Ultrasonic Phased Array System Research Articles

Inspection of wind turbine bolted connections using the ultrasonic phased array system

This study explores the inspection of bolted connections in wind turbines, specifically focusing on the application of Phased Array Ultrasonic Testing (PAUT). The research comprises four sections: Acoustoelastic Constant calibration, high tension investigation on bolts, blind tests on larger bolts, and Finite Element Analysis (FEA) verification. The methodology shows accurate results for stress while the bolt is under operative loads, and produces a clear indication of when it is above these loads and beginning to deform. PAUT emerges as a promising tool for bolt inspection, offering multiple imaging modes for simultaneous stress monitoring and defect detection. The study advocates for PAUT as a robust method to enhance wind turbine safety, longevity, and future in-situ testing.

Anisotropy Corrected FMC/TFM Based Phased Array Ultrasonic Imaging in an Austenitic Buttering Layer

For the narrow gap dissimilar weld between a ferritic steel and a nickel base superalloy, a nickel base alloy buttering layer is deposited on the ferritic steel side as an intermediate layer. The bonding between the buttering layer and the ferritic steel is required to be inspected from the buttering layer side. The buttering layer exhibits very high elastic anisotropy due to elongated columnar grains with preferred orientations. In this paper, the effect of elastic anisotropy on the phased array ultrasonic imaging of defects in the buttering layer is demonstrated for data acquired in full matrix capture (FMC) mode and reconstructed with the total focusing method (TFM). The anisotropy in the buttering layer leads to distorted flaw images, which limits the lateral resolution and defect detection sensitivity. Angle-dependent ultrasonic velocity measured in through-transmission FMC mode has been used for processing the FMC data to obtain high-resolution TFM images with improved sensitivity. The velocity values used are in line with the grain orientations observed by electron-backscatter diffraction (EBSD) studies. Further, an alternate approach is also proposed to obtain a TFM image with improved resolution using a suitable isotropic velocity. The approach can be implemented in any commercial phased array ultrasonic system having the FMC-TFM feature.

Hybrid geometrical full waveform inversion for ultrasonic defect characterisation

A hybrid geometrical full waveform inversion (GFWI) method is presented in this article for accurate ultrasonic defect characterisation using a phased array. The proposed method combines two steps: (1) A newly developed multi-mode topological energy method (TEM) is used to provide a high-resolution image for defect classification and a good initial defect model for the second step. (2) A GFWI procedure is executed to reconstruct the defect shape through iteratively reducing the mismatch in waveforms between the measurements and synthetic data from the defect model. The GFWI procedure enables direct inversion of the defect shape by deforming the elements attached at its boundaries from finite element formulation, controlled by the preconditioned boundary gradient. To suppress the cross-talk among different geometrical parameters with distinct units, the BFGS and the subspace methods are implemented together with GFWI, which enables reconstructing defects of various shapes by taking all the wave physics into the inversion automatically. Numerical examples are shown with a volumetric defect, a straight crack, a curved crack and a surface-breaking notch, giving accuracy of defect sizing within fractions of a wavelength. Two experiments using an ultrasonic phased array system further demonstrate the feasibility of this method.

Design of ultrasonic standing wave levitation support for three-dimensional printed filaments.

Fused deposition modeling (FDM) three-dimensional (3D) printing is the process of forming a part by depositing molten thermoplastic materials layer by layer. Support structures need to be added below the overhangs or bridges in 3D printing. This paper proposes an idea for support-free FDM printing by studying the method of filament levitation. In this paper, an ultrasonic phased array device is designed, and different slender objects with length much longer than the sound wavelength are levitated in the air by multiple standing wave points. Experiments show that slender objects can be stably held at the sound pressure nodes in the standing wave field. After adding the ultrasonic field in FDM printing, the maximum deformation of single filament due to gravity on the bridge structure decreases from 5 to 2 mm. This proves that it is feasible for an ultrasonic phased array system to play an important role in the field of support-free FDM printing.

Effect of non-metallic inclusions (NMI) on crack formation in forged steel

Effect of non-metallic inclusions on crack formation in forged steel components is presented in this work. Ultrasonic phased array system was used to locate and identify the defects in the forged steel samples. X-Ray Computed Tomography (XCT), Scanning Electron Microscopy (SEM), optical metallographic and image analysis, Optical Emission Spectrometry (OES) techniques were used for defect analysis and material characterization. Few subsurface cracks were found in the rejected sample of quench tempered steel acquired after the forging process. Defects were clustered near the core of the specimen. Ultrasonic phased array transducer system and XCT confirmed the presence of approximately 100 µm wide and 10 mm long cracks. Optical and SEM images suggested that the cracks were discontinuous and revealed a predominant presence of MnS and Al2O3 inclusions along with traces of SiO2 and SiC inclusions. Further, alumina inclusions were found to be clustered near the core of specimen, which is the crack zone. Cracks could have been initiated due to quench stress and augmented by the clustered alumina inclusions and propagated through the grain boundaries. Strain analysis using EBSD was performed in a sample near the crack to study the distortion of crystal lattice around the alumina inclusions. Considerable strain distribution could be observed in the matrix containing alumina inclusion, but strain seems to be relieved near the crack. It was presumed that alumina inclusions in the matrix acted as a stress concentration factor and led to the crack initiation mechanism.

Development of phased array ultrasonic system for detecting rail cracks

In this study, a phased array ultrasonic system for detecting rail cracks (PAUSR) was developed which consists of two phased array (PA) ultrasonic transducers, a water tank, a display monitor, a battery, a commercial 64 channel PA board, and its control software. To accomplish this, the acoustic fields and crack detection images of newly developed PA ultrasonic transducers were simulated and analyzed by the CIVA (CIVA 2016, NDE CIVA, USA) software. The major design factors for the PAUSR is the capability of evaluating crack size (over 2 mm), generating proper acoustic fields in the rail and easy and safe handling for operators. For the performance test of the designed PA ultrasonic transducer, Non-destructive Characterization and Verification of Ultrasonic Phased Array Equipment, Part 2: Probes (EN ISO 18563-2:2017) was conducted. In addition, artificial crack detection images were simulated by the CIVA software, and an experiment under the same CIVA simulation conditions was also performed for comparison purposes. For the last verification, natural defective specimens with bolt-hole star-cracking, longitudinal vertical cracking and welding defects were scanned by the developed PAUSR, and its results were analyzed and compared with the radiographic testing (RT) and CIVA simulation outcomes.

Coalescence Dynamics of Acoustically Levitated Droplets.

The contactless coalescence of a droplet is of paramount importance for physical and industrial applications. This paper describes a coalescence method to be used mid-air via acoustic levitation using an ultrasonic phased array system. Acoustic levitation using ultrasonic phased arrays provides promising lab-on-a-drop applications, such as transportation, coalescence, mixing, separation, evaporation, and extraction in a continuous operation. The mechanism of droplet coalescence in mid-air may be better understood by experimentally and numerically exploring the droplet dynamics immediately before the coalescence. In this study, water droplets were experimentally levitated, transported, and coalesced by controlled acoustic fields. We observed that the edges of droplets deformed and attracted each other immediately before the coalescence. Through image processing, the radii of curvature of the droplets were quantified and the pressure difference between the inside and outside a droplet was simulated to obtain the pressure and velocity information on the droplet’s surface. The results revealed that the sound pressure acting on the droplet clearly decreased before the impact of the droplets. This pressure on the droplets was quantitatively analyzed from the experimental data. Our experimental and numerical results provide deeper physical insights into contactless droplet manipulation for futuristic lab-on-a-drop applications.

Feasibility Study of Droplet Transportation via Ultrasonic Phased Array System

Feasibility Study of Droplet Transportation via Ultrasonic Phased Array System

Ultrasonic phased array inspection of a Wire + Arc Additive Manufactured (WAAM) sample with intentionally embedded defects

In this study, Wire + Arc Additive Manufacture (WAAM) was employed to manufacture a steel specimen with intentionally embedded defects which were subsequently used for calibration of an ultrasonic phased array system and defect sizing. An ABB robot was combined with the Cold Metal Transfer (CMT) Gas Metal Arc (GMA) process to deposit 20 layers of mild steel. Tungsten-carbide balls (ø1-3 mm) were intentionally embedded inside the additive structure after the 4th, 8th, 12th and 18th layers to serve as ultrasonic reflectors, simulating defects within the WAAM sample. An ultrasonic phased array system, consisting of a 5 MHz 64 Element phased array transducer, was used to inspect the WAAM sample non-destructively. The majority of the reflectors were detected successfully using Total Focusing Method (TFM), proving that the tungsten carbide balls were successfully embedded during the WAAM process and also that these are good ultrasonic reflectors. Owing to a lack of standards and codes for the ultrasonic inspection of WAAM samples (Lopez et al., 2018), a calibration method and step-by-step inspection strategy were introduced and then used to estimate the size and shape of an unknown lack of fusion (LoF) indication. This was then validated by destructive analysis, showing a good correlation with the phased array results.

HPEFT for Hierarchical Heterogeneous Multi-DAG in a Multigroup Scan UPA System

Multidirected acyclic graph (DAG) workflow scheduling is a key problem in the heterogeneous distributed environment in the distributed computing field. A hierarchical heterogeneous multi-DAG workflow problem (HHMDP) was proposed based on the different signal processing workflows produced by different grouping and scanning modes and their hierarchical processing in specific functional signal processing modules in a multigroup scan ultrasonic phased array (UPA) system. A heterogeneous predecessor earliest finish time (HPEFT) algorithm with predecessor pointer adjustment was proposed based on the improved heterogeneous earliest finish time (HEFT) algorithm. The experimental results denote that HPEFT reduces the makespan, ratio of the idle time slot (RITS), and missed deadline rate (MDR) by 3.87–57.68%, 0–6.53%, and 13–58%, respectively, and increases relative relaxation with respect to the deadline (RLD) by 2.27–8.58%, improving the frame rate and resource utilization and reducing the probability of exceeding the real-time period. The multigroup UPA instrument architecture in multi-DAG signal processing flow was also provided. By simulating and verifying the scheduling algorithm, the architecture and the HPEFT algorithm is proved to coordinate the order of each group of signal processing tasks for improving the instrument performance.

Improved scheduling algorithm for signal processing in asynchronous distributed ultrasonic total-focusing-method system.

Compared to the conventional ultrasonic phased-array system, a large-element phased-array system employing the total focusing method (TFM) can yield improved image resolution and accuracy, providing more flexible scanning methods and image merging functionality. In order to meet various forms of ultrasonic multi-group scanning, an architecture for multi-group scan integration called the “asynchronous distributed ultrasonic TFM system” is proposed, and a novel scheduling algorithm called “the sum of start time and processing time adjacent (SSPA) algorithm” is presented. The architecture adds a focus and group scheduler (FGS) and signal processing scheduler (SPS) to the traditional ultrasonic phased array system and constructs a signal processing arbitration (SPA) with several signal processing modules (SPMs). The FGS provides the focus parameters, pixel memory range, and number of pixels in each group. The SPS controls the SPA for the ultrasonic scanning data obtained from the elements, with SPM-sharing output data; hence, the optimal priority order and SPM assignment are realized, enabling switching of reading operations among the first-in−first-out memories for signal processing and minimal time-slot waiting. The SSPA algorithm is used to solve the job-shop scheduling problem with start time, which considers the processing time and start time, in order to reduce the time slot after each scheduling using adjacent operations. Therefore, the architecture enhances the flexibility of the multi-group scan, and this algorithm decreases the makespan, achieving higher efficiency compared to conventional scheduling algorithms. The reliability and validity of the algorithm are substantiated after its implementation using FPGA technology. The SPM utilization rate and the real-time performance of the ultrasonic TFM are improved. Thus, the proposed algorithm and architecture have considerable potential application in multi-sensor systems.

Counter-faced ultrasonic phased array system for non-contact flow manipulation

Counter-faced ultrasonic phased array system for non-contact flow manipulation

A spectral method for sizing cracks using ultrasonic arrays

Ultrasonic phased array systems are becoming increasingly popular as tools for the inspection of safety-critical structures within the non-destructive evaluation industry. The data-sets captured by these arrays can be used to image the internal structure of individual components, allowing the location and nature of any defects to be deduced. Although there exist strict procedures for measuring defects via these imaging algorithms, sizing flaws which are smaller than two wavelengths in diameter can prove problematic and the choice of threshold at which the defect measurements are made can introduce an aspect of subjectivity. This paper puts forward a completely objective approach specific to cracks based on the Kirchhoff scattering model and the approximation of the resulting scattering matrices by Toeplitz matrices. A mathematical expression relating the crack size to the maximum eigenvalue of the associated scattering matrix is derived. Analysis of this approximation shows that the method will provide a unique crack size for a given maximum eigenvalue whilst providing a quick calculation method which avoids the need to numerically generate model scattering matrices (the computation time is up to times faster). A sensitivity analysis demonstrates that the method is most effective for sizing defects that are commensurate with or smaller than the wavelength of the ultrasonic wave. The method is applied to simulated FMC data arising from finite element calculations where the crack length to wavelength ratios range between 0.6 and 1.9. The recovered objective crack size exhibits an error of 12%.

A Fast Method to Calculate the Spatial Impulse Response for 1-D Linear Ultrasonic Phased Array Transducers.

A method is developed to accurately determine the spatial impulse response at the specifically discretized observation points in the radiated field of 1-D linear ultrasonic phased array transducers with great efficiency. In contrast, the previously adopted solutions only optimize the calculation procedure for a single rectangular transducer and required approximation considerations or nonlinear calculation. In this research, an algorithm that follows an alternative approach to expedite the calculation of the spatial impulse response of a rectangular linear array is presented. The key assumption for this algorithm is that the transducer apertures are identical and linearly distributed on an infinite rigid plane baffled with the same pitch. Two points in the observation field, which have the same position relative to two transducer apertures, share the same spatial impulse response that contributed from corresponding transducer, respectively. The observation field is discretized specifically to meet the relationship of equality. The analytical expressions of the proposed algorithm, based on the specific selection of the observation points, are derived to remove redundant calculations. In order to measure the proposed methodology, the simulation results obtained from the proposed method and the classical summation method are compared. The outcomes demonstrate that the proposed strategy can speed up the calculation procedure since it accelerates the speed-up ratio which relies upon the number of discrete points and the number of the array transducers. This development will be valuable in the development of advanced and faster linear ultrasonic phased array systems.

Indirect Measurement of Effective Throat Thickness in T-joint Weld by Ultrasonic Method Phased Array

The article deals with non-destructive measurement of the effective throat thickness of fillet weld with deep penetration in T-joint. Ultrasonic Phased Array technology is used to indirectly measurement of effective weld throat thickness. Phased Array ultrasonic systems utilise multi-element probes, which are individually excited under computer control. By exciting each element in a controlled manner, a focused beam of ultrasound can be generated. Software enables the beam to be steered. Two and three dimensional views can be generated showing the sizes and locations of any flaws detected. The results of Phased Array ultrasonic measurements are compared with the real results obtained from the real macrostructural analysis. The methodology is appropriate for verifying compliance with the design weld throat thickness in the production of steel structures.

Особенности контроля главного циркуляционного трубопровода на примере контроля образца сварного соединения

Introduction. Testing of reactor coolant pipe (RCP) weld joints and matters of testing quality ensuring are considered in the article. The aim of the study was to demonstrate the potential of phased array ultrasonic systems for testing of RCP as well as to show capabilities of portable X-ray fluorescence analyzers for composition express analysis of weld joints.
 Method. Real fragments of RCP weld joints Du580 were chosen for the experiment. Phased array ultrasonic flaw detector OmniScan MX was used as a testing instrument; testing data were analyzed and interpreted with TomoView software. Chemical analysis was fulfilled with PMI Master UVR and Olympus DELTA devices.
 Results. Fragments of RCP weld joints Du580 have been examined. Chemical analysis results have confirmed that a portable X-ray fluorescence analyzer can be used for determining the main alloying elements. Benefits and drawbacks of phased array ultrasonic testing for RCP weld joints have been revealed; recommendations for time corrected gain adjustment and pulse repetition frequency selection have been given; questions of improvement of testing productivity and quality have been considered.
 Conclusion. Application of phased array at ultrasonic testing of complex and important objects increases objectivity of the testing results. Using real fragments of reactor coolant pipe as specimens for adjustment makes it possible both to avoid interpretation mistakes and develop detailed testing techniques.

Infrared thermography and ultrasonics to evaluate composite materials for aeronautical applications

The attention of this paper is focused on the suitability of two techniques: infrared thermography and ultrasonics to evaluate impact damaged carbon/epoxy specimens. The obtained results are compared by highlighting advantages and disadvantages of each technique, as well their limits in view of an integrated use. In this context, a crucial task may be to assess the extension of delamination caused by an impact event, which may ask one to guess between sound and damaged materials at the edge of the instrument background noise. To help fixing this problem, results obtained with either lock-in thermography, or an ultrasonic phased array system, are analysed with the aid of thermographic data collected during impact tests.

Experimental study of the impactor mass effect on the low velocity impact of carbon/epoxy woven laminates

In this work, the analysis of the impactor mass effect on the behaviour of carbon/epoxy woven laminates under low velocity impact is carried out. To this end experimental test were performed by means of a drop weigh tower in a range of energies varying from 10 to 110J, and using three different impactor masses. Two different laminate thicknesses were considered in order to take into account its possible influence. An analysis of the impact tests is performed using the Composite Structure Impact Performance Assessment Program, in order to observe the influence of impactor mass. Once impacted, the laminates were inspected by means of a C-Scan (to quantify the delamination extension) and a phased array ultrasonic system (to analyse the failure through the thickness); this non-destructive analysis will determine the influence of the impactor mass on the laminate failure.

Fundamental study of molten pool depth measurement method using an ultrasonic phased array system

The molten pool depth measurement method using an ultrasonic phased array system has been developed. The molten pool depth distribution is evaluated by comparing the times taken by the ultrasonic wave to propagate through a molten pool and a solid-phase and through only the solid-phase near the molten pool. Maximum molten pool depths on a flat type-304 stainless-steel plate, formed with a gas tungsten arc welding machine for different welding currents from 70 to 150 A, were derived within an error of ±0.5 mm.

A model-based approach to crack sizing with ultrasonic arrays.

Ultrasonic phased array systems have become increasingly popular in the last 10 years as tools for flaw detection and characterization within the nondestructive testing industry. The existence and location of flaws can often be deduced via images generated from the data captured by these arrays. A factor common to these imaging techniques is the subjective thresholding required to estimate the size of the flaw. This paper puts forward an objective approach which employs a mathematical model. By exploiting the relationship between the width of the central lobe of the scattering matrix and the crack size, an analytical expression for the crack length is reached via the Born approximation. Conclusions are then drawn on the minimum resolvable crack length of the method and it is thus shown that the formula holds for subwavelength defects. An analytical expression for the error that arises from the discrete nature of the array is then derived and it is observed that the method becomes less sensitive to the discretization of the array as the distance between the flaw and array increases. The methodology is then extended and tested on experimental data collected from welded austenitic plates containing a lack-of-fusion crack of 6 mm length. An objective sizing matrix (OSM) is produced by assessing the similarity between the scattering matrices arising from experimentally collected data with those arising from the Born approximation over a range of crack lengths and frequencies. Initially, the global minimum of the OSM is taken as the objective estimation of the crack size, giving a measurement of 7 mm. This is improved upon by the adoption of a multifrequency averaging approach, with which an improved crack size estimation of 6.4 mm is obtained.