YOUNG'S MODULUS ESTIMATION OF NATURAL FIBER COMPOSITES WITH FLUCTUATION IN FIBER ORIENTATION

摘要

Natural fibers are usually used as reinforcement in green composites. These natural fibers have a larger scatter than the traditional glass fiber in mechanical properties as in the strength, Young's modulus and so on. Furthermore, the fluctuation in fiber orientation occurs in green composites because the natural fiber is supplied as a sliver in molding process. It is well known that the fluctuation causes the reduction of the Young's modulus. Then a new analysis to estimate the Young's modulus of the green composites with fluctuation in fiber orientation was proposed in this study. In our analytical model, it is assumed that the composite with the fluctuation can be divided into many fine segments, and each segment can be a lamina with an arbitrary fiber orientation angle. Consequently, the composite structure may be regarded as a chain of laminates, and lamination theory can be applied for the composites. For kenaf/PLA unidirectional composites, the fiber orientation angle in each segment was measured using the optical microscope, and the Young's modulus of green composites was calculated through the proposal model. Finally, we discussed about the reduction of Young's modulus due to the fluctuation of fiber orientation in green composites and the effective Young's modulus of kenaf fibers in composites.