Abstract
It is known that a single yarn is formed by spinning natural short fibers and a twist yarn consists of some single fibers in order to achieve high stiffness and strength of natural fiber composites. Generally, it is found that the amount of twist obtained by the spinning process, called twist per inch (TPI), plays an important role in yarn properties because the twist is essential to hold the fibers together. In fact, twisted yarns are normally used for increasing the lateral cohesion of the fibers and also for ease of handling. The purpose of this study is to investigate the effect of TPI of natural fiber yarns on adhesive estimation of interface for yarn reinforced green composites. The single yarn composites with three kinds of TPI from 3.5 to 9.5 were prepared. The fragmentation tests using these yarn composites under a polarization microscope were carried out. The multiple fiber breakages were experimentally confirmed, but the effect of TPI on the adhesive estimation was not cleared quantitatively. It was considered that the factors of these unwilling results were the twist angle, project and surface areas of fibers because the stress recovery length depends on these factors. In order to investigate the stress concentration of sound fibers and the adhesive estimation, some finite element analyses were conducted. From the analyses, it was found that the load shearing behaviors between sound fibers were different because the twist angle effects on the fiber axial direction change.
