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Journal articleCombaniere J, Cawley P, McAughey K, et al., 2019,
Interaction between SH0 guided waves and tilted surface-breaking cracks in plates
, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol: 66, Pages: 119-128, ISSN: 0885-3010The interaction between SH0 guided waves and simple defects is well understood and documented, and the SH0 and related torsional guided waves are commonly used in inspection. However, tilted and branching cracks, for which vertical notches are a poor approximation, are found in some environments, particularly when pipes are buried in alkaline soils. This paper studies the interaction between SH0 guided waves and tilted, surface-breaking cracks, investigating the effect of the tilt and depth of the defect. The incident wave interacts with the tilted crack to generate a transmitted wave, a reflected wave and a wave trapped below the crack. It is shown that the direction of the tilt of the crack relative to the incident wave direction does not affect the scattering behaviour. Additionally, the axial extent of the crack plays a major role in the reflectivity of the crack, leading to transmission nulls in some configurations. These transmission nulls appear for all crack depths, the frequency range over which the transmission is significantly reduced increasing with crack depth. This behaviour is shown to be analogous to the acoustic energy flow in a duct when a Helmholtz resonator is introduced. The null is not seen above the SH1 cut-off as the propagating signals are no longer mono-modal. The existence of a transmission null and corresponding reflection maximum is promising for the detection of small defects and measurement of the frequency at which the null occurs will assist with defect characterisation. Experimental validations of the key results are presented.
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Conference paperCawley P, 2019,
Ultrasonic structural health monitoring - current applications and potential
, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, Pages: 2107-2109, ISSN: 1948-5719- Author Web Link
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- Citations: 1
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Journal articleLan B, Carpenter MA, Gan W, et al., 2018,
Rapid measurement of volumetric texture using resonant ultrasound spectroscopy
, Scripta Materialia, Vol: 157, ISSN: 1359-6462This paper presents a non-destructive evaluation method of volumetric texture using resonant ultrasound spectroscopy (RUS). It is based on a general theoretical platform that links the directional wave speeds of a polycrystalline aggregate to its texture through a simple convolution relationship, and RUS is employed to obtain the speeds by measuring the elastic constants, where well-established experimental and post-processing procedures are followed. Important lower-truncation-order textures of representative hexagonal and cubic metal samples with orthorhombic sample symmetries are extracted, and are validated against independent immersion ultrasound and neutron tests. The successful deployment of RUS indicates broader applications of the general methodology.
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Journal articleLan B, Britton TB, Jun T-S, et al., 2018,
Direct volumetric measurement of crystallographic texture using acoustic waves
, Acta Materialia, Vol: 159, Pages: 384-394, ISSN: 1359-6454Crystallographic texture in polycrystalline materials is often developed as preferred orientation distribution of grains during thermo-mechanical processes. Texture dominates many macroscopic physical properties and reflects the histories of structural evolution, hence its measurement and control are vital for performance optimisation and deformation history interogation in engineering and geological materials. However, exploitations of texture are hampered by state-of-the-art characterisation techniques, none of which can routinely deliver the desirable non-destructive, volumetric measurements, especially at larger lengthscales. Here we report a direct and general methodology retrieving important lower-truncation-order texture and phase information from acoustic (compressional elastic) wave speed measurements in different directions through the material volume (avoiding the need for forward modelling). We demonstrate its deployment with ultrasound in the laboratory, where the results from seven representative samples are successfully validated against measurements performed using neutron diffraction. The acoustic method we have developed includes both fundamental wave propagation and texture inversion theories which are free from diffraction limits, they are arbitrarily scalable in dimension, and can be rapidly deployed to measure the texture of large objects. This opens up volumetric texture characterisation capabilities in the areas of material science and beyond, for both scientific and industrial applications.
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Journal articleKhalili P, Cawley P, 2018,
The choice of ultrasonic inspection method for the detection of corrosion at inaccessible locations
, NDT and E International, Vol: 99, Pages: 80-92, ISSN: 0963-8695Inspection for corrosion and pitting defects in the petrochemical industry is vital and forms a significant fraction of the operating expenditure. Low frequency guided wave inspection is frequently employed as it gives large area coverage from a single transducer position. However, detection becomes problematic at inaccessible regions such as pipe supports or beyond T-joints since the low frequency guided waves produce a significant reflection from the feature itself, hence limiting the defect detectability of the method. This suggests testing at higher frequencies which helps to minimise the reflection from the feature and also improves the sensitivity to smaller defects. There are a number of guided wave and related techniques implemented for corrosion inspection including the S0 mode (at ∼ 1 MHz-mm), SH0 and SH1 modes (at ∼ 3 MHz-mm), CHIME, M-skip and Higher Order Mode Cluster (A1 mode at ∼ 18 MHz-mm). This paper presents a systematic analysis of the defect detection performance of each method with sharp and gradual defects, as well as their sensitivity to attenuative coatings, liquid loading, surface roughness and ability to test beyond features such as T-joints. It is shown by finite element analysis backed up by experiments that the A1 mode provides the best overall performance when dealing with surface features such as T-joints and coatings because of its low surface motion. Additionally a combination of two or more methods is suggested for corrosion inspection at inaccessible locations: The A1 mode in reflection for severe, sharp, pitting type defects; long range guided waves in reflection for large-area thinning and the SH1 mode in transmission for shallow, gradual defects.
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Journal articleCawley P, 2018,
Structural health monitoring: closing the gap between research andindustrial deployment
, Structural Health Monitoring, Vol: 17, Pages: 1225-1244, ISSN: 1475-9217There has been a large volume of research on structural health monitoring since the 1970s but this research effort has yielded relatively few routine industrial applications. Structural health monitoring can include applications on very different structures with very different requirements; this article splits the subject into four broad categories: rotating machine condition monitoring, global monitoring of large structures (structural identification), large area monitoring where the area covered is part of a larger structure, and local monitoring. The capabilities and potential applications of techniques in each category are discussed. Condition monitoring of rotating machine components is very different to the other categories since it is not strictly concerned with structural health. However, it is often linked with structural health monitoring and is a relatively mature field with many routine applications, so useful lessons can be read across to mainstream structural health monitoring where there are many fewer industrial applications. Reasons for the slow transfer from research to practical application of structural health monitoring include lack of attention to the business case for monitoring, insufficient attention to how the large data flows will be handled and the lack of performance validation on real structures in industrial environments. These issues are discussed and ways forward proposed; it is concluded that given better focused research and development considering the key factors identified here, structural health monitoring has the potential to follow the path of rotating machine condition monitoring and become a widely deployed technology.
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Journal articleCorcoran J, Nagy PB, 2018,
Magnetic stress monitoring using a directional potential drop technique
, Journal of Nondestructive Evaluation, Vol: 37, ISSN: 0195-9298An alternating current potential drop technique is presented that exploits anisotropic magnetostriction to monitor changes inapplied stress in steel. The background to the technique is provided together with an ad hoc approximation that describes thesensitivity of the sensor to the underlying properties. A uniaxial loading experiment has been conducted on duplex and mildsteel specimens showing that changes in stress are measureable. Saturation and hysteresis afflict the measurement, which, inaddition to sensitivity to temperature and magnetisation, may undermine inversion. With the capabilities and limitations ofthe proposed technique introduced, guidance on possible suitable applications are given, concluding that use for monitoringthe number and relative size of fatigue stress cycles may be a suitable and attractive opportunity.
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Journal articleChoi W, Shi F, Lowe MJS, et al., 2018,
Rough surface reconstruction of real surfaces for numerical simulations of ultrasonic wave scattering
, NDT and E International, Vol: 98, Pages: 27-36, ISSN: 0963-8695The scattering of waves by rough surfaces plays a significant role in many fields of physical sciences including ultrasonics where failure surfaces are often rough and their accurate identification is critical. The prediction of the strength of scattering can be hampered when the roughness is not adequately characterised and this is a particular issue when the surface roughness is within an order of the incident wavelength. Here we develop a methodology to reconstruct, and accurately represent, rough surfaces using an AutoRegressive (AR) process that then allows for rapid numerical simulations of ultrasonic wave rough surface scattering in three dimensions. Gaussian, exponential and AR surfaces are reconstructed based on real surface data and the statistics of the surfaces are compared with each other. The statistics from the AR surfaces agree well with those from actual rough surfaces, taken from experimental samples, in terms of the heights as well as the gradients, which are the two main factors in accurately predicting the wave scattering intensities. Ultrasonic rough surface scattering is simulated numerically using the Kirchhoff approximation, and comparisons with Gaussian, exponential, AR and real sample surfaces are performed; scattering intensities found using AR surfaces show the best agreement with the real sample surfaces.
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Journal articleEckel SF, Huthwaite P, Lowe M, et al., 2018,
Establishment and validation of the channelized hotelling model observer for image assessment in industrial radiography
, NDT and E International, Vol: 98, Pages: 1-7, ISSN: 0963-8695A new method for industrial radiography is presented to assess image quality objectively. The assessment is performed by a modelled observer developed to interpret radiographic images in order to rate the detectability of structural defects. For the purpose of qualifying radiographic NDE procedures, computational tools simulate the image, but should additionally automatically assess the associated image quality instead of relying on human interpretation. The Channelized Hotelling Model Observer (CHO) approach, originally developed for medical imaging, is here developed for industrial NDE applications to measure objectively the defect's detectability. A validation study based on a comparison of the model's efficiency of observing circular and elongated flaws shows that the CHO outperforms other detectability models used by industry. Furthermore, the model's reliability was verified by comparing it to psychophysical data.
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Journal articleZhang C, Huthwaite P, Lowe M, 2018,
Eliminating backwall effects in the phased array imaging of near backwall defects
, Journal of the Acoustical Society of America, Vol: 144, Pages: 1075-1088, ISSN: 0001-4966Ultrasonic array imaging is widely used to provide high quality defect detection and characterization. However, the current imaging techniques are poor at detecting and characterizing defects near a surface facing the array, as the signal scattered from the defect and the strong reflection from the planar backwall will overlap in both time and frequency domains, masking the presence of the defect. To address this problem, this paper explores imaging algorithms and relevant methods to eliminate the strong artefacts caused by the backwall reflection. The half-skip total focusing method (HSTFM), the factorization method (FM) and the time domain sampling method (TDSM) are chosen as the imaging algorithms used in this paper. Then, three methods, referred to as full matrix capture (FMC) subtraction, weighting function filtering, and the truncation method, are developed to eliminate or filter the effects caused by the strong backwall reflection. These methods can be applied easily with few tuning parameters or little prior knowledge. The performances of the proposed imaging techniques are validated in both simulation and experiments, and the results show the effectiveness of the developed methods to eliminate the artefacts caused by the backwall reflections when imaging near backwall defects.
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Journal articleHeinlein S, Cawley P, Vogt T, et al., 2018,
Blind Trial Validation of a Guided Wave Structural Health Monitoring System for Pipework
, MATERIALS EVALUATION, Vol: 76, Pages: 1118-1126, ISSN: 0025-5327 -
Journal articleJarvis R, Farinha A, Kovac M, et al., 2018,
NDE sensor delivery using unmanned aerial vehicles
, Insight (Northampton): non-destructive testing and condition monitoring, Vol: 60, Pages: 463-467, ISSN: 1354-2575The robotic deployment of NDE sensors has great cost-saving potential in cases where the measurement cost is high due to access restrictions or the need to temporarily decommission the test structure. Unmanned aerial vehicles (UAVs) are able to quickly reach inaccessible components to perform visual inspection and deploy NDE sensors. In this work, a mechanical sensor release mechanism is presented that has enabled electromagnetic acoustic transducers (EMATs) to be deployed onto a ferromagnetic pipe and a plate, after which the component wall thickness measurements can be transmitted wirelessly to a remote location. The reliability of the method and the most promising areas for future development are discussed.
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Journal articlePhillips R, Duxbury D, Huthwaite P, et al., 2018,
Simulating the ultrasonic scattering from complex surface-breaking defects with a three-dimensional hybrid model
, NDT and E International, Vol: 97, Pages: 32-41, ISSN: 0963-8695© 2018 Elsevier Ltd Modelling is increasingly relied on for the design and qualification of ultrasonic inspections applied to safety-critical components. Numerical methods enable the simulation of the ultrasonic interaction with realistic defect morphologies; however, the computational requirements often limit their deployment. The hybrid simulation technique, which combines semi-analytical and numerical methods, realises the potential of high fidelity numerical modelling without the limiting computational factors. The inspection of thick section components for near-backwall surface-breaking defects results in large propagation distances, making them a key application of hybrid modelling. This work presents a methodology for efficiently simulating the ultrasonic inspection of complex surface-breaking defects using a hybrid model. The model is initially verified against full numerical simulation; further validation is presented by comparison to an experimental scan over an artificially machined surface-breaking notch. The potential of the new hybrid method is then demonstrated by carrying out a Monte Carlo analysis on the scattered field from surface-breaking defects with randomly rough surfaces and the results are compared to the Kirchhoff approximation.
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Conference paperCegla F, Herdovics B, 2018,
Coded excitation, motion and signal-to-noise ratio
, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, ISSN: 0271-4302Previous work has shown that coded excitation can be used to considerably improve the signal-to-noise ratio (SNR) of signals received by transducers of poor sensitivity such as electromagnetic acoustic transducers (EMATs). EMATs are usually driven with signal powers of the order of kWs so that adequate SNR is achieved. With coded excitation these powers can be reduced to as low as 1-5W. A particular feature of the transmitted codes is that they are temporally long and contain intermittent intervals in which reception takes place. Because of the signal length there is concern that excessive movement of the probe or target can result in deterioration of the performance of such a system. Therefore, in this paper we investigate the effect that physical motion of the test piece can have on the acquired signals. Simulated results will be presented and discussed here.
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Journal articleCorcoran J, Davies C, 2018,
Monitoring power-law creep using the failure forecast method
, International Journal of Mechanical Sciences, Vol: 140, Pages: 179-188, ISSN: 0020-7403Creep is considered to be the life limiting damage mechanism in many load bearing high temperature components. A range of different parameters determine the creep life of a component, many of which are unlikely to be known to sufficient accuracy to enable satisfactory estimation of remnant life. Instead,the integrity of a component shouldbe established through direct measurement of the response of the component to the operating conditions. Creep deformation is shown to be a positive feedback mechanism; anincreasein strain leadsto an increasing strain rate. It has recently been shown that as a consequence of positive feedback the Failure Forecast Method, a generalised framework for predicting time to criticality based on rates of change of damage, may beapplied for remnant life calculations. A range of strain rate based assessments have been proposed in the literature but it is proposed that the Failure Forecast Method unifies many of these techniques and provides additional insight into creep behaviour by virtue of the underlying positive feedback. The methodology has been demonstrated using experiment datasets that are pertinent to creep in high temperature pressure vessels and piping; it is shown that failure times are accurately predicted shortly after the minimum creep strain rate.
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Journal articleVan Pamel A, Sha G, Lowe MJS, et al., 2018,
Numerical and analytic modelling of elastodynamic scattering within polycrystalline materials
, Jornal of the Acoustical Society of America, Vol: 143, Pages: 2394-2408, ISSN: 0001-4966The elastodynamic behavior of polycrystalline cubic materials is studied through the fundamental propagation properties, the attenuation and wave speed, of a longitudinal wave. Predictions made by different analytical models are compared to both numerical and experimental results. The numerical model is based on a three-dimensional Finite Element (FE) simulation which provides a full-physics solution to the scattering problem. The three main analytical models include the Far-Field Approximation (FFA), the Self-Consistent Approximation (SCA) to the reference medium, and the herein derived Second Order Approximation (SOA). The classic Stanke and Kino model is also included, which by comparison to the SOA, reveals the importance of the distribution of length-scales described in terms of the two-point correlation function in determining scattering behavior. Further comparison with the FE model demonstrates that the FFA provides a simple but satisfactory approximation, whereas the SOA shows all-around excellent agreement. The experimental wave velocity data evaluated against the SOA and SC reveal a better agreement when the Voigt reference is used in second order models. The use of full-physics numerical simulations has enabled the study of wave behavior in these random media which will be important to inform the ongoing development of analytical models and the understanding of observations.
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Conference paperBudyn N, Bevan R, Croxford AJ, et al., 2018,
Sensitivity Images for Multi-View Ultrasonic Array Inspection
, 44th Annual Conference on Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, ISSN: 0094-243X -
Conference paperHoward R, Cegla F, 2018,
The Effect of Pits of Different Sizes on Ultrasonic Shear Wave Signals
, 44th Annual Conference on Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, ISSN: 0094-243X -
Journal articleShi F, Huthwaite P, 2018,
Ultrasonic wave-speed diffraction tomography with undersampled data using virtual transducers
, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol: 65, Pages: 1226-1238, ISSN: 0885-3010Ultrasonic diffraction tomography (DT) offers a way to achieve high-resolution imaging of the wavespeed map, and hence has strong potential applications in medical diagnosis and Nondestructive evaluation (NDE). Ideal images can be obtained with a complete array of sensors surrounding the scatterer, provided that the measurement data are fully sampled in space, obeying the Nyquist criterion. Spatial undersampling causes the image to be distorted and introduce unwanted circular artefacts. In this paper we propose an iteration approach using virtual transducers to achieve high-resolution tomographic imaging with undersampled measurements. At each iteration stage, the extent constraint estimated from the shape of the object of interest is applied on the image space to obtain a regularized image, based on which the ultrasonic measurement data at virtual transducers are calculated using a forward model. The full dataset composed of original and virtual measurements is then used for tomography in the next stage. A final image with sufficiently high resolution is obtained after only a few iterations. The new imaging method yields improvements in the robustness and accuracy of ultrasonic tomography with undersampled data.We present numerical results using complicated wavespeed maps from realistic corrosion profiles. In addition, an experiment using guided ultrasonic waves is performed to further evaluate the imaging method.
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Journal articleCawley P, Khalili P, 2018,
Relative ability of wedge coupled piezoelectric and meander coil EMAT probes to generate single mode Lamb waves
, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol: 65, Pages: 648-656, ISSN: 0885-3010Ultrasonic guided waves are used extensively when checking for defects in petrochemical and other industries and are mostly generated using piezoelectric transducers on an angled wedge or EMATs in different configurations. Low frequency inspection allows for long distance propagation but it is best suited for detecting relatively large defects, while at higher frequencies, the presence of multiple wave modes limit defect detectability, so achieving practical single Lamb mode excitation via careful transduction is very beneficial. This paper investigates the relative ability of angled piezoelectric and meander coil EMAT probes to produce single mode transduction in the medium (~1 to 5 MHz-mm) and high (> 5 MHz-mm) frequency-thickness regions of the dispersion curves. The nature of each transducer is studied analytically by simulating the corresponding surface forces, followed by the use of a Fourier transform in time and space (2-D FFT) to highlight the excitation region in wavenumber-frequency space. With angled wedge excitation there is a linear relationship between the excitation frequency and the wavenumber which means the excitation tends to track typical dispersion curves, allowing for easier pure mode generation. In contrast, the EMAT controls frequency and wavenumber separately which makes it more difficult to generate a pure mode when dispersion curves are close together; however, by narrowing the frequency bandwidth via a large number of cycles in the excitation signal, pure mode generation via an EMAT was shown to be possible even in areas of closely spaced modes. As example cases, analytical results, backed up by experiments, showed that signals dominated by the A0 mode at 1.5 MHz-mm and also the A1 mode at 18 MHz-mm can be generated with both angled piezoelectric and EMAT probes.
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