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Structural Engineering and Mechanics
  Volume 28, Number 5, March30 2008, pages 525-548

Quantitative nondestructive evaluation of thin plate structures using the complete frequency information from impact testing
Sang-Youl Lee, Guillermo Rus and Taehyo Park

    This article deals the theory for solving an inverse problem of plate structures using the frequency-domain information instead of classical time-domain delays or free vibration eigenmodes or eigenvalues. A reduced set of output parameters characterizing the defect is used as a regularization technique to drastically overcome noise problems that appear in imaging techniques. A deconvolution scheme from an undamaged specimen overrides uncertainties about the input signal and other coherent noises. This approach provides the advantage that it is not necessary to visually identify the portion of the signal that contains the information about the defect. The theoretical model for Quantitative nondestructive evaluation, the relationship between the real and ideal models, the finite element method (FEM) for the
forward problem, and inverse procedure for detecting the defects are developed. The theoretical formulation is experimentally verified using dynamic responses of a steel plate under impact loading at
several points. The signal synthesized by FEM, the residual, and its components are analyzed for different choices of time window. The noise effects are taken into account in the inversion strategy by designing a filter for the cost functional to be minimized. The technique is focused toward a exible and rapid inspection of large areas, by recovering the position of the defect by means of a single accelerometer, overriding experimental calibration, and using a reduced number of impact events.
Key Words
    inverse problem; quantitative non-destructive evaluation (QNDE); real and ideal model; finite element method (FEM); impact testing; noise effect.
Sang-Youl Lee: Dept. of Civil and Engineering, Hanyang University, 17 Haedang-Dong, Sungdong-Gu,
Seoul 133-791, Korea
Guillermo Rus: Dept. of Structural Mechanics, University of Granada, Politecnico de Fuentenueva,
18071 Granada, Spain
Taehyo Park: Dept. of Civil and Engineering, Hanyang University, 17 Haedang-Dong, Sungdong-Gu,
Seoul 133-791, Korea

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