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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.

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.

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.

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.

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.

Acoustic emission baseline data was generated on fiberglass-epoxy composite specimens taken from booms of hydraulically operated aerial man-lift equipment. Acoustic emission signals were recorded while notched and notch-free specimens were tested in cyclic bending until failure. The transition to a load regime with no Kaiser effect was observed with an average K value of 0.58 measured for notch-free specimens. Frequency analysis of the stress waves caused by deformation of fiberglass specimens was helpful in determining appropriate frequency ranges for acoustic emission monitoring.

The internal microstructure of large melt‐grown paraffin (n‐eicosane, C20H42) single crystals was examined by the Lang x‐ray diffraction projection topographic technique. Crystal selection was facilitated by use of an electro‐optical system which permitted instantaneous display of Laue transmission x‐ray diffraction patterns on a television monitor. The crystals were oriented and topographic diffraction planes were selected by the use of a standard (001) stereographic projection plotted from computed angles between crystallographic planes. A second electro‐optical system which permitted direct viewing of the topographic images was use for rapid alignment of the Lang camera and ensured uniformly exposed topographs. X‐ray topographs were obtained from crystals in the as‐grown, plastically deformed, and γ‐irradiated states. The results indicate that both plastic deformation and γ irradiation caused marked changes in the microstructure of the crystals, and that x‐ray topography can be successfully exploited to determine such changes in hydrocarbon crystals.

The usual sensor for acoustic emission is the piezoelectric transducer. Although this transducer is readily available, reasonably inexpensive, and very sensitive to ultrasonic transients, it has several serious drawbacks as a transducer: It distorts the signals being measured, it exhibits resonances, it has limited bandwidth, it responds differently to surface acoustic waves and bulk waves (because of its large sensitive area), and its calibration is a matter of considerable uncertainty. Essentially, it is a qualitative transducer. Furthermore, it cannot measure local effects within a millimeter of an emission source, where the mechanisms causing the ultrasonic transient are presumably most clearly distinguishable. Optical transducers, on the other hand, have the great advantage of providing accurate, quantitative, highly localized information; they do not disturb the waves being measured and are not limited by frequency response.

A description of the current state-of-the-art of real-time X-ray diffraction systems for investigation of metal deformation processes is presented. Among the systems discussed are conventional, flash, and synchrotron X-ray sources and electro-optical X-ray detectors for rapid display and recording of X-ray diffraction patterns and topographic images. Applications considered are dynamic measurement of crystal deformation and lattice rotation accompanying tensile elongation, mechanical deformation of explosively loaded metal, and plastic deformation caused by high power ultrasound. Comments will be made as to the influence of the results of these measurements on presently accepted mechanical theories regarding these processes.

With the increased use of acoustic emission as a nondestructive testing tool, it has become extremely important to document and to understand the emissions characteristic of various modes of deformation and fracture. In the present work, results are reported of acoustic emission measurements made during mechanical deformation of indium single crystals. Although the metal indium is of little structural importance, it develops well‐delineated twins with associated acoustic emissions, and therefore affords an excellent medium with which to develop techniques and to generate interpretations which can be applied to structurally important materials. By recording the acoustic emission signals on a video‐tape recorder it was possible to play them back as often as desired and to observe them in slow and stop motion. The experimental results show that a correspondence exists between the duration of the acoustic signal and the volume of twinned material as determined by cinematographic observation of the generation ...

Acoustic emission monitoring has become a well‐recognized technique for the nondestructive evaluation of materials and structures. The usual procedure is to count the number of acoustic emission bursts and record either the total count or the burst rate. A rough measure of the burst amplitude or of the burst duration is obtained by ringdown counting or by peak or threshold detection. In this paper we demonstrate that further information is obtainable from accurate waveform determinations, which can be obtained by our optical method. We find that there is good agreement between at least some natural acoustic emission waveforms and theoretical seismic pulse waveforms.

X‐ray transmission asymmetric crystal topography was used to investigate the changes in defect structure which occur during the solid‐state polymerization of macroscopic single crystals of a diacetylene. Comparison of x‐ray topographs made before and after gamma‐ray‐induced polymerization indicate that lattice strain increases during polymerization, but important defect structures present in monomer crystals are retained in the polymer crystals. A cross‐pattern defect structure along 〈201〉 crystallographic directions is typically observed in both monomer and polymer single crystals.

A flash x‐ray diffraction system has been constructed which permits x‐ray diffraction patterns to be recorded from shaped charge jets. The system was tested by recording an x‐ray diffraction pattern from an aluminum jet 80 μsec after charge detonation with a single pulse of 70 nsec duration. This result represents the first successful recording of an x‐ray diffraction pattern from a shaped charge jet and indicates that the system should be an important new device for determination of internal jet structure.

The practical aspects of asymmetric crystal topography are described. In this technique, asymmetric Bragg diffraction is utilized to obtain a monochromatic and well collimated x‐ray beam large enough to cover the entire area of sample crystals. Thus, the recording of diffracted beams from a sample crystal provides topographic images of the entire sample crystal. Advantages of this technique are simplicity (no scanning device), excellent sensitivity to crystal imperfections (strain fields), and versatility. Information is given on the general alignment of the camera, magnification of the x‐ray beam width, preparation of the first crystal, and divergence of the beam due to the first crystal. The practical aspects of this topographic system are demonstrated using thick Cu and Ni crystals of various degrees of perfection. An inexpensive image intensifier is also described, which is used routinely to aid in the alignment of sample crystals.

Results are presented of an experimental study of ultrasonic wave diffraction for the acoustical modes propagating along the [112], [110], and [111] directions in single crystal sodium chloride. Laser beam optical probing in the Raman‐Nath regime was used to map the sound intensity distribution in the farfield of circular transducers. Calculations of the diffraction spread based on representation of the acoustic field by an angular spectrum of plane waves are in agreement with the experimental measurements. A simple method for estimating the diffraction spread based on the geometry of the inverse speed (slowness) surfaces is presented.

The orientation dependence of dislocation damping in the five hexagonal metals Mg, Cd, Be, Zn, and Ti has been predicted by calculation of the appropriate factors relating the stress field of the elastic waves to the slip systems in which the dislocations are moving. The four metals having basal slip systems have very similar qualitative behavior of the orientation factors. Titanium, with prismatic slip systems, has a quite different behavior and the orientation factors are smaller for all orientations than the values for the basal slip metals. For Zn, Cd, Mg, and Ti, the values of the orientation factors for standing waves (resonance technique) are larger than the corresponding values for the traveling waves (pulse‐echo technique). For Be, the orientation factors for both types of waves are nearly equal. Crystal orientations and wave types of particular interest for experimental study are delineated.

A cascaded image intensifier has been incorporated in a system which permits study of dynamic changes in x‐ray diffraction patterns. An RCA C70021A three stage, magnetically focused, image tube is coupled by a f/0.87 Super‐Farron lens to a 15.2 cm diam fluorescent screen to permit direct viewing of transmission x‐ray diffraction patterns. The image on the output phosphor is of sufficient intensity to be viewed directly, to be recorded cinematographically, or to be displayed by vidicon pick‐up on a television monitor.

Elastic wave velocities, particle displacement vectors, and directions of energy flux have been calculated and are given as a function of the polar angle θ in the five hexagonal metals Be, Cd, Mg, Ti, and Zn. Because of elastic transverse isotropy around the hexagonal axis, the wave characteristics are functions of the angle between the hexagonal axis and the direction of propagation in the crystal only. The results of these calculations are especially useful for experimental investigations utilizing the ultrasonic pulse‐echo technique.

A general method for determining crystallographic orientation by measurement of velocities of propagation of ultrasonic waves is given. The method supplements optical and x‐ray techniques and is primarily designed for orienting crystals to be used in ultrasonic pulse experiments. Aluminum and zinc single crystals are used as specific examples of the method. The required accuracy for such measurements is discussed.

Theoretical consideration is given to the equation governing the shapes of molten zones when they are not necessarily surfaces of revolution. This equation is seen to reduce to equations previously given for both vertical and horizontal molten zones when the shape is a surface of revolution. Solution of the equation governing the shape of the vertical molten zone when it is a surface of revolution gives corrected values for the maximum stable zone lengths for large rod radii. Detail consideration is given to the influence of a surface film on vertical zone stability.

General consideration is given to the analogies that exist between the propagation of light waves and the propagation of ultrasonic waves in anisotropic media. A historical survey is given of prior work in this area, followed by a comparison of present views of the analogies with those of other investigators. The inability to obtain a direct one‐to‐one analogy for all phenomena is discussed.

A flash x‐ray diffraction system is described which weighs less than 27.2 kg and which permits Laue transmission x‐ray diffraction patterns to be obtained with exposure times as short as several microseconds using multiple pulses of 60 nsec duration each. The system consists of a pulsed x‐ray generator incorporating a tungsten target beryllium window x‐ray tube and a specially designed collimator. Diffraction photographs are presented which permit comparison of the pattern obtained with the portable flash x‐ray diffraction system with that obtained using a conventional x‐ray diffraction system incorporating a heated filament tube.

A simple technique to estimate the angular beam width of acoustic modes propagating along arbitrary directions in crystals is proposed. This technique is based on considerations of the relationship between the energy flux vectors and the geometry of the inverse speed surfaces of the acoustic modes. Experiments on sodium chloride and quartz single crystals and fused quartz, utilizing optical beam probing techniques, confirm the usefulness of the present method.

A multiparameter system has been developed which, for the first time, permits simultaneous measurement of sufficient quantities to test all of the proposed mechanisms for the influence of high‐power ultrasound on metal specimens. Results of measurements using this system give new insight into the mechanical and thermal processes involved. Data are presented which show typical results obtained during tensile elongation of polycrystalline and single‐crystal aluminum specimens.

This paper will discuss the various nondestructive techniques which have been used or which are potentially useful for detection of fatigue damage. The ideal nondestructive testing technique would permit very early detection of fatigue damage so that proper assessment of the severity and rate of severity increase of the structural damage leading to failure can be made. Thus, the most sensitive systems would be capable of detecting motion, pileup, and breakaway of dislocations; the next most sensitive systems would be capable of detecting microcracks; the least sensitive systems would only be capable of detecting macrocracks. It is practically expedient to have nondestructive techniques which can successfully detect fatigue damage in each of these regimes since some components can tolerate larger amounts of fatigue damage or larger crack sizes than others without serious concern for the structural integrity of the component. It will be shown that the best nondestructive technique for detecting and sizing o...

A new, general definition is given for the critical angle of reflection in anisotropic materials. While the critical angle for reflection at a liquid‐isotropic‐solid interface can be written in the form sinθc = vI/vR, we show here that, in general, for an anisotropic solid, the right‐hand side of this expression must be modified by the factor cosφ/cosβ, where φ is the angle between the normal to the refracted wave in the solid and its energy flux vector and β is the angle between the energy flux vector and the component of the refracted wave normal on the interface. Numerical calculations have been made for this general definition for a water‐quartz interface for planes of incidence about the z axis (the xy Diane being the interface). These calculations are compared with the value of the critical angle as determined by the unmodified definition. It is shown that this earlier definition can lead to large errors when one uses the experimental technique of measuring the critical angle to evaluate the elastic...

The elastic constants c11, c12, c13, c33, c44 of single crystals of ice have been determined through the measurement of elastic wave velocities by an ultrasonic pulse method.

The critical angle of reflection for a wave incident from water upon the xy plane of quartz has been measured for planes of incidence about the z axis. These experimental measurements are compared with the theory that predicts that the critical angle for reflection from an interface of an anisotropic material occurs when the energy flux vector of the refracted wave becomes parallel to the interface. This differs from the usual definition of the critical angle as that angle for which the refracted wave normal becomes parallel to the boundary. The new definition of critical angle modifies the usual expression sinθc = VI/VR by the factor cosφ/cosβ as discussed in the previous abstract.

Theoretical consideration is given to the problem of reflection of a shock wave in water from an overlying ice layer. Expressions are derived for the sound field in the ice, in the water, and in the bottom.