FREE-VIBRATION ANALYSIS OF COMPOSITE LAMINATED RIGHT TRIANGULAR PLATES WITH THE FINITE-ELEMENT METHOD

The free vibration problem of composite laminated right triangular pla tes is analyzed based on Mindlin plate theory by using the finite-elem ent method. The element is at first a rectangular plate element, and t here are 4 degrees of freedom (w, beta(x), beta(y), partial derivative (2)w/partial derivative x partial derivative y) on each node point. Th en the degree of freedom partial derivative(2)w/partial derivative x p artial derivative y on each node point of the rectangular plate elemen t is condensed by using static condensation. With geometric transforma tion this rectangular plate element is transformed to a general-four-n ode-point plate element with degrees of freedom w, beta(x), beta(y) on each node point in order to use this element to analyze the dynamic p roblem of an irregular laminated plate. The effects of the fiber orien tation, boundary conditions, material properties, and geometric ratio am on the vibration frequencies of the laminated triangular plates are studied after confirming the validity of this element model. Some con clusions are obtained.