NDT 20 years on — a personal opinion

An outline is given of the ways in which recent advances in techniques such as digital signal processing may be expected to lead to improved NDT instrumentation and methods over the next 20 years. Different changes are envisaged in the two distinct areas of in-service inspection and manufacturing inspection.     

NDI of interfaces in coating systems using digital interferometry

This paper describes a new application of two laser interferometry techniques to the non-destructive inspection (NDI) of coated surfaces. The purpose is to detect interfacial disbond between the coating and the substrate. Debonding is detected by properly exciting the surface of the object under inspection in such a way that the interference fringe pattern is modified rendering the disbond readily visible. The fringe patterns resulting from the associated images were captured using electronic speckle pattern interferometry (ESPI) and shearography. Image processing techniques are applied to enhance the detection and better definition of the debonded layer. Some results and discussions are presented to illustrate the applicability of these two optical techniques to thermal barrier coatings.     

NICKEL ALUM1NIDES - NEW ADVANCED ALLOYS

New advanced alloys based on Ni Al intermetallic compounds have been introduced. This paper deals with the potential applications for the new alloys, the status of their processing technology, property data, and the commercial sources for the material. The processing technology includes conventional techniques, innovative near-net-shape techniques, and powder metallurgy and superplastic forming. Tensile and creep properties, as influenced by processing techniques, microstructure, and cold work, are presented.     

A Design Study of an Automatic System for On-line Detection and Classification of Surface Defects on Cold-rolled Steel Strip

In collaboration with the British Steel Corporation, Sira Institute Ltd is currently pursuing the development of sophisticated equipment for the automatic inspection of cold rolled steel strip. This paper will examine the special difficulties associated with the application of optical inspection techniques to a dull metallic surface at line speeds of up to 50 ms m 1. The development work has centred on the use of high-speed scanned laser systems, unique in their ability to provide diffraction-limited resolution with intrinsically high optical throughput. In order to detect and delineate all significant defects down to the most subtle imperfections, the polar scattering characteristics of the surface have been exploited and optimum signal processing techniques are being identified. The paper will discuss some of the optical, mechanical and electronic constraints imposed by the inspection requirement.     

Reducing the absorbed dose in analogue radiography of infant chest images by improving the image quality, using image processing techniques

Radiographic inspection is one of the most widely employed techniques for medical testing methods. Because of poor contrast and high un-sharpness of radiographic image quality in films, converting radiographs to a digital format and using further digital image processing is the best method of enhancing the image quality and assisting the interpreter in their evaluation. In this research work, radiographic films of 70 infant chest images with different sizes of defects were selected. To digitise the chest images and employ image processing the two algorithms (i) spatial domain and (ii) frequency domain techniques were used. The MATLAB environment was selected for processing in the digital format. Our results showed that by using these two techniques, the defects with small dimensions are detectable. Therefore, these suggested techniques may help medical specialists to diagnose the defects in the primary stages and help to prevent more repeat X-ray examination of paediatric patients.     

基于TRIZ理论的轨检小车机械结构创新设计

目的针对轨检小车机械结构存在的缺陷,应用TRIZ理论进行创新设计。方法按提出的基于TRIZ理论的已有产品的改进创新设计框架,对轨检小车的机械结构进行组件分析,建立功能模型,结合轨检小车使用过程中存在的问题和功能分析的结果找到技术系统的薄弱点,应用TRIZ理论方法对功能模型存在的问题进行解决,高效地产生创新方案。结论形成了基于TRIZ理论的已有产品的改进创新设计框架,应用此方法对轨检小车的机械结构进行了创新设计,解决了轨检小车在实际使用中存在的问题。     

A Comparative Study of Enhanced Infrared Image Processing for Foreign Object Detection in Lightweight Composite Honeycomb Structures

The interest toward lightweight composites in the aeronautical industry grows year by year. The challenge is the identification and characterization of defects by using an integration of different techniques. The use of the infrared thermography (IRT) method for the inspection of lightweight composites is poorly documented in the open literature, due to the low heat diffusion through the honeycomb cores. In this study, IRT was used to retrieve the unknown positions of internal inserted objects in three different lightweight composite structures, by using three new thermal image processing integration methods. The corresponding post-processed results were compared against the traditional principal component thermography and pulsed phase thermography image processing techniques. The comparison showed that the integrated signal smoothing processing enhanced the image quality compared to the established techniques. Then, a thermal-physical analysis corresponding to the experimental results was conducted, in order to explain the experimental results. Finally, the advantages and disadvantages of the different presented methods when applied on the different lightweight composite structures were summarized.     

Automated vision system for IC lead inspection

An automated vision system for the inspection of Small Outline Package (SOP) and Dual In-Line Package (DIP) IC lead flaws is presented. This system consists of a special lighting and image acquisition system, a series of processing techniques to measure the lead coplanarity and to inspect the skewed lead frame. In this research, a new algorithm for determining the reference plane of an IC and measuring the coplanarity was developed, and compared with a traditional algorithm. Experimental results show that the proposed image acquisition system is helpful for IC lead image acquisition and the proposed lead inspection system can effectively detect skewed lead ICs and faulty coplanarity ICs. In addition, the proposed algorithm for finding the reference plane results in better performance in processing speed and detection accuracy than the traditional algorithm.     

Compression moulding of glass and polypropylene composites for optimised macro- and micro- mechanical properties-1 commingled glass and polypropylene

The continuing desire in the automotive industry to reduce cost and weight while increasing safety requires innovative materials and processing routes. Glass-mat-reinforced thermoplastics have been used to produce semi-structural components but a higher and aligned glass fibre content is required in moulding materials for structural applications. Experimental design was used to investigate the non-isothermal processing of commingled fabrics which were woven from yarns of intimately mingled glass and polypropylene fibres. Processing models were generated by regression techniques to predict laminate properties over a range of processing conditions. Void contents were measured by image analysis techniques. Preheat temperature had the greatest effect on laminate flexural properties and porosity. A compaction time of 54 s was required to consolidate, cool and reduce the void content in laminates. A two-fold increase in stiffness was found compared with equivalent glass-mat-reinforced thermoplastic laminates. The intimate distribution of matrix and reinforcement reduced moulding pressures by a factor of 10.     

Erhöhung der Verschleißfestigkeit von Elastomerverarbeitungsmaschinen durch innovative Beschichtungsverfahren

Increasing the resistance to wear of elastomer processing machines by innovative coating processes A goal of the subsequent work is the evaluated of selected surface coating processes with respect to the attainable abrasion characteristics of the generated layers regarding to their suitability for the abrasion protection of elastomer processing equipment (e.g. interior kneading machines). Additionally the specifications of various commercial coating companies were layers compared to data concerning to the wear resistance of the created sections. On this base own experimental tests are performed dedicated to designated application cases and were evaluated by an abrasion test on its wearing properties. Apart from classical deposition‐welding, the Plasma‐Transferred‐Arc process, above all the innovative thermochemical techniques were applied. Due to of their steadily increasing market shares, particularly the arc and HVOF‐Spraying got in the center of attention thereby.     

Innovative Fügeverfahren zur Herstellung von Al‐Leichtbaustrukturen im Schienenfahrzeugbau

Innovative joining techniques for creating light‐weight aluminium structures in railway vehicle production Starting from the development in railway vehicle manufacture, the authors describe today's materials, types of construction, joining techniques, joint and weld types, filler materials and regulatory documents. In addition, they present new processing equipment and engineering principles. On the basis of these findings, they show the perspectives of new construction principles for light‐weight aluminium structures and identify the requirements, the new joining techniques have to meet. The innovative joining techniques, such as: • electron‐beam welding under atmosphere (NV‐EBW) • Friction Stir Welding (FSW) • Laser beam welding (LBW) • Laser beam/electric arc hybrid welding (LBW/LB) are studied with regard to their • properties and particularities • advantages and disadvantages • available equipment • possible applications for railway vehicle manufacture. In addition, costs are compared and an analysis of the benefit is made. Finally, the authors give an outlook on possible applications of the innovative procedures.     

钢管漏磁在线检测技术的研究

介绍了钢管漏磁检测的基本原理，对钢管在线漏磁检测系统进行总体设计。分析了漏磁场理论模型和讨论了影响缺陷漏磁信号的一些因素及补偿方法，针对该系统的特点设计了高速数据采集板，借助Windows系统平台，在所研制硬件的基础上，采用多线编程和虚拟设备驱动技术编制了数据采集、分析、状态显示、实时控制等面向对象、多功能模块化的软件，详细叙述了漏磁信号数据分析的方法和过程。这种系统具有检测速度快、数据吞吐量大、效率高、钢管缺陷分辨率高等特点。     

Fabrication of PDMS-Based Nitrite Sensors Using Teflon AF Coating Microchannels

This study shows a novel polydimethylsiloxane (PDMS) nitrite sensor using liquid-core waveguide techniques. A 6 cm straight and Teflon AF 1601S coated PDMS microchannel (600 mum width and depth) replicated from a SU-8 master and sealed with a glass slide with the same coating. This formed a low index of refraction channel in which a high index aqueous solution was flowed. Light generated by a fiber-coupled tungsten halogen lamp propagated by total internal reflection to the end of the channel where the light was detected using a palm-size CCD array spectrometer. The result shows a dramatic difference between channels with and without a Teflon coating. The absorbance response of this sensor varies linearly with concentration and adheres to Beer's law. Moreover, calculations of absorbance using this sensor are in excellent agreement with a commercial spectrometer. This innovative technique provides a potentially low-cost and high efficient approach to fill the inspection technology gap between in situ and laboratory analyses. It is believed that the novel PDMS-based nitrite sensor is expected to give an impact to the aqueous inspection and to create a highly value-added technology in optical test and measurement industry.     

Noncontact, high-resolution ultrasonic imaging of wood samples using coded chirp waveforms

A noncontact ultrasonic inspection technique has been developed to study the properties of wood samples in air. The system makes use of two broad bandwidth capacitive transducers, combined with signal processing techniques. A coded chirp signal was used in the current application to provide a waveform that could be postprocessed to provide sufficient sensitivity for transmission across samples of wood. It will be shown in this paper that the signal-to-noise ratio (SNR) can be greatly improved using two signal recovery techniques, namely pulse compression and swept frequency multiplication (SFM). A simulation of both techniques is presented and compared to experimental data. As will be seen from the experimental results, it is possible to perform noncontact ultrasonic experiments to extract a range of useful information such as ring density and the presence of microcracks.     

Digital ultrasonic image construction using electronic ordered dither techniques

The use of a digital microprocessor based system for the acquisition of ultrasonic C-scan information is investigated. The C-scan information is displayed on a binary display device using electronic ordered dither techniques to represent gray levels. The digital system with a binary display increases system flexibility and yields better reproducibility and constant image quality independent of the display medium. Images may be stored on magnetic tape or disk for later retrieval and image processing. The techniques which are described allow for image magnification and a reduction in scan time by replacing the mechanical linkage between the scanner and the display with digital signals. A detailed comparison is made between two dither signals, and the advantages of each are discussed. The combination of digital signal processing and imaging techniques produces results which utilize the capabilities of ultrasonic inspection to the point where the transducer becomes the limiting factor.     

An Innovative Microwave-Imaging Technique for Nondestructive Evaluation: Applications to Civil Structures Monitoring and Biological Bodies Inspection

Industrial and biomedical applications of microwave-imaging techniques based on inverse scattering integral relations become more and more important. In order to reduce computational costs and hence allow a quasi real-time processing, an innovative inversion procedure based on the use of a genetic algorithm and on the Sherman-Morrison-Woodbury matrix inversion method is presented. Selected numerical results concerning various scenarios and scatterer dimensions are presented in order to give some indications on the effectiveness and also current limitations of the proposed approach     

Nuclear NDT development at Harwell

A review is presented of nuclear-oriented NDT development work at Harwell, illustrating the synergy between this and the National NDT Centre's non-nuclear programme. Most of the work in recent years has been concerned with automated ultrasonic inspection techniques for the proposed Sizewell ‘B’ PWR pressure vessel, and Harwell's part has been to develop the time-of-flight diffraction method (TOFD) as a stand-alone technique for defect detection and sizing. The value of this technique, which originated in the Centre's non-nuclear work, has been amply demonstrated in trials involving thick plate weld and nozzle specimens. Currently the main item in the nuclear programme is the improvement of ultrasonic inspection capability for austenitic castings and welds, for both PWR and fast reactor applications, by means of advanced scanning and signal processing techniques. In examining this and other current interests, the strong influence of theoretical modelling is noted. The development o of automatic defect classification techniques makes use of the image analysis resources at Harwell. Future nuclear-oriented NDT work is expected to extend the current developments, with emphasis on ease of technology transfer, and exploitation of new techniques, including electromagnetic and optical generation of ultrasound.     

超声波技术在食品生产检测和食品安全检测中的应用进展

超声波这项新技术被用于研究和诊断领域已经有很多年了。本文分别例举了超声波技术在乳品品质检测,肉制品品质检测,面粉品质检测,果蔬产品品质检测,添加剂分析,农药残留分析和金属元素分析上的应用。旨在对其目前在食品生产领域和食品安全检测领域中的应用及其进展进行介绍,为新检测技术研究者提供参考资料。     

Infrared Lock-in Thermography Crack Localization on Metallic Surfaces for Industrial Diagnosis

Optical lock-in thermography with a modulated laser excitation is used for the qualitative assessment of surface cracks in metallic samples. In order to identify and localize an open defect, a novel dedicated image processing of the recorded IR amplitude sequence is proposed. The obtained results demonstrate the potentiality of active lock-in thermography as a contactless measurement tool for the localization of breaking cracks located into specific regions difficult to reach by other conventional non-destructive testing (NDT) techniques such as eddy currents or ultrasound techniques. Crack localization without a prior preparation of the inspected surface can be a possible alternative to penetrant inspection in industrial processes. Various applications illustrating the proposed procedure are presented.     

On the considerations for the design of an automated aircraft sheet metal component production loft generation system

In this paper an ambitious production loft generation system (PLGS) is created to incorporate innovative and unique features of aircraft sheet metal component (SMC) lofts meeting the stringent standards of aircraft industry owing to non-availability of suitable public domain software. This system is fully tested and validated with the support of the aircraft industry. It provides for automated blank layout generation based on surface models utilizing some unique algorithms and vector logics created through research and development over a period of 15 years taking into account the material properties, flow direction and plasticity and strives to eliminate post forming trimming operations by utilizing the databases of the aircraft industry. For the first time such a custom built system is created, which incorporates industrial process data and provides a host of processing options, together with various design cum production features like mould lines, joggles, bend relief, tooling holes, pilot holes, cut outs, chamfers/fillets, inspection angles etc. and displays features needed for quality assurance as essential ingredients. It has inbuilt, intelligent, high efficiency processing features such as the utilization of symmetry facilitating fractional processing of the SMC. This paper includes a brief account of various issues related to the chronology of design of the systems, implementation of the design options, intricacies of methods deployed, their efficacy and combinatorial suitability. Crucial ground breaking new algorithms relevant to the production features are also elucidated in this paper.