NDT Applications Research Articles

Perbandingan Antara Neuro Developmental Treatment (NDT) Dengan Kombinasi NDT Dan Sensory Integration Untuk Meningkatkan Keseimbangan Berdiri Pada Anak Berkebutuhan Khusus

Abstract: Comparison of NDT, Combined NDT & SI, Standing-Balance. There upon, the purposes of the study are: (1) to determine the effects of NDT in the standing- balance trainings, (2) to determine the effects of combined NDT and Sensory Integration application in standing-balance training, (3) to compare the effects of treatment a combined NDT and sensory integration application versus sole NDT application in standing-balance training for children with special needs. The study is a pre and post-test experimental study design that compares two treatment groups. The first group received solely the NDT applications only while the other one received a combined NDT and sensory integration approach as the treatments. Sixteen Balance Test was used as a measurement instruments, which were conducted prior to and following the treatments in each group. Data were analyzed with the use of the parametric pair wise comparison test (paired sample t-test) and a parametric test(independent sample t-test) was used to investigate the compatibility of the data in the two groups before treatments. The last and above test was conducted adjacent to the fact that normal data distribution was founded. The study results are: (1) a sole NDT application improves the standing-balance ability amongst the children (p = 0.000). (2)The combination of NDT methods and Sensory Integration improves the standing- balance ability amongst children with special needs (p = 0.000). (3) The combination of NDT methods and Sensory Integration is proven to be better in developing standing- balance ability than just sole applications of NDT methods; in terms of improvingstanding-balance ability (p = .0.002) within children with special needs

Ultrasound imaging of immersed plates using high-order Lamb modes at their low attenuation frequency bands

This paper focuses on the use of a Lamb wave-based methodology for ultrasound imaging of immersed plate structures. In these cases Lamb waves can be strongly attenuated due to leaky waves and viscous losses in the liquid, but there are low attenuation frequency bands that may be used for NDT applications. Experimental measurements were conducted to validate the existence of these low attenuation frequency bands, which were also theoretically predicted for some propagation modes, between the frequencies-thickness products of 0.5MHzmm and 9.0MHzmm. Using a 5MHz linear-array and phased-array techniques, A1 and S1 modes are used to obtain images of an immersed aluminum plate with artificial defects. The signals are post-processed in order to select the desired propagation mode and to obtain an image with dynamic focusing in reception. While the A1 mode is strongly attenuated, the S1 mode, at 3.4MHzmm, can be used to detect and localize defects in the immersed plate.

Development of a 55 μm pitch 8 inch CMOS image sensor for the high resolution NDT application

A CMOS image sensor (CIS) with a large area for the high resolution X-ray imaging was designed. The sensor has an active area of 125 × 125 mm2 comprised with 2304 × 2304 pixels and a pixel size of 55 × 55 μm2. First batch samples were fabricated by using an 8 inch silicon CMOS image sensor process with a stitching method. In order to evaluate the performance of the first batch samples, the electro-optical test and the X-ray test after coupling with an image intensifier screen were performed. The primary results showed that the performance of the manufactured sensors was limited by a large stray capacitance from the long path length between the analog multiplexer on the chip and the bank ADC on the data acquisition board. The measured speed and dynamic range were limited up to 12 frame per sec and 55 dB respectively, but other parameters such as the MTF, NNPS and DQE showed a good result as designed. Based on this study, the new X-ray CIS with ∼ 50 μm pitch and ∼ 150 cm2 active area are going to be designed for the high resolution X-ray NDT equipment for semiconductor and PCB inspections etc.

Investigation of the coupled Lamb waves propagation in viscoelastic and anisotropic multilayer composites by Legendre polynomial method

In this paper, the attenuation of guided waves in damped multilayered arbitrary anisotropic composite laminates is investigated using a Legendre orthogonal polynomial approach. The laminate is made of the graphite–epoxy composite material with the layering sequence [0/ϕ/0]. The validity of the polynomial approach is illustrated through a comparison with exact solution obtained from the Stiffness matrix method and a comparison with earlier known Lamb wave solution of pure elastic multilayered plate. The dispersion and attenuation of coupled Lamb waves with different layering sequences are investigated. The viscous effect on dispersion curves is shown. The combination of frequencies and modes with minimum attenuation in high and low frequencies are determined. These frequencies and modes are of great importance for NDT applications since they play a critical role in the selection of the optimal inspection frequencies.

Comparing cone beam laminographic system trajectories for composite NDT

We compare the quality of reconstruction obtainable using various laminographic system trajectories that have been described in the literature, with reference to detecting defects in composite materials in engineering. We start by describing a laminar phantom representing a simplified model of composite panel, which models certain defects that may arise in such materials, such as voids, resin rich areas, and delamination, and additionally features both blind and through holes along multiple axes. We simulate ideal cone-beam projections of this phantom with the different laminographic trajectories, applying both Simultaneous Iterative Reconstruction Technique (SIRT) and Conjugate Gradient Least Squares (CGLS) reconstruction algorithms. We compare the quality of the reconstructions with a view towards optimising the scan parameters for defect detectability in composite NDT applications.

Inspection of notch depths in thin structures using transmission coefficients of laser-generated Lamb waves

The non-contact feature of the Laser/EMAT ultrasonic (LEU) technique is attractive for its NDT applications. However, it is challenging to apply it in thin structures because of the difficulties in the signal interpretations. In this work, the LEU technique is used to inspect the notch depths in thin steel plates. A Continuous Wavelet Transform (CWT)-based algorithm is developed to calculate the transmission coefficients of laser-generated Lamb waves. The effect of varying notch depths on Lamb waves’ transmission coefficients is investigated both numerically and experimentally. The transmission coefficients of laser-generated Lamb waves calculated using CWT have been used successfully to predict the notch depths in thin structures.

The aircraft structural elements corrosion study using strain gauge method and pulse video thermography

Simultaneous influence of corrosion, static and dynamic loads on the elements of aircraft structures influence to a large extent their mechanical properties and the foreseen length of their service. The paper presents the influence of corrosion on physical and mechanical properties of the test bars made from materials for a wide range of applications which are used in aircraft structural elements manufacturing. Study comprises laboratory testing of bars for the simultaneous influence of corrosive environment, static and dynamic load. The problems are pinpointed regarding the use of strain gauges for continuous monitoring of the condition in real time. In addition, this paper deals with a modern non-destructive testing and evaluation system (NDT&E), whose operation is based on thermal image processing. Thermographic method has been used to detect a hidden corrosion in the aircraft structure in real life. The study results have shown the possibility of NDT application in simple and quick detection of areas affected by corrosion that are visually invisible.

Optimized microwave excitation probe for general application in NDT of wall thinning in metal pipes of arbitrary diameter

Generalized approaches to developing a microwave NDT for flaws inside an arbitrary diameter pipe through optimizing a microwave-exciting probe were investigated. A microwave probe obtained from a parameter-optimizing scheme based on transmission characteristics is proposed. Three-dimensional finite element simulation of five microwave probes indicates that a larger optimization parameter enables reduced microwave reflection, as well as improved single-mode propagation inside the pipe as compared with conventional probes. Experimental verification, using straight brass pipes of various diameters confirmed that the optimized microwave probe exhibits a larger signal-to-noise ratio for internal flaws when compared with conventional probes, thereby validating the new optimization parameter.

An Ultrasonic Pulse Velocity Test on Fly-Ash Based Geopolymer Concrete in Frequency Domains

The Non-Destructive Test techniques on concrete, which can assess the properties of materials without damages, have been developed as the deteriorations of existing structures increase. Among them, the ultrasonic pulse velocity (USPV) method is widely used because it can investigate the states of one material for a long time and repeatedly. However, there have been few researches on the NDT application to geopolymer concrete which is environment friendly construction material without any cement. This paper investigates the variations of ultrasonic pulse velocity and peak frequency of geopolymer concrete under monotonically increasing loads to assess the material conditions with various compressive strength levels by measuring P-wave signals. The pulse velocities and peak frequencies were higher in high strength geopolymer concrete specimens. There are not explicit relations between strength levels and peak frequencies but the peak frequencies are strongly influenced by the applied stress levels. In addition, a predicting equation for compressive strength of geopolymer concrete is derived based on experimental data in similar form for normal concrete.

Electrical method for crosstalk cancellation in transducer arrays

In this paper, we report a new and simple electrical method to cancel crosstalk in the acoustical arrays. This solution has several advantages compared with that proposed in a previous paper (Bybi et al 2013) [17] where adapted electrical voltages were applied to each neighboring element of the active element in order to reduce the displacement field on their active surface. Firstly, it allows obtaining accurate correction electrical voltages, since it requires average electrical measurements (impedance and current measurements) instead of the displacement measurement in each point at the surface of the radiated element. In addition to this, the method does not need a laser vibrometer which is expensive in terms of time and difficult to use accurately for displacement measurement in water. To demonstrate the ability of the proposed solution an array composed of seven-elements, similar to those used in medical imaging and NDT applications, made of a conventional piezo-ceramic material PZT-27 is fabricated. Then an electrical method based on electromechanical equivalent circuits for piezoelectric materials and motional current measurements is applied. The experimental and numerical results obtained demonstrate the ability of the proposed technique to reduce crosstalk as well as its robustness and ease of implementation.

Development of sputtered AlN thin-film ultrasonic transducers for durable high-temperature applications

This paper presents some of the recent experimental work on developing AlN ultrasonic transducers for high-temperature NDT applications. C-axis oriented AlN films were grown on stainless steel SS316 substrate by RF sputtering deposition. The high-temperature performance and durability of the transducer were examined by pulse-echo experiments after heating to different temperatures. It can be shown that the sputtered AlN film transducer is capable of highly stable and durable performance at 400°C or above, with appropriate choice of substrate, buffer layer, electroding materials and electroding approaches. Experimental evidence also indicates that transducers made of sputtered AlN film and a molybdenum buffer layer on a stainless steel substrate could potentially operate at up to 800°C.

Numerical study of the cross-talk effects in acoustical transducer arrays and correction

Cross-talk in acoustical transducer arrays is an undesirable phenomenon which decreases seriously the performances of these sensors. Indeed, when one element of the array is driven, it generates parasitic displacement fields at the radiating surfaces of the neighboring elements, which changes the directivity of the antenna. To well understand this phenomenon a transducer array similar to those used in medical imaging and NDT applications is modeled by finite element method. The research work, investigated systematically the effects of the cross-talk. First, it inspected the acoustical and mechanical cross-talk throughout the propagating medium and the filling material. Second, it studied the influence of the matching layer and the backing on the acoustical performances of the transducer. It is shown that the filling material and the matching layer are the major factor contributing to this phenomenon. In order to cancel the cross-talk a correction method previously developed by the author has been used. This solution consisted in applying adapted electrical voltages on each neighboring element of the active one in the purpose to reduce the displacement field on their active surface. This method was tested numerically and the obtained results clearly demonstrated its ability to reduce the cross-talk.

A crystalline D-π-A organic small molecule with naphtho[1,2-b:5,6-b′]dithiophene-core for solution processed organic solar cells

In this work, we have designed and synthesized a new naphtho[1,2-b:5,6-b′]dithiophene-containing enlarged π-conjugated donor–acceptor (D–A) small molecule, NDT(TTz)2, for use in solution-processed organic photovoltaics. NDT(TTz)2, which contains a thiophene-bridged naphtho[1,2-b:5,6-b′]dithiophene as the central fused core and triphenylamine-flanked thiophene thiazolothiazole as a spacer, was synthesized via sequential Suzuki and Stille coupling reactions. The thermal, physiochemical, and electrochemical properties of NDT(TTz)2 have been evaluated by differential scanning calorimetry, thermogravimetry, UV–Vis spectroscopy, photoluminescence spectroscopy, X-ray diffraction, and cyclic voltammetry. As desired for photovoltaic applications, NDT(TTz)2 possesses good solubility, thermal stability, and a well-ordered, π–π stacked, crystallinity. The optical band gap and HOMO level of NDT(TTz)2 were determined to be 2.0eV and −5.23eV, respectively. In addition to organic thin film transistor studies, application of NDT(TTz)2 to preliminary photovoltaic devices has also been investigated by fabricating solution-processed bulk heterojunction solar cells together with PC71BM in a typical layered device structure, ITO/PEDOT:PSS/NDT(TTz)2:PC71BM/LiF/Al. Without extensive optimization of the device, NDT(TTz)2 in these devices shows a maximum power conversion efficiency of 1.44% under AM 1.5 illumination at a 100mW/cm2 intensity.

Defect characterisation using pulsed eddy current thermography under transmission mode and NDT applications

Pulsed eddy current (PEC) thermography has been successfully applied to detect cracks in metal alloy and carbon fibre reinforced plastic (CFRP) in previous works. In these applications, an inductor and infrared camera are on the same side of components, named reflection mode. In this work, the transmission mode, where the inductor and infrared camera are on opposite sides of component is investigated for defect characterisation through the analytical analysis and experimental studies. The studies show that the detection mechanisms for impact and delamination in CFRP are totally different. Carbon structure can be observed on the early stage of heating phase and impact leading to decreasing conductivity can be also detected in heating phase. However, delamination can be characterised using late stage of cooling phase. Combing the detection mechanisms, principal components analysis and independent components analysis, image reconstruction method is used to improve the sensitivity.

Stress Dependent Magnetization and Vector Preisach Modeling in Low Carbon Steels

Measurements of magnetic properties have been performed on commercially available low carbon steels (Armco and non-oriented electrical steels) in order to construct and test a Preisach model for materials under stress. The measurements include hysteresis loops of samples under tensile stress taken during loading and after unloading at given strain levels. A vector Preisach model using the SW model as the elementary operator, superposition to account for easy axes dispersion and a weighed mixture of normal distributions to account for the long-range interactions established through the magnetoelastic coupling is proposed. The model reproduces the effect of applied stress, verifying the experimental finding that the permeability of a material under tensile stress decreases. The Preisach density is constructed in such a way as to account for the strong magnetostatic interactions observed in the high induction regions in the case of built-in stresses, so the model is also able to capture the effect of the residual compressive stresses in unloaded materials. The use of the differential permeability and its first derivative are proposed as parameters to be monitored in NDT applications.

Adaptive Method for Non-Intrusive Spectral Projection—Application on a Stochastic Eddy Current NDT Problem

The Non-Intrusive Spectral Projection (NISP) method is widely used for uncertainty quantification in stochastic models. The determination of the expansion of the solution on the polynomial chaos requires the computation of multidimensional integrals. An automatic adaptive algorithm based on nested sparse grids has been developed to evaluate those integrals. The adapted algorithm takes into account the weight of each random variable with respect to the output of the model. To achieve that it constructs anisotropic sparse grid of the mean, leading to a reduction of the number of numerical simulations. Furthermore, the spectral form of the solution is explicitly identified from the constructed quadrature scheme. Numerical results obtained on an industrial application in NDT demonstrate the efficiency of the proposed method.

Non-contact position tracking using phase correlation of sample images for NDT applications

Non-destructive testing methods are used in an increasing number of applications, some of which require precise knowledge of the relative position between transducer and surface. Conventionally, this has been determined using a contact method such as a linear/rotary encoder. An alternative is demonstrated here, using a digital camera and the phase correlation technique. Linear sample movement has been determined to sub-pixel precision, confirmed manually as a median accuracy of 0.01 mm of linear movement (0.06 of a pixel) in this case, despite uneven illumination and the use of a basic low-resolution camera.

Non-contact characterisation of conductivity gradient in isotropic polycrystalline graphite using inductance spectroscopy measurements

The two main graphite ageing processes in advanced gas-cooled reactors (AGRs) are fast neutron damage and radiolytic graphite oxidation. These processes change the properties of the graphite core and lead to a reduction in the graphite density, ie a weight loss. Electrical conductivity measurement of the graphite material is among the possible methods for estimating the weight loss and hence provides a measure of the graphite ageing. The inductance spectroscopy technique using eddy current sensors has been implemented in a wide variety of NDT applications, since it enables the possibility of extracting the electrical parameters variation from eddy current measurements and examining more fully the internal material structure. In this paper we present a non-contact eddy current method for determining non-destructively the electrical conductivity gradient through 100 mm-thick graphite sections using inductive spectroscopic measurements collected by a gradiometer. The method employs the commercial finite element software COMSOL to generate the data from a model of a real profile distribution. This data is translated to the profile conductivity of the graphite test object via the solution of an inverse problem. The linear Tikhonov regularisation method and the non-linear regularised Gauss Newton technique are employed in the solution of the inverse problem. During the optimisation, the forward problem is evaluated using COMSOL. Numerical optimisation tests have been carried out for different cases of step conductivity profiles. Initial results using simulated data show that representative estimates of the conductivity profile of the modelled graphite sections have been obtained.

Quantitative material analysis by dual-energy computed tomography for industrial NDT applications

Dual-energy computed tomography (DECT) is an established method in the field of medical CT to obtain quantitative information on a material of interest instead of mean attenuation coefficients only. In the field of industrial X-ray imaging dual-energy techniques have been used to solve special problems on a case-by-case basis rather than as a standard tool. Our goal is to develop an easy-to-use dual-energy solution that can be handled by the average industrial operator without the need for a specialist. We are aiming at providing dual-energy CT as a measurement tool for those cases where qualitative images are not enough and one needs additional quantitative information (e.g. mass density ρ and atomic number Z) about the sample at hand. Our solution is based on an algorithm proposed by Heismann et al. (2003) [1] for application in medical CT . As input data this algorithm needs two CT data sets, one with low (LE) and one with high effective energy (HE). A first order linearization is applied to the raw data, and two volumes are reconstructed thereafter. The dual-energy analysis is done voxel by voxel, using a pre-calculated function F( Z) that implies the parameters of the low and high energy measurement (such as tube voltage, filtration and detector sensitivity). As a result, two volume data sets are obtained, one providing information about the mass density ρ in each voxel, the other providing the effective atomic number Z of the material therein. One main difference between medical and industrial CT is that the range of materials that can be contained in a sample is much wider and can cover the whole range of elements, from hydrogen to uranium. Heismann’s algorithm is limited to the range of elements Z=1–30, because for Z>30 the function F( Z) as given by Heismann is not a bijective function anymore. While this still seems very suitable for medical application, it is not enough to cover the complete range of industrial applications. We therefore investigated the possibilities of extending the afore mentioned approach to dual-energy imaging to a wider range of materials.

Analysis of Approximations and Aperture Distortion for 3D Migration of Bistatic Radar Data with the Two-Step Approach

The two-step approach is a fast algorithm for 3D migration originally introduced to process zero-offset seismic data. Its application to monostatic GPR (Ground Penetrating Radar) data is straightforward. A direct extension of the algorithm for the application to bistatic radar data is possible provided that the TX-RX azimuth is constant. As for the zero-offset case, the two-step operator is exactly equivalent to the one-step 3D operator for a constant velocity medium and is an approximation of the one-step 3D operator for a medium where the velocity varies vertically. Two methods are explored for handling a heterogeneous medium; both are suitable for the application of the two-step approach, and they are compared in terms of accuracy of the final 3D operator. The aperture of the two-step operator is discussed, and a solution is proposed to optimize its shape. The analysis is of interest for any NDT application where the medium is expected to be heterogeneous, or where the antenna is not in direct contact with the medium (e.g., NDT of artworks, humanitarian demining, radar with air-launched antennas).