Array Inspection Research Articles

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.

Sizing Subwavelength Defects With Ultrasonic Imagery: An Assessment of Super-Resolution Imaging on Simulated Rough Defects.

There is a constant drive within the nuclear power industry to improve upon the characterization capabilities of current ultrasonic inspection techniques in order to improve safety and reduce costs. Particular emphasis has been placed on the ability to characterize very small defects which could result in extended component lifespan and help reduce the frequency of in-service inspections. Super-resolution (SR) algorithms, also known as sampling methods, have been shown to demonstrate the capability to resolve scatterers separated by less than the diffraction limit when deployed in representative inspections and therefore could be used to tackle this issue. In this paper, the factorization method (FM) and the Time Reversal Multiple-Signal-Classification (TR-MUSIC) algorithms are applied to the simulated ultrasonic array inspection of small rough embedded planar defects to establish their characterization capabilities. Their performance was compared to the conventional total focusing method (TFM). A full 2-D finite-element (FE) Monte Carlo modeling study was conducted for defects with a range of sizes, orientations, and magnitude of surface roughness. The results presented show that for subwavelength defects, both the FM and TR-MUSIC algorithms were able to size and estimate defect orientation accurately for smooth cases and, for rough defects, up to a roughness of 100 [Formula: see text]. This level of roughness is representative of the thermal fatigue defects encountered in the nuclear power sector. This contrasted with the relatively poor performance of TFM in these cases which consistently oversized these defects and could not be used to estimate the defect orientation, making through-wall sizing with this method impossible.

A model for multi-view ultrasonic array inspection of small two-dimensional defects.

The multi-view total focusing method (TFM) is an imaging algorithm for ultrasonic full matrix array data that exploits internal reflections and mode conversions in the inspected object to create multiple images, the views. Modelling the defect response in multi-view TFM is an essential first step in developing new detection and characterisation methods which exploit the information present in these views. This paper describes a ray-based forward model for small two-dimensional defects and compares its results against finite-element simulations and experimental data for the inspection of a side-drilled hole, a notch and a crack. A simpler version of this model, based on a single-frequency approximation, is derived and compared. A good agreement with the multi-frequency model and a speed-up of several orders of magnitude are achieved.

Ultrasonic Phased Array Inspection of Wire + Arc Additive Manufacture Samples Using Conventional and Total Focusing Method Imaging Approaches

In this study, three aluminium samples produced by wire + arc additive manufacture ‎‎(WAAM) are inspected using ultrasonic phased array technology. Artificial defects are ‎machined using a centre drill, o3 mm, and electro-discharge machining (EDM), o0.5-1 mm, ‎in a cylindrical through hole topology. The sample was first inspected by a single element ‎wheel probe mounted on a KUKA robot in order to investigate the feasibility of using a ‎conventional ultrasonic transducer approach. Unfortunately, the wheel probe was found to ‎be unsuitable for scanning of the WAAM specimens and ultrasonic phased arrays were ‎employed next. The setup included 5 MHz and 10 MHz arrays (128 elements) in direct ‎contact with the sample surface using both conventional and total focusing method (TFM) ‎imaging techniques. Using FIToolbox (Diagnostic Sonar, UK) as the controller, a phased ‎array aperture of 32 elements was used to perform a focussed B-scan with a range of ‎settings for the transmit focal depth. All the reflectors (including those located near the ‎WAAM top surface) were successfully detected by a combination of conventional phased ‎array and TFM, using a range of settings and setups including bottom surface inspection, ‎application through a Plexiglas wedge and variation of the scanning frequency.‎

Eddy Current Array Inspection of Zlin 142 Fuselage Riveted Joints

Abstract Aircraft fuselage is subject under the influence of many negative factors during its operation. Non-destructive testing methods are primarily used to minimize the possibility of possible failure. For early detection of any anomalies that may occur at aircraft fuselage are used mainly electromagnetic non-destructive testing and evaluation methods. This paper deals with inspection of riveted joints of the fuselage and wings of aircraft Zlin 142. The aircraft manufacturer determines the prescribed time intervals for the inspection of the fuselage. During the inspection, we will try to detect possible cracks and reveal a presence of hidden corrosion. A suitable method for the inspection of these riveted joints is eddy current testing method (ECT). Eddy current testing is one of the widely utilized electromagnetic NDE methods. It works based on an interaction of time-varying electromagnetic field with a conductive structure according to the Faraday’s electromagnetic induction law. This electromagnetic method is suitable for reliable detection of surface and subsurface defects of the riveted joints. Experiments will utilize Olympus OmniScan MX device with presence of ECA module. Eddy current array probes SAB-067-005-032 and SBB-051-150-032 are used, respectively. Harmonic eddy current excitation is used for this purpose.

Eddy Current Array Inspection of Riveted Joints

A Non-destructive Testing (NDT) plays an important role in the safety of aircraft components and structures. As this term suggests, NDT refers to test methods that use special devices and approaches to explore an object without damaging or affecting its future usefulness. NDT is mainly used to detect and characterize hidden defects or damage to critical components or structures, but it also has applications in dimensional measurements and the evaluation of some material properties. NDT is a very broad and interdisciplinary area that finds application in many sectors where failure of critical parts could jeopardize public security. NDT is used as a quality control tool during production to ensure materials and finished products that do not contain internal errors, or that the abnormalities detected are below the size considered potentially dangerous. NDT is also used during the operation of objects to detect cracks, corrosion or other forms of degradation and damage that can cause components or systems to fail or interfere with their proper functioning. This paper deals with the inspection of the riveted joints of the produced riveted specimen, which simulates damage around the riveted joints. Surface and subsurface damage as well as corrosion in the region of riveted joints are simulated. Experiments will utilize Olympus OmniScan MX device with presence of ECA module. Eddy current array probes SAB-067-005-032 and SBB-051-150-032 are used, respectively. Harmonic eddy current excitation is used for this purpose.

Critically Evaluate the Capabilities of Ultrasonic Techniques Used for Tracing Defects in Laminated Composite Materials

A Non-Destructive Test (NDT) technique is the fundamental strategy to look at a large portion of the materials, composite materials specifically. There are an excessive number of NDT techniques to assess the materials, for example, Visual Inspection, Liquid Penetrate Inspection, Eddy-Current Inspection, Phased Array Inspection, Magnetic Particle Inspection and Ultrasonic Inspection. The report delineates the Ultrasonic Test (UT) research centre examination that was directed with the group number 5 in the University lab, a few references and resources are utilised as a part of this investigation to completely exhibit the applications and deformity traceability of UT in covered composites. The paper finishes up the examination with the capacities and restrictions of the two systems and prescribes techniques to endeavour lessening the confinements.

An online health monitoring system for photovoltaic arrays based on the B/S architecture

In order to improve the working efficiency of the photovoltaic (PV) array inspection system, the application of online monitoring systems for the PV arrays is quickly rising. In this paper, an online PV array monitoring combining with B/S architecture, Python language, and Flask framework is developed to monitor and diagnose the status of PV arrays which can display the data of the PV array and facilitate the staff to monitor the working status of PV array. When a fault occurs, the staff can also register the fault information on the website quickly. The developed system is composed of three parts: data acquisition, data transmission and PV online monitoring website. Firstly, the system uses the Raspberry Pi3 to collect the data when the PV array operates in maximum power point (MPP), and the acquired data is stored locally in the Raspberry Pi. And then, the data is uploaded to the PC side via the FileZilla server software and further transmitted to online monitoring website. Finally, the PV array online monitoring website displays received data, and perform the fault diagnosis of PV array using a kernel based Extreme Learning Machine (KELM). Experimental results show that the total classification accuracy for ten different operating conditions can reach 97.2%.

Development of the specular echoes estimator to predict relevant modes for Total Focusing Method imaging

Total Focusing Method imaging is an ultrasonic testing method which has emerged in recent years as an alternative to standard phased array inspection methods in non-destructive testing, due to its high resolution and the realistic images of defects that it provides.In the case of crack-like defects, it provides images where the profile and the tips of the defects are reconstructed. TFM imaging is a procedure which yields the spatial position of the reflectors from which the main transient signals observed in the data are originated from. Thereby, diffraction echoes are located at the tips of the defect, and specular echoes appear along the profile of the defect. This signature allows the characterization of the planar nature of the defect.However, a correct reconstruction requires the use of the relevant ultrasonic path to produce the echoes wanted among a large number of possible paths between the array transducer and the reflector.In this paper, we have developed a method based on physical considerations, for predicting relevant paths. The tool is applied in several inspection configurations involving notches nearby welds. Validation is achieved from a variety of synthetic and experimental results.

A transdimensional Bayesian approach to ultrasonic travel-time tomography for non-destructive testing

Traditional imaging algorithms within the ultrasonic non-destructive testing community typically assume that the material being inspected is primarily homogeneous, with heterogeneities only at sub-wavelength scales. When the medium is of a more generally heterogeneous nature, this assumption can contribute to the poor detection, sizing and characterisation of defects. Prior knowledge of the varying wave speeds within the component would allow more accurate imaging of defects, leading to better decisions about how to treat the damaged component. This work endeavours to reconstruct the inhomogeneous wave speed maps of random media from simulated ultrasonic phased array data. This is achieved via application of the reversible-jump Markov chain Monte Carlo method: a sampling-based approach within a Bayesian framework. The inverted maps are used in conjunction with an imaging algorithm to correct for deviations in the wave speed, and the reconstructed flaw images are then used to quantitatively assess the success of this methodology. Using full matrix capture data arising from a finite element simulation of a phased array inspection of a heterogeneous component, a six-fold improvement in flaw location is achieved by taking into account the reconstructed wave speed map which exploits almost no a priori knowledge of the material’s internal structure. Receiver operating characteristic curves are then calculated to demonstrate the enhanced probability of detection achieved when the material speed map is accounted for.

Full non-contact laser-based Lamb waves phased array inspection of aluminum plate

Lamb waves defect detection technique is suitable to detect long-range defects and multi-defects in plates because of its attractive properties such as multi-modes, low attenuation, and multi-defect sensitivity. As the laser beams have the tiny size and noncontact property, in this paper a full non-contact laser-based Lamb waves phased array inspection technique was proposed for defect detection in an aluminum plate. A Q-switched Nd: YAG pulse laser generating Lamb waves and a continuous laser inspection system was used to inspect the out-of-plane displacements. The laser-generated Lamb waves have the broadband property and low temporal resolution that are not suitable for defects detection directly. So the continuous wavelet transform was used to extract narrowband signals from laser-generated Lamb wave and a linear mapping algorithm was adopted to compensate for the dispersion of the extracted narrowband signals. Two experiments were carried out to verify the applicability and effectiveness of the developed full non-contact laser-based Lamb waves phased array inspection technique. Two compact phased array imaging algorithms, the total focusing method and the sign coherence factor algorithm, were adopted to image the defects with processed signals. The experimental results accurately located the positions of the defects.

Index-based triangulation method for efficient generation of large three-dimensional ultrasonic C-scans

The demand for high-speed ultrasonic scanning of large and complex components is driven by a desire to reduce production bottlenecks during the non-destructive evaluation (NDE) of critical parts. Emerging systems (including robotic inspection) allow for the collection of large volumes of data in short time spans, compared to existing inspection systems. To maximise throughput, it is crucial that the reconstructed inspection datasets are generated and evaluated rapidly without loss of detail. This requires new data visualisation and analysis tools capable of mapping complex geometries while guaranteeing full coverage. This paper presents an entirely new approach for the visualisation of three-dimensional (3D) ultrasonic C-scans, suitable for application to high data throughput ultrasonic phased array inspection of large and complex parts. Existing reconstruction approaches are discussed and compared with the new index-based triangulation (IBT) method presented. The IBT method produces 3D C-scan representation, presented as coloured tessellated surfaces, and the approach is shown to work efficiently, even on challenging geometries. An additional differentiating characteristic of the IBT method is that it allows for easy detection of lack of coverage (an essential feature for ensuring that inspection coverage can be guaranteed on critical components). The results demonstrate that the IBT C-scan generation approach runs over 60 times faster than a C-scan display based on Delaunay triangulation and over 500 times faster than surface reconstruction C-scans. In summary, the main benefits of the new IBT technique include: high-speed generation of C-scans on large ultrasonic datasets (orders of magnitude improvement compared to surface reconstruction C-scans); the ability to operate efficiently on 3D mapped datasets (allowing 3D interpretation of C-scans on complex geometry components); and intrinsic indication of lack of inspection coverage.

Application of the Factorisation Method to Limited Aperture Ultrasonic Phased Array Data

This paper puts forward a methodology for applying the frequency domain Factorisation Method to time domain experimental data arising from ultrasonic phased array inspections in a limited aperture setting. Application to both synthetic and experimental data is undertaken and a multi-frequency approach is explored to address the difficulty encountered in empirically choosing the optimum frequency at which to operate. Additionally, a truncated singular value decomposition (TSVD) approach is implemented in the case where the flaw is embedded in a highly scattering medium, to regularise the scattering matrix and minimise the contribution of microstructural noise to the final image. It is shown that when the Factorisation Method is applied to multi-frequency scattering matrices, it can better characterise crack-like scatterers than in the case where the data arises from a single frequency. Finally, a volumetric defect and a lack-of-fusion crack are both successfully reconstructed from experimental data, where the resulting images exhibit only 3\% and 10\% errors respectively in their measurement.

Ultrasonic Phased Array Inspection of Electrofused Joints Implemented in Polyethylene Gas Piping Systems

Ultrasonic Phased Array Inspection of Electrofused Joints Implemented in Polyethylene Gas Piping Systems

Acceptance for phased array inspection of small bore butt welds in power generation

Acceptance for phased array inspection of small bore butt welds in power generation

Simulation and experiment for the inspection of stainless steel bolts in servicing using an ultrasonic phased array

The non-destructive testing of small-sized (M12–M20) stainless steel bolts in servicing is always a technical problem. This article focuses on the simulation and experimental research of stainless steel bolts with an artificial defect reflector using ultrasonic phased array inspection. Based on the observation of the sound field distribution of stainless steel bolts in ultrasonic phased array as well as simulation modelling and analysis of the phased array probes' detection effects with various defect sizes, different artificial defect reflectors of M16 stainless steel bolts are machined in reference to the simulation results. Next, those bolts are tested using a 10-wafer phased array probe with 5 MHz. The test results finally prove that ultrasonic phased array can detect 1-mm cracks in diameter with different depths of M16 stainless steel bolts and a metal loss of Φ1 mm of through-hole bolts, which provides technical support for future non-destructive testing of stainless steel bolts in servicing.

Nonintrusive estimation of anisotropic stiffness maps of heterogeneous steel welds for the improvement of ultrasonic array inspection.

It is challenging to inspect austenitic welds nondestructively using ultrasonic waves because the spatially varying elastic anisotropy of weld microstructures can lead to the deviation of ultrasound. Models have been developed to predict the propagation of ultrasound in such welds once the weld stiffness heterogeneity is known. Consequently, it is desirable to have a means of measuring the variation in elastic anisotropy experimentally so as to be able to correct for deviations in ultrasonic pathways for the improvement of weld inspection. This paper investigates the use of external nonintrusive ultrasonic array measurements to construct such weld stiffness maps, representing the orientation of the stiffness tensor according to location in the weld cross section. An inverse model based on a genetic algorithm has been developed to recover a small number of key parameters in an approximate model of the weld map, making use of ultrasonic array measurements. The approximate model of the weld map uses the Modeling of anIsotropy based on Notebook of Arcwelding (MINA) formulation, which is one of the representations that has been proposed by other researchers to provide a simple, yet physically based, description of the overall variations of orientations of the stiffness tensors over the weld cross section. The choice of sensitive ultrasonic modes as well as the best monitoring positions have been discussed to achieve a robust inversion. Experiments have been carried out on a 60-mm-thick multipass tungsten inert gas (TIG) weld to validate the findings of the modeling, showing very good agreement. This work shows that ultrasonic array measurements can be used on a single side of a butt-welded plate, such that there is no need to access the remote side, to construct an approximate but useful weld map of the spatial variations in anisotropic stiffness orientation that occur within the weld.

Velocity Correction of Total Focusing Method and its Application to Ultrasonic Inspection of Composite Laminate

The reliable detection of composite material is dramatically important with its wide application in the aerospace industry. A new post-processing mode of ultrasonic array inspection, entitled total focusing method(TFM), offers significant advantages including high sensitivity and greater inspection coverage. Based on this mode, a wave velocity correction method for the elastic anisotropic of composites is put forward. Subsequently, practical application is carried out to image and locate the defect in a composite laminate sample to demonstrate the advantage of the described method. The results show that the proposed method can effectively improve the ability to detect and evaluate defects in composite laminates.

A probabilistic approach for the optimisation of ultrasonic array inspection techniques

Ultrasonic arrays are now used routinely for the inspection of engineering structures in order to maintain their integrity and assess their performance. Such inspections are usually optimised manually using empirical measurements and parametric studies which are laborious, time-consuming, and may not result in an optimal approach. In this paper, a general framework for the optimisation of ultrasonic array inspection techniques in NDE is presented. Defect detection rate is set as the main inspection objective and used to assess the performance of the optimisation framework. Statistical modelling of the inspection is used to form the optimisation problem and incorporate inspection uncertainty such as crack type and location, material properties and geometry, etc. A genetic algorithm is used to solve the global optimisation problem. As a demonstration, the optimisation framework is used with two objective functions based on array signal amplitude and signal-to-noise ratio (SNR). The optimal use of plane B-scan and total focusing method imaging algorithms is also investigated. The performance of the optimisation scheme is explored in simulation and then validated experimentally. It has been found that, for the inspection scenarios considered, TFM provides better detectability in a statistical sense than plane B-scan imaging in scenarios where uncertainty in the inspection is expected.

Efficient immersion imaging of components with nonplanar surfaces.

Ultrasonic array inspection of a component with a nonplanar surface can be achieved in immersion using a liquid layer to couple ultrasonic waves from an array probe into a solid structure. This paper presents an efficient way to compute the appropriate element time delays in immersion without compromising the measurement accuracy. In the proposed imaging process, the surface geometry is first measured ultrasonically by forming an image of the component surface in the couplant. This leads to a set of discrete points that define the surface profile of the component. The propagation time from an array element to a point in the component is then determined by a grid search of candidate ray-paths through each surface point to identify the one that yields the shortest traveling time. Propagation times in the component are first generated on a coarse mesh of points and then these values are linearly interpolated to find the propagation time to each image pixel. The computed propagation times are finally used to reconstruct an image of the component interior. An analytical model is developed to determine a relationship between estimated propagation time errors and their effect on the array inspection in terms of signal amplitude from a reflector. For nominally normal incidence inspection of a metallic component with a minimum surface radius of 30 wavelengths immersed in water, it is found that the surface of the component can be adequately described by points spaced by one wavelength and that delays can be computed on a coarse grid of points spaced at 3 wavelengths. With these parameters, the reduction in amplitude of a point target in the component is shown to be less than 1 dB.