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Iowa State University

1993

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Articles 1 - 30 of 107

Full-Text Articles in Physics

Lattice-Dynamical Study Of The Premartensitic State Of The Cu-Al-Be Alloys, Lluís Mañosa, Jerel L. Zarestky, Thomas A. Lograsso, Dwight W. Delaney, C. Stassis Dec 1993

Lattice-Dynamical Study Of The Premartensitic State Of The Cu-Al-Be Alloys, Lluís Mañosa, Jerel L. Zarestky, Thomas A. Lograsso, Dwight W. Delaney, C. Stassis

Ames Laboratory Publications

Neutron-scattering techniques have been used to study the premartensitic state of a family of Cu-Al-Be alloys, which transform from the bcc phase to an 18R martensitic structure. We find that the phonon modes of the TA2[110] branch have very low energies with anomalous temperature dependence. A slight anomaly at q=2/3 was observed; this anomaly, however, does not change significantly with temperature. No elastic peaks, related to the martensite structure, were found in the premartensitic state of these alloys. The results are compared with measurements, performed under the same instrumental conditions, on two Cu-Al-Ni and a Cu-Zn-Al ...


Inclusion Of Charge Correlations In Calculations Of The Energetics And Electronic Structure For Random Substitutional Alloys, Duane D. Johnson, F. J. Pinski Oct 1993

Inclusion Of Charge Correlations In Calculations Of The Energetics And Electronic Structure For Random Substitutional Alloys, Duane D. Johnson, F. J. Pinski

Duane D. Johnson

Currently, the coherent-potential approximation (CPA) implemented via the multiple-scattering theory of Korringa, Kohn, and Rostoker (KKR) gives the best first-principles description of the electronic structure for random substitutional alloys. However, the total energy has an important component of electrostatic energy missing, namely, that arising from the correlation of charges with varying atomic environments. We develop a ‘‘charge-correlated’’ CPA method (cc-CPA) which includes (some) local environmental charge correlations within the KKR-CPA method. We investigate the cc-CPA energetics for several alloys and show that the formation energies are in better agreement with experimental results. These calculations show that the excess charge on ...


Photoemission Study Of Ce-Catalyzed Oxidation Of W(110) And W(111), C. Gu, C. G. Olson, David W. Lynch Oct 1993

Photoemission Study Of Ce-Catalyzed Oxidation Of W(110) And W(111), C. Gu, C. G. Olson, David W. Lynch

Physics and Astronomy Publications

Different catalytic oxidation effects of Ce on W(110) and W(111) were observed with photo- emission spectroscopy. On Ce-covered W(110), the top W layer is quickly oxidized to a surface monoxide at room temperature. Oxidation is almost halted after the completion of one monolayer of WO. On Ce/W(111), instead of WO, WO3 grows on the surface under the same conditions. The monolayer suboxide formation found on Ce/W(110) and Ce/Ta(110) (as reported earlier) is a direct consequence of the most densely packed structure of the bcc (110) surfaces. The more effective oxidation promotion ...


Correlation Functions For Ionic Motion From Nmr Relaxation And Electrical Conductivity In The Glassy Fast-Ion Conductor (Li2s)0.56(Sis2)0.44, Ivar Svare, Ferdinando Borsa, D. R. Torgeson, Steve W. Martin Oct 1993

Correlation Functions For Ionic Motion From Nmr Relaxation And Electrical Conductivity In The Glassy Fast-Ion Conductor (Li2s)0.56(Sis2)0.44, Ivar Svare, Ferdinando Borsa, D. R. Torgeson, Steve W. Martin

Materials Science and Engineering Publications

The Li7 NMR spin-lattice relaxation and the electrical conductivity in the typical glassy fast-ion conductor (Li2S)0.56(SiS2)0.44 are discussed from models of Li+ionic motion with distributions of activation energies, as well as from stretched-exponential time-correlation functions. The measured correlation times from the two effects differ by two orders of magnitude, and the derived distributions are shifted greatly relative to each other. We relate the great differences to percolation around the high barriers in the distribution. We present a phenomenological theory that yields good quantitative fits to the observed NMR relaxation with a Gaussian distribution, and ...


Resistivity Of The High-Temperature Metallic Phase Of Vo2, Werner W. Schulz, Philip B. Allen, Renate M. Wentzcovitch, Paul C. Canfield Aug 1993

Resistivity Of The High-Temperature Metallic Phase Of Vo2, Werner W. Schulz, Philip B. Allen, Renate M. Wentzcovitch, Paul C. Canfield

Paul C. Canfield

Measurements are reported on the electrical resistivity ρ(T) along the c axis of a single crystal of VO2, from the metal-insulator transition at T=333 K up to 840 K. The temperature dependence is very linear, and a fit to Bloch-Grüneisen theory gives a residual resistivity ρ0=65 μΩ cm and a ratio ρ(840 K)/ρ0=8. With the help of a local-density-approximation band-structure calculation, we further pursue the conventional (Bloch-Boltzmann) interpretation by extracting the electron-phonon coupling constant λ=1.1 and the mean free path l(800 K)=3.3 Å. The short mean free path implies ...


Enhanced Differential Magnetostrictive Response In Annealed Terfenol‐D, N. Galloway, M. P. Schulze, R. D. Greenough, David C. Jiles Aug 1993

Enhanced Differential Magnetostrictive Response In Annealed Terfenol‐D, N. Galloway, M. P. Schulze, R. D. Greenough, David C. Jiles

Ames Laboratory Publications

The field and pressure dependencies of the magnetostriction of Tb0.316Dy0.684Fe1.982 have been measured in a grain‐oriented rod after thermally annealing for 1 day at 850 °C and for 4 days at 950 °C in an argon atmosphere. The results of the heat treatment are a fivefold increase in the strain coefficient d 33(=dλ/dH) and a 100% increase in the maximum strain (λ). There was also an increase in the λ‐vs‐Hhysteresis. Under compressive uniaxial stress there was virtually no bulk change in magnetostrictive strain until the ...


Dynamical X-Ray Diffraction From An Icosahedral Quasicrystal, S. W. Kycia, Alan I. Goldman, Thomas A. Lograsso, Dwight W. Delaney, D. Black, M. Sutton, E. Dufresne, R. Brüning, B. Rodricks Aug 1993

Dynamical X-Ray Diffraction From An Icosahedral Quasicrystal, S. W. Kycia, Alan I. Goldman, Thomas A. Lograsso, Dwight W. Delaney, D. Black, M. Sutton, E. Dufresne, R. Brüning, B. Rodricks

Ames Laboratory Publications

We present direct evidence of dynamical diffraction of x rays from a quasicrystal. High-resolution x-ray-diffraction measurements of the Al-Pd-Mn face-centered icosahedral quasicrystal were performed, revealing a mosaic full width at half maximum of less than 0.001°. In a second experiment, the anomalous transmission of x rays (the Borrmann effect) was observed. These measurements show that nearly perfect quasicrystals may be grown to centimeter-size dimensions allowing x-ray techniques based upon dynamical diffraction to be brought to bear on the analysis of icosahedral structures.


Three-Point Correlation Functions In Uniformly And Randomly Driven Diffusive Systems, K. Hwang, Beate Schmittmann, R. K. P. Zia Aug 1993

Three-Point Correlation Functions In Uniformly And Randomly Driven Diffusive Systems, K. Hwang, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

Driven far away from equilibrium by both uniform and random external fields, a system of diffusing particles with short-range attractive forces displays many singular thermodynamic properties. Surprisingly, measuring pair correlations in lattice-gas models with saturation drives, we find little difference between the uniform and random cases, even though the underlying symmetries are quite distinct. Motivated by this puzzle, we study three-point correlations using both field-theoretic and simulation techniques. The continuum theory predicts the following: (a) The three-point function is nonzero only for the uniformly driven system; (b) it is odd under a parity transformation; and (c) there exists an infinite ...


A Model For Hysteretic Magnetic Properties Under The Application Of Noncoaxial Stress And Field, Martin J. Sablik, S. W. Rubin, L. A. Riley, David C. Jiles, David A. Kaminski, S. B. Biner Jul 1993

A Model For Hysteretic Magnetic Properties Under The Application Of Noncoaxial Stress And Field, Martin J. Sablik, S. W. Rubin, L. A. Riley, David C. Jiles, David A. Kaminski, S. B. Biner

Center for Nondestructive Evaluation Publications

Although descriptions of the effect of stress on spontaneous magnetization within a single domain already exist, there remains no adequate mathematical model for the effects of noncoaxial magnetic field and stress on bulk magnetization in a multidomained specimen. This article addresses the problem and provides a phenomenological theory that applies to the case of bulk isotropic materials. The magnetomechanical hysteresis model of Sablik and Jiles is thus extended to treat magnetic properties in the case of noncoaxial stress and magnetic field in an isotropic, polycrystalline medium. In the modeling, noncollinearity between magnetization and magnetic field is taken into account. The ...


Measurements Of Magnetic Circuit Characteristics For Comprehension Of Intrinsic Magnetic Properties Of Materials From Surface Inspection, Z. J. Chen, Michael K. Devine, David C. Jiles May 1993

Measurements Of Magnetic Circuit Characteristics For Comprehension Of Intrinsic Magnetic Properties Of Materials From Surface Inspection, Z. J. Chen, Michael K. Devine, David C. Jiles

Ames Laboratory Publications

A transfer function is presented for calculating magnetic field and flux density inside a test material as a result of surface measurement. By considering flux leakage, we introduce a parameter η, called the leakage coefficient, which can be experimentally determined. It is introduced into the equations to make the transfer function more practical. The distribution of field inside a test material is then discussed in accordance with a surfacemagnetic charge model.


Magnescope: Applications In Nondestructive Evaluation, Michael K. Devine, David C. Jiles, A. R. Eichmann, David A. Kaminski, S. Hardwick May 1993

Magnescope: Applications In Nondestructive Evaluation, Michael K. Devine, David C. Jiles, A. R. Eichmann, David A. Kaminski, S. Hardwick

Ames Laboratory Publications

This paper describes recent results obtained with the Magnescope, which has been used on location in industrial environments and has successfully detected impending fatigue failure, creep damage, applied stress, and microstructural differences. It is concluded that the device provides a useful nondestructive method for evaluating the mechanical properties of materials through the measurement of their structure sensitive magnetic properties.


Analytic Model Calculation Of Magnetic Field In A Magnetic Half‐Space Due To Surface Magnetic Charge, Z. J. Chen, Madhav Rao Govindaraju, David C. Jiles May 1993

Analytic Model Calculation Of Magnetic Field In A Magnetic Half‐Space Due To Surface Magnetic Charge, Z. J. Chen, Madhav Rao Govindaraju, David C. Jiles

Ames Laboratory Publications

By analogy with electrostatic field, a simple analytic model is presented on the distribution of magnetic field inside a test material as a result of surface inspection with a magnetic probe. According to this model, the penetration depth of the magnetic field is defined and the permeability of the material at different depths is calculated. Finally, the magnetic flux inside the inspection head when placed on samples of different thicknesses is calculated and compared with experimental results.


Evaluation Of Fatigue Damage In Steel Structural Components By Magnetoelastic Barkhausen Signal Analysis, Madhav Rao Govindaraju, Andrew Strom, David C. Jiles, S. B. Biner, Z. J. Chen May 1993

Evaluation Of Fatigue Damage In Steel Structural Components By Magnetoelastic Barkhausen Signal Analysis, Madhav Rao Govindaraju, Andrew Strom, David C. Jiles, S. B. Biner, Z. J. Chen

Ames Laboratory Publications

This paper is concerned with using a magnetic technique for the evaluation of fatigue damage in steel structural components. It is shown that Barkhausen effect measurements can be used to indicate impending failure due to fatigue under certain conditions. The Barkhausen signal amplitude is known to be highly sensitive to changes in density and distribution of dislocations in materials. The sensitivity of Barkhausen signal amplitude to fatigue damage has been studied in the low‐cycle fatigue regime using smooth tensile specimens of a medium strength steel. The Barkhausen measurements were taken at depths of penetration of 0.02, 0.07 ...


Modeling Of Micromagnetic Barkhausen Activity Using A Stochastic Process Extension To The Theory Of Hysteresis, David C. Jiles, Levent B. Sipahi, G. Williams May 1993

Modeling Of Micromagnetic Barkhausen Activity Using A Stochastic Process Extension To The Theory Of Hysteresis, David C. Jiles, Levent B. Sipahi, G. Williams

Materials Science and Engineering Publications

Recent work by Bertotti [IEEE Trans. Magn. MAG‐24, 621 (1988)] and others has shown that it is possible to model the micromagnetic Barkhausen discontinuities at the coercive point using a two‐parameter stochastic model. However, the present formulation of the model is restricted to limited regions of the hysteresis curve over which dM/dH is approximately constant and whendH/dt is held at a constant rate. A natural extension of this model is to take the basic result, in which the level of Barkhausen activity in one time period is related to the activity in the previous time ...


Comprehensive Analysis Of Barkhausen Emission Spectra Using Pulse Height Analysis, Frequency Spectrum, And Pulse Wave Form Analysis, Levent B. Sipahi, David C. Jiles, D. Chandler May 1993

Comprehensive Analysis Of Barkhausen Emission Spectra Using Pulse Height Analysis, Frequency Spectrum, And Pulse Wave Form Analysis, Levent B. Sipahi, David C. Jiles, D. Chandler

Materials Science and Engineering Publications

The dependence of magnetic Barkhausen emissions (MBE) upon both field excitation and detection frequencies and excitation wave form was studied in order to investigate two of several crucial factors which affect the emissions. Sinusoidal, triangular, and square wave forms were used to generate the MBE and the pulse height spectra, frequency spectra, and pulse wave forms of these signals were analyzed. The frequency spectra of sinusoidal and triangular alternating field excitations showed similar behavior but the spectrum under square wave excitation was different due to the existence of high frequency components during square wave switching. As yet, no common standard ...


Strain Tolerant Microfilamentary Superconducting Wire, Douglas K. Finnemore, Theodore A. Miller, Jerome E. Ostenson, Louis A. Schwartzkopf, Steven C. Sanders Feb 1993

Strain Tolerant Microfilamentary Superconducting Wire, Douglas K. Finnemore, Theodore A. Miller, Jerome E. Ostenson, Louis A. Schwartzkopf, Steven C. Sanders

Iowa State University Patents

A strain tolerant microfilamentary wire capable of carrying superconducting currents is provided comprising a plurality of discontinuous filaments formed from a high temperature superconducting material. The discontinuous filaments have a length at least several orders of magnitude greater than the filament diameter and are sufficiently strong while in an amorphous state to withstand compaction. A normal metal is interposed between and binds the discontinuous filaments to form a normal metal matrix capable of withstanding heat treatment for converting the filaments to a superconducting state. The geometry of the filaments within the normal metal matrix provides substantial filament-to-filament overlap, and the ...


Scattering Of A Sagittal Surface Acoustic Wave From A Large Amplitude Ridge Or A Deep Groove, A. Baghai-Wadji, A. A. Maradudin Jan 1993

Scattering Of A Sagittal Surface Acoustic Wave From A Large Amplitude Ridge Or A Deep Groove, A. Baghai-Wadji, A. A. Maradudin

Review of Progress in Quantitative Nondestructive Evaluation

In [1] we presented a Green’s function theory for obtaining the frequencies of acoustic surface shape resonances of sagittal polarization associated with an isolated ridge or groove of rather general shape on a planar, stress-free surface of an isotropic elastic medium (for details we refer to [2]). It was shown that employing Green’s second theorem, and using tensor Green’s functions associated with the boundary value problem, the initial coupled partial differential equations can be converted into a coupled system of integral equations. Further, it was shown that by discretizing the boundary and using the method of moments ...


Application Of Diffracto Sight Ot The Nondestructive Inspection Of Aircraft Structures, Jerzy Komorowski, Ronald W. Gould, David L. Simpson, Omer Hageniers Jan 1993

Application Of Diffracto Sight Ot The Nondestructive Inspection Of Aircraft Structures, Jerzy Komorowski, Ronald W. Gould, David L. Simpson, Omer Hageniers

Review of Progress in Quantitative Nondestructive Evaluation

The D Sight optical set up was first assembled nearly ten years ago at Diffracto Ltd. It has received several patents, the first of which was in the United States [1]. Since the mid 1980’s, D Sight has been successfully applied to surface quality inspections, particularly in the automotive and plastics industries. Recently, Komorowski et al. [2–5] have shown several potential applications of D Sight in the field of nondestructive inspection of aircraft structures. The technique has been shown to be particularly effective in locating nonvisible impact damage on large surfaces of aircraft structures built from composite materials ...


Interaction Of Gaussian Acoustic Beams With Plane And Cylindrical Fluid-Loaded Elastic Structures, Jinguang Zhang, Dale E. Chimenti, Smaine Zeroug, Leopold B. Felsen Jan 1993

Interaction Of Gaussian Acoustic Beams With Plane And Cylindrical Fluid-Loaded Elastic Structures, Jinguang Zhang, Dale E. Chimenti, Smaine Zeroug, Leopold B. Felsen

Review of Progress in Quantitative Nondestructive Evaluation

Nonspecular reflection effects for ultrasonic beams incident from a fluid onto solid surfaces have been studied continuously since the early investigations by Schoch [1]. He calculated the reflected held for both the fluid-loaded halfspace and the plate using a series expansion for the phase of the reflection coefficient. A more accurate expression for Gaussian beam reflection has been derived by Bertoni and Tamir [2], who approximated the reflection coefficient by leading terms in a Laurent series, performing the resulting integrals analytically. Many researchers have contributed to this literature from the experimental [3–5], theoretical [6,7], and numerical sides [8 ...


Laser Generation Of Rayleigh And Lamb Waves For Ultrasonic Nondestructive Testing, R. Costley Jr., Yves H. Berthelot Jan 1993

Laser Generation Of Rayleigh And Lamb Waves For Ultrasonic Nondestructive Testing, R. Costley Jr., Yves H. Berthelot

Review of Progress in Quantitative Nondestructive Evaluation

Laser ultrasonics has been the focus of several research efforts over the last two decades. The main advantage of the technique is its noncontact nature which alleviates the problem of sensor coupling inherent in conventional techniques. However, laser ultrasonics has some limitations When operated in the thermoelastic regime, where no damage is inflicted on the surface of the specimen, the signal-to-noise ratio (SNR) is very small, particularly when compared with conventional piezoelectric generation.[1] Several authors have proposed increasing the SNR by producing a source with spatial periodicity designed to enhance a particular wavelength. Royer and Dieulasaint [2] have used ...


Advances In Pultiple-Pulse Radio-Frequency-Gradient Imaging Of Solids, John Marohn, David N. Shykind, Margat H. Werner, Daniel P. Weitekamp Jan 1993

Advances In Pultiple-Pulse Radio-Frequency-Gradient Imaging Of Solids, John Marohn, David N. Shykind, Margat H. Werner, Daniel P. Weitekamp

Review of Progress in Quantitative Nondestructive Evaluation

Magnetic resonance imaging (MRI) has become the premier tool for the non-destructive evaluation of soft tissue in living systems [1]. Established liquid-state MRI strategies are generally found to be inappropriate for the imaging of rigid solids, because the linewidth for nuclear magnetic resonance in solids is orders-of-magnitude larger than in liquids. Methods currently under development for the NMR imaging of solids either involve the use of very large (fringe-field) magnetic field gradients to encode spatial information over very short periods of time [2], or employ multiple-pulse line-narrowing techniques that prolong a solid’s apparent transverse relaxation time [3–7]. In ...


Laser Ultrasonic And Photoacoustic Characterization Of Subsurface Structures, Meng-Chou Wu, F. Raymond Parker, William P. Winfree Jan 1993

Laser Ultrasonic And Photoacoustic Characterization Of Subsurface Structures, Meng-Chou Wu, F. Raymond Parker, William P. Winfree

Review of Progress in Quantitative Nondestructive Evaluation

There is a strong interest in applying laser ultrasonic and photoacoustic techniques to the NDE of some high performance structures, for example, the actively cooled panels of the National Aero-Space Plane. Both laser ultrasonic and photoacoustic techniques have been developed for years. Much significant work has been done on either the generation of waves, the mechanisms [1–3] or various techniques for the detection of these waves [4–6]. A few applications being pursued or conducted since the early stage of the development for these techniques [5–7]. However, there is little work concentrating on the interaction of these waves ...


Ultrasonic Propagation Through A Surface With A Step Discontinuity: Validation Of A Hybrid, Gauss-Hermite Ray Tracing Beam Model, M. Greenwood, J.-L. Mai, A. Minachi, I. Yalda-Mooshabad, R. Bruce Thompson Jan 1993

Ultrasonic Propagation Through A Surface With A Step Discontinuity: Validation Of A Hybrid, Gauss-Hermite Ray Tracing Beam Model, M. Greenwood, J.-L. Mai, A. Minachi, I. Yalda-Mooshabad, R. Bruce Thompson

Review of Progress in Quantitative Nondestructive Evaluation

This research continues our cooperative effort to study the effects of large-scale surface roughness on ultrasonic transmission through interfaces and updates our previously-reported results [1], The Center for Nondestructive Evaluation has developed a model for the propagation of ultrasound through a surface and into an isotropic metal and this model is undergoing experimental validation at Battelle PNL. Once validated, this model will be used as an engineering tool to study the effects of surface conditions upon an ultrasonic inspection of nuclear reactor components. The goal is to quantify and develop requirements to limit the adverse effects of surface conditions during ...


Numerical Calculation Of Diffraction Coefficients In Anisotropic Media, J. Temple, L. White Jan 1993

Numerical Calculation Of Diffraction Coefficients In Anisotropic Media, J. Temple, L. White

Review of Progress in Quantitative Nondestructive Evaluation

Ultrasonic inspection is used to detect and size crack-like defects in pressure vessels and pipework used in the nuclear industry. Reliable inspection can only be achieved if the inspection technique is understood, is optimised and subsequently applied correctly. Austenitic steels are used because of their corrosion resistance and toughness. Welds and centrifugally cast materials tend to crystallise with grains larger than the ultrasonic wavelength required to achieve the desired resolution in the inspection and thus appear anisotropic. Since the grains in a weld grow along the, varying, directions of maximum heat flux during cooling, the welds are inhomogeneous as well ...


High-Speed Time-Resolved Holography For Imaging Transient Events, Michael Ehrlich, James W. Wagner Jan 1993

High-Speed Time-Resolved Holography For Imaging Transient Events, Michael Ehrlich, James W. Wagner

Review of Progress in Quantitative Nondestructive Evaluation

A time-resolved holographic system was developed to study detonation dynamics in dispersed solid particulate explosives. This required a system capable of recording a rapid sequence of exposures during the approximate 1/µs lifetime of the detonation event.


Progress Towards The Application Of Laser-Ultrasonics In Industry, Jean-Pierre Monchalin Jan 1993

Progress Towards The Application Of Laser-Ultrasonics In Industry, Jean-Pierre Monchalin

Review of Progress in Quantitative Nondestructive Evaluation

Ultrasonic techniques are widely used in industry for thickness gauging, flaw detection and materials characterization. The ultrasonic waves are usually generated and detected by piezoelectric transducers and coupled to the inspected part either by direct contact or through a water bath or a water jet. Although widespread and generally cost effective, these conventional ultrasonic techniques suffer from essentially two severe limitations, which impact upon their use for on-line process control and the inspection of advanced materials.


Rapid Inspection Of Composites Using Laser-Based Ultrasound, Andrew Mckie, Robert C. Addison Jr. Jan 1993

Rapid Inspection Of Composites Using Laser-Based Ultrasound, Andrew Mckie, Robert C. Addison Jr.

Review of Progress in Quantitative Nondestructive Evaluation

Current techniques for automated ultrasonic inspection of airframe structures can only be used to examine limited areas which have large radii of curvature. Manual inspection techniques are required in areas having small radii. Laser-based ultrasound (LBU) offers the potential to rapidly inspect large-area composite structures having contoured geometries, without restriction to large radii of curvature [1–4]. The key components that comprise an LBU rapid inspection system are the generation and detection lasers, a 2D scanner and a suitably fast data acquisition system. These must be integrated to provide an areal scan rate of at least 100 ft2/hr based ...


Source Efficiency And Sensor Detectability Factors In Laser Ultrasonics, James Wagner Jan 1993

Source Efficiency And Sensor Detectability Factors In Laser Ultrasonics, James Wagner

Review of Progress in Quantitative Nondestructive Evaluation

Perhaps the greatest fundamental deterrent to the application of current laser ultrasonic technology has been the fact that the detection sensitivity or detectability of laser receiver systems, compared with their piezoelectric counterparts, is rather poor. That is to say that in general, and especially on a dollar-for-dollar basis, piezoelectric transducers are able to detect much smaller surface displacements than can easily be detected by laser methods. As will be discussed shortly, there are several strategies which may be used to overcome these detectability shortcomings. Indeed, several of these strategies have been investigated at the laboratory level and some implemented in ...


Improved Laser Interferometry For Ultrasonic Nde, Peter Nagy, Gabor Blaho, Laszlo Adler Jan 1993

Improved Laser Interferometry For Ultrasonic Nde, Peter Nagy, Gabor Blaho, Laszlo Adler

Review of Progress in Quantitative Nondestructive Evaluation

In spite of its obvious advantages over conventional contact and immersion techniques, laser interferometry has not yet become a practical tool in ultrasonic nondestructive evaluation since its sensitivity is insufficient in most practical applications. Part of the problem is that the maximum signal-to-noise ratio often cited in scientific publications and manufacturers’ specifications cannot be maintained on ordinary diffusely reflecting surfaces. Although these surfaces reflect a fair amount (5–50%) of the incident laser light, this energy is randomly distributed among a large number of bright speckles. Unless the detector happens to see one of these bright speckles, the interferometer’s ...


Laser Ultrasound For The Study Of Thin Sheets, C. Edwards, A. Al-Kassim, S. B. Palmer Jan 1993

Laser Ultrasound For The Study Of Thin Sheets, C. Edwards, A. Al-Kassim, S. B. Palmer

Review of Progress in Quantitative Nondestructive Evaluation

Laser ultrasound is now an accepted and mature technology. However it is still seeking its first fully commercial industrial application although there are several potential uses in prototype form. The major advantage of laser ultrasound is that it is a non contact technique and can therefore be used on hot or moving components. The pulsed laser source generates simultaneously longitudinal and shear bulk waves and Rayleigh surface waves. When the material is in the form of a thin sheet the latter propagate as Lamb or plate waves providing the ultrasonic wavelength is greater than the sheet thickness.