(491e) Simulation of Semi-Flexible Fiber Orientation and Configuration during Molding Operations

Authors: 
Baird, D. G., Virginia Tech

The use of long fiber reinforced thermoplastics has gained increasing interest as a means to enhance a part’s mechanical properties created through traditional melt processing techniques.  Injection molding creates a complex microstructure to develop caused by the flow field within the mold.  Accurate predictions of fiber orientation can allow for mold design to be tailored to achieve a desired microstructure and mechanical properties.  In this work simulations utilize the Bead-Rod orientation model adapted for concentrated suspensions to account for semi-flexible fibers (i.e. long fibers) by representing a fiber as two adjoined vectors that are free to rotate around the connecting point.  This work uses orientation model parameters extracted either from basic rheological data or from orientation data taken along the center plane at the transition between the gate and plaque.  The entire mold cavity is simulated under non-isothermal conditions including the entry region to the plaque and the fountain flow behavior at the advancing front.  Simulations of the semi-flexible model are compared to the Strain Reduction Factor (SRF) model developed for rigid fibers following the same simulation procedure.  Predictions are compared to experimental data measured along and away from the plane of symmetry.  Improvement in orientation predictions are obtained from the Bead-Rod model which greatly out performs the rigid fiber model away from the center plane.