Experimental Investigation of Lamb Wave Propagation in Bent Plates

Abstract

The Lamb wave reflection and transmission characteristics in bent plates were investigated experimentally. The specimen was fabricated by performing a three-point bending for a flat aluminum alloy plate of 1 mm thickness. The lowest-order symmetric (S0) and antisymmetric (A0) Lamb modes were excited separately for the incident wave to the bent zone in the frequency range lower than the cutoff frequencies of the higher-order modes using a piezoelectric transducer with polymethylmethacrylate (for S0 mode) and polytetrafluoroethylene (for A0 mode) wedges placed on the flat zone of the specimen. The temporal reflection (including the incident wave) and transmission waveforms were then measured on a plate surface on both sides of the bent zone using a laser Doppler vibrometer. The signals corresponding to S0 and A0 modes were extracted from the recorded waveforms using rectangular windows, Fourier transformed, and normalized by the amplitude spectrum of incident wave to obtain the amplitude reflection and transmission spectra. Both S0 and A0 modes were found to be generated in the reflected and transmitted fields even in the case of single mode incidence of either S0 or A0 mode to the bent zone. Furthermore, the reciprocal relation was shown to nearly be satisfied. In other words, the amplitude reflection and transmission coefficients of A0 mode for the S0 mode incidence were favorably compared with those of S0 mode for the A0 mode incidence.