Nondestructive Testing Imaging Research Articles

Digitised Frequency Modulated Thermal Wave Imaging for Non-destructive Testing and Evaluation of Glass Fibre Reinforced Polymers

ABSTRACTThe active thermal non-destructive testing and evaluation techniques have gained wide acceptance in health monitoring of various solids materials such as metals, composites and semiconductors. The most popular active infrared thermographic methods for non-destructive testing and evaluation applications are pulse based thermography and lock-in thermography techniques. But the usage of these techniques is limited due to their inherent limitations. To overcome the limitations of the existing approaches, the present work demonstrates the effectiveness of digitized frequency modulated thermal wave imaging technique for detection of different shaped defects in a glass fibre reinforced polymer specimen. Further, the usage of post-processing scheme facilitates defect detection with high resolution and also preserves the shape of defects.

Effect of through-thickness electrical conductivity of CFRPs on lightning strike damages

Making carbon fiber reinforced plastics electrically conductive is an amended solution to the current lightning strike protection technology. However, optimization of the through-thickness electrical conductivity to meet a safety requirement of aircraft against lightning strikes remains unexplored. In this work, four carbon fiber reinforced plastics panels with different through-thickness electrical conductivity were fabricated using a polyaniline-based conductive resin. Their through-thickness electrical conductivity was tailored to achieve specific values using a controlled thermal treatment. The fabricated carbon fiber reinforced plastics panels were tested against a simulated lightning current of 40 kA, and the influence of through-thickness electrical properties on the performance of lightning strike protection was studied. Thermography data and ultrasonic non-destructive testing images confirmed least damage on the sample with higher electrical conductivity. Specimen with through-thickness electrical conductivity of around 110 S/m was able to retain about 92% of the residual flexural strength after the lightning test.

Modeling for detecting weld defects based on magneto-optical imaging.

A magneto-optical (MO) imaging nondestructive testing (NDT) method for ferromagnetic weldments has been proposed. The mechanism of MO imaging was analyzed by the Faraday MO effect, magnetic domain theory, and magnetic hysteresis loops. Then, the relation between MO images and their corresponding excitation voltages was investigated. To explain the MO imaging system, magnetic domain distribution models of various welding states were established. These models are excited by two kinds of magnetic fields. One is the external magnetic field (Hex), and the other is a weldment remanence field (Mr) after Hex is removed. Relations of magnetic field excitation voltages, thickness of the spacer plate, and the corresponding MO images were also researched, which indicates the proposed NDT method can be used to detect incomplete penetration defect. Then, an experiment that uses MO imaging to detect the defects of high-strength steel (HSS) weldment was performed. Experimental results proved this method can detect crack, sag, and incomplete penetration of weldment effectively. Finally, a series of welded joint MO images of the HSS weldment were captured, which are used as the input data of the defect classification model established by using principal component analysis and an error backpropagation neural network, and the accuracy of this classification model can achieve 92.8%.

Coded cone-beam x-ray diffraction tomography with a low-brilliance tabletop source

X-ray diffraction tomography (XDT) probes the spatially variant x-ray diffraction (XRD) profile within volumetric objects. Here, we demonstrate a tabletop XDT setup with coded cone-beam illumination that accelerates the acquisition process of three-dimensional (3D) objects. Compared to the attenuation-based x-ray computed tomography (CT), XDT images display high contrast and specificity among materials with similar absorption coefficients. However, due to the weak signal level of diffraction and the low efficiency in source utilization and detection, conventional XDT systems require high-brilliance synchrotron sources to manage the acquisition time. In this paper, we propose a coded-illumination XDT system that utilizes the cone-beam from a tabletop x-ray tube and eliminates the detector-side collimation. The multiplexed measurement promotes parallelization in the data acquisition and enables simple implementation of compressive measurements, addressing the need of tabletop XDT systems in industrial nondestructive testing and medical imaging applications. We have demonstrated 1 order of magnitude reduction in XDT acquisition time, making high-contrast 3D x-ray imaging accessible to various research and application areas.

Thermal wave imaging for non-destructive testing and evaluation of reinforced concrete structures

Thermal wave imaging for non-destructive testing and evaluation of reinforced concrete structures

Magneto-optical imaging characteristics of weld defects under alternating magnetic field excitation

This paper examines the characteristics of magneto-optical images of weld defects under alternating magnetic field excitation. Weld defects such as non-penetration, surface cracks and sub-surface cracks were detected by a magneto-optical imaging method. Magneto-optical imaging nondestructive testing experiments under alternating magnetic field excitation were carried out to detect the weld defects. Image processing methods which include contrast enhancement of original image, fused image, contrast enhancement of fused image were applied to extract the defect information of the magneto-optical images. What's more, the difference among the magneto-optical images of weld defects was obtained by contrast analysis. Experimental results show that non-penetration welding images possess significant differences in brightness and darkness, and this difference in cracks is smaller than non-penetrating ones. Under the same excitation conditions, the leakage flux of welds with non-penetration is stronger than that of weld cracks.

Acceleration of Range Points Migration-Based Microwave Imaging for Nondestructive Testing

A microwave ultrawideband radar offers advantages of high-range resolution and deep penetration depth in low-loss media, and is a promising efficient nondestructive testing technique. The traditional delay-and-sum (DAS)-based imaging algorithm inherently suffers from insufficient accuracy in determining the detailed structure of any buried foreign body. As a promising alternative, the range points migration (RPM)-based imaging method has been developed. However, this method faces a problem in terms of high computational cost, particularly in the case of three-dimensional objects, because it requires a densely sampled outer boundary to maintain its reconstruction accuracy. Therefore, this study accelerates the RPM-based method without sacrificing the reconstruction accuracy, exploiting the feature of Envelope-based outer boundary extraction. Finite-difference time-domain numerical simulation and experimental results indicate that our proposed method accurately reconstructs small air cavities buried in a concrete object with considerably low computational cost.

Nondestructive assessment and imaging methods for internal inspection of timber. A review.

Abstract This paper reviews state-of-the-art in nondestructive testing (NDT) and semidestructive testing (SDT) methods applicable for imaging the condition of structural timber. Both NDT and SDT imaging reveal defects, damages, and decay, while the extent of wood decay can also be quantified. Combined with an appropriate data interpretation concerning the internal defects, the mechanical properties of the material can also be assessed. The possibilities and limitations of the most relevant individual NDT and SDT methods, also in combination with each other, are outlined and compared. To facilitate comparison, many observations are reported based on the same test specimen.

The Application Status of Infrared Thermal Imaging Non-destructive Testing

The infrared thermal imaging nondestructive testing is to get the temperature distribution of the component by extrinsic stimulation，there are a lot of advantages when compared with other methods, and the application prospect is widespread. This paper shows three types of infrared thermal imaging nondestructive testing technology, the research status at home and abroad, and the application of it. We think the infrared thermography technology is fast, real-time detection and no contact. it is going to be a very effective detection method.

Application of image fusion for the IR images in frequency modulated thermal wave imaging for Non Destructive Testing (NDT)

The raw images obtained in infrared Non-destructive Testing (NDT) should be processed by image processing techniques to improve the data usefulness. In this study, we attempted image fusions techniques to enhance the defect detection capability in glass fiber reinforced composite (GFRP) sample with 25 squared Teflon inserts of various sizes and located at different depths were investigated by means of frequency modulated thermal wave imaging.. Present work highlights application of image fusion based approaches for the defect detection using frequency modulated thermal excitation scheme and comparison has been made on these proposed schemes with respect to SNR improvements at each defect.

An electron beam linear scanning mode for industrial limited-angle nano-computed tomography.

Nano-computed tomography (nano-CT), which utilizes X-rays to research the inner structure of some small objects and has been widely utilized in biomedical research, electronic technology, geology, material sciences, etc., is a high spatial resolution and non-destructive research technique. A traditional nano-CT scanning model with a very high mechanical precision and stability of object manipulator, which is difficult to reach when the scanned object is continuously rotated, is required for high resolution imaging. To reduce the scanning time and attain a stable and high resolution imaging in industrial non-destructive testing, we study an electron beam linear scanning mode of nano-CT system that can avoid mechanical vibration and object movement caused by the continuously rotated object. Furthermore, to further save the scanning time and study how small the scanning range could be considered with acceptable spatial resolution, an alternating iterative algorithm based on ℓ0 minimization is utilized to limited-angle nano-CT reconstruction problem with the electron beam linear scanning mode. The experimental results confirm the feasibility of the electron beam linear scanning mode of nano-CT system.

Global mapping of stratigraphy of an old-master painting using sparsity-based terahertz reflectometry

The process by which art paintings are produced typically involves the successive applications of preparatory and paint layers to a canvas or other support; however, there is an absence of nondestructive modalities to provide a global mapping of the stratigraphy, information that is crucial for evaluation of its authenticity and attribution, for insights into historical or artist-specific techniques, as well as for conservation. We demonstrate sparsity-based terahertz reflectometry can be applied to extract a detailed 3D mapping of the layer structure of the 17th century easel painting Madonna in Preghiera by the workshop of Giovanni Battista Salvi da Sassoferrato, in which the structure of the canvas support, the ground, imprimatura, underpainting, pictorial, and varnish layers are identified quantitatively. In addition, a hitherto unidentified restoration of the varnish has been found. Our approach unlocks the full promise of terahertz reflectometry to provide a global and detailed account of an easel painting’s stratigraphy by exploiting the sparse deconvolution, without which terahertz reflectometry in the past has only provided a meager tool for the characterization of paintings with paint-layer thicknesses smaller than 50 μm. The proposed modality can also be employed across a broad range of applications in nondestructive testing and biomedical imaging.

Sparse Representations to Replace TOFD Images in Non-destructive Testing of Materials

This paper describes a proposed method for the selection of relevant samples of ultrasonic signals during automatic material inspection. Instead of the well-known time of flight diffraction (TOFD) images, data are stored as a sparse matrix in which the elements only indicate whether a defect has been detected. This technique avoids storage of useless signals received during probe displacement in cases of low and high signal-to-noise ratios that correspond to coarse-grained and fine-grained materials, respectively. The approach is based on comparing the positions of maximum amplitudes, which are randomly located when signals only consist of noise but are in the same signal range when a defect is detected. The matrix elements are then applied as inputs to a self organizing map by neural networks to produce a normalized sparse matrix as the output, with a constant number of elements. This approach will be beneficial to enable the use of selected data in intelligent systems requiring a fixed number of inputs to characterize defects.

Shape recognition of acoustic scatterers using the singularity expansion method

Acoustic target recognition for two-dimensional (2D) acoustic scatterers is investigated using the singularity expansion method (SEM). Based on the Watson transformation series of the scattering field, the SEM poles can be calculated and their physical interpretation given, along with the exact normal mode for any acoustic scattering problem. Typical oscillatory phenomena appear as a series of damped sinusoidal signals in the time domain and as a standing-wave distribution in the space. These external oscillation modes are associated with the SEM poles. We note that the positions of these poles in the complex frequency plane are uniquely determined by the shape and flexible characteristics of the target regardless of the waveforms and positions of the incident signals. We then infer that SEM poles can be used as the characteristic parameters for target shape recognition. The relationship between the positions of SEM poles and the geometrical characters of 2D scatterers has been established not only for cylinders but also for other general 2D scatterers. The new method and the related calculation results provide an effective way to perform shape recognition using an acoustic scattering field, with potential applications in non-destructive testing and acoustic imaging.

Feasibility Study for Improving the Image Characteristics in Digital Tomosynthesis (DTS) Using a Compressed-Sensing (Cs)-Based Pre-Deblurring Scheme

ABSTRACTDigital tomosynthesis (DTS) has been widely used in both industrial nondestructive testing and medical x-ray imaging as a popular multiplanar imaging modality. However, although it provides some of the tomographic benefits of computed tomography (CT) at reduced dose and imaging time, the image characteristics are relatively poor due to blur artifacts originated from incomplete data sampling for a limited angular range and also aspects inherent to imaging system, including finite focal spot size of the x-ray source, detector resolution, etc. In this work, in order to overcome these difficulties, we propose an intuitive method in which a compressed-sensing (CS)-based deblurring scheme is applied to the projection images before common DTS reconstruction. We implemented the proposed deblurring algorithm and performed a systematic experiment to demonstrate its viability for improving the image characteristics in DTS. According to our results, the proposed method appears to be effective for the blurring problems in DTS and seems to be promising to our ongoing application to x-ray nondestructive testing.

Three‐dimensional bistatic array imaging using range migration algorithm

Millimetre wave imaging systems are widely used in many fields, such as non-destructive testing, security screening and medical imaging. For security-related personnel screening, the geometries of planar and cylindrical-scanning antenna arrays are often adopted. A planar array imager is capable of acquiring a three-dimensional image in real time, but the information on the back side of the object will be lost. A cylindrical scanning imager is well suited for constructing an image in full 360° directions, what is lost is the time that it takes to complete a full scan. Regardless, mechanical scanning geometry is not always the best approach for real-time systems. In this letter, an imaging scenario is proposed, which is composed of two parallel arrays facing each other. Multiple input multiple output technology is applied to the pair of arrays. Range migration algorithm is adapted specially for this scenario, through which nearly 360°-images of high quality can be constructed in real time when an object is placed between the two arrays.

Characterizing the behavior of scattered radiation in multi-energy x-ray imaging

Scattered radiation results in various undesirable effects in medical diagnostics, non-destructive testing (NDT) and security x-ray imaging. Despite numerous studies characterizing this phenomenon and its effects, the knowledge of its behavior in the energy domain remains limited. The present study aims at summarizing some key insights on scattered radiation originating from the inspected object. In addition, various simulations and experiments with limited collimation on both simplified and realistic phantoms were conducted in order to study scatter behavior in multi-energy x-ray imaging. Results showed that the spectrum shape of the scatter component can be considered preserved in the first approximation across the image plane for various acquisition geometries and phantoms. The variations exhibited by the scatter spectrum were below 10% for most examined cases. Furthermore, the corresponding spectrum shape proved to be also relatively invariant for different experimental angular projections of one of the examined phantoms. The observed property of scattered radiation can potentially lead to the decoupling of spatial and energy scatter components, which can in turn enable speed ups in scatter simulations and reduce the complexity of scatter correction.

Acoustic Characterization of Fluorinert FC-43 Liquid with Helium Gas Bubbles: Numerical Experiments

In this work, we define the acoustic characteristics of a biphasic fluid consisting of static helium gas bubbles in liquid Fluorinert FC-43 and study the propagation of ultrasound of finite amplitudes in this medium. Very low sound speed and high sound attenuation are found, in addition to a particularly high acoustic nonlinear parameter. This result suggests the possibility of using this medium as a nonlinear enhancer in various applications. In particular, parametric generation of low ultrasonic frequencies is studied in a resonator cavity as a function of driving pressure showing high conversion efficiency. This work suggests that this medium could be used for applications such as parametric arrays, nondestructive testing, diagnostic medicine, sonochemistry, underwater acoustics, and ultrasonic imaging and to boost the shock formation in fluids.

Pulsed Neutron Imaging for Non-destructive Testing using Simulated Nuclear Fuel Samples

An integrated assessment method for a nuclear fuel with high decay heat and high radioactivity is required to establish fast reactor system with Trans-Uranium (TRU) fuel containing minor actinides. In addition, a Pu quantitation method with rapidity and accuracy is also necessary in a viewpoint of nuclear security. For these demands, a quantitative evaluation technique for nuclei concentration, thermal property and physical information of such fuel has to be developed. The present study focuses on the non-destructive imaging using pulsed neutrons. Experiments are carried out at Hokkaido University Neutron Source (HUNS) and a gas electron multiplier (GEM) is applied to obtain 2-D information of time-of-flight (TOF). To simulate a nuclear fuel pellet, a sample with equivalent thermal neutron cross-section to the enriched uranium fuel is prepared and the transmitted images of the simulated sample are acquired. Furthermore, a small piece of In, which simulates the Pu spot in the actual fuel, is inserted into the sample and the detectability of the small spot is discussed.

Method for Quantitative 3D Evaluation of Defects in CFRP Using Active Lock-in Thermography

To guarantee an economic application of carbon fibre reinforced plastics (CFRP) throughout the entire product life cycle, the long term operational reliability and reparability of the products must be assured. The typical repair process starts with the defect detection and the defect evaluation. Based on the size and position of the defects the mechanical properties are evaluated and the most efficient repair process is selected. Therefore, the accuracy of the defect detection is essential for an economic repair process.One approach to detect defects in CFRP is the active lock-in thermography, which is an imaging non-destructive testing method. The application of image processing algorithms on phase images enables automated defect detection in CFRP components. The determination of the depth position of defects is still a challenge since the phase images contain a superposition of different depth layers.This paper introduces a method to quantitatively evaluate the 3D defect geometry from a stack of thermography images captured with different excitation frequencies. The phase images of blind bore holes are analysed. Digital evaluation criteria, e.g. area, enveloping circle and position, are defined. Algorithms for image correction, feature extraction and image analysis are implemented for automated defect detection.The stack of thermography images captured with different excitation frequencies is used to estimate the defect's depth range. With the given thermal diffusivity and the excitation frequency the depth information is calculated. The results are visualized three-dimensionally. The method is validated by the comparison of the experimental results with calibrated coordinate measuring machine data.