Ti-6Al-4V alloy specimens cut form a forged plate with a duplex microstructure, similar to the microstructure used in fan blades were tested under conditions of high-cycle fretting fatigue. The contact geometry, the normal stress, as well as the cyclic stress were selectee such that the mixed, slip-stick regime prevails during the experiments. Following testing, the specimens as well as the fretting pads were characterized by a variety of techniques including white light interference profilometry, scanning electron microscopy, ultrasonic force microscopy, microhardness testing, and electron dispersive spectroscopy (EDS). The results revealed that the surface roughness of the slip region increases compared to the roughness of the stick, and non-contact ones. In addition, at the higher spatial frequencies, the power spectral density (PSD) of the slip region increases compared to the PSD of the stick and non- contact regions, thus revealing that an increase of the population of the smaller size asperities occurs. The microstructure of the material below the slip zone was found to be transformed to a finer one; and the percentage of the transformed beta phase has been decreased substantially. The elastic property variation of this region was determined by ultrasonic force microscopy; the results revealed that in contrast to what found for the bulk of the material, there are significant local differences of the elastic properties inside the fretting-affected zone. In addition, the changes in the plastic behavior of the region below the slip zone, was determined using microhardness measurements. It was found that this transformed microstructure area, has also a higher hardness compared to the hardness of the bulk structure. Booth elastic and plastic property variations were attributed to the increased percent of alpha phase and the decreased amount of beta in the transformed zone, since the former phase exhibits higher elastic moduli as well as flow stresses.In addition, changes in the concentration of the oxygen at the specimen's surface as well as inside the transformed zone were examined by energy dispersive spectroscopy (EDS). The EDS analysis revealed a high concentration of oxygen on the specimen's surface only at the slip region of the two contacting materials. This finding indicates that elevated temperatures were developed during the fretting fatigue testing, which enable the diffusion of oxygen from the atmosphere to the alloy. However, within the transformed zone, no detectable differences in the oxygen concentration were revealed. This finding allowed us to assume that stress induced transformation is the most probable mechanism.

Wavelet analysis is being used to rationalize information at various scales in several branches of science, including particle physics, biology, electrical engineering, fluid mechanics, and medicine. However, this powerful technique has not been applied to characterizing structures of materials, fretting damage for the present case, even though many critical questions could be addressed. In particular, the following unsolved problems are considered in this paper: (a) The first problem deals with the quantitative characterization of fretted surface in a Ti-6Al-4V alloy. This investigate by analyzing profilometric digital images of fretted surfaces obtained at a range of magnifications. Wavelet analysis of the data is able to identify, by examining the wavelet coefficients, dominant length scales as those regions in the scale-space where the energy of the wavelet transform and/or peaks of local concentration dominate. For the range of magnifications examined, i.e., from 1.25x to 100x, the 20x magnification is identified as the one with the most useful information. (b) An alternative procedure is employed for the second use of wavelets which deals with the non-uniformity of the contact regions. Recent theoretical work has shown that during contact with partial slip, the morphology of the partially slipping regions does not change. Wavelet analysis is employed to identify those regions, which result in the 'pattern' of the fretted surface morphology.

The parameters that govern the life of metallic materials under conditions of fretting fatigue may be divided into two broad categories. The first category deals with the materials properties and characteristics while the second includes the externally imposed loading conditions and contact geometry. The two materials in contact may either stick, slip or stick-clip with each other. It has been shown that the life reduction is highest under partial slip. The objective of the present research effort is focused to the prediction of the particular fretting fatigue regime and hence get an estimate of the life reduction of a particular materials/component. The above may be accomplished by using as input to a specific model, a series of data obtained from non-destructive and other characterization techniques. To this end, the bodies in contact is developed and hence the different materials as well as external parameters which influence the process are identified. Although the external are implied by the should be determined quantitatively. This is accomplished by white light interference profilometry, which was used to characterization were used as input into the model to predict the actual contact conditions. Experimental results concerned with the fatigue life were plotted on the fretting maps; the fretting fatigue regimes indicated by the latter enabled the interpretation of the experimental data.

In recent years, the US Air Force has focused attention on extending the life of its aging fleet. Consequently, the Air Force is concerned about a growing number of aging aircraft that require extensive maintenance. One of the main causes of aging aircraft failure is due to corrosion damage and fatigue of its aluminum alloy parts. Many parts of corrosion damage can affect the aluminum structures of an aircraft. In this paper, result on controlled pitting corrosion will be discussed. Pitting corrosion triggers serious damage in aircraft structures because pits act as one of the nucleation sites for fatigue crack formation. To study the role of pits in fatigue crack initiation, pits were created on high strength aluminum alloy 2024-T3 samples by an accelerated electrochemical method. These pits have a variety of diameters and depths. The scanning electronic microscopy. The pitted surface was examined, and parameters such as average roughness and pit depth were determined. In addition, 3D images of the pitted surface were recorded. These result provide the details of the critical pit size that can lead to fatigue crack initiation in Al 2024-T3. The understanding of the role of pitting in crack initiation aids in extending the fatigue life of the aging aircraft.

The paper documents a novel method for characterizing pitting corrosion damage in structural materials such as Al 2024-T3. Specimens of such alloys are corroded in a controlled environment and the pits' geometry is captured digitally using white light interference microscopy. The digital data are then processed with wavelet-based analysis thus making possible a multi-resolution description of the geometrical features. The analysis reveals several interesting features of the pits that are similar for all the experimental data analyzed herein, and independent of the process followed for creating them. The first property identified as common to all pits is their geometrical scaling with a (Hurst) exponent of 0.63 +/- 0.12. Furthermore, the ratio (omega) of the surface area of the pit as represented at coarse scales through the wavelet representation, over the area of its intersection with the plane at zero depth is found to be 1.17 +/- 0.07 consistently. The ratio of the total surface area over its intersection is found to be 1.6 +/- 0.2. Either one of these ratios together with the Hurst exponent provide sufficient information for obtaining a pit's geometry from images capturing its 2D shape only, a capability important for efficient characterization. Additionally, such a characterization is paramount for rigorously addressing fatigue crack initiation and propagation.

TPL, in collaboration with Xerox Palo Alto Research Center and Thermotrex, is developing advanced amorphous silicon sensor arrays for primary application to nondestructive evaluation. Amorphous silicon flat panel technology provides unique capabilities which are directly applicable to a number of NDE and process verification applications. Like other digital radiography technologies, amorphous silicon arrays (ASAs) greatly reduce inspection time, materials use and waste products associated with conventional radiographic inspection. Unlike techniques based on charge coupled devices, ASAs also provide a format that is analogous to the use of film; that is direct exposure and large area imaging. This unique combination of traits from both film-like systems and camera-like systems makes ASAs ideal for a wide range of applications. With careful considerations of the advantages and limitations of ASA technology, implementation of high performance, cost-effective inspection systems based on this enabling technology can be achieved. This paper discusses the current state of ASA technology, as well as the potential for ASA technology advances, and presents results pertinent to NDE applications.

The use of composite materials, in particular glass/epoxy systems for structural applications has seen widespread growth. Recent examples include a bridge in Butler County, Ohio and a covered pedestrian bridge that is scheduled to be installed in Akron, Ohio. Both of these structures employ pultruded composites for the main structural members due to their high strength, light weight and the ease of manufacture into common structural shapes such as wide flanges, I-beams and box sections. The use of these shapes gives the designer the ability to use many of the same types of structural details that are common to steel design. This paper will examine the most common method of joining structural members, bolted connections. The analysis of bolted connections in composite materials has been widely reported in the literature. Analysis methods have ranged from two and three dimensional finite element analysis to more empirical methods of calculating the stress concentration factors based on experimental data. This paper will focus on the use of the thermoelastic stress analysis method to determine the stress concentration around a steel pin loaded in double shear by a pultruded glass fiber composite. Further studies were conducted to determine the time dependent material behavior on the thermoelastic stress analysis signal output. The following is a description of the theory, experimental setup, and a summary of results.

The paper aims to illustrate three advantages of IR thermography as a nondestructive, noncontact and real time technique, (a) to observe the progressive damage processes and mechanisms of leather failure, and (b) to detect the occurrence of intrinsic dissipation localization. The parameter, investigated in this paper, is the heat generation due to intrinsic dissipation caused by inelasticity and/or inelasticity of leather. It readily describes the damage location and the failure evolution of leather for sport foot-wear.

To simulate the testing conditions experienced by aircraft engine turbine blades, a new experimental facility was developed capable of providing interactive low cycle fatigue (LCF)/high cycle fatigue (HCF) loading. The new facility is based on a HCF cell that can operate in the 10-40 kHz frequency range. This HCF testing cell can also be interfaced to a servo-hydraulic load frame, which provides a second fatigue cycle. Sample geometry is critical for the HCF cell to produce the desired applied load on the specimen. The objective of this research is to develop analytical modeling necessary for the design of test coupons to be used in the new HCF testing cell operating at ultrasonic frequencies, and also to demonstrate the capabilities of the new device by performing LCF/HCF interaction studies in Ti-6Al-4V. The results of these studies clearly showed the effect of the HCF component of the load in spite the fact that the HCF component was only 15-19 percent of the overall load. It was also found that the HCF component of the load was the major cause of observed damage with the LCF component having much less effect. Eliminating the HCF component completely resulted in increasing the fatigue life at least an order of magnitude.

An in-situ technique to measure sound velocity, ultrasonic attenuation and acoustic nonlinear property has been developed for characterization and early detection of fatigue damage in aerospace materials. A previous experiment using the f-2f technique on Ti-6Al-4V dog bone specimen fatigued at different stage of fatigue has shown that the material nonlinearity exhibit large change compared to the other ultrasonic parameter. Real-time monitoring of the nonlinearity may be a future tool to characterize early fatigue damage in the material. For this purpose we have developed a computer software and measurement technique including hardware for the automation of the measurement. New transducer holder and special grips are designed. The automation has allowed us to test the long-term stability of the electronics over a period of time and so proof of the linearity of the system. For the first time, a real-time experiment has been performed on a dog-bone specimen from zero fatigue al the way to the final fracture.

The objective of this work is to develop a methodology for predicting material failure by evaluating changes in material characteristics directly prior to unstable crack growth. In an effort to establish and document these changes, several Ti-6Al-4V flat, notched samples have been subjected to fatigue loading to partial life. After a fatigue crack was initiated characterization was performed during in-situ application of an incrementally increased static load. White light interference microscopy was found to be a successful nondestructive tool for characterizing changes in the deformation zone in front of the crack tip. A relationship between the applied load and the surface area of the deformation zone was obtained. This relationship was exponential directly prior to failure of the specimen. Surface observations during in-situ testing allowed samples to be brought near to failure without compete fracture. This result can have important applications for optimizing the service life of airframe structural components.

Innovative optical NDE techniques are being developed for the full-field detection and evaluation of surface defects and defect precursors in titanium and aluminum based alloys. The techniques are based on frequency-translated holography and optical correlation principles, and use bacteriohodopsin (bR) holographic films and temporal correlation techniques for real-time storage and retrieval of Surface Acoustic Waves (SAW) features and embedded surface defect information. The SAW waves induced on the material surface being studied are made to interfere with optical light waves, and fringes are produced that are a function of optical Doppler shifts induced by phonon-photon interaction on the surface of the materials. Visualization of these SAW patterns allow for NDE characterization of features on and near the surface of the materials, including defect and defect precursor sites. Preliminary results are provided for real-time bR holographic recordings of acoustic patterns induced on Al2024-T3 material surfaces.

An advanced electronic phase stepped interferometry (EPSI) system is described for quantitative out-of-plane displacement and surface topography measurements for NDE applications. Image processing algorithms were developed using novel techniques to extend the sensitivity of EPSI and provide near real-time measurement capability. EPSI is known to provide out-of-plane displacement and surface topography measurements on the order of 1/20-1/100 microns. Noise can be a limiting factor, however, and robust phase unwrapping, which is required, remains an open and active research area. A prototype EPSI system was developed and tested using simulated and real data sets of known displacement fields. A robust maximum-likelihood binary-tree (MLBT) phase unwrapping technique was developed, providing greater robustness in the presence of noise than standard techniques. In addition, the MLBT algorithm lends itself to efficient and fast parallel implementations for near-real time implementation. The use of these advanced algorithms improves the capabilities of existing EPSI techniques, providing more robustness and near real-time measurements. Results are provided for deformations in Ti-6Al-4V and Al2024-T3 aerospace materials.

The primary objective of this study involved the utilization of the thermoelastic stress analysis (TSA) method to demonstrate the mean stress dependence of the thermoelastic constant. Titanium and nickel base alloys, commonly employed in aerospace gas turbines, were the materials of interest. The repeatability of the results was studied through a statistical analysis of the data. Although the mean stress dependence was well established, the ability to confidently quantify it was diminished by the experimental variations. If calibration of the thermoelastic response to mean stress can be successfully implemented, it is feasible to use the relationship to determine a structure residual stress state.

The Knowledge Based Inspection System (KBIS), comprised of neural network classification of ultrasonic data and advanced ultrasonic sizing methodologies, is being developed under a Navy Manufacturing Technology Program. The intent of the KBIS program is to provide a tool with which an ultrasonic inspector can obtain enhanced information to improve the probability of correctly accepting or rejecting weld discontinuities. Ultimately, the use of KBIS should reduce the long-term cost of ownership of vessels due to elimination of detrimental discontinuities only.

Acoustography is being developed as an alternative to conventional point-by-point ultrasonic scanning commonly employed for composite inspection. In acoustography, an area detector is used to produce full-field images of the test component in near real time, which makes the method suitable for providing rapid ultrasonic inspection of composites. Although the possibility of using acoustography to inspect composites has recently been demonstrated, a side-by-side comparison of acoustography with conventional ultrasonic scanning has not been made. In this work we will report on studies conducted toward establishing a direct comparison between acoustography and conventional ultrasonic scanning.

Development of ultrasound nondestructive evaluation techniques (NDT) has involved a combination of both analytic and experimental methods. In contrast, relatively little work has been done on the use of computational methods for experimental design and analysis in NDT. This is due to the relative lack of availability of software for such computations. While computational methods and associated software implementations abound in the electromagnetic and structural analysis engineering communities, no such paradigm exists for ultrasound researchers and engineers. This paper demonstrates a software package, Wave2000, which computes the full solution to the 2D viscoelastic wave equation. 2D objects are represented by graphical images and are comprised of a number of solids and/or liquids. Each material is specified in terms of its material density, the first and second Lame constants, and the first and second viscosities. The program computers the displacement vector was a function of Cartesian coordinates x and y and of time t, and the solution includes effects of diffraction, scattering, reflection, and attenuation of the propagating wave. Wave2000 implements a finite difference solution on a standard personal computer running Microsoft Windows 95 or NT. Sources and receivers may be located anywhere in or on the surface of the object. The source waveform can be practically any temporal function desired, including data collected from an actual transducer, and the receiver data can be sorted in a data file for subsequent processing. Several examples of the use of Wave2000 are given, including simulations of scattering from cracks and propagation through layers of materials and fluid-filled porous structures. Results demonstrate that computational methods can play an important can play an important role in NDT specifically and in ultrasonics in general.

In this work a preliminary study of an ultrasound application, as a non destructive technique, for the evaluation of some chilean wood species is shown. By means of this technique the elasticity moduli (MOE) along the fibers for different positions of the samples with respect to the pith and different moisture contents are determined. At the same time the wood anisotropy properties are evaluated as the ratio between velocities along the main directions of the tree. In general, the obtained results show a high correlations between the MOE obtained by mechanic and ultrasound essays while the anisotropy values correspond mainly to the expected results. Finally, it is considered that the application of this technique as a complement to other non destructive techniques conform an excellent tool for evaluation and quality control of wood products.

This paper addresses the growing need for modern nondestructive evaluation (NDE) techniques for quality control during the construction/fabrication stages of transportation infrastructure. While the use of NDE techniques for in-service monitoring of infrastructure is increasing, very little effort is currently being made to use NDE for construction quality control. This paper proposes the use of modern NDE techniques for inspection of materials and quality control during construction of transportation infrastructure. The paper also discuses the use of conventional nondestructive and mildly destructive techniques. Examples of potential NDE applications for quality control in transportation construction have been presented. A short discussion on current impediments to NDE field use and possible solutions has been included.

The velocity, attenuation and scattering of ultrasonic waves measured in concrete, mortar and cement structures can be used to evaluate their quality with weathering and aging. In this investigation the hardening of concrete mixture with time is monitored by ultrasonic waves under different conditions of temperature and water to cement ratio. The measured ultrasonic parameters can then be utilized to determine the final quality of the completely cured concrete structure from initial measurement. The quality of a concrete structure is determined by its resistance to compression and its rigidity, which should be within the acceptable values required by the design specifications. The internal and external flaws that could lower its strength can also be detected by ultrasonic technique. Aging process of concrete by weathering can be simulated in the laboratory by subjecting the concrete to extremes of cold and hot cycles in the range of temperatures normally encountered in summer and winter. In this research ultrasonic sensors in low frequency range of 40 to 100 kHz are used to monitor the quality of concrete. Ultrasonic pulses transmitted through the concrete sample are recorded for analysis in time and frequency domains. ULtrasonic waves penetration in concrete of the order of few feet has been achieved in laboratory. Data analyses on ultrasonic signal velocity, spectral content, phase and attenuation, can be utilized to evaluate, in situ, the quality and mechanical strength of concrete.

Optical coherence tomography (OCT) is a non-destructive and non-contact technique that images microstructure within scattering media. In this work, the versatility of OCT for non-destructive evaluation is demonstrated through imaging of composite microstructure and damage. Imaging of composite microstructure is demonstrated through tomographic reconstructions of an epoxy/unidirectional E-glass composite and an epoxy/0-90 degree woven E-glass composite. Imaging of damage is shown by tomographic reconstruction of impact damage in a epoxy/unidirectional E-glass composite. The volumetric reconstruction of the composite is re-sliced along the thickness axis to reveal the propagation of cracks through the reinforcement layers. Advantages and limitations of OCT are discussed.

A new laser based remote NDE method named RAID is described and some selected results are presented in this paper. This system has demonstrated its ability to detect defects in solid laminates; honeycomb/carbon, where defects at the rear have been observed; bonding defects in ceramic and also defects such as cracking in the new carbon foam materials, both of these latter materials have extremely high acoustic attenuation. Additionally the system has recently demonstrated its feasibility to detect and quantify subsurface corrosion in aluminum riveted and boded structures such as lap joints; to date 5 percent metal loss has been detected. Defects in other metal structures such as tear straps in airframe fuselages of transport aircraft are rapidly detectable.

The Carderock Division of the Naval Surface Warfare Center is evaluating nondestructive evaluation techniques for the inspection of flexible rubber composites in a shipboard service environment. The composite components are constructed of low-loss rubber materials, with several layers of reinforcement fabric located in the mid-thickness of the material. In a preliminary investigation, specimens aged in a laboratory environment and specimens removed form in-service platforms were inspected using near-field microwave techniques. The aged specimens contained small cracks and surface imperfections, while the in-service specimens exhibited delaminations between the rubber base material and the fabric plies. Inspections using a 33.375 GHz, open-ended rectangular waveguide demonstrated the ability to detect delaminations between the rubber casings and fabric plies, as well as for the detection of cord breakage of the fibers. Additional work is being planned to quantify the inspection capabilities relative to an acceptance criterion and to conduct in-service pilot studies with naval inspection personnel.

This paper describes the development of an instrumented tap test and imaging system for the inspection of defects and damages in composite aircraft structures, especially honeycomb sandwich constructions. The resulting tap test images based on the impact duration and displayed in a C- scan format can readily reveal the shape and extent of honeycomb core damages. The images also reveal considerable detail of internal substructures such as core splices, ply build-up, and changes of foam core density. Based on a grounded-spring mechanical model, the tap scan images can be converted into images that show the quantitative changes of the local stiffness. A manual tap scan imaging system was assembled for laboratory experiments. Using actual composites parts for airplanes, impact damages and substructures were imaged. In addition, effects of the tapper mass, impactor radius, tap velocity and operator dependence were studied. A compact fieldable system is being built and an automated tapping and imaging system is also under development. The technique was compared to other similar devices currently available.

Optical fiber sensor have numerous advantages over conventional sensing technologies. One exciting capability of optical fiber sensor is their ability to operate in high temperature environments. While most conventional strain, pressure, etc. sensors do not operate reliably over 300 degrees C, fused silica based optical fiber sensor can survive up to 900 degrees C. High temperature materials such as sapphire and silicon carbide can be used to construct sensors that can survive up to 2000 degrees C. A suite of high temperature strain, pressure, and temperature sensor are being developed using the Extrinsic Fabry-Perot Interferometer technology for NDE characterization of advanced composite materials. These sensors have been demonstrated in several applications. High temperature strain and temperature sensors were used to conduct fatigue testing of composite compounds at 600 degrees C. High temperature pressure senors are being developed as microphones for high temperature acoustic testing. The result from these specific high temperature applications are presented along with future applications and directions for these sensors.

Although laser ultrasound is a promising technique for many applications, the signal-to-noise ratio of laser ultrasound is poorer than for contact ultrasonics. In this paper we present some of our current work in optimizing the excitation of laser ultrasound in composite materials. We are characterizing laser generated ultrasound as a function of laser parameters, composite material properties, and their interaction. Experimental results for a number of different laser wavelengths and pulse widths, for several materials, are presented.

Fiber optic phase shifting Electronic Speckle Pattern Interferometer system has been used for the Non-Destructive Testing of Composite laminates. This paper describes the application of this system to assess delamination and fiber breakage in Glass Fiber Reinforced Plastic (GFRP) laminates by analyzing the fringe patterns and by applying phase shifting techniques. GFRP laminates have been studied using the ESPI system in various optical configurations. This technique provides the full-field, non-contact method for NDE of composite specimens.

In this paper, ultrasonic-atomic force microscopy was applied for obtaining qualitative and quantitative information of binder distribution in spray dried ceramic slurries. Embedded granules were mounted on the surface of a transducer generating acoustic waves, 0 to 500KHz. These samples were vibrated at their resonant frequency while surfaces were scanned with a cantilever. Thus, both hardness and topography images were collected simultaneously. Since the contrast of the two materials is related to hardness, the distribution of binder and ceramic can be found immediately from the hardness images. By modeling the cantilever with its deflection vibration, the quantitative modulus of the binder and ceramic mixture was acquired while the sample and cantilever were vibrated at their resonance frequency. From the calibration with an Al₂₂O₃ sample, those measurement were reconfirmed.

This paper reports on the evaluation of three different techniques to detect delaminations at interfaces of ceramic/metal joints. The three techniques were optical microscopy, scanning electron microscopy and scanning acoustic microscopy. The ceramic/metal joints consisted of plates of silicon nitrate and steel jointed with copper at the interface. The delaminations were introduce by a micro- Vickers indentor. Of the three techniques only scanning acoustic microscopy was successful in detecting the delamination. The V(z) curve technique was used to measure values for the surface acoustic wave velocity along the interface and for the defective specimens showed evidence of residual stress. Thus this study present useful guidelines in discriminating between good and defective ceramic/metal joints with scanning acoustic microscopy emerging as the most useful tool.

An optical interferometric nondestructive evaluation technique is introduced. Based on electronic speckle-pattern interferometry and a recent theory of plastic deformation, this technique is capable of visualizing stress concentration and predicting the location and timing of the failure of the object. The operation of the technique is demonstrated for tensile analyses of aluminum alloy samples.

Frescoes, icons and composite materials show analogies in terms of defects, both present layer-to-layer detachments and delaminations and surface cracks; past experiences demonstrated that the study of surface vibrations could be used to locate defects position and size. At present a non- invasive diagnostic system is under development and the aim of this work is to propose and compare different kinds of structural exciters. After initial measurement set-ups based on accelerometers and impact hammers, a novel system based on laser vibrometers and acoustic stimulation has been assembled; full remote and contactless investigation of detachments and delaminations is thus possible with a very high accuracy. At present three different types of acoustic sources are employed: unbaffled standard loudspeakers, horn loudspeakers and an elliptic mirror sound focuser. The last source has been developed to concentrate sound power in a very small area so to excite only localized defects of the structures and void annoying noises to be propagated around them. A new kind of exciter, namely a piezo actuator, has also been introduced in the measurement chain and its effectiveness in finding defects in icons will be demonstrated. This paper will present experimental result gathered from sample showing differences in data due to different exciting sources. A comparison with results furnished by traditional techniques will be shown.

The presence of residual stress gradients is often revealed by x-ray diffraction analysis. Because x-rays always detect an averaged information due to absorption, in the past some approaches have been employed to retrieve the true-z- profiles from the measured (tau) -profiles where (tau) is in general the 1/e information depth of the diffracted intensity. However, all problems which can be described as so called inverse problems like x-ray diffraction analysis are often extremely ill-conditioned. What makes the wavelet basis interesting is that individual wavelet functions are quite localized in space and simultaneously they also are quite localized in frequency. This particular kind of dual localization achieved by wavelets renders operators to be sparse to some high accuracy, when transformed into the wavelet domain. However, the number of required wavelet coefficients for the representation of a residual stress gradients in general still exceeds the number of measurements. therefore, a multilayer feed forward neural network approach has been investigated. With the implementation of a fast backtracking algorithm, suitable learning rates can be achieved. The advantages of this neural network approach, which to the authors knowledge is first introduce in the field of residual stress analysis, will be discussed.

Concerning the appearance of fine ripples on the surface of members and structures in which fatigue damage is produced, investigations from a variety of points of view have been made. Each of these investigations were made with the aid of various types of measurement apparatus. In this study, surface damage of the members and structures in the fatigue process was examined using direct naked-eye observation as the primary investigate measure. This type of examination has enable d the authors to better understand the state of the surface corresponding to the change of metallographic structure in the materials fatigue process. Thus, the authors have successfully gathered data that will be useful in predicting fatigue failure from a nondestructive evaluation.

Deformation-induced martensite and reversed austenite of a metastable austenitic stainless steel sheet were evaluated by a scanning acoustic microscope with frequencies 600MHz and 800 MHz. The sheet was elongated up to 40 percent at and below the room temperature to produce martensite, followed by annealing for reversion. First martensite content was measured by a Feritscope. Next using a complex V(z) curve, leaky Rayleigh wave velocity was measured. The deformed and annealed grain structure s were observed with the frequency 800MHz and compared with those by the optical microscope. Rayleigh wave velocity is dependent on the elongation and ambient temperature in elongation and the annealing temperature, which agrees well with the one by the Feritscope. Deformed grains are more clearly observed by the scanning acoustic microscope with 800MHz. The measured value of the velocity is compared with the theoretical one which can be calculated by Young's modulus, Poisson's ratio and the density. The measured Rayleigh wave velocity is well agreement with the theoretical one.

The implementation of an ultrasonic method of evaluation of composite plates requires a good knowledge of the interaction of ultrasonic beam emitted by the transducers, with such a plate immersed in a fluid. The model of ultrasonic propagation in anisotropic multilayered materials developed here makes the study of this interaction possible. The interaction of ultrasonic beams with fluid-loaded multilayered anisotropic structures is treated numerically by combining the propagator matrix and the angular spectrum decomposition technique. The numerical model developed during the course of investigation is used to calculate the reflection and transmission profiles for a Gaussian beam incident on a multilayered composite. The model allows the calculations of the reflected and transmitted ultrasonic fields for a multilayered composite, absorbing or not. The emphasis is placed on the regime of nonspecular reflection that is characterized by the strong cooling between the specularly reflected beam and the leaky waves supported by the structure corresponding to the incidence in the vicinity of multilayered Rayleigh modes.

An ultrasonic C-mode imaging system incorporating an ultrasonic phase conjugator has been built and images have been obtained at a frequency of 10MHz. This system is free from the influence of wavefront distortion due to the reflection or the refraction at the rough surface of the samples and visualizes the net attenuation of ultrasonic waves.

In ceramic tile industry, delamination is one of the more important and difficult problems to detect. Among all the general non-destructive evaluation methods, optical inspection technique seem to be particularly suitable. A method based on acquisition and processing of IR thermal images is proposed. Measurements have been performed by artificial heating by an IR quartz lamp. The performance of the technique has been evaluated experimentally and results show that the examine defects in the measured samples have been correctly detected. Another proposed technique for detection of delaminations and voids in structures is vibration monitoring by a scanning laser doppler vibrometer (SLDV). The basic idea is that a defected area will show as a higher velocity one. Structure excitation may be performed by acoustic means, thus allowing for a remote contactless measurement system. Our tests put in evidence that IR thermal images provide a very fast defect detection method appropriate for on line applications, while SLDV results show a better geometrical definition of defects shapes.

An important research theme in today's dentistry is the selection of the appropriate resin to be used for the filling of drilled cavities. Some resins in fact may cause high sensitivity or pain in the patient also few days after their application. This phenomenon of high sensitivity seems to be used by the creation of likeages at the interface between dentin and resin.

Whole deformation processes and slipboard propagation of aluminum alloy in tensile experiments are directly observed on whole field in real time by dynamic speckle interferometry. In plastic deformation, an inclined white band appears. It sweeps the specimen surface repeatedly in a certain sped and band width along the tensile direction. Sometimes the inclined angle of the white band transfers symmetrically. With plastic deformation increasing, the band speed decreases gradually, and the specimen cracks finally at the position where the band stops. Transient process of the white band formation is captured with a high speed CCD camera. It is revealed that the white band is a sharp slip deforming region consisted of concentrated inclined fringes. An interesting phenomenon that the strain value at a point of the specimen surface changes like a stair shape is accounted by the sweeping movement of the slipboard. The moving picture encoding technique is introduced to encode all of the sequential fringe patterns as one MPEG2 file. By watching the moving picture, the analysis of a huge volume of fringe patterns becomes easy, and subtle changes of fringe patterns can be observed clearly.