异形构件的超声检测方法研究

由于异型构件上端直径小、壁薄、内壁存在内棱角等,给超声检测带来很大的闲难,且内棱波严重干扰了超声回波信号的识别.提出使用超声爬波检测异型构件的方法,在此基础上采用提取回波信号的时间与幅度双特征量的信号处理方法进行缺陷识别.测试结果表明:该检测与信号处理方法可满足在线检测技术的实时性、准确性和可靠性等要求,具有广泛的应用前景.     

凝汽器管板区传热管的涡流MRPC探头检测

为了解决凝汽器传热管在管板区的涡流Bobbin探头检测存在的检测盲区,文章提出了采用MRPC探头检测这一区域的方法。通过试验研究,区分了不同类型缺陷信号并归纳了不同类型缺陷的信号特征。通过建立伤深-相位曲线,实现了对于不同类型人工缺陷的缺陷深度测量。为了检验该方法的有效性,采用该方法检测了模拟管板传热管中不同位置的人工缺陷,取得了良好的检出效果,深度测量值与实际值接近。     

涡流X-probe探头的试验及应用

探头是阵列涡流检测的关键部件,介绍了一种新型的内穿过式涡流阵列探头——X-probe。分析了X-probe探头的工作原理,并通过试验研究,归纳了X-probe探头检测的不同类型缺陷信号特征、支撑下缺陷响应以及伤深与相位的关系。并介绍了X-probe探头在核电厂凝汽器传热管涡流检查的应用情况。试验结果表明,X-probe探头能够获取缺陷轮廓并依据AF和CF通道的幅值分辨出缺陷方向。现场应用证实X-probe探头具有良好的管板区缺陷检出能力,能很好地检测分辨并测量周向复合缺陷的伤深。     

基于超声检测的镁合金棒材缺陷识别及定位

针对镁合金棒材的近中心缺陷和近表面缺陷,分别采用探头垂直入射或偏心入射的超声检测方式,然后运用滤波去噪等信号处理方法对原始信号及特征回波信号进行特征提取,寻找特征信号规则,进而判定缺陷类型,如孔状缺陷、裂纹状缺陷等。利用小波变换原理增强原始信号,使B扫描成像图清晰易辨别,最终根据棒材和B扫描图比例关系,计算出缺陷位置。为合金类构件的缺陷检测提供了一种有效的简单快捷的检测手段。     

天燃气小径管对接焊缝超声波探伤

论述了影响小径管对接焊缝超声探伤的因素；对探头前沿值选取引入计算不等式；采用区域段定位判伤法以提高缺陷检测能力和分析缺陷性质。     

梅花形内孔构件超声检测系统

针对梅花形内孔构件的复杂结构特征,采用爬波和纵波相结合的方法,通过多探头融合模式,研制了梅花形内孔构件超声自动在线检测系统,较好地完成了梅花形内孔构件缺陷的定性、定量检测。通过对人工平底孔(直径0.8 mm,深度3 mm)和台阶处自然裂纹缺陷的检测结果可以看出,轴向、垂直和周向探头分别对自然裂纹及人工孔检测效果良好,达到了系统设计的要求。     

复合材料层状薄板超声特征扫描成像检测

传统超声B扫描和C扫描成像方法不能满足复合材料的检测需求。简要介绍了超声特征扫描(F扫描)成像方法的原理、扫描系统的设计和聚焦探头的制作等。F扫描是以波形上升时间、下降时间、脉冲周期和频谱特性等波形特征或缺陷类型、形状和大小等缺陷特征为特征量进行信号提取和重构并最终成像的方法。试验样件为2 mm厚的复合层状薄板,在板中距上表面0.6和1.4 mm处的两层结合层中分别制作了三个最小直径为1.2 mm的分层缺陷。试验表明,设计的超声特征扫描系统可采用幅度成像、深度成像和底波成像方法成功检测出预制缺陷,并且可实现层析成像功能,还可用于层状薄板的密度和硬质合金的厚度成像,具有强大的功能和多种材料分析用途。     

漏磁检测探头的选择及其检测信号特性

给出了漏磁检测探头和标准缺陷的分类.详细分析了点式、线式检测探头对点状、线状和体状标准缺陷检测时的信号特征和优缺点,最后提出了漏磁检测探头设计原则,即缺陷的深度检测采用点式检测探头、缺陷的截面积缺失检测选择线式探头、缺陷的长度检测用点检探头阵或点线组合式探头、斜向裂纹仅能采用点检探头阵检测.     

浅薄缺陷的脉冲漏磁信号特征量提取

为提高脉冲漏磁对浅薄缺陷的检测能力,提出了一种处理检测信号的二次差分方法,分离出在涡流效应的阻尼作用下产生的脉冲漏磁信号中的涡流分量,即二次差分信号。从二次差分信号中提取出了浅薄缺陷深度的新特征量——峰值时间Pt,并验证了二次差分方法的可行性。试验结果表明,和信号幅值大小相比,将Pt作为浅薄缺陷特征量,在检测浅薄缺陷时对缺陷深度的分辨率较高,同时能够克服检测探头提离所引起的缺陷特征量分辨率严重下降的问题。     

利用超声横波上扩散角检测瓷绝缘柱表面缺陷

利用超声横波在瓷绝缘柱中折射角为75°~84°的上扩散角检测瓷绝缘柱表面缺陷,克服了常规用爬波探头灵敏度低的弊端;对超声波探头角度、尺寸、接线柱位置以及瓷绝缘柱试块进行了相应设计,为瓷绝缘柱的检测提供了检测方法和判伤依据。     

改进的希尔伯特-黄变换(HHT)在多模式Lamb波检测中的应用

Lamb波的主要特点在于它的多模式和频散,在任一给定的激发频率下,至少存在两种Lamb波模式。各模式的频散特性使Lamb波检测变得非常复杂,所以,Lamb波检测的关键在于缺陷信号特征参数的提取和精确的信号解释。首先采用HHT直接对多模式Lamb波检测信号进行了分析,通过分析,得出了直接对多模式Lamb波信号进行EMD分解来得到信号的瞬时频率和瞬时幅值的方法是不适合的结论。采用改进后的HHT方法进行分析,有效消除了噪声干扰和各模式Lamb波的相互干扰,得到的信号时频集聚性较好,有利于特征参数的提取和进一步分析。针对不同大小和深度的孔型人工缺陷的检测试验,分别提取了信号瞬时幅值的峰值和瞬时频率的均值作为检测信号的特征参数进行线性回归分析,发现采用瞬时幅值的峰值作为孔型缺陷检测的特征参数比采用瞬时频率的均值这一参数要好。同时提出可采用瞬时幅值的峰值回归直线的斜率K来标定特征参数对缺陷孔径变化的敏感性,从而可对未知缺陷的大小进行预判。     

基于超声TOFD法直通波幅度分布的近表面缺陷检测

针对超声衍射时差法（TOFD）的近表面检测盲区问题,提出一种基于直通波幅度分布分析的近表面缺陷检测方法。在近表面缺陷检测信号的直通波部分选取多个关键点,揭示了各关键点幅度分布与近表面缺陷深度的关系,获得了用于近表面缺陷检测的幅度分布特征值。试验结果表明,该方法能准确检测出埋深1．0mm的人工缺陷,有效地提高了对近表面缺陷的识别能力。     

Reliability assessment of manual ultrasonic time of flight diffraction (TOFD) inspection for complex geometry components

Experimental probability of detection (POD) and probability of sizing (POS) curves are developed for the detection and sizing of surface-breaking cracks in components having complex geometry. A manual ultrasonic time of flight diffraction (TOFD) inspection system has been used to develop these POD and POS curves. Initially, it was assumed and subsequently verified that signal responses have a normal distribution. The effects of probe angle and probe center-to-center spacing on both POD and POS were observed. Unlike the PODs previously reported for conventional ultrasonic amplitude based flaw sizing techniques, the PODs associated with TOFD in the range of defect sizes considered here, exhibit a decreasing trend for a fixed set of experimental parameters. It is important to emphasize that the curves obtained in this work are specific to the geometry, specimen dimensions, set of notches and the specific probes used in the experiment. However, when using a manual TOFD inspection system, these curves can be useful for planning the risk-based inspection of components having complex geometry (such as a steam turbine rotor shaft).     

基于超声杂波抑制的缺陷检测

超声TOFD(time of flight diffraction,衍射时差)法检测的D扫描图像中,作为背景杂波的侧向波与近表面缺陷波会发生混叠,致使近表面缺陷不易于检测. 针对这一问题,提出一种基于杂波抑制的缺陷检测方法. 该方法通过图像能量分布统计,确定背景杂波分量并予以去除,从而分离出与其混叠的缺陷信号,实现近表面缺陷的检测. 建立了的超声TOFD法检测信号的数学模型,阐明了基于图像能量分布的杂波抑制原理. 制作了人工缺陷试块及实际焊缝试块,并对其检测获取的图像进行了杂波抑制处理. 结果表明,提出的方法可有效去除图像中的非缺陷目标、提取近表面缺陷波,从而提高系统的有效检测范围.     

基于横波多次反射法的弹簧扁钢缺陷定位方法及扫查方式研究

为提高弹簧扁钢的无损检测速率,分析多次反射波在传播过程中各次跨距的差异及反射波幅度随传播距离的变化,以及检测探头扫描步进对缺陷多次反射波信号的影响,提出基于横波多次反射的缺陷定位、定量方法及适用于高效检测的探头扫查方式,为在线检测弹簧扁钢提供技术基础。结果表明:基于横波多次反射波可准确评价缺陷位置和当量,采用5P8×12K1横波斜探头检测厚度为13 mm的弹簧扁钢,可检测距离探头入射点311 mm、直径1 mm、长10 mm的横孔,横孔距探头入射点水平距离及深度的定位误差均小于3 mm;依据不同直径横孔的反射特征提出缺陷定量方法。基于横波多次反射法结合所提出的扫查方式,可高效、可靠地全面检测弹簧扁钢。     

NDT flaw mapping of steel surfaces by continuous magnetic Barkhausen noise: Volumetric flaw detection case

This paper reports the use of a non-destructive, continuous magnetic Barkhausen noise (CMBN) technique to investigate the size and thickness of volumetric defects, in a 1070 steel. The magnetic behavior of the used probe was analyzed by numerical simulation, using the finite element method (FEM). Results indicated that the presence of a ferrite coil core in the probe favors MBN emissions. The samples were scanned with different speeds and probe configurations to determine the effect of the flaw on the CMBN signal amplitude. A moving smooth window, based on a second-order statistical moment, was used for analyzing the time signal. The results show the technique's good repeatability, and high capacity for detection of this type of defect.     

基于多探头源数据融合的焊缝缺陷识别

当今的无损检测领域中,缺陷性质的识别是检测的难点,为此研究了一种基于多探头源数据融合的焊缝缺陷识别新方法.该方法通过对多探头信息的融合,提高了检测结果的可靠性及缺陷识别的准确性.选用两个不同入射角度的斜探头对含有气孔、夹渣、裂纹、未焊透和未熔合五类典型焊接缺陷的焊件分别进行了检测,提取缺陷的超声回波信号特征,构建基于特征层和决策层两级融合的多探头源缺陷智能识别分类器,实现五类焊缝缺陷的多源数据融合识别.在特征融合层采用了BP神经网络作为特征融合器,并利用其融合输出构建每个探头源的基本概率分布函数及其对每类缺陷的基本概率赋值.在决策融合层利用D-S证据理论,合并每个探头源的基本概率分布函数,实现缺陷的融合智能识别.结果表明,该方法融合了多探头源的互补信息,有效的提高了缺陷的识别率,有助于焊缝质量的评定.     

Experimental and analytical study for detectability of the back-side flaws of flat ferromagnetic plates by RFECT

In the present study, two types of ferrite core probes were prepared with different pick-up coil positions for remote field eddy current testing. One probe has a pick-up coil on the beam of the U-type ferrite core, and the other probe has a pick-up coil on the pole of the U-type ferrite core. The two types of probes were examined for their capability to create an effective remote field to detect a back-side defect. The results showed that the pick-up coil at the pole of the U-type ferrite core can detect an effective remote field phenomenon. In addition a time harmonic analysis was carried out, and the flow of the magnetic flux of the direct field was used to analyze the difference in the results with the two probes.The detectability for back-side flaws was confirmed with the proposed probes. Compared to a previous study, the signal measured from back-side flaws with the type II probe was large. However, the signal-to-noise (SN) ratio for the detection of back-side flaws did not improve because of the different background signal before and after the back-side flaw.     

Comparison of Lamb waves and pulse echo in detection of near-surface defects in laminate plates

One of the problems faced in ultrasonic nondestructive testing (NDT) of composite laminates is near-surface delaminations which may be due to impact damage. The normal incidence pulse echo technique has difficulty in resolving echoes from this type of defect since they often lie within the length of the transmitted ultrasonic pulse. Although a high frequency probe may be used, it has its limitations and could be problematic in composite materials in which ply reflections may interfere with defect reflections. The use of an acoustic delay, together with a high frequency probe, may improve the detection. In this paper, a different approach has been developed using the fundamental Lamb wave (S₀ mode) to detect delaminations in unidirectional fibre composite materials. It has been found that the Lamb wave amplitude decreases significantly over a delamination region. The decrease in amplitude is strongly dependent upon the depth of the delamination and is most sensitive to the delaminations near to the surface of the laminate. By scanning the transducer over the surface, it is possible to measure the size and depth of this kind of delamination. This technique is comparable to the delayed pulse echo technique and can be used to complement other techniques.     

搅拌摩擦焊焊缝缺陷的超声相控阵检测技术

采用超声相控阵技术对不同厚度铝合金搅拌摩擦焊焊缝的缺陷进行了探测,通过改变相控阵的扫描角度、聚焦深度、焦点尺寸等参数对焊缝内部缺陷进行了准确定量和图像再现,并对缺陷信号标记部位进行了解剖、观察了缺陷的宏观形貌.结果表明,探头检测灵敏度高,易于快速分辨焊缝内部缺陷,结合不同的扫查方式直观给出缺陷三向视图,可准确定位缺陷的位置、尺寸、分布;缺陷形状直接影响回波的形状和峰值,小孔洞为单一尖锐波峰,峰值高大;包铝层和疏松由多簇波峰构成,S显示疏松亮点比包铝层密集且分布面较大.