Nondestructive Testing Of Materials Research Articles

Using signals of special form in multi-frequency eddy current testing

An eddy current testing method based on the use of an exciting signal of special shape is proposed. Subsequent digital processing of the detected output signal makes it possible to calculate the measuring sensor parameters at different frequencies and to construct an experimental hodograph of the sensor–test object system. Experiments performed for materials with different physical and geometrical characteristics of constructing hodographs have shown that the proposed method provides a reliable separation of the main factors affecting the results of multi-frequency eddy current measurement. The results can be used in automated systems for inspection and non-destructive testing of materials and products.

Modeling the ultrasonic testing echoes by a combination of particle swarm optimization and Levenberg–Marquardt algorithms

This paper presents an accurate and easy-to-implement algorithm for estimating the parameters of the asymmetric Gaussian chirplet model (AGCM) used for modeling echoes measured in ultrasonic nondestructive testing (NDT) of materials. The proposed algorithm is a combination of particle swarm optimization (PSO) and Levenberg–Marquardt (LM) algorithms. PSO does not need an accurate initial guess and quickly converges to a reasonable output while LM needs a good initial guess in order to provide an accurate output. In the combined algorithm, PSO is run first to provide a rough estimate of the output and this result is consequently inputted to the LM algorithm for more accurate estimation of parameters. To apply the algorithm to signals with multiple echoes, the space alternating generalized expectation maximization (SAGE) is used. The proposed combined algorithm is robust and accurate. To examine the performance of the proposed algorithm, it is applied to a number of simulated echoes having various signal to noise ratios. The combined algorithm is also applied to a number of experimental ultrasonic signals. The results corroborate the accuracy and reliability of the proposed combined algorithm.

Production integrated nondestructive testing of composite materials and material compounds – an overview

Composite materials and material compounds are of increasing importance, because of the steadily rising relevance of resource saving lightweight constructions. Quality assurance with appropriate Nondestructive Testing (NDT) methods is a key aspect for reliable and efficient production. Quality changes have to be detected already in the manufacturing flow in order to take adequate corrective actions. For materials and compounds the classical NDT methods for defectoscopy, like X-ray and Ultrasound (US) are still predominant. Nevertheless, meanwhile fast, contactless NDT methods, like air-borne ultrasound, dynamic thermography and special Eddy-Current techniques are available in order to detect cracks, voids, pores and delaminations but also for characterizing fiber content, distribution and alignment. In Metal-Matrix Composites US back-scattering can be used for this purpose. US run-time measurements allow the detection of thermal stresses at the metal-matrix interface. Another important area is the necessity for NDT in joining. To achieve an optimum material utilization and product safety as well as the best possible production efficiency, there is a need for NDT methods for in-line inspection of the joint quality while joining or immediately afterwards. For this purpose EMAT (Electromagnetic Acoustic Transducer) technique or Acoustic Emission testing can be used.

Light scattering by porous oriented polypropylene films

Oriented porous polypropylene films with lamellar crystal structure are studied by the laser radiation scattering method. The dependence of the scattering pattern on the degree of film orientation is determined. It is shown that the sizes of the central maximum of the scattering pattern depend linearly on the degree of film extension. The results obtained can be used in developing methods of optical nondestructive testing of polymeric materials.

Development prospects for nondestructive testing of heterogeneous nonmetallic materials by the parameters of electrical response to a shock action

Theoretical and experimental research has been conducted into the mechanisms of generation of electric fields under elastic shock excitation of heterogeneous nonmetallic materials that contain two types of mechanoelectric transductions, viz., double electrical layers at interphase boundaries and piezoelectric inclusions. Using the example of electrical responses from samples of heavy- and light-weight concretes and based on numerical modeling results, prospects are shown for using this phenomenon in nondestructive testing of heterogeneous nonmetallic materials that do not contain piezoelectric inclusions, e.g., layered and reinforced ones.

Application of dual energy method for non-destructive testing of materials designed to work in extreme conditions

The description of the dual energy method (DEM) for non-destructive testing (NDT) of materials and products is presented. It highlights the key factors that determine its accuracy and performance and shows the possibilities for its further improvement. The correlation between the quantum noise level and the DEM precision of the effective atomic number was found.

Mechanism analysis of influence of surface-breaking orientation on magnetic leakage field distribution

Magnetic flux leakage (MFL) has been widely applied to the nondestructive testing (NDT) of ferromagnetic materials due to its simple operation, low cost, and steady signal. Its defects are evaluated based on the relationship between MFL signal and the geometrical characteristic of defect. In this paper, a three-dimensional (3D) mathematical model is developed for the magnetic leakage field of surface-breaking defects that are arbitrarily oriented inside ferromagnetic material. Firstly, a finite-length rectangular slot is used as a simplified and convenient representation of a surface-breaking defect. Then, the magnetic charge densities of slot walls in different surface-breaking orientations are analyzed theoretically. The distribution of the magnetic leakage field can ultimately be derived by vector synthesis. Both simulations and experiments are conducted to analyze the magnetic leakage field distributions in different magnetization orientations. The results show that with increasing the angle between the defect orientation and the magnetic field, the horizontal component of the leakage magnetic field increases as demonstrated by increasing the prominence of its single peak. At the same time, however, the vertical component shows a bimodal distribution. The proposed model can effectively describe the influence of defect orientation on MFL signals, which can offer practical guidelines for optimizing MFL detectors and improving defect assessment.

Miniaturized UWB Antipodal Vivaldi Antenna and Its Application for Detection of Void Inside Concrete Specimens

A miniaturized antipodal Vivaldi antenna to operate from 1 to 30 GHz is designed for nondestructive testing and evaluation of construction materials, such as concrete, polymers, and dielectric composites. A step-by-step procedure has been employed to design and optimize performance of the proposed antenna. First, a conventional antipodal Vivaldi antenna (CAVA) is designed as a reference. Second, the CAVA is shortened to have a small size of the CAVA. Third, to extend the low end of frequency band, the inner edges of the top and bottom radiators of the shortened CAVA have been bent. To enhance gain at lower frequencies, regular slit edge technique is employed. Finally, a half elliptical-shaped dielectric lens as an extension of the antenna substrate is added to the antenna to feature high gain and front-to-back ratio. A prototype of the antenna is employed as a part of the microwave imaging system to detect voids inside concrete specimen. High-range resolution images of voids are achieved by applying synthetic aperture radar algorithm.

Ultrasonic Imaging in Solids Using Wave Mode Beamforming.

This paper discusses some improvements to ultrasonic synthetic imaging in solids with primary applications to nondestructive testing of materials and structures. Specifically, the study proposes new adaptive weights applied to the beamforming array that are based on the physics of the propagating waves, specifically the displacement structure of the propagating longitudinal (L) mode and shear (S) mode that are naturally coexisting in a solid. The wave mode structures can be combined with the wave geometrical spreading to better filter the array (in a matched filter approach) and improve its focusing ability compared to static array weights. This paper also proposes compounding, or summing, images obtained from the different wave modes to further improve the array gain without increasing its physical aperture. The wave mode compounding can be performed either incoherently or coherently, in analogy with compounding multiple frequencies or multiple excitations. Numerical simulations and experimental testing demonstrate the potential improvements obtainable by the wave structure adaptive weights compared to either static weights in conventional delay-and-sum focusing, or adaptive weights based on geometrical spreading alone in minimum-variance distortionless response focusing.

Three-dimensional thermography for non-destructive testing and evaluation

Three-dimensional (3D) vision based scanning for metrology and inspection applications is an area that has attracted increasing interest in the industry. This interest is driven by the recent advances in 3D technologies, which enable high precision measurements at an affordable cost. 3D vision allows for the modelling and inspection of the visible surface of objects. When it is necessary to detect subsurface defects, active infrared (IR) thermography is one of the most commonly used tools today for the non-destructive testing and evaluation (NDT&E) of materials. Fusion of these two modalities allows the simultaneous detection of surface and subsurface defects and the visualisation of these defects overlaid on the 3D model of the scanned and modelled parts or their 3D computer-aided design (CAD). In this work, we present a framework for automatically fusing 3D data (scanned or CAD) with the infrared thermal images for an NDT&E process in 3D space. The captured 3D images and their thermal infrared counterparts are aligned and fused using automatically detected features. This fusion is undergone on 3D space, thus allowing 3D visualisation of subsurface defects on a 3D model (or CAD). Additionally, the defects are extracted using image processing techniques and overlaid over their virtual position in 3D space. Their positioning at a certain distance from the part’s 3D surface is proportional to the computed depth using phase image analysis in the Fourier domain. This depth represents the real position of the detected subsurface defect and is extracted using thermograms (temporal sequence of thermal images). The results obtained are promising and show how this new technology can be used efficiently in a combined NDT&E-Metrology analysis of manufactured parts, in areas such as aerospace and automotive, among others.

Aperiodic Thermal Wave Imaging Approach for Non-Destructive Testing and Evaluation of Steel Material: A Numerical Study

Aperiodic Thermal Wave Imaging Approach for Non-Destructive Testing and Evaluation of Steel Material: A Numerical Study

Temperature and microwave near field imaging by thermo-elastic optical indicator microscopy.

A high resolution imaging of the temperature and microwave near field can be a powerful tool for the non-destructive testing of materials and devices. However, it is presently a very challenging issue due to the lack of a practical measurement pathway. In this work, we propose and demonstrate experimentally a practical method resolving the issue by using a conventional CCD-based optical indicator microscope system. The present method utilizes the heat caused by an interaction between the material and an electromagnetic wave, and visualizes the heat source distribution from the measured photoelastic images. By using a slide glass coated by a metal thin film as the indicator, we obtain optically resolved temperature, electric, and magnetic microwave near field images selectively with a comparable sensitivity, response time, and bandwidth of existing methods. The present method provides a practical way to characterize the thermal and electromagnetic properties of materials and devices under various environments.

Qualitative Evaluations of the AlSi7Mg0.3 Microstructure by the X-Ray Diffractometry

Nowadays it's very important to minimalize the costs of casted parts, what obviously conclude to reduction in time that is necessary for the heat treatment. Despite this fact it's necessary to keep or moreover increase mechanical properties like a strength, ductility, toughness and dimensional stability. Better mechanical properties lead to the better material utilisation, this parameter is represented by the following formula: Q = Rm + k.logA5, known as a Quality index and increase of this parameter conclude to weight reduction of casted part. For obtaining good quality of the casted part it's very important to watch the cast's internal composition, hence the microstructure of the casted part. For the facts mentioned above, this paper deals with evaluation of the microstructure of aluminium alloy AlSi7Mg0.3 by an X-ray diffractometry using the Debye-Scherrer method with configuration for rebound reflection and comparison of the results with metallographic observations using the light microscopy. Work is showing the opportunities of the X-ray diffraction for the nondestructive material testing of the casted aluminium parts, because in this field there are not enough knowledge about the comparison and evaluation between the microstructure and diffraction. Great advantage of the X-ray diffraction is that the testing surface doesn't needs to be specially treaded. This technology is non-destructive for the surface analyses so for the testing of the internal material composition it's necessary etching.

Theory for optical detection of picosecond shear acoustic gratings

A theoretical formalism describing the heterodyne detection of plane inhomogeneous shear acoustic waves by probe laser-induced gratings is developed. An inhomogeneous plane shear acoustic wave is a purely shear wave with a plane phase front and mechanical displacement vector, which is sinusoidally spatially modulated in magnitude. It could be generated by laser-induced gratings and could be useful for the acoustic testing of sub-micrometer thick membranes and coatings in the gigahertz frequency range. The theory reveals the potential advantages and disadvantages of this wave application in non-destructive testing of materials and fundamental research from the point of view of the feasibility of their experimental detection.

Nondestructive testing of advanced materials using sensors with metamaterials

This work presents a method for nondestructive evaluation (NDE) of advanced materials that makes use of the images in near field and the concentration of flux using the phenomenon of spatial resolution. The method allows the detection of flaws as crack, nonadhesion of coating, degradation or presence delamination stresses correlated with the response of electromagnetic sensor.

Developing topologies of thin-film SQUID sensors for measuring extremely subtle magnetic fields

A topology of thin-film SQUID sensors that are based on Nb/AlO x /Nb tunnel junctions has been developed and optimized for nondestructive testing of materials and for other systems with a magnetic field sensitivity of <10 fT/Hz1/2.

A REVIEW ON EDDY CURRENT THERMOGRAPHY TECHNIQUE FOR NON-DESTRUCTIVE TESTING APPLICATION

Eddy current thermography is one of the non-destructive testing techniques that provide advantages over other active thermography techniques in defect detection and analysis. The method of defect detection in eddy current thermography has become reliable due to its mode of interactions i.e. eddy current heating and heat diffusion, acquired via an infrared camera. Such ability has given the technique the advantages for non-destructive testing applications. The experimental parameters and settings which contribute towards optimum heating and defect detection capability have always been the focus of research associated with the technique. In addition, the knowledge and understanding of the characteristics heat distribution surrounding a defect is an important factor for successful inspection results. Thus, the quantitative characterisation of defect by this technique is possible compared to the conventional non-destructive which only acquired qualitative result. In this paper, a review of the eddy current thermography technique is presented which covers the physical principles of the technique, associated systems and its applications. Works on the application of the technique have been presented and discussed which demonstrates the ability of eddy current thermography for non-destructive testing of conductive materials.

Mechanical design of a novel MEMS resonant sensor for monitoring in-plane magnetic fields

We present the mechanical design of a novel MEMS-based magnetic field sensor with optical sensing for monitoring in-plane magnetic fields. It has a diamond-shaped resonator composed by four polysilicon beams (198 × 12 × 2.25 µm), an aluminum loop (957 × 8 × 0.7 µm) and two mirrors (31 × 32 × 0.7 µm), which are designed considering the Sandia Ultra-planar Multi-level MEMS Technology process. The sensor exploits Lorentz force to detect different components of in-plane magnetic fields, which are related with the mirrors displacements. Analytical models are developed to predict the damping, resonant frequency, and mirrors displacements caused by temperature shifts. In addition, Castigliano's second theorem is used to obtain an analytical model of the mirrors displacements at resonance as a function of in-plane magnetic fields with inclination angles from 0 to 360° and electrical currents. The results of the analytical models agree well with those determined by finite element method models. The sensor operates at resonant frequency of 33.6 kHz, a quality factor of 98, a power consumption of 259 mW and a sensitivity of 259 nm·mTź1. This sensor design could have potential applications in non-destructive testing of ferromagnetic materials.

Comparison of quantitative defect characterization using pulse-phase and lock-in thermography.

Using optical excitation sources for active thermography enables a contactless, remote, and non-destructive testing of materials and structures. Currently, two kinds of temporal excitation techniques have been established: pulse or flash excitation, using mostly flash lamps; and periodic or lock-in excitation, using halogen lamps, LED, or laser arrays. From the experimental point of view, both techniques have their advantages and disadvantages. Concerning the comparison of the testing results of both techniques, only very few studies have been performed in the past. In this contribution, the phase values obtained at flat bottom holes in steel and CFRP and the spatial resolution measured at crossed notches in steel using flash and lock-in excitation are compared quantitatively.

Impact non-linear reverberation spectroscopy applied to non-destructive testing of building materials

The development of non-destructive testing techniques to detect early micro damage in concrete and other building materials is important for efficient maintenance and management of existing infrastructure. Nonlinear acoustic methods have shown potential for the identification of early damage in brittle materials such as concrete. Commonly, these methods evaluate relative nonlinearity parameters from multiple resonance tests at different amplitudes. We demonstrate a recently developed alternative method, Impact Nonlinear Reverberation Spectroscopy (INRS), where quantitative nonlinearity parameters are evaluated from a single impact resonance test. The recorded reverberation of the measured signal is matched to a synthetic nonlinear damped signal. The proposed model allows instantaneous true physical amplitude, frequency, and damping of each mode to be characterized as a function of time, allowing for quantitative information of the nonlinear parameters. The hysteretic material nonlinearity can be quantitatively characterized over a notably wider dynamic range compared to conventional methods. Two examples from the application to concrete and stabilized soil are presented. In addition quantitative values of the hysteretic nonlinear parameter from stabilized soil samples are compared with the measured ultimate compressive strength of each sample.