Full Matrix Capture Research Articles

Dual-tandem phased array method for imaging of near-vertical defects in narrow-gap welds

Near-vertical flaws in thick-section narrow-gap welds are notoriously difficult to detect and size using traditional Phased Array Ultrasonic Testing (PAUT) techniques. Self-tandem shear inspection has been considered for detection but lacks appropriate full weld sensitivity. The dual-tandem phased array inspection method is proposed to enable multi-mode Total Focusing Method (TFM) pulse-echo imaging with longitudinal through-transmission inspection, by introducing a second, opposite-facing probe on the far weld side. Pulse-echo and through-transmission datasets are obtained in a single Full Matrix Capture (FMC) acquisition, for each weld side. Analysis of the optimum Probe Centre Spacing (PCS) based upon image sensitivity suggests that a spacing corresponding to a longitudinal beam crossover at 2/3 sample thickness provides greatest weld coverage. Testing on near-vertical EDM notches in a 120 mm thick mock narrow-gap carbon steel sample has shown high sensitivity TFM imaging, at notch depths of 27.5 mm, 60 mm and 92.5 mm. Pitch-catch through-weld transmission imaging has exhibited tip-diffraction images with a Signal-to-Noise Ratio (SNR) of up to 17.3 dB. Pulse-echo imaging using multi-mode TFM has shown tip-diffraction and reflection with up to 19.2 dB and 34.8 dB SNR respectively. The possibility of image mixing by considering image defect response type has provided full 2D notch reconstruction. These results demonstrate the strength of the dual-tandem method in enhancing the detection reliability and detection of near-vertical defects in thick-section narrow-gap welds.

Study of curved structures health monitoring with flexible omnidirectional guided-wave transducers

In this paper, structure health monitoring (SHM) of curved plates with improved flexible transducers capable of generating and receiving omnidirectional guided waves is studied. The improved thin and flexible transducer consists of a dual-layer ring coil and a thin magnetostrictive patch is firstly proposed to generate and receive a single-mode and almost non-dispersive guided wave omnidirectionally in curved plates. A finite element simulation is then used to investigate the design of the transducer. The flexible omnidirectional guided-wave (GW) transducers made with flexible printed circuits (FPC) and handwound coils, respectively, are measured and compared by experiment. Finally, a sparse array system based on the proposed flexible omnidirectional GW transducer is developed for the SHM of the curved plate. The influence of the curvature of the plate on the performance of the developed transducer is investigated. A post-processing method based on full matrix capture (FMC) and total focusing method (TFM) with the sparse array of flexible omnidirectional GW transducers is applied to inspect and image the defect in the curved plate. • A new flexible GW transducer can generate and receive a single-mode and almost non-dispersive guided wave omnidirectionally in curved plates. • The O-GW MPT is light in weight, small in size, and flexible in structure. • The experiment results show that the curvature and deformation of the plate almost do not influence the performance of the flexible O-GW transducer. • Combined with the post-processing method, the omnidirectional transducer can apply to inspect and image the defect in the curved plate.

High signal-to-noise-ratio ultrasonic imaging of crack defects in particles filled composite explosives

<sec>Polymer bonded explosive (PBX) is a kind of composite material with highly filled molding explosive particles (normally more than 95%) and a small quantity of binders (less than 5%). The effective detection of internal cracks in PBX is of great significance in evaluating structural integrity and safety reliability.</sec><sec>Ultrasonic phased array detection and imaging methods show great advantages and potential in detecting crack defects. But acoustic test results indicate that the PBX has unique characteristics with low longitudinal wave velocity (～3000 m·s<sup>–1</sup>) and strong attenuation (attenuation coefficient ～400 dB·m<sup>–1</sup> for 2.5 MHz ultrasound). When the defect is imaged by traditional ultrasonic total focusing method (TFM), the structural noises at the boundaries between particles lead to low signal-to-noise ratio (SNR) in the FMC signals and strong background noise in reconstructed image, which will disturb the detection of cracks.</sec><sec>To realize the high SNR imaging of crack defects in PBX, an ultrasonic imaging algorithm based on baseband nonlinear synthetic focusing (BB-NSF) is proposed. By utilizing the spatial coherence of the received signals in full matrix capture (FMC) data, the pixel intensity at defect position can be enhanced while the background noise can be drastically weakened. The delay rule of the algorithm is modified according to the characteristics of PBX surface configuration. In this way, the high SNR imaging of crack defects with different orientations of PBX surface configuration is realized, and the quality of the reconstructed images is compared and evaluated quantitatively. Meanwhile, the base band transformation in calculation process optimization could significantly reduce calculation burden and increase imaging efficiency.</sec><sec>Experimental results show that the proposed algorithm can effectively suppress background noise and significantly improve the ability to detect the PBX cracks. The effective suppression to background noise makes the defect more highlighting and distinguished easily. For the BB-NSF algorithm, spatial coherence coefficient <i>p</i> is a crucial parameter used for dynamically regulating the SNR of reconstructed image. When <i>p</i> value is more than 2.0, the SNR of the ultrasonic reconstructed image of PBX crack defect is improved by more than 10 dB compared with that of the traditional linear synthetic focusing imaging. With the increase of <i>p</i> value, the SNR is further improved, while the calculation efficiency for a single image is almost kept stable. Moreover, the increase of SNR to some extent will improve the far-field detect capability.</sec><sec>Besides, with the BB-NSF algorithm, flexible transducer inhibits different imaging characteristics of for cracks with different orientations and depths in curved PBX specimens. For defects with large orientation angle and buried depth, the tip, root and shape of cracks can be completely present. For defects with small orientation angle and buried depth, part of shape and contour features will be lost.</sec><sec>In conclusion, the BB-NSF algorithm shows the advantage of high SNR and calculation efficiency in imaging PBX cracks, and exhibits great application prospect in imaging internal defects of other strongly attenuated composites.</sec>

Total focusing method (TFM) and phase coherence imaging (PCI) applied to various industrial cases

Imaging techniques based on ultrasonic Total Focusing Method (TFM1) are more and more applied for industrial applications. Adoption of the technique has been made easier with the publication of the revised ASME V and ISO 23864 and 23865 standards. TFM is an inspection technique that involves two steps: the first one is the data acquisition process called Full Matrix Capture (FMC) and the second one is the data reconstruction itself called TFM. TFM is able to focus the energy at every pixel within a region of interest providing a high-resolution image. Efforts have been made to improve the productivity of the technique using various excitation modes such as Plane Wave Imaging (PWI) to reach scanning speeds comparable to standard phased-array inspections while maintaining code compliance. While TFM is based on the extraction of the amplitudes of the FMC matrix, another technique called Phase Coherence Imaging (PCI2) uses the phase information from those signals. The PCI image shows high values when all the elements contribute in phase. This is the case for small diffractors that tend to send energy in all directions such as small cracks (HTHA, porosities???), tips from cracks and grain noise. At the opposite, specular echoes tend to be minimized since few elements contribute to the echo. In this paper, we???ll show the advantages of both techniques on various industrial cases.

High-resolution ultrasonic imaging of the defects in coarse-grained steel by a weighted total focusing method

Ultrasonic testing of coarse-grained materials is strongly influenced by high-level scattering noise. In addition, the signalto-noise ratio (SNR) and spatial resolution of imaging by the traditional total focusing method (TFM) are relatively low. In this study, we focused on the reconstruction of high-resolution ultrasonic images from full matrix capture datasets. A weighted TFM image by combining the inverse problem-based method and traditional TFM is proposed to detect defects in coarse-grained steel. The proposed method was used to image defects with the full matrix data obtained through simulations and experiments. The simulation and experimental results show that the weighted total focusing method can significantly improve the SNR of ultrasonic imaging in coarse-grained steel and, moreover, it can improve the resolution of imaging and distinguish adjacent defects with a centre distance less than the Rayleigh criteria.

Laser ultrasonic imaging of complex defects with full-matrix capture and deep-learning extraction

Phased array-based full-matrix ultrasonic imaging has been the golden standard for the non-destructive evaluation of critical components. However, the piezoelectric phased array cannot be applied in hazardous environments and online monitoring due to its couplant requirement. The laser ultrasonic technique can readily address these challenging tasks via fully non-contact inspection, but low detection sensitivity and complicated wave mode conversion hamper its practical applications. The laser-induced full-matrix ultrasonic imaging of complex defects was displayed in this study. Full matrix data acquisition and deep learning method were adapted to the laser ultrasonic technique to overcome the existing challenges. For proof-of-concept demonstrations, simulations and experiments were conducted on an aluminum sample with representative defects. Numerical and experimental results showed good agreement, revealing the excellent imaging performance of proposed method. Compared with the total focusing method based on ray-trace model, the deep learning method could create superior images with additional quantitative information through end-to-end networks, which use the hierarchical features and generate details from all the relevant imaging and physical characteristics information. The proposed method may help assess defect formation and development at the early stage in a hazardous environment and understand the in-situ manufacturing process due to its couplant-free nature.

An optimized total focusing method based on delay-multiply-and-sum for nondestructive testing

Total focusing method (TFM) attracts much interest because of high image resolution and large inspection coverage. However, the synthetic focusing approach based on delay-and-sum beamforming employs only the defect information contained in the dataset while ignoring the spatial information of the array signals, leading to limited imaging performance mixed with artifacts and noise. In addition, the signal-to-noise ratio (SNR) suffers due to single-element emission of full matrix capture. This work combines a modified delay-multiply-and-sum (DMAS) beamforming approach with conventional synthetic focusing in the TFM algorithm, to achieve optimization of TFM imaging performance. DMAS-based TFM is able to take full advantage of the defect and spatial information in the array dataset, and to generate new frequency components for better image reconstruction. As demonstrated on a series of comparative simulation and experimental results, the imaging results of the optimized TFM provide a considerable improvement in SNR. Better lateral spatial resolution is also achieved due to the increased number of equivalent transducer elements and second harmonic component. Therefore, this work provides a quite promising alternative solution for the post-processing of ultrasonic phased array with improved imaging performance.

Sizing limitations of ultrasonic array images for non-sharp defects and their impact on structural integrity assessments

Existing structural integrity assessment procedures typically assume flaws to be infinitely sharp when they cannot be considered as local thinned areas. This assumption is often over-conservative, resulting in a pessimistic assessment of structural components and a significant underestimation of their margins of safety against fracture. One of the main challenges while adopting non-destructive evaluation techniques is distinguishing between sharp cracks (e.g., fatigue) and non-sharp defects and identifying the more severe ones. Towards this broader challenge, the present work aims to examine the sizing limitation and accuracy of ultrasonic array image-based techniques for non-sharp defects (surface breaking u-notches) and investigate how these measurements would affect the structural integrity assessment of components. Parametric numerical simulations and experimental measurements are performed to generate full-matrix capture datasets, which are then processed using the total focusing method to form an image. The image-based sizing approach is shown to perform efficiently for notch depths higher than the inspection wavelength (λL), i.e. as small as 0.2 mm, and semi-notch widths as small as 0.1 mm. The influence of ultrasonic measurements on structural integrity assessments is highlighted using different case studies in the context of non-sharp defects of fatigue and fracture strength estimates. For the cases under analysis, resolving non-sharp defects led up to 5× and 3× values of effective fracture toughness and fatigue strength, respectively. We have also seen that a 30 % uncertainty in semi-notch width sizing would result in a 30 % and 20 % error in fatigue strength and fracture toughness estimations, respectively.

An ultrasonic wave‐based framework for imaging internal cracks in concrete

Nondestructive detection and sizing of internal cracks initiated in reinforced concrete have been critical problems. Geometric characterization of internal cracks and delaminations contributes to predicting their propagation path and failure pattern followed by structural prognostics. There have been limited studies on quantitative detection and characterization of vertical cracks in concrete using wave-based NDE techniques. This study focuses on solving the problem of imaging deep internal crack planes in the concrete medium by leveraging the ultrasonic shear horizontal (SH) waves from a transducer array. Post-processing the array full matrix capture (FMC) data with both total focusing method (TFM) and plane wave imaging (PWI) reveals their efficiency in mapping planar defects inclined between 0° and 60°. However, their performance on vertical/near-vertical defects is found to be inferior with imaging limited to the tip of the defect planes. Further, half-skip modes of wave dispersion have been adopted in addition to the directly scattered pulses for imaging the vertical and near-vertical cracks. We propose an imaging framework based on the outcomes of our investigation on the best suitable methodology to detect and map planar defects like cracks inclined in the range of 0–90°. Statistical quantification of defect inclinations from the reconstructed images is compared to the ground-truth orientations, and they are found to be 94%–99% accurate. Besides accuracy, the computational efficiency of the proposed techniques makes them desirable and reliable for quick on-site inspections on built infrastructure.

Enhanced ultrasonic total focusing imaging of CFRP corner with ray theory-based homogenization technique

Ultrasonic testing is effective in defect characterization and quality assurance of Carbon Fiber Reinforced Plastic (CFRP) components in the aerospace industry. Due to the coupling between complex shape and elastic anisotropy, the Phased Array Ultrasonic Testing (PAUT) and time-based Total Focusing Method (TFM) face significant challenges in the calculation of wave propagation. A wave velocity distribution model is established for a multidirectional convex corner of CFRP based on a homogenization theory and the above coupling effects are also incorporated. A ray-tracing method is proposed based on Dijkstra’s shortest path search algorithm. The predicted time of flight ensures that this technique, the homogenized TFM, could synthesize a high-quality focused image by post-processing on the full matrix capture data. Experiments on a laminate with three ϕ1.5 mm Side-Drilled Holes (SDHs) in different circumferential directions confirm a successful homogenized TFM imaging that all SDHs can be effectively detected. As compared to the isotropic scenario, the maximum positioning error is reduced to 0.12, 0.08, and 0.38 mm, and the Signal-to-Noise Ratios (SNRs) are increased by 2.1, 1.1, and 11.8 dB, respectively. It is suggested that the ray-tracing assisted TFM technique can effectively improve the imaging of corners in CFRP components.

New trends in the ultrasonic imaging of concrete structures by means of 3D-FMC technology

The novel technologies in ultrasound generation and data processing offer new opportunities for three-dimensional imaging of concrete structures. Especially the Full-Matrix-Capture (FMC) technique with its real-time imaging capability can be successfully utilized for quality assurance in the construction industry. Although, the available testing instruments on the market implement the principle of linear transducer array with its two-dimensional reconstruction of B-Scan images based on the Synthetic Aperture Focusing Technique (SAFT) principle. The Dry-Point-Contact (DPC) transducers utilized in commercially available instruments for concrete testing with their matrix-like layout offer a direct opportunity to implement a three-dimensional Full-Matrix-Capture (FMC) data acquisition cycle. The obtained data can be in real-time processed by 3D-TFM reconstruction and visualized and evaluated three-dimensionally. In the present contribution both state-of-the-art and novel true-3D imaging approaches and data assessment are considered on real concrete inspection objects and the advantages of enhanced data processing with respect to improved information content and easiness of result, interpretation is discussed.

Adaptive optimisation of multi-aperture ultrasonic phased array imaging for increased inspection speeds of wind turbine blade composite panels

Ultrasonic phased array testing is a commonly used inspection modality in a range of non-destructive testing (NDT) fields. The recent rapid growth in demand for wind turbine installations means that blade manufacturers must address any potential NDT bottlenecks. Multi-aperture (MA) beamforming has previously been shown to increase frame rates, and hence inspection speed, when compared to traditional linear beamforming, in both NDT as well as medical applications.In this work an adaptive MA and spacing concept is presented to autonomously optimise the MA focal laws for the sample in question as well as a critical defect size. For this, full-matrix capture (FMC) data from a calibration sample, designed specifically for the target defect size and spacing, is used to drive the resultant optimised inspection scenario. A 6.7-fold increase in scanning speed with no degradation in resolution or defect sizing accuracy is reported. Three inspection scenarios are presented using firstly linear beamforming at 3.0 mms−1 and 22.0 mms−1 and finally MA beamforming at 22.0 mms−1. Resolutions of 0.8, 5.4 and 0.8 mm in the scan axis are recorded and consequently the optimum scenario, allowing for high resolution at the higher scanning speed, is presented. The concept and process are verified and validated by C-scan inspections of a carbon fibre re-enforced plastic (CFRP) sample, at varying inspection parameters, commonly used in high-power blade construction.

Lamb Wave Based Total Focusing Method for Integral Grid-Stiffened Plate Damage Identification

The integral grid-stiffened plate is often used as the outer wall structure of spacecraft, which can reduce weight and increase strength. The Lamb wave is often used to detect damage of plate structure due to its advantages of strong penetration and minimum attenuation over long distances. When the Lamb wave crosses the stiffeners, the dispersion, reflection, transmission and mode conversion waves will be superimposed, resulting in difficulties in damage detection and structural health monitoring (SHM). This paper proposed an improved total focusing method (TFM) to locate damage in integral grid-stiffened plates based on distributed piezoelectric wafer active sensors (PWAS) array. Firstly, the appropriate working frequency was selected to generate the A0 mode Lamb wave depending on the structure and sensors, and the full matrix capture (FMC) method was introduced to collect data. Secondly, TFM was used to obtain the initial imaging results and the possible area of damage can be assessed and identified. Thirdly, the double window functions were proposed to extract the scattering signal related to the damage for the specific mode (A0). Lastly, the TFM was used again to obtain the final imaging results and the damage can be correctly identified. The proposed method has been verified by three-dimensional finite element (FE) simulation as well as experiments. The experimental results show that the damage in an aluminum alloy integral grid-stiffened plate can be located with the error of 13mm.

Lamb Wave Frequency Diverse Array.

The imaging method based on the conventional phased array (PA) can only realize angle focusing. To break through the above limitations, frequency diverse array (FDA) is first introduced from radar to Lamb wave, which opens up a possibility to realize angle-range focusing in damage localization. The energy pattern of FDA without considering the features of radar signals is re-derived, and a corresponding FDA focusing imaging method for Lamb wave is developed. In the presented method, by appending various frequency offsets to the redesigned anti-dispersive excitations, the desired FDA focusing and the dispersion elimination for Lamb wave are achieved simultaneously. Furthermore, based on full matrix capture being the data acquisition approach, a novel total focusing is realized with comprehensive consideration of positive and negative frequency offsets. Benefiting from FDA focusing, compared with the PA methods, the proposed method exhibits superior adjacent defects' identification ability and preferable interference suppression capability with excellent location accuracy and strong parameter robustness. Its superiority is validated by the experiment on aluminum plate with multiple adjoining surface and inner defects.

3D ultrasonic imaging of surface-breaking cracks using a linear array

Ultrasonic linear arrays have great potential to generate high-quality three-dimensional (3D) images by scanning the array. However, the generated images suffer from low resolution in the elevation plane, limiting the image quality for a reliable 3D Non-Destructive Testing (NDT) inspection. Although several ultrasonic imaging methods have been implemented to inspect different types of defects, there has been limited research to characterise surface-breaking cracks (SBCs) in 3D quantitatively. To improve the characterisation of surface-breaking cracks (SBCs), a 3D hybrid imaging method is proposed by combining the Half Skip Total Focusing Method (HSTFM) and the Synthetic Aperture Focusing Technique (SAFT) using a linear array. This paper proposed the implementation of an array with a reduced element length for full matrix capture (FMC) data acquisition. In conjunction with the hybrid imaging method, a reduced element array enables the utilisation of the information from a broad ultrasonic beam in the elevation direction to achieve improved image resolution. The imaging capability is assessed via a point spread function (PSF) as well as numerical simulations. From the PSF measurements, the image resolution is shown to improve with the smaller element length of the array, which is attributable to the combination of wide beamwidth and hybrid imaging method. Thereafter, experimental validation was performed with arrays of different elevation lengths, where an excellent match with the numerical results was observed. Furthermore, the crack sizing was performed using a 6-dB-drop rule, which assisted in accurately predicting the shape and size of the SBCs and is shown to measure the depth of SBCs with greater confidence. It is shown that a reduced array elevation with the hybrid imaging method and sizing method yields improved image resolution contrary to conventional linear arrays. This approach can offer a significant improvement in manifesting complete comprehension of the spatial defect relationship, enabling NDT engineers to analyse the inspection results quantitatively in 3D for progressive reliability.

Ultrasonic time-reversal-based super resolution imaging for defect localization and characterization

In this paper, time reversal with multiple signal classification (TR-MUSIC) and its phase-coherent form (PC-MUSIC), the two typical ultrasonic time-reversal-based super resolution imaging techniques, have been introduced and explored to image defects in metallic samples. The principles for super resolution imaging technique and defect characterization based on ultrasonic image have been presented firstly. And then both TR-MUSIC and PC-MUSIC are tested with experimental ultrasonic array data acquired from the metallic samples including defects using the full matrix capture (FMC) process. Here, if the size of defect is smaller than the central ultrasonic wavelength, the defect can be regarded as point-like target. On the contrary, if the size of defect is larger than the central ultrasonic wavelength, it can be regarded as extended target. The comparison on super resolution imaging for point-like and extended targets has been investigated. For point-like targets, TR-MUSIC as well as PC-MUSIC can distinguish and locate the position, and the overall performance of TR-MUSIC is better than that of PC-MUSIC. For extended target, TR-MUSIC can only determine the area where the defect occurs. PC-MUSIC can distinguish and assess the length of extended target parallel to the array, the lowest error is 9.62% when the dimension of signal subspace is set to be 10 for the case considered. In addition, the defect characterization based on ultrasonic super-resolved image has been studied, and a sizing strategy is introduced. The length and angle of extended targets oblique to the array can be obtained from the PC-MUSIC images. The worst errors for assessing the length and angel are 9.14% and 13.3% respectively. And for the cases considered in the experiment, the longer the length of extended target, the smaller the error.

Acoustic Signal Imaging Method Based on Synthetic Aperture Focusing and Full Matrix Capture

In order to observe and understand the effect of acoustic signal detection more intuitively, imaging analysis is needed to obtain clearer detection results, and the detection situation is analyzed manually. The commonly used imaging method is B-scan imaging, which is also widely used in medical imaging. In this paper, an acoustic signal imaging method based on synthetic aperture focusing and full matrix capture is proposed. The application of synthetic aperture focusing method in acoustic signal imaging was improved. Hilbert transformation was used to construct complex signal sequence, and the imaging processing process of full matrix method is proposed. From the aspects of data acquisition, analysis and processing, the echo signals are analyzed, and the differences between synthetic aperture focusing and full matrix method in acoustic signal imaging are compared.

Increasing the speed of automated ultrasonic inspection of as-built additive manufacturing components by the adoption of virtual source aperture

Wire + Arc Additive Manufacture (WAAM) is an economicalmanufacturing technique to build components.To maintain the commercial and technical benefits, inspection is desired at each layer of the build. New conformable phased array roller-probes offer the potential to inspect the as-built sample in-process or on completion.A challenge with such inspections is the refraction of the ultrasonic waves at multiple interfaces. The SyntheticAperture Focusing Technique (SAFT) and Total Focusing Method (TFM), combined with Full Matrix Capture (FMC) acquisition enabled imaging through the as-built WAAM surface. However, single-element firings, associated with FMC are a limiting factor due to the lower energy at transmission, while the high number of firings and subsequent larger data size negatively affect inspection speed.This work introduces the concept of Virtual Source Aperture (VSA) for ultrasonic roller-probe inspection, through modelling of VSA on custom-designed calibration WAAM block. The concept is then demonstrated on a mock as-built WAAM sample inspection with reference defects. Theresults demonstratethat a markedlylowernumber of transmissionsarerequiredto match the performance oftheFMC counterpart while increasing the energy levels.Moreover,an almost 50% reduction inthedatasizeenabled a doubling of the inspection speed.

Collaborative Robotic Wire + Arc Additive Manufacture and Sensor-Enabled In-Process Ultrasonic Non-Destructive Evaluation.

The demand for cost-efficient manufacturing of complex metal components has driven research for metal Additive Manufacturing (AM) such as Wire + Arc Additive Manufacturing (WAAM). WAAM enables automated, time- and material-efficient manufacturing of metal parts. To strengthen these benefits, the demand for robotically deployed in-process Non-Destructive Evaluation (NDE) has risen, aiming to replace current manually deployed inspection techniques after completion of the part. This work presents a synchronized multi-robot WAAM and NDE cell aiming to achieve (1) defect detection in-process, (2) enable possible in-process repair and (3) prevent costly scrappage or rework of completed defective builds. The deployment of the NDE during a deposition process is achieved through real-time position control of robots based on sensor input. A novel high-temperature capable, dry-coupled phased array ultrasound transducer (PAUT) roller-probe device is used for the NDE inspection. The dry-coupled sensor is tailored for coupling with an as-built high-temperature WAAM surface at an applied force and speed. The demonstration of the novel ultrasound in-process defect detection approach, presented in this paper, was performed on a titanium WAAM straight sample containing an intentionally embedded tungsten tube reflectors with an internal diameter of 1.0 mm. The ultrasound data were acquired after a pre-specified layer, in-process, employing the Full Matrix Capture (FMC) technique for subsequent post-processing using the adaptive Total Focusing Method (TFM) imaging algorithm assisted by a surface reconstruction algorithm based on the Synthetic Aperture Focusing Technique (SAFT). The presented results show a sufficient signal-to-noise ratio. Therefore, a potential for early defect detection is achieved, directly strengthening the benefits of the AM process by enabling a possible in-process repair.

Early detection of high temperature hydrogen attack using the ultrasonic full matrix capture and advanced post-processing methods

In this work, advanced ultrasonic algorithms are studied for the detection of early-stage High Temperature Hydrogen Attack (HTHA). This degradation mechanism occurs when hydrogen reacts with carbon or carbides to create micro voids in the samples that degrade mechanical properties. Full matrix captures were postprocessed into scattering matrices and using advanced Total Focusing Methods (TFM) such as Delay Multiply and Sum (DMAS), weighted images and amplitude-free images. The main objective of this work is to detect HTHA when micro voids are not yet linked. For this purpose, finite element simulations are used to model HTHA degradation and noise generated by the grains in carbon steel material. Amplitude-free imaging methods showed promising results for low noise material. When using weighted images or DMAS in materials with stronger grain boundary noise, the amplitude of indications associated with HTHA was up to 272% above standard TFM. Finally, the scattering matrix provided the earliest detection for all the simulated configurations. These results were then validated with measurements made on three field samples extracted from equipment with HTHA damage. The level of HTHA of the three samples was confirmed with a metallographic study.