11 June 2002 Detection and estimation of defects in a circular plate using operational deflection shapes
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Abstract
This paper investigates dynamic characteristics (mode shapes and natural frequencies) and defect detection of circular plates using a scanning laser vibrometer. Exact dynamic characteristics of a circular aluminum plate having a clamped inner rim and a free outer rim are obtained using two methods; one uses Bessel functions and the other uses a multiple shooting method. An in-house finite element code GESA is also used to analyze the circular plate using the DKT plate element. Numerical results show that some reports in the literature are incorrect and that high-frequency Operational Deflection Shapes (ODSs) are needed in order to locate small defects. Detection of two defects in the circular aluminum plate is experimentally studied using the distributions of RMS velocities under broadband periodic chirp excitations. RMS velocities of ODSs, symmetry breaking of ODSs, splitting of natural frequencies and ODSs, and a Boundary Effect Detection (BED) method. The BED method is non-destructive and model-independent; it processes experimental ODSs to reveal extra local boundary effects caused by defects to reveal locations of defects. Experimental results show that small defects in circular plates can be pinpointed by these approaches. Moreover, a new concept of using the balance of elastic and kinetic energies within a mode cell for detecting defects in two- dimensional structures of irregular shapes is proposed.
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Perngjin Frank Pai, Perngjin Frank Pai, Yunje Oh, Yunje Oh, Byeong-Seok Kim, Byeong-Seok Kim, "Detection and estimation of defects in a circular plate using operational deflection shapes", Proc. SPIE 4702, Smart Nondestructive Evaluation for Health Monitoring of Structural and Biological Systems, (11 June 2002); doi: 10.1117/12.469898; https://doi.org/10.1117/12.469898
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