基于PECT-EMAT复合检测方法的铁磁性材料的复合缺陷检测

铁磁性材料在现代能源工业设备关键结构上广泛应用。一些关键部位由于生产、使用时产生的拉应力状态及环境影响，易萌生表面应力腐蚀裂纹，同时在弯管或焊缝处经长期冲蚀也可能出现内部局部减薄缺陷，对工业设备结构的安全可靠性构成了严重的威胁。本研究提出并开发了基于脉冲涡流-电磁超声复合电磁无损检测方法来检测铁磁性试件的表面裂纹和底部减薄缺陷。并开发了基于频谱滤波的信号分离方法，成功提取出复合检测中的脉冲涡流信号和电磁超声信号。实验结果表明，其中脉冲涡流信号可以有效检测试件的表面裂纹，电磁超声信号可以很好地定量试件底部减薄缺陷的残余厚度。由此可见，本研究开发的新型方法可以同时检测试件上下表面两种类型的缺陷，具有明显的优势。     

胶结波纹夹芯板水浸超声相控阵检测

首次采用水浸相控阵超声检测方法对加工或使用过程中的胶结波纹夹芯板粘结质量进行了无损检测,与射线、激光、常规超声等检测方法相比,该方法具有分辨率高、检测速度快等优点;设计制作了具有2mm~50mm不同尺寸脱粘缺陷的波纹夹芯板试样并进行了漏粘、脱粘缺陷人工检测实验,研究了本文方法的检测可行性和检测精度(精度至少可达2mm)。     

有限单元法在超声导波检测技术中的应用

超声导波检测技术具有对波导结构中的缺陷进行远距离无损检测的能力,多年来一直是无损检测领域关注的热点之一.有限单元法具有对各种复杂动力学问题进行计算的能力,已成为超声导波检测技术研究的重要工具.本文结合超声导波检测技术研究领域中的热点问题,对相关的有限单元法进行了简要综述.介绍了有限单元法的发展及其在多物理场耦合机制下导波的激励与接收、线弹性和黏弹性结构中导波的传播特性、非线性超声导波等多个方面的应用研究情况. 最后,基于超声导波检测技术研究趋势展望了相关有限单元法的未来研究重点和发展方向.      

超声柱面导波技术及其应用研究进展

综述无损检测中的超声柱面导波技术及其应用研究进展。给出导波的频散及多模式特征,着重评述超声导波的模式和频率选择、导波的激励和接收方法、导波与缺陷的相互作用、信号处理与特征提取以及导波技术在无损检测中的应用前景。      

一种用于无损检测的数字剪切散斑干涉系统

剪切电子散斑干涉技术在工业无损检测领域有广阔的应用前景.本研究基于迈克耳逊干涉光路,设计了全动式的干涉剪切镜,研制了便携式的激光无损检测设备.采用相关算法生成剪切电子散斑条纹图,获得了高质量的物面缺陷检测条纹.同时采用了条纹的自适应滤波技术和相移技术,进一步提高了缺陷处条纹的清晰度和对比度.配合热流和负气压两种加载方式,该设备可应用在多种材料的无损检测中.实验表明,对于铝蜂窝夹层板,该设备可检测直径大于3mm的缺陷,且该设备具有使用方便的特点,可替代一些常规的检测方法.本文同时给出了该方法的其他实验例证.     

材料力学性能退化的超声无损检测与评价

材料性能退化总是伴随着某种形式的材料非线性力学行为, 从而引起超声波传播的非线性, 即高频谐波的产生.基于此,材料和结构的超声无损检测与主人技术发展成起来.首先介绍固体介质内的非线性超声波动方程的基础, 并综述了利用超声波传播的非线性特性对结构材料和粘结面的力学性能退化进行无损检测与评价的研究进展.之后对材料在疲劳、拉伸以及蠕变载荷作用下, 其力学性能退化进行超声无损检测与评价的试验研究进行了介绍;综述了超声波传播非线性的机理研究, 以及利用超声波对粘结面的粘结强度及其力学性能退化评估所开展的研究. 最后指出了今后该领域需要进一步研究的问题.      

基于边缘采样UKF滤波的捷联惯导初始对准方法

设计了基于四元数的捷联惯导非线性初始对准模型,同时指出该模型仅仅是姿态误差四元数和速度误差的非线性函数,而对于惯性器件误差而言则是线性的。针对该模型的部分线性特性,设计了基于边缘采样的UKF滤波算法,该算法仅对状态量中的非线性子集进行采样,因此对于部分线性模型而言,该算法在不损失滤波精度的前提下能够有效降低算法计算量。仿真及车载实测数据实验表明所研究的初始对准模型和相应的滤波算法是有效的,而且较传统方法具有明显的计算量方面的优势;在达到相同对准精度的前提下,所设计算法的计算量较传统算法降低了52%。     

板背部缺陷的单侧非接触式超声无损检测方法

随着板状结构在石化、航空航天和电力等工业领域中的广泛应用,急需发展相应的无损检测技术,对其结构完整性进行定期评估,以保证结构的安全运行。基于空气耦合换能器的Lamb波技术,可以非接触快速地对板状结构进行扫描,在结构安全检测领域有广阔的应用前景。本文采用基于势函数法的空气耦合板状结构声传播模型,通过理论求解得到其Lamb波临界角随频厚积的变化规律。实验中采取空气耦合换能器激发和接收Lamb波,采用傅里叶变换和信号滤波技术识别S0和A0模式,并通过与理论结果比较进行确认。最后,分别采用S0和A0模式对板背部半通孔缺陷进行定位,结果显示该单侧非接触式超声无损检测方法可用于板状结构背部缺陷的检测。     

一种新的红外脉冲热成像后处理方法

脉冲热成像技术作为一种新兴的无损检测技术已被广泛应用于红外领域,然而由于试样表面加热不均匀及表面发射率低导致的红外图像对比度低、噪声大等问题给缺陷的检测带来困难。本文基于长脉冲热成像技术对碳纤维增强塑料(carbon fiber reinforced polymer,CFRP)板和304不锈钢进行了无损检测研究,提出了比温度的图像后处理方法。该方法对温度序列图像的每一帧图像与前一帧图像进行作商的后处理操作,得到比温度的图像序列。从比温度序列中获取信噪比最大的图像,以进行缺陷识别和缺陷定量。结果表明,与此前的方法相比,该方法显著提高了图像的信噪比,更有利于检测更深、更小的缺陷,相比原始图像,信噪比提高了近98.46%。将该方法与半高全宽法相结合,对试样的尺寸进行定量检测。通过仿真和实验验证,该方法具有良好的鲁棒性,显著降低了缺陷尺寸定量的误差,该方法可作为一种有效的红外图像后处理及缺陷尺寸定量方法。     

去除Lamb波频散的线性映射法

Lamb波常被用于板壳结构的无损检测,然而Lamb波的频散效应会导致板中损伤反射信号的渡越时间信息无法准确提取,因而影响损伤定位及成像的精度。本文引入线性映射方法,用线性频率-波数关系取代原有非线性的频散关系,从而去除激励中心频率附近的频散效应。分别采用数值模拟和实验的方法分析了频散去除的效果,进而结合相控阵成像算法对金属板中的损伤进行成像研究。结果表明,利用线性映射法去除频散可以显著提高含损伤散射信号的信噪比,提升相控阵损伤成像方法对损伤定位的准确性。     

Beam generating and sound field modeling of flexible phased arrays for inspecting complex geometric components

The flexible phased array ultrasonic technology has been developed to tackle the long-term challenge of damage inspection in complex-profiled components. However, due to the influences of curved interfaces, it is sometimes difficult to control the transmission signal of the sound field, thereby creating unreliable transducer performances. This paper proposes the time delay laws for generating steering or focusing beams on curved surfaces (concave, convex, concave/convex) based on the ray acoustics theory. Then, we derive the analytic expression of the entire flexible array ultrasonic field based on the multiple line source model and the time delay laws. Finally, the acoustic pressure distribution of curved structures is simulated to verify the feasibility of the derived principles. The numerical results show that the beams can realize dynamic steering and focusing without distortions or disorientations even when the steering angle reaches 45 degrees. Furthermore, the influences of the specimen surface profile, steering angle and focusing distance on the acoustic field are also analyzed by the axial sound pressure plots. These preliminary results represent an essential step in the development of a nondestructive testing (NDT) system for inspecting components with complex surfaces.     

Discriminating linear from nonlinear elastic damage using a nonlinear time reversal DORT method

The DORT method is a selective detection and focusing technique originally developed to detect defects and damages which induce linear changes of the elastic moduli. It is based on the time reversal (TR) where a signal collected from an array of transducers is time reversed and then back-propagated into the medium to obtain focusing on selected targets. TR is based on the principle of spatial reciprocity. Attenuation, dispersion, multiple scattering, mode conversion, etc. do not break spatial reciprocity. The presence of defects or damage, may cause materials to show nonlinear elastic wave propagation behavior that will break spacial reciprocity. Therefore the DORT method will not allow focusing on nonlinear elastic scatterers. This paper presents a new method for the detection and identification of multiple linear and nonlinear scatterers by combining nonlinear elastic wave spectroscopy, time reversal and DORT method. In the presence of nonlinear hysteretic elastic scatterers, forcing the solid with a harmonic excitation, the time reversal operator can be obtained not only at the fundamental frequency of excitation, but also at the odd harmonics. At the fundamental harmonic, either inhomogeneities and linear damages can be individually selected but only at odd harmonics nonlinear hysteretic elastic damages exist. A procedure was developed where by decomposing the operator at the odd harmonics, it was possible to focus on nonlinear scatterers and to differentiate them from the linear inhomogeneities. A complete mathematical nonlinear DORT formulation for 1 and 2D structures is presented. To model the presence of nonlinear elastic hysteretic scatterers a Preisach–Mayergoyz (PM) material constitutive model was used. Results relative to 1 and 2 dimensional structures are reported showing the capability of the method to focus and discern selectively linear and nonlinear scatterers. Furthermore, an analysis was conducted to study the influence of the number of sources and their location on the imaging process showing that using a higher numbers of sensors does not automatically bring to a minor uncoupled behaviour between the nonlinear targets.     

Analytical extension of Finite Element solution for computing the nonlinear far field of ultrasonic waves scattered by a closed crack

Nonlinear scattering of ultrasonic waves by closed cracks subject to contact acoustic nonlinearity (CAN) is determined using a 2D Finite Element (FE) coupled with an analytical approach. The FE model, which includes unilateral contact with Coulomb friction to account for contact between crack faces, provides the near-field solution for the interaction between in-plane elastic waves and a crack of different orientations. The numerical solution is then analytically extended in the far-field based on a frequency domain near-to-far field transformation technique, yielding directivity patterns for all linear and nonlinear components of the scattered waves. The proposed method is demonstrated by application to two nonlinear acoustic problems in the case of tone-burst excitations: first, the scattering of higher harmonics resulting from the interaction with a closed crack of various orientations, and second, the scattering of the longitudinal wave resulting from the nonlinear interaction between two shear waves and a closed crack. The analysis of the directivity patterns enables us to identify the characteristics of the nonlinear scattering from a closed crack, which provides essential understanding in order to optimize and apply nonlinear acoustic NDT methods.     

Inverse method for detection and sizing of cracks in thin sections using a hybrid genetic algorithm based signal parametrisation

A hybrid-GA method, based on signal parameterization, has been reported here for the improved detection and sizing of surface cracks of small sizes/depths in thin sections. The method relies on parameterizing the composite reference from the defect into its individual components i.e., the crack tip diffracted echo and the corner trap echo and subsequently use the relative arrival time technique (RATT). The phased array ultrasonic technique was employed in the investigation. Both experimental and simulated signals were used in the study. It is shown through both simulations and experiments that the hybrid-GA is successful in parameterizing both non-overlapping and overlapping echoes encountered in thin sections. It is additionally shown that the hybrid-GA improves the signal to noise ratio and correct for under-sampling of data.     

Assessment of Heat Treated Inconel X-750 Alloy by Nonlinear Ultrasonics

The nonlinear ultrasonic technique is known as a promising tool for monitoring material states related with micro-structural changes, with improved sensitivity compared to conventional nondestructive testing techniques. It is well known that degradation of material properties is generally accompanied by the increase of material nonlinearity. However, the trend has been rarely investigated in the opposite way for improved material properties. In this paper, nonlinear ultrasonic waves are used to assess the material condition of heat treated Inconel X-750 alloy based on the nonlinear acoustic parameters. Material property testing is conducted to compare the influence of heat treatment for comparison with the nonlinear parameter based prediction. The material properties of specimens are improved by applying heat treatment, with significant decreases in the acoustic nonlinearity. The better the mechanical property achieves via heat treatment, the smaller the acoustic nonlinearity becomes. It can be concluded that the nonlinear acoustic technique can be used to evaluate the effect of heat treatment nondestructively, and to optimize the process, thus providing another indication of the feasibility of using the nonlinear ultrasonic technique for material characterization.     

Wave generation and scattering by periodic baffle system in application to beam-forming analysis

Directional excitation and detection of sound in the periodic baffle system are analyzed using the method developed earlier in electrostatics. The phenomenon is exploited in phased array transducers applied in ultrasonography, nondestructive evaluation and testing. The nice feature of the applied method is that the matrices of the resulting system of the equations are relatively easy for computations and that the results satisfy exactly the energy conservation law. Illustrative numerical examples present the far-field wave-beam steering generated in a baffle system that may be considered as a model of a linear ultrasonic transducer array.     

Elasto-optic technique for measurement of elastic wave propagation in solids

The modulation of the optical path of the beam of a laser vibrometer in a specimen under acoustic excitation is measured at two planes, separated by a precisely known distance. The phase shift and the decrease in magnitude are used to calculate the phase velocity and attenuation, respectively. The method is demonstrated for a homogeneous specimen, and the results compare favorably with those obtained by a conventional ultrasonic technique. The method is then applied to measure specular and first diffraction-order reflection from a coplanar periodic array of particles in an elastic matrix and phase velocity spectra in a tetragonal periodic particulate composite. As expected, in a periodic composite the establishment of dispersive Floquet-type waves is observed throughout the entire periodic particulate composite.     

Nonlinear Lamb waves in plate/shell structures

鉴于常规超声检测技术对分布式材料细微损伤和接触类结构损伤的检测效果不佳,近年来非线性超声技术逐渐引起广泛关注.超声波在板壳结构中通常以兰姆波的形式进行传播,然而由于兰姆波的频散及多模特性,使得非线性兰姆波的理论和实验研究进展缓慢.本文从经典非线性理论出发,总结了源于材料固有非线性诱发的非线性兰姆波的理论和实验两个方面的研究进展,并综述了兰姆波的二次谐波发生效应在材料损伤评价方面的若干应用;从接触声非线性理论出发,讨论了目前由于接触类结构损伤诱发的非线性兰姆波的研究现状.最后展望了非线性兰姆波的未来研究重点及发展趋势.     

Nonlinear wave propagation and reflection — Comparing the numerics with the analytics

The accuracy of numerical methods needs always a special attention. In this paper, analytical and numerical methods have been compared to describe the initial stage of nonlinear propagation and reflection of longitudinal ultrasonic waves. The perturbation method has been used to derive the analytical solution and the finite difference scheme to find the numerical solution for multiple free-boundary reflections of a harmonic burst at ultrasonic frequencies. The comparison of results at relatively small nonlinearities reveals a good qualitative and quantitative agreement between the analytical and numerical solutions. The method for determining analytically the exact region of interaction for counter-propagating waves is outlined in detail. At higher frequencies and larger nonlinear effects some quantitative differences between analytical and numerical results appear. The results are applicable in modelling nonlinear wave motion, including NDT and nonlinear one-dimensional vibrations.