Abstract

In this work, natural frequencies of composite plates are studied based on the shape of the fibers. The natural frequencies are studied for composite materials strengthened by isotropic composite material plates, as short fibers, and orthotropic composite materials plates, as long fibers, with the effect of crack orientation effect with different aspect ratio of plate for simply supported plate. The method used to find the natural frequency of composite plate is supposed analytical solution to solve the equation of motion considering the effect of crack orientation with different crack position and crack size on the natural frequency of the composite various aspect ratio of isotropic and orthotropic plate. A comparison made between the analytical results and the results get by finite element solution using ANSYS (ver. 14) program. The comparison shows the error percentage is not exceeds of 2.5%.The results show that the natural frequency decreases as crack size (length or width) increases. The effect of crack when it reaches the middle is higher than when it is in the other places. The natural frequency is decreases as plate width increases, (aspect ratio and plate thickness) and the natural frequency of composite plate decrease with increasing of crack orientation.