FREE VIBRATIONS OF BIMODULUS COMPOSITE PLATES

Abstract

During the past two decades, composites have emerged as potential structural materials. These materials are now finding extensive application in aeroplanes, sub-marines and helicopter blades. The advantage of the composite materials structures lies in that they can be suitably designed for high strength and stiffness with light weight - the requirements which are otherwise difficult to be met with the conventional materials. With increasing usage, research for better design with composites has become important. In structures, most of the members may be grouped as plate and beam elements. For this reason, the problem of static and dynamic analyses of composite beams and plates is of- basic interest in the design of composite structures. In this dissertation, the problem of free vibration analysis of two-layer composite plates has been taken up. Some work on cross-ply plates is available in the litera- ture. This work presents more detailed results of the cross-ply plates.'The analysis has been extended to angle-ply plates as well and results of the angle-ply plate are compared with those of cross-ply plates. In Chapter 1 of the dissertation, a review of the literature on static and dynamic analyses of composite beams and plates is given'. Chapter 2 provides the mathe-matical details of the problem. The composites are -iv- orthotropic bimodulus materials. Therefore, this chapter begins with some details of stress-strain relation. The usual theory of plate vibration is applicable to the composite plates as well, however, the stiffness matrices are to be defined appropriately to account for orthotropic bimodulus nature and the orientation of the layers in the plate. These details included in the chapter give a complete analytical information of the problem to a reader. Chapter 3 of the dissertation providesthe results of the work. At first, an efficient scheme developed for the problem is described. The results obtained with the present,. software show anexcellent agreement with some of the results of the available literature. The results given in Chapter 3 include the frequencies of fundamental mode of vibration and the corresponding neutral surface locations of the two layers for both cross-ply and angle-ply plates with simply supported edge condition. The cross-ply plates have been studied in a greater detail in respect of geometry and material combinations. For the angle-ply the results are for square plates with a wide range of the orientation of the two layers.