Fiber Orientation Kinetics of a Concentrated Short Glass Fiber Suspension in Start up of Shear Flow

The common approach for simulating the evolution of fiber orientation during flow in concentrated suspensions is to use an empirically modified form of Jeffery’s equation referred to as the Folgar-Tucker model. Direct measurements of fiber orientation were performed in startup of shear flow for a 30 wt % short glass fiber-filled polybutylene terephthalate (PBT-30); a matrix that behaves similar to a Newtonian fluid. The experimental results show that the fiber orientation evolves much slower than the models predict. Furthermore, fiber orientation measurements suggest that a steady state is not reached as the fiber orientation continues to slowly evolve, even up to 200 strain units. This is in contrast to the model predictions that predict a steady state is reached in roughly 50 strain units.