A far-field airborne radar NDT technique for detecting debonding in GFRP–retrofitted concrete structures

A far-field airborne radar (FAR) nondestructive testing (NDT) technique integrating inverse synthetic aperture radar (ISAR) measurements and a backprojection algorithm for the condition assessment of glass fiber reinforced polymer (GFRP)–wrapped concrete structures is proposed. The method is directed toward the detection of near-surface defects and delaminations located in the vicinity of GFRP–concrete interface. Normal and oblique incidence measurement schemes were adopted and studied for their effectiveness in detecting near-surface anomalies. This technique is also applied to the detection of rebars in reinforced concrete cylinders. Laboratory measurements in the frequency range 8–12 GHz were made on artificially damaged GFRP–concrete cylinders for validating the concept of this technique. Spatial resolutions (range and cross-range) are improved by integrating radar measurements at different azimuth angles and in different frequencies, and implementing the developed progressive image focusing scheme. The feasibility of the proposed FAR NDT technique for distant inspection is validated through these studies.     

Imaging of internal cracks in concrete structures using the surface rendering technique

The impact echo method is effective in the inspection of concrete defects. If the test area is large and many tests are performed, it is difficult to get a picture of the concrete interior by examining a series of test spectra. In order to provide the engineers with a more direct way of detecting the defects in the structure, this study proposes a three-dimensional (3D) imaging method to depict the internal cracks in concrete structures. To acquire the test data, a mesh is drawn on the surface of the concrete. Then, impact echo tests are performed at the grids. The recorded signals are processed to obtain the depth spectra of the concrete. Finally, the surface rendering technique is adopted to construct the 3D image of the concrete interior. Both numerical simulations and model tests are used to verify the proposed imaging method. It is seen that surface rendering technique can be used to show the internal cracks in the concrete specimens successfully.     

A new technique to detect defect size and depth in composite structures using digital shearography and unconstrained optimization

Advanced composite materials are finding increasing application in aerospace, marine and many other industries due to their performance and structural efficiency. Maintenance inspection of these light-weight structures is a relatively new and difficult task for Non-Destructive Testing (NDT), which need robust methods to be applicable in industrial environments. In this paper, a new numerical-experimental procedure to detect size and depth of flat bottom holes in metallic and laminated composite structures by digital shearography (DISH) is proposed. The flaw detection capabilities of DISH have been evaluated by measuring the dynamic response of defects to applied stresses. Vibration dynamic loading is used to reveal flat bottom holes made with different sizes and placed at different depths in CFRP laminates. The shearographic methodology is based on the recognition of the (0 1) resonance mode per defect. A simplified model of thin circular plate, idealized above each flaw position, is used to calculate the natural frequency of vibrating defects. Then, the numerical difference between experimental resonance frequencies and those computationally obtained is minimized using an unconstrained optimization algorithm in order to calculate the defect depth. Considering the simplicity and rapidity of this technique, the laser shearography methodology is evaluated reliable as NDT method.     

A hybrid nondestructive testing method of pulsed eddy current testing and electromagnetic acoustic transducer techniques for simultaneous surface and volumetric defects inspection

In this paper, a hybrid nondestructive testing (NDT) method combining with the pulsed eddy current testing (PECT) method and the electromagnetic acoustic transducer (EMAT) method has been proposed and validated through numerical simulations and experiments. First, a numerical code is developed for the simulation of hybrid EMAT/PECT signals based on the developed EMAT and PECT code. Second, based on the numerical simulation, the influences of the eddy current induced by the excitation coil and the eddy current due to the velocity effect of the ultrasonic wave are compared and analyzed. In addition, the features of the EMAT and the PECT signals are analyzed respectively. Third, several signal separation and extraction methods are proposed on the basis of the spectral analysis and filtering strategies for extracting EMAT and PECT signals from the mixed signals of the hybrid EMAT/PECT method and their validity are evaluated through experiments. Finally, hybrid EMAT/PECT experiments are conducted and three types of defects (surface defects, bottom thinning defects, composite defects) in an aluminum plate and a SUS304 plate are successfully detected at the same time using the proposed hybrid NDT method and the signal feature parameters. Based on the numerical and experimental results, the proposed hybrid PECT/EMAT NDT method is demonstrated both high detectability and high efficiency for detecting surface and volumetric defects at the same time.     

Advanced NDT methods for evaluating concrete bridges and other structures

Several advances in methods and equipment for sonic and ultrasonic non destructive testing (NDT) of concrete structures are presented, including advances for methods applicable to large structures such as bridges and dams. These new advances and methods greatly increase the speed and accuracy of many NDT investigations, and allow collection of NDT information previously not readily obtainable. The first topic presented is a brief overview of the impact echo (IE) method along with a case history on how is has been employed in testing concrete structures. The IE method is used to locate damage and determine member thickness when access is available from one side only. The next topic is a relatively new N DT method for concrete using surface waves analysis, in a method known as the spectral analysis of surface waves (SASW) technique. This allows the determination of the shear wave velocity profile versus depth for any layered system and is particularly applicable to testing pavements, slabs, tunnels, shaft liners, and massive concrete structures. For bridges and dams, the technique is particularly effective in determining the depth of weathering effects on the concrete. Included is an overview of the method and the principles behind it, as well as some case history examples. The final topic presented is an advance in the technique of ultrasonic plus velocity (UPV) testing. This advance involves the use of rapid scanning techniques to greatly increase the speed and utility of UPV testing. The U PV method uses compression wave energy which is sent through a member and the arrival time, wave amplitude, and velocity are recorded and computed. This new scanning technology allows the near-continuous acquisition of data along any given path over a structure. Included is test data collected using the scanning system to show the great increase in testing speed and utility of scanner-collected data when compared to traditional point-by-point methods.     

管材涡流探伤最佳频率数值模拟与试验验证

目前广泛采用的确定涡流探伤频率的方法主要是特征频率法和试验法,两种方法得出的频率通常不是最佳频率。采用ANSYS数值计算方法对人工标准缺陷的信号进行数值模拟,从而找出对内外壁缺陷信号的幅度都比较大,并且内外壁缺陷信号的相位差接近极大的激励频率。经过试验验证,计算结果与试验结果完全符合。结论认为,用ANSYS信号模拟方法可以找出最佳的激励频率,既能兼顾内外壁缺陷的检测灵敏度,又能从相位上区分内外壁缺陷的激励频率。     

On the NDT and E for the diagnosis of defects using infrared thermography

The increasingly recognized applicability of infrared thermography has caused developments of remote-sensing diagnoses for various engineering applications. A significant advantage of this technique is that we can diagnose invisible defects nondestructively and safely. For maintaining and managing various structures satisfactorily, it is very important to detect many kinds of invisible defects such as separation, cavity, inclusion and so on. Although the infrared thermography for NDT and E has therefore been examined extensively, few fundamental investigations have addressed the numerical computation to evaluate the detection mechanism and the quantitative limit under various conditions. It is important to discuss them theoretically with the aid of the appropriate numerical computation. In this paper, therefore, we certify them using a series of fundamental numerical computation with the aid of the concerned experimental investigation using the infrared thermography. From the numerical and experimental investigations, the effects of defect's depth and size on the detection are elucidated. In addition to the fact, it is obvious that the applicability of the present NDT and E depends on a heating condition and a relative difference of thermophysical property between the defect and its surrounding.     

土木工程中的无损检测技术及其应用

土木工程中无损检测（简称ＮＤＴ－ＣＥ）有着广泛的应用和广阔的前景,ＮＤＴ－ＣＥ不仅用来对新建的建筑物进行质量监测,而且可对已有的建筑物结构的寿命进行评估,保养和修理。从应用的角度对ＮＤＴ－ＣＥ中常用的振动分析、冲击回波法、超声脉冲回波法、声发射、雷达、激光干涉以及红外线成像等技术的原理、应用局限性和发展前景作了简要介绍。     

Dual EMAT and PEC non-contact probe: applications to defect testing

For many non-destructive testing (NDT) applications, more information and greater reliability can be gained by using different techniques for defect detection, especially when the methods are particularly sensitive to different types of defects. However, this will often lead to a much longer and more expensive test and is not always practical due to time and cost constraints. We have previously discussed initial experiments using a new dual-probe combining electromagnetic acoustic transducers (EMATs) generating and detecting ultrasonic surface waves, and a pulsed eddy current (PEC) sensor [1]. This enables more reliable detection and sizing of surface and near-surface defects, with a reduced testing time compared to using two NDT techniques separately. In this paper, we present experiments using the dual-probe on samples which are more representative of real defects, for example testing for surface defects in rails. Several aluminium calibration samples containing closely spaced and angled slots have been measured, in addition to rail samples containing manufactured and real defects. The benefits of using the dual-probe are discussed.     

基于CEEMD的冲击回波分析方法研究

冲击回波法检测混凝土结构缺陷过程中由于存在面波和噪声干扰,反射层纵波难以从频谱特征直接识别出来。针对该问题,本研究将完备集成经验模态分解（CEEMD）方法引入冲击回波检测信号分析中,提出基于CEEMD冲击回波信号分析方法。通过对模拟和实验的冲击回波信号分析和研究,结果表明:CEEMD方法从冲击回波信号分解出的特征模态函数IMF1~IMF10,中间模态IMF5、IMF6的频谱反映出混凝土内部缺陷位置和板厚信息,据此频谱能准确确定内部夹层缺陷位置和混凝土板厚。CEEMD方法能分离面波和噪声干扰,可作为处理冲击回波信号的一种常规方法。     

脉冲涡流和电磁声换能器双探头无损检测

在许多情况下，只应用一种NDT技术存在不足，这就迫使NDT操作人员使用一种以上的技术以保证检测出危害被检物使用寿命或功能的缺陷。但分别实施多种技术的检测，就会延长检验时间。介绍了一种新的NDT设施，采用两种不同的非接触无损检测技术进行互补，即电磁声换能器（EMAT）和脉冲涡流（PEC）探头。检测结果表明，脉冲涡流和电磁声换能器因是非接触，所以可应用于材料生产过程中的自动在线检验，也可用于在役检验。     

Application of infrared thermography to the non-destructive testing of concrete and masonry bridges

Within recent years there has been an increase in the use of NDT methods to detect defects and anomalies in various civil engineering structures. Infrared thermography, which has been successfully used in the USA in civil engineering applications, is being increasingly applied in the UK as an NDT technique. For example, the technique is now included in the Building Regulations for the assessment of thermal insulation for all new non-domestic buildings from April 2002.One of the perceived limitations of infrared thermography is that in temperate climates it is too cold to use this technique since there is rarely the extreme solar exposure that has enabled the successful use of thermography to detect render debonding and concrete spalling utilising solar heating. However, with the advancements in modern technology it is now possible to detect smaller changes in temperature (down to 0.08 °C). This paper shows that even with the low ambient temperatures experienced in Europe it is possible to use infrared thermography to identify correctly known areas of delamination in a concrete bridge structure and also to investigate the internal structure of a masonry bridge.     

压力容器无损检测--超高压容器的无损检测技术

超高压容器广泛运用在化学、石化、人造水晶、合成金刚石、等静压处理、超高静液压挤压、粉末冶金、金属成型、地球物理和地质力学等行业或领域。在其制造、使用过程中,无损检测是保证产品质量和保证安全使用的有效手段之一。由于超高压容器一般为锻造的厚壁筒体结构,制造过程中的无损检测以超声检测、磁粉检测和渗透检测为主。在用超高压容器的无损检测以表面检测为主,方法有工业内窥镜检查、磁粉检测、渗透检测、磁记忆检测和涡流检测等。超声检测既要检测部件内部又要兼顾内表面缺陷的检测。在容器使用过程中可用声发射进行实时监测。     

Online nondestructive testing for fine steel wire rope in electromagnetic interference environment

The diameter of fine steel wire rope (FSWR) is generally a few millimeters. Its magnetic flux leakage (MFL) signal is weak, and the number of magnetic sensors installed for defect detection is limited because of the small diameter. In FSWR production workshops, different kinds of machinery work together, deteriorating the power quality and making the spatial electromagnetic environment complex; the weak MFL is thus interfered with further. It is difficult to carry out online nondestructive testing (NDT) of FSWR in the process of manufacturing. In this paper we present a novel MFL method for FSWR NDT in a strong electromagnetic interference environment. We use a three-dimensional finite element method (FEM) to analyze the MFL signals. A simplified magnetic circuit is presented to excite the FSWR; the circuit comprises two half-sized radial magnetizing ring NdFeB magnets, and because there is no need for a magnetic yoke, the device is simple and light. A single Hall sensor is used to measure the flux leakage field. A stable performance power system is designed for the NDT power supply, which is not only resistant to voltage sags, but also has very low output noise. To enhance the signal-to-noise ratio (SNR) of the MFL defects signal, a signal conditioning and processing circuit are designed to enhance the detectability of signals in MFL data. The novel and small FSWR NDT system realizes on-line testing in an environment of strong electromagnetic interference, and for the experiment with a 1.5-mm-diameter wire rope twisted by 19 wires, the minimum damage of a pit on half of a wire can be identified.     

无损检测可靠性的模糊定义及其检测概率分析

基于模糊集合理论,建立了在无损检测(NDT)可靠性分析中关于检测概率(POD)的模糊定义.引入半梯形和降岭形的隶属函数,并给出隶属度函数来描述缺陷尺寸与检测概率之间的模糊关系.在此基础上,采用NDT可靠性的对数正态格式,对检测概率进行了计算.     

Automatic weld defect detection method based on Kalman filtering for real-time radiographic inspection of spiral pipe

A method based on Kalman filtering is proposed for weld defect detection in real-time radiographic NDT of spiral pipes. The existence of the image noises and the inhomogeneity of the background contrast induce numerous false alarms. In this paper, the trajectory continuity of the defects in the image sequence is detected by Kalman filtering for the identification of true defects. Potential defect regions without continuous motion are considered as false alarms and are eliminated. Experiments are performed to demonstrate the adaptability of the proposed method. The robustness of the method is also verified under unstable detection velocity.     

船机零件的无损检测技术

分析大型船舶机械零件缺陷的危害性以及超声波、磁粉与渗透探伤在船机零件无损检测中的作用,讨论无损检测在改进船机维修模式和维修技术中的作用,并对无损检测技术在现代船机维修中的发展趋势提出了看法。     

胶接接头的无损检测

保证胶接质量的最好办法是严格控制接头制作过程中的各个环节。简要论述胶接接头的无损检测；介绍几种有前景的接头性能评价的无损检测方法。现有的大多数无损检测方法是针对缺陷的，目前对胶接接头粘附性能和内聚性能的无损检测与评价仍无稳定可靠的方法。     

尿素合成塔检测技术

综述了尿素合成塔在使用过程中可能出现的腐蚀和缺陷形态,并根据失效的可能性给出了有效的检测方法,包括宏观检查、厚度检测、磁粉检测、渗透检测、硬度检测、声发射检测、金相检查和金属磁记忆检测等技术.分别介绍了这些无损检测方法的特点,以及如何在尿素合成塔检验中进行实施.     

导弹发动机的热波无损检测

针对传统无损检测方法的局限性,把热波无损检测技术引入到导弹发动机的检测当中。介绍了该技术的基本原理和检测系统的组成。利用数值仿真手段,模拟了热波在含缺陷复合材料中的热传导过程,并研究了缺陷大小、深度、热扩散系数、加热热流密度、表面对流换热系数和表面辐射等因素对热波检测灵敏度的影响。结果表明：热渡检测技术是一种快速、高效、直观的检测方法,能够对缺陷进行精确地定位,并对缺陷的大小进行准确的判断。