The multi-layer structure of GFRPs can result in layered defects during production and service, which can significantly impact the integrity and safety of equipment. To achieve precise quantitative characterization of delamination defects in GFRPs, a novel method is proposed to detect the depth and thickness of defects. We establish a mathematical relationship between the depth and thickness of the defect and amplitude of the echo signal. Employing the verified mathematical model, we successfully solve for the depth and thickness of the defect by analyzing amplitude of the echo signal based on least square method. According to our findings, the proposed method demonstrates the capability to simultaneously measure the depth and thickness of defects. Notably, the method exhibits outstanding accuracy, with the detected thickness error being within 0.01 mm and the depth error within 0.1 mm.

The debonding defect is one of the critical flaws that have been posing a severe threat to structural integrity of Glass Fibre Reinforced Polymer (GFRP). In this paper, a sweep-frequency microwave testing method based on Cross-polarization Microwave Reflectometry (CMR) is proposed for detection and imaging of debonding defects in a unidirectional GFRP. Simulations and experiments are carried out to investigate the feasibility and applicability of the proposed method. The characteristics regarding the testing signal in Ka band (26.5GHz~40GHz) is scrutinized along with the correlation of the signal feature with the defect sizing parameters. In experiments a direct wave suppression method is proposed for enhancement of the defect image quality. The debonding area is subsequently assessed by using an edge-recognition algorithm.

Thermal barrier coating (TBC) is a key component of the heavy duty gas turbine blade to protect the substrate material from high working temperature. Thinning of the top coating and the thermally grown oxide (TGO) layer formed between TC and BC cause TBC thickness reduction, which may significantly affect the in-service performance of TBC. High frequency eddy current testing (HF ECT) is considered as an efficient technique for nondestructive evaluation of the TBC thickness but its measurement accuracy is not satisfied up to now. Aiming to realize a high precision TBC thickness evaluation with HF ECT signals, a numerical method for simulating HF ECT of TBC was developed and implemented with consideration of the dielectric properties of TC and TGO material. It was found that the thickness of the TC layer can be evaluated with a 10 μm accuracy for the plate TBC specimens, which reveals the HF ECT method and new ECT probe are suitable for sizing of TBC thickness.

In this paper, a ferrite-cored funnel-shaped probe of pulse-modulation eddy current (PMEC) is proposed for quantitative screening of pitting corrosion in conductive heterostructures. Closed-form expressions of field quantities regarding the proposed probe are formulated via the semi-analytical modelling. Results from theoretical simulations reveal good characteristics of the probe particularly in terms of high-sensitivity testing of the pitting corrosion buried in the conductor and capability of balancing the defect detection depth and spatial resolution. Experiments are being conducted to further investigate the imaging and evaluation of pitting corrosion via PMEC, which alongside the theoretical investigation would confirm the superiority of the proposed probe.

In eddy current testing, lift-off signals are often larger than crack signals; therefore, post signal processing and/or probe design are used to suppress lift-off signals in surface inspection. We have proposed a differential tangential eddy current probe with dual induction. The dual induction is induction in which self and mutual inductions are performed simultaneously. In simulation using the finite element method, it is confirmed that lift-off signals of the self and mutual inductions have an anti-phase property, and the proposed probe suppresses lift-off signals by 80 - 90% when adjusting the mutual induction excitation current.

Thickness of thermal barrier coating (TBC) is one of the key parameters of its thermal insulation ability. It is very essential to evaluate the thickness of TBC nondestructively. There is still a lack of a nondestructive evaluation technique to efficiently measure the thickness of TBC of a large area. In this paper, two spots pulse laser thermography methods, i.e., the array spots laser thermography and the scanning spots laser thermography, were adopted to measure the thickness of TBC by using the time at the minimum 2nd derivative of the falling edge of the temperature evolution curve. Both numerical simulation and experimental results show that the laser spot methods are feasible for the thickness measurement of TBC specimen prepared by using the atmospheric plasma spraying technique.

This study evaluates the effect of how currents are injected on the accuracy of electrical impedance tomography using the monotonicity-based inverse analysis algorithm. Electrical Impedance Tomography (EIT) is a technique to evaluate the distribution of electrical impedance inside a target from the voltage on the surface of the target. One of the largest problems associated with EIT is that the inverse problem it deals with is significantly ill-posed because there is no clear mathematical background that assures the uniqueness of the solution, unlike X-ray computed tomography.The results revealed the importance of choosing a proper condition, such as the number of electrodes and the current pattern, to evaluate the impedance inside the target.

This study evaluated the effect of current injection pattern on the accuracy of EIT results obtained using algorithm which is based on the monotonicity principle. The results obtained revealed that a proper condition, such as the number of electrodes and the current injection pattern, depends on the target.

Magnetic field has been playing an important role in many key fields. Measuring magnetic field is quite important for us to understand and make better use of it. Magnetic field measuring sensors are important components to transform information of invisible magnetic field into visual information. In this study, we proposed a novel sensor based on the magneto-thermal effect of the magnetic nanoparticles. We used the sensor to measure the magnetic field distribution of different alternating magnetic fields, by taking the temperature rise rate of the sensing unit to characterize the magnetic field intensity, converting magnetic information into infrared temperature images. The effectiveness of the sensor was also verified through both simulation calculations and comparative experiments. It is found that the proposed novel sensor can be flexible, arrayed, passive and wireless, and it breaks through the measurement of high frequency magnetic field.

This study estimated the profiles of a fatigue crack from eddy current signals probabilistically based on Bayesian estimation. Artificial rectangular slits and fatigue cracks were measured by eddy current testing to obtain the likelihood functions and test data, respectively. Numerical simulation was also conducted by the 3-dimensional finite element method. Experiment and numerical signals were used to estimate the profiles of the fatigue crack.

Rectangular wave eddy current testing is a technique that can simultaneously acquire both low- and high-frequency information, thus allowing detection of surface and backside flaws. During flaw detection, the excitation field affects the accuracy of the detected signal. Therefore, a compensation coil is employed to compensate for the direct magnetic field from the excitation magnetic field. A 12 mm-thick aluminum plate with flat-bottom drilled holes on its backside is used as a specimen. The diameter of the holes is 3 mm, and the depths of the holes are 2, 4, and 6 mm. Results show that flaw signals of 4 and 6 mm are successfully detected.

The bidirectional radiation pattern of conventional shear vertical wave electromagnetic acoustic transducers(SV-EMAT) reduces the signal energy and makes it difficult to locate the scatterer. In this work, we propose a new unidirectional SV wave EMAT with an oblique bias magnetic field(OMF-EMAT). Oblique magnetization changes the distribution of the ultrasonic field over the two obliquely incident SV waves and improves the unidirectionality and signal amplitude. Firstly, the magnetic circuit superposition approach is selected to generate oblique magnetic fields; Then, the OMF-EMAT is designed and the corresponding time-domain simulation model is established to further analyze the effect of the oblique magnetic field on the unidirectionality of the ultrasonic beam. It is found that when the magnetic field oblique angle is in the range of 45°, the unidirectionality of the acoustic beam gradually increases with the increase of the magnetic field oblique angle, and the signal amplitude shows a trend of first increase and then decrease.

Electromagnetic thermography detection technology holds significant importance in the field of non-destructive detect, necessitating further research. Recent years have witnessed substantial advancements in electromagnetic thermography detection. The theoretical investigations focused on the analysis of uniform detection regions that facilitate the amplification of thermal contrast for the detection of subtle signals. In terms of sensor coil design, a novel L-shaped electromagnetic sensor capable of generating a uniform magnetic field was proposed, yielding significant improvements in the detectability and thermal contrast of omnidirectional micro fatigue cracks. A multi-physical structure, integrating eddy current detection and electromagnetic thermography, was proposed for defect diagnosis in dynamic experiments. Building upon these results, an electromagnetic thermography detection system employing a long return-loop three-turn coil was developed, enabling defect detection experiments on an actual calibrated line under the conditions of a 30mm lift-off and an 80 km/h detection speed. Remarkably, 11 calibration wounds of varying depths were successfully detected.

Terahertz (THz) nondestructive testing has been considered as a promising method for measuring the thickness of thermal barrier coatings. However, there are few reports concerning the online evaluation of the results without destructing specimens. Thus, a physics-based transfer learning framework is presented to build the relationship between the residual signals and errors of thickness measurements. To decrease the training cost, the source domain and target domain are simulated and experimental residual signals, respectively, but the differences between these two types of data cannot be ignored due to the THz dispersion. A physical constraint layer is proposed to improve their similarity for decreasing the errors. The results show that our method evaluates the thickness measurements of the actual specimens with an accuracy of 95.2%.

Metal structures are widely used in industrial fields, for which various composite defects are probably produced from manufacture to service. For example, both the surface and bottom of structures emerge defects. Facing the composite defects, a single electromagnetic nondestructive testing (ENDT) method usually cannot meet all needs. However, two or more targeted ENDT methods have the problems of low efficiency. To solve this problem, a novel pulsed eddy current and electromagnetic ultrasonic (PECT-EMAT) hybrid testing method is developed. For this developed method, the surface defects and bottom defects can been detected synchronously only by one set of testing system and probe based on the demodulated electromagnetic components and ultrasonic components. In addition, as a novel ENDT method, it is necessary to evaluate the detection capability of the PECT-EMAT hybrid testing method. Therefore, a reliability evaluation method based on probability of detection (POD) is developed.

One of the plasma-facing unit design options for the divertor in a nuclear fusion reactor is a tungsten mono-block with a screw pipe that has grooves on the inner wall for high heat removal capability. To develop a non-destructive inspection method for the cooling pipe, this study evaluates the applicability of high-frequency ultrasonic tests to inspect the interface between the pipe and mono-block. Samples with grooved surfaces were prepared and inspected by an ultrasonic microscope. The results indicate that defect detection performance is reduced due to ultrasonic scattering from the screwed inner wall.

In this paper, a numerical scheme for simulation of infrared thermography images under ultrasonic excitation is proposed and validated. A FEM code is updated at first to calculate the vibration of the inspection object with internal cracks excited by body ultrasonic wave. The relative displacement at the crack interface and contact force are subsequently extracted to find the strength of inner heating flux. Using the obtained pulsed inner heating source, the temperature field is calculated by treating the ultrasonic heating flux as a quasi-static equivalent heating source. The numerical scheme is finally validated by comparison its results with that using commercial software.

In service pipelines are prone to various defects such as corrosion and cracks on the inner and outer surfaces under complex working conditions. Magnetic permeability perturbation testing (MPPT) owns the advantage of high sensitivity for both inner and outer surfaces defects in ferromagnetic pipes. A method of distinguishing internal and external defects based on layered magnetization with variable pole shoe thickness is proposed. The effects of pole shoe thickness on the magnetization are analyzed by FEA model. The simulation and experiment results show that the method performance well for distinguishing internal and external defects.

A method is proposed to estimate the radiation source distribution inside the fuel debris storage canister from the γ-ray energy spectrum detected by NaI crystals placed outside the storage canister. This method is a combination of a particle transport Monte Carlo simulation and a neural network for machine learning. It was shown that the estimation accuracy for simple physical models was high.

The paper reports on the development of a new EMAT sensor using a configuration based on Halbach magnet to detect defects in long metallic plates, up to 3.5 meters. Optimizations of the EMAT sensor, related to Halbach magnet configuration and others, enable greatly increase the signal-to-noise ratio of the defects. The defects are located on the opposite side of the surface from the EMAT sensor position, with depths up to 20% of plate thickness and at much greater distances (meters) from the sensor, in a frequency range below 1 MHz. Experimental measurements confirm the feasibility of the method, and the new EMAT opens up the possibility of faraway detection of defects in the meter range, as compared with the standard EMAT method until now limited to a 0.1~0.4 m applicability in metallic plates.

Engineering structures are prone to damages from stress and environmental factors. An effective way of monitoring structural health of these structures is by using the ultrasonic nondestructive evaluation (NDE) technique. In general, ultrasonic techniques are contact methods requiring use of a couplant to couple the energy into the test object. To address this problem, Electromagnetic Acoustic Transducer (EMAT) techniques were introduced which use Lorentz force acting on induced currents to generate an elastic wave. EMAT’s are effective on conductive or ferromagnetic samples. This paper presents a novel EMAT for use with non-conductive samples. Numerical model and simulation results are presented to demonstrate the feasibility of generating an elastic wave in the non-conductive sample.