A Method for Determining Orientation Function of Glass Fiber in Fiber Reinforced Plastic Sheets and Nonwoven Mats by Dielectric Constant

Abstract

A method is proposed for determining the orientation functions of fibers of isotropic materials such as glass and gamma alumina in FRP sheets and nonwoven mats. The method consists of (1) measurement of the anisotropy of inplane dielectric constant of a sheet sample with polarized microwave, (2) theoretical estimation of the difference between the dielectric constants parallel and perpendicular to the fiber direction of a perfectly oriented sheet, and (3) determination of the mean orientation angle and orientation function of the fiber from the results of (1) and (2). Regarding the second process (2), three of theoretical models which have been reported are examined and compared with experimental data of unidirectional glass/air and glass/epoxy and are found to be equally suitable. The orientation functions obtained for laminates of continuous fibers of glass and gamma alumina are in agreement with the theoretical values calculated from the stacking structure within 5% deviation. Orientation functions are also determined on FRP sheets and nonwoven mats of short glass fiber and the anisotropies in modulus of elasticity and in ultrasonic propagation velocity are calculated from them. The differences between the calculated values and the directly measured values are less than 10%.