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Showing papers in "Ndt & E International in 2001"


Journal ArticleDOI
TL;DR: In this paper, the state of the art of non-destructive testing (NDT) methods as applied to the civil engineering industry in the Millennium Year, 2000 is reviewed.
Abstract: This paper reviews the state of non-destructive testing (NDT) methods as applied to the civil engineering industry in the Millennium Year, 2000. The basic principles of NDT methods are described with particular reference to the five major factors that influence the success of a survey: depth of penetration, vertical and lateral resolution, contrast in physical properties, signal to noise ratio and existing information about the structure. The main NDT methods used in engineering investigations are discussed and illustrated with brief case histories from the literature. The integration of NDT surveys into the investigation of structures is described. The underlying reasons why NDT methods are perceived as ‘not working’ by the structural engineer are identified as: a lack of understanding of variability of both the construction materials used and NDT methods themselves.

584 citations


Journal ArticleDOI
TL;DR: In this paper, two modifications of this technique have been developed: Vibro-Modulation (VM) and Impact-Induced Vibrations (IM), employing CW and impact-induced vibrations, respectively.
Abstract: Recent theoretical and experimental studies demonstrated that a weakly or incompletely bonded interfaces exhibit highly nonlinear behavior. One of acoustic manifestations of such nonlinearity is the modulation of a probing high-frequency ultrasonic wave by low-frequency vibration. The vibration varies the contact area modulating the phase and amplitude of higher frequency probing wave passing through the interface. In the frequency domain, the result of this modulation manifests itself as side-band spectral components with respect to the frequency of the probing wave. This modulation effect has been observed experimentally for various materials (metals, composites, concrete, sandstone, glass) with various types of contact-type defects (interfaces): cracks, debondings, delaminations, and microstructural material damages. Study of this phenomenon revealed correlation between the developed modulation criterion and the quantitative characteristics of the interfaces, such as its size, loading condition, and bonding strength. These findings have been used for the development of an innovative nondestructive evaluation technique, namely Vibro-Acoustic Modulation Technique. Two modifications of this technique have been developed: Vibro-Modulation (VM) and Impact-Modulation (IM), employing CW and impact-induced vibrations, respectively. The examples of applications of these methods include crack detection in steel pipes, aircraft and auto parts, bonded composite plates etc. These methods also proved their effectiveness in the detection of cracks in concrete.

390 citations


Journal ArticleDOI
TL;DR: The sensitivity of nonlinear elastic wave spectroscopy (NEWS) methods to the detection of damage features (cracks, flaws, etc.) is far greater than can be obtained with linear acoustical methods as mentioned in this paper.
Abstract: Nonlinear elastic wave spectroscopy (NEWS) represents a class of powerful tools which explore the dynamic nonlinear stress–strain features in the compliant bond system of a micro-inhomogeneous material and link them to micro-scale damage. Hysteresis and nonlinearity in the constitutive relation (at the micro-strain level) result in acoustic and ultrasonic wave distortion, which gives rise to changes in the resonance frequencies as a function of drive amplitude, generation of accompanying harmonics, nonlinear attenuation, and multiplication of waves of different frequencies. The sensitivity of nonlinear methods to the detection of damage features (cracks, flaws, etc.) is far greater than can be obtained with linear acoustical methods (measures of wavespeed and wave dissipation). We illustrate two recently developed NEWS methods, and compare the results for both techniques on roofing tiles used in building construction.

303 citations


Journal ArticleDOI
TL;DR: In this paper, a technique is presented for quickly predicting the rate of spreading of a dispersive wave-packet as it propagates, which limits the resolution that can be obtained in a long-range guided wave inspection system.
Abstract: The dispersion of ultrasonic guided waves causes wave-packets to spread out in space and time as they propagate through a structure. This limits the resolution that can be obtained in a long-range guided wave inspection system. A technique is presented for quickly predicting the rate of spreading of a dispersive wave-packet as it propagates. It is shown that the duration of a wave-packet increases linearly with propagation distance. It is also shown that the duration of a wave-packet after a given propagation distance can be minimised by optimising the input signal. A dimensionless parameter called minimum resolvable distance (MRD) is defined that enables a direct comparison to be made between the resolution attainable at different operating points. Some conclusions are made concerning the resolution of various operating points for the case of Lamb waves in an aluminium plate.

286 citations


Journal ArticleDOI
TL;DR: In this paper, a systematic laboratory-based experimental programme under the auspices of a major European Commission (Brite-Euram III Framework 4) funded project has been presented with practical implications related to field surveys of structural concrete.
Abstract: Sub-surface radar is becoming increasingly popular as an inspection method Interpretation can be enhanced if uncertainties about the dielectric properties of the concretes under investigation are removed The need for reliable data to identify possible variations of the dielectric properties of different concrete mixes and their condition on site has led to a systematic laboratory based experimental programme under the auspices of a major European Commission (Brite-Euram III Framework 4) funded project Some key results from this recently completed work are presented in this paper with practical implications related to field surveys of structural concrete

196 citations


Journal ArticleDOI
TL;DR: In this paper, the authors explore a wide range of applications for infrared thermography, particularly relating to structural investigation situations, and provide guidance on optimum timing, conditions and viewing locations for the various situations described as well as limitations of the technique.
Abstract: Infrared thermography (thermal imaging) is an important and powerful technique for consideration when investigating any structural situation where a ready source of surface heating (or cooling) is available, or where the item under investigation itself supplies such conditions. The methods used are totally non-destructive and non-invasive, and can be highly cost-effective. This paper explores a wide range of applications; particularly relating to structural investigation situations. Some guidance is given on optimum timing, conditions and viewing locations for the various situations described as well as limitations of the technique.

161 citations


Journal ArticleDOI
TL;DR: The linear polarisation resistance (LPR) measurement may be dependent upon the temperature at the time of sampling and on any wetting/drying effects resulting from rainfall and wind or sunshine as mentioned in this paper.
Abstract: The linear polarisation resistance (LPR) method can be used to measure the active rate of corrosion of steel reinforcement in concrete structures. However a single measurement may be sensitive to the ambient environmental conditions and thus may not be representative of the mean annual rate of corrosion. The LPR measurement may be dependent upon the temperature at the time of sampling and on any wetting/drying effects resulting from rainfall and wind or sunshine. Recent studies have examined the behaviour of a series of reinforced concrete specimens subject to chloride contamination or carbonation induced corrosion in a controlled laboratory environment. LPR measurements taken at frequent intervals have been related to a wet/dry cycle imposed upon the specimens to promote corrosion activity. In addition, similar studies have been carried out, of an in situ reinforced concrete specimen exposed to the ambient weather conditions. The study is only partly completed, but interim results show the variability of LPR measurements and the influences the environment may exert on single spot measurements.

131 citations


Journal ArticleDOI
TL;DR: In this article, a numerical model that takes into account the anisotropy of composite materials is developed to predict the dispersion curves (phase velocity, group velocity or wave number versus frequency) and the displacement fields of plate waves, the plane of propagation being either a plane of symmetry or not.
Abstract: Electrostatic, air-coupled, ultrasonic transducers are used to generate and detect guided waves in anisotropic solid plates. Waves considered in this study are Lamb-type and SH-type, guided modes. If the plane of propagation coincides with a plane of symmetry of the material, then Lamb modes only are launched and detected by the transducers. If the plane of propagation does not coincide with a plane of symmetry of the material, then Lamb modes are still generated and detected, but guided, SH-like modes are, too. The variation of phase velocity with frequency is measured for several modes propagating in different directions along a glass–epoxy composite plate. A numerical model that takes into account the anisotropy of composite materials is developed to predict the dispersion curves (phase velocity, group velocity or wave-number versus frequency) and the displacement fields of plate waves, the plane of propagation being either a plane of symmetry or not. The experimental phase velocities are in good agreement with the predicted dispersion curves, thus showing that the forward problem concerning the propagation of plate waves in anisotropic, homogeneous, composite material plates is properly solved. The dispersion curves associated with the predicted displacement fields show that guided modes in composite plates have different behaviors depending on their direction of propagation.

107 citations


Journal ArticleDOI
TL;DR: A de-noising method based on the wavelet technique and uses the Morlet wavelet as the mother wavelet, because its time–frequency resolution can be adjusted to adapt to the signal to be analyzed.
Abstract: Machine sound always carries information about the working of the machine. But in many cases, the sound has a very low SNR. To obtain correct information, the background noise has to be removed or the sound must be purified. A de-noising method is given in this paper and is successfully used in feature sound extraction. We can easily diagnose a machine using the purified sound. This de-noising method is based on the wavelet technique and uses the Morlet wavelet as the mother wavelet, because its time–frequency resolution can be adjusted to adapt to the signal to be analyzed. The method is used for extracting the sound of some vehicle engines with different types of failure. The feature sound is extracted successfully.

100 citations


Journal ArticleDOI
TL;DR: In this article, a new sensor-system called expansion-ring-system was developed to monitor the corrosion risk for existing structures as well, which consists of six measuring rings (anodes) separated by sealing rings as parts of the main sensor and a "cathode-bar" which are installed in small holes, to be drilled into the concrete.
Abstract: Since 1990, a special macrocell system, the so-called anode-ladder-system, has been used world-wide to monitor the corrosion risk of new concrete structures, besides other systems. This sensor-system indicates the depth of the critical chloride content initiating corrosion, i.e. the critical depth of the reinforcement with respect to corrosion. Subsequently, the time-to-corrosion can be determined, enabling the owners of buildings to initiate preventive protection measures before cracks and spalling occur. By measurement of the potentials and the electrical resistance of the concrete around the sensors, an estimation of the humidity, the availability of oxygen and the corrosion behaviour after depassivation is possible. To be able to monitor the corrosion risk for existing structures as well, a new sensor-system has been developed called expansion-ring-system. It consists of six measuring rings (‘anodes’) separated by sealing rings as parts of the main sensor and a ‘cathode-bar’, which are installed in small holes, to be drilled into the concrete.

93 citations


Journal ArticleDOI
TL;DR: Sonic tests and other diagnostic techniques were systematically carried out on the existing walls of the Cathedral of Noto as discussed by the authors, and the results show that sonic tests can be successfully applied for the diagnosis and the effectiveness control of repair techniques.
Abstract: Sonic tests and other diagnostic techniques were systematically carried out on the existing walls of the Cathedral of Noto. The right aisle and most of the dome of the Cathedral collapsed in 1996. The aim of the research was to verify the state of damage and/or conservation of the walls and piers in view of the reconstruction of the damaged part of the Cathedral. Sonic tests were used to control the effect of grout injection used as a possible technique of repair of the damaged masonry. The results show that sonic tests can be successfully applied for the diagnosis and the effectiveness control of repair techniques.

Journal ArticleDOI
TL;DR: In this paper, an ultrasonic method is presented to monitor bolt axial stress using a noncontacting shear-wave electromagnetic acoustic transducer (EMAT), which generates and detects the shear wave propagating in the axial direction of the bolts.
Abstract: An ultrasonic method is presented to monitor bolt axial stress using a noncontacting shear-wave electromagnetic acoustic transducer (EMAT). The EMAT generates and detects the shear wave propagating in the axial direction of the bolts. We evaluated the axial stress from the phase shift of the top-to-bottom echo and from the resonance frequency shift; both are induced by the acoustoelastic velocity change and the bolt extension under the tensile load. The received echo was processed through a superheterodyne phase-sensitive detector, and its phase or amplitude spectrum is obtained for the stress measurements. The contactless aspect of the EMAT allows a much easier and quicker stress evaluation, and also leads to high reproducibility by eliminating error sources associated with the use of contacting piezoelectric transducers.

Journal ArticleDOI
TL;DR: In this article, the longwavelength (Rayleigh) scattering of a 5 MHz ultrasonic pulse propagating at the surface of a sample under cyclic tensile loading is used to monitor the growth of small surface-breaking cracks.
Abstract: The long-wavelength (Rayleigh) scattering of a 5 MHz ultrasonic pulse propagating at the surface of a sample under cyclic tensile loading is used to monitor the growth of small surface-breaking cracks. The scattered signals are used to detect the presence of cracks as small as 80 μm in length, in the specimens made of AISI 4130 steel, even in the presence of strong curvature of the surface in the path of the Rayleigh waves. Ultrasonic data is recorded as a function of the number of cycles and compared with crack length measured optically with a microscope. Experiments indicate that the rms amplitude of the scattered signal is proportional to the square of the crack radius measured optically. On specimens with rougher surfaces, ultrasonic detection occurs before optical detection of the cracks. Results also indicate that the short-time Fourier transform (STFT) may be useful to determine whether a single crack (high cycle fatigue) or a distribution of cracks (low cycle fatigue) is present.

Journal ArticleDOI
TL;DR: In this paper, the influence of structural features in masonry on the propagation of electromagnetic impulses emitted by radar was investigated, where different physical models containing various brick materials were constructed, including full and empty joints, layered structures and larger air voids.
Abstract: For the investigation of the influence of structural features in masonry on the propagation of electromagnetic impulses emitted by radar, different physical models containing various brick materials were constructed. As structural defects, full and empty joints, layered structures and larger air voids were considered. Some of the simpler models were stored in a tank filled with distilled water or with salt solution containing 2 mass% of NaCl. Radar measurements were performed using the nominal 500 MHz, 900 MHz, 1 GHz and 1.5 GHz antennas in reflection configuration. Horizontal and vertical traces were recorded in different polarisations of the electric field. In some cases, the results are presented as time slices visualising the position of defects. It was possible to determine moisture distributions, as well as to estimate the moisture content. As structural inhomogeneities, full and empty joints, larger air voids as well as interfaces between layers of different materials could be detected. These results are very important for further investigation especially related to inhomogeneous historic brickwork.

Journal ArticleDOI
TL;DR: In this article, a Bragg sensor was used for bending tests on bare optical fibres and the results demonstrate the applicability of Bragg sensors for continuous monitoring of composite materials.
Abstract: Tests carried out on bare optical fibres with a Bragg sensor show the feasibility of using these sensors for strain sensing. They have been embedded into simple composite laminates and have been subjected to static loading in bending tests. The measured strain from the Bragg sensor is perfectly linear with the applied force. Optical fibres with a Bragg sensor have also been embedded into filament wound pressure vessels. Tests carried out on such a pressure vessel include both static and slowly varying load schemes. The Bragg signal is nearly perfectly linear with the applied pressure. The results demonstrate the applicability of Bragg sensors for continuous monitoring of composite materials.

Journal ArticleDOI
TL;DR: In this paper, the potential of fiber optic sensors for the monitoring of concrete structures is assessed and the advantages of optical sensors over electrical gauges and transducers are also discussed, and two novel fiber-optic sensors are proposed for the measurement of cracking and delamination in concrete structures without requiring a priori knowledge of the damage locations.
Abstract: Fiber optic sensing systems have been successfully developed for many engineering applications. The objective of this review paper is to assess the potential of fiber optic sensors for the monitoring of concrete structures. In this paper, some current applications of fiber optic sensors in concrete structures are first reviewed to demonstrate their applicability in conventional monitoring applications. The advantages of optical sensors over electrical gauges and transducers are also discussed. Then, we will focus on two novel fiber optic sensors for the monitoring of cracking and delamination in concrete structures without requiring a priori knowledge of the damage locations. Through these two examples, it is demonstrated that the proper design of optic sensors can provide useful sensing capabilities unprecedented with conventional sensors. With further research focusing on the development of novel sensing concepts and the reduction of sensor cost, the widespread use of optical sensors in concrete structures can become a reality in the future.

Journal ArticleDOI
Hyunjo Jeong1
TL;DR: In this article, a new approach for the analysis of transient waves propagating in anisotropic composite laminates is presented, where the wavelet transform (WT) using the Gabor wavelet is applied to the time-frequency analysis of dispersive flexural waves in these plates.
Abstract: A new approach is presented for the analysis of transient waves propagating in anisotropic composite laminates. The wavelet transform (WT) using the Gabor wavelet is applied to the time-frequency analysis of dispersive flexural waves in these plates. It can be shown that the peaks of the magnitude of WT in a time-frequency domain is related to the arrival times of the group velocity. Experiments were performed using a lead break as the simulated acoustic emission source on the surface of unidirectional and quasi-isotropic laminates. A method was developed to obtain the group velocity of the flexural mode as a function of frequency. Theoretical predictions were made using the Mindlin plate theory, which includes the effects of shear deformation and rotatory inertia. Our predictions on the dispersion of the flexural mode showed good agreement with the experimental results.

Journal ArticleDOI
TL;DR: In this article, the authors used ultrasonic tomography to identify voiding in the metallic tendon ducts in a post-tensioned bridge beam with a 10-m long beam at the Transport Research Laboratory (TRL), Crowthorne, UK and a short beam constructed at Stanger Science and Environment, Elstree, UK.
Abstract: Some concern exists over the safety and durability of the 600 post-tensioned bridges in the UK, and the much larger number worldwide. The objective of the work reported herein was to identify voiding in the metallic tendon ducts in these bridges. Voiding can give rise to two sets of problems: (a) possible ingress of chlorides, which would cause corrosion; and (b) a lack of redistribution of stress within the beam. It was against this background that it was important to first of all identify the extent of voiding in post-tensioned bridges. The new technique of ultrasonic tomography was used for the trials reported in this paper. Two test beams were examined: a 10 m long beam at the Transport Research Laboratory (TRL), Crowthorne, UK and a short test beam constructed at Stanger Science and Environment, Elstree, UK. The ducts in the TRL beam were 40 mm in diameter. This is smaller than would normally be encountered in a post-tensioned bridge beam. A more usual duct diameter would be 100–110 mm with a cover of around 125 mm. The second test beam at Stanger Science and Environment, Elstree contained 100-mm diameter ducts. The time-of-flight tomography data obtained demonstrated that it is a potentially highly successful method of investigating post-tensioned concrete beams. The method is somewhat time consuming and so should be used in conjunction with a simpler testing method, e.g. sonic impact-echo, which identifies areas of interest. The smaller the ducts to be investigated, the smaller the required distances between testing stations. This therefore significantly increases the testing time.

Journal ArticleDOI
TL;DR: In this paper, a number of post-impact mechanical tests have been carried out, including tensile tests, three-point bending and indentation, using either a staircase or a continuous loading program.
Abstract: The present study aims to characterise damage due to low velocity impact on jute fibre reinforced polyester composites. To attain this goal, a number of post-impact mechanical tests have been carried out, including tensile tests, three-point bending and indentation, using either a staircase or a continuous loading programme. On all these tests acoustic emission activity (AE) was monitored. The results, compared with damage observed under an optical microscope, show that AE is able to perform a reliable measurement of the level of damage also, on a natural fibre reinforced laminate. The main limitations of this study are owing to the rather low ultimate stress of the material and to the need to apply a loading to evaluate the damage produced by the impact event.

Journal ArticleDOI
TL;DR: In this paper, the surface residual stresses in steel rods made of the same material but with different heat treatments have been studied from Rayleigh wave velocity measurements using the laser ultrasonics technique and piezoelectric transducers.
Abstract: The surface residual stresses in steel rods made of the same material but with different heat treatments have been studied from Rayleigh wave velocity measurements using the laser ultrasonics technique and piezoelectric transducers. The Rayleigh wave velocities, both along the circumference and in the axis direction on the cylindrical surface of every rod, are measured and compared with one another in order to evaluate qualitatively the surface stress state for each rod. The experimental results clearly show that the Rayleigh wave velocities on the cylindrical surfaces of these rods are different, and the results obtained by laser ultrasound are in good agreement with those measured with piezoelectric transducers. From the measured velocities, different stress states have been identified for these rods according to the heat treatments they have undergone.

Journal ArticleDOI
M. R. Clark1, R. Gillespie1, T. Kemp1, D. M. McCann1, Michael Forde1 
TL;DR: In this article, the dielectric properties of railway track ballast using Ground Penetrating Radar (GPR) have been investigated for identifying defects in railway track bed and the implications of the findings for radar velocity are discussed.
Abstract: Laboratory experiments were undertaken to identify and characterise the dielectric properties of railway track ballast using Ground Penetrating Radar (GPR). Better results were obtained with lower frequency antennas. Clear distinctions were obtained between wet and dry and clean and spent ballast. The laboratory experiment is described in detail and sample radar scan plots given — the final analysis of dielectric constants is also given. The implications of the findings for radar velocity are discussed. The application to identifying defects in railway track bed is discussed.

Journal ArticleDOI
TL;DR: Magnetic Barkhausen noise (MBN) measurements were made on hot-rolled mild steel samples uniaxially deformed to differing magnitudes of plastic strain, to study the dependence of MBN activity on plastic strain this article.
Abstract: Magnetic Barkhausen noise (MBN) measurements were made on hot-rolled mild steel samples uniaxially deformed to differing magnitudes of plastic strain, to study the dependence of MBN activity on plastic strain. The results indicated an initial increase in MBN energy with increasing plastic strain followed by a decrease at higher plastic deformations. At still higher plastic deformations, the MBN energy was found to be almost independent of plastic strain. The results are explained in terms of different mechanisms of interaction of domain walls with dislocations, with increasing plastic strain. The behavior of MBN energy with plastic strain was found to be anisotropic and the angular MBN measurements indicated that the deformation-induced easy axis of magnetization changed direction with increasing plastic strain. At higher deformations, the MBN activity was largely controlled by the deformation-induced anisotropy, due to residual stress.

Journal ArticleDOI
TL;DR: In this article, the use of an ultrasonic array system is described, which can be used combined with 3D reconstruction calculations to measure the concrete cover of utility pipes in a tunnel and the examination of transversal ducts in a bridge plate.
Abstract: The use of an ultrasonic array system is described, which can be used combined with 3D reconstruction calculations. In this way ultrasonic reflection and backscatter from the inside of concrete members can be imaged and interpreted. The application of the system is demonstrated for two examples: measuring the concrete cover of utility pipes in a tunnel and the examination of transversal ducts in a bridge plate.

Journal ArticleDOI
H.C Park1, Dong-Soo Kim1
TL;DR: In this paper, a method based on the harmonic wavelet transform (HWT) was proposed to evaluate dispersive phase and group velocities in a multi-layered system.
Abstract: The evaluation of the dispersive phase and group velocities having sensible physical meaning is of practical importance in various NDT techniques. In this paper, we propose a method based on the harmonic wavelet transform to evaluate dispersive phase and group velocities. To apply the harmonic wavelet transform in the evaluation of dispersive velocity, the meaning of the harmonic wavelet coefficient is interpreted from a different point of view. Based on these concepts, the step-by-step procedure to evaluate the dispersive phase and group velocities was proposed. In the proposed method, both phase and group velocities can be obtained directly from information extracted from data based on the harmonic wavelet transform. To evaluate the validity of the proposed method, numerical simulations of the multi-layered system were performed and the phase and group velocities determined by the proposed method match very well with theoretical velocities showing the good potential of the proposed method.

Journal ArticleDOI
TL;DR: In this article, several IDE ultrasonic methods to estimate porosity of mortar are presented and evaluated, which is related to the material structural noise, sound velocity and ultrasonic attenuation.
Abstract: Premature damage of mortar and concrete structures, due to environmental action, demands procedures to estimate durability of this type of components Mortar or concrete composition (eg grain size, type and percentage of sand) may have some influence in the durability, but it is mainly related to porosity, which determines the interaction between aggressive agents and material In this work, several IDE ultrasonic methods to estimate porosity of mortar are presented and evaluated In these methods, porosity is related to (1) the material structural noise, (2) sound velocity and (3) ultrasonic attenuation In all these methods, mortar is consider to be formed by only two phases: solid and pores

Journal ArticleDOI
TL;DR: In this article, the first UK site installation of a monitoring system that detects the fracture of wires in post-tensioning tendons by listening with acoustic sensors attached to the surface of the concrete.
Abstract: The paper describes the first UK site installation of a monitoring system that detects the fracture of wires in post-tensioning tendons by listening with acoustic sensors attached to the surface of the concrete. Trials have shown the system to work reliably for grouted and ungrouted tendons. Acoustic events from other sources such as road traffic are discarded using software and hardware filters at the unattended site. Data from possible wire-fracture events are sent off site for final identification and positioning. The system is running continuously on site, on a viaduct, with close to 100% up-time. In open and blind trials on the viaduct, 41 out of 44 wire break or facsimile events were correctly located and identified and a further two were correctly located. The system can assist in the management of bridges where the post-tensioning system is at risk from corrosion.

Journal ArticleDOI
TL;DR: In this article, the authors used ground penetrating radar (GPR) to assess pavements and verify its practicality using twelve different flexible pavement sections, which comprised different layers/materials, are incorporated in the Virginia Smart Road test facility.
Abstract: Twelve different flexible pavement sections, which comprised different layers/materials, are incorporated in the Virginia Smart Road test facility. These sections provide a good opportunity to explore the feasibility of using ground penetrating radar (GPR) to assess pavements and to verify its practicality. Thirty-one copper plates, serving as a reflecting material, were placed during construction at different layer interfaces throughout the pavement sections. Results show that enough radar energy is reaching the subgrade, but due to low dielectric contrast between some pavement materials, energy is not reflected back. In these cases, the copper plates indicate where the interface between each two layers occurs. Reflections from the copper plates are also used to determine the dielectric constant of pavement materials over the GPR frequency range. This paper presents an overview of the Virginia Smart Road test facility, data obtained from different sections using two GPR systems, and a method to calculate the complex dielectric constant of hot-mix asphalt over the frequency range of 750–1750 MHz using an air-coupled GPR system.

Journal ArticleDOI
TL;DR: In this article, mild steel specimens were uniaxially strained in tension at strain levels varying from 0.5 to 10% followed by X-ray diffraction residual stress and Barkhausen noise (BN) measurements.
Abstract: Mild steel specimens were uniaxially strained in tension at strain levels varying from 0.5 to 10% followed by X-ray diffraction residual stress and Barkhausen noise (BN) measurements. After this tension and compression loading was applied to the specimens. BN measurements were carried out during the whole reloading sequence. These measurements showed that prestrain increased the tensile stress value at which the BN saturated. The linear range of the stress vs. BN curve shifted towards the tensile stress range as a function of prestrain. In the linear range the stress sensitivity remained unchanged despite the prestrain. The obtained stress vs. BN relation was used in the residual stress measurements of a welded tube segment. The residual stress values measured by the BN were compared to X-ray diffraction residual stress values. When the BN values were within the linear range of the stress vs. BN curve, the BN residual stress values agreed quite well with the X-ray diffraction residual stress values.

Journal ArticleDOI
TL;DR: In this paper, a wavelet-based method is proposed to perform the analysis of NDE ultrasonic signals received during the inspection of reinforced composite materials, which is tested on cryogenic glass/epoxy hydrogen reservoir samples.
Abstract: A wavelet-based method is proposed to perform the analysis of NDE ultrasonic signals received during the inspection of reinforced composite materials. The non-homogenous nature of such materials induces a very high level of structural noise which greatly complicates the interpretation of the NDE signals. By combining the time domain and the classical Fourier analysis, the wavelet transform provides simultaneously spectral representation and temporal order of the signal decomposition components. To construct a C-scan image from the wavelet transform of the A-scan signals, we propose a selection process of the wavelet coefficients, followed by an interpretation procedure based on a windowing process in the time–frequency domain. The proposed NDE method is tested on cryogenic glass/epoxy hydrogen reservoir samples.

Journal ArticleDOI
TL;DR: In this paper, an experimental procedure, by means of thermographic technique, was set up in order to detect typical defects, which could be found in composite material sandwich structures, and the material thermal response was investigated for different artificially defects inserted in some specimens; every kind of defect was listed.
Abstract: In this paper an experimental procedure, by means of thermographic technique, was set up in order to detect some typical defects, which could be found in composite material sandwich structures. The material thermal response was investigated for different artificially defects inserted in some specimens; every kind of defect was listed. Then the experimental procedure was applied to study a wind-turbine blade made of sandwich composite structure. The results fulfilled the expectations and confirmed the reliability of the thermographic technique to be used both in laboratory and in service.