Loading effects on A0 Lamb-like waves in full and partially filled thin-walled tubes

We report the results of two experiments on water's loading effects on the lowest order flexural Lamb-like wave (A(o) mode) in a stainless steel thin-walled cylinder and in an aluminum thin-walled cylinder. The experiments are interesting in that they analyze the case where the loading is on the internal wall of the cylinders only. The two cylinders provide a comparable reduction (21% and 25%) in the group velocity of the A(o) wave. In addition, different effects are shown to occur in the two samples as a result of the difference in acoustic impedance match between the water and the stainless steel and aluminum shells. For the poor match of the stainless steel shell, the acoustic energy remains mostly in the tube wall, whereas in the case of the aluminum shell the match is relatively good, most of the acoustic energy is found to quickly leak into the water. The echoes received by pulse-echo technique demonstrate the difference in the path of an acoustic pulse in the two systems. (C) 1999 Elsevier Science S.A. All rights reserved.