In structural health monitoring (SHM) of composite members, the choice of sensor positions, frequency band and signalinterpretations are directly affected by the attenuation levels. Hence, it is important to consider the influence ofattenuation for quantitative interpretation of signals in SHM applications. In this paper, attenuation of the twofundamentals Lamb wave modes, namely the symmetric mode S0 and antisymmetric A0 were experimentally measuredin Carbon Fiber Reinforced Polymer (CFRP) laminates. The stress waves were launched using piezoelectric wafersbonded to the center of the laminate. Symmetric and antisymmetric modes were excitation through appropriatecombination of two piezoelectric wafers bonded on opposite surfaces of the plate at the same location. The out of planedisplacements corresponding to both modes were measured using a scanning laser vibrometer (SLV), along differentorientations starting from 0~0 to 90~0 at 15~0 increments. Attenuation coefficients were obtained from 100 kHz to 350 kHzfor both cross-ply as well as quasi-isotropic laminates. The attenuation coefficients ranged from about 5 nepers/m to 40nepers/m. The experimental results as obtained by the scanning laser vibrometer compared favorably with resultsavailable in the literature. The antisymmetric mode was found to undergo significantly higher attenuation compared tothe symmetric mode. The attenuation of the two modes further depends on the direction of propagation and theirfrequency components. Because of the dependence of the attenuation level on the Lamb wave mode, frequency, anddirection of propagation, a wide frequency content signal such as acoustic emission will undergo substantial changesbefore being detected by sensors. Successful acoustic emission monitoring will have to take such attenuation intoaccount to get reliable results.
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