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Previous constant amplitude laboratory tests have shown that supersonic particle deposition (SPD) can be used, as an alternative to mechanically fastened doublers, to enhance the structural integrity of aircraft structures. This paper compliments these findings via a numerical study into the potential for SPD scarf repairs to repair simulated corrosion in thin aircraft structural components. The results of this study, when taken in concert with the results of prior applications to full scale fatigue tests and laboratory tests, suggest that a SPD scarf repair to simulated corrosion damage subjected to load spectra representative of helicopters, fighter, maritime, and transport aircraft has the potential to give lives that are compare favourably with either the original design objectives or the stated operational life of the aircraft.

A formed laser source, using a four-element lenticular array, is used in the ablative regime to generate select, narrowband, acoustic plate waves. The arrangement of the array produces acoustical signals that have frequencies compatible with the response of the broadband capacitive air-coupled transducer used in this study. A simplified concept is presented to explain the effect of a line array source on the frequency content of acoustic waves. The analytical model for a point pulse surface displacement is derived from the point load solution to Lamb's problem. The point pulse displacement elements of a line array source are summed mathematically, taking into account all applicable propagation modes and dispersion of plate waves. The model considers only the out-of-plane displacement of the antisymmetric plate modes to represent the detection capability of the broadband receiver. The distribution function of the laser beam energy profile is modified to depict the actual energy distribution that illuminates the surface of the plate. Filtering functions are made compatible with the sensitivity of the broadband receiver so as to retain only the detected frequencies in the model. The theoretical model showed good agreement with experimental results.

Proper preventative diagnosis of different art objects, including wooden, bronze and marble sculptures, frescoes, and paintings (on canvas, wood, metal, and glass), is very important for conservation purposes. Various advanced ultrasonic imaging methods for analysis and assessment of art objects can bring about drastic changes in the regular evaluation and inventory carried out by museums and can bring advanced, powerful, and new techniques for objective assessment of physical conditions of museum resplendence. Using these methods, it will be possible to plan ad hoc repair works on art objects, and, as a result, we will preserve our heritage. The goal of this review is to introduce recent advances in acoustical imaging and quantitative acoustical imaging for the evaluation of art objects. Physical principles as well as experimental fundamentals for quantitative characterization of the contrast response in the acoustic imaging, together with the recent results of technical developments in this field, are d...

Non-contact generation and detection of acoustic and ultrasound waveforms is of practical importance, since it permits making acoustic and ultrasonic measurements at elevated temperatures, in corrosive and other hostile environments, in geometrically difficult to reach locations, in outer space and doing this at relatively large distances from the test structure. Non-contact acoustical and ultrasonic techniques currently available are laser generation, optical interferometric detection, electromagnetic acoustic transducers (EMATs), air(gas)-coupled systems and hybrid combinations of the above. The present paper will describe how several such systems have been used in unique materials characterization applications.

There is currently widespread use of high-strength steel tendons for prestressing and post-tensioning of concrete structures and as suspension cables for long-span bridges. Tendons normally consist of one or more seven-wire, helically wound steel strands or solid rods. There are more than 130,000 prestressed bridges in the United States that contain these tendons, and approximately 3,000 new bridges are constructed each year. The prestressing tendons are critical structural elements because the forces in the tendons counteract tensile stresses in the concrete that result from loads acting on a bridge. The tendons are frequently inaccessible for visual inspections and there is currently no accepted nondestructive evaluation technique to assess the condition of these tendons. The goal of this research is to examine ultrasonic stress measurement techniques for the condition assessment of prestressing tendons. This information could be used to compare the actual force in the tendon with its design va...

A novel non-contact nondestructive evaluation system is proposed for sensing bond quality in tow-placed graphite/PEEK thermoplastic composites. The inspection tool consists of a hybrid ultrasonic system which employs laser generation of narrow-band surface waves with fiberoptic light delivery, and signal detection by air-coupled transduction. The fiberoptic link enhances flexibility and remoteness of the laser source from the test piece. The system output is not influenced by the poor light reflectivity of the test graphite/PEEK material. Signal narrow-banding by light spatial modulation enhances the measurement sensitivity and avoids detrimental material ablation while allowing control of the surface wave penetration depth. The theory of the laser generation of narrow-band surface waves is reviewed and the generation efficiency as a function of the wave propagation direction in the composite is discussed. The inspection capabilities of the proposed system are demonstrated by successful detection of a series of subsurface defects in a tow-placed unidirectional AS-4/APC-2 cylinder provided by Boeing Commercial Aircraft. The defects examined include regions of poor consolidation, inter-laminar linear porosity (voids elongated along the fibers with 1.5% volume fraction), and delamination or interlaminar weakness. The ultrasonic inspection unit is non-contact, flexible, light-weight and allows for high inspection rates. These characteristics, coupled with a large signal-to-noise ratio of the measurements, show promises for the use of the proposed sensor in on-line control of the thermoplastic tow-placement process with in situ consolidation.

We demonstrate that electronic shearography with thermal loading can be effectively applied to the nondestructive detection of debonds in thick polyurethane/steel structures usually employed in the hulls of military ships. A compact fiber-optics shearographic interferometer has been developed that allows remote full-field measurements in real time. Three known debonds in a polyurethane/steel test panel are clearly detected by observing their increased deformation as they cool down after the application of a thermal load. It is also shown that the debond edges can be identified. The results obtained indicate that the shearographic interferometer is well-suited for field detection and sizing of debonds in such panels. Future refinements to the system will include the use of high-power, pulsed illumination for the imaging of large areas and consequent real-time mapping of possible debonds.

A beam-steering C-scan system for laser generation and detection of ultrasound in opaque solids has been developed. For ultrasound detection, the system uses a confocal Fabry-Perot interferometer that is stabilized at its high-sensitivity point by implementing a novel procedure that does not require a reference beam. This stabilization procedure effectively compensates for slowly varying (up to 2 Hz) disturbances and, more important, for any change in the interferometer illumination conditions while probing different scanning points. For the latter reason, the proposed stabilization appears to be more effective than previous approaches for high-sensitivity ultrasound detection in beamsteering scans. Noise performance and sensitivity limit of the system are evaluated. Ultrasonic echoes are detected in aluminum samples having optically rough surfaces with single-pulse generation signal-to-noise ratios on the order of 20 dB. A C-scan inspection is performed where a known defect in the test piece is successfully detected by time-of-flight gating of the ultrasonic signals.

This paper presents experimental observations of the influence of a contact transducer on ultrasound measurements in materials. Through-transmission optical detection of the ultrasonic waves at the transducer/sample interface shows an amplitude attenuation of the order of 1.6 dB (peak-to-peak) due to the intrusive presence of the transducer. A similar result is confirmed in pulse-echo measurements. Alternatively, no significant effect of the contact transducer on the frequency content of the measured ultrasonic waves is observed. It also appears that the measured attenuation in ultrasound amplitude is primarily due to the loading of the sample by the contact transducer.

Resonant ultrasound spectroscopy is the study of spectra obtained by forced mechanical resonance of samples by swept frequency excitation. A novel apparatus is used to measure the amplitude/frequency resonance spectrum of a right rectangular parallelepiped specimen of AS4/3501-6 carbon epoxy composite material ([0, 60, 120] 192 lay-up) at 1 °C intervals between −177 °C and 25 °C. It is important to know the mechanical properties of this material at low temperatures for underwater, polar and space applications. The spectra indicate increasing stiffness with decreasing temperature and phase transitions. The damping decreases slightly with decreasing temperature. Analysis of the resonance spectrum, calculation of theoretical resonance spectrum, and computation of elastic stiffness tensor will be discussed.

The resonance spectrum of any specimen is dependent on its symmetry, density, geometry, elastic properties, and the boundary conditions. By using specimens with simple known geometry and models including speci‐ men symmetry, resonance ultrasound spectrosopy can determine the full elastic stiffness tensor to great precision with one measurement. This measurement is fast, taking less than a minute with state‐of‐the‐art instrumentation, making it appropriate for measuring properties as a function of temperature. Parts per million changes in specimen density, geometry, elastic moduli, temperature, and boundary conditions can be detected in carbon fiber reinforced epoxy composite materials with resonance ultrasound spectroscopy. It is important to know the mechanical properties of carbon fiber reinforced epoxy composite materials at low temperatures for underwater, space, and polar applications. The amplitude/frequency resonance spectra of four different lay‐ups of AS4/3501‐6 carbon fiber reinforced epoxy comp...

Air-coupled ultrasound, a noncontact, nondestructive testing technique, has detected splits, checks, delaminations, cleavage, and voids in various materials. The system has inspected highly anisotropic and inhomogeneous materials such as wood and wood products, with surfaces layers of gesso, gesso and linen, paper, and wood veneer. Two paintings were tested; one was an oak-cradled panel painting and the other was illustration board mounted on hardboard. The air-coupled ultrasound technique yielded information additional to that provided by visual examination, xeroradiography, and infrared thermography.

Synchrotron white beam transmission topography of GaAs as previously reported by the authors relied on scanning specimen and film synchronously through the incident x-ray beam to record transmission topographic images en film. Sometimes the total dose required for reasonable contrast on film carried with it enough thermal deposition to cause elastic warping of the wafer. To escape these problems, a real time system was assembled. This system included an image intensifier, a solid state camera, a computer board to frame-grab and digitize images, and appropriate image processing software. With this system, a three inch specimen was scanned from edge to edge in one minute. At this scan rate, the incident x-ray beam had to be significantly attenuated to avoid saturating the intensifier output.

Although nondestructive techniques have been used almost exclusively to detect macroscopic defects in structures or devices, it has become increasingly evident that it is both practical and cost-effective to expand the role of nondestructive evaluation to include all aspects of materials production. In recent years, classical nondestructive testing techniques have been augmented by more sophisticated methods for characterizing the microstructure and the associated physical and chemical properties of materials.

Residual thermomechanical stresses in a Nicalon® SiC/7740 glass composite system were measured directly. Residual stresses for both single-tow and two-dimensional cloth-reinforced samples were completely described via a digital microphotoelastic technique. Normal stresses approaching 4 MPa were observed in this composite system that had a thermal expansion coefficient mismatch of only 1.8%. The advantages of using this direct, full-field technique over other theoretical and composite model approaches are also discussed.

Special problems associated with ultrasonic wave propagation in anisotropic materials are discussed. Included in the treatment are modes of propagation, energy flux deviation, diffraction beam spreading, and th6 influence of non-linear effects. Comments will be made with respect to the possibility of successfully implementing ultrasonic tomographic imaging in anisotropic materials.

Comparisons of driving and demographic characteristics were made on 407 driver fatalities (DFs) and 407 motorists convicted of driving under the influence (DUI). Significantly more DUI offenders (DOs) than DFs were men and had previous DUIs, accidents, license suspensions, and weekend "index" events. DFs with a blood or brain alcohol concentration (BAC) of 100 or above mg/dL matched most closely with DOs on negative driving events, "index" event days, and demographics. Conversely, DFs with negative BACs differed significantly with DOs on virtually all characteristics. High-BAC DFs and DOs may well be drawn from the same subpopulation of deviant drivers, whereas DFs with negative BACs seem similar to licensed drivers in general.

Single layer silicon carbide cloth reinforced glass composites were fabricated and subjected to three-point bending in order to develop better models of failure mechanisms. Acoustic emission (AE) monitoring was also performed during the bend tests to help isolate these mechanisms. During the basic flexural tests, discrete failure modes, which were often not visible from specimen surfaces, displayed their existence through characteristic load-deflection curve unloading regions and abrupt changes in acoustic activity. Microscopic three-point bend tests were then performed to elaborate on the results of the conventional bend tests. Observations made during the microscopic bend tests provided a one-to-one correlation with load-deflection curve anomalies and acoustic emission activity. As a result of the different mechanical, optical and acoustical techniques used, discrete failure mechanisms for the cloth reinforced ceramic matrix composite (CMC) were conclusively established.

White beam transmission topography was used to image defect structures in gallium arsenide single crystal substrates representative of those used for microwave integrated circuit fabrication. A scanning topographic camera was developed for Beamline X-19C at the National Synchrotron Light Source. Acquiring film topographs within a particular range of scan rates and x-ray fluxes was found to produce distorted images. The distortions were shown to be thermoelastic, arising from inhomogeneous deposition of thermal energy through the absorption of residual x-rays. The problem could be circumvented using faster scans with some sacrifice in spatial resolution. Real time electrooptic topographs were recorded using x-ray fluxes about one percent of those used for the film topographs. The potential for reducing the flux requirement to even lower levels which would be accessible to flash x-ray generators is considered.

The normalized change in ultrasonic "natural" velocity as a function of stress and temperature was measured in a unidirectional laminate of T300/5208 graphite/ epoxy composite using a pulsed phase locked loop ultrasonic interferometer. These mea surements were used together with the linear (second order) elastic moduli to calculate some of the nonlinear (third order) moduli of this material.

Long- and short-range acoustic-signal interaction with surface-breaking cracks and geometric boundaries of the rail-wheel tread area are presented in this article. Ultrasonic signals are generated using a laser-line source of varying length and distance from a crack and are detected with a 1-MHz contact transducer to map the sound field behind the crack in the near, intermediate, and far fields of the insonified region. The factors that affect the behavior of a laser-generated surface acoustic wave propagating along the tread area of a rail wheel are discussed. A signal normalization method is proposed to help in sensing the presence of a crack from the transmitted signal unaffected by the boundary effect of the complicated wheel geometry, diffraction of the acoustic wave around the crack tip, and source-to-crack length ratio and separation distance.

Laser generation and air-coupled detection were combined as a hybrid ultrasonic technique for the inspection of surface flaws in rails. Narrowband acoustic signals were generated using a formed laser source by focusing the laser light to a point and to a line on the surface of the rail. The pulse energy, and therefore the intensity of the laser source, varied such that the generated signal transitioned from the weak thermoelastic to the strong ablative regime. The detection of flaws using a laser-generated surface acoustic wave, in the presence of surface flaws, was compared between both point and line laser sources operating under different pulse energy levels. The line source was found to be more sensitive to the presence of surface flaws than a point source. The sensitivity of the laser-generated acoustic signal appeared to be independent of the severity of the flaw and, within the ablative regime, independent of the laser-pulse energy. Theoretical analysis is provided to explain the underlying cause that influences the interaction of a formed laser-generated surface acoustic wave to surface flaws and how this sensitivity may vary between the thermoelastic and ablative regimes.

A narrow band laser-generated acoustic signal was created using a 4-element lenticular array. This arrangement of the array produces an acoustical signal with frequency content that is compatible with the response of a noncontact and remote broadband receiver, such as a capacitive air-coupled transducer. To support the experimental observations, a simplified concept is presented to explain the effect of a line array source on the frequency content of a surface acoustic wave. The analytical model solution for the wave front shape is derived from the point load solution of Lamb's problem that represents the displacement of a surface acoustic wave generated by an ablative line array. The distribution function, which was used for the model to represent the laser light energy, was tailored to depict the actual energy distribution that illuminates the lenticular array. Filtering functions are applied to the resultant surface displacement function to retain frequencies similar to those detected by the broadband 50 kHz-2.25 MHz receiver. The theoretical model showed good agreement with experimental results.

This paper provides a brief overview of some of the techniques for imaging acoustic waves inside and on the surface of solids. Optical methods show the influence of material anisotropy on acoustical wave propagation in transparent solids. Multiple-pulse holography images waves on the surface of materials without the necessity of scanning. Optical interferometry permits non-contact detection of unmodified acoustic emission waveforms. Electron acoustics maps the internal structure of microelectronic chips not shown with conventional electron microscopy. Non-contact ultrasound provides process control for composite tape placement, detects defects in composite panels, and cracks in railroad rails. Acoustic microscopy images an embedded optical fiber in a thick composites.

The goal of this research was to examine ultrasonic stress measurement techniques for the condition assessment of prestressing tendons. Acoustoelastic measurements were made in prestressing rods and strands, and constants are reported that relate the change in ultrasonic velocity to the change in stress. The effects of dispersion in prestressing tendons, which act as circular wave guides for ultrasonic waves, were measured and evaluated. For this research, narrow-band, noncontact Electromagnetic Acoustic Transducers (EMATs) were designed to launch and receive ultrasonic waves propagating within the tendons.

Scanning Acoustic Microscope (SAM) is used as an important nondestructive test tool in semiconductor reliability evaluation and failure analysis. However, inspections of the adhesive interface between thin die and Cu lead frame has proven difficult as the reflected signals from the die top and bottom are superimposed. In this paper, in order to overcome this difficulty, a new signal processing method based on a deconvolution technique combined with wavelet transform is discussed. If we use the conventional deconvolution technique without wavelet transform then the processed signal becomes very noisy because the waveform of the reflected echo is quite different from the incident waveform. On the other hand, in our method, only the waveform similar to the incident waveform is extracted from the echo signal, first by using the wavelet transform, and then a deconvolution is applied. Performances of this method are demonstrated through computer simulations using model signals and experiments for the fabricated semiconductor samples. Satisfactory results were obtained.

We have investigated several linear and nonlinear ultrasonic methods to study different cure conditions of adhesive bonds in an aluminum/adhesive/aluminum system. In this paper, we report on some theoretical aspects and experimental results obtained using a normal incidence harmonic generation setup in which the sample is embedded in water. In our approach, ultrasonic tone burst signals at increasing power levels and over a wide frequency range are coupled into a sample in order to analyze its nonlinear resonance behavior. Using a local strain analysis in the linear approximation, we will discuss excitation-power dependent changes observed particularly in the higher harmonic frequency transfer spectrum.

A series of fifteen mechanical test specimens made from a nickel-based superalloy were supplied by Siemens Westinghouse in order that Asymmetric Crystal Topography (ACT), an x-ray diffraction technique, be used to confirm which samples were single crystal samples and which samples contained low angle grain boundaries. It had been determined (by another investigator) prior to the manufacture of the mechanical test specimens, which “raw” material contained low angle grain boundaries and which material was single crystalline in nature. Siemens Westinghouse requisitioned the production of mechanical test specimens from several manufacturers, with specific requirements that some of the samples were to be single crystalline and that other samples were to contain low angle grain boundaries within the gauge length. Once completed, Siemens Westinghouse wanted to confirm that the samples were properly manufactured and selected a representative portion of the mechanical test samples to be examined via ACT.

This paper describes nondestructive x-ray characterization techniques which detect macroscopic and microscopic defects, determine the overall crystallographic perfection, and detect any unwanted secondary crystals both on the external surface as well as in the interior of single crystal blades. The method of Asymmetric Crystal Topography for diffraction imaging the surfaces of single crystal turbine blades and the method of White Beam Transmission Topography for diffraction imaging through the thickness of single crystal turbine blades are both discussed and illustrated with representive diffraction images (topographs). It is clear that the images gained from these methods have a capability for providing information about the details of crystalline perfection (or lack thereof) in nickel-based alloy single crystal turbine blades. Such information can provide considerable leverage for the crystal grower to help in adjusting processing variables to enhance quality of a critical product. And the same methods of topography can conceiveably provide tools for evaluating the finished product in a way which has not been available to date.

A beam-steering laser ultrasonic C-scan system and a laser generation/aircoupled detection hybrid ultrasonic system are here presented. The C-scan system employs a confocal Fabry-Perot interferometer for ultrasound detection, which is stabilized by using only the object beam. This stabilization effectively compensates for slowly-varying disturbances and, more importantly, for changes in the interferometer illumination conditions while probing different scanning points. The hybrid ultrasonic system proves to be well-suited for on-line control of the tow-placement process in thermoplastic composites. This system features fiberoptic high-power laser light delivery for enhanced remoteness, safety and flexibility. Narrow-band surface wave generation improves the sensitivity of the measurements, while retaining thermoelastic generation conditions. In addition, the theory of the narrow-band generation of surface acoustic waves by spatially-modulated illumination sources is improved by accounting for possible str...

To date, the nondestructive determination of the integrity and true strength of an adhesively bonded structure still represents a significant challenge for the NDE community. While much progress has been made in recent years, theoretically as well as experimentally,1–4 which has led to increased interest in nonlinear ultrasonic techniques, it is often times difficult to experimentally realize some of these potential methods.

Technological advances in recent years have led to the development of single crystal, nickel based alloys for turbine blade applications. Among the problems encountered with single crystal turbine blades is the determination of the overall crystalline perfection of the final blades. The existing method relies upon chemical etching and visual inspection. While the problems associated with visual inspection are self evident, there are intricacies associated with the etch process. Following visual inspection of the etched blades, those which meet with approval are then “unetched.” That is, a mechanical peening process is used to remove the shiny finish produced from the etch. The final step in the crystal perfection/orientation process for single crystal turbine blade inspection is to determine the crystallographic orientation of a “good” blade by performing Laue x-ray diffraction, in the back-reflection configuration, at one point on the blade. It is interesting to note that none of the inspection processes above can determine the crystalline perfection of the interior of the blades; as will be discussed below, this is a legitimate concern.

X-ray diffraction in metals and alloys involves only low energy x-rays because of the typical interatomic spacings encountered in single crystals of these materials. Since these low energy diffracted x-rays are readily absorbed in alloys involving elements of higher atomic numbers, a diffraction imaging technique in transmission is not necessarily trivial for these materials. Several nickel-based alloy single crystal turbine blades have been examined using the x-ray diffraction technique known as “White Beam Transmission Topography”, (WBTT), in combination with the extremely high flux of low energy x-rays available from the National Synchrotron Light Source at Brookhaven National Laboratory. The technique is described, and diffraction images are presented and discussed for several specific cases.

Initial on-orbit calibration results of the advanced visible and near infrared radiometer (AVNIR) onboard ADEOS were presented. When ADEOS returned over the Japan ground station mask on Sept. 1, 1996, AVNIR was first activated to evaluate performance. AVNIR calibration was then conducted using the reference signal sources (internal lamps, natural target data, NASA's airborne sensor data, etc.). The evaluation indicated that AVNIR has sufficient sensitivity to function as a high- resolution imager and is useful for the land monitoring, though some noises are to be removed.

In this paper, we describe a method to monitor changes in the diameter of through holes in thin plates. The method has the potential for applications in the industry.

Several emerging technologies affording new opportunities for the nondestructive evaluation of aging aircraft structures. Among these technologies are ultrasonic attenuation detection of fatigue and corrosion damage; non-contact ultrasound including laser-laser, laser-EMAT, laser-air, and air-air; laser based acoustic emission source identification; full-field double-pulse holographic imaging; non-linear assessment of adhesive bond quality; x-ray diffraction topographic imaging of the quality of nickel based alloy single crystal turbine blades.

Anti-seize lubricant commonly used on threaded fasteners makes it difficult to prepare surfaces adequately for magnetic particle and liquid penetrant testing. In high temperature applications, the lubricant forms a tenacious residue on the threaded fastener. An alternative surface examination technique requiring minimal surface preparation would reduce inspection cost and duration. Two types of threaded fasteners, reactor pressure vessel closure studs and turbine casing studs, have been targeted for investigation. Eddy current techniques requiring minimal surface preparation and capable of detecting flaws are being developed for these two applications. Other advantages of eddy current inspection over magnetic particle testing and liquid penetrant testing include the absence of consumable materials, capability to provide permanent digital records, and the potential for automation.

This paper describes the results of the comparison of a variety of nondestructive evaluation techniques to monitor the development of fatigue damage in thick graphite/epoxy composites. Three inch long, one inch square cross-section test specimens were fatigue tested in compression. Most specimens incorporated stress (strain) concentration notches at their mid- section in order to localize the primary fatigue damage regions in an optimum location for nondestructive monitoring. The nondestructive techniques evaluated were ultrasonic B- and C- scan, ultrasonic velocity and attenuation, ultrasonic second harmonic generation, acoustic microscopy, acoustic emission, thermography, real-time high-speed digital/video laser speckle decorrelation, magnetic resonance imaging, radio-opaque penetrant enhanced x-radiography, and eddy current. Mechanical resonance spectroscopy was used to measure the second order (linear) elastic moduli. Optical and electron microscopy on cut and polished specimens were used to verify the results of the nondestructive tests.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Synchrotron white beam transmission topography of GaAs as previously reported by the authors relied on scanning specimen and film synchronously through the incident x-ray beam to record transmission topographic images on film. Sometimes the total dose required for reasonable contrast on film carried with it enough thermal deposition to cause elastic warping of the wafer. To escape these problems, a real time system was assembled. This system included in image intensifier, a solid state camera, a computer board to frame-grab and digitize images, and appropriate image processing software. With this system, a three inch specimen was scanned from edge to edge in one minute. At this scan rate, the incident x-ray beam had to be significantly attenuated to avoid saturating the intensifier output. The topographs acquired by this real time system were very similar to the ones recorded on film, but they needed only about 0.0002 of the dose originally used for the film. 5 refs., 2 figs.

Damage in composite materials has been detected using ultrasonic nondestructive techniques.1–5 These studies were all performed on thin composite samples subjected to either a quasi-static tensile force or a constant amplitude tensile fatigue load. Changes in basic ultrasonic parameters, attenuation or velocity, were used as an indicator of damage. Damage was detected once a sufficient amount was present. Attenuation was observed to be dependent on the frequency of the ultrasonic transducers that provides an indication of the dispersive nature of these materials.

X-ray diffraction topography and infrared imaging techniques were used in situ with aluminum and zinc specimens undergoing high-power insonation using a 20 kHz ultrasonic horn. X-ray topographic techniques allowed for a nonintrusive study of the mechanical alterations in the structure of the metal specimens, while the infrared system allowed for a study of the specimens’ thermal properties. It should be noted that all testing was performed in real-time with x-ray and infrared images recorded simultaneously on video tape.

Fiber reinforced polymer composites have become quite popular in recent years and have been used for a wide variety of applications ranging from sports equipment to advanced aircraft components. There has recently been considerable interest in the behavior of thick composite laminates under compressive loadsl. This interest stems from the development of novel materials for applications in submersed vessels. A submersible vessel hull is one of the few structures in which the material would experience nearly pure compressive loads. For a structure which is designed to be brought to the depths normally encountered by submarines, a skin of material several inches thick is required. In order to utilize composites for this purpose research into the compressive strength and fatigue life of these materials is needed. In addition, in service inspection techniques must be developed to assess the integrity of such a structure.