Papers by Keyword: Non-Destructive Evaluation (NDE)

Abstract: Recent research in Structural Health Monitoring (SHM) showed the ability of guidedwave based sensors networks to detect, localize and classify damage in its early stage. But, most of them still require the wiring of numerous devices. To avoid this technical restraint, particularly in airborne structures, wireless SHM system offer mass and cost savings, but powering the devices remains heavy. In this paper, actuators and sensors are powered by piezoelectric microgenerators, which harvest energy from the environing mechanical stress. The efficiency of the extraction process is optimized by a non-linear processing of the piezovoltage named Synchronized Switch Harvesting. Previous work showed that such techniques provide a stand-alone power source, whose performances meet the requirements of Wireless Transmitters and Receivers. Indeed, each sensing node has to feature its own power source in order to acquire its logical autonomy and thus, provide decentralized intelligence to SHM network. Although the diagnosis will be centralized, the amount of data passed to the central core of the network should be reduced to preserve a positive energy balance of the node. Various algorithms are compared in terms of sensitivity and computational cost, the latter directly impacting the consumption.

Abstract: A method is presented to demonstrate the use of artificial neural networks (ANNs) in providing additional information regarding defects or flaws when used in conjunction with the ultrasonic A-scan method. ANNs were employed both as pattern classifiers and as function approximators to maximise the amount of data available from the temporal A-scan signal. A steel bar was modelled in 2D using ABAQUS finite element analysis (FEA) software. A single defect was introduced to the bar, modelled as a void, and parametric studies conducted to record data with the defect at various locations. An ultrasonic Lamb wave was introduced at the top of the bar. The longitudinal wave propagated along the length of the bar and was partially reflected by the defect. Multiple cases were simulated, modelling voids between 1mm and 6mm in width in various locations. Mean displacement of all the nodes at the top of the bar was recorded throughout the simulation, and features extracted from this waveform to create the data set for the ANNs. The ANNs were trained with a percentage of the data collected, selected at random, and assessed with the remaining data. The target data for the ANNs were the depth and size of the defect. The case of two separate defects was also investigated. The procedure was carried out in the same manner as for one defect, but in this case the target data for the ANNs were the depth of the first defect and the distance between the defects. A separate ANN was employed as a pattern classifier, to determine if the reflected A-scan signal represented one or two defects. The final system was tested using previously unseen data, and provided very good results both in determining the number of defects and the size and location of the defects, even with data to which noise had been added.

Abstract: In this paper a new data evaluation technique is presented for non-destructive magnetic measurements. This method is based on the multiphase hyperbolic model of magnetization and it is called model based data evaluation (MBDE) technique. The MBDE method allows us to separate the magnetic contribution of the magnetizing yoke from the measured magnetization curves. Therefore the determined magnetic properties of the tested sample are independent of the parameters of the applied magnetic yoke and the lift-off. The proposed method could become a useful tool in magnetic non-destructive evaluation (NDE).

Abstract: As stress waves decay as they pass through the pile foundation system, it is extremely challenging for all nondestructive testing methods to evaluate the pile integrity of a shaft underneath a structure. In this study, time–frequency signal analysis (TFSA) is used for signal processing and adopted to interpret the pile integrity testing signal. An experimental case with pile lengths of 58m with caps, were tested by the low strain sonic echo method. Traditional time domain analyses can not identify the pile tip response signals 58m lengths. After time-history curves are transformed into a time–frequency domain distribution, the results indicate the pile tip can be located more easily and clearly than the traditional time-domain analyses of pile integrity testing allowed for.

Abstract: Thermoelectric power coefficient measurement techniques have been developed for numerous applications to guarantee material integrity by providing a non-destructive electronic property correlation to material microstructure, phase stability, specific solute additions, and lattice strain. How the electron concentration, the effective mass, and the dominating scattering mechanisms allow for non-destructive evaluation of materials will be described. Because thermoelectric power (TEP) is dependent upon numerous variables, additional non-destructive techniques are necessary to further characterize or classify the material or weldment. The concept of an electronic metallography laboratory is developed using additional collaborative NDE technologies.

Abstract: This paper presents a basic research on a measurement of strain in the bulk of materials by using high energy white X-ray from a synchrotron radiation source of SPring-8 in Japan. A high-tensile strength steel (JIS-SHY685) was used as a specimen loaded with bending. Strain distribution in it was evaluated by the energy dispersive method using diffracted X-ray transmitted through the specimen. As a result, the internal strain of high-tensile steel of 5, 10 and 15 mm thickness could be evaluated using white X-ray which range of energy from 50 keV to 150 keV. The measurement with a high degree of accuracy was accomplished using α-Fe321 diffraction in this material. The results showed that the internal strain measurement in the depth of the order of millimeter using the high energy white X-ray is practicable at SPring-8.

Abstract: Radiography inspection (X-ray or gamma ray) is one of the most commonly used Non-destructive Evaluation (NDE) methods. More and more digital X-ray imaging is used for medical diagnosis, security screening, or industrial inspection, which is important for e-manufacturing. In this paper, we firstly introduced an automatic welding defect inspection system for X-ray image evaluation, defect image database and applications of Artificial Neural Networks (ANNs) for NDE. Then, feature extraction and selection methods are used for defect representation. Seven categories of geometric features were defined and selected to represent characteristics of different kinds of welding defect. Finally, a feed-forward backpropagation neural network is implemented for the purpose of defect classification. The performance of the proposed methods are tested and discussed.

Abstract: The scanning laser line source (SLLS) technique is a novel laser-based inspection method for the ultrasonic detection of small surface-breaking defects. The SLLS approach is based on monitoring the change in laser generated ultrasound as a laser line source is scanning over a defect. It has provided enhanced signal-to-noise performance compared to the traditional pitch-catch or pulse-echo ultrasonic methods. In this paper, an experimental method is presented to detect surface acoustic waves (SAW) with polyvinylindene fluoride(PVDF) transducer. The ultrasonic signal is converted into electric signal by piezoelectricity of the PVDF, which is attached to a micro-knife edge clamped on a metal device. The SAW are excited by employing a pulsed Nd:YAG laser on aluminum plate with artificial surface-breaking defects. The laser line source is accurately shifted by the motorized translation stage, while the PVDF is located at a fixed position on the specimen. When the laser line source is scanning over the defect, the ultrasonic signals are monitored, meanwhile the characteristic changes in the amplitude and frequency content are observed. Consequently, the position of the defect can be determined by analyzing the obtained signals. The experimental system with high sensitivity provides a detection method of small surface-breaking defects on metal and gives convincing experimental evidence for the interaction mechanism between the SAW and the surface-breaking defects.

Abstract: The apparent activation energy for rupture life sometimes changes from a high value of short term creep to a low value of long term creep. This change results in overestimation of rupture life recognized recently in advanced high Cr ferritic steels. The present study examined how to detect the decrease of activation energy in 9-12 %Cr steels with tempered martensitic lath microstructure. During aging without stress hardness of the tempered martensite microstructures remains almost constant in short term, whereas it decreases with increasing time after long term exposure. The onset of hardness drop can be a good measure of the decrease of activation energy. Causes of the hardness drop and the decrease of activation energy are discussed.

Abstract: This paper presents the perspective of the Structural Mechanics program of the Air Force Office of Scientific Research on the damage assessment of structures. It is found that damage assessment of structures plays a very important role in assuring the safety and operational readiness of Air Force fleet. The current fleet has many aging aircraft, which poses a considerable challenge for the operators and maintainers. The nondestructive evaluation technology is rather mature and able to detect damage with considerable reliability during the periodic maintenance inspections. The emerging structural health monitoring methodology has great potential, because it will use on-board damage detection sensors and systems, will be able to offer on-demand structural health bulletins. Considerable fundamental and applied research is still needed to enable the development, implementation, and dissemination of structural health monitoring technology.