Infrared thermography investigations in transitional supersonic boundary layers

The study of boundary-layer transition in supersonic flows is conducted employing infrared thermography (IRT). Several models of swept wings are tested in a blow-down facility at Mach number 2.4. The effects of wing sweep and other parameters (angle of attack, leading-edge contour, presence/absence of surface roughness) are successfully observed. The transition front is clearly identified, demonstrating the utility of IRT for this type of study. The technique is particularly indicated for flows that are sensitive to surface alterations (roughness), such as transitional boundary layers, because it does not require interaction with the model or the flow under investigation. The additional advantage of no need for special apparatus, except for the infrared camera, makes IRT well suited for both wind-tunnel and in-flight testing. Practical problems and limitations encountered when dealing with IRT in high-speed flows are also discussed.     

A novel physics-informed framework for reconstruction of structural defects

The ultrasonic guided wave technology plays a significant role in the field of non-destructive testing as it employs acoustic waves with the advantages of high propagation efficiency and low energy consumption during the inspect process. However, the theoretical solutions to guided wave scattering problems with assumptions such as the Born approximation have led to the poor quality of the reconstructed results. Besides, the scattering signals collected from industry sectors are often noised and nonstationary. To address these issues, a novel physics-informed framework (PIF) for the quantitative reconstruction of defects by means of the integration of the data-driven method with the guided wave scattering analysis is proposed in this paper. Based on the geometrical information of defects and initial results obtained by the PIF-based analysis of defect reconstructions, a deep-learning neural network model is built to reveal the physical relationship between the defects and the noisy detection signals. This learning model is then adopted to assess and characterize the defect profiles in structures, improve the accuracy of the analytical model, and eliminate the impact of the noise pollution in the process of inspection. To demonstrate the advantages of the developed PIF for the complex defect reconstructions with the capability of denoising, several numerical examples are carried out. The results show that the PIF has greater accuracy for the reconstruction of defects in the structures than the analytical method, and provides a valuable insight into the development of artificial intelligence (AI)-assisted inspection systems with high accuracy and efficiency in the fields of structural integrity and condition monitoring.     

基于红外热成像技术的电子封装缺陷无损检测方法

在电子器件封装制造和服役过程中,工艺及温度载荷容易引起器件内部界面分层等缺陷,严重影响产品良率和可靠性,及时发现这些内部缺陷十分重要.红外热成像检测技术由于非接触、实时记录、检测速度快、定量分析等特点,已逐渐成为无损检测等领域有效的检测手段.本文采用主动双面红外测量方法对塑封料和铜界面间的缺陷进行检测,得到了试样的表面温度分布与缺陷的尺寸和深度的对应关系.通过试验数据对缺陷深度理论计算方法进行了对比研究,实现了试样内部缺陷特征的定量化识别.     

基于小波变换及Wigner-Ville变换方法的超声导波信号分析

对结构中缺陷的检测和识别是无损检测中的一项重要研究课题,超声导波由于可在短时间内检测很远距离,故它的一个重要应用便是管材的检测。因而对导波检测信号的处理成为一重要研究内容,本文利用时-频分析方法中的小波变换和Wigner-Ville变换对管道和抽油杆缺陷的导波检测信号进行了分析处理。实验结果表明,进行小波变换后,缺陷回波信号的信噪比大大提高,直径仅1mm的小孔缺陷可容易地被识别出来,准确检测出其位置;通过对信号进行Wigner-Ville的相关变换,可同时在时频两域内对缺陷的回波信号进行分析,使缺陷辨别起来简单易行。两种信号处理方法的超声导波应用研究为以后导波信号的处理提供了新的实现依据。     

基于红外热成像的编织复合材料低速冲击和冲击后压缩试验研究

针对二维三轴编织复合材料（two-dimensional triaxially braided composite, 2DTBC）在低速冲击和冲击后压缩（compression after impact, CAI）载荷下的损伤失效机理,开展了2DTBC试样的不同能量低速冲击试验以及相应的CAI试验,并采用红外热像仪监测在低速冲击和CAI试验过程中的温升现象。通过C扫描表征了不同能量低速冲击后试样的分层损伤情况,讨论了试样背面温度场分布特性及其随冲击能量的演化规律;对比分析了2DTBC冲击后剩余压缩强度与冲击能量的对应关系,基于数字图像相关（digital image correlation, DIC）技术监测了CAI试验中的全局应变场,结合热成像、变形场和光学图像数据,阐明了不同能量冲击后2DTBC的压缩失效特性,讨论了基于红外热成像技术表征编织复合材料损伤失效行为的有效性。试验结果显示:编织复合材料低速冲击和CAI试验中的温度场分布图与编织几何构型有明显关联度;低速冲击试验的温升幅值随冲击能量的增加而快速上升,CAI试验的温升现象随着冲击能量的增加而减弱;分层面积随冲击能量的增大而增大,冲击后剩余压缩强度随冲击能量的增大而降低。研究结果表明:红外热成像技术能够很好地捕捉试样破坏瞬间释放断裂能所产生的温升现象,温度场图像相较于全局应变场能更好地捕捉破坏的起始位置和失效特征。     

Understanding delamination behaviour in a circular laminate

Composite materials are prone to a wide range of defects and damage which may significantly reduce their residual strength. Of the various types of defects possible, interply delaminations arising from in-service damage are probably the most insiduous because of their effects on residual compressive strength and difficulties associated with their detection. In this study, a finite element analysis of the self similar growth of a circular delamination in a compressed laminate is undertaken, and the results are compared with an analytical solution.     

基于无基底焦平面阵列的红外图像复原算法

与传统有基底焦平面阵列不同,无基底焦平面阵列的感热单元吸收的红外辐射以点扩散函数的形式向相邻单元进行热传导,该热力学特性虽然能够大幅提高红外探测性能,使红外目标在背景中更加凸显,但同时降低了系统对红外目标细节的分辨能力,使图像模糊。通过分析这种热扩散叠加效应对红外成像质量的影响,利用数字图像处理方法,提出了针对性的红外图像复原算法。仿真和实验均表明该算法能够有效增强红外图像细节轮廓,提升图像质量。     

光机械式红外探测器中镜面弯曲对探测灵敏度的影响(英文)

光学读出式红外成像技术是近年来研究的热点,本文讨论了镜面弯曲对光学检测灵敏度的影响。由双材料微悬臂梁组成的非致冷焦平面阵列通过体刻蚀工艺加工而成,由于残余应力的影响,制成的焦平面阵列将会发生弯曲,应力导致的镜面弯曲将会降低光学探测灵敏度。本文通过傅立叶光学模拟了镜面弯曲对光学探测灵敏度的影响,并通过实验验证了该模型。实验和模拟结果表明,在镜面曲率为0 .1mm-1时,光学探测灵敏度将会降低到理想情况的40 %。最后我们用这个模型评价了通过表面修饰来提高光学性能的效果。     

光机械式红外探测器中镜面弯曲对探测灵敏度的影响

光学读出式红外成像技术是近年来研究的热点，本文讨论了镜面弯曲对光学检测灵敏度的影响。由双材料微悬臂梁组成的非致冷焦平面阵列通过体刻蚀工艺加工而成，由于残余应力的影响，制成的焦平面阵列将会发生弯曲，应力导致的镜面弯曲将会降低光学探测灵敏度。本文通过傅立叶光学模拟了镜面弯曲对光学探测灵敏度的影响，并通过实验验证了该模型。实验和模拟结果表明，在镜面曲率为0．1mm-1时，光学探测灵敏度将会降低到理想情况的40％。最后我们用这个模型评价了通过表面修饰来提高光学性能的效果。     

接合残余应力在界面端的应力奇异性

接合残余应力对异种接合材料强度的影响很大，正确地分析接合残余应力在界面端附近的分布及其奇异特性，是研究异材强度评价方法的关键问题之一，本文利用弹性学中的Ｇｏｕｒｓａｔ公式和有关微分方程解的理论，求得了平面近似下的界面端附近的残余应力场及其应力奇异性，与单纯的外力作用时的情况不同，残余应力在界面端有可能出现对数型的应力奇异性，并且不能仅用Ｄｕｎｄｅｒｓ的异材参数来描述。     

An analytical approach to reconstruction of axisymmetric defects in pipelines using T(0, 1) guided waves

Torsional guided waves have been widely utilized to inspect the surface corrosion in pipelines due to their simple displacement behaviors and the ability of longrange transmission. Especially, the torsional mode T (0, 1), which is the first order of torsional guided waves, plays the irreplaceable position and role, mainly because of its non-dispersion characteristic property. However, one of the most pressing challenges faced in modern quality inspection is to detect the surface defects in pipelines with a high level of accuracy. Taking into account this situation, a quantitative reconstruction method using the torsional guided wave T (0, 1) is proposed in this paper. The methodology for defect reconstruction consists of three steps. First, the reflection coefficients of the guided wave T (0, 1) scattered by different sizes of axisymmetric defects are calculated using the developed hybrid finite element method (HFEM). Then, applying the boundary integral equation (BIE) and Born approximation, the Fourier transform of the surface defect profile can be analytically derived as the correlative product of reflection coefficients of the torsional guided wave T (0, 1) and the fundamental solution of the intact pipeline in the frequency domain. Finally, reconstruction of defects is precisely performed by the inverse Fourier transform of the product in the frequency domain. Numerical experiments show that the proposed approach is suitable for the detection of surface defects with arbitrary shapes. Meanwhile, the effects of the depth and width of surface defects on the accuracy of defect reconstruction are investigated. It is noted that the reconstructive error is less than 10%, providing that the defect depth is no more than one half of the pipe thickness.     

A Fully Non-Contact Ultrasonic Propagation Imaging System for Closed Surface Crack Evaluation

Cracks are one of the most common types of damage occurring in engineering structures. A reliable nondestructive evaluation technique is essential to detect any possible damage at the initiation phase. Real fatigue closed-surface cracks are difficult to detect through visual inspection. Ultrasound has been widely used, but conventional contact ultrasonic inspection techniques are not suitable for couplant-sensitive structures. In addition, these techniques are generally laborious for large field structures and the inspection speed is relatively slow. We present a novel fully non-contact hybrid ultrasonic propagation imaging (UPI) system that uses laser ultrasonic scanning excitation and piezoelectric air-coupled sensing. Ultrasonic frequency tomography and wavelet-transformed ultrasonic propagation imaging algorithms are used to extract damage features. These features are used to perform a thorough diagnosis of damage. The system enables remote and fully non-contact automatic one-sided inspection for temporal reference-free damage evaluation, and is also applicable to in-field structures. Optimization provides improved performance of air-coupled transducers (ACTs) used as receivers for the hybrid UPI system, as shown by our experimental results. Surface crack evaluation results were analyzed on the basis of ease of damage visualization, accuracy of crack size estimation, and sensitivity. The proposed hybrid UPI system is sensitive enough to detect a real fatigue closed-surface micro-crack with size detection accuracy as high as 96%. We also show that the relation between the scanning interval and crack width affects damage visualization performance, and the accuracy and sensitivity of damage size estimation.     

混凝土损伤识别中的时间逆转成像方法

时间逆转成像技术具有定位准确和操作简单之特点,本文将其运用于混凝土结构损伤的检测．通过提取各换能器单元的发射信号和损伤散射信号构建超声波传播的传递矩阵然后对其进行奇异值分解,获得包含损伤信息的奇异向量;采用多重信号分类(multiple signal classification, MUSIC)算法,分别基于数值模拟数据和实验实测数据对混凝土结构内部损伤进行成像,实现了准确的损伤定位,并将成像结果与偏移成像法进行对比．此工作探索了将时间逆转成像技术应用于混凝土结构内部损伤实际工程检测可行性,为无损检测技术人员定性或定量分析混凝土结构的内部缺陷提供理论参考．     

Singular stress field near the edge of interface of bonded dissimilar materials with an interlayer

For bonded dissimilar materials, the free-edge stress singularity usually prevails near the intersection of the free-surface and the interface. When two materials are bonded by using an adhesive, an interlayer develops between the two bonded materials. When a ceramic and a metal are bonded, the residual stress develops because of difference in the coefficient of thermal expansion. An interlayer may be inserted between the two materials to defuse the residual stress. Stress field near the intersection of the interface and free-surface in the presence of the interlayer is then very important for evaluating the strength of bonded dissimilar materials.In this study, stress distributions on the interface of bonded dissimilar materials with an interlayer were calculated by using the boundary element method to investigate the effect of the interlayer on the stress distribution. The relation between the free-edge singular stress fields of bonded dissimilar materials with and without an interlayer was investigated numerically. It was found that the influence of the interlayer on the stress distributions was confined within a small area of the order of interlayer thickness around the intersection of the interface and the free-surface when the interlayer was very thin. The stress distribution near the intersection of the interface and the free-surface was controlled by the free-edge stress singularity of the bonded dissimilar materials without the interlayer. In this case, the interlayer can be called free-edge singularity-controlled interlayer. If a stress distribution on the interface is known for one thickness of an interlayer h, stress distributions on the interface for other values of h can be estimated.     

桥梁结构水下基础表观缺陷立体视觉检测试验

针对桥梁结构水下基础表观缺陷检测实际需求,提出立体视觉表观缺陷检测方法。采用SIFT算法完成表观缺陷图像特征提取与匹配,选用MATLAB编译立体视觉表观缺陷检测评定软件,集成桥梁结构水下基础表观缺陷立体视觉检测系统。使用该系统在实验室环境完成水及空气两种环境下混凝土剥落、裂缝及楔槽三种缺陷的检测对比试验,得到每种混凝土试块表观缺陷在不同环境下的检测结果。试验结果表明,立体视觉表观缺陷检测方法能准确评定表观缺陷几何尺寸,从而验证了该方法用于桥梁结构水下基础表观缺陷评定的实用性及可行性。     

Additive-subtractive phase-modulated shearography with synchronized acoustic stressing

A robust electronic shearography technique is described that is immune to ambinet noise. In this technique, additive speckle-interference images containing information about the same two states of deformation of a test object undergoing acoustic stressing are acquired in each video frame. When a spatially nonuniform phase modulation is introduced in every other frame during the video sequence (using a tilting mirror) and the additive interference images are subtracted sequentially using a real-time image processor, the self-interference component of sheared-speckle interference pattern is removed. The susceptibility of this method to environmental noise caused by induced thermal noise and low frequency vibration is demonstrated to be lower than that of conventional substractive shearography methods; fringe visibility and contrast are significantly improved as well. The ability of this technique to work in a turbulent environment is demonstrated, and application to detection of structural defects in adhesively bonded structures, a problem of interest in nondestructive evaluation of structures, is shown.     

基于LabVIEW的便携式锚杆长度检测系统开发

基于LabVIEW软件平台开发了便携式锚杆长度检测系统。该系统包括一个带有信号激励接收功能的便携式工控机、探头和上层控制软件。首先通过软件设置硬件参数,TB-1000信号激励接收卡在探头上激励出超声导波信号并采集反射回波,经模拟滤波器处理后进入NIPCI-5102数据采集卡,将模拟信号转换为数字信号输入PC计算机。本系统软件可对激励接收卡设置激励信号参数,并具有对采集到的信号进行频域变换、希尔伯特变换、小波降噪、快速傅利叶变换(STFT)、扫频成像等处理功能。通过实验,证明了该软件系统具有较高的实时性和可操作性,较好地实现了锚杆长度的快速检测,扩大了超声导波在此领域的应用。     

Rapid evaluation of the fatigue limit in composites using infrared lock-in thermography and acoustic emission

Fatigue limit determination via the conventional Wöhler-curve method is associated with extended experimental times as it requires testing of a large number of specimens. The current paper introduces a methodology for fast, reliable and experimentally economic determination of the fatigue limit in monolithic and composite materials by means of combined usage of two nondestructive inspection methods, namely infrared (IR) lock-in thermography and acoustic emission (AE). IR thermography, as a real-time and non-contact technique, allowed the detection of heat waves generated due to thermo-mechanical coupling as well as of the energy dissipated intrinsically during dynamic loading of the material. AE, on the other hand, was employed to record the transient waves resulting from crack propagation events. Aluminum grade 1050 H16 and cross-ply SiC/BMAS ceramic matrix composites were subjected to fatigue loading at various stress levels and were monitored by an IR camera and AE sensors. The fatigue limit of the monolithic material, obtained by the lock-in infrared thermography technique and supported by acoustic emission was found to be in agreement with measurements obtained by the conventional S–N curve method. The fatigue limit of the ceramic matrix composite was validated with acoustic emission data.     

Thermal stresses in one-sided bond repair: geometrically nonlinear analysis

The problem of thermal stresses in an infinite isotropic plate rigidly bonded with an unsymmetrical, polygon-shaped reinforcement is analyzed within large deflection plate theory, using the equivalent inclusion method [J. Thermal Stresses 26 (2003) 457]. For simplicity, the plate assumes to be cooled down uniformly from a stress free temperature. The earlier approach proposed in [J. Thermal Stresses 26 (2003) 457] has been extended in the present paper to include geometric nonlinearity. Extension of the method to address residual thermal stresses associated with curing of the adhesive is also discussed.     

一种基于深度学习的超声导波缺陷重构方法

超声导波检测因其传播效率高、耗能少等优势成为了无损检测领域的重要研究方向。目前已有的利用超声导波进行结构缺陷探测和定量化重构的方法主要由相关的导波散射理论推导得出。然而,由于导波散射问题本身的高复杂性,使得在推导上述理论方法时引入一些近似假设,降低了重构结果的质量。另外,有些方法通过优化迭代的方式提高重构精度,又会增加检测的时间成本。有鉴于此,本文探索了一种将卷积神经网络与导波散射理论模型以局部融合的方式实现缺陷定量化重构的新方法。应用样本数据训练后的神经网络实现缺陷定量化重构,弥补缺陷重构过程中的理论模型误差,同时去除在实际检测过程中所存在的环境噪声。本文以利用SH导波重构平板中的减薄缺陷为研究对象,通过数值模拟验证了该方法在缺陷重构时具有高效率和高精度的特点,特别是对矩形缺陷的重构,新方法的结果精度比波数空间域变换法的精度提高了近200%。