Prediction Method for Temporal Change in Fiber Bundle Orientation on Cylindrical Braided Preforms

Abstract

An advantage of braided composites is that the fiber bundle orientation angle, called the ″braiding angle,″ can be changed, because the braiding angle affects the mechanical properties. Control of the angle is an important means of adjusting the stiffness distribution as required. However, when the braiding angle is changing from an initial braiding angle to a targeted braiding angle designated by the longitudinal velocity of the mandrel, some delay occurs before the actual braiding angle reaches the targeted braiding angle. The delay is caused by movement of ″creating point″ which is defined as a fell-down point with the braiding yarn on the mandrel. After the creating point reaches the targeted point, the braiding angle will be constant. In order to obtain the temporal change in braiding angle under unsteady-state conditions, this paper presents a step response model in braiding angle on a cylindrical braided fabric. The mechanism in the temporal change is simple. Velocity of the creating point is in proportion to distance between the current creating point and the steady-state creating point designated as the targeted angle. The solution can be described by a time constant, because the motion equation is the first-order of differential equation which is derived from geometrical position of a braiding yarn. Furthermore, the method is verified with the experimental data. As a consequence, the model has proved effective for predicting fiber orientation on a cylindrical braided preform under unsteady-state conditions.