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A finite difference time domain method (FDTD) is based on a grid‐based time domain differential technique, in which wave equations are solved in a leapfrog manner. It is required to discretize a whole target domain into computational grids with an adequate size. Therefore computational burden increases if the computational domain is much larger than the wave length. To solve such a large‐scale problem in high speed, we apply a parallel computing technique to the FDTD. OpenMP is an interface to execute program codes in parallel using a shared memory system of computers. As an example of large‐scale analysis, SH wave propagations in concrete material are demonstrated in this study.

This study is concerned with a non‐linear inverse scattering technique called Time‐Domain Topological Gradient (TDTG) for 2D wave equation. The TDTG is a recently developed shape optimization technique for elastodynamic problems with several potential advantages. The method, however, hasn't been used in the context of array ultrasonic imaging. In this study, performance of the TDTG is investigated numerically and experimentally by solving two example problems. The first is a numerical example in which a vertical slit in a plate is reconstructed from simulated data. The second one is a reconstruction from experimental data. Ultrasonic signals from a side‐drilled hole in a steel block specimen are measured by an array transducer. The profile of the hole is reconstructed from those ultrasonic signals in the second problem. The results show that the TDTG can effectively use the phase focused beam fields, and very accurate in reconstructing not only a flat object but also a round one.

The scope of research activity that Bruce Thompson embraced was very large. In this talk three different research topics that the author shared with Bruce are reviewed. They represent Bruce's introduction to NDE and include nonlinear acoustics, nondestructive measurements of adhesive bond strengths in honeycomb panels, and studies of flexural wave dispersion in honeycomb materials. In the first of these, four harmonics of a 30 Mhz finite amplitude wave were measured for both fused silica and aluminum single crystals with varying lengths and amounts of cold work using a capacity microphone with heterodyne receiver with a flat frequency response from 30 to 250 Mhz. The results for fused silica with no dislocation structure could be described by a model due to Fubini, originally developed for gases, that depends upon only the second and third order elastic constants and not the fourth and higher order constants. The same was not true for the aluminum with dislocation structures. These results raised some questions about models for harmonic generation in materials with dislocations. In the second topic, experiments were made to determine the adhesive bond strengths of honeycomb panels using the vibrational response of the panels (Chladni figures). The results showed that both the damping characteristics of panel vibrations as a whole and velocity of propagation of elastic waves that travel along the surface and sample the bondline can be correlated with destructively determined bond strengths. Finally, the phase velocity of flexural waves traveling along a 1-inch honeycomb sandwich panel was determined from 170 Hz to 50 Khz, ranging from 2.2×104 cm/sec at the low end to 1.18×105 cm/sec at 40 Khz. The dispersion arises from the finite thickness of the panel and agreed with the results of continuum models for the honeycomb. Above 40 Khz, this was not the case. The paper concludes with a tribute to Bruce for his many wonderful contributions and lessons beyond his technical legacy for all of us.

Surface ultrasonic waves have been shown to have many uses in non-destructive testing, in particular for gauging the depth of surface defects. Much of the previous work has assumed that these defects are oriented normal to the surface. However, this is not always the case; for example, rolling contact fatigue in rails propagates at an angle of around 25° to the surface, and this angle may affect the characterisation. We present results using non-contact ultrasonic methods to generate and detect ultrasound on samples with a range of defect angles, and compare these with finite element method (FEM) models. We use both electromagnetic acoustic transducers (EMATs) and laser ultrasound. The depth calibration when measuring ultrasound transmission is considered, and what affect the angle of a defect has. Several other methods of characterising crack depth and angle are also discussed, including the arrival times of reflected and mode-converted waves, the delay in the transmission of the high-frequency Rayleigh wave, and the enhancement of the signal at the defect in both the in-plane and out-of-plane components.

AIP Conf. Proc. Volume 1335; International audience; The design of an ultrasonic array and its settings for a specific inspection involves multiple parameters and is the result of a compromise between different requirements and limitations. Parametric studies based on simulation tools are often performed to ensure that the transducer has suitable performances in terms of detection of the defects sought. An automatic optimization tool, based on an evolutionary algorithm driving CIVA's simulation data, is proposed and tested in realistic applications to design inspection parameters (designing, positioning and/or setting the transducer).

Two thermography techniques, passive and active, are used to detect damage initiation and progression in a cyclically loaded composite cylinder. The passive thermography tracks damage progression in real time during cyclic loading. Active flash thermography, using a flash tube enclosed within the cylinder, images delaminations. A differential thermography processing technique eliminates normal material variations and improves sensitivity to and sizing of delaminations. The thermography results were compared to non‐immersion ultrasonic results.

Nondestructive evaluation is used widely in many engineering and industrial areas to detect defects or flaws such as cracks inside parts or structures during manufacturing or for products in service. The standard statistical model is a simple empirical linear regression between the (possibly transformed) signal response variables and the (possibly transformed) explanatory variables. For some applications, such a simple empirical approach is inadequate. An important alternative approach is to use knowledge of the physics of the inspection process to provide information about the underlying relationship between the response and explanatory variables. Use of such knowledge can greatly increase the power and accuracy of the statistical analysis and enable, when needed, proper extrapolation outside the range of the observed explanatory variables. This paper describes a set of physical model‐assisted analyses to study the capability of two different ultrasonic testing inspection methods to detect synthetic hard...

A nonlinear vibration technique has been developed for the nondestructive characterization of damage introduced by alkali‐silica reactions (ASR) in concrete. The response of a concrete specimen to increasing impact load is analyzed to obtain a relationship between the amplitude of the response and the resonance frequency, and thus the nonlinearity of the specimen. As commonly observed in nonlinear hysteretic materials, the resonance frequency of a specimen decreases with an increasing level of excitation strain. Concrete is a nonlinear hysteretic material to begin with, but the progress of the alkali‐silica reaction causes an increase in nonlinearity through the formation of expansive ASR gel and the resulting microcracks. This increase in material nonlinearity is measured with the aforementioned procedure. The specimens used in the research are of varying reactivity with respect to ASR, which is induced in accordance with ASTM C 1293. The results show a substantial difference in nonlinearity between samples with highly reactive aggregate, and those with a non‐reactive one. Complementary expansion measurements are also performed to independently verify the reactivity of the aggregate used. These results show that the developed nonlinear vibration technique has the potential to characterize the amount of ASR‐induced damage in concrete.

The use of composite materials in aircraft industry is becoming more common because of high stiffness‐to‐weight ratio. Adhesively bonded, metallic stiffeners are also widely used for increasing the transverse stiffness of thin composite components. However, small defects in the adhesive (porosity, cracks, …) may exist after the bonding is realized, and become larger during the in‐service life, thus causing severe damages to the whole structure. For obvious safety reasons, the non‐destructive testing of such critical bond‐lines is very important. More specifically, it is of importance to size disbonds that may exist between a stiffener and a composite component. Recently, a 2D, Finite‐Element‐based inverse technique has been developed for sizing defects in plates, using Lamb waves. Here, this technique is used for sizing the width of a disbond running parallel to an Aluminum stiffener adhesively attached to a Carbon‐Epoxy plate. A pure incident S0 mode is experimentally sent towards the stiffener, and the ...

The use of ultrasonic arrays to detect crack‐like defects is an important area in nondestructive evaluation. The array data, which contains scattered ultrasonic waves from a scatterer, can be used to reconstruct a high resolution image, e.g., using the total focusing method (TFM). In this paper, the TFM images from smooth and rough crack‐like defects are compared. It is shown that roughness can be either beneficial or detrimental to the detectability of crack‐like defects.

Infrared Imaging of coatings is not new. In the past it has been accomplished either comparatively, for example using additional thickness standards, as a point‐wise inspection or as a simple non‐quantitative image showing debonds at most. In the present paper we describe the first quantitative infrared image of both coating thickness and integrity. No reference standard is necessary. This coating thickness imaging can be applied over 100% area of complex‐shape components such as airfoils. It is fast and a by‐product of this inspection is an image of coating integrity which may be graded from complete disbond to poorly‐coupled, for example, indications of porosity at the bondline. We will present a first quantitative coating thickness IR image.

Most modern railways use Continuous Welded Rail (CWR). A major problem is the almost total absence of expansion joints that can create severe issues such as buckling in hot weather and breakage in cold weather. A related critical parameter is the rail Neutral Temperature (NT), or the temperature at which the net longitudinal force in the rail is zero. In June 2008 the University of California, San Diego (UCSD), under the sponsorship of a Federal Railroad Administration (FRA) Office of Research and Development (R&D) grant, began work to develop a technique for in‐situ measurement of NT and detection of incipient buckling in CWR. The method under investigation is based on ultrasonic guided waves, and the ultimate goal is to build and test a prototype that can be used in motion. A large‐scale full rail track (70 feet in length) has been constructed at UCSD’s Powell Structural Laboratories, the largest laboratories in the country for structural testing, to validate the NT measurement and buckling detection te...

Work is being conducted to develop phased array inspection of stainless steel welded pipes. Defects can occur anywhere along the weld fusion face. Optimum inspection performance across the entire weld face can be facilitated by collecting data as Full Matrix Capture (FMC) and applying a processing technique that allows focusing to be ideal for every pixel within the Bscan image. Further improvements to the Bscan image can be made by having a split aperture that varies as a function of focal depth. This paper introduces the FMC principle and describes the variable split aperture signal processing. The inspections were also modeled using the CEA CIVA software which was compared to experimental results.

The surface wave acoustic method is applied to the in‐situ monitoring of fatigue crack initiation and evolution on tension specimens. A small low‐frequency periodic loading is also applied, resulting in a nonlinear modulation of reflected pulses. The acoustic wave reflections are collected for: each experimental cycle; a range of applied tension and modulation load levels; and a range of spatial propagation positions, and are presented in image form to aid pattern identification. Salient features of the image are then extracted and processed to evaluate the initiation time of the crack and its subsequent size evolution until sample failure. Additionally, a method for enhancing signal to noise ratio in Ti‐6242 alloy samples is demonstrated.

In this paper, we propose a sizing methodology of pipe wall thinning using data acquisition by electromagnetic acoustic transducer (EMAT). First, a mathematical model of nondestructive test is given by eddy current systems and a linear elastic system. Secondly, an artificial corrosion is characterized by ellipsoid function with geometrical parameters. Thirdly, a parameter estimation problem is discussed using principle components analysis (POD). The proposed method deploys a reduced order model in order to save the computational cost of the forward analysis. Finally, an inverse analysis is performed for recovering corrosion shape using the measurement data.

A PRSEUS test article was subjected to controlled impact on the skin face followed by static and cyclic axial compressions. Phased array ultrasonic inspection was conducted before impact, and after each of the test conditions. A linear phased array probe with a manual X‐Y scanner was used for interrogation. Ultrasound showed a delamination between the skin and stringer flange adjacent to the impact. As designed, the stitching in the flange arrested the lateral flaw formation. Subsequent ultrasonic data showed no delamination growth due to continued loading.

A laser-ultrasonic approach based on the propagation of surface skimming longitudinal wave (P-wave) and Rayleigh wave (SAW) is investigated for the measurement of crystallographic texture in moderately thick steel plates. The angular dependence of the P-wave and SAW velocities presents different patterns, both of amplitude of a few % attributed to texture. Results obtained from fitting the angular profiles using relevant expressions for P-wave and SAW confirm that texture coefficients may accurately be measured by this approach. Moreover, the difference of the P wave and SAW profiles is shown to be very robust against small path length changes or other detrimental effects such as surface roughness. For actual measurements on large plates, a solution based on the rotation of a generation line using an axicon lens is tested. Texture variations across the width of steel plates and the influence of residual stress are discussed., QNDE 2010 Annual Review of Progress in Quantitative Nondestructive Evaluation, July 18-23, 2010, San Diego, California, USA, Series: AIP Conference Proceedings; no. 1335

Non‐oriented steels, with low carbon, are widely used in the fabrication of electrical motor nucleus. The performance of these motors is affected by the level of recrystallization. These steels can come from the steel plant in two different conditions: totally processed or semi‐processed. The semi‐processed steels have a partially deformed structure and are submitted to the final annealing process after reaching the end shape. An adequate annealing heat treatment is important to get an appropriate magnetic property. In the present study, samples of an electric steel, with the composition (0.05 wt% C, 1.28wt% Si, 0.29wt% Mn), cold rolled 50% in thickness, were withdrawn during the industrial heat treatment at temperatures of 575, 580, 600, 620 and 730 °C with the objective of evaluating the evolution of recrystalization with temperature. Magnetic properties were measured at room temperature in a vibrating sample magnetometer. Although the changes in magnetic hysteresis loop with temperature are difficult t...

The integration of magneto‐resistive sensors into eddy current probes can significantly expand the capabilities of conventional eddy current nondestructive evaluation techniques. The room temperature solid‐state sensors have typical bandwidths in the megahertz range and resolutions of tens of microgauss. The low frequency sensitivity of magneto‐resistive sensors has been capitalized upon in previous research to fabricate very low frequency eddy current sensors for deep flaw detection in multilayer conductors. In this work a modified probe design is presented to expand the capabilities of the device. The new probe design incorporates a dual induction source enabling operation from low frequency deep flaw detection to high frequency high resolution near surface material characterization. Applications of the probe for the detection of localized near surface conductivity anomalies are presented. Finite element modeling of the probe is shown to be in good agreement with experimental measurements.

Portable, in‐situ damage detection techniques for large structures during depot maintenance can find great utility if such capability can be realized, thereby saving considerable time and labor. Contemporary fixed location detection systems, such as the water‐coupled ultrasound imaging with the “squirter,” for instance require structural disassembly and transport to and from dedicated NDE system. For larger aircraft structures this can add weeks to the NDE process. An ultrasound field mapping method, using fiber Bragg gratings embedded in a flexible, removable sheet that can be re‐used over different structures, has been implemented. It is shown that this can be used to map guided wave ultrasonic fields over approximately 2 square feet area in a few tens of minutes. The test sample used is a composite skin with aluminum metal honeycomb of an aircraft structure. The data thus collected, comprising 612 locations over the area, can enable in‐situ damage detection once signal analysis algorithms are applied.

The paper showcases a collaborative benchmark project evaluating NDE methods for deterioration monitoring of laboratory bridge decks. The focus of this effort is to design and build concrete test specimens, artificially induce and monitor corrosion, periodically perform multi‐sensor NDE inspections, followed by 3D imaging and destructive validations. NDE methods used include ultrasonic echo array, ground penetrating radar (GPR), active infrared thermography with induction heating, and time‐resolved thermography with induction heating.

A new laser‐based ultrasonic (LBU) receiver was recently introduced. The novel architecture is based on two‐wave mixing in photorefractive materials and allows simultaneous measurement of in‐plane and out‐of‐plane displacements (two‐ component). By taking advantage of recent developments in electronic processing and our knowledge on multi‐channel interferometer, we achieved a compact optical system using only a single collecting aperture and a single laser probe beam. We will characterize the system performances and present experimental results demonstrating the capability for this compact two‐component interferometer.

The US Army is investigating the use of composite materials to deliver lightweight and more effective armor protection systems to soldiers and other army assets. However, widespread use of such hybrid armor will require a reliable but fast NDE methodology to ensure integrity of these components during manufacturing and while in service. Traditional ultrasonic inspection of such hybrid armor structures may prove to be very effective, but point‐by‐point ultrasonic scanning is inherently time‐consuming and manufacturing slowdowns could develop in high‐volume production of such armor systems. In this paper, we report on the application of acoustography for the NDE of hybrid armor structures. Acoustography differs from conventional ultrasonic testing in that test objects are inspected in full field, analogously to real time x‐ray imaging. The approach uses a novel, super high resolution large area acousto‐optic (AO) sensor, which allows image formation through simple ultrasound shadow casting, analogous to x‐ray image formation. This NDE approach offers significant inspection speed advantage over conventional point‐by‐point ultrasonic scanning procedures and is well‐suited for high volume production. We will report initial results on a number of hybrid armor plate specimens employing composite materials that are being investigated by the US Army. Acoustography NDE results will also be verified using other complimentary NDE methods.

In this paper, a method for obtaining a three dimensional crack model from a radiographic image is discussed. A genetic algorithm aiming at close simulation of crack’s shape is presented. Results obtained with genetic algorithm are compared to those achieved in authors’ previous work. The described algorithm has been tested on both simulated and real‐life cracks.

Region of Interest (ROI) Computed Tomography (CT) is a radiographic inspection technique that inspects only part of a sample. However, ROI images normally suffer from reconstruction artefacts that can affect the inspection by obscuring defects. This paper describes the development of two data completion methods which minimise the reconstruction artefacts, allowing the technique to be applied without compromising defect detection. The techniques were developed for specific application to inspection of Carbon Fibre Reinforced Plastic (CFRP) laminate panels. The results presented include both fan‐beam and cone‐beam system geometries.

Corrosion under insulation is a significant cause of pipeline failure in the oil and gas industry. This paper describes the initial developmental stages of a technique which uses the structure of an insulated pipeline as a coaxial waveguide to support the propagation of microwaves. These microwaves are used to inspect the insulation layer for the presence of water, which will indicate the regions of the pipe at risk from corrosion.

The focus law and acoustic field computation method about circular arc linear phased array have been discussed in the paper. Acoustic field of transducers is given by the use of the coordinate transformation and an approximation with rectangle element instead of circular arc element, and was validated using Rayleigh‐Sommerfeld Integral and nonparallel multiple Gaussian beam model respectively. The results of two methods match well.

Mathematical transforms are used in signal processing in order to extract what is known as “hidden” information. One of these mathematical tools is the Discrete Wavelet Transform (DWT), which has been increasingly employed in non‐destructive testing and, more specifically, in image processing. The main concern in the present work is to employ DWT to suppress noise without losing relevant image features. However, some aspects must be taken into consideration when applying DWT in image processing, mainly in the case of weld radiographs, in order to achieve consistent results. Three topics were selected as representative of these difficulties, as follows: 1) How can image matrix be filled to fit the 2n lines and 2n rows requirement? 2) How can the most suitable decomposition level of the DWT function and the correct choice of their coefficient suppression be selected? 3) Is there any influence of the scanning direction and the weld radiograph image, e.g., longitudinal or transversal, on the final processing ...

Experiments are conducted on aluminum plates containing fastener holes as well as aluminum plates containing a bolted joint. Cyclic mechanical loading is interrupted to perform structural health monitoring with the S0 fundamental Lamb wave mode. An array of surface bonded piezoelectric disk transducers having a pair of transducers at each of five bolt holes is employed. A correlation between the transmission coefficient and crack size is suggested by the data.

For several years, simulation tools aiming at predicting results of ultrasonic inspection have been developed and integrated into the CIVA simulation platform software at CEA‐LIST. Those models have recently been extended in order to take account of more complex phenomena, as multiple skips (over backwall, surface, lateral walls of components), mode conversion arising in internal medium of heterogeneous parts, and interaction between branches of ramified flaws. In addition to canonical (planar and cylindrical parts), parametric (nozzles) and 2D CAD components (complex profile and translation or revolution extrusion) already dealt with, those skills are now also available for 3D CAD components. Dedicated tools have also been developed in order to help for interpretation, settings and time saving of the computation : advanced ray tracing for displaying different echo modes (one or several skips, mode conversions, possibility to display only rays coming back to the receiving probes, selection of specific echoes), selection of specific zones over a 3D component to define echogeneous areas… These developments are illustrated through several industrial applications.