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

复合材料的强度取决于纤维和界面的强度。由于界面的粘附力，纤维受到剪切应力。因此，为了获得坚固的复合材料，我们需要有坚固的界面。对于短纤维复合材料来说，界面强度尤其重要。但是，由于基体为聚合物材料，在高温环境下，复合材料的强度随着界面结合力的降低而降低。获得高强度界面的方法有两种，一种是化学粘接，另一种是锚效应。前者取决于温度。而对于后者，纤维表面不规则地粗糙化，由于表面粗糙度的增加，界面强度增加。但表面粗糙度引起的应力集中会降低纤维强度。为了提高短纤维复合材料的强度，作者研制了一种新型的纤维端部扩张复合材料。在此基础上，利用二维弹塑性有限元法计算了光纤端面的形状和尺寸。计算结果表明，纤维的形状为直径为纤维直径5倍的球形端头。实际上，纤维的端部形成为盘状，并且它们插入GFRP的层合板之间。在树脂转变温度下，复合材料的拉伸强度提高了30%左右。在相同温度下，新复合材料的疲劳强度比疲劳极限提高了25%左右，尤其是尼龙12树脂。

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.