NDE: An effective approach to improved reliability and safety. A technology survey

Technical abstracts are presented for about 100 significant documents relating to nondestructive testing of aircraft structures or related structural testing and the reliability of the more commonly used evaluation methods. Particular attention is directed toward acoustic emission; liquid penetrant; magnetic particle; ultrasonics; eddy current; and radiography. The introduction of the report includes an overview of the state-of-the-art represented in the documents that have been abstracted

Characterisation of surface and sub-surface discontinuities in metals using pulsed eddy current sensors

Due primarily to today's rigorous safety standards the focus of non-destructive testing (NDT) has shifted from flaw detection to quantitative NIDT, where characterisation of flaws is the objective. This means information such as the type of flaw and its size is desired. The Pulsed Eddy Current (PEC) technique has been acknowledged as one of the potential contenders for providing this additional functionality, due to the potential richness of the information that it provides. The parameters mainly used to obtain information about the detected flaws are the signal's peak height and arrival time. However, it has been recognised that these features are not sufficient for defect classification. In this research, based on a comprehensive literature survey, the design of PEC systems and the interpretation of PEC signals, mainly for flaw classification, are studied. A PEC system consisting of both hardware and software components has been designed and constructed to facilitate the research work on PEC signal interpretation. After a comparative study of several magnetic sensing devices, probes using Hall device magnetic sensors have also been constructed. Some aspects related to probe design, such as coil dimensions and the use of ferrite core and shielding have also been studied. A new interpretation technique that uses the whole part of PEC responses and is able to produce more features has been proposed. The technique uses Principal Component Analysis (PCA) and Wavelet Transforms, and attempts to find the best features for discrimination from extracted time and frequency domain data. The simultaneous use of both temporal and spectral data is a logically promising extension to the use of time domain only with the signal-peak-based technique. Experiments show that the new 1 technique is promising as it performs significantly better than the conventional technique using peak value and peak time of PEC signals in the classification of flaws. A hierarchical structure for defect classification and quantification has been presented. Experiments in the project have also shown that the signal-peak-based technique cannot be used for flaw detection and characterisation in steels, both with and without magnetisation. The new proposed technique has shown to have potential for this purpose when magnetisation is used. The new technique proposed in the report has been successfully used for ferromagnetic and non-ferromagnetic materials. It has also been demonstrated that the new proposed technique performs better in dynamic behaviour tests, which shows its better potential for on-line dynamic NDT inspection which is required in many industrial applications. In addition to testing calibrated samples with different discontinuities, a study case using an aircraft lap joint sample from industry has further supported the statement regarding the potential of the new technique.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

An electromagnetic imaging system for metallic object detection and classification

PhD ThesisElectromagnetic imaging currently plays a vital role in various disciplines, from engineering to medical applications and is based upon the characteristics of electromagnetic fields and their interaction with the properties of materials. The detection and characterisation of metallic objects which pose a threat to safety is of great interest in relation to public and homeland security worldwide. Inspections are conducted under the prerequisite that is divested of all metallic objects. These inspection conditions are problematic in terms of the disruption of the movement of people and produce a soft target for terrorist attack. Thus, there is a need for a new generation of detection systems and information technologies which can provide an enhanced characterisation and discrimination capabilities. This thesis proposes an automatic metallic object detection and classification system. Two related topics have been addressed: to design and implement a new metallic object detection system; and to develop an appropriate signal processing algorithm to classify the targeted signatures. The new detection system uses an array of sensors in conjunction with pulsed excitation. The contributions of this research can be summarised as follows: (1) investigating the possibility of using magneto-resistance sensors for metallic object detection; (2) evaluating the proposed system by generating a database consisting of 12 real handguns with more than 20 objects used in daily life; (3) extracted features from the system outcomes using four feature categories referring to the objects’ shape, material composition, time-frequency signal analysis and transient pulse response; and (4) applying two classification methods to classify the objects into threats and non-threats, giving a successful classification rate of more than 92% using the feature combination and classification framework of the new system. The study concludes that novel magnetic field imaging system and their signal outputs can be used to detect, identify and classify metallic objects. In comparison with conventional induction-based walk-through metal detectors, the magneto-resistance sensor array-based system shows great potential for object identification and discrimination. This novel system design and signal processing achievement may be able to produce significant improvements in automatic threat object detection and classification applications.Iraqi Cultural Attaché, Londo

The Application of Electromagnetic NDT Method to the inspection of Non- ferrous Cast Materials

Inspection of non-ferrous cast material is routinely carried out looking for casting defects inherent for the manufacturing process. The NDT methods employed are Radiography and Ultrasonics, primarily for sub-surface or internal defects and Penetrants fo r surface breaking defects. Electromagnetic techniques have not been used on cast material except maybe for conductivity determination. This limitation resulting fi7om the surface roughness normally associated with cast surfaces and the fact the other techniques mention above have been very successful in finding and evaluating the discontinuities sought. The possible application of Electromagnetic techniques on surfaces in the as-cast condition of non-ferromagnetic material came about because of specific problems experienced by industry. Two major investigations were offered namely; 1) Investigation of CNC material - CuNiCr [1.6%Cr] castings exhibiting oxide entrapment in the form of networks. 2) Investigation of NAB - Nickel Aluminium Bronze exhibiting selective phase corrosion on immersion in seawater. The detection and measurement of both oxide entrapment and phase selective corrosion was difficult and in cases impossible with conventional NDT methods employed for quality control of these material/component types. Time of Flight DiMaction Ultrasonics did give some 50% detectability of phase selective corrosion, but the method was found to be expensive and very time consuming. The metallurgical properties of the material and morphology of the defects have been studied for both Cupro Nickel Chromium and Nickel Aluminium Bronze cast alloys. An investigation was then conducted to study the effects of eddy current signals and their potential in detecting, both linear and cluster type defects which were predominantly interdendritic with some reported as intergranular in nature. For inspecting Cupro Nickel Chromium castings two successful eddy current methods have been developed. Detection of surface flaws was achieved by high frequency [2MHzj examination and subsurface flaws by using low frequencies [1--'IKHz] but using specifically developed sensors that provided good penetration but maintained sensitivity to the fine defects. In the case of Nickel Aluminium Bronze material, the investigation was to look at electromagnetic techniques, which best utilizes the inherent feature of permeability/conductivity associated with this non- ferromagnetic material and any changes that phase selective corrosion may produce. Some meaningful results were obtained using a combination of edd'y current excitation with detection via magneto -re s istive sensors. Testing through 30-40mm of material to detect small magnetic variation produced by only 1-2 mm of corrosion penetration was difficult to quantify. Detection and assessment however appeared hopeful when examination was carried out from the corroded surface. With quantifiable samples a meaningful technique using eddy current excitation and magneto-resistive sensor for detection can be developed

A Multidisciplinary Analysis of Frequency Domain Metal Detectors for Humanitarian Demining

This thesis details an analysis of metal detectors (low frequency electromagnetic induction devices) with emphasis on Frequency Domain (FD) systems and the operational conditions of interest to humanitarian demining. After an initial look at humanitarian demining and a review of their basic principles we turn our attention to electromagnetic induction modelling and to analytical solutions to some basic FD direct (forward) problems. The second half of the thesis focuses then on the analysis of an extensive amount of experimental data. The possibility of target classification is first discussed on a qualitative basis, then quantitatively. Finally, we discuss shape and size determination via near field imaging

Preliminary study of an innovative Non-Destructive Testing technique concept for detection of surface cracks in non-ferromagnetic materials

The research presented in this thesis is framed in the preliminary study for the development of an innovative Non-Destructive Testing (NDT) technique concept based on deposition of a ferrofluid consisting of magnetic nanoparticles in the test-piece surface. The proposed technique is applicable to inspection of any type of materials except to ferromagnetic materials. Thus, it is specially suited to detect surface defects in a wide range of materials typically used in aerospace applications, i.e., non-ferromagnetic materials like aluminum alloys or composite materials like CFRP or GFRP. The proposed technique aims at meeting the requirements of NDT end-users in the form of a significant reduction of surface inspection costs, as compared with the most commonly used techniques at present day, aside from visual inspection.La investigacio presentada en aquesta tesi s’emmarca en l’estudi preliminar d’un concepte innovador per al desenvolupament d’una tècnica d’assajos no destructius (NDT). Aquesta tècnica es basa en la deposiciió d’un ferrofluid format de nanopartícules magnètiques sobre la superfície de la peça de prova. La tecnologia proposada és aplicable per a la inspecciió de qualsevol tipus de materials excepte els materials ferromagnètics. Així doncs, és especialment adequat per detectar defectes en la superfície d’una amplia gamma de materials utilitzats típicament en aplicacions aeroespacials, és a dir, materials no ferromagnètics com són els aliatges d’alumini o materials compostos com els CFRP o els GFRP. La tècnica proposada te com a objectiu el compliment dels requisits tècnics dels usuaris d’NDT aconseguint una reducció significativa dels costos d’inspecció, en comparació ́amb les tècniques més utilitzades en l’actualitat, a part de la inspecció visual

Development of an ultrasonic NDE&T tool for yield detection in steel structures

Nondestructive Evaluation and Testing (NDE&T) is a commonly used and rapidly growing field that offers successful solutions for health assessment of structures. NDE&T methods have gained increasing attention in the last few decades especially with the contribution of the advancements in computer and instrumentation technologies. The applications of numerous NDE&T methods in civil engineering mostly focus on material characterization and defect detection. Techniques for nondestructively identifying the stress state in materials, on the other hand, mostly rely on the Theory of Acoustoelasticity. However, the sensitivity and the accuracy of acoustoelasticity are affected by several factors such as the microstructure of the material, temperature conditions, and the type, propagation and polarization directions of the signals used. This dissertation presents the results of an experimental study that investigates the changes in the characteristics of ultrasonic signals due to the applied stresses. Using a specially built testing system, ultrasonic signals were acquired from four different groups of steel specimens subjected to uniaxial tension below and above the yield stress of the material. The experimental database was first analyzed in terms of the acoustoelastic theory. Then, well known Digital Signal Processing (DSP) methods were used to calculate a total of seven time and frequency domain characteristics of the first three echoes of the acquired signals. The investigated time domain parameters were the peak positive amplitudes and the signal energies of the echoes, while the peak amplitude of the Fast Fourier and Chirp-Z Transforms, peak and peak-to-peak amplitudes and the root mean square of the Wavelet coefficients were used for the spectral analyses. Even though the acoustoelastic effects can be very small for certain measurement cases and they can be influenced by several other factors, clear distinctions between prior to and post yielding were observed for all investigated time and frequency domain parameters. The results were further analyzed with statistical methods and Receiver Operating Characteristics (ROC) curves in order to investigate the potential of the presented study for being used as a nondestructive testing tool for yield detection in steel structures

Nondestructive Testing of Turbomachinery Components

SealsPg. 161-166Nondestructive evaluation is becoming increasingly important in determining the quality of materials and fabrications used in the manufacture and maintenance of rotating machinery. NDE has long been used as a tool for failure analysis. However, more and more techniques are being incorporated as required steps in manufacturing to ensure defect-free parts. NDE can be defined as a science that incorporates methods of detecting and measuring the major properties and performance capabilities of materials, parts, assemblies, equipment and structures using techniques that do not impair serviceability. NDE uses a variety of probing techniques to assist in the discovery of hidden faults and properties of materials and products. Since most of the techniques used in nondestructive evaluation are based on well-established principles, the proper choice and application of the correct method or methods will determine the final usefulness of the examination. Each of these common classical "Big Five" NDE techniques are reviewed along with their capabilities and shortcomings. In addition, some of the more recent developments in evaluation methods are presented