emission (AE) techniques to monitor damage evolution in reinforced concrete (RC) beams strengthened in flexure with carbon fiber reinforced polymer (CFRP) sheets is investigated. The objective is to initiate the creation of a user-friendly health monitoring system for RC structures strengthened with CFRP sheets using AE techniques. Five beams, 200 mm×300 mm in cross-section, were tested under three-point bending over a span of 1700 mm. One of the beams was tested in its virgin condition to serve as reference; the remaining four beams were tested after being strengthened with CFRP sheets bonded on the tension face. The parameters investigated in this study include both the amount of CFRP sheets and construction imperfections (the CFRP sheets were intentionally bonded without adhesive in the centermost 10% and 20% bonding area). The AE signals were collected and analyzed for all specimens. The AE parameters were analyzed for four levels of damage based on initial crack, propagation, yielding of main bars, and fracture or rip-off of the CFRP sheets. The frequency-peak magnitude distribution of the AE parameters was used to determine the b-value, defined by the Gutenberg–Richter relationship, for evaluating the damage evolution and fracture process of RC beams strengthened in flexure with CFRP sheets. From the results of this study, the signal characteristics – event, amplitude versus frequency, and amplitude versus duration – show clear differences in the different loading stages, depending upon the active damage mechanism. The b-value is correlated to the fracture process of the RC beams bonded with CFRP sheets and the degree of localization of damage. The AE technique is a useful nondestructive technique for monitoring the behavior of RC beams that are externally reinforced in flexure with CFRP sheets.     

声发射技术在热障涂层失效机理中的研究进展及展望

热障涂层（TBCs）具有优异的高温抗氧化、高温力学和抗热腐蚀性能而备受关注,广泛应用于航空发动机和燃气轮机热端部件中。热障涂层服役环境的恶劣和涂层体系结构的复杂,极易导致涂层发生界面分层或剥落失效,因此通过对热障涂层的裂纹萌生和扩展问题进行实时监测,对于失效机理研究显得尤为重要。简述光激发荧光压电光谱（PLPS）、红外热成像（IRT）、阻抗谱（IS）的原理及其在热障涂层失效行为研究中的应用,重点介绍声发射技术在热障涂层失效机理方面的研究成果。基于声发射的热障涂层失效过程的信号分析和深度处理,结合声发射技术在热障涂层中的参数分析和波形分析,对热障涂层失效过程及失效形态进行模式识别,通过损伤程度的定量评估来进行热障涂层的寿命预测。对声发射技术在热障涂层失效预测及寿命评估指明了方向,并创新性地对未来声发射技术在热障涂层的疲劳损伤方面研究趋势提出展望。     

2.25Cr-1Mo材料在拉伸过程中的声发射信号聚类分析

声发射(AE)技术能用来区分发生在受载材料内的不同损伤模式,而聚类分析能在无先验知识的情况下通过揭示数据内部结构对数据进行分类。声发射波形包含了丰富的声发射源信息,而常规的特征参数并不能满足深层次的声源识别要求。文章尝试从波形的频率分布特征、形状特征和强度特征三个方面分别选取小波变换能量特征系数、波形裕度因子和幅值作为描述声发射波形的新参数。基于波形新参数的聚类分析能有效地区分加氢反应器材料2.25Cr-1Mo带裂纹和无裂纹试件拉伸过程中屈服阶段塑性变形信号、微裂纹扩展信号和断裂失稳信号。     

蜂窝夹层复合材料的压缩损伤声发射特征

应用声发射技术对蜂窝夹层复合材料压缩损伤过程进行了试验研究。分析载荷与声发射信号关联图,依据其损伤过程和声发射特征,发现随着加载条件下载荷的增加,复合材料的损伤逐步增大。在加载初始阶段,仅有少量声发射信号,各种表征信号量小幅度增加;在加载中期,声发射信号增多,各种表征信号量不断增大;在加载后期,声发射信号有明显突增,各种表征信号量急剧增加。复合材料压缩损伤破坏与声发射的幅值、能量、撞击、上升时间、持续时间和计数等参量特征相关。根据各阶段特征参量滤波后所得信号分布与实际断裂位置相吻合。     

Fatigue-life prediction of SiC aluminum composite using a Weibull model

The feasibility of the acoustic emission technique in predicting the residual fatigue life of 6061-T6 aluminum matrix composite reinforced with 15 vol.% SiC particulates (SiC_p) is presented. Fatigue damages corresponding to 40, 60 and 80% of total fatigue life were induced at a cyclic stress amplitude. The specimens with and without fatigue damage were subjected to tensile tests. The acoustic emission activities were monitored during tensile tests. The number of cumulative AE events increased exponentially with the increase in strain during tensile tests. This exponential increase occurred when the material was in the plastic regime and was attributed mainly to SiC particulate/matrix interface decohesion. Cumulative events during post fatigue tensile tests reduced with a decrease in the residual fatigue life. Based on the high cycle fatigue damage accumulation model, a Weibull probability distribution model is developed to explain the post fatigue AE activity of specimens during tensile tests. Using the model, the residual fatigue life can be predicted by testing the specimen in tension and monitoring the AE events. In high cycle fatigue, it was observed that the residual tensile strengths of the material did not change significantly with prior cyclic loading damages since the high cycle fatigue life was dominated by the crack initiation phase.     

Comparison of Acoustic Emission Characteristics for C/SiC Composite Component Under Combination of Heating and Mechanical Loading

The acoustic emission(AE) characteristics of C/SiC composite component under various conditions were compared, with the purpose of identifying the possible damage and failure mechanism. During the process of the single mechanical loading, the highest amplitude of the AE signal was less than 85 dB and the main damage forms of matrix cracking and interface debonding were involved. For the heating process, high-energy AE signals with an amplitude more than 85 dB were detected and fiber fracture mechanism was determined as well due to the thermal stress caused by the mismatch of the thermal expansion coefficient between the reinforced fiber and matrix. During the combination process of the heating and mechanical loading, it was concluded that the degree of damage was much severer than the simple superposition of damage produced by the individual mechanical loading and the individual heating process.     

2D-C/SiC陶瓷基复合材料拉伸试验的声发射特性

对2D-C/SiC陶瓷基复合材料试样在室温条件下单调拉伸试验和循环拉伸试验的损伤声发射信号进行研究,利用无监督层次聚类分析方法对单调和循环拉伸试验的声发射信号进行损伤模式识别,得出了两种拉伸试验下试样都有相同的损伤分类。对每次单调加/卸载试验分别进行应力和声发射信号分析,得到了在循环加载区间和卸载区间试样的损伤情况。对比分析两种拉伸试验的声发射信号,得到两次试验中首次加载相同应力时,两个试样有同一种类的声发射损伤信号,从而说明循环加载对试样的主要损伤影响较小。     

Q345R疲劳损伤过程声发射信号特征分析

制冷系统压力容器应用非常广泛，对于该类在役压力容器还没有可靠的实时动态监测方法。提出采用声发射检测技术对制冷系统压力容器进行实时监测，通过对容器制造材料Q345R钢的疲劳载荷试验，采集材料损伤全过程的声发射信号进行特征参数分析、波形和频谱分析，发现材料从裂纹萌生到断裂失效过程的转折点，并对不同损伤阶段声发射信号波形和频谱的特性进行对比研究，找出各个阶段声发射信号的特征，为实现Q345R声发射动态监测和评价提供可靠依据。     

基于声发射技术的CFRP钢管混凝土受弯破坏过程

研究了CFRP钢管混凝土在弯曲荷载作用下的破坏过程及声发射变化规律。结果显示,整个破坏过程可分为弹性段、弹塑性段、下降段和软化段四个阶段,而声发射参数变化及波形特征与试件破坏过程表现出较好的对应关系。证明了利用声发射技术能有效地监测CFRP钢管混凝土弯曲过程损伤程度和破坏历程。     

Study on arall failure behaviour under tensile loading

This paper studies the failure behaviour of ARALL (Aramid Aluminum Laminate) under tensile loading by means of acoustic emission (AE), optical metallography (OM) and scanning electronic microscope (SEM), and analyzes the fracture appearance of ARALL and its fracture characteristics. The damage models of ARALL are concluded in this paper. The results show that ARALL will yield under tensile loading, and its strength will decrease as the content of resin increases. During fracture process, AE amplitude distribution curves show that there are three obvious peaks, which respectively correspond to separation of the interface between fibers and resin, local delamination damage and fracture of a small quantity of fibers, and delamination damage of large area and final fracture of a large numbers of fibers. Dynamic damage and fracture process of ARALL can be detected by AE.     

模态声发射——声发射信号处理的得力工具

模态声发射是声发射信号处理技术的得力工具。介绍它在声发射源定位、复合材料损伤源识别、疲劳裂纹萌生和扩展的声发射监测以及日历损伤声发射评价等工程实践中的应用。     

某型飞机飞行载荷疲劳试验过程中的声发射监测

介绍了某型飞机全尺寸机体飞行载荷疲劳试验过程中对关键部件(包括不可接近部件)疲劳损伤的声发射(AE)实时监测技术。在强冲击、高振动背景下,利用基于时间、空间、幅度或能量滤波等多种信号处理方式,对预处理后的AE信号以趋势分析为主,多参数分析综合验证,另辅以其它方法(包括波形分析),对一些关键部位的健康状态进行AE实时在线监测。成功预报了机翼对接区域某螺栓孔夹层裂纹的萌生,为保证机体飞行载荷疲劳试验顺利进行起到了重要作用。     

飞机主起落架疲劳试验中的声发射信号处理

详细介绍了某型飞机主起落架疲劳试验过程中,利用声发射技术实时监测主起落架梁的健康状况。在一次试验进程中,利用趋势分析、幅值分析、空间分析等方法发现主起落架梁某区域内有高幅值、高能量的异常信号存在。为进一步验证主起落梁的疲劳损伤是否存在,利用基于相关分析的趋势分析方法对声发射信号进行再处理,排除了疲劳裂纹的存在,利用Fisher线性判别法建立了正常信号与故障信号的判别模式,保障了试验的顺利进行,为以后的数据处理、疲劳损伤信号与故障信号的判别提供了参考。     

异种材料摩擦焊件的多物理信息融合临界失效监测新方法

疲劳断裂是异种材料摩擦焊零件常见的失效形式。为减少摩擦焊零件突然断裂造成的重大事故,本文从疲劳能量耗散和微观缺陷演化等角度,探讨了联合应用微红外、声发射和微电阻无损检测技术同步动态监测摩擦焊试件临界疲劳损伤的可行性。研究发现疲劳试验过程中,三种信号可同步采集,互不干扰,互相印证。进入临界断裂阶段后,对于试件的异常和正常疲劳断裂,微电阻与声发射的幅值和能量参数变化规律存在良好的映射关系,它们均可作为预警临界断裂失效的参数。虽然红外热像技术常被用于通过监测试样温度场的变化预测材料疲劳极限,但指数增长式的温度快速上升阶段在临界断裂前未必出现。与单信号监测相比,多物理信息融合健康监测预警的可信度更高,有利于提高摩擦焊零件的服役安全性和可靠性。     

Real-Time Debonding Monitoring of Composite Repaired Materials via Electrical, Acoustic, and Thermographic Methods

The electrical properties of composite materials have been thoroughly investigated recently for the detection and monitoring of damage in carbon fiber-reinforced polymers (CFRPs) under mechanical loading. Carbon nanotubes are incorporated in the polymer matrix of CFRPs for the enhancement of their electrical properties. The electrical properties have shown to be sensitive to the damage state of the material and hence their monitoring provides the profile of their structural deterioration. The aim of the paper is the cross-validation and benchmarking of an electrical potential change monitoring (EPCM) technique against acoustic emission (AE) and lock-in thermography (LT). All techniques successfully identified damage and its propagation. Thermography was more efficient in quantifying damage and describing dynamically the debond topology, as it provided full 2D imaging of the debond in real time. EPCM was successful in providing quantitative information on debond propagation and its directionality. AE provided consistent information on damage propagation. All techniques identified three stages in the fatigue life of the interrogated coupons. The representation of the fatigue behavior as a function of life fraction, the correlation of AE data with EPCM and LT data, and most importantly the consistent behavior of all tested coupons allowed for both the direct and indirect cross-correlation of all employed methodologies, which consistently identified all aforementioned fatigue life stages.     

氧化铝陶瓷疲劳损伤过程的数字描述

用非对称正弦波动态载荷变化的方式跟踪了不同粘土结合剂添加量对利用铝型材厂废渣合成的氧化铝陶瓷的疲劳损伤过程的影响,用系统分析方法定义的疲劳损伤参数作为主要评价指标,结合试样的晶相结构和显微结构分析讨论了影响氧化铝陶瓷疲劳特性的因素,确定了最佳的结合剂添加量.结果表明,影响氧化铝陶瓷疲劳寿命的主要因素为试样中玻璃相的含量,当粘土添加量为18%时,试样的裂纹萌生寿命达到最高,为22500周,此时,体系内刚玉相含量为75%,玻璃相含量为20%.     

常压储罐声发射检测技术

声发射检测技术可用于常压储罐腐蚀评价。讨论了常压储罐中声发射信号产生的机制和传播过程,试验研究了液体介质中声发射源的定位、波速的计算及声发射信号的衰减规律,提出了声发射信号的分析方法以及结果评价方法。指出由于信号传播路径的不确定,使定位分析较困难,而从每个通道单位时间的撞击数来判断更有实际意义,并给出了工程实例。     

基于磁记忆机理的焊缝疲劳累积损伤特征

通过20号钢焊接平板试件的拉-拉疲劳试验,研究了在单周期和多周期循环载荷下焊缝疲劳累积损伤的磁记忆信号特征。结果表明,由于试件内部初始状态下各处应力分布不均匀,焊缝原始磁信号表现为起伏较大;随着循环周次的增加,试件内部应力集中重新分布,信号趋于稳定;在周期累积循环试验中,磁记忆信号随着循环周次的增加出现螺旋上升的趋势,呈现出磁弹性效应变化特征;通过建立磁记忆信号与损伤度函数的模型,可根据磁记忆信号的变化准确判断裂纹扩展趋势,用于焊缝剩余寿命的预测。     

胶合板拉伸过程中的声发射特征

针对传统的力学试验方法对胶合板破坏过程的表征不足,提出了用声发射检测技术全程监测胶合板拉伸破坏过程。试验表明,材料的损伤破坏具有阶段性,不同阶段的声发射信号特征有明显的区别。研究发现声发射特征参数能够表征材料受载过程中的损伤演化规律和损伤类型,能直观地反映材料的损伤特征。因此,声发射检测技术可作为材料测试、质量评定的有效手段,也是传统力学方法的有益补充。     

疲劳损伤过程的热能耗散分析

利用能量作疲劳损伤基本参量,建立了疲劳损伤的能耗结构,在试验的基础上,围绕着疲劳损伤过程中的不可逆能耗分析,系统地研究了循环过程及循环内的疲劳损伤热能耗散变化规律,并寻找出疲劳过程中循环滞回能与有效能耗(储能)之间联系。