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  • 1
    Electronic Resource
    Electronic Resource
    Approximate model for wave propagation in piezoelectric materials. II. Fibrous composites (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 2347-2354 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A continuum mixture theory with microstructure is developed for guided wave propagation in unidirectional fibrous composites of piezoelectric materials exhibiting hexagonal symmetry. The theory leads to the simple system of coupled equations for the actual composites which retain the integrity of the propagation process in each constituent but allow them to coexist under analytically derived interaction parameters. As a consequence of the analysis, effective mixture properties of the composite are obtained in the zero-frequency (static) limit. The utility of the resulting equations is demonstrated by studying the propagation of harmonic waves in the system. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369548
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  • 2
    Electronic Resource
    Electronic Resource
    An approximate model for wave propagation in piezoelectric materials. I. Laminated composites (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 2337-2346 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A continuum mixture theory with microstructure is developed for guided wave propagation in bilaminated periodic composites of piezoelectric materials. The theory leads to the simple governing coupled equations for the actual composites which retain the integrity of the propagation process in each constituent but allow them to coexist under analytically derived interaction parameters. As a consequence of the analysis, effective mixture properties of the composite are obtained in the zero-frequency (static) limit. The accuracy of the approximation is demonstrated by direct comparison with the exact solution for the propagation of harmonic waves in the system. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369547
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  • 3
    Electronic Resource
    Electronic Resource
    Thermoelectric detection of spherical tin inclusions in copper by magnetic sensing (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6495-6500 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Inclusions and other types of imperfections in metals can be nondestructively detected by noncontacting magnetic measurements that sense the thermoelectric currents around such flaws when the specimen is subjected to directional heating and cooling. This article presents experimental data for the magnetic field produced by thermoelectric currents around surface-breaking spherical tin inclusions in copper under external thermal excitation for different lift-off distances between the sensor and the surface of the specimen. The diameter of the inclusions and the lift-off distance varied from 2.4 to 12.7 mm and from 12 to 20 mm, respectively. A fairly modest 0.7 °C/cm temperature gradient in the specimen produced peak magnetic flux densities ranging from 1 to 250 nT. These results were found to be in good agreement with recently published theoretical predictions [P. B. Nagy and A. H. Nayfeh, J. Appl. Phys. 87, 7481 (2000)]. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1322591
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  • 4
    Electronic Resource
    Electronic Resource
    On the thermoelectric magnetic field of spherical and cylindrical inclusions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 7481-7490 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It was recently discovered that inclusions and other types of inhomogeneities can be nondestructively detected by thermoelectric measurements in an entirely noncontact way by using high-sensitivity superconducting quantum interference device magnetometers to sense the weak thermoelectric currents around the affected region when the specimen is subjected to directional heating or cooling. In this article we present theoretical models capable of predicting the magnetic field produced by thermoelectric currents around spherical and cylindrical inclusions under external thermal excitation. We investigated how the magnetic signal to be detected depends on (i) the relevant physical properties of the host and the inclusion, (ii) the size of the inclusion, (iii) the depth of the inclusion below the surface of the specimen, (iv) the polarization of the magnetometer, (v) the lift-off distance of the magnetometer from the specimen, and the (vi) direction and (vii) strength of the external heating or cooling applied to the specimen. The analytical models presented are numerically evaluated to illustrate the strength and polarization of the magnetic field for different lift-off distances and inclusion depths. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373013
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  • 5
    Electronic Resource
    Electronic Resource
    Role of anisotropy in noncontacting thermoelectric materials characterization (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 225-231 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Inclusions and other types of imperfections in metals can be nondestructively detected by noncontacting magnetic measurements that sense the thermoelectric currents that appear when the specimen is subjected to directional heating and cooling. The detectability of small imperfections is ultimately limited by the intrinsic thermoelectric anisotropy and inhomogeneity of the material to be inspected. This article presents an analytical method for calculating the magnetic field produced by thermoelectric currents in anisotropic materials under two-dimensional directional heating and cooling. Experimental results from a textured Ti–6Al–4V titanium-alloy plate are shown to be in very good agreement with the predictions of this model. The described analytical method can be used to optimize thermoelectric inspection procedures and to evaluate the macroscopic texture of metals from their characteristic magnetic signatures. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1416852
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  • 6
    Electronic Resource
    Electronic Resource
    Leaky Lamb waves in fibrous composite laminates (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 4531-4538 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of experimental measurements and theoretical calculations on ultrasonic leaky Lamb-wave propagation in fiber-reinforced, unidirectional composite laminates are presented. With the Lamb wave vector oriented parallel to the fiber direction, dispersion curves of phase velocity versus frequency and plate thickness have been constructed from measurements of ultrasonic reflection from fluid-loaded composite plates. The experimental results are supported by a theoretical model of Lamb-wave propagation in the composite plate. The model begins with an approximate calculation of the effective, homogeneous, transversely isotropic elastic behavior of a unidirectional composite laminate in the long-wavelength limit, using a two-step procedure based on alternating layered media. This intermediate continuum result is then incorporated into a calculation of the ultrasonic reflection coefficient of a fluid-loaded anisotropic plate, which is assumed to approximate the fibrous composite laminate. Good quantitative agreement with the model is found if the fiber volume fraction is taken to be an adjustable parameter. However, not all portions of the dispersion curves predicted by the model can be observed in the data. It is conjectured that relative differences in mode coupling account for this discrepancy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336268
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  • 7
    Electronic Resource
    Electronic Resource
    Acoustic-wave reflection from water/laminated composite interfaces (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 1328-1333 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analytical results are presented for the reflection of acoustic waves from liquid-laminated composite interfaces. The composite is oriented such that the laminates are stacked normal to the x3 directions with propagation confined to the x1-x2 plane. The fluid-composite interface is assumed to be normal to x2. Because of the complex microstructure of composites, continuity conditions exist on both the macro (liquid/composite interface) and micro (laminate interface) scales. Because of the number and nature of these conditions, exact solutions are exceedingly difficult, if not impossible, to obtain. As an alternative, we formulate an approximate analysis in which the composite medium is replaced by a homogeneous, yet dispersive, medium. In the process of replacing the composite with such a material model, the microcontinuity conditions are utilized. Numerical results are presented to demonstrate the dispersive behavior of leaky surface waves on the composite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339959
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  • 8
    Electronic Resource
    Electronic Resource
    Generalized formula for the surface stiffness of fluid-saturated porous media containing parallel pore channels (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1827-1829 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface stiffness of a fluid-saturated porous solid is defined as the ratio between a small change in capillary pressure and the average displacement of the boundary due to the resulting rise or fall of the fluid level in the pore channels. When the surface pores are structurally open, the surface stiffness is entirely due to the stiffness of the microscopic fluid membranes extended by capillary forces over the surface pores. Due to interfacial tension between the immiscible wetting fluid in the pores and nonwetting fluid (air) above the surface, essentially closed-pore boundary conditions can prevail at the interface. It has recently been shown that the surface stiffness of a porous material containing cylindrical pores can be calculated simply as the surface tension of the saturating fluid divided by the static permeability of the porous solid [P. B. Nagy, Appl. Phys. Lett. 60, 2735 (1992)]. In this letter, we show that the same simple relationship can be generalized for the surface stiffness of fluid-saturated porous media containing parallel prismatic pore channels of any number, size, or shape. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115416
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  • 9
    Electronic Resource
    Electronic Resource
    Thermoelastic waves in a laminated composite with a second sound effect (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2733-2738 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The propagation of thermoelastic harmonic waves in bilaminated periodic waveguide is studied in the context of the generalized theory of thermoelasticity. A continuum mixture theory is developed for waves traveling in the direction parallel to the layering. As a result, the problem is transformed into a quasi-one-dimensional one. The resulting approximate expressions are found useful in obtaining a qualitative description of the response. The symmetric mode of an exact solution is used to check the validity of the mixture theory. Quasi-elastic and quasi-thermal modes are investigated for the cases when the thermal relaxation time is either included or neglected. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363191
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  • 10
    Electronic Resource
    Electronic Resource
    Ultrasonic reflection and guided waves in fluid-coupled composite laminates (1990)
    Springer
    Journal of nondestructive evaluation 9 (1990), S. 51-69 
    Details
    ISSN: 1573-4862
    Keywords: Composites ; ultrasound ; lamb waves ; leaky waves ; layered media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In this article, we review the present authors' own approach to elastic wave modeling and experimental measurements in fibrous composites. The materials and structural problem addressed here concerns the propagation of guided elastic leaky waves in continuous-fiber composite plates. The guided wavevector may be oriented along the fibers or in an arbitrary azimuthal direction. These plates can be structured as single-layer or multilayer media, where each successive layer contains fibers in different directions. Further, the multiaxial plates are loaded by a fluid or by different fluids on each boundary. Each of these cases has been investigated both experimentally and theoretically. It is found that some reasonable approximations lead to significant simplifications in treating these complicated structures and yet preserve the accuracy needed to make useful predictions of realistic sound wave behavior. Comparisons of the results of model calculations and experimental measurements of ultrasonic reflection show very good agreement over a wide range of experimental parameters and types of composites. Suggestions are offered at the end of the article for extensions of the modeling to account for non-ideal behavior of the materials and the chosen means of interrogation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566384
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