Area Of Nondestructive Testing Research Articles

Basic procedures in the production of reference materials for ultrasonic non-destructive testing

Conducting reliable measurements with traceability is a basic premise in commercial relations between nations. This role is performed by the national standardization institutes (NMI) and coordinated by the Bureau International des Poids et Mesures (BIPM). The use of Reference Materials (RM) and Certified Reference Materials (CRM) have contributed for decades, mainly to the pharmaceutical and biological products industry, providing high-quality measurements and adding value to the products. This research presents the primary standards and guidelines relevant to the definition of RM and CRM for the area of non-destructive testing (NDT) by ultrasound. The generation process of these materials must occur from short- and long-term stability and homogeneity tests following ISO Guide 35. Following a basic protocol defined for the experiments, the first results generated for the RM and CRM validation process are presented for the first results generated for a production process of a set of 24 carbon steel blocks for property calibration regarding ultrasonic velocity.

Learned Anomaly Detection with Terahertz Radiation in Inline Process Monitoring

Terahertz tomographic imaging as well as machine learning tasks represent two emerging fields in the area of nondestructive testing. Detecting outliers in measurements that are caused by defects is the main challenge in inline process monitoring. An efficient inline control enables to intervene directly during the manufacturing process and, consequently, to reduce product discard. We focus on plastics and ceramics, for which terahertz radiation is perfectly suited because of its characteristics, and propose a density based technique to automatically detect anomalies in the measured radiation data. The algorithm relies on a classification method based on machine learning. For a verification, supervised data are generated by a measuring system that approximates an inline process. The experimental results show that the use of terahertz radiation, combined with the classification algorithm, has great potential for a real inline manufacturing process. In a further investigation additional data are simulated to enlarge the data set, especially the variety of defects. We model the propagation of terahertz radiation by means of the Eikonal equation.

Efficient Algebraic Image Reconstruction Technique for Computed Tomography

Industrial computed tomography (CT) has seen widespread adoption within certain areas of non-destructive testing (NDT), with many commercial systems capable of acquisition and reconstruction of cone-beam CT data. The majority of these systems utilise reconstruction algorithms based on the traditional filtered back-projection (FBP) methods, which are imperfect with respect to limited-angle cone-beam data. These techniques are also inherently restricted in the source trajectories that can be utilised due to the use of Fourier slice theorem. This restricts FBP-based techniques to a circular or helical trajectory. Iterative reconstruction algorithms provide a solution to these limitations as the volume reconstruction does not depend on the location or orientation of the source and detector, allowing the possibility of scanning trajectories that satisfy well-known CT data-sufficiency conditions. This paper proposes a method of reconstruction based on computationally efficient computer graphics algorithms with data collected from points in 3D space not restricted to a single circular trajectory, which is useful within NDT for automated robotic inspection. The algorithms developed allow for rapid processing of the algebraic reconstruction technique (ART) for use with X-ray transmission data for CT reconstruction. Experimental results are presented for reconstructions for circular trajectory and points on a sphere to demonstrate the suitability for NDT applications.

Numerical predictions of the interaction between highly nonlinear solitary waves and the microstructure of trabecular bone in the femoral head

The unique properties of highly nonlinear solitary waves in granular chains have prompted extensive research in the area of non-destructive testing and led to the development of new diagnostic schemes with potential applications in the healthcare industry. Here, we study numerically the interaction between highly nonlinear solitary waves in a granular chain and the microstructure of trabecular bone in the femoral head. High-resolution finite element models of bone microstructures with varying bone volume fraction are generated using a topology optimization-based bone microstructure reconstruction scheme. The obtained FE models of the trabecular bone were then used to develop a hybrid discrete/finite element model able to simulate the propagation of highly nonlinear solitary waves in a vertical array of steel particles, and their interaction with the adjacent bone microstructure model was studied. Two test modes were considered, one where the granular chain was placed in direct contact with the bone microstructure model, while in the second test mode, a face sheet was included between the chain and the bone model. For both test modes, we found that the characteristic features of the reflected solitary waves are sensitive to the effective compressive modulus of the bone microstructure models and follow similar trends than those obtained for a homogeneous, non-porous solid. It was also found that the use of the face sheet substantially reduces the sensitivity of the predictions to small changes in the bone topology, making it a robust and reliable method for non-destructive evaluation of the effective elastic modulus of cellular materials with small structural dimensions, as it is required for the site-specific evaluation of the mechanical properties of trabecular bone.

Local Sparseness and Image Fusion for Defect Inspection in Eddy Current Pulsed Thermography

Defect feature extraction and the analysis based on eddy current pulsed thermography (ECPT) technique are a research focus in non-destructive testing area. In this paper, a new feature extraction method based on thermography is proposed to enhance quantitative defect information. The proposed method included entropy-based image selection, local (element-wise) sparse and low-rank decomposition, and image fusion can increase the contrast of defect area and background and extract more useful defect features than other two common feature extraction algorithms in ECPT. The experiments including comparison results are provided to demonstrate the capabilities and benefits of the proposed algorithm. More meaningful defect information of the experimental specimens is reserved from raw ECPT data and background are suppressed severely compared with other feature extraction algorithms.

Nondestructive Testing for Shallow Defect of Ferromagnetic Objects Based on Magnetic Probe Structure

The Electromagnetic inspection technique plays an important role in the nondestructive testing (NDT) for many decades. Today, this NDT area is rather wide and significant. The magnetic flux leakage (MFL) technology is one of the most widely used electromagnetic nondestructive testing (NDT) techniques. MFL tools use permanent magnets to magnetize the detected object near to saturation flux density [1], [2]. Generally, the magnetizer mechanism of MFL are bulky and heavy. Although the shape of the opening and the depth profile of an arbitrary three-dimensional (3-D) defect from MFL measurements can be estimated [3], the inversion method is complicated and susceptible by the magnetization factors. For different shapes and different sizes of detected object, the magnetizer mechanism of MFL should be designed individually, and this requires a lot of time and experimentation. In this paper, a simple and portable magnetic detection device is designed with permanent magnets, magnetic probe structure and the Hall sensors. Compared with the magnetizer mechanism of MFL, the magnetic detection device is very light, low cost and easy to design and manufacture. The magnetic detection device can make qualitative, and quantitative evaluation for shallow defect of ferromagnetic objects.

A Novel Eddy Current Testing Scheme by Transient Oscillation and Nonlinear Impedance Evaluation

Eddy current testing technique is widely used in nondestructive testing area. A novel eddy current testing scheme by transient oscillation and nonlinear impedance evaluation is proposed in this paper. A sensing coil with a ferrite core is used as the eddy current probe. The probe is connected in series with a capacitor and a simulated negative resistor to establish a second-order circuit. A square-wave voltage signal is utilized as the excitation source. By adjusting the value of the negative resistor within an appropriate range, the response signal will exhibit free damped oscillations within the transient durations. The transient oscillations are sampled as the response signal and first processed by singular spectrum analysis to remove noises. Then, Hilbert transform is further used to calculate the instantaneous frequency and the instantaneous damping coefficient of the transient oscillation. After that the nonlinear impedance carrying the defect information of the specimen under test can be finally obtained. Subsurface defects of 304 stainless steel specimens are experimentally detected. The results indicate that the proposed scheme is competent to detect subsurface defects. An interesting phenomenon is that the impedance nonlinearity of the probe-specimen system can be extracted from the transient oscillations. The nonlinear impedance causes critical damping in theory. Therefore, an online defect detection can be implemented by simply measuring the envelope of the transient oscillations.

Design of multiplexer for electrical impedance tomography

Electrical impedance tomography is a relatively new method in the field of structural health monitoring and non-destructive testing area. The electrical resistance tomography is a non-intrusive method enabling mapping of the spatial distribution of electrical conductivity of the monitored object. This paper describes the development of the multiplexer, which is one of the essential parts of the impedance tomography system. Frequency bandwidth, off isolation, and channel-to-channel cross talks are verified in the supposed frequency range. Basic multiplexer functionality is demonstrated on an image reconstruction of a carbon fiber reinforced polymer composite coupon damaged by an impact.

In Memoriam

Professor Rémi Vaillancourt passed away on November 29, 2015. He was born in Maniwaki, Quebéc, Canada, in 1934. After completing his undergraduate studies at the University of Ottawa, he defended his PhD thesis at the Courant Institute of Mathematical Sciences in New York under the supervision of P.D. Lax and K.O. Friedrichs in 1969. Later, together with A.P. Calderón, Rémi Vaillancourt obtained important results in the theory of pseudo-differential operators. Since 1970, professor Vaillancourt had worked at the University of Ottawa. He had more than 180 published papers in refereed journals. Professor Rémi Vaillancourt was very active in promoting mathematics and mathematical education. In 1975–1981, he served as a vice-president and president of the Canadian Mathematical Society and later as the president of the Canadian Society of Applied Mathematics. He was also the chairman of the Canadian National Commitee for the International Mathematical Union in 1979–1988. For many years, professor Rémi Vaillancourt was a member of the editorial board of the journal „Scientific proceedings of Riga Technical University”. His contribution to research with the staff of the Department of Engineering Mathematics of the Riga Technical University in the areas of non-destructive testing and fluid mechanics was very significant. We worked with Rémi Vaillancourt for many years. He had an extremely pleasant personality and was always willing to help his colleagues. We had a great pleasure to meet Rémi’s family in Ottawa. During these years, research collaboration with Rémi evolved into closer ties also with his family. We were deeply saddened by the news of Rémi’s passing. He will always be in our hearts.

Optical design and evaluation of a 4 mm cost-effective ultra-high-definition arthroscope.

High definition and magnification rigid endoscope plays an important role in modern minimally invasive medical surgery and diagnosis. In this paper, we present the design and evaluation methods of a high definition rigid endoscope, specifically an arthroscope, with a large depth of field (DOF). The incident heights and exit angles of the sampled rays on the relay lens are controlled during the optimization process to ensure an effective field view (70°) and a normal ray path within the limited lens diameter of 2.7 mm. The lens is set up as a multi-configuration system with two extreme and one middle object distances to cover a large DOF. As a result, an entrance pupil of 0.3 mm is achieved for the first time, to bring the theoretical resolution to 23.1 lps/mm in the object space at a working distance of 20 mm, with the wavelength of 0.532 um. The modulation transfer function (MTF) curves approach diffraction limit, and the values are all higher than 0.3 at 160 line pairs/mm (lps/mm) in the image space. Meanwhile, stray light caused by total internal reflection on the inner wall of the rod lenses and the objective lens is eliminated. The measured resolution in the object space at a 20 mm working distance is 22.3 lps/mm, and test results show that other performance characteristics also fulfill design requirements. The relay lenses are designed with only one type of the spacer and two types of lenses to greatly reduce the fabrication and assembly cost. The design method has important research and application values for lens systems used in modern minimally invasive medical surgery and industrial non-destructive testing area.

An Improved Iteration Back Projection Imaging Technique for Surface Penetrating Radar Applications

Traditional back projection(BP) imaging algorithm can be used to obtain 2-dimensional subsurface imaging results of testing materials and thus provide useful information for material nondestructive testing(NDT). But it’s restricted by heavy computation burden and cannot be widely used in surface penetrating radar(SPR) NDT area. To meet the needs of high resolution imaging and low computation burden, an improved iteration back projection imaging algorithm is presented. With the multi scale iteration processing and local maximum extraction method, it can get appropriate resolution imaging results with much lower computation. The simulation of this algorithm is processed and experimental results validate the feasibility of this algorithm.

Improving the Spatial Resolution of Magneto Resistive Sensors via Deconvolution

State-of-the-art GMR sensors are becoming increasingly popular for a variety of applications, due to of the progress in the area of magnetic field sensor technologies in the recent years. Especially in the area of nondestructive testing, the number of applications based on magnetic field sensors is steadily increasing. Until now, a major concern of these applications has been to improve the sensors sensitivity to be able to measure even minimal magnetic field variations. However, an equally important characteristic, the sensors spatial resolution, is often neglected in discussions. In this paper, the spatial resolution of two different GMR sensors is analyzed. The sensors are modeled as linear space-invariant systems. With the analytical solution for the magnetic field above a current carrying conductor and a corresponding measurement, the attainable spatial resolution is determined comparing two different deconvolution methods, an inverse and a Wiener filter. Finally, the determined sensor characteristics are used to improve the measurement accuracy significantly.

National Primary Standard for the Units of the Propagation Velocities of Longitudinal, Shear, and Surface Ultrasonic Waves in Solids

Improvements in the national standard for the unit of the propagation velocity of longitudinal ultrasonic waves in solids are examined. The measurement techniques and standard measures for velocity are described. The composition and metrological characteristics of the new standard are discussed. In accordance with the scientific and technical program "Standards of Russia" and the steps planned for the intro- duction of the national primary standard for the unit of the propagation velocity of longitudinal ultrasonic waves in solids, GET 189-2010 (1), work has been under way at the Far Eastern Branch of the All-Russia Research Institute of Physicotech- nical and Radio Measurements (VNIIFTRI) during 2010-2012 to improve the standard, including the development and intro- duction of two new standards facilities as part of the standard for measuring the propagation velocities of shear and surface ultrasonic waves in solids. Thus, the new national primary standard GET 189-2012 ensures the uniformity of measurements of the propagation velocities of the main types of acoustic waves in solids. This standard is at the top of the national verifi- cation scheme for means of measuring the propagation velocity of ultrasonic waves in solids, which establishes the order of transfer of reproduced units to working standards and means of measurement. The need for measurements of the propagation parameters of ultrasonic waves in solids arises from fundamental, as well as applied research. The propagation parameters of ultrasonic waves are used in fundamental research for calculating the elastic constants and moduli of elasticity - the most important characteristics of solids (2). These parameters are also need- ed for determining the physical and mechanical characteristics, as well as the endurance properties of solids, and are of the greatest importance for creating new materials, and in developing techniques for producing and using these in technology and industry. However, the demand for measurements of the propagation velocity of ultrasonic waves is primarily related to the need to ensure the uniformity of measurements in the area of nondestructive testing of the quality of materials and work pieces using acoustic methods and means of measurement. An analysis of Russian and foreign literature in this area shows that the most promising approach for the develop- ment of original standard means of measurement in solid-state acoustics is the use of contactless methods for generating and receiving ultrasonic waves: optical and capacitive (3-8). Optical methods form the basis of the standard GET 189-2012. The standard laser-interference system for measuring the propagation velocity of longitudinal ultrasonic waves in the standard GET 189-2010 (1) serves as the basis for creating the unified standard facility for reproduction of the units of the prop-

Extraction of weld defects dimension from radiographic images using the level set segmentation without re-initialization

Radiographic images segmentation is the major interest for the weld defect diagnosis and monitoring in the field of industry. In this work we present a method that takes ownership of local segmentation geodesic active contours. The goal of the method presented in this paper is to automate the process of extracting dimension of weld defects from radiographic images using level set segmentation. The information would be used in the area of nondestructive testing (NDT). This method is found to be effective and robust.

3D robust Chan–Vese model for industrial computed tomography volume data segmentation

Industrial computed tomography (CT) has been widely applied in many areas of non-destructive testing (NDT) and non-destructive evaluation (NDE). In practice, CT volume data to be dealt with may be corrupted by noise. This paper addresses the segmentation of noisy industrial CT volume data. Motivated by the research on the Chan–Vese (CV) model, we present a region-based active contour model that draws upon intensity information in local regions with a controllable scale. In the presence of noise, a local energy is firstly defined according to the intensity difference within a local neighborhood. Then a global energy is defined to integrate local energy with respect to all image points. In a level set formulation, this energy is represented by a variational level set function, where a surface evolution equation is derived for energy minimization. Comparative analysis with the CV model indicates the comparable performance of the 3D robust Chan–Vese (RCV) model. The quantitative evaluation also shows the segmentation accuracy of 3D RCV. In addition, the efficiency of our approach is validated under several types of noise, such as Poisson noise, Gaussian noise, salt-and-pepper noise and speckle noise.

Sparse Arrays and Image Compounding Techniques for Non-Destructive Testing Using Guided Acoustic Waves

Piezoelectric array transducers applications are becoming usual in the ultrasonic non-destructive testing area. However, the number of elements can increase the system complexity, due to the necessity of multichannel circuitry and to the large amount of data to be processed. Synthetic aperture techniques, where one or few transmission and reception channels are necessary, and the data are post-processed, can be used to reduce the system complexity. Another possibility is to use sparse arrays instead of a full-populated array. In sparse arrays, there is a smaller number of elements and the interelement spacing is larger than half wavelength. In this work, results of ultrasonic inspection of an aluminum plate with artificial defects using guided acoustic waves and sparse arrays are presented. Synthetic aperture techniques are used to obtain a set of images that are then processed with an image compounding technique, which was previously evaluated only with full-populated arrays, in order to increase the resolution and contrast of the images. The results with sparse arrays are equivalent to the ones obtained with full-populated arrays in terms of resolution. Although there is an 8 dB contrast reduction when using sparse arrays, defect detection is preserved and there is the advantage of a reduction in the number of transducer elements and data volume.

Impact Damage Detection in GFRP Laminates through Ultrasonic Imaging

Composite materials are increasingly used in aerospace, naval and automotive vehicles due to their high specific strength and stiffness. In the area of Non destructive testing, ultrasonic C-scans are used frequently to detect defects in composite components caused during fabrication and damage resulting from service conditions. Ultrasonic testing uses transmission of high frequency sound waves into a material to detect imperfections or to locate changes in material properties. The most commonly used ultrasonic testing technique is pulse echo and through transmission wherein sound is introduced into a test object and reflections (echoes) are returned to a receiver from internal imperfections. Under low-velocity impact loading delaminating is observed to be a major failure mode. This report presents the use of above two techniques to detect the damage in glass fiber reinforced plastic (GFRP) laminates. Pulse echo is used to locate the exact position of damage and through transmission is used to know the magnitude of damage in composite. This paper work will be carried out on two different thicknesses and at impact energy levels varying from 7 to 53J. The ensuring delamination damage will be determined by ultrasonic C-scans using the pulse-echo immersion method for through transmission. Delamination areas were quantified accurately by processing the raw image data using a digital image processing technique. Based on the data obtained, correlation will be established between the delamination area and the impact energy.

New approach to the excitation of plate waves for piezoelectric thick-film devices

A method is presented for exciting the propagation of plate waves in elastic guides. It is implemented in a device whose minimum working structure consists of a non-piezoelectric plane guide and two piezoelectric transducers operating as a generator and detector. The device is entirely in accordance with thick-film technology standard procedures. Both transducers are composed of a PZT ferroelectric layer deposited on a ceramic substrate and a suitable system of three coplanar metal electrodes placed inside the same layer. Beside setting the wavelength of propagation, the electrode system promotes piezoelectric deformations parallel to the substrate simultaneously contracting and extending contiguous active regions in the layer. Pure shear stresses are then induced on the involved guide surface, alternately distributed, with the spatial periodicity of the wave that will propagate in the guide. The propagation of several kinds of guided waves is possible so the selection of the one that meets a specific device design best is allowed. This work describes the design, realization and operation of a prototype structure consisting of an alumina plate guide and two pairs of piezoelectric thick-film transducers realized on it. The results related to the propagation of symmetric and asymmetric Lamb modes are reported. Moreover, the potential of the method is highlighted, emphasizing its effectiveness, easy implementation and application in the development of devices for the sensing and non-destructive testing areas.

Diffusion-Based Thermal Tomography

Thermal imaging is one of the fastest growing areas of nondestructive testing. The basic idea is to apply heat to a material and study the way the temperature changes within the material to learn about its composition. The technique is rapid, relatively inexpensive, and, most importantly, has a wide coverage area with a single experimental measurement. One of the main research goals in thermal imaging has been to improve flaw definition through advanced image processing. Tomographic imaging is a very attractive way to achieve this goal. Although there have been some attempts to implement tomographic principles for thermal imaging, they have been only marginally successful. One possible reason for this is that conventional tomography algorithms rely on wave propagation (either electromagnetic or acoustic) and are inherently unsuitable for thermal diffusion without suitable modifications. In this research program, a modified approach to thermal imaging is proposed that fully accounts for diffusion phenomena in a tomographic imaging algorithm. Here, instead of the large area source used in conventional thermal imaging applications, a raster scanned point source is employed in order to provide the well-defined source-receiver positions required for tomographic imaging. An algorithm for the forward propagation problem, based on the Galerkin finite element method in connection with the corresponding weak formulation for the thermal diffusion is considered. A thermal diffusion modified version of the algebraic reconstruction technique (ART) is used for image reconstruction. Examples of tomographic images are presented from synthetically generated data to illustrate the utility of the approach.

Quantitative numerical analysis of transient IR-experiments on buildings

Impulse-thermography has been established as a fast and reliable tool in many areas of non-destructive testing. In recent years several investigations have been done to apply active thermography to civil engineering. For quantitative investigations in this area of application, finite difference calculations have been performed for systematic studies on the influence of environmental conditions, heating power and time, defect depth and size and thermal properties of the bulk material (concrete). The comparison of simulated and experimental data enables the quantitative analysis of defects.