DETERMINATION OF THE FUNDAMENTAL-FREQUENCY OF TRANSVERSE VIBRATION OFRECTANGULAR-PLATES WHEN THE THICKNESS VARIES IN A DISCONTINUOUS FASHION

The problem outlined in the title is solved, in an approximate fashion , for the situation where a discontinuous variation of the thickness t akes place over a concentric, rectangular subdomain of the plate. Nume rical values of the fundamental frequency coefficient are obtained for several combinations of clamped and simply supported edges and the go verning geometric parameters. Two approaches have been used: (a) the o ptimized Rayleigh-Ritz method employing polynomial coordinate function s, and (b) the finite dement method. An important practical conclusion of the present investigation is the fact that dynamic stiffening of t he plate is achieved for all the situations considered in this paper w hen the plate possesses a free, concentric, rectangular hole.