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《振动与冲击》2019,(21)
以碳纤维复合材料(Carbon Fiber Reinforced Plastics, CFRP)的超声背散射信号为研究对象,创新性地提出运用递归定量分析(Recursive Quantitative Analysis,RQA)方法获得其信号特征,实现对材料局部孔隙缺陷的识别及评估。首先,对含有孔隙率为0.2%~5.92%的标准试块的超声背散射信号分别进行递归图分析和递归定量分析。结果表明,不同孔隙率试块所对应的递归图特征表现出明显差异,同时,RQA的特征量参数——递归率与递归熵均随孔隙率的增大而增大。然后,运用RQA方法对某未知孔隙率试块进行局部孔隙缺陷评估,基于上述结论,识别得到该试块中最有可能含有局部孔隙缺陷的区域。最后,剖开该未知孔隙率试块作微观形貌观察实验,实验发现该试块实际孔隙缺陷区域与RQA识别得到的结果相同,从而验证了递归定量分析方法用于CFRP局部孔隙缺陷识别的有效性。 相似文献
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为研究基于超声的无损探伤方法在水利工程金属结构焊缝缺陷识别中的应用,利用常规超声检测技术、超声相控阵技术、衍射时差法(Time of Flight Diffraction, TOFD)超声检测技术对水利工程金属结构焊接试块缺陷进行识别,分析了各种缺陷在超声无损探伤技术中的特征显示。研究结果表明:常规超声检测技术、TOFD检测技术均能对各种缺陷实现信号显示,超声相控阵检测技术对气孔和横向裂纹的显示不够明显,但对其它缺陷的检出效果较为明显;常规超声检测技术对操作人员的要求较高,对缺陷的定性困难,精度不高;TOFD检测结果中气孔和横向裂纹的显示呈现出一种特殊的弧形,有一定高度的内部裂纹和未熔合的信号由上下尖端衍射波组成,根部未焊透上下尖端信号不够明显;相控阵检测结果直观,可以较精确地测量缺陷的埋藏深度、自身高度、长度等,但在扫查点状缺陷或者与超声声束平行的裂纹缺陷时,检出率极低。 相似文献
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利用超声相控阵检测系统对含有裂纹缺陷的外包菌型低压汽轮机叶轮圆盘实验试块进行检测.针对超声波脉冲反射法中缺陷方向难以确定,尺寸容易误判等问题,提出一种频谱分析方法,研究线状缺陷方向变化对于超声回波的影响.对于3种倾斜角度的裂纹缺陷回波信号,分析其功率谱并进行小波包的分解和重构,用"频率-能量"的方法提取各方向缺陷回波信号的能量特征.实验结果表明,各方向缺陷回波信号的能量特征差别明显,并绘制出声束轴线与缺陷的夹角和高频带所占能量之间关系曲线.该方法实现了缺陷方向的识别,并为后续线状缺陷的准确定量提供依据. 相似文献
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针对温度变化引起超声衍射时差技术(time of flight diffraction,TOFD)测量结果误差的现象,以含不同预置缺陷Q235A试块为测试样品,采用TOFD超声检测技术,并结合A扫结果,研究不同温度对缺陷检测结果的影响。研究发现,当试块表面温度超过40℃时,底面小缺陷的检测难度会提高,检测结果的不稳定性提升;随着试块表面温度继续升高,TOFD测量缺陷的最小分辨率会降低到3 mm,同时小缺陷波的A扫波形已经无法从背景噪声中识别。通过比较不同温度下纵波在固体介质中传播速度,发现温度升高导致纵波速度衰减,进而导致仪器分辨力的下降和实际测量误差的增大。 相似文献
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M. Khelil Jean-Hugh Thomas L. Simon R. El Guerjouma M. Boudraa 《Journal of Nondestructive Evaluation》2017,36(2):31
The aim of this study is to characterize the structural noise for a better flaw detection in heterogeneous materials (steels, weld, composites...) using ultrasonic waves. For this purpose, the continuous wavelet transform is applied to ultrasonic A-scan signals acquired using an ultrasonic non destructive testing (NDT) device. The time-scale representation provided, which highlights the temporal evolution of the spectral content of the A-scan signals, is relevant but can lead to misinterpretation. The problem is to identify if each pattern from the wavelet representation is due to the structural noise or the flaw. To solve this problem, a detection technique based on statistical significance testing in the time-scale plane is used. Information about the structural noise signals is injected into the decision process using an autoregressive model, which seems relevant according to the spectral content of the signal. The approach is tested on experimental signals, obtained by ultrasonic NDT of metallic materials (austenitic stainless steel) then on a weld in this steel and indeed enables to distinguish the components of the signal as flaw echoes, which differ from the structural noise. 相似文献
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Shanglei Li Anish Poudel Tsuchin Philip Chu 《Research in Nondestructive Evaluation》2013,24(2):90-106
This article presents the application of a signal correlation technique to automatically classify ultrasonic A-scan signals for defect and defect-free regions in isotropic and anisotropic materials. First, feature extraction was implemented by generating a reference A-scan signal of a defect-free area using an autocorrelation function and statistics. Then, a cross-correlation function, utilized as a feature detector, was applied to the reference signal and a signal of interest (SOI) to detect defect-free features in an SOI. The correlation result was considered as a pattern containing both defect and defect-free features. Next, the pattern was classified by measuring the similarity between features of the reference signal and an SOI based on their Euclidean distance. Each A-scan signal classification result was then plotted on a 2D map based on its position on the specimen. The present work uses multiple correlation functions and statistics to classify defect signals rather than relying on an inspector’s prior knowledge to interpret C-scan data, and has particular value in automated ultrasonic signal classification and characterization. 相似文献
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设计了一种全波形采集超声自动检测系统,实现了A,B,C 3种扫描方式且具有记录被检材料上所有检测点超声A扫描波形的功能,支持材料超声检测、评价技术研究.该系统由高速A/D卡、超声检测仪、自动扫描器、运动控制系统和CSCAN软件等组成,作为核心部件的高速A/D卡选用PCI-9820型,负责从超声检测仪采集A扫描波形信号.自动扫描过程中,A/D卡与超声检测仪、运动控制系统之间通过硬件信号实现同步,使A扫描波形数据的采集与被检材料上声传播的渡越时间、预定测量点位置相对应,采集得到的A扫描波形数据通过A/D卡的板载SDRAM及DMA功能异步传输至计算机内存,并由CSCAN软件进一步实现数据压缩、滤波、存储以及不同方式成像等处理.测试结果证明,该系统运行速度快,成像精度高且性能稳定. 更多还原 相似文献
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Kerbrat E. Prada C. Cassereau D. Fink M. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(8):1103-1113
In ultrasonic nondestructive testing, the iterative time-reversal process is an adaptive technique that can be used to detect flaws in complex samples with a large array of transducers. The decomposition of the time-reversal operator (DORT) method is a detection technique that is derived from the mathematical analysis of the iterative time-reversal process. Contrary to time-reversal techniques, the DORT method does not require programmable generators, and it allows the simultaneous detection and separation of several defects. In this paper, the method is applied to a Ti6-4 titanium cylindrical sample to separate the echo of a defect from the speckle due to microstructure contribution. The grain structure of this titanium alloy makes detection very difficult and, for large depths, conventional techniques do not allow the detection of small flaws with a satisfactory signal-to-noise ratio. The efficiency of the DORT method to detect a flat bottom hole with a diameter of 0.4 mm located at a depth of 140 mm in a titanium alloy sample is shown. 相似文献
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为厘清碳纤维增强树脂基复合材料(Carbon fiber reinforced plastics,CFRP)复杂几何构件相控阵超声检测中声传播规律,围绕CFRP材料R区开展了弹性特性表征、有限元建模、声场计算及实验验证工作。基于超声液浸背反射法和模拟退火算法求解了CFRP单向板刚度矩阵反问题,并借助Bond变换实现了R区弹性特性的定量描述。结合微观组织分析等获取材料、几何特征,建立了虑及曲面形状、叠层、弹性各向异性的R区相控阵超声检测有限元模型,计算了R区相控阵超声检测A、B扫描信号,发现存在结构噪声和缺陷伪像。在此基础上研究CFRP材料R区瞬态声场并与CFRP平板、弹性各向同性R区和0°单向板R区情况对比,阐明了结构噪声和缺陷伪像的形成机制:弹性各向异性叠层结构导致倾斜入射的超声波发生反射和折射,与沿肋板传播的快速波混叠在R区形成结构噪声,同时多向板R区两侧肋板反射导致缺陷伪像,即材料弹性各向异性与构件曲面叠层结构耦合共同影响缺陷的精准辨识。 相似文献
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目的 利用水浸聚焦超声C扫描对2524铝合金回填式搅拌摩擦点焊(RFSSW)接头进行检测并完成缺陷识别。方法 以A扫描时域信号为对象,绘制能量谱与金相作对照,确定焊合区;分析未焊合、聚集型孔洞及弥散型孔洞的时域和频域波形特征,并对频域信号进行小波分析,提取特征量。结果 缺陷区反射回波的归一化能量不低于0.02;不同形式的缺陷(聚集型孔洞、弥散型孔洞、弱连接)其频谱形状特征不同,具有不同的峰值个数。结论 通过金相验证,表明超声波C扫描对接头缺陷可进行有效的检测和区分。 相似文献
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无损检测是保证焊接构件生产质量及保障其使用安全性的重要技术环节。在众多的无损检测方法中,应用最为广泛的是基于声学的无损检测方法。主要阐述了超声C扫描、超声TOFD、超声相控阵、声发射及其他相关声学技术的技术特点、在国内焊接领域上的工程应用及科学研究。在此基础上,结合实验室的研究经历,简要分析了相关研究方法存在的问题,并指出了技术优势及亟待解决的问题。进而论述了超声C扫描图像识别困难、边界模糊及缺陷面积难以计算、克服检测盲区可拓展超声TOFD法的应用范围,以及排除干扰信号对声发射尤为重要的研究现状。最后展望了基于声学无损检测的未来发展趋势。 相似文献
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Jennifer E. Michaels Thomas E. Michaels Bao Mi 《Journal of Nondestructive Evaluation》2006,25(1):2-15
Ultrasonic testing is generally recognized as being the preferred nondestructive evaluation (NDE) method for measuring the size of cracks in metals, particularly when access is restricted. Using ultrasonic methods for structural health monitoring imposes the requirement of fixed transducers, which limits the articulation of transducers that is common for NDE. Here we consider the specific problem of in situ sizing of fatigue cracks emanating from fastener holes in aluminum structural components. A dual angle beam through transmission technique is employed whereby the regions of expected crack initiation are interrogated with vertically polarized shear waves. Fatigue cracks partially block the leaky creeping wave spiralling around the hole, and thus reduce the energy of the received signal. The reduction in received energy is directly related to the extent and shape of any open cracks, and this energy is modulated by the applied load as the cracks open and close. The ratio of energy received from the specimen under load to that received under no load is monitored, and this ratio is empirically related to the total crack area. A model is developed to explain this relationship for known crack shapes by assuming an ultrasonic energy profile in the plane of the crack. Data calculated from the model show very good agreement with the experimental results. 相似文献