Showing papers in "Quantitative Nondestructive Evaluation in 2002"
TL;DR: In this paper, a finite element (FE) technique for computing the properties of guided waves that can exist in an isotropic beam of arbitrary cross section is presented, which uses a two-dimensional mesh to represent a cross section through the beam and cyclic axial symmetry conditions to prescribe the displacement field perpendicular to the mesh.
Abstract: A finite element (FE) technique for computing the properties of guided waves that can exist in an isotropic beam of arbitrary cross section is presented The FE model uses a two-dimensional mesh to represent a cross section through the beam and cyclic axial symmetry conditions to prescribe the displacement field perpendicular to the mesh FE results are presented for plate and angle sections Excitability functions are calculated and implications for transducer placement are considered
70 citations
TL;DR: In this paper, an air-coupled sensor detects propagating leaky surface waves generated by a point impact event applied on the concrete surface, which can be easily detected by the sensor due to the large out-of-plane motion of the waves.
Abstract: This research investigates air-coupled sensors used for non-contact NDT of concrete structures. An air-coupled sensor detects propagating leaky surface waves generated by a point impact event applied on the concrete surface. Compared to conventional body waves, leaky surface waves can be easily detected by the sensor due to the large out-of-plane motion of the waves. The computed velocity of the sensed leaky waves indicates the nature of the wave: Rayleigh surface waves are generated in the thick wall and Lamb waves in the thin slab. The study shows the potential of this sensing method for rapid inspection of concrete structures.
50 citations
TL;DR: This paper discusses basic concepts, design issues, and preliminary performance of wireless sensors, including a temperature-threshold indicator and a chloride-th threshold indicator.
Abstract: Wireless sensors can be realized by integrating a sensor with a passive commercial radio-frequency identification (RFID) chip. When activated, the chip responds with a digitally encoded signal that not only identifies the sensor but also contains information about the sensor state. Two devices have been developed to date: a temperature-threshold indicator and a chloride-threshold indicator. This paper discusses basic concepts, design issues, and preliminary performance.
42 citations
TL;DR: In this paper, a one-sided, non-contact, real-time and rapid nondestructive testing (NDT) technique for detecting and characterization of delaminations between an FRP composite and a concrete surface is presented.
Abstract: Fiber reinforced polymer (FRP) composites are increasingly being used for the rehabilitation of concrete structures. Detection and characterization of delaminations between an FRP composite and a concrete surface are of paramount importance. Consequently, the development of a one sided, non-contact, real time and rapid nondestructive testing (NDT) technique for this purpose is of great interest. Near-field microwave NDT techniques, using open-ended rectangular waveguide probes, have shown great potential for detecting delaminations in layered composite structures such as these. The results of some theoretical and experimental investigations on a specially prepared cement paste specimen are presented here.
30 citations
TL;DR: In this article, a study of the energy velocities and attenuations of Lamb waves in anisotropic and absorbing plates is presented, where an experimental set-up has been developed using a laser sensor.
Abstract: The aim of this work is to gain a better understanding of the propagation of Lamb waves in anisotropic and absorbing plates. A study of the energy velocities and attenuations of Lamb waves in such media is presented here. In the first part, propagation in principal directions has been studied. In order to measure the attenuation of guided modes, an experimental set-up has been developed using a laser sensor. Predictions and experimental results for a unidirectional Glass Epoxy plate are described and discussed. In the second part of this work, the non-principal direction problem is approached. Preliminary results of the steering angle phenomena for guided modes are obtained and discussed.
30 citations
TL;DR: In this article, the authors proposed a technique based on elastic guided wave propagation through the rail to identify broken rail by either utilizing an impact device or energy propagating from the train wheel in contact with the rail, and a feasibility demonstration is presented for a train going 50 miles per hour (90 km/hour) towards a broken rail with sensors fixed on rails close to the break.
Abstract: A technique is presented to identify broken rail. The technique is based on elastic guided wave propagation through the rail. Broken rail detection is possible by either utilizing an impact device or energy propagating from the train wheel in contact with the rail. In principle, elastic guided wave energy propagates along the track, a natural wave-guide, until a broken rail is encountered. Pulse echo reflection is then used to identify broken rail. Considering an exponential decrease in penetration power from a source as a function of distance and natural energy filtering mechanisms of a rail, a simple model of guided wave propagation in rail is discussed. A feasibility demonstration of the concept is presented for a train going 50 miles per hour (90 km/hour) towards a broken rail with sensors fixed on rails close to the break.
29 citations
TL;DR: In this paper, a low frequency (15 to 40 kHz) ultrasonic transducer is used to fill the sample with sound that causes frictional heating at crack interfaces, which can be applied equally well to quite large and irregularly shaped objects, and to small delicate objects using the same apparatus.
Abstract: We describe recent developments in thermosonic crack detection This technique uses a single short pulse of sound to cause cracks to heat up and become visible in the infrared A low frequency (15 to 40 kHz) ultrasonic transducer fills the sample with sound that causes frictional heating at crack interfaces We show that the technique can be applied equally well to quite large and irregularly shaped objects, and to small delicate objects using the same apparatus We present examples of this technology applied to cracks as small as 20 microns and as large as several inches, and to materials ranging from brittle ceramics, to soft metals and composites
27 citations
TL;DR: In this paper, a theoretical model is presented to describe the thermosonic imaging of surface-breaking and sub-subsurface cracks, together with illustrative comparisons with experimental measurements.
Abstract: A theoretical model is presented to describe the thermosonic imaging of surface-breaking and sub-subsurface cracks, together with illustrative comparisons with experimental measurements.
25 citations
TL;DR: In this article, an ultrasonic sensor for detection of ultrasonic waves in liquids and solid structures is proposed, which contains a fiber probe which is a single mode fiber with a Bragg grating; a tunable narrowband laser source; and a photodetector.
Abstract: An ultrasonic sensor for detection of ultrasonic waves in liquids and solid structures is proposed. The sensor contains a fiber probe which is a single mode fiber with a Bragg grating; a tunable narrowband laser source; and a photodetector. When an ultrasonic wave impinges the fiber probe the pitch of the grating is modulated by the acoustically induced mechanical strain through the elasto-optic effect. The corresponding changes in reflectivity of the grating are detected by a photodetector. Main advantages of the sensor are direct modulation of laser intensity by ultrasound, simplicity of design, and high sensitivity over broad frequency range.
25 citations
TL;DR: In this paper, several key features of pulsed eddy current transient responses from probe coils have been identified and related to specific test parameter and material property changes, such as lift-off variations and interlayer separations in multi-layered structures.
Abstract: Several key features of pulsed eddy current transient responses from probe coils have been identified and related to specific test parameter and material property changes. While many features are related to flaw size and location, most, such as maximum amplitude, are severely affected by probe lift-off variations and interlayer separations in multi-layered structures. We present several PEC signal features and interpretation techniques for locating and quantifying metal loss in calibration specimens and naturally corroded lap splices exhibiting common noise sources.
24 citations
TL;DR: In this article, the pulsed eddy current was used for detecting and quantifying fatigue cracks under installed fasteners in an aircraft NDE system, and the potential of this technique was evaluated.
Abstract: Improving the detectability of fatigue cracks under installed fasteners is one of the many goals of the aging aircraft nondestructive evaluation (NDE) community. The pulsed eddy current offers new capabilities to address this requirement. The aim of the paper is to evaluate the potential of this technique for detecting and quantifying notches under installed fasteners.
TL;DR: In this article, the authors compared the predictions of four measurement models for the 2002 Ultrasonic Benchmark Problem, which involves the pulse-echo responses of spherical and cylindrical cavities.
Abstract: The predictions of four measurement models are compared for the 2002 Ultrasonic Benchmark Problem. The problem involves the pulse‐echo responses of spherical and cylindrical cavities. The ultrasonic waves are considered to be generated and detected by either a planar or spherically focused probe, each of finite diameter and positioned to produce normally incident or refracted waves (longitudinal or shear) of the desired angle. Among the results are a new expression for the response of the cylindrical cavity and a quantitative comparison of the various models. Noteworthy is the differences in the predictions of the beam models, for refracted angles near critical angles and for focused probes.
TL;DR: A redesign of the NASA Langley Research Center developed giant magnetoresistive-based Rotating Probe System has been performed based upon experimental and finite element analyses as mentioned in this paper, which reduced the probe footprint without significantly affecting the depth of detection of the device.
Abstract: A redesign of the NASA Langley Research Center developed Giant Magnetoresistive-based Rotating Probe System has been performed based upon experimental and finite element analyses. The resulting probe footprint has been greatly reduced without significantly affecting the depth of detection of the device. Electronics for the probe drive and signal detection circuitry have also been updated. The new electronics deliver variable phase outputs for drive and feedback signals and produces high gain at flaw detection frequencies. The complete system configuration is presented, along with results for the detection of fatigue cracks in sub-layer airframe components.
TL;DR: In this paper, the suitability of lower frequency modes for such a test, through the modelling of wave behavior and the analysis of test results, was examined through the analysis results.
Abstract: Rock bolts are used to reinforce coal mine roadways, and a suitable non-destructive test for their integrity is required. Previous work has shown that high frequency, low-leakage guided waves can be used to inspect straight rock bolts, and an alternative mode is required to inspect bolts that have become deformed through ground movement. This paper examines the suitability of lower frequency modes for such a test, through the modelling of wave behavior and the analysis of test results.
TL;DR: The ability of VIC-3D© to model eddy-current probes has been significantly enhanced to include coils of virtually any shape, such as racetrack, D-shaped, and square, and oriented in virtually any direction.
Abstract: The ability of VIC-3D©, a proprietary volume-integral code, to model eddy-current probes has been significantly enhanced to include coils of virtually any shape, such as racetrack, D-shaped, and square, and oriented in virtually any direction. This allows the ability to model such well-known probes as the split-core differential probe, even when tilted relative to the workpiece, and the plus-point probe, that is often used in the nuclear power industry.
TL;DR: In this article, a lock-in thermography approach was devised which provides a map of the two first harmonics of temperature and a mapping of the temperature mean rise, and experiments performed on steel XC48, 316L and Al 7010, Al 2024 showed the high potential of this method.
Abstract: The design of mechanical structures that are subject to repeated loads relies upon the knowledge of the fatigue limit of the constitutive materials. Conventional methods for the fatigue limit evaluation are lengthy and therefore expensive. We propose a new approach for this problem. It is based on the detection of a modification of the thermomechanical couplings occurring together with the damage onset. A specific lock-in thermography approach was devised which provides a map of the two first harmonics of temperature and a map of the temperature mean rise. Experiments performed on steel XC48, 316L and on Al 7010, Al 2024 show the high potential of this method.
TL;DR: In this article, the authors used thermal depth imaging to identify the characteristic signature of planes of dense porosity in composites and compared with results from thermal theory and modeling of porosity and with ultrasonic characterization.
Abstract: Porosity evaluation in composites has been extensively studied with ultrasonics There are far fewer examples of porosity evaluation using thermal imaging One reason for this dearth of work has been the qualitative nature of most thermal characterization In this paper we use quantitative thermal depth imaging to identify, for the first time, the characteristic signature of planes of dense porosity in composites The observations are compared with results from thermal theory and modeling of porosity and with ultrasonic characterization This approach should eventually lead to a quantitative thermal evaluation of volume % porosity in composites
TL;DR: In this article, the utility of Hilbert-Huang Transform (HHT) for analyzing machining machining data is demonstrated, and preliminary analyses of vibration signals from end-milling tests are promising for future implementation of HHT in condition/health monitoring systems.
Abstract: The machining process is highly dynamic, involving complicated interactions between a workpiece, cutting tool, and the machine tool itself Appropriate vibration signal analysis can provide insight into the condition of both machine and process In this paper, the utility of a new time-frequency technique for analyzing complicated time series data, known as the Hilbert-Huang Transform (HHT), is demonstrated Preliminary analyses of vibration signals from end-milling tests are promising for future implementation of HHT in condition/health monitoring systems
TL;DR: In this paper, it was shown that the elastic wave amplitude is a minimum (zero if no noise were present) at the field for which the magnetostriction derivative is zero and magnetostrictively couples to the material.
Abstract: Elastic waves are generated in a ferromagnetic material in a static magnetic field by a time-varying magnetic field which magnetostrictively couples to the material. We present modeling showing that this coupling is proportional not to the magnetostriction, but to the magnetization derivative of the static magnetostriction. We present experimental evidence showing that the elastic wave amplitude is a minimum (zero if no noise were present) at the field for which the magnetostriction derivative is zero and magnetostriction is maximum. No such minimum is found in steel when the field is high enough to make the magnetostriction go through zero and become negative. Thus, experiment also indicates that the coupling is proportional to the derivative of the magnetostriction, and not to the magnetostriction itself.
TL;DR: In this article, paraxial beam models are used in conjunction with approximate and exact flaw scattering models to demonstrate the effects of various modeling assumptions on the waveforms predicted for these benchmark problems.
Abstract: A series of ultrasonic benchmark problems have been defined for use in comparing different model-based approaches. Here, paraxial beam models are used in conjunction with approximate and exact flaw scattering models to demonstrate the effects of various modeling assumptions on the waveforms predicted for these benchmark problems.
TL;DR: In this paper, a double-blind experiment was conducted to identify structural flaws in aging aircraft structures, using a number of identical aluminum plates, into which representative flaws have been introduced prior to scanning with an existing Lamb wave tomography system and verification with traditional ultrasonic C-scans in an immersion tank.
Abstract: Lamb waves are guided ultrasonic waves capable of propagating relatively long distances in plates and laminated structures, such as airframe skins, storage tanks and pressure vessels. Their propagation properties in these media depend on the vibrational frequency as well as on the thickness and material properties of the structure. Structural flaws such as disbonds, corrosion and fatigue cracks represent changes in effective thickness and local material properties, and therefore measurement of variations in Lamb wave propagation can be employed to assess the integrity of these structures. Lamb wave measurements can be made for a number of relative transducer positions (projections) and an image of the flawed region can be reconstructed tomographically to give a quantitative map of a quantity of interest, e.g. thickness loss due to corrosion. As a test of the Lamb wave scanning apparatus and diffraction tomography reconstruction algorithms, we have undertaken an experiment which is double-blind in the medical sense. Since our motivation is identifying flaws in aging aircraft structures, we have purchased a number of identical aluminum plates, into which representative flaws have been introduced prior to scanning with our existing Lamb wave tomography system and verification with traditional ultrasonic C-scans in an immersion tank. All personnel “calling the flaws” from the reconstructions are blinded from both the Lamb wave and immersion scanning results, with scoring metrics determined before hand. These and other results will be presented in this talk.
TL;DR: In this article, a new method for compensating EC signals for variations in lift-off is described, where the signals are transformed to obtain a zero liftoff equivalent signal that can be subsequently used for defect characterization.
Abstract: Eddy current (EC) testing methods are widely used in a variety of applications including the inspection of steam generator tubes in nuclear power plants, aircraft parts and airframes. A key factor that affects the EC signal is lift-off. In practice, it is difficult to keep track of the actual value of the lift-off, which is essential for accurate interpretation of the signal. Hence it is necessary to have a scheme to render the EC signal invariant to the effects of lift-off. This paper describes a new method for compensating EC signals for variations in lift-off. The signals are transformed to obtain a zero lift-off equivalent signal that can be subsequently used for defect characterization.
TL;DR: In this paper, a finite element modal solution method was used to derive the dispersion curves and mode shapes for waves travelling along a curved pipe and the main characteristics of dispersion curve in toroidal structures have also been highlighted.
Abstract: This paper focuses on the improvement of the understanding of guided wave propagation through pipes with bends. A Finite Element modal solution method was used in order to derive the dispersion curves and mode shapes for waves travelling along a curved pipe. The main characteristics of the dispersion curves in toroidal structures have also been highlighted.
TL;DR: In this article, the case-hardening process modifies the near-surface permeability and conductivity of steel, as can be observed through changes in eddy current probe signals measured over a range of frequency.
Abstract: The case-hardening process modifies the near-surface permeability and conductivity of steel, as can be observed through changes in eddy current probe signals measured over a range of frequency. In this work, experiments have been performed using normal absolute probe coils on flat steel specimens and coils encircling case-hardened steel rods. By fitting model results to the experimental data, estimates of electrical material properties are found. The approach also allows an assessment of the sensitivity of the measurements to the case depth.
TL;DR: In this paper, a drive pulse and the response is analyzed in terms of Fourier transform (FT) to understand the scope of material penetration with PEC and the advantages and limitations of the technique are discussed.
Abstract: Capabilities of the Pulsed Eddy Current (PEC) method to perform in-depth scanning have been successfully demonstrated for hidden corrosion detection. In the present work, a drive pulse and the response is analyzed in terms of Fourier Transform to understand the scope of material penetration with PEC. Variations of the drive pulse shape can be an effective technique to control the depth of penetration of conductive materials. An observation time interval and a sampling rate are the components that can be used for “in-depth slicing” of conductive media. Two-dimensional scanning of multi-layered structures such as aircraft skin structures with a PEC probe provides detection of subsurface defects. Experiments have been performed on aluminum panels with flat bottom holes. An image processing routine is applied to reconstruct geometry of the component from a series of eddy current images obtained with a two-dimensional scanner. A problem of accurate reconstruction of the internal geometry of the component under test is considered. The advantages and limitations of the technique are discussed.
TL;DR: In this article, an ice detection system, using ultrasonic guided waves, was demonstrated in-flight and was shown to be successful in detecting ice bonded to the aircraft wing leading edge.
Abstract: Ultrasonic guided waves provide a convenient and reliable method to detect contaminants on the surface of the structure the wave travels in Classifying the contaminants is possible by selecting the guided wave mode with the appropriate wave structure An ice detection system, using this technology, designed at Sensor Systems, Goodrich Corporation is described The system is demonstrated in-flight and is shown to be successful in detecting ice bonded to the aircraft wing leading edge
TL;DR: In this article, a point source superposition technique is applied to model transducer-radiated transient wavefields assuming anisotropic material and attenuation symmetry, where viscoelasticity is taken into consideration via a complex, frequency-dependent elastic tensor.
Abstract: A point source superposition technique is applied to model transducer-radiated transient wavefields assuming anisotropic material and attenuation symmetry. For composite materials, viscoelasticity is taken into consideration thru a complex, frequency-dependent elastic tensor. The generation and propagation of quasi-shear vertical waves in transversely isotropic weld material and of quasi-longitudinal waves in an orthotropic composite are considered.
TL;DR: In this paper, the elastic constants of the α/β-single and α-phase SAW signals were determined using time-resolved line-focus acoustic microscopy for determining elastic constants.
Abstract: Time-resolved line-focus acoustic microscopy is performed for determining elastic constants of Ti-6242 α/β-single colony and Ti-6 α-phase single crystal Surface acoustic wave (SAW) velocities are obtained as a function of the propagation angle from measured time-delays of SAW signals The propagation of surface waves in a semi-infinite half space formed by anisotropic layers inclined arbitrarily to the sample surface is studied to model a quasi-random lamellar structure of the Ti-6242 α/β-single colony Effective elastic constants of the multilayered structure are derived and verified through the comparison with exact ones, based on which SAW velocities in non-principal planes are calculated Effective and constituent elastic constants of the α/β-single colony and the α-phase single crystal are inversely determined from the measured and calculated SAW velocities The α- and β-phase elastic constants from the α/β-single colony so determined are compared with those from the α-single crystal and data in the literature
TL;DR: The Scanning Laser Source (SLS) technique is based on monitoring the changes in the laser generated ultrasonic signal as the source is scanned over the area of inspection as mentioned in this paper.
Abstract: The Scanning Laser Source (SLS) technique is based on monitoring the changes in the laser generated ultrasonic signal as the source is scanned over the area of inspection. The SLS imaging scanning system includes a portable Nd-YAG laser, free space or fiberized scanners, an ultrasonic detector, and signal processing software. High resolution ultrasonic images of small EDM notches and fatigue cracks on flat and curved specimens are presented. A Mass-Spring Lattice Model is adopted as the numerical method for the simulation and visualization of the SLS technique. The SLS imaging system offers an effective solution for high resolution non-contact inspection of critical components of complicate shape.
TL;DR: In this paper, the authors describe some of the weld inspections using phased arrays, where a scan pattern is rapidly multiplexed across a component, and the angle of inspection is varied, and combinations of these two Electronic scanning increases inspection speed using linear scanning, while sectorial sweeping permits the beams to be precisely targeted at selected portions of welds.
Abstract: Ultrasonic phased arrays are well suited to weld inspections Phased arrays can perform electronic scanning (where a scan pattern is rapidly multiplexed across a component), sectorial scanning (where the angle of inspection is varied), and combinations of these two Electronic scanning increases inspection speed using linear scanning, while sectorial sweeping permits the beams to be precisely targeted at selected portions of the welds The combination permits customized, high speed scans, which create high quality, tailored inspections This paper describes some of the weld inspections using phased arrays