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11 June 2002 Identifying damage in plates by analyzing Lamb wave propagation characteristics
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The goal of this paper is to discuss different data interpretation concepts for structural health monitoring based on Lamb wave propagation. Surface-mounted piezoelectric transducers are used as wave emitters and receivers. The waves emitted interact with discontinuities and experience a change in their propagation characteristics when damage is generated. By comparing sensor signals collected before and after damage has been generated, the condition of the structure can be determined. Two approaches are proposed for characterizing the damage. The initial approach analyzes only the first wave packet reflected at the damage and is based on a simple time-of-flight analysis in conjunction with a geometric method. The size of the damage can be estimated with this technique by using several pairs of piezoelectric conversion processes. This technique offers the potential for enhancing measurement accuracy. An estimation of the size and location of the damage becomes possible with just three piezoelectric sensors. It has been found that, in practice, the superposition of wave packets represents one of the main problems in realizing this approach. The decomposition of superimposed wave packets is investigated using wavelet transform and the pulse compression technique. It is shown that noise and dispersion represent a major drawback, hence rendering signal analysis distinctly more difficult.
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Michael Kehlenbach and Santanu Das "Identifying damage in plates by analyzing Lamb wave propagation characteristics", Proc. SPIE 4702, Smart Nondestructive Evaluation for Health Monitoring of Structural and Biological Systems, (11 June 2002);

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