Non-destructive Testing Of Defects Research Articles

Magnetic focusing sensor and its characterizations of defect non-destructive testing for ferromagnetic steel plate

The fast development in precision manufacturing and product quality inspection of ferromagnetic material desperately demands that the defect determining the performance, service life and reliability of the mechanical part should be accurately sensed, detected and evaluated. However, conventional defect detection methods and related magnetic induction sensors are usually characterized with low accuracy in small defect detection, which makes the non-destructive testing (NDT) for ferromagnetic material full of challenges. Thus, a new magnetic focusing sensor is proposed and designed for the precision defect detection of ferromagnetic steel plate here. First, the theoretical principle analysis of the magnetic focusing sensor is introduced, and the preliminary finite element modeling (FEM) is conducted to demonstrate the feasibility of the magnetic focusing sensor in tiny defect inspection. Then, both the static and coupling dynamic characterizations of the magnetic focusing sensor are investigated using the FEM method. The optimal structural parameters of the magnetic focusing (MF) sensor in static conditions are summarized. Furthermore, the effects of the dynamic movement of the MF sensor on the multi-physical fields of the magnetization field, electric field, electromagnetic attraction force field and thermal field are all revealed. Finally, experiments regarding the performance evaluation and comparison between the MF sensor and other two magnetic flux leakage (MFL) sensors are conducted, and the prominent capabilities of accurate and precise defect detection for the MF sensor is demonstrated through the defect detection with different sizes. The effectiveness and feasibility of the MF sensor in detecting tiny defects on ferromagnetic object, as well as its great potential for practical application is therefore validated. Additionally, the main conclusions, advantages of the MF sensor are summarized and the future work is discussed.

Nano-Additive Manufacturing and Non-Destructive Testing of Nanocomposites.

In the present work, the recent advancements in additive manufacturing (AM) techniques for fabricating nanocomposite parts with complex shaped structures are explained, along with defect non-destructive testing (NDT) methods. A brief overview of the AM processes for nanocomposites is presented, grouped by the type of feedstock used in each technology. This work also reviews the defects in nanocomposites that can affect the quality of the final product. Additionally, a detailed description of X-CT, ultrasonic phased array technology, and infrared thermography is provided, highlighting their potential application in non-destructive inspection of nanocomposites in the future. Lastly, it concludes by offering recommendations for the development of NDT methods specifically tailored for nanocomposites, emphasizing the need to utilize NDT methods for optimizing nano-additive manufacturing process parameters, developing new NDT techniques, and enhancing the resolution of existing NDT methods.

Investigating the effects of defects and the effect of geometric anisotropy in stainless steel pipes: phased array ultrasonic test, SH-wave

Today, Phased Array Ultrasonic Testing (PAUT) is a suitable method for detecting defects in Non-destructive Testing (NDT). This simulation was done with a new method on a stainless steel pipe with a diameter of 500 mm and a length of 1,000 mm, and cracks were modeled on the external and internal surfaces and corrosion defects on the internal surface. Four probes with a characteristic of 2 MHz were used simultaneously, each probe having 64 elements. By increasing the number of probes and their elements, more accurate information about the defects is obtained, which makes it easier to detect the location and leads to a reduction of scattered signals and noise, which can detect even small size defects. Considering this important advantage, a new use of the method of increasing the number of probes in PAUT is reported in this study to detect defects, especially corrosion defects. The results of geometric anisotropy studies of group velocity and phase of horizontally polarized shear waves (SH-waves) for stainless steel pipe were presented. Due to the isotropic properties of the pipe material, the speed on the outer surface of the pipe in the direction of the cover is 40 m/s higher than the generatrix.

Study of the effect of hole defects on wood heat transfer based on infrared thermography

From a quantitative perspective using infrared thermography, this study examines the impact of various surface defect sizes on the heat transfer of wood under the condition of wood along-grain excitation. Firstly, the correlation between the defect size and the temperature change ΔT in the thermal steady state phase and the cooling coefficient Ve in the unsteady state phase were built by theory analyzed. And then, a theoretical analysis conducted under wood along-grain excitation conditions examines the theoretical relationship between the diameter D and depth H of the hole defect and the two thermodynamic properties ΔT and Ve. Second, using larch (Larix gmelinii) as the study's object, thermal excitation experiments and natural cooling experiments were conducted on wood specimens in the down-grain direction. The temperature field changes on the specimens' surfaces were recorded using a thermal imaging camera in order to obtain ΔT and Ve for various hole defect sizes. Then, using finite element modeling, the prediction models of ΔT and Ve are built, respectively, for the case of hole defects of various sizes. The model demonstrates that: A very strong negative correlation between the defect diameter D and the thermal steady-state temperature change ΔT (R2 > 0.946) and a very strong positive correlation with the cooling coefficient Ve (R2 > 0.985); The defect depth H has an extremely strong positive correlation with Ve (R2 > 0.946). In addition, as H increases ΔT increases first and then decreases, which is in line with the quadratic curve distribution (R2 > 0.991). Finally, the prediction model was compared with the experimental data for validation. The validation results revealed that the established model's ΔT was similar to the experimental ΔT variation pattern (R2 = 0.864) and that it was able to more accurately predict the pattern and value of Ve (R2 = 0.846, MAPE = 5.44%). The research results could lay some preliminary theoretical foundation for the formation of wood defect nondestructive testing technology based on infrared thermography.

A Modified Wavenumber Algorithm of Multi-Layered Structures with Oblique Incidence Based on Full-Matrix Capture

Full-matrix capture (FMC)-based ultrasonic imaging provides good sensitivity to small defects in non-destructive testing and has gradually become a mainstream research topic. Many corresponding algorithms have been developed, e.g., the total focusing method (TFM). However, the efficiency of the TFM is limited, especially in multi-layered structures. Although the appearance of wavenumber algorithms, such as extended phase-shift migration (EPSM) methods, has improved imaging efficiency, these methods cannot be applied to cases with oblique incidence. Therefore, a modified wavenumber method for full-matrix imaging of multi-layered structures with oblique array incidence is proposed. This method performs a coordinate rotation in the frequency domain to adapt it to the oblique incidence. It then utilizes wave-field extrapolation to migrate the transmitting and receiving wave field to each imaging line, and a correlation imaging condition is used to reconstruct a total focused image. The proposed method can deal with any incident angle without precision loss. Moreover, it inherits the computational efficiency advantages of the wavenumber algorithms. The simulation and experimental results show that the proposed method performs better in terms of accuracy and efficiency than the TFM. Specifically, it is nearly 60 times faster than the TFM when processing an FMC dataset with a size of 4096 × 64 × 64.

Characterization of image sequences of a defect using pulsed eddy current signals

Pulsed eddy current testing (PECT) has the advantages of rich information, efficiency and noncontact among defect nondestructive testing. Pulsed eddy current imaging technology also has a wide range of applications. However, the imaging method based on single feature is mostly adopted at this stage. In order to make better use of pulsed eddy current signals, signal slice based method was proposed for pulsed eddy current sequence imaging. Through the difference analysis of air-subtracted signal (ASS) and non-defect-subtracted signal (NDSS), sequence imaging in different ways is carried out. The influence of defects was explained by visualizing the diffusion of eddy currents in different specimens using a finite element model. ASS and NDSS image sequences were evaluated through image quality evaluation and quantitative identification. The result shows that there are some image frames in the image sequence that are better than the images generated by a single feature value in the image quality evaluation and quantitative analysis. It proves that the image sequence contains more defect information, which also illustrates the information richness of pulse eddy current detection.

Nondestructive Testing of Defects in Polymer–Matrix Composite Materials for Marine Applications Using Terahertz Waves

Fibreglass components employed in the marine environment are susceptible to moisture ingress, resulting in a degradation of mechanical properties. The nondestructive testing and evaluation of such materials using acoustic methods is possible under certain conditions, but the detection of internal voids and delaminations is masked by the presence of water in such internal flaws. Herein, we present an investigation into the use of terahertz technology to overcome these limitations, for the detection of damage and water ingress in thick woven glass-fibre composites. This investigation is facilitated by terahertz time-domain spectroscopy, coupled with physical raster scanning to realize object-penetrating imaging. Air-filled defects within the fibreglass volume are clearly identified using this technique. A spectroscopic investigation on the alteration of the terahertz-range dielectric properties of the fibreglass material due to water ingress is performed and a small change is measurable, although likely to be obfuscated by the interaction of terahertz-frequency radiation with the internal fibreglass structure. Moisture-ridden laminates do not impede propagation of terahertz radiation, and therefore wetted materials may be inspected for volumetric defects. A simulation of water-filled volumetric defects shows promise for practical application.

Identification of weld geometry from ultrasound scan data using deep learning

The identification of welding defects in Non-Destructive Testing (NDT) data is a complex task, achieved by experienced analysts. Recent deep learning implementations enable the automatic classification and assessment of welding defects in NDT data. However, current implementations do not indicate the context of the defects, i.e. they do not situate the defect inside a geometric representation of the weld. This study develops a deep learning framework to automatically identify and localize the geometrical elements of welds such as the heat-affected zone to create a three-dimensional representation of the weld structure directly from the ultrasound scan data.

Research progress of acoustic emission detection technology based on modal theory

The essence of modal acoustic emission theory is to study acoustic emission waves using Lamb wave theory. Different from the traditional acoustic emission research, the modal acoustic emission analyzes the entire waveform of the signal received by the sensor, distinguishes various modal waves in the composite material, and improves the detection accuracy of the composite material. At present, the research on acoustic emission technology of composite materials at home and abroad mainly focuses on five aspects of Lamb wave dispersion characteristics, finite element simulation of defect detection, experimental system design, time-frequency analysis of Lamb wave signal, damage location and damage imaging. From these five aspects, the research progress of the composite defect nondestructive testing technology is reviewed, and the problems to be further solved are put forward.

Application of linear frequency modulated laser ultrasonic radar in reflective thickness and defect non-destructive testing

Radar technology plays an important role in modern aviation and navigation. Radar systems use pulse-compression and match-filtering to detect large moving objects in the sky or in water, or small defects hidden inside industrial components, the object of this paper. We introduce a nondestructive testing (NDT) modality based on frequency-domain laser ultrasound (FDLU) by means of implementing radar principles: Linear-frequency-modulated (LFM chirp) excitation CW laser-beam intensity to perform, ultrasonic signal cross-correlation with the reference signal using pulse-compression and match-filtering, leading to reconstruction of time-domain sequences through inverse Fourier transformation at acceptable signal-to-noise ratios. Theoretically, the laser ultrasound radar (LUR) signal was modelled with both one- and three-dimensional thermoelastic equations, a combination of which was used to simultaneously predict the correct location and relative amplitude of experimental targets with relatively simple mathematical expressions that could not be used either in the 1-D (too simplistic) or in the 3-D (too complicated) approach alone. This methodology was further used to detect buried defects inside a metal alloy. The results demonstrated that the LUR system is capable of determining the thickness of the alloy material and quantitatively estimate the subsurface depth of defects in a signal generation process akin to echolocation.

Measurements of Vibrations Produced by Current Pulses in Elements of Electrical Equipment

The effects of vibration response of a conductor on the action of current pulses in the absence or presence of static loads have been studied. During the tests, three-component piezoelectric accelerometers were used to control the amplitude and time characteristics of vibration against a background of the effect of separate current pulses. The main characteristic used to determine vibrations was the acceleration of surface layers of metal. Single current pulses have no appreciable thermal effects on a sample. The experimental data that show that the main contribution, in the formation of mechanical oscillating processes, is made by an electrodynamic process determined by changes in the magnetic field and skin effect. It has been found that an increase in the static load leads to an increase in the decrement of oscillating process attenuations caused by the action of pulse current. A technique for measuring vibrations produced by the current pulses has been suggested. This technique of determining vibrations under the action of pulse current can be recommended for nondestructive testing of defects in structures, including in cases of their static load. The analysis of these results allows one to determine the service life of elements in windings of powerful energy equipment starting from normal operational modes to emergency conditions.

A flexible film type EMAT for inspection of small diameter pipe

Pipe structures are widely applied in industries, and different kinds of defects may occur in the structures during their long-time service. For non-destructive testing of defects in pipes of small diameter, it has to be conducted from the inner side of the pipe when there is no space for detection from the outside or the geometry of the outside tube surface is too complicated. In this work, a flexible film type Electromagnetic acoustic transducer (EMAT) probe with a dual coil configuration is developed. The new probe is flexible and can be inserted into the pipe for inspection. First, the feasibility of the new probe was studied through numerical simulation. Then the feasibility of the proposed flexible EMAT for detection of wall thinning in small diameter pipe was verified experimentally. It was found that the new EMAT method is suitable for the detection of wall thinning defects for small pipes.

A New Approach of Waveform Interpretation Applied in Nondestructive Testing of Defects in Rock Bolts Based on Mode Identification

Due to the characteristics of dispersion of guided waves, the waveforms recorded in ultrasonic nondestructive testing (NDT) of rock bolts are complicated to interpret. With a goal to increase the inspection sensitivity and accuracy in NDT of rock bolts, an approach of waveform interpretation based on wave modes identification is developed. The numerical simulation of full rock bolt and rock bolts with grout defect by Finite Element Method (FEM) is applied to illustrate the approach; it is found that the sensitive and low attenuation wave modes exist. Laboratory tests on full rock bolt and rock bolt with grout loss using NDT are conducted to evaluate the efficacy of the approach of waveform interpretation. In addition to that, a parametric study was conducted on rock bolt models with different sectional defect size. Based on the waveform interpretation, the mode-based reflection coefficientRis proposed to evaluate the sensitivity of wave modes to the defect size of sectional area. It is found that the sensitivity of the wave mode does not change with the defect sectional area, and the amplitude depends on the size of the defect.

Thermography pattern analysis and separation

Analysis of thermography spatial-transient patterns has considerable potential to enable automatic identification and quantification of defects in non-destructive testing and evaluation. This Letter proposes a non-negative pattern separation model for eddy current pulsed thermography to automatically extract important spatial and time patterns according to the transient thermal sequences without any pre-training or prior knowledge. In particular, the method is scale-invariant, such that large differences in surface emissivity, hot spots, and cool areas with dynamic range of thermal contrast can be extracted. Finally, an artificial slot in a steel sample with shining, black strip on the surface is tested to validate the proposed method.

Metropolis Monte Carlo for tomographic reconstruction with prior smoothness information

The Metropolis Monte Carlo algorithm was applied to produce tomographic reconstructions from scarce projection data supplemented by prior information about the smoothness of the object. The prior information is represented by means of local energy functions, which are added to the projection error. The proposed prior function is an extension of previous proposals of border filters, the novelty introduced here being an adaptive control of the filter during the reconstruction process. The method was tested on synthetic phantoms and the reconstructions of a real object from a small number of projections. The technique shows good results in images with piecewise homogeneous regions, and can be useful in certain applications, where the scanning views are within an angular range that is either limited or sparsely sampled, as the detection of material defects in non-destructive testing or special anatomical components in medical images. Finally, the method is applied to the reconstruction of an industrial application of a stainless-steel BNC elbow from very few projections.

Pulsed eddy current imaging and frequency spectrum analysis for hidden defect nondestructive testing and evaluation

Hidden defect characterisation in some complex structures is difficult. Pulsed Eddy Current (PEC) imaging based on rectangular excitation coil is investigated in this paper and hidden defect nondestructive testing and evaluation (detection, classification, and quantification) is carried out based on the various C-scan images. Experimental results have illustrated that hidden defects can be identified effectively by particular character in C-scan imaging results and sub-surface defects can be discriminated to correct class by selecting the rising time from response in time domain. The quantification information of hidden defects is preliminarily obtained based on the contour and 3D images. In addition, PEC imaging and frequency spectrum analysis are effective to detect, classify, and evaluate the sub-surface defects under the influence of edge effect of specimen. To sum up, PEC imaging is an effective approach to characterise hidden defects and sub-surface defects.

Application of Ultrasonic Wave and Resistograph for Nondestructive Testing of Defects in Standing Trees

In order to carry out non-destructive testing on standing trees, explore the propagation characteristics and the influence factors of the ultrasonic wave spreading in the standing trees. Take simon poplar as the research object, Resistograph were employed to test 30 sample (simon polar) standing trees and it gave a preliminary estimate of the internal defects in the samples, and RSM-SYS5 ultrasonic device were employed to test the ultrasonic propagation velocity spreading in simon poplar standing trees, with the statistics of the ultrasonic propagation velocity spreading separately in the health trees and standing trees with defects, and did a regression analysis of the relationship between the size of the defacts and the ultrasonic propagation velocity. The results show that: 1) When the diameter of sample trees are between 30 and 55cm, the radial velocity of ultrasonic spreading in healthy simon poplar standing trees are in the range of 1029.96m/s ~ 1200m/s, all more than 1000m/s; however, when there are defects in simon poplar standing trees, the ultrasonic radial velocity are less than 1000m/s. 2) The defacts in standing trees have an significant influence on the ultrasonic radial propagation velocity spreading in simon poplar standing trees, defect size and the radial velocity is significantly negatively correlated, and the correlation coefficient R is 0.887.

Laser-Generated Thermoelastic Waves in an Anisotropic Infinite Plate: FEM Analysis

ABSTRACT In recent years, the study of thermoelastic waves generated by focused laser beams has been undertaken by several researchers because the technique provides a means for noncontact generation of ultrasonic waves. Laser-generated ultrasonic waves have diverse applications ranging from material characterization to nondestructive testing of defects. Transient ultrasonic guided waves generated in an anisotropic infinite plate by a pulsed laser beam are investigated in this study. A semi-analytical finite element method (SAFEM) is adopted for this purpose. In this method, the plate is divided into parallel layers through its thickness and the displacement and temperature in each layer are approximated by quadratic polynomials in the thickness direction (z). They are assumed to be continuous functions of time and in-plane cartesian coordinates (x, y). Transient response is calculated using Fourier transformations in time and space variables (x, y). The analysis technique is applicable to a generally anisotropic plate. Results for dispersion of guided waves and transient displacement in infinite silicon nitride (Si3N4) plates are presented. Numerical results show that for the assumed form of heat deposition by the laser mainly the lowest Lamb modes, namely, the lowest symmetric (S 0) and antisymmetric (A 0) modes, are excited. They also show that the transient response is dominated by the antisymmetric mode A 0, which shows characteristic dispersion. This study provides a quantitative model for laser-generated thermoelastic waves in an anisotropic plate and can be used for nondestructive evaluation.

Photoanisotropic Effects in Poly(vinyl-cinnamate) Derivatives and Their Applications

The effect of LC photo-aligning by poly(vinyl-cinnamate) (PVCi) derivatives is consequent to the phenomena of the photo-induced optical anisotropy, found in PVCi films during their illumination by UV-light within the self-absorption band of the PVCi film. We proved in our experiment, that the phenomena of the photo-induced birefringence in thin films of PVC derivatives takes place due to the two main factors: described earlier irreversible photochemical process (2 + 2) cycloaddition of cinnamoyl groups and reversible photophysical reorientation of the chromophore groups, that accumulates photochemical non-active part of the UV-light energy. We reviewed various applications of the effect of photo-induced optical anisotropy in PVCi films including: writing the polarization holograms and images, optical data processing, development of different polarization optical elements, non-destructive testing of defects, LC photo-aligning. Most of the early papers, devoted to the above mentioned applications were published in 1977–1987 in USSR only and are not well known worldwide.

Ультразвуковые средства неразрушающего контроля дефектов в изделиях из композиционных материалов

Ультразвуковые средства неразрушающего контроля дефектов в изделиях из композиционных материалов