4aEA1. Mode control of ultrasonic guided waves in thick cylinders for crack detection.

Session: Thursday Morning, May 16

Time: 8:00

Author: Zongbao Li
Author: Yves H. Berthelot
Location: School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332-0405


Experiments on ultrasonic propagation in thick annular structures show that one can simplify the modal structure of the received signals by carefully controlling the wedge angles of the generation and detection transducers. This is important if one is to detect cracks along the path between source and receiver. In particular, one should excite and detect only those modes whose energy is concentrated where the cracks are expected to form. To do so, the following methodology is used: First, experimental signals are obtained for various source--receiver configurations with a standard pulser/receiver; a wavelet transform is then applied to the signals to localize precisely in time the arrival of a given mode packet at a given frequency and to determine the corresponding group velocity. These modes are then identified by comparing the results with predictions from theoretical dispersion curves. One can then predict the energy distribution within the structure by using the method of normal mode expansion for transients. [Work supported by the ONR, Code 332.]

from ASA 131st Meeting, Indianapolis, May 1996