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8 April 2009 Structural intensity in dual-mode propagation for damage characterization
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In complex structures such as lap joints, extracting the information associated with damage from the measured signal can be challenging. An approach is presented, based on the use of high frequency bursts injected into a structure using an actuator and the measurement of structural intensity using a compact array of sensors, located remotely from the damage. The approach implements structural intensity estimation using the Timoshenko beam formulation, including dual-mode propagation above the cut-off frequency of the A1 Lamb mode. The structural intensity is first expressed within Timoshenko beam theory and the use of the wave decomposition approach is proposed to allow its measurement. Simulations are then conducted to illustrate localized time-domain structural intensity measurement for a burst propagating in a semi-infinite beam with a notch represented by a thickness variation. Results show that below the cut-off frequency, the burst propagates as a shear-dominated wave (mode A0) while a moment-dominated burst also propagates above the cut-off frequency (mode A1). Experimental results show that both shear and moment components of intensity can be measured for frequencies below and above the cut-off frequency and that the notch can be detected. Structural intensity measurement is then applied to the detection of a notch in a simulated lap joint region of a beam. The results demonstrate the potential benefit of using the structural intensity to extract useful information from the dual-mode interference for characterizing the location and depth of the notch.
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Patrice Masson and C. Roger Halkyard "Structural intensity in dual-mode propagation for damage characterization", Proc. SPIE 7295, Health Monitoring of Structural and Biological Systems 2009, 729520 (8 April 2009);

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