Optimum Design for the Strength of Fibrous Composite Materials

Abstract

The fiber reinforcements to improve the strength are discussed by use of fiber reinforced plastics. The strength laws of unidirectional fiber reinforced plastics of carbon fibers and Kevlar are formulated on the basis of the experimental results of the strengths under combined stress state. By combining the unidirectional strength laws and the laminated plate theory, the strength of angle ply laminated plates are obtained under combined stress states. Using the strength laws of various ply angles, the optimum fiber orientations are determined for given combined stress states. The specific strength of fiber reinforced plastics with the optimum fiber orientations are compared with metal specific strength and the superiority of fiber reinforced plastics are shown. As an application of fiber reinforced plastics to machine elements, fiber reinforced plastic gears are presented. The gear teeth are reinforced along the teeth configurations by carbon or glass cloths. The bending strength of the reinforced tooth is investigated by the stress analysis. The effects of reinforcing material constitutions on the bending strength are discussed. It is shown that the fiber reinforcement is effective to improve the tooth strength of plastic gear.