Nondestructive Evaluation

J Nondestruct Eval (2010) 29: 38–42 DOI 10.1007/s10921-010-0063-7 Acoustic Properties of Selected Tropical Wood Species Yahya Sedik · Sinin Hamdan · Ismail Jusoh · Mahbub Hasan Published online: 12 February 2010 © Springer Science+Business Media, LLC 2010 ...

The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique [IEEE Trans. UFFC, 45:30 (1998)] has demonstrated sensitive detection of subwavelength channel defects (38-m diameter reliably and 6-m diameter occasionally) in flexible 220-m-thick food package seals (17.3 MHz, Ϸ 86 m). However, the underlying subwavelength defect detection mechanism is poorly understood. In this contribution, a theoretical modeling study was undertaken to elucidate the mechanism. The subwavelength diameter channel was fused in-between two plastic package films by applying heat from one side of the films. The sample cross-section microstructure was characterized from both optical and acoustic images. The cross-section impedance profiles along sample thickness dimension were determined. Although identical in nominal impedance properties before sealing, the two binding films showed an asymmetric impedance profile after sealing. Transient finite-element heat conduction analysis and impedance profiles of multiple-sealed package samples showed that the single-sided heating process caused an asymmetric impedance profile. A generalized impedance model was proposed based on these observations. An efficient two-dimensional simulation tool using a finite-difference time-domain method and the perfectly matched layer numerically evaluated the defect detection behavior of the radio-frequency (rf) echo waveforms. The normalized correlation coefficients between the simulated and the measured rf echo waveforms were greater than 95% for this generalized model, which suggested the validity of the proposed impedance model.

Austenitic stainless steels (hereafter A-STS) such as STS304 and STS316 are paramagnetic metals. However, a small amount of partial magnetization is generated in A-STS because of the imperfect final heat treatment and mechanical processing. Surface cracks on paramagnetic metal with a partially magnetized region (hereafter PMR) are difficult to inspect. In this paper, we propose a method for high speed inspection and evaluation of a crack on A-STS. Cracks can be inspected with high speed by using 64 arrayed Hall sensors (HSA) with 3.5 mm spatial resolution and a sheet type induced current (STIC). Then, a crack can be evaluated quantitatively by using the detailed distribution of the magnetic field obtained by using single Hall sensor scanning (SSS) around the inspected crack area. Several cracks on A-STS with partially magnetized areas were examined and the experimental formulas were derived.

Fatigue damage is closely related to plastic deformation and heat dissipation, which affect the temperature of the materials. In the current research, a state-of-the-art infrared-thermography camera has been used as a nondestructive evaluation (NDE) method to investigate the temperature evolutions in both crystalline and amorphous materials during fatigue experiments. Fatigue-damage processes, such as the Lüders band growth in reactor-pressure-vessel (RPV) steels and shear-band evolution in bulk metallic glasses (BMGs), have been observed in situ and analyzed by thermography. Theoretical models combining fracture mechanics and thermodynamics have been formulated to quantify the temperature-evolution processes during fatigue. Specifically, the plastic work in RPV steel during low-cycle fatigue has been calculated and the fatigue life has been predicted from the observed temperature. The prediction matches the experimental data quite well. q

In order to design structural components using composite materials a deep understanding of the material behaviour and its failure mechanisms is necessary. To create a better understanding of the initiation, growth and interaction of the different types of damage, damage monitoring during mechanical loading is very important. To this direction, AE is a powerful non destructive technique for real time monitoring of damage development in materials and structures which has been used successfully for the identification of damage mechanisms in composite structures under quasi static and dynamic-cycle loading. In this present work, pure resin plate and GFRP composite laminates with stacking sequence of [0 0 ] 6 , are fabricated using Hand lay-up method. During the layup a Teflon tape of width 45 mm is kept in the mid plane of the laminate which serves as an initiator for delamination during loading. As per ASTM STD D5528 01 DCB (Double Cantilever Beam) specimens are cut out from the laminates and are subjected to tensile test in the transverse direction along with acoustic emission monitoring. While loading, Markings are made on the sides of the specimen to track the crack front using a magnifying lens. Parametric analysis is performed on the AE data obtained during crack propagation to discriminate the failure modes. Fast Fourier Transform (FFT) enabled the calculation of frequency content of each damage mechanism. Further STFFT analysis is performed on a portion of the waveforms representing the dominant frequency content pertaining to each damage mechanism.

J Nondestruct Eval (2010) 29: 38–42 DOI 10.1007/s10921-010-0063-7 Acoustic Properties of Selected Tropical Wood Species Yahya Sedik · Sinin Hamdan · Ismail Jusoh · Mahbub Hasan Published online: 12 February 2010 © Springer Science+Business Media, LLC 2010 ...

For many years, applications of the TNDE (Thermographic NonDestructive Evaluation) technique has been limited due to the complex non-linearity nature of related inversion problems such as defect depth estimation. Arti®cial neural networks have recently obtained success in revealing and providing quantitative information concerning defects in TNDE. In this paper, a three dimensional thermal model for nonhomogenous materials such as carbon ®ber reinforced plastic (CFRP) is ®rst given. The modeling results are compared with the analytical solution based on Duhamel's theorem. Two back propagation neural networks (NN) as defect detector and depth estimator are then presented. Finally, simulated and experimental results are presented and discussed.

Operating Deflection Shapes (ODS) has emerged as one of the powerful techniques in vibration analysis to understand and to evaluate the absolute dynamic behaviour of a machine, component or an entire structure. Traditionally, accelerometers have been used to get the ODS of a structure. However, recent development shows that certain situation may not allow direct contact with the structure under investigation. Therefore, Scanning Laser Doppler Vibrometer (SLDV) has become popular in the investigation. In this paper, a new ODS Frequency Response Function (ODS FRF) for investigations using SLDV is formulated. The ODS FRF is used to construct the ODS of the structure. A new form of scale factor for the ODS FRF is also introduced to normalize the effects from variable excitation force. The importance of this scale factor is demonstrated on a beam and plate under the excitation of varying forces. It is found that the suggested ODS FRF and the scale factor give the desired result in comparison with theory.

Nondestructive optical methods based on image analysis have been used for determining quality of tomato fruit. It is rapid and requires less sample preparation. A samples of fresh tomatoes were picked at different maturity stages, and determining chromaticity values (L*,a*,b*,a*/b*,h˚and ΔE) by image analysis and colorimeter. Total soluble solids (TSS), were measured by refractometer, lycopene extracting and expressed as mg/kg fresh tomato (FW). Results indicated that, during ripening both L*, b*, h˚, and ΔE tendency to decline, opposite tendency was determined with a*, a*/b* ratio, TSS and lycopene content. Chromaticity values have an important impact in internal quality parameters. Where, avg. of TSS, entire class and lycopene content had a positive linear correlation with a*/b* ratio. Contrary correlation was determined between avg. of TSS, entire class and both h˚ and ΔE. Meanwhile, h˚ and ΔE, had a negative logarithmic correlation with lycopene content. On the other hand, there...

The work explores the possibilities of application of ultrasonic testing in the assessment of fibre metal laminates. Basic problems concerning the use of ultrasonic methods in the research of laminates are explained, and methods for solving these problems are suggested. Tests were conducted using two phased array methods: ultrasonic pulse-echo and through transmission. The efficiency of both selected ultrasonic methods are compared with respect to detecting and dimensioning defects in laminate structures. Based on the analyses and proposed solutions, it has been proven that the developed through transmission phased array (TTPA) method ensures a much more effective, in terms of quality and quantity, assessment of the condition of hybrid laminates than conventional ultrasonic methods, irrespective of the degree of surface deformation and the type of laminate structure.

The corrosion of metallic reinforcement is a major threat to aging infrastructure. Prestressed structures such as the bridges built in the early 1950's and 1960's are showing signs of deterioration. The current corrosion detection methods for embedded or encased steel reinforcement suffer from several significant drawbacks. A nondestructive evaluation technique has been developed that is capable of determining the location and severity of corrosion of embedded or encased steel rebar and strands. This technique utilizes time domain reflectometry (TDR). By applying a sensor wire alongside of steel reinforcement (such as a prestressing strand), a transmission line is created. Physical defects of the reinforcement will change the electromagnetic properties of the line. Both analytical models and small-scale laboratory tests have shown that TDR can be effectively utilized to detect, locate and identify the extent of damage in steel reinforcement in this manner. Currently, the TDR...

Active thermography has been extensively investigated in the past few years for the nondestructive evaluation of different types of materials. Composites in particular have received considerable attention given that active thermography has shown to be well suited for the detection and characterization of most kinds of defects typically found in these materials such as impact damage, delaminations, disbonds and inclusions. Signal processing is a necessary step of the inspection process, especially if defect characterization is required. A wide variety of techniques have been developed from the classical thermal-based techniques to signal transformation algorithms (adapted from the area of machine vision) on which temporal data is transformed to a different domain (frequency, Hough, principal components, Laplace, high-order moments, etc.) with the purpose of simplifying data analysis. In this paper, a review of some of these processing techniques is presented and exemplified using a Kevlar ® panel and a GLARE specimen.

In this study, the effect of density on the velocity of an ultrasonic wave in wood is investigated. The aim of the present study was to analyze the influence of density on the longitudinal velocity of an ultrasonic wave, propagated in the longitudinal direction. Experiments were conducted on 5 cm · 5 cm · 5 cm wood specimens selected from the following species: pinus caribea (Pinus caribea var. caribea), eucalyptus citriodora (Eucalyptus citriodora), eucalyptus grandis (Eucalyptus grandis), cupiú ba (Goupia glabra) and jatobá (Hymenaea sp.). The relationship between density and velocity was analyzed in two different manners: between and within species. The results obtained between species indicated that ultrasonic velocity tends to increase with increasing density. The results obtained within species also showed an increasing trend in ultrasonic velocity as density increased, but the relationship was not as significant as it was for between species.

This paper proposes a method for segmenting defects depicted in a thermal image of petrochemical equipments by means of passive thermography. The technique first enhances the contrast of the defects based on local neighborhood pixel intensity operation. This local intensity operation works in two modes, either brightening the pixels for detecting hot spots or darkening the pixels for detecting cold spots. The next step is to segment the defects using simple histogram-based thresholding techniques. We propose three thresholding methods: mean absolute thresholding (MAT), mean relative thresholding (MRT), and minimum frequency thresholding (MFT). Compared to existing techniques, we found that our proposed methods have better detection and success rate.

Experiments were conducted to investigate the influence of overbalance pressure on formation damage during drilling operations. An innovative ultrasonic method was employed to measure mud invasion depth. It was observed that mud invasion depth decreases with increasing overbalance pressure until it reaches a critical pressure. Beyond that, invasion depth increases with overbalance pressure. The above phenomenon reflects a strong physical relationship between overbalance pressure and mud fines and filtrate invasion depth. D

The optimization of crashworthiness in aerospace and automotive industries is one of the key  research  targets  of  the  leading  respective  industries.  In  the  past  few  decades;  the  use  of composites  in  structural  applications  has  been  increasingly  used  in  aerospace  and  advanced transportation industries because of their excellent mechanical properties and better strength-to-weight ratio than metal. In this paper composite materials constituent and their application in  aerospace  industry  and  their  failure  modes  has  been  presented.  The  effects  of  the  impact damage  on  the  carbon  fiber  composites  as  the  one  of  the  most  common  materials  in  the aerospace  industry  has  been  investigated  and  evaluated  by  using  non-destructive  testing methods.  This  review  considered  the  capabilities  of  the  most  common  methods  of  NDT  in composite  materials.  Damage  modes  interaction,  types  of  velocity,  and  influence  of  various factors on impact behavior was investigated and must be considered to predict any failure in composite materials.

Quality control during fabrication and failure monitoring during service have gained importance in the field of metal matrix composites because of their growing uses, especially for structural applications. This review aims to provide a survey of quality control and nondestructive testing relevant to metal matrix composites. The first part presents the determination of the reinforcement parameters which play a very important role in controlling the performance of metal matrix composites. The second part describes the main relevant nondestructive techniques used to identify the defects produced during fabrication or in service. It also shows that the validation of nondestructive techniques and the relationship between their results and component performance should be particularly emphasized in future research work on metal matrix composites. ; Fax: ϩ32 16 32 1992.

This research seeks the rational organization and integration of nondestructive evaluation (NDE) technologies, the methods of structural identification, and concepts of reliability and fault detection, each according to its merits, within a system devoted to monitoring the state-of-health of an instrumented structure. A global NDE methodology has been developed based upon the structural identification concept, employing truckload testing, modal testing, and instrumented monitoring as its principal experimental tools. The test results are transformed to both strain influence lines and modal flexibility, which have been demonstrated to be a conceptual, quantitative, comprehensive, and damage-sensitive signature. These parameters also provide an accurate condition index, since it may be used to conveniently obtain the stress profiles and deflected shapes of a bridge under any loading pattern. The capacity rating for the instrumented section and/or an estimation of the remaining fatigue life for the instrumented member/connection based upon the relevant AASHTO codes can be obtained immediately following the controlled truckload testing of the bridge. This methodology has provided several unique deliverables to the aforementioned field of expertise:

The National Spent Nuclear Fuel Program (NSNFP) has developed standardized DOE SNF canisters for handling and interim storage of SNF at various DOE sites as well as SNF transport to and SNF handling and disposal at the repository. The final closure weld of the canister will be produced remotely in a hot cell after loading and must meet American Society of Mechanical Engineers (ASME) Section III, Division 3 code requirements thereby requiring volumetric and surface nondestructive evaluation to verify integrity. This paper discusses the use of eddy current testing (ET) to perform surface examination of the completed welds and repair cavities. Descriptions of integrated remote welding/inspection system and how the equipment is intended function will also be discussed.

Local decorrelation of speckle patterns scattered by a surface is used for nondestructive evaluation of the state of conservation of wooden artifacts. Some experiments have been carried out on models with simulated internal flaws and on real, ancient, wooden panel paintings. The setup is very simple and can easily be used by nonoptically skilled operators.

ABSTRACT The capabilities of non-destructive testing (NDT) methods for defect detection in civil engineering are characterized by their different penetration depth, resolution and sensitivity to material properties. Therefore, in many cases multi-sensor NDT has to be performed, producing large data sets that require an efficient data evaluation framework. In this work an image fusion methodology is proposed based on unsupervised clustering methods. Their performance is evaluated on ground penetrating radar and infrared thermography data from laboratory concrete specimens with different simulated near-surface defects. It is shown that clustering could effectively partition the data for further feature level-based data fusion by improving the detectability of defects simulating delamination, voids and localized water. A comparison with supervised symbol level fusion shows that clustering-based fusion outperforms this, especially in situations with very limited knowledge about the material properties and depths of the defects. Additionally, clustering is successfully applied in a case study where a multi-sensor NDT data set was automatically collected by a self-navigating mobile robot system.

With the rapid development of science and technology, the number of large span bridge is increasing to meet the needs of growing traffic. Due to the extremely important role and very expensive cost of them, these bridges need to be maintained frequently. However, this process is often difficult because of their specific conditions. Therefore, the development of monitoring systems for large span bridges are essential for cost savings for maintenance, operation and traffic safety for these bridges. This special subject aims to introduce a monitoring system for large-span bridges in the world and Vietnam as well as its important role in the process of design, construction and operation of the bridge.

The leaky Lamb wave (LLW) technique is approaching a matmity level that is making it an attractive quantitative NDE tool for composites and bonded joints. Since it was first observed in 1982, the phenomenon has been studied extensively, particularly in composite materials. The wave is i n d u d by oblique insonification using a pitch-catch arrangement and the plate wave modes are detected by identiwi minima m the reflected spectra to obtain the dispersion data. The wave behavior in multi-orientation laminates has been well docmnted and combomted experimentally with high accuracy. The sensitivity of the wave to the elastic constants of the material and to the boundary conditions led to the capability to masure the elastic properties of bonded joints.

YONAPAVE, a direct and simple method for evaluating the structural needs of flexible pavements,
was presented at the 2003 Annual Meeting of the Transportation Research Board (TRB) in
Washington D.C. The method uses falling-weight deflectometer (FWD) deflection basins to
determine the effective structural number and the equivalent subgrade modulus of the pavementsubgrade
system without previous knowledge of the layer thicknesses above the subgrade.
An extension of YONAPAVE is hereby presented to determine the asphalt concrete (AC) overlay
required to account also for the fatigue of the AC layer under future traffic loadings. The scheme is
based on commonly accepted relationships between AC fatigue cracking and the radial tensile strain
at the bottom of the AC layer. The real layered pavement is characterized by an equivalent twolayer
system which is determined from the measured FWD deflection basins. Thus, no coring
operations are needed since the whole scheme remains basically independent of layers thicknesses.
YONAPAVE algorithms can be solved using a spreadsheet or a handheld PC making it suitable to
handle large amounts of data, even in field conditions. The extended method can be used at the
network level for the evaluation of the flexible pavement overall structural capacity and the AC
overlay needed to accommodate future traffic. With local calibration and experience YONAPAVE
can be also used at the project level. YONAPAVE has been used successfully in numerous
pavement evaluation and rehabilitation projects providing reasonable and useful results.

The paper presents analytical and experimental modal analysis of a steel footbridge for modal parameter identification. 3D finite element model is established for the steel footbridge based on the design drawing and modal parameters are obtained from deformed configurations. The field test is carried out by ambient vibration test under human walking excitation. Both Peak Picking method in the frequency domain and the Stochastic Subspace Identification method in the time domain are used for the output-only modal identification. From the study, good agreement is found between mode shapes, but some differences in the natural frequencies and analytical frequencies are bigger.

This paper describes an efficient nondestructive evaluation (NDE) eddy-current (EC) system using an improved giant magnetoresistance magnetometer (IGMRM) and a simple single wire as inducer. A three-dimensional finite-element method (3-D FEM) was implemented to evaluate the theoretical expected response of the system. The model was based on a modified magnetic vector potential and a reduced magnetic scalar potential, in conducting and nonconducting regions, respectively. The model robustness is established by comparing numerical and experimental results on a given benchmark aluminum plate sample. This efficient 3-D FEM model helps to understand the system performances. Moreover, the excitation frequency effect on the sensed signal is analyzed versus the benchmark sample thickness and the crack sizes. Results are also given and discussed in terms of signal-to-noise ratio.

Woven carbon/epoxy laminate samples were subjected to low-velocity impact loading at energy levels of 15, 30 and 45 J. Samples were subjected to different moisture conditioning before subjecting to impact loading which included cold–dry and cold–moist for a period of 3 and 6 months. Impact parameters like peak load, absorbed energy, time to peak load and energy at peak load were evaluated and compared. Ensuing damage was measured on the impact surface as well as the back surface. Further, laminates were subjected to ultrasonic c-scanning to determine the impact damage. In general, samples subjected to conditioning exhibited better impact behavior in terms of the impact parameters. Damage sizes as determined from ultrasonic nondestructive evaluation (NDE) were comparable to room temperature samples except in the case of samples that were subjected to cold–dry conditioning for 6 months.

This paper presents a nondestructive testing method in evaluating bridge condition in comparison with visual inspection that has been used for ages. While condition ratings are all qualitative and defined primarily as sets of visual indicators in routine inspection, nondestructive testing are more quantitative and has large potential in determining damages inside the structure that are not visible. Hence, an attempt to integrate the nondestructive evaluation and bridge management system has been carried out by several researchers. This study is aimed to determine bridge strength through nondestructive testing and thus establish correlation between visual inspection rating and the nondestructive testing results. 75 concrete bridges under the supervision of Public Works Department (Malaysia) have been selected for the preliminary testing which includes the Rebound Hammer test, Ultrasonic Pulse Velocity, and electromagnetic cover meter. However, this paper will only discuss the methodology and results from Rebound hammer test. Generally, this study indicates good correlation between visual rating and strength from Rebound Hammer result. Ratings assigned to the bridge during visual inspection are within an acceptable range in reflecting the bridge strength. Rebound hammer has a potential to be a preliminary test in evaluating the bridge condition. However, since the nondestructive testing is not always readily available and there may be problems occurred with the lack of experienced inspectors to conduct the test, the implementation of this method in routine inspection may be limited. Therefore, an initial study to develop an intelligent rating system combining both nondestructive test data and visual inspection rating has been conducted in the later stage of this research as part of the solution to this problem.

The outstanding mechanical properties of austempered ductile irons (ADI) are linked to the microstructure of the matrix obtained by subjecting a ductile iron with an appropriate composition to a heat treatment called austempering. Then the microstructure of the matrix consists of bainitic ferrite with different volume fractions of retained austenite. The aim of this work is to use the magnetic Barkhausen noise (MBN) as a nondestructive method for characterizing the microstructure of ADI. First, it is shown that the amplitude and position of the peak-shaped MBN response is quite sensitive to the microstructure of the matrix of ductile irons. Thus each type of constituent (equiaxial ferrite, pearlite, martensite or bainite) exhibits a typical response and, in turn, it can be identified from the MBN response. Furthermore, a good correlation is found between MBN signal parameters and ADI heat treatment parameters, indicating that MBN is also quite sensitive to fine evolutions of the microstructure of ADI. MBN peak position is especially sensitive to the type of bainite, whereas peak amplitude is linked to the progress of the bainite reaction. Hence MBN measurements appear to be a powerful tool to assess some important microstructural features of ADI castings.

This paper gives a review of acoustic and ultrasonic optical fiber sensors (OFSs). The review covers optical fiber sensing methods for detecting dynamic strain signals, including general sound and acoustic signals, high-frequency signals, i.e., ultrasonic/ ultrasound, and other signals such as acoustic emissions, and impact induced dynamic strain. Several optical fiber sensing methods are included, in an attempted to summarize the majority of optical fiber sensing methods used to date. The OFS include single fiber sensors and optical fiber devices, fiber-optic interferometers, and fiber Bragg gratings (FBGs). The single fiber and fiber device sensors include optical fiber couplers, microbend sensors, refraction-based sensors, and other extrinsic intensity sensors. The optical fiber interferometers include Michelson, Mach-Zehnder, Fabry-Perot, Sagnac interferometers, as well as polarization and model interference. The specific applications addressed in this review include optical fiber hydrophones, biomedical sensors, and sensors for nondestructive evaluation and structural health monitoring. Future directions are outlined and proposed for acousto-ultrasonic OFS.

Ultrasonic beam steering characteristics for linear phased array transducers are simulated numerically by visualizing the full-field acoustic pressure field of the waves radiated from a linear phased array transducer. The influences of various transducer parameters on the beam steering properties are studied, including number of elements, inter-element spacing, element size, frequency of the transducer and the steering angle. In addition, the effects of these parameters on the near field characteristics are investigated by analyzing the acoustic pressure profile in the steering direction. The simulation results agree well with the analytical solutions which are valid only in the far field. A suggested scheme for optimal transducer design is presented.

In this paper, terahertz (THz) characterization of dielectric substrates, THz planar and quasi-optical components, THz probing of planar devices, and THz nondestructive evaluation (NDE) are demonstrated. In particular, the goals of this paper are: 1) characterization of dielectric substrates for THz packaging applications; 2) design, fabrication, and evaluation of THz components built using some of these dielectric substrates; and 3) the use of the dielectric characterization approach and dielectric properties in NDE of electronic packages. The background theory for characterizing dielectric substrates using THz time-domain signals is provided. The Nelder and Mead modified simplex optimization algorithm is utilized in order to extract the dielectric properties of different packaging materials encompassing organic, inorganic, and composite materials. A planar THz power splitter, a dielectric probe, and a low-cost polymer-based quasi-optical band-stop interference filter are demonstrated. THz NDE of electronics packages is demonstrated for packaging delamination and moisture ingression in dielectric films.

Advances in magnetoresistive (MR) type sensors provide a new technique for nondestructive evaluation NDE of metal structures. MR sensors include high sensitivity and reduced size. Being produced by thin film processing techniques, the manufacturing cost of these sensors is low. This paper provides an attempt to develop an NDE system that depends on one type of MR sensors, namely the giant MR (GMR) elements. An example is considered of detecting defects in printed circuit boards. System details and experimental results are provided. Computational modeling validation is introduced based on finite element analysis.

This paper gives a review of acoustic and ultrasonic optical fiber sensors (OFSs). The review covers optical fiber sensing methods for detecting dynamic strain signals, including general sound and acoustic signals, high-frequency signals, i.e., ultrasonic/ ultrasound, and other signals such as acoustic emissions, and impact induced dynamic strain. Several optical fiber sensing methods are included, in an attempted to summarize the majority of optical fiber sensing methods used to date. The OFS include single fiber sensors and optical fiber devices, fiber-optic interferometers, and fiber Bragg gratings (FBGs). The single fiber and fiber device sensors include optical fiber couplers, microbend sensors, refraction-based sensors, and other extrinsic intensity sensors. The optical fiber interferometers include Michelson, Mach-Zehnder, Fabry-Perot, Sagnac interferometers, as well as polarization and model interference. The specific applications addressed in this review include optical fiber hydrophones, biomedical sensors, and sensors for nondestructive evaluation and structural health monitoring. Future directions are outlined and proposed for acousto-ultrasonic OFS.

To prevent hot-cracking, austenitic stainless steel welds generally contain a small percent of delta ferrite. Although ferrite has been found to effectively prevent hot-cracking, it can lead to embrittlement of welds when exposed to elevated temperatures. The aging behavior of type-308 stainless steel weld has been examined over a range of temperatures 400-850~ for times up to 10,000 hr. Upon aging, and depending on the temperature range, the unstable ferrite may undergo a variety of solid state transformations. These phase changes affect creep-rupture and Charpy impact properties.

Results of a three dimensional (3D) guided wave evaluation of the stress waves generated by the impulse response method show that the conventional interpretation technique based on 1D wave propagation theory is essentially a special application of the first branch of longitudinal wave modes with frequency components up to several thousand hertz. To extend the frequency range and incorporate special wave characteristics of higher modes so that the integrity of an embedded pile can be evaluated in a more thorough manner, a frequency-controlled method capable of exciting waveforms with higher and selective frequency components is introduced to nondestructively evaluate prototype concrete piles. Experimental results on a prototype pile are analyzed by processing the responding signals in the joint time-frequency domain, then comparing the processed waveforms with the theoretically computed results. These results show that the mode attributes of the experimentally excited waves are consistent with the results of theoretical evaluations. Based on this finding, this guided wave approach can be applied to evaluate the integrity of a drill shaft with appropriately determined parameters of the soil-pile system.

Wood poles are among the main components of electrical distribution systems. They have to be replaced every 20-30 years due to wood decay. To reduce costs, utilities need an efficient nondestructive tool to determine the appropriate replacement time. Different techniques exist for this purpose, such as X-or gamma-ray tomography, indentation, and methods based on measurement of electrical conductivity, ultrasonic propagation, or simply bacterial culturing. Since none of these methods satisfy these utilities, it was decided to study in detail infrared thermography (NDT) in this particular context. The hypothesis is that in this particular context, wood decay corresponds to a different moisture content with respect to sound wood.

This guide was prepared to assist field foresters in the use of stress wave timing instruments to locate and define areas of decay in standing timber. The first three sections provide background information, the principles of stress wave nondestructive testing, and measurement techniques for stress wave nondestructive testing. The last section is a detailed description of how to apply stress wave nondestructive testing methods to standing timber. A sample field data acquisition form is included.

A junction between two similar, or dissimilar, materials represents generally a weak structural point and so it requires accurate choice of the most adequate joining technique and nondestructive evaluation of joined parts whatever the joining technique. The attention of the present paper is focused on the aid provided by infrared thermography for nondestructive evaluation of three types of joints: aluminum adhesively bonded joints, stainless steel laser welded joints and Glare â mechanical fastened joints. Both techniques, pulse and modulated thermography with optical stimulation, are used. The attention is particularly focused on the second method because phase images are practically not affected by local nonuniform heating and/or local variation of the emissivity coefficient as thermal images.