超声导波在钢管中的传播特性

根据有限元理论,通过建立钢管的3D模型,模拟超声纵向导波L（0,2）在钢管中的传播模态。在弹性动力学的基础上,分析得出了超声导波在钢管中传播时存在着多模态和频散特性。根据钢管的频散曲线选取了激励L（0,2）模态的高频信号的频率,利用有限元软件ANSYS／LS--DYNA进行仿真。根据仿真结果中回波信号时间计算得出的波速结果与频散曲线的值相符;通过查看两个节点的位移时间历程曲线图,验证了导波在传播过程中存在的衰减和多模态现象。     

磁致伸缩导波在钢管中传播的研究

介绍了导波在无限长钢管中传播的频散现象和多模式特点，研制了用于磁致伸缩导波检测的实验系统。通过正确的电磁屏蔽措施和合适的信号处理方法，改善了系统的信噪比，在钢管上进行了低阶纵向模态波传播实验，观察和分析了频散现象。用实验结果验证了理论计算。     

L（0,2）模态导波检测充水管道的试验研究

从理论上分析了充水管道中纵向模态导波的频散方程,研究了L（0,2）模态在常用输气和输油直径101.6mm、壁厚6mm未充水和充水钢管中的频散特性。结果表明,不同于未充水管道,充水钢管中所有纵向模态都存在模态耦合现象,具有模态分支和群速度低的传播特性。未充水和充水管道的对比试验表明L（0,2）模态导波适合检测充水管道中非轴对称支撑特征信号。     

不锈钢管材中弯曲模态导波试验

使用单探头激励法在管壁中激励弯曲模态的导波,以频散曲线为切入点,研究了弯曲模态导波在不锈钢管材中的传播规律以及对缺陷检测的可行性。根据频散曲线选定F(n,3)及L(0,2)模态,进而确定激励频率和入射角。得到弯曲模态导波可对φ1 mm(含φ1 mm)的通孔进行有效检测的结论。     

扭转模态超声导波在弯管中的检测试验

超声导波在弯管中的传播较在直管中人传播更为复杂,而在实际工程现场,弯管弯头部位的检测尤为重要。利用磁致伸缩超声导波激励出扭转模态T(0,1),研究了超声导波在弯管中典型部位的缺陷检测问题及不同检测频率对弯管缺陷识别的影响。试验结果表明:检测频率低会导致超声导波反射信号在拱背外侧缺陷和弯头焊缝处发生频散而难以分离;检测频率高,得到的弯头拱背内侧缺陷与拱背外侧缺陷的信号幅值都很小。因此选择合适的检测频率,才能更好地对弯头缺陷进行有效识别。T(0,1)模态导波经过弯头时,能量会在拱背外侧产生聚焦,在拱背内侧出现发散,拱背外侧缺陷比拱背内侧缺陷更容易检出;信号经过弯头后,能量衰减严重,衰减后的能量约为原来的一半。     

一种基于导波技术检测锚杆长度及缺陷的新方法

分析了自由钢杆与置于土壤中钢杆的频散曲线,并利用所建立的试验系统,采用导波技术,对上述两种锚杆的长度进行了检测。结果表明,频散曲线可以作为导波检测的理论指导,利用频散曲线选择合适的频率范围,通过激励纵向轴对称L(0,1)模态的导波可有效地检测锚杆长度;与置于空气中锚杆相比,置于土壤中锚杆的端面回波的信号幅度有所衰减,并且利用L(0,1)模态实现了对埋于土壤中锚杆缺陷的检测。     

管道超声导波模态的频散分析

超声导波检测是一种高效的管道无损检测新技术,导波模态和频率是其研究的关键技术。通过改变钢管的内径和壁厚,分析得到了内径、壁厚对导波频散区域和模态数量的不同影响。根据L(0,2)模式和F(0,3)模式在空管中的传播特性,分析了超声导波单探头检测可能存在的漏检区域。     

基于检测信号的导波频散曲线获取方法

频散曲线是导波检测的重要依据,现有方法通过数值计算获得特定波导的频散曲线,然而目前有非常多的波导构件,由于结构的复杂性无法计算其频散曲线。研究了通过导波检测信号实现频散曲线获取的方法。基于检测信号的时频分析结果,利用信号的能量最大值实现频散曲线的手动和自动获取。利用上述方法对钢棒、钢管等规则构件的检测信号实现特定模态频散曲线的获取,结果与数值求解的理论频散曲线符合得很好,验证了该方法的正确性。利用该方法得到了预应力钢绞线这一非规则结构波导的特定模态频散曲线。     

钢轨轨底斜裂纹的超声导波散射特性

钢轨轨底斜裂纹的超声导波散射特性是超声导波检测钢轨轨底技术的基础。首先对钢轨轨底导波传播特性及激发频率对导波散射特性的影响进行了数值分析,再进一步基于ABAQUS软件建立了钢轨轨底不同角度斜裂纹散射特性的有限元模型,对横向振动模态和垂直振动模态下钢轨轨底不同角度斜裂纹的散射特性进行了分析。数值分析和波场快照显示,横向振动模态较垂直振动模态下超声导波在钢轨轨底斜裂纹上的频散相对严重,垂直振动模态下导波检测钢轨斜裂纹效果更好,为后续钢轨轨底导波检测试验提供了理论基础。     

基于杜芬混沌振子的磁致伸缩导波信号识别

在无损检测中,磁致伸缩导波技术已得到普遍应用。由于导波在波导中传播时会发生频散,使得信号能量在空间中散播,增加了检测小缺陷的难度。根据导波信号检测的特点,从系统输入输出特性出发,提出了基于杜芬混沌振子的导波信号识别方法。在考虑电磁脉冲的影响下,把钢绞线实验导波信号输入杜芬混沌系统,发现可以通过系统由大尺度周期状态到混沌状态的改变来辨识出小缺陷信号,为提高导波检测精度提供了一种方法。     

粘接结构质量超声检测和信号处理方法

粘接结构的粘接质量无损检测要求越来越高,而超声检测方法具有更突出的优点被广泛应用。结合现有的研究状况,介绍目前在粘接质量检测上使用的几种超声检测方法,全面分析了这些方法的应用特点,超声导波检测方法具有更广阔的应用前景,可以预期采用超声导波检测方法检测粘接结构质量将是未来一段时间研究的热点之一。最后对3种常用的超声检测信号时频处理方法进行了分析,这些方法具有不同侧重点,可根据不同需求采用相应处理方法。     

Simultaneous determination of wave velocity and thickness on overlapped signals using Forward Backward algorithm

This paper presents a method to simultaneously determine the wave velocity and the thickness of an unknown sample in case of overlapped ultrasonic signals. Indeed, the determination of the time delay in an ultrasonic signal can be critical to allow the simultaneous characterization of parameters of the studied material, such as the thickness and the wave velocity. Therefore, a forward-backward algorithm is applied to the overlapped signal using a reference signal in order to retrieve the excitation signal. Firstly, the method is explained and a validation on synthetic signal is performed to observe its robustness. Secondly, a time retrieval is performed on real signals to determine thickness and wave velocity in aluminium plates. The results show that this method is suitable to simultaneously retrieve thickness and wave velocity, even for overlapped signals (up to 65%), with a discrepancy as low as 1%.     

Hybrid analysis of surface wavefield data from Portland cement and asphalt concrete plates

Impact-echo and multi-channel analysis of surface wave (MASW) methods were combined for a hybrid analysis of multi-channel surface wavefield data sets to iteratively solve for the thickness, elastic modulus, and Poisson's ratio of Portland cement and asphalt concrete plates. The time-frequency method was used to evaluate the plate thickness resonance frequency of the zero group velocity component of the first-order symmetric Lamb wave mode for use in the impact-echo analysis. It was observed that the thickness resonance frequency may not be resolved using focusing or amplifying signal processing techniques when plate/base interface conditions result in weak reflection amplitudes. Hybrid analysis results compared favourably against longitudinal resonant frequency tests of both cast cylinders and drilled cores from Portland cement concrete plates. It was shown that the hybrid analysis technique can be used to provide accurate compression wave velocity estimates used in impact-echo surveys.     

Enhancement of detecting defects in pipes with focusing techniques

Ultrasonic guided waves have been widely utilized for long range inspection of structures such as oil and petrochemical pipes. However, weldments, support, insulation, and attenuation make it difficult to examine pipe-like structures. In order to overcome such difficulties, it is desired to focus ultrasonic guided wave at the area under interrogation. In this paper, we discuss two focusing techniques: angular profile tuning and signal based focusing. The angular profile tuning approach relies on a theoretical prediction of pressure field of ultrasonic guided wave produced by an ultrasonic transducer mounted on the pipe. And, the signal based focusing is focusing ultrasonic guided waves using cross-correlation analysis. To compare the performance of these two techniques, non-axisymmetric guided waves are focused to abnormalities such as a through-wall hole and a circumferential notch, using an ultrasonic guided wave array system that has been specially fabricated for this purpose. The advantages and limitations of these two focusing techniques are addressed.     

混合谱二维傅里叶变换法识别兰姆波模式

在分析二维傅里叶变换原理的基础上,将快速傅里叶变换（FFT）和自回归（AR）参数估计相结合,采用混合谱二维傅里叶变换方法,对铝板中的兰姆波模式进行识别。试验结果表明,与二维快速傅里叶变换相比,混合谱估计方法能精确检测多模式超声兰姆波相速度,对兰姆波模式识别力大大提高。混合谱二维傅里叶变换方法在超声导波检测研究中具有广泛的应用前景。     

Defect detection in brazed weldment with lattice structure using ultrasonic Lamb wave technique

In this paper, defects detection in brazed weldment with lattice structure is studied using ultrasonic Lamb wave. Based on the ultrasonic guided wave theory, the frequency dispersion curves for phase and group velocity of 1Cr18Ni9Ti are obtained by solving the Rayleigh-Lamb equation. The incident angles of different modes are determined through theoretical calculation and experimental analyses. Artificial defects of through-wall slots with different dimensions are made and tested. Experimental scattering effects of the fundamental symmetric mode S_2 and asymmetric modes A_1 and A_0 are analysed and compared. The results show that mode A_0 is suitable for detecting artificial defect, and the amplitude of the received signals are in good agreement with the defect size. Brazed weldment specimen containing lack of brazing with certain dimensions is made. Using the same methodology, scattering effects produced by weld defects are measured. The results show that the clutter wave brought about by the filler metal will certainly disturbs the identification of defect signal. But, when the defect is 3.0mm in width, the presented mode A_0 could be used potentially.     

基于时频判别特征的焊缝超声检测缺陷分类

根据超声检测信号的瞬变特性,针对焊缝检测的缺陷分类问题,提出用判别追踪算法提取缺陷信号的局部时频判别特征,并结合概率神经网络实现了焊缝超声检测信号的缺陷分类.在提取时频判别特征时,提出考虑新选原子与已选原子的相关性的判别基提取方案,以降低特征之间的冗余,使提取出的特征能更有效地鉴别不同类别的缺陷.用该方法对一电子束焊缝试块中的缺陷进行了分类,结果表明,时频判别特征适合超声信号的缺陷分类,并能有效地抑制晶粒噪声的影响,考虑判别原子间相关性后可获得更高的分类正确率.     

以聚焦能量为导向导波非穿透型缺陷检测研究

为了达到导波的检测能量尽可能聚焦于缺陷处的目的,结合时间反转聚焦理论,采用模拟计算与实验研究相结合的方法对含有不同尺寸的非穿透型裂纹缺陷的管道进行检测研究,得到时间反转导波反射回波系数是直接导波反射回波系数的3倍,由此证明了时间反转法的时-空聚焦的特性,即时间反转导波同时到达缺陷位置,实现了能量的汇聚,论证了时间反转聚焦理论可用于管道导波的缺陷检测、提高小缺陷的检出能力。     

超声导波检测技术的研究进展

综述近年来超声导波检测研究的最新进展。介绍导波在不同材料和结构中的频散特性及与之相关的理论成果。从导渡的结构出发，分析了导波在介质中能量与位移的分布。论述了导波检测技术领域中数值分析方法和信号处理方面的一些新技术。