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Wednesday, July 10 • 12:30 - 12:50

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The inspection of adhesively-bonded joints using attached PZT transducers is one application envi-sioned for structural health monitoring (SHM). In order to promote sensitivity to bonding degrada-tion, this paper addresses the generation of a targeted velocity field at a given location along the joint and over the joint width. The presented approach involves generating an ultrasonic targeted velocity field propagating along waveguides that have a finite cross section using an array of bounded PZTs. The uncertainty related to any real SHM system (PZT bonding and dynamics, mate-rial properties, effect of changes in environment, e.g. temperature...) hinders the determination of the required electrical signals to apply to PZTs for a specific guided wave profile. With the theoreti-cal mode shapes, the targeted guided wave profile is expressed in the modal domain as a set of tar-geted M complex modal amplitudes. Moreover, the M-modal amplitude time response is estimated with the measured velocity time responses and the theoretical mode shapes. Because the N-PZT ex-citation signals are controlled in amplitude and phase, there are N complex values to control M complex modal amplitudes. The optimal command sent to PZTs can be expressed as an optimiza-tion problem that can be solved by the pseudo-inverse computation of the N×M transfer functions matrix at the central frequency of the excitation signal. Experimental results with an adhesively-bonded joint (600 × 50 mm) instrumented with N=8 PZTs are presented. The two-dimensional semi-analytical finite element (SAFE 2D) analysis is used to compute the M=5 guided wave modes that can be observed at the frequency of excitation (30 kHz). The ultrasonic velocity field is meas-ured using a laser Doppler vibrometer along the joint width 10 cm away from the array of PZTs. An iterative Newton-Raphson algorithm is used to reach the optimal control parameters (amplitude and phase) of the bursts (Hanning window, 5 cycles) in few iterations. Advantages, drawbacks and po-tential of this method are finally discussed.

Wednesday July 10, 2019 12:30 - 12:50 EDT
Westmount 1

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