Development of Functional Composites with Metallic Fiber of Expanded-ends.

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Strength of composites depends on strength of fibers and interface. Fibers are subjected to shear stressdue to the adhesive force of interface. Therefore, to obtain a strong composite we need to have strong interface. Interface strength is especially important in the case of short-fiber composite. But, as the matrix is polymeric materials, the strength of composites decreases with decrease of adhesive force of interface under the high-temperature environments. There are two ways to obtain interface of high strength, one is chemical adhesion and the other is anchor effect. The former depends on the temperature. On the other side, for the latter, surface of fiber is irregularly roughened, and the strength of interface increased due to the surface roughness. But the fiber strength decrease by stress concentration from the surface roughness. In the present study, to improve the strength of short-fiber composites, authors developed new composites with fiber of expanded-ends. In advance, the shape and size of fiber-ends are calculated by using two-dimensional elasto-plastic FEM. The results of calculation were that the shape was spherical-ends with the diameter five times bigger than a fiber. Practically, ends of fibers were formed into disk shape and they are inserted between the laminates of GFRP. The tensile strength of new composites increased by about 30% at the transition temperature of resin. The fatigue strength of new composites increased by about 25% on endurance limit at the same temperature, especially used Nylon-12 resin.