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Structural Integrity Assessment Using Laser Measured Surface Vibration

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Final rept. 1 Jan-18 Dec 2008

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This SERDP SEED Project was focused on extending the applicability of the NRL-developed structural acoustic fault monitoring technique using laser measured surface vibration to the materials and fabrics associated with historic buildings. In this regard, flexural wave inversion was successfully demonstrated numerically on thin plates of plaster, steel, and concrete and on thick plaster and steel plates with flaws at different depths. A new orthotropic inversion algorithm was developed and demonstrated on a similarly generated numerical data base on a wood slab. Two novel adaptive inversion approaches were developed and demonstrated, one using the flexural wave and generalized force algorithms sequentially, and the other based on high order equations of motion with unknown coefficients. A finite element-based study of a plaster dome ceiling with a detached section and a deconsolidated inclusion was carried out using acoustic speaker excitation. A model was developed for predicting flaw size detectability and for generalizing to other ceiling conditions. A new conformal spatial transform was developed and applied to the elliptical dome ceiling showing marked differences in the wave-number spectra associated with the two flaw types. Finally, a laboratory demonstration was carried out on a large wooden ceiling support beam in whose interior was created a small, thin cavity filled with sawdust. Direct observation of the band-averaged SLDV scans clearly detected and localized the defect. The orthotropic inversions indicated very large spatial variations in the wood beam elastic properties.

Subject Categories:

  • Lasers and Masers
  • Structural Engineering and Building Technology
  • Acoustic Detection and Detectors

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