Side-drilled Hole Research Articles

Fracture and determination of a lifetime of in-service mechanical components with porosity cluster in an aluminium alloy

This paper focuses on the fatigue lifetime estimation of metallic components containing group of porosities as manufacturing defects. In order to represent these defects, six test specimens with different Side Drilled Holes (SDH) clusters, have been made of 7075-T6 aluminium alloy. Main characteristics of such defect (elementary size of porosities, spatial density or gradient of elementary sizes) have been studied by taking it into account in a FEM modelling in fatigue to determine their influence on the lifetime. Experimental tensile fatigue tests have been performed on all SDH samples with load ratio R=0.1. Semi-elliptical surfaces with a size of a typical Mg2Si particle of the studied alloy have been chosen as initial cracks for multiple crack propagation. Indeed, such a particle is often responsible for the initiation of a crack in this type of material. For crack growth, Paris’ type propagation law has been used. Local stress redistribution due to presence of the SDH implies mix-mode behaviour which has been considered by using G-theta method. Simulations results allowed realistic lifetime estimation according to the experimental ones. Moreover, a strong dependency of the crack paths and fatigue lifetime on the defect characteristics has been proved and quantified.

Surface reconstruction accuracy using ultrasonic arrays: Application to non-destructive testing

The accurate non-destructive inspection of engineering structures using ultrasonic immersion imaging requires a precise representation of the surface of the structure. Here we investigate the relationship between surface geometry, surface measurement error using ultrasonic arrays and the total focusing method (TFM) and how this impacts on the ability to image a feature within a component. Surfaces shaped as sinusoids covering combinations of surface wavelengths (0.8 to 32λwater) and amplitudes (0.6 to 9λwater) are studied. The surface reconstruction errors are shown to cause errors in imaging, such as reduced amplitude and blurring of the image of a side-drilled hole. These reconstruction errors are shown to increase rapidly with the maximum gradient of the sinusoid. Sinusoidal surfaces with maximum gradients <45° lead to average surface reconstruction errors <λwater and amplitude imaging errors within 6 dB of the flat-surface case. It is also shown that very poor results are obtained if the surface gradient is excessively steep.

Model-Assisted Approach for Probability of Detection (POD) in High-Temperature Ultrasonic NDE Using Low-Temperature Signals

Advanced piezoelectric-based ultrasonic transducers offer the potential for in-coolant nondestructive testing (NDT) measurements at high temperatures (HTs), including during hot standby (~260°C) for liquid-sodium–cooled advanced small modular reactors. The reliability of the NDT measurements is typically quantified by the probability of detection (POD) measured at the corresponding temperature. Obtaining such data in liquid sodium is challenging. Using a model-assisted POD approach, a transfer function is reported that enables data obtained on low carbon steel specimens at room temperature to give an estimated POD at an HT. A primary source of the difference in POD between room temperature and HT is due to the transducer material temperature-dependent performance. This paper demonstrates the transfer function approach using data for modified lead zirconium titanate (PZT-5A). A physics-based model was developed using a finite element method and used to quantify reduction in the scattering amplitude for standard reflectors, side drilled holes (SDHs), for a range of sizes, from 15°C to 195°C. Scattering amplitudes for the room-temperature–simulated data are compared with the experimental data measured at 2.25 MHz. A temperature correction and transfer functions were developed to transform the simulated temperature effect in the physics-based model to compare with the experimental data. The model-based approach was validated with experimental data. It was seen and validated for a PZT-5A ultrasonic transducer operating at 2.25 MHz that the 95% POD at 15°C was 0.58 λ, and due to variation in temperature-dependent properties of PZT-5A, the 95% POD was achieved only for a 1.41 λ SDH diameter.

Ultrasonic sparse-TFM imaging for a two-layer medium using genetic algorithm optimization and effective aperture correction

This paper introduces a sparse total focus method (TFM) as a viable solution to the trade -off between the imaging precision and computational efficiency. A corrected two-layer TFM algorithm is first established; then the element layout in the sparse arrays is optimized by the genetic algorithm to improve the spatial resolution and contrast resolution. Using the effective aperture theory, the weighting functions of the optimized sparse array elements are investigated, and the corrected sparse-TFM algorithm is developed. Experiments are conducted on the side-drilled holes in a wedged specimen. Results indicate that the proposed sparse-TFM can greatly increase the computational efficiency while maintaining a relatively low error.

Analysis on Ultrasonic TOFD Imaging Testing for Ultra-thick-walled EBW Joint of Aluminum Alloy

Abstract In order to complete the defect inspection and welding performance evaluation of the ultra-thick-walled aluminum alloy welded joint by electron beam welding (EBW), the ultrasonic time of flight diffraction (TOFD) D-scan imaging inspection investigations were carried out for the welded joint with the thickness of 165mm. Aiming at accurately identifying the defect information in the whole thickness area of the weld joint, a multiple scanning method combined with the double surface inspection with different separations of transducers and different refraction angle of acoustic beam was proposed to make the main beam of the transmitted and received transducers cover the whole weld zone. The experiments with different inspection parameters were performed by the top and bottom surface scanning for the four artificial side-drilled holes (SDHs) in different depth. The testing results of A-surface and B-surface scanning with the separation of 160mm and the refracted angle of 45° show that the defects in the depth more than 20mm can be accurately sized and positioned, while that in the depth less than 20mm at the vicinity of top surface are in the inspection blind zone. However, the defect diffracted waves are distinguished from the lateral waves obviously in the A-surface scanning with the separation of 72mm and the refracted angle of 68°. Large numbers of welding defects in the middle depth area and two sides of the weld zone can be observed by D-scan image. It is shown that the novel scanning method can effectively improve the inspection difficulties of ultra-thick-wall aluminum alloy weld and its inspection blind zone.

Эталонирование чувствительности и обеспечение её равномерности в прозвучиваемом сечении при ультразвуковом контроле сварных соединений с применением ФР-преобразователей

Introduction. The approach and practical implementation for the sensitivity calibration and its equalizing within entire insonified cross-section of the material have been presented in the article for 3 most common reference artificial reflectors, namely the flat bottom hole (FBH) situated at parallel to the weld bevel plane, the EDM notch (N), and the side drilled hole (SDH).&#x0D; The method. The issue of inhomogeneous sensitivity over cross-section covered through phased array (PA) sectorial scan plan is due to several factors, which are highlighted and explained. 5 of them are independent on the reference reflector’s shape. In addition the FBH and N reference reflectors are characterized by the strong dependency of the echo amplitude on the angle, under which the ultrasonic wave hits their surface (factor 6, which differs the FBH and N from the omnidirectional SDH). The approach for equalizing the sensitivity over sectorial-scan-insonified cross-section of the material for all types of reference reflectors has been proposed and explained. It is based on the ability of ultrasonic PA flaw detector to implement each pulsing-receiving cycle among the plurality of the scan-plan-forming set of focal laws with individually and independently settled gain and other key settings including Distance Amplitude Correction / Time Corrected Gain (DAC / TCG). The Sonotron NDT’s ISONIC Series PA instruments (ISONIC 3510, ISONIC 2010, and ISONIC 2009 UPA Scope) are featured with the said ability uniquely: in the said units the DAC / TCG mechanism is used purely for compensating the dependency of echo amplitude on the material travel distance while the feature of varying Gain per Focal Law is utilized just for the forming of easy-reproducible Angle Gain Compensation (AGC) plan. Both the DAC / TCG and AGC plans are created independently on each other with use of the same reference reflectors.&#x0D; The results. Combining of the independent DAC / TCG and AGC mechanisms for the first time ever provides the equalizing of the sensitivity for all types of reference reflectors independently on their X, Y position over the entire cross-section of the material — this is confirmed by a number of experimental results presented.&#x0D; Conclusion. At last the single group sectorial scan only becomes sufficient for the complete coverage of the whole cross-section of the weld. This allows reducing the dimensions of required PA probes and wedges in use and the width of the area for the scanning along the fusion line. And finally this increases the maximal possible speed of scanning along with reducing of the inspection cost.

Ultrasonic array imaging of multilayer structures using full matrix capture and extended phase shift migration

Multilayer structures have been widely used in industrial fields, and non-destructive evaluation of these structures is of great importance to assure their quality and performance. Recently, ultrasonic array imaging using full matrix capture, e.g. the total focusing method (TFM), has been shown to increase sensitivity to small defects and improve imaging resolution in homogeneous media. However, it cannot be applied to multilayer structures directly, due to the sound velocity variation in different layers and because refraction occurs at layer interfaces, which gives rise to difficulties in determining the propagation path and time. To overcome these problems, an extended phase shift migration (EPSM) is proposed for the full matrix imaging of multilayer structures in this paper. Based on the theory of phase shift migration for monostatic pulse-echo imaging, full matrix imaging using EPSM is derived by extrapolating the wavefields in both transmission and reception, and extended to the multilayer case. The performance of the proposed algorithm is evaluated by full matrix imaging of a two-layer structure with side-drilled holes conducted both in the simulation and the experiment. The results verify that the proposed algorithm is capable of full matrix imaging of a layered structure with a high resolution and signal-to-noise ratio. For comparison, full matrix imaging using the TFM with root-mean-squared velocity is also performed, and the results demonstrate that the proposed algorithm is superior to the TFM in improving both the image quality and resolution.

A generic hybrid model for the simulation of three-dimensional bulk elastodynamics for use in non-destructive evaluation.

A three-dimensional generic hybrid model is developed for the simulation of elastic waves in applications in Non- Destructive Evaluation that efficiently links different solution strategies but, crucially, is independent of the particular schemes employed. This is an important step forward in facilitating rapid and accurate large-scale simulations and this advances the twodimensional generic hybrid methodology recently developed by the authors. The hybrid model provides an efficient and effective tool for creating highly accurate simulations that model the wave propagation and scattering, enabling the interpretation of inspection data; the new methodology is verified against other numerical simulations. Furthermore, its deployment to simulate wave reflection from side-drilled holes, comparing the results with experimental measurements, provides a realistic demonstration as well as further validation.

High Temperature Gallium Orthophosphate Transducers for NDT

A transducer has been manufactured leading towards development of an ultrasonic system to operate up to 580°C for non-destructive testing (NDT) and monitoring in power plants. The manufactured transducer has a simple design based on the piezoelectric single crystal gallium orthophosphate (GaPO4) which allows ultrasonic measurements to be performed up to considerably high temperature (HT) levels required in this study. Usually a critical aspect when performing HT ultrasonic NDT– acoustic coupling to the test-material, has been resolved using a commercially available HT silver adhesive which provides permanent installation of the transducer on the structure to be tested. This also means that for future application in an industrial environment drilling and/or machining intervention requirements will be reduced significantly. Finally, the GaPO4 transducer's sensitivity (f=3.5MHz) has been successfully tested through measurements on a steel block containing an artificial defect with known geometry (side-drilled hole (SDH) with d=0.8mm) up to the target temperature of 580°C keeping the defect's signal-to-noise ratio (SNR) above 6dB which is high enough for NDT practice.

Sparse deconvolution method for ultrasound images based on automatic estimation of reference signals

Sparse deconvolution is widely used in the field of non-destructive testing (NDT) for improving the temporal resolution. Generally, the reference signals involved in sparse deconvolution are measured from the reflection echoes of standard plane block, which cannot accurately describe the acoustic properties at different spatial positions. Therefore, the performance of sparse deconvolution will deteriorate, due to the deviations in reference signals. Meanwhile, it is inconvenient for automatic ultrasonic NDT using manual measurement of reference signals. To overcome these disadvantages, a modified sparse deconvolution based on automatic estimation of reference signals is proposed in this paper. By estimating the reference signals, the deviations would be alleviated and the accuracy of sparse deconvolution is therefore improved. Based on the automatic estimation of reference signals, regional sparse deconvolution is achievable by decomposing the whole B-scan image into small regions of interest (ROI), and the image dimensionality is significantly reduced. Since the computation time of proposed method has a power dependence on the signal length, the computation efficiency is therefore improved significantly with this strategy. The performance of proposed method is demonstrated using immersion measurement of scattering targets and steel block with side-drilled holes. The results verify that the proposed method is able to maintain the vertical resolution enhancement and noise-suppression capabilities in different scenarios.

Improvement of SAFT by Implementation of Approximate Wave Solution in Fluid-Solid Two-Phase Media: A Case Study on Imaging of Aluminum Rod with Side-Drilled Holes

In ultrasonic testing, Synthetic Aperture Focusing Technique (SAFT) is a signal processing technique to produce flaw images by superposing of A-scan waveforms. With rapid development in computing technology, recently, SAFT has become easier in data acquisition and faster in computation. However, additional signal processing techniques may be integrated into SAFT to get ultrasound image with higher resolution. Wave theory is one of the most important keys in SAFT improvement since it can lead to better understanding of ultrasonic wave phenomena. In this paper, the approximate wave solution (AWS) in fluid-solid two-phase media is used to compute the beam radiations inside target of inspection. Multiplying A-scan waveforms by the ultrasonic beam radiations obtained by AWS, wave diffraction characteristics which are spatial functions between transducer and target are incorporated into the SAFT. The performance of the improved SAFT, so-called AWS–SAFT, is experimentally tested in ultrasonic imaging of a side-drilled hole (SDH) in an immersed rod. It is shown that AWS–SAFT can improve a flaw image, especially in that a flaw image with narrower side lobes is obtained, and artifacts due to L-mode are eliminated in T-mode SAFT images. Eventually, an efficient way in using AWS–SAFT to obtain an accurate ultrasound image of an immersed rod with SDHs is proposed and tested.

Reconstruction of reflector images using the C-SAFT method with account for the anisotropy of the material of the test object

A modification of the combined SAFT (C-SAFT) method for reconstructing reflector images in a test object, which consists of several regions with different acoustic properties, in particular, anisotropy properties, is proposed. A method for the direct construction of a family of rays, which exit from the point where a transmitter is positioned, is used to calculate the ray trajectories with consideration for the anisotropy. After the family of rays is constructed, it is possible to analyze their attribution to a certain acoustic scheme and to approximate the calculated delays on the spatial grid of the region of iterest (ROI). This will allow one to calculate the pulse travel time from a transmitter to any point of the ROI and back to the receiver and to use the C-SAFT method for reconstructing reflector images. During processing of echo signals that were calculated in the CIVA program, the efficiency of the proposed method was demonstrated. Accounting for the anisotropy in a model experiment increased the focusing quality when reconstructing images of side-drilled holes in a specimen with a repair weld.

The Potential in Simulation and Metamodeling for the Understanding and Development of NDE

AbstractBy combining detailed mathematical modeling of the physics involved in NDE with a broader and robust engineering approach based on the sequential steps of screening, modeling and optimization, it is possible to generate metamodels that can support NDE engineering efforts to evaluate the applicability of NDE in a wider context, as a complement to the repeatability, reproducibility and capability studies normally performed. The aim of the initial screening phase is to effectively evaluate and prioritize NDE control parameters from a wider perspective regarding the demands of a specific application and to prioritize parameters of lesser importance for the outcome on the basis of economic and practical considerations. The aim of the second and third steps is to study the influence of the important parameters and to perform sensitivity analyses of reproducibility and repeatability, for example, followed by procedure development, respectively. The methodology is straightforward when it comes to smooth response surfaces of lower order (up to second or third order). Generally, the recommendation for the screening phase is ‘to be bold’ for the definition of the experimental range for each parameter – meaning to make them as wide as possibly relevant for the specific application. For NDE applications not following the Berens assumption for POD studies, e.g., large cracks yield large response signals, such as the varying signal amplitudes from surface breaking notches in ultrasonic testing, the mentioned recommendation of ‘be-bold’ screening phase may lead to incorrect prioritization of parameters. In this publication, this is illustrated by how the width of the experimental range for the control parameters tested during screening actually influences the screening results. Two basic ultrasonic testing set-ups have been compared using the SimSUNDT simulation software package: surface breaking notch (SBN) and side drilled hole (SDH). Even though the results were anticipated, they pointed out the need to further develop the screening methodology supporting NDE engineering, especially when it comes to addressing the issue of applicability. Does the data collected tell us what we actually want to know about the tested application? Or does it only tell us something about the NDE method?

The calibration of an ultrasonic antenna array installed on a wedge

A method that is proposed for calibrating an antenna array that is installed on a wedge provides refinement of the coordinates of the centers of piezoelectric elements. Precise knowledge of the coordinates will make it possible to obtain images in which reflections from reflectors will coincide with their actual positions with an accuracy no worse than a half wavelength. The calibration principle involves the minimization of the objective function that describes the difference between the antenna-array-measured echo signals from a 2-mm-diameter side drilled hole (SDH) at a depth of 12 mm and the calculated echo signals from the same hole. The algorithm operation was tested for echo signals calculated in the CIVA program. The calibration results for several antenna arrays on wedges and images of an SDH are presented, which were obtained using the method for digital antenna-array focusing (DAAF) for various acoustic systems.

Full matrix capture with time-efficient auto-focusing of unknown geometry through dual-layered media

This paper presents a method for time-efficient auto-focusing through a profile of unknown geometry applicable to immersion testing. It is demonstrated that capture of the complete time domain signal using the full matrix capture technique allows for rapid ultrasonic profile mapping of a complex geometry through the use of Fermat's principle to find the point of incidence at the reflective interface. Through advanced optimisation and parallelisation of the algorithms over the graphic processing unit, it is demonstrated that rapid inspections are possible, given that the geometry falls within the limits defined for the algorithm. To demonstrate this, a linear array transducer is mounted to a perspex shoe where auto-focusing is performed to generate ultrasonic imagery of side-drilled holes through a curved surface.

Applications of Flexible Ultrasonic Transducer Array for Defect Detection at 150 °C

In this study, the feasibility of using a one dimensional 16-element flexible ultrasonic transducer (FUT) array for nondestructive testing at 150 °C is demonstrated. The FUT arrays were made by a sol-gel sprayed piezoelectric film technology; a PZT composite film was sprayed on a titanium foil of 75 μm thickness. Since the FUT array is flexible, it was attached to a steel pipe with an outer diameter of 89 mm and a wall thickness of 6.5 mm at 150 °C. Using the ultrasonic pulse-echo mode, pipe thickness measurements could be performed. Moreover, using the ultrasonic pulse-echo and pitch-catch modes of each element of FUT array, the defect detection was performed on an Al alloy block of 30 mm thickness with a side-drilled hole (SDH) of ϕ3 mm at 150 °C. In addition, a post-processing algorithm based on the total focusing method was used to process the full matrix of these A-scan signals of each single transmitter and multi-receivers, and then the phase-array image was obtained to indicate this defect- SDH. Both results show the capability of FUT array being operated at 150 °C for the corrosion and defect detections.

Investigation of UT Procedure for Crack Depth Sizing by Phased Array UT in Ni-Based Alloy Weld

Recently, it has been reported that the primary water stress corrosion cracking (PWSCC) has occurred in nickel based alloy weld components such as steam generator safe end weld, reactor vessel safe end weld, and so on, in PWR. Defect detection and sizing are important in order to ensure the reliable operation and life extension of nuclear power plants. In the reactor vessel safe end weld, it was impossible to measure crack depth of PWSCC. The cracks have occurred in the axial direction of the safe end weld. Furthermore, the cracks had some features such as deep, large aspect ratio (ratio of crack depth and length), sharp geometry of crack tip, and so on. Therefore, development and improvement of defect depth sizing capabilities by ultrasonic testing (UT) have been required. Phased array UT technique was applied with regard to defect depth sizing at the inside inspection in Ni-based alloy welds. Phased array UT was examined a standard block specimen with side drilled holes (SDHs). From the experimental results, the performance of linear array probes and dual matrix array probe were investigated. In the basis of the results, UT procedure for defect depth sizing was investigated and proposed. The UT procedure was applied to the defect depth measurement in Ni-based alloy weld specimen with electric discharge machine (EDM) notches. From these results, good accuracy of defect depth sizing by phased array UT for the inside inspection was shown. Therefore, it was clarified the effectiveness of the UT procedure for defect depth sizing in Ni-based alloy weld.

Imaging composite material using ultrasonic arrays

As carbon fibre composite becomes more widely used for primary structural components in aerospace and other applications, the reliable detection of small defects in thick-sections is increasingly important. This article describes an experimental procedure for improving the detectability of such defects based on modifications to the Total Focusing Method (TFM) of processing ultrasonic array data to form an image. First the TFM is modified to include the directional dependence of ultrasonic velocity in an anisotropic composite laminate, and practical procedures for measuring the direction-dependent velocity profile are described. The performance of the TFM is then optimised in terms of the signal to noise ratio for Side-Drilled Holes (SDHs) by tuning both the frequency-domain filtering of data and the maximum aperture angle used in processing. Finally an attenuation correction is applied to the image so that the background structural noise level is uniform at all depths. The result is an image where the sensitivity (i.e. the signal to noise ratio) to a particular feature is independent of depth. Signals from 1.5mm diameter SDHs in the final image at depths of 4, 10 and 16mm are around 15dB above the root-mean-square level of the surrounding structural noise. In a standard TFM image, the signals from the same SDHs are not visible above the structural noise.

Elastic wave scattering by a rectangular crack near a non-planar back surface

A 3D model of non-destructive ultrasonic testing for cracks near a non-planar back surface is presented. The scattering by an interior rectangular crack in a thick-walled component with a back surface of general geometry is considered. The 3D wave scattering problem is solved using boundary integral equation methods (BIEMs): the boundary element method (BEM) for the back surface displacement is combined with an analytical technique for the hypersingular traction boundary integral equation for the crack opening displacement. The solution method generates many unknowns, but by applying a threshold criterion a sparse approximation of the system matrix is obtained such that a fast sparse solver may be used. The computations are accelerated further using the stationary phase approximation for the computation of probe field integrals. The action of ultrasonic probes in transmission and reception, calibration by side-drilled holes and effects of material damping are taken into account in the model, and a few numerical examples illustrate the influence of the back surface geometry.

Ultrasound Nondestructive Evaluation (NDE) Imaging with Transducer Arrays and Adaptive Processing

This paper addresses the challenging problem of ultrasonic non-destructive evaluation (NDE) imaging with adaptive transducer arrays. In NDE applications, most materials like concrete, stainless steel and carbon-reinforced composites used extensively in industries and civil engineering exhibit heterogeneous internal structure. When inspected using ultrasound, the signals from defects are significantly corrupted by the echoes form randomly distributed scatterers, even defects that are much larger than these random reflectors are difficult to detect with the conventional delay-and-sum operation. We propose to apply adaptive beamforming to the received data samples to reduce the interference and clutter noise. Beamforming is to manipulate the array beam pattern by appropriately weighting the per-element delayed data samples prior to summing them. The adaptive weights are computed from the statistical analysis of the data samples. This delay-weight-and-sum process can be explained as applying a lateral spatial filter to the signals across the probe aperture. Simulations show that the clutter noise is reduced by more than 30 dB and the lateral resolution is enhanced simultaneously when adaptive beamforming is applied. In experiments inspecting a steel block with side-drilled holes, good quantitative agreement with simulation results is demonstrated.