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  • 1
    Electronic Resource
    Electronic Resource
    Noncontact monitoring of surface-wave nonlinearity for predicting the remaining life of fatigued steels (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 438-442 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A nonlinear acoustic measurement is studied for fatigue damage monitoring. An electromagnetic acoustic transducer (EMAT) magnetostrictively couples to a surface-shear-wave resonance along the circumference of a rod specimen during rotating bending fatigue of carbon steels. Excitation of the EMAT at half of the resonance frequency caused the standing wave to contain only the second-harmonic component, which was received by the same EMAT to determine the second-harmonic amplitude. Thus measured surface-wave nonlinearity always showed two distinct peaks at 60% and 85% of the total life. We attribute the earlier peak to crack nucleation and growth, and the later peak to an increase of free dislocations associated with crack extension in the final stage. This noncontact resonance-EMAT measurement can monitor the evolution of the surface-shear-wave nonlinearity throughout the metal's fatigue life and detect the pertinent precursors of the eventual failure. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1376668
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  • 2
    Electronic Resource
    Electronic Resource
    Noncontact measurement of ultrasonic attenuation during rotating fatigue test of steel (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3677-3684 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Acoustic resonance technique has been applied to monitor the fatigue damage process of steel pipes exposed to rotating bending fatigue. The technique incorporates a superheterodyne spectrometer and an electromagnetic acoustic transducer (EMAT). The EMAT was newly developed for this purpose, and uses the magnetostrictive mechanism of ferromagnetic metals and excites and detects axial shear waves traveling around the sample pipe with axial polarization. Noncontact ultrasonic spectroscopy permits the accurate determination of the resonant frequency and the attenuation coefficient throughout the fatigue life. The attenuation coefficient shows a sharp peak around 80%–90% of the life. The evolution is interpreted as reflecting dislocation multiplication, depinning, and formation of cell structures, which is supported by transmission electron microscopy observations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365489
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  • 3
    Electronic Resource
    Electronic Resource
    Acoustic study of dislocation rearrangement at later stages of fatigue: Noncontact prediction of remaining life (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1849-1854 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This study is devoted to clarifying the mechanism of the surface-shear-wave attenuation peak observed during rotating bending fatigue of carbon steels. We have developed electromagnetic acoustic resonance to make a contactless monitoring of the attenuation throughout the fatigue test. The attenuation peak occurs at a fixed fraction to lifetime, being independent of the bending stress (0.49–1.20 of the yield stresses) and the carbon content (0.22–0.45 mass %). Low-temperature heat treatment reduces the peak attenuation back to the previous value, which indicates a dominant contribution of dislocations. Microstructure observations with transmission electron microscopy, surface crack study with replicas and the acoustic measurements show that a large-scale change occurs in the dislocation structure (persistent slip bands to cells) at the attenuation peak and that it is triggered by the inward growth of cracks. This change is completed in a short time, a few percent of the total lifetime. The acoustic-resonance technique can be an important means for the exact prediction of the remaining life of fatigued steels.© 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1433178
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  • 4
    Electronic Resource
    Electronic Resource
    Anisotropic elastic-stiffness coefficients of an amorphous Ni–P film (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 4857-4862 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This study presents a complete set of effective elastic-stiffness coefficients of a Ni80P20 amorphous-alloy thin film deposited on an aluminum-alloy substrate by electroless plating. The film thickness was 12 μm. The electromagnetic-acoustic-resonance method detected resonance frequencies of the triple-layered specimens (film/substrate/film), which enabled us to determine all five independent elastic-stiffness coefficients of the film using known substrate elastic properties. The resulting coefficients were those of a transverse isotropic material. There was strong anisotropy between the in-plane and normal directions; the in-plane Young's modulus is larger than the normal Young's modulus by 34%, for example. The anisotropic coefficients can be interpreted by considering a micromechanics model for local incomplete cohesion (thin ellipsoidal voids) aligned parallel to the film surface. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1457542
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  • 5
    Electronic Resource
    Electronic Resource
    Resonance acoustoelasticity measurement of stress in thin plates (1992)
    Springer
    Research in nondestructive evaluation 4 (1992), S. 127-138 
    Details
    ISSN: 1432-2110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A computer-driven, swept-frequency measurement technique is developed on the basis of resonance birefringence acoustoelasticity to evaluate the stresses in thin plates. The resonance frequency depends on the thickness and the elastic wave velocity; they change with stress because of the Poisson effect and the acoustoelastic effect. The resonance frequency is obtained from the spectral response curve in the electric impedance of the piezoelectric transducer. The frequency displacement induced by acoustically coupling the transducer can be minimized by employing the resonance peak closest to the transducer fundamental frequency. To illustrate the method, the residual stress is measured in butt-welded aluminum alloy plates and is compared with the results of conventional methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01617523
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  • 6
    Electronic Resource
    Electronic Resource
    First principles calculation of the optical properties and stability of hydrogenated silicon clusters (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 1113-1119 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical properties and stability of hydrogenated silicon clusters are investigated using density functional pseudopotential calculation. The dipole transitions between the band-edge orbitals are allowed, in contrast to the indirect gap in bulk silicon. Evolution of a small amount of hydrogen atoms enhances the dipole transition, increasing the photoluminescence intensity. Further dehydrogenation creates gap states due to dangling bonds, which may decrease the photoluminescence intensity via nonradiative recombination processes. The Stokes shift is also estimated by calculating the relaxed structure of the excited state within the local density approximation. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520433
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