It has become well known that the roadway infrastructure in the United States has been deteriorating over the pst 20 years. Recently, the Federal Highway Administration has listed nearly 50 percent of the countries bridges as either structural deficient or functionally obsolete. In this group, approximately 75 percent are located on rural or secondary roads and are in the small to medium span range. In order to prioritize the structures in most need of repair or replacement, inspection methods need to be introduced that will take into account all types of bridges including those constructed of concrete, steel and timber.

Confinement of concrete columns for earthquake retrofit and new construction is being studied extensively and has been implemented in some applications. Large-scale, composite- confined concrete cylinders were tested to failure in compression to investigate scale effects on the response of the material, to allow more thorough instrumentation, and to study the feasibility of long-term monitoring of composite civil structures using embedded sensors. Bragg grating optical fiber strain gages were embedded in three hoop-wrapped, filament-wound, carbon/epoxy composite cylinders. Multiple optical fiber gages were placed in both the axial and circumferential directions. Resistive gages were placed near the optical fiber locations. The 12-inch diameter cylinders were filled with concrete and tested in axial compression. A triaxial state of strain was induced in the optical fibers -- axial compression from the load, radial pressure from the expanding concrete, and circumferential tension to contain the radial pressure. The extensive data recorded in the optical fiber and resistive strain gages during compression loads to failure allowed a detailed study of transverse strain effects on Bragg gratings. Conventional mechanics of materials models and micromechanical finite element models were used to predict the relationship between surface strains measured by resistive gages and Bragg grating wavelength shifts. Various models were used to account for the effects of the three strain components on the response of the Bragg grating. Although the average error between resistive and optical fiber readings could be reduced by correcting for transverse strains, there were still significant differences (over 20%). The embedded optical fiber strain gages did provide a sufficiently repeatable and accurate measurement of strain in these structures for long- term damage monitoring or post-earthquake inspection.

A thermographic technique for detecting disbonds and delaminations in concrete beams reinforced with bonded sheets of unidirectional carbon fiber reinforced plastic is described. Concrete slab test specimens are fabricated with seeded flaws of various thickness and depth from the surface. The specimens are briefly heated with a projector heat source and infrared images are captured. Digital image processing techniques are applied in order to improve image quality. Flaws are identified. Advantages and limitations of this method are discussed.

Two remote and nondestructive testing techniques for the study of the decay mechanism of stone and plaster surfaces are presented. While electronic speckle pattern interferometer (ESPI) measures the 3-D-microdeformations of the surface, transient thermography shows at the same time invisible defects and structural faults as a reaction to the impact of short heat pulses. The combination of these two different techniques demonstrates its feasibility to detect restorative work and shows the compatibility of classical and modern substitutes and restoration techniques to historical materials.

Near-field nondestructive reflection property characterization of concrete based materials using open-ended rectangular waveguide probes is presented. The statistical distribution of multiple reflection property measurements are used as a tool to determine the water-to-cement (w/c) ratio as well as the coarse aggregate volumetric distributions in several concrete mixtures. These results may be used to determine the compressive strength of concrete. In this effort, concrete specimens with 0.50 w/c ratio were used. For these specimens sand-to-cement (s/c) ratio of 1.0 was used along with coarse aggregate-to-cement (ca/c) ratios of 1.0, 1.5, and 2.0, respectively. The microwave reflection coefficient of these specimens were measured at x-band (10 GHz) and S-band (3 GHz) using an HP8510 vector network analyzer. The results of these measurements, from the point of view of their probability distribution functions are presented, in addition to discussions regarding their implementation for nondestructive characterization of concrete based materials.

High strength steel alloys (such as 300 M) used in naval aircraft engine and landing gear components are subjected to cyclic loading in service and found to be highly susceptible to fatigue cracking. There is a critical need for nondestructive evaluation techniques which can detect both cracking and potential crack nucleation sites within these components. An innovative electromagnetic technology called the stress induced-magnetic-anisotropy (SMA) technique has been proposed to be used to detect and evaluate residual stresses. SMA measures residual stresses by sensing the changes in magnetic flux induced in directions parallel and perpendicular to the stress. A novel probe and instrumentation is being developed to simultaneously detect both subsurface residual stresses and stress-induced cracking in coated and uncoated ferromagnetic structures. Finite element analysis has been used to determine the distribution of magnetic flux density and inductance of the probe under varying AC fields. Using ANSYS^TM EMAG, the effect of varying frequency of the excitation field, permeability and dimensions of the core have been analyzed. The paper describes how finite element analysis can be used in design and development of the probe and in understanding its behavior.

Energy loss per cycle is one of the most common parameters to determine the magnitude of hysteresis damping. The measured hysteresis loops for materials during dynamic measurements are often irregular and general equations for defining the force- displacement-time relations of materials are unavailable in almost all cases. In order to analyze the complicated nature of the behavior of nonlinear hysteresis damping under non- sinusoidal loading, a new method was developed by the author for the damping characterization of materials subjected to any arbitrary dynamic loading. This method uses quadrature spectrum of displacement and restoring force signals to calculate the damping properties of materials at any frequency. It was proven that the quadrature spectrum method is an excellent tool for practical hysteresis damping measurement. The dynamic damping density function was also defined and discussed in this paper.

Frescoes and icons show analogies in terms of defects, both present layer-to-layer detachments and delaminations and surface cracks; our aim is to develop a diagnostic system for the measurement of the defects position and size. We employ laser vibrometers and acoustic simulation of structures to allow full remote and contactless investigation of detachments and delaminations. The use of advanced measuring devices combined with computer data backup systems allow the restorers to follow damage evolution during time and to verify the effectiveness of their work. A full working experimental measurement set-up is described along with the results obtained. Extensive measurement sessions were performed with on purpose built frescoes and icons samples, presenting a wide range of defects positions and dimensions and different surface finishes and colors; results were then compared with those obtained by professional restorers by manual techniques. Further to this, we demonstrate that the simultaneous use of a complementary technique, IR thermography, allows also the measurement of complex defect structures, especially of superimposed defects at different layers interfaces.

The Pacific Northwest National Laboratory (PNNL) is developing a methodology for estimating the size and density distribution of fabrication flaws in U.S. nuclear reactor pressure vessels. This involves the nondestructive evaluation (NDE) of reactor pressure vessel materials and the destructive validation of the flaws found. NDE has been performed on reactor pressure vessel material made by Babcock & Wilcox and Combustion Engineering. A metallographic analysis is being performed to validate the flaw density and size distributions estimated from the 2500 indications of fabrication flaws that were detected and characterized in the very sensitive SAFT-UT (synthetic aperture focusing technique for ultrasonic testing) inspection data from the Pressure Vessel Research User Facility (PVRUF) vessel at Oak Ridge National Laboratory. Research plans are also described for expanding the work to include other reactor pressure vessel materials.

Advances in radioscopic testing have occurred very recently with the availability of the ASTM radioscopic specifications and new equipment designs. Improvements in image quality and variable geometry portable x-ray systems lead the advances. Cost reductions are realized when these systems are utilized for immediate feedback for process control. Storage of as- built product images allows for future reference and additional processing of these digital images for failure analysis.

One advantage of working with digital images is the opportunity for enhancement. While it is important to preserve the original image, variations can be generated that yield greater understanding of object properties. It is often possible to effectively increase dynamic range, improve contrast in regions of interest, emphasize subtle features, reduce background noise, and provide more robust detection of faults. This paper describes and illustrates some of these processes using real world examples.

The Naval Research Laboratory has developed a novel one-sided NDE system for inspecting steel reinforced rubber sonar domes without drydocking. The submersible x-ray system scans the dome through an aluminum window in contact with its surface and uses collimated backscatter imaging to create tomographs of the dome structure. In this paper we discuss backscatter imaging, describe the system, and present results from in-situ inspections of sonar domes on several frigates.

Thick triangularly shaped structural sections used in a variety of applications are inspected using open-ended microwave rectangular waveguide probes. Previous work has shown the ability of microwave techniques to detect and locate planar defects in thick composite structures. In all of those applications, the microwave sensor aperture has been parallel to the surface under inspection. However, in certain cases involving triangular joints, the geometry may require that the microwave sensor be positioned at an angle to the joint surface. Therefore, the inspection is conducted with the waveguide maintaining a certain angle with the surface of the sample. This angle causes the incident fields to bend at an angle which can be determined using Snell's law and the dielectric properties of the sample under inspection. The bending of the fields causes defects and internal structural features to appear at positions at which they are not actually located. The proper location of defects can be found by using Snell's law along with the geometrical and dielectric properties of the material under inspection. The preliminary results of this investigation, including the results of a simple mathematical model and several experimental results, are presented.

Both microwave and ultrasonic techniques for NDE are based on wave propagation and scattering from discrete defects in materials. Conventional ultrasound provides good separation of refections from material boundaries and defects by using short-pulse excitation for transducers of wide bandwidth and damping. Microwave propagation and scattering in nonmetallic composites follow similar principles as ultrasound, with the important difference that the intrinsic difference in wave impedance between material and small voids are less here than in ultrasound. As a consequence, in thick, highly inhomogeneous and somewhat porous composites, microwave NDE may be a good alternative to ultrasound which may suffer from large signal loss due to scattering from voids over a long path length. In this paper we present microwave and ultrasound pulse-echo data in thick composites to illustrate the capabilities of microwave techniques to provide defect information generally sought after by ultrasound, viz. defect location, size, and shape.

A laser optoacoustic sensor (LOAS) for the nondestructive characterization of layered structures of composite materials is presented. The method employs laser pulses for the generation of wide-band acoustic transients in the ultrasonic frequency range from 100 kHz to 10 MHz. The acoustic transient signal is generated at the very surface of materials under testing. The laser wavelength is chosen to achieve the desirable optical attenuation in the material and, thus, to induce acoustic transients within desirable frequency range. The detection of laser-induced ultrasonic signal, its temporal profile and the ultrasonic spectrum, may be performed either in transmission mode or in reflection mode. The laser optoacoustic sensing in transmission mode (LOAS-T) is performed at the surface opposite to the irradiated surface. LOAS-T utilizes measurements of acoustic attenuation coefficient as a function of ultrasonic frequency within the range of laser-induced frequencies. The laser optoacoustic sensing in reflection mode (LOAS-R) permits measurements of ultrasonic transients scattered from the volume of the material under testing. The ultrasonic signal is detected at the site of laser irradiation. The measurements of the reflected ultrasonic signal is frequently the only mode available for the nondestructive evaluation, because usually only one side of the evaluated object is accessible. Samples of layered graphite-epoxy composite materials with volume percentage of micropores from 0 to 1.2% were studied with LOAS. In the ultrasonic frequency range from 1 to 5 MHz, the acoustic attenuation coefficient was found to increase with an increase of relative volume of micropores. The 'noise' component of the scattered acoustic pulse sharply increases with the increase of relative volume of micropores. A 1% increase in the relative volume of micro-pores results in a 3 times greater 'noise' component in the laser optoacoustic signal. Results indicate possibility for the LOAS to be utilized as a diagnostic system for the quantitative characterization of composite materials.

Wide-band acoustic spectroscopy with laser excitation of ultrasound was carried out for glass-fiber-reinforced composite samples. Attenuation coefficient of ultrasonic waves in these samples was measured in the frequency range 1 divided by 20 MHz. Resonant peaks of ultrasound attenuation were found for green-state composite samples caused by periodic structure of composite. Transformation of ultrasound attenuation spectra was observed for samples after service life testing because of fatigue changes of composite structure.

As part of the FAA's National Aging Aircraft Research Program to foster new technologies for civil aircraft maintenance and repair, use of bonded composite doublers on metal aircraft structures has been advanced. Research and validation of such doubler applications on U.S. certified commercial aircraft has begun. A specific composite application to assess the capabilities of composite doublers was chosen on a L-1011 aircraft for reinforcement of the corner of a cargo door frame where a boron-epoxy repair patch of up to 72 plies was installed. A primary inspection requirement for these doublers is the identification of disbonds between the composite laminate and the aluminum parent material. This paper describes the development of an ultrasonic pulse-echo technique using a modified immersion focus transducer where a robust signal amplitude signature of the composite/aluminum interface is obtained to characterize the condition of the bond. Example waveforms and C-scan images are shown to illustrate the ultrasonic response for various transducer configurations using a boron-epoxy/aluminum skin calibration test sample where disbonds and delaminations were built-in. The modified focus transducer is compatible with portable ultrasonic scanning systems that utilize the weeper or dripless bubbler technologies when an ultrasonic inspection of the boron-epoxy composite doublers installed on aircraft is implemented.

The initial results (stage 1) of this research were presented in the 96 'SPIE's Symposium on Nondestructive Evaluation Techniques for Aging Infrastructure & Manufacturing.' It was shown, that aging of adhesives and bonded joints can be evaluated non-destructively by vibration analysis, based on the internal friction (damping) effect. Good correlation between the specific damping capacity (SDC) and the shear strength of bonded joints, consisting of flat aluminum slabs as adherends and two kinds of polyurethane adhesives was found for three aging procedures. The present work is an additional step towards the target application -- developing a tool for characterizing the aging effect on joint strength in bonded devices. Unlike the rapidly developing field of Resonance US, this work is concentrating mainly on the damping capacity, which is directly correlated with joint strength. Additional adhesives and adherends as well as various geometries and sizes of the bonded joints were tested. The effect of the following factors was established: adhesive aging or shear strength, adherends, temperature, sample size (up to diameter of 14') and sample shapes (flats and rings). The results show that the prospects of practical application of the method are most promising, although they are better for some structures and worse for others. Some guidelines were determined in this work. For more reliable wide ranging guidelines, theoretical analysis is required. The only generally applicable way to do it is by numerical simulation of vibrational stresses.

Acoustography provides an alternative to the conventional point-by-point ultrasonic scanning approach commonly used for composite inspection. In acoustography, an area detector (sonoplate) is employed for near real-time imaging of composites. In this paper, we report on the application of acoustography for ultrasonic inspection of tight-radii in composite components/specimens, where conventional point-by- point ultrasonic scanning may not be practical and/or cost- effective.

Leaky Lamb wave (LLW) propagation in composite materials has been studied extensively since it was first observed in 1982. The wave is induced using a pitch-catch arrangement and the plate wave modes are detected by identifying minima in the reflected spectra to obtain the dispersion data. The wave behavior in multi-orientation laminates was well documented and corroborated experimentally with a very high accuracy. The sensitivity of the wave to the elastic constants of the material and to its boundary condition led to several studies where the elastic properties were inverted and the characteristics of bonded joint were evaluated. Recently, the authors modified their experimental setup to allow measuring dispersion curves at a significantly higher speed than ever recorded. A set of 20 angles of incidence along a single polar angle of a composite laminate are acquired in about 45 seconds. The reflection spectra are acquired in real time while filtering the high frequency noise providing reliable data at amplitude levels that are significantly lower that were acquired in prior studies. This new method makes the LLW a practical quantitative tool for both inversion of the elastic properties and characterization of flaws. The emphasis of the current study is on the detection and characterization of flaws. The composite is modeled as transversely isotropic and dissipative medium and the effect of flaws is analyzed and compared to the experimental data using a C-scan mounted LLW scanner.

A new capacitive array sensor has been developed for process verification and NDE of polymers and composites. Unlike existing dielectrometer technology, the new sensor incorporates several innovations to maximize sensitivity to material properties while minimizing the effects of temperature, humidity and electromagnetic interference. Conventional dielectric measurement systems require sensors to be embedded within a material and discarded after a single use. Furthermore, conventional sensors are so sensitive to environmental variables that cure monitoring is based solely on changes in the material ionic conductivity; no absolute measure of cure state is possible. The configuration of these new sensors greatly reduces sensitivity to environmental variables and permits external, rather than embedded, measurement making both post-process cure verification and NDE possible. Since the sensor is not discarded, the cost per measurement is greatly reduced.

The results of an investigation on the bulk electrical properties of carbon fiber cement composites (CFCC) with the prospect of developing a new nondestructive testing method are presented. The addition of carbon fibers to portland cement- based concrete or mortar improves the structural performance and at the same time significantly decreases the bulk electrical resistivity. This makes CFCC responsive to interrogation by electrical methods. This paper presents experimental data on the electrical behavior of CFCC as a multi-phase medium consisting of conducting and insulating phases. The volume electrical resistivity of CFCC samples was recorded as a function of curing time. The dependence of this electrical resistivity on the water-cement ratio, sand-cement ratio and volume fraction of carbon fibers in the mix was determined. Three different electrode configurations were investigated for their applicability in measuring electrical resistivity of CFCC samples.

Possibilities of direct radiothermography and indirect techniques for determination of temperature field homogeneity in operating microwave camera are considered. Mathematical model descriptions and experimental setups for realization of given techniques are brought. Results of model experiments are given. Prospects of systems creation for on-line NDE monitoring of thermosetting resins microwave reticulation are discussed.

Applying thermography in thermal non destructive testing (TNDT) gives the new possibilities in detection and defining of the defects in material. Because the temperature distribution on the material surface reflects the situation of its inside structure (including possible defects) each disturbances of temperature field can be used for estimation of the material homogeneity. Numerical methods enables the simulation of unsteady heat transfer through the material, giving the surface temperature distribution for various defects in material. Therefore they help a lot in TNDT research. The paper presents the results of the research carried out on the specimen having different defects under material surface, by means of both mentioned methods.

The influence of the waveguide flange, frequency of operation and liftoff on crack detection sensitivity using the dominant mode as well as the higher-order mode approaches are presented. The results indicate that the optimal choice of these parameters can significantly enhance crack detection sensitivity in practical applications.

The shaping of thin alumina ceramic plates with lasers appears to be an advantageous method for manufacturing. Unfortunately the failure rate is high because of crack initiation during the application of the high power laser. We have begun to address the issue of crack initiation by the use of in-process and post-process analysis. Here we present our results on the evaluation of cracks by optical, scanning laser, scanning electron and scanning acoustic microscopy. We present images of surface and subsurface micro-cracks generated at different power levels of our high power CO₂ system. The spatial variation of the Rayleigh wave velocity is measured by the V(z) curve technique. These preliminary data suggest that with improvement the V(z) technique may provide residual stress variation with high spatial resolution. The evaluation described should lead to insight into the fracture mechanism and eventually provide guidance for the choice of laser parameters (e.g., power, focus, scanning rate, emitting duration, or the like).

Conjugate wave holographic interferometry (CWHI) is a non- contact method for measuring deformation and strain on ordinary surfaces. It has not been widely used, however. In this paper three experiments are performed: the measurement of displacement in a simply supported beam, the measurement of the crack mouth opening displacement in a notched specimen, and a qualitative study of thermal expansion in a simply supported beam. The experimental results agreed well with the values predicted by theory. Additionally, the thermal expansion study indicated that CWHI can show the interaction of various parts of the test apparatus which can aid in interpreting experimental results. Overall, it can be concluded that CWHI is a useful method of isolating and quantitatively determining in-plane deformations with submicron precision. Based on these results, it appears that CWHI would be useful for certain nondestructive evaluation applications on components where displacements and/or strain would provide critical information. Although CWHI has only been demonstrated in a laboratory setting, its potential for nondestructive evaluation of structural composites and materials appears promising. One such example is its use for examining the behavior of graded composite materials under mechanical or thermal load. This is presently being investigated. In general, the method would be appropriate for applications where Moire interferometry could not be used.

Holographic interferometry with three illumination directions can be applied to determine all components of a displacement vector without previous knowledge of the main deformation direction. Combined with a microscopic arrangement this method is utilized for the investigation of the operating parameters of sensor micro-components. The interferometer is adapted to the microscopic demands by conjugate reconstruction. Matching holographic and microscopic requirements is the fundamental assumption for correct operation of the holographic microscope. By the application of all advantages of conjugate reconstruction the holographic microscope has been optimized in optical and numerical parameters for the evaluation of all components of the deformation vector. Phase shifting and carrier fringe techniques have been applied for interferogram evaluation according to the object shape and deformation behavior. When absolute values of the deformation were already determined, electro-optic holography can be used for routine measurements because of its time savings. The method was used for the calibration of cantilevers for micromechanical sensors, the determination of the deformations of a circular micromembrane, and a solder joint in a microelectronic printed circuit boards. The influence of different object orientation on the measurement results was investigated additionally.

The most widely utilized welding evaluation technique is visual testing (VT). Major limitations of visual inspection are the subjectivity of judgments of the acceptability of the weld and time required to perform the inspection. Machine vision technology can replace or augment VT to curtail these limitations. Pre-weld inspection is an effective and efficient means of determining size and fit-up problems as well as seam tracking. Post-weld inspection with machine vision is efficient in that it saves time, provides a record of the inspection, and establishes a quantitative standard for measurements. This paper discusses laser-based, structured- light machine vision technology and its application toward automated pre- and post-weld inspection. Practical industrial applications including small, laser-welded tailored blanks and larger fillet welds are discussed along with results of initial testing.

There is a very easy technique for detecting where the part of a structure undergoes failure due to fatigue loading; this technique if of great practical value in its employment to prevent fracture. It is well known that when yield stress is applied to a low-carbon steel plate, Lueders' lines become observable on its surface to the naked eye. It is a plausible hypothesis that the locations on the surface of the plate where the Lueders' lines appear are in a state of failure. The correlation of cyclic loading and Lueders' lines should confirm whether or not Lueders' lines reliably indicate where failure results from fatigue loading. The Ra value of the surface roughness of the specimen before and after the appearance of Lueders' lines is used to ascertain this correlation. The present paper takes up cyclic tensile loading with shoulder fillets as a concrete example of the correlation of failure and stress.

Ultrasonic technique has been increasingly used in recent years for nondestructive evaluation of defects and material properties (e.g., stiffness) in structural members made up of concrete, steel, wooden, and composite materials. Ultrasonic evaluation of structural members in the past has relied primarily on time-of-flight and velocity measurements. While these measurements lead to fair estimate of stiffness and detection of defects in structural members, the sensitivity of the measurements is not adequate to detect defects in their early stages. In order to enhance the sensitivity of the ultrasonic technique, this paper proposes to use ultrasonic signal amplitude measurements in conjunction with traditional velocity measurements. The conditions necessary to make repeatable amplitude measurements are described, and the data analysis techniques suitable for defect detection are discussed. Also, the advantages of signal amplitude measurement technique are presented using examples of defective steel, wooden, and composite members. The measurement and analysis techniques presented here can be easily generalized to structural members made from other materials such as concrete.