A FINITE-DIFFERENCE SIMULATION OF ULTRASONIC LAMB WAVES IN METAL SHEETS WITH EXPERIMENTAL-VERIFICATION

This paper describes a simple finite-difference method to simulate s(0 ) and a(1) Lamb wave modes in plane metal sheets. The simulation is us ed to predict time-domain histories of field displacements vertical to the sheet at groups of points on the sheet. The time-space data so ob tained are transformed by two-dimensional FFT to yield frequency-waven umber representations for comparison with the Lamb mode dispersion wav es. An experimental rig is developed for transmission and reception of Lamb waves in sheet metal, with adjustable transducer positions on th e Lamb wave axis. The rig enables two-dimensional time-space, and by t ransformation, frequency-wavenumber, data to be obtained experimentall y. An electronic system to provide appropriate band-limited signals fo r single-mode Lamb wave excitation is outlined and used in conjunction with the physical rig. Experimental results show good agreement with simulation.