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  • Open Access

    ARTICLE

    Estimating Changes in SHM Performance Using Probability of Detection Degradation Functions

    Jeffrey D. Kuhn1, Som R. Soni2
    Structural Longevity, Vol.2, No.1, pp. 1-10, 2009, DOI:10.3970/sl.2009.002.001
    Abstract Structural Health Monitoring (SHM) has been proposed by many researchers as a way to reduce maintenance cost and increase availability of aircraft fleets. But long term exposure to the aircraft environment can have a degrading effect on the performance of a given SHM system. Predictable performance of SHM systems after extended exposure to aircraft environmental factors is key to the effective implementation of SHM on aircraft fleets. This study shows how existing NDE reliability techniques can be extended to model changes in SHM system performance due to extended exposure to the aircraft environment. Degradation coef- ficients are added to the… More >

  • Open Access

    ARTICLE

    Series-connected Interdigitated Surface Acoustic Wave Sensors for Structural Health Monitoring

    Goutham R.Kirikera1,2, Sridhar Krishnaswamy2,3
    Structural Longevity, Vol.2, No.1, pp. 11-24, 2009, DOI:10.3970/sl.2009.002.011
    Abstract Active health monitoring using narrowband Raleigh-wave or modeselective Lamb-wave actuation and reception involves the use of a pair of matched multi-element transducer arrays. The spacing of the elements of the transducer arrays dictates the Lamb mode wavelength, and by appropriate choice of drive frequency, a specific mode can be selected. Typically, the elements of the transducer array are all connected in a parallel configuration and are used for both excitation and reception. It is shown in this paper that for reception a series connected transducer array results in better performance. Connecting multiple electrodes in a series configuration allows the summing… More >

  • Open Access

    ARTICLE

    Bonded Composite Patch Geometry Effects on Fatigue Crack Growth in Thin and Thick Aluminum Panels1

    S. Mall2,3, J. J. Schubbe1,4
    Structural Longevity, Vol.2, No.1, pp. 25-47, 2009, DOI:10.3970/sl.2009.002.025
    Abstract Effects of various geometric factors on the crack growth behavior of thin and thick aluminum panels repaired with asymmetric boron/epoxy bonded composite patch were investigated. Two widths, three patch lengths, three panel thicknesses and several patch-to-panel stiffness ratios were considered. Asymmetric repair introduces initial thermal curvature (or bending) in the repaired panels. The radius of curvature decreased with increase in the patch length in the thicker plates (6.350 or 4.826 mm thickness). On the contrary, the radius of curvature in the thin plate (i.e. 3.175 mm thickness) increased with increase in the patch length. The effects of stiffness ratio and… More >

  • Open Access

    ARTICLE

    A Novel Quadrant Array for Material Characterization and SHM of Orthotropic Plate-like Structures

    J Vishnuvardhan1, C V Krishnamurthy2, Krishnan Balasubramaniam1
    Structural Longevity, Vol.2, No.1, pp. 49-62, 2009, DOI:10.3970/sl.2009.002.049
    Abstract A novel small footprint sensor patch (single-quadrant double-ring SingleTransmitter Multiple-Receiver (STMR) array) has been developed and demonstrated successfully for the simultaneous reconstruction of the elastic moduli, material symmetry, orientation of principal planes and defect imaging. The sensor array contains a single transmitter in the center of the array and two sets of receivers at two different radii on a single quadrant. A slowness based reconstruction algorithm is used to determine elastic moduli from measured fundamental Lamb wave mode velocities using the direct received signals at different angles in a quadrant. A method proposed by Cowin and Mehrabadi (1987) is used… More >

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