ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

3pEA9. Vibration signature monitoring using analytical models of slotted beams.

XiuTing C. Man

Robert D. Finch

Mech. Eng. Dept., Univ. of Houston, 4800 Calhoun Rd., Houston, TX 77204-4792

Vibration signatures may be used in monitoring structural integrity. A procedure was established in which the experimental data were processed using analytical models of the physical structures. Steal beams were used as examples. Saw-cut slots of different sizes and locations were the ``damage'' to be detected. An analytical model based on a perturbation method was developed, which leads to direct relationships between the modal properties and the slot parameters. The modal frequencies were estimated experimentally using modal analysis techniques. The frequency reductions were computed as the difference between the experimentally estimated modal frequencies and the values theoretically calculated from a uniform beam of identical conditions. The first three modal frequency contours were calculated from the perturbation model and used to quantify the slot depths and slot locations. The slot locations were determined with great accuracy, although the slot depths were estimated lower than the actual values. The reason was that the perturbation model predicted the modal frequency shifts smaller than the actual values, and when used inversely, it tended to give a slot depth of higher value.