Nondestructive Testing Of Materials Research Articles

Barker-Coded Thermal Wave Imaging for Non-Destructive Testing and Evaluation of Steel Material

Thermal non-destructive testing (TNDT) is one of the emerging inspection and evaluation techniques mostly used for subsurface defect detection in various industrial components. Besides the conventional thermography techniques (such as lock-in and pulse), recently introduced non-stationary thermal wave imaging (NSTWI) techniques gained its applicability in TNDT community due to their inherent testing capabilities such as improved sensitivity and enhanced resolution in inspecting and evaluating various solid materials for detecting subsurface defects. Barker-coded thermal wave imaging (BCTWI) is a one of the widely used NSTWI techniques, which facilitates the use of low peak power heat sources in moderate experimentation time in contrast to conventional TNDT techniques. In this paper, the pulse compression favorable NSTWI (BCTWI), the reconstructed pulsed (main lobe) data have been considered and processed using independent component analysis and named Barker-coded independent component thermography (BCICT). This proposed BCICT is implemented on a mild-steel sample to detect the artificially simulated flat bottom circular holes located at different depths inside it. The proposed technique extracts the sub-surface details such as flaws/defects hidden inside the sample by an unsupervised learning process, which helps in eliminating the manual interpretation of subsurface defects. The applicability of the proposed algorithm has been evaluated and validated experimentally with two different excitations schemes by considering the contrast and signal-to-noise ratio (SNR) as figure of merit. The results indicate that the BCICT technique offers higher contrast and SNR in comparison to conventional pulse-based TNDT technique.

Terahertz Scattering and Spectroscopic Characteristics of Polymethacryl Imide Microstructures

The translucency of terahertz wave through many polymer composite materials, particularly foams, makes it a good complement to another nondestructive testing (NDT) methods. Terahertz time-domain spectroscopy (THz-TDS) technology can obtain amplitude and phase information simultaneously. It is a powerful tool for nondestructive testing of foam materials to embody the depth information of defects while acquiring defect location, size, and nature. In the process of NDT, the refractive index is one of the important factors that affect the detection effect. In previous studies, the effective refractive index of polymethacryl imide (PMI), a commonly employed foam material, in the THz band is found to be very close to that of air. However, based on systematic measurements of the THz spectra and scattering parameters of PMI with a variety of thicknesses and densities, it is found that THz attenuation in PMI has a strong frequency dependence and that the size of the particles making up the material has a great influence on the attenuation: the larger the size of the micro particles and the faster the attenuation of the THz wave. This paper attempts to explain this phenomenon through combined experimental study and theoretical analysis, supported by the numerical simulation based on the Mie scattering model.

THE DEVELOPMENT OF OPTICAL TESTING TECHNOLOGY OF PCM STRUCTURES BY FIBER-OPTIC SENSORS

The ways of development of optical control technology of polymer composite materials structures by fiber-optic sensors during production and operation are described and investigated. A mathematical model describing the process of PCM monitoring using fiber optic sensors based on fiber Bragg gratings, clarifying the parameters of a mathematical model by experimentally determining the sensitivity coefficient of fiber optic sensors integrated in PCM, makes it possible to reduce the error in measuring strain by 5 – 7 times. The interaction in the system fiber-optic sensors – PCM and found that the integration of fiber-optic sensors based on quartz fibers in PCM, there is a partial destruction of the protective acrylate shell, which leads to the effect of microslip, which does not significantly affect the quality of measurements and can be compensated for by calibration. The requirements for the placement of fiber-optic sensors in the PCM at the manufacturing stage, including the formation of the input / output zone are formulated. The technology of optical non-destructive testing of composite materials with fiber-optic sensors is described, taking into account the features of the interaction of fiber-optic sensors with composite structures.

Finite element simulation in laser ultrasound for non-destructive testing of aluminum defect materials

激光超声技术能够在材料表面形成超声波，是实现材料缺陷无损检测的重要环节。借助Abaqus有限元分析工具，基于激光超声热弹机制建立了轴对称铝板的表面缺陷模型，模拟了激光激发产生的表面波在材料中的传播特性及其与铝板缺陷的相互作用过程。数值模拟实验表明，铝板表面缺陷的分布深度值越大，反射波越强，并且当缺陷深度达到一定程度时，反射波的幅值趋于稳定；但缺陷的分布宽度对于反射波的影响则十分有限。所得结论为基于激光超声的材料缺陷的定量检测及识别提供有效的理论依据。

Analysis of the Effect of a Constant Magnetic Field on the Results of Infrared Thermography Quality Control of the Polymeric Parts

This article studies the effect of a constant magnetic field (CMF) on the temperature signal characterizing premature curing of a binder during nondestructive testing of the polymeric materials by the infrared thermography method. Diagrams and thermographs, showing the change of the temperature distribution on the surface of the controlled specimen in case of the deviation of the curing agent amount from the norm by 5 wt % under the effect of the magnetic field, are presented. Orientational phenomena in the polymeric material under the influence of CMF are demonstrated by controlling the damping effect of the light energy in the polarized light. A replica of the magnetic state of the specimen is presented.

Correlating non-linear behavior of in-plane magnetic field and local domain wall velocities for quantitative stress evaluation

There is a need in industry to supply safe, effective and reliable technique to characterize the stress of steel components and structures, both at the manufacturing stage and in service. Bridging the correlation between micro and macro magnetic properties and the applied tensile stress is the first conceptual step to come up with a new method of non-destructive material testing. We investigate the stress-associated changes in domain wall dynamics in grain-oriented electrical steel by in-situ magnetic imaging using magneto-optical indicator films. The 180° domain walls velocity distribution is used as a parameter for applied stress determination. Additionally, the in-plane magnetic stray field above the surface of the sample is synchronously measured for stress evaluation. The variations in magnetic stray field outside the sample under different loading are investigated for the analysis of the domain wall dynamics. From this, an interrelation of the domain wall dynamics and magnetic stray fields with varied tensile stress is derived. The results provide substantial microscopic and macroscopic insight for the interplay of domain wall dynamics and stress-induced demagnetizing effect.

Dynamical behavior of integro-differential boundary value problem arising in nano-structures via Cellular Nanoscale Network approach

Piezoelectrical solid with nano-holes under time-harmonic anti-plane load is studied in the paper. The model is defined by the system of two partial differential equations and the boundary conditions which define the generalized stress. We reduce the model into an integro-differential boundary value problem and construct Cellular Nanoscale Network (CNN) architecture. Dynamical behavior of the obtained CNN model is studied by means of describing function technique. The simulations are provided which illustrate the theoretical results. The results of this paper are applicable in the field of non-destructive testing and fracture mechanics of multi-functional materials and structural elements based on them.

Identification of incipient pitting corrosion in reinforced concrete structures using guided waves and piezoelectric wafer transducers

Corrosion poses a great threat to ageing civil infrastructure in the world, and researchers are seeking methods to monitor the corrosion in reinforced concrete structures. Detection of corrosion at its incipient stage has been an impending task in the non-destructive testing of materials. Several non-destructive testing methods to assess the presence of corrosion exist. The limitation of the current methods is that either they require measurement at several points or they require a large network of sensors. Guided wave-based monitoring overcomes these limitations because a large area can be scanned using fewer sensors. The process of corrosion is complex, and it leads to a simultaneous reduction in the diameter and the debonding between concrete and reinforcing steel bars in reinforced concrete structures. However, some of the recent studies that explore the use of guided waves focus only on the detection of the individual effect of diameter reduction and debonding of the rebars in reinforced concrete by artificially inducing the damage. In this study, an accelerated corrosion setup is deployed to induce pitting corrosion in reinforced concrete beams using the impressed current method. These beams are continuously monitored using ultrasonic guided waves that are generated and received by piezoelectric wafer transducers that are attached to the rebars. It is shown that the incipient stage of pitting corrosion can be detected successfully, and the mechanism of corrosion process, which involves the corrosion initiation, progression, and diameter reduction-and-cracking phases, can be established from the signal characteristics of the longitudinal and flexural-guided wave modes. The impressed current flow in the corrosion cell also confirms the various phases of corrosion.

Electromagnetic Effect of Eddy Currents in Composites with Conductive Components: Magnetic Field Strengthening and its Simple Analytical Estimation

Composites and dynamic materials that include conductive components are becoming a suitable choice in different applications. The eddy currents are generated when the conductive components are placed in alternating magnetic field. The eddy currents decrease the primary field and this effect has been well studied and it is used for electromagnetic shielding. Besides, the magnetic field increases in small space near edges of the conductive components. While this effect of magnetic field strengthening is known, it is rarely examined. We will introduce a simple model that can be appropriate for the conductive components in form of long thin sheets. We analytically analyze the model and obtain expressions that give upper bounds for increasing of the net magnetic field. The electromagnetic effect of strengthening should be taken into account when considering an application of the composites. The results are useful for electromagnetic compatibility analysis, non-destructive testing and monitoring of composite and dynamic materials with conductive components.

Solenoid model for visualizing magnetic flux leakage testing of complex defects

Magnetic flux leakage (MFL) techniques are widely used for nondestructive testing of ferromagnetic materials. An analytical model of the MFL field is essential for precise determination and reconstruction of defects. In this paper, we proposed a solenoid model based on magnetization mechanisms of the magnetic medium to explain the MFL principle and simulate the MFL field. By introducing the interaction of solenoids and the Jiles–Atherton model, this model can accurately calculate the MFL field of complex defects, particularly the field distortion caused by the coupling of the defect's components. The solenoid model was experimentally demonstrated with a Z-shaped defect in the specimen and proved to be valid for precise calculation of the magneto-optical image. This work reveals the MFL testing principle from the viewpoint of the magnetic medium and thus helps elucidate and eradicate the simulation errors. The more accurate simulation than the common magnetic dipole model facilitates the inverse calculation of defects, even if field distortion is involved.

Air-coupled ferroelectret ultrasonic transducers for nondestructive testing of wood-based materials

Air-coupled ultrasound (ACU) is used in through transmission to detect delamination, rot, and cracks in wood without altering the structure permanently. Novel ferroelectret transducers with a high signal-to-noise ratio enable high-precision structure recognition. Transducers made of cellular polypropylene are quite suitable for ACU testing due to their extremely low Young’s modulus and low density resulting in a favorable acoustic impedance for the transmission of ultrasonic waves between the transducer and air. Thus, structures with great dimensions, with a thickness of up to 300 mm and material densities below 500 kg/m3, can be inspected. Promising results were obtained under laboratory conditions with frequencies ranging from 90 to 200 kHz. The advantage of ACU transducers is that they do not require contact to the sample; they are accurate and cost-effective. Ultrasonic quality assurance for wood is an important avenue to increase the acceptance of wooden structures and toward sustainability in civil engineering in general.

MANUFACTURING AND QUALITY ASSURANCE OF LIGHTWEIGHT PARTS IN MASS PRODUCTION

Production-related preliminary damage and residual stresses have significant effects on the functions and the damage development in fiber composite components. For this reason, it is important, especially for the safety-relevant components, to check each item. This task becomes a challenge in the context of serial production, with its growing importance in the field of lightweight components. The demand for continuous-reinforced thermoplastic composites increases in various industrial areas. According to this, an innovative Continuous Orbital Winding (COW) process was carried out within the framework of the Federal Cluster of Excellence EXC 1075 “MERGE Technologies for Multifunctional Lightweight Structures”. COW is aiming for mass-production-suited processing of special semi-finished fiber reinforced thermoplastic materials. This resource-efficient and function-integrated manufacturing process contains a combination of thermoplastic tape-winding with automated thermoplastic tape-laying technology. The process has a modular concept, which allows implementing other special applications and technologies, e.g. integration of different sensor types and high-speed automated quality inspection. The results show how to control quality and improve the stability of the COW process for large-scale production. This was realized by developing concepts of a fully integrated quality-testing unit for automatic damage assessment of composite structures. For this purpose, the components produced in the COW method have been examined for imperfections. This was performed based on obtained results of non-destructive or destructive materials testing.

Implementation of feedback control in kitchen sink production

The quality of deep drawn parts is affected by many different influences. These can be separated into material related, temperature related and tool related influences. In the case of the stainless steel used in kitchen sink production, the temperature not only influences the friction but also the material properties. Therefore, a continuous monitoring and adjustment of the process is needed. The present paper shows a possibility of monitoring the current state of the part in combination with a control system for the adjustment of the press to compensate for non-measurable influences. The proposed monitoring system consists of an optical measuring device for the part state, as well as a non-destructive material testing system for the determination of material properties. The control system uses the blank holder forces as actuators. Also, the performance of the proposed system in the production line is shown.

Non-destructive testing and evaluation of materials using active thermography and enhancement of signal to noise ratio through data fusion

Active thermography has emerged as an attractive and reliable technique for non-destructive testing and evaluation of a variety of materials, structures, and components due to its non-contact, whole-field, high speed and qualitative and quantitative inspection capabilities. However, the existence of non-uniform heating, low spatial resolution, and environmental noise cause some difficulties for defect detection and characterisation; demanding the necessity of various signal processing methods. Fourier transform has proved to be an effective method to extract amplitude and phase images from the recorded thermal sequences. Phase image has received extensive attention to the quantitative analysis, even though the amplitude image may contain useful information as well. Present work explores the possibility of enhancing the signal to noise ratio of inclusion defects in a GFRP composite sample through data fusion of amplitude and phase images as an innovative approach. Amplitude and phase images with several simulated inclusions of various shapes and sizes at different depth levels were considered. The well established and recognised pixel-level data fusion based on PCA and DWT techniques was performed and compared to detect and evaluate the inclusions.

Multi-Band RF Planar Sensor Using Complementary Split Ring Resonator for Testing of Dielectric Materials

In this paper, an attractive multi-band RF planar sensor, suitable for non-destructive testing of dispersive materials, is proposed. The proposed sensor is based on a number of complementary split ring resonator (CSRR) unit cells etched in the ground plane of the microstrip line. Each CSRR unit cell can be represented by a narrow band reject filter with its center frequency corresponding to the resonant frequency of the respective CSRR cell. The proposed technique is used to design the two, three and four band microwave sensors operating at 1.5 GHz, 2.45 GHz, 3.8 GHz, and 5.8 GHz. The distance between the two adjoining CSRRs is minimized for each case without appreciably increasing the inter-cell coupling effect. The transcendental equations required for determining the complex permittivity of the material under test in terms of the resonant frequency are derived from the numerical data obtained using the electromagnetic solver, the CST studio. These numerical equations are then used to obtain the dielectric properties of various test samples, which are measured using the vector network analyzer. The detailed air gap analysis is also performed for checking the accuracy of the designed planar sensor under the real situation. The proposed sensors are fabricated on 0.8 mm thick FR4 substrates using the standard photolithography technique. A number of standard samples are tested using the fabricated sensors in multiple frequency bands, and a good agreement between the obtained results and the data available in literature shows the applicability of the proposed scheme.

Elastic pseudospin transport for integratable topological phononic circuits

Precise control of solid-state elastic waves’ mode content and coherence is of great use nowadays in reinforcing mechanical energy harvesting/storage, nondestructive material testing, wave-matter interaction, high sensitivity sensing, and information processing, etc. Its efficacy is highly dependent on having elastic transmission channels with lower loss and higher degree of freedom. Here, we demonstrate experimentally an elastic analog of the quantum spin Hall effects in a monolithically scalable configuration, which opens up a route in manipulating elastic waves represented by elastic pseudospins with spin-momentum locking. Their unique features including robustness and negligible propagation loss may enhance elastic planar-integrated circuit-level and system-level performance. Our approach promotes topological materials that can interact with solid-state phonons in both static and time-dependent regimes. It thus can be immediately applied to multifarious chip-scale topological phononic devices, such as path-arbitrary elastic wave-guiding, elastic splitters and elastic resonators with high-quality factors.

Deep hashing network for material defect image classification

Common non‐destructive material testing technology has some well‐known problems such as slow detection, low detection accuracy, and low level of information obtained. To solve these problems, this study applied recent advances in convolution neural networks to propose an effective deep learning network using casting datasets. The approach achieves non‐destructive material testing with automatic, intelligent detection technology. For most existing deep learning networks, an image is eventually transformed into a multidimensional visual feature vector for comparison and classification. However, such vectors may not optimally improve detection precision and speed, and can lead to significant storage problems. A deep hashing network is proposed in which images are mapped into compact binary codes. There are three key components: (i) a sub‐network with multiple convolution‐pooling layers to capture image representations; (ii) a hashing layer to generate compact binary hash codes; (iii) an encoder module to divide the image feature vector from the output of the sub‐network above into multiple branches, each encoded into one hash bit. Extensive experiments using a casting dataset show promising performance compared with the state‐of‐the‐art approach.

Contactless Transient THz Temperature Imaging by Thermo-transmittance Technique on Semi-transparent Materials

THz waves have shown to be effective for several applications, such as security, non-destructive testing, and water content monitoring for porous materials and food products. This study aims to highlight the use of THz radiation to measure temperature variations of thin insulating materials opaque in the visible or IR range (PVC, PTFE, PMMA, and wood) by using a spectral thermo-transmittance technique. THz wave optical transmittance in materials show high sensitivity to temperature variations. The goal of this paper is to demonstrate the transient temperature gradient dependence of THz transmitted signals inside materials to develop a new contactless method for measuring temperature of thin materials semi-transparent to THz radiation. The principle is based on synchronous detection, using an infrared camera coupled with a THz to infrared thermal converter (TTC) with modulated millimeter-scale waves (2.7 mm). The results show a correlation between the transient temperature and the optical transmittance coefficient. Several types of samples semi-transparent to THz radiation are tested, and the corresponding thermo-transmittance coefficients as reported for PVC, PTFE, PMMA, and wood are respectively 0.805, 0.395, 0.640, and 1.177 K−1 m−1.

Application of Image Processing Algorithm in Chemical Production Technology

With the development and application of industrial CT technology, the nondestructive testing of materials and the manufacturing errors of materials can be effectively monitored and controlled. The basic principle of Industrial CT technology is to adopt the ray bundle of passing through the measured object to get the fault projection data, and then with the image reconstruction method the projection data will be scanned to get two- dimensional grey image. The traditional industrial CT technology is also facing the problem of image quality and image segmentation in image processing field. The industrial CT technology has been improved, in order to make expanders which can meet the needs of LNG liquefaction factories, and effectively control the quality of expanders. First of all, this paper analyzes the expander of LNG production equipment. Secondly, it introduces the industrial CT technology in detail. Then, it introduces the algorithm of image processing. Finally, combined with the new industrial CT technology, it conducts some experiments to verify that the proposed method can effectively detect the equipment like the core components of the expansion machine.

Dual-Laser Integrated Microwave Imaging System for Nondestructive Testing of Construction Materials and Structures

Microwave near-field imaging techniques have been successfully used for the nondestructive testing of construction materials in civil infrastructures. In this technique, the distance between the microwave antenna and the material, which is referred to as standoff distance is an important parameter. The standoff distance should be kept constant during the scanning process or there should be a proper compensation method to overcome any change in the distance. The undesired change in the standoff distance may mask the indication of flaws. However, civil infrastructures are composed of construction materials with different geometrical shapes and sharp edges, and maintaining the constant standoff distance during the scanning process is a challenging task. For this purpose, a novel dual-laser integrated microwave imaging system is proposed. The proposed system consists of a novel integrated sensing unit with two laser displacement sensors and a single microwave antenna that automatically follows the contour of the material under test at a constant standoff distance and generates microwave images. The proposed system performs contour following at hardware level and does not require any calibration or complex compensation algorithm. The comparison of two microwave antennas is performed to find the suitable antenna for different materials. The proof of concept of the developed system for the nondestructive testing of construction materials with different geometrical shapes is provided.