复杂结构焊缝的非线性超声检测方法

振动声调制技术是一种新出现非线性超声无损检测方法. 文中简要介绍了此技术的检测原理,并对其在复杂结构焊缝质量检测中的应用进行了初步研究. 制作了小径管座角焊缝试样,分别在单频激励和扫频激励条件下进行检测. 结果表明,缺陷试样的调制强度均高于参考试样,且在特定高频频率范围内,二者差别显著,更有利于焊缝质量判别. 而采用扫频技术可快速得到合适的高频频率范围,提高检测效率. 与超声C扫描检测结果相比,采用振动声调制技术对小径管座角焊缝进行检测是可行的,但缺陷的定位定量分析等问题还需要进一步研究.     

地质雷达对京珠高速公路桥面层厚度检测的应用研究

介绍了地质雷达检测桥面层厚度的原理,应用美国GSSI公司生产的Handy scan手持地质雷达对京珠高速公路某段的三座大桥进行了无损检测,对实测采集到的地质雷达信号应用专业处理软件Radan进行数字信号处理,处理的内容包括压制随机的和规则的干扰,滤频及以最大分辨率显示实测图像,获得了桥面各层厚度变化的连续清晰图像,提取反射波参数计算了桥跨多点的各层检测厚度,得到每跨各层的检测平均厚度,同时进行了钻孔取芯检测,应用研究发现,采用中心频率为1GHz的地质雷达在混凝土结构中可探测的深度为20cm左右,属浅层地质雷达,可测得桥面结构前三层的厚度,应用效果较好;对于第四层结构,由于其距离表面较深,雷达波的衰减较为明显,检测效果不明显,可采用更低中心频率的地质雷达进行进一步的检测工作。地质雷达对于前三层结构厚度的检测结果是可信的,可作为工程质量评价的依据。     

Non-destructive evaluation of plasma sprayed functionally graded thermal barrier coatings

Acoustic emission (AE) as a non-destructive evaluation technique has recently been used in a number of studies to investigate the performance and failure behavior of plasma sprayed thermal barrier coatings. The mechanism of coating failure is complex, especially when considering the composite nature of the coating. In the present paper, the thermal shock tests with in situ acoustic emission are used to study the cracking behavior of plasma sprayed functionally graded thermal barrier coatings. Each thermal cycle consists of 8 min heating in the furnace at 1000°C and 8 min cooling from 1000°C to the room temperature by a compressed air jet. The AE signals are recorded during the quench stage. Three, four and five layer functionally graded coatings have been tested. The results show that the five layer functionally graded coatings appear to have the best thermal shock resistance in the specimens tested, because of the gradual changes in material properties. Higher AE energy counts and cumulative counts recorded by the tests are associated with the macro-crack initiation and growth. On the other hand, micro cracking and phase transformation only give rise to lower AE signals.     

智能无损评价系统

现今,无损评价技术朝着三个方向发展：现有技术的进一步改进、新兴技术的贯彻以及具有能自我检测、评估的人工智能仪器的应用,第三个发展方向将做详细介绍。对于智能一般有两种观点：分级智能与等级智能。无论基于哪种观点,智能都可以分为计算与非计算两种。计算智能能被某种算法所描述,非计算智能则不能。因此,人工智能系统或许只能基于计算智能。讨论了某个基于计算智能的人工智能系统运用在在焊接质量无损评价上的例子,其间所采用的间接技术、人工神经网络技术以及模糊逻辑技术被逐一介绍,并总结归纳了其各自的特点。     

Ultra-low noise front-end electronics for air-coupled ultrasonic non-destructive evaluation

Air-coupled ultrasonic inspection has been demonstrated to be a non-contact method of great interest in non-destructive evaluation (NDE) applications. The absence of direct contact or a liquid couplant provides this technique very attractive benefits in front of the well-known and well-developed liquid-coupled ultrasonic inspection systems. A wide range of defects can be detected by means of ultrasound coupled to and harvested from the specimen in absence of contact when using appropriate transducers designed for their operation in air.This paper presents an easy way to integrate air-coupled piezoelectric transducers in conventional ultrasonic NDE equipment. The design of a specific front-end electronics by using an ultra-low noise amplifier enables existing inspection systems to be used for the dry-coupled ultrasonic test of materials and structures. The amplifier provides the receiver with a signal-to-noise ratio large enough for good quality signal processing and imaging. System dynamic ranges of more than 100 dB are achieved.     

Lockin-ESPI interferometric imaging for remote non-destructive testing

Electronic-speckle-pattern-interferometry (ESPI) is a sensitive interferometric imaging technique that responds to changes of surface topography caused, e.g., by pressure changes or by thermal expansion. Hidden defects are revealed by the inhomogeneity of such deformation fields. Unfortunately, field distortion may also be caused by, e.g., inhomogeneous excitation. Therefore the lockin technique has been transfered to ESPI in order to enhance its sensitivity by this kind of phase-sensitive narrow-band filtering where finally a self-normalised phase-angle image is obtained. Such an image displays features which are usually deeply hidden in noise, as will be shown on various examples.     

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.     

镁合金超声检测的相关增强小波去噪技术

提出了一种基于相关增强与小波阈值相结合的超声信号去噪方法,将该方法用于AZ91镁合金的超声检测能够有效地去除噪声,提高检测精度.由于同类缺陷信号之间相关性较大,因此对同类缺陷的超声信号进行相关处理能够增强缺陷信号;结合小波分析的多分辨分析特点,从频率和时域对增强后的信号进行阈值处理,最终获得了良好的去噪效果.实验结果表明:该方法能够有效去除由粗晶散射引起的结构噪声,对微弱缺陷信号的检测是很有效的,且灵活便捷.     

Study on defect classification in multi-layer structures based on Fisher linear discriminate analysis by using pulsed eddy current technique

Pulsed eddy current (PEC) is an emerging non-destructive testing technique with wide application potential. In this study, defect parameter identification in multi-layer structures is examined by using the PEC technique, and a Fisher linear discriminate analysis (FLDA)-based defect classification method is proposed. Defect localization and shape identification are investigated, and defects on the surface and subsurface of the third layer are discriminated. The time domain characterization method is introduced and researched by using the peak time and zero-crossing time of PEC response signals, the principal component analysis algorithm and the FLDA method. The feature extraction results of the three methods are used as the input values of support vector machine for defect classification and feature extraction, and the classification methods are compared. Theoretical analysis and experimental results show that the proposed method can contribute to effective classification for defect parameter identification.     

Concrete damage evolution analysis by backscattered ultrasonic waves

In the case of in situ non-destructive evaluation of concrete, the one side access and the lack of knowledge of structure depth often increase the difficulties to control the material. The backscattered ultrasonic waves' exploitation can be a solution. Scatterers present in the medium return information resulting from interaction with the incident wave. We study the modelling of the backscattered waves and their experimental measurement. The signal model is adapted to simulate the concrete damage incidence on the ultrasonic waves. The limits of its exploitation are deduced. Experimentally, concrete specimens were examined for five states of thermal damage. According to the model the backscattered waves' attenuation evolves with the damage. The sensitiveness of an ultrasonic indicator to microstructural evolutions is analysed.     

Bispectra-based impact acoustic non-destructive evaluation

This paper presents a novel cost-effective non-destructive evaluation (NDE) method for detecting defects in tiled-walls of high-rise buildings. The method is based on impact acoustic technique which identifies the bonding quality of tiles by analyzing the acoustic vibration signals generated by tapping a structure with an impacting device. However, the basic impact acoustic method, which uses a single impacting device, can only provide a single-point inspection and will take time to inspect a large high-rise building. To speedup the evaluation process, impacting the structure simultaneously with multiple impacting devices are being developed to increase the coverage area of the inspection. However, the sound signals generated by multiple impacting devices are more complicated than those from a single impacting device. Through the analysis of the raw sound data, this paper proposes a regional integrated bispectra method to extract the feature vector and a threshold method for classifying the bonding quality of tiles for multiple impacting devices. The experimental results confirm the validity of the proposed method.     

Non-destructive determination of residual stress state in steel weldments by Magnetic Barkhausen Noise technique

The purpose of this study is non-destructive determination of residual stresses in the welded steel plates by Magnetic Barkhausen Noise (MBN) technique. A MBN-stress calibration set-up and a residual stress measurement system with scanning ability were developed. To control the accuracy and the effectiveness of the developed system and procedure, various MBN measurements were carried out. The MBN results were verified by the hole-drilling method. Microstructural investigation and hardness measurements were also conducted. It was concluded that if the calibration procedure including the effect of microstructure is appropriate then MBN is a very promising method for non-destructive, fast and accurate prediction of residual stresses in the welded plates.