To predict fiber orientation for injection molded parts, it is important to use a slow-kinetics orientation model and pay careful attention to the role of flow kinematics on orientation evolution speed. A model incorporating the impact of flow type on the fiber reorientation rate was tested by comparing with experimental data measured in an injection molded center-gated disk for both short and long glass fiber thermoplastics. Unlike the existing orientation models using a constant factor, a variable strain reduction factor (SRF) is expressed as a function of an objective flow-type parameter reflecting local flow kinematics. The use of this model improved the fiber orientation predictions at locations where the constant SRF, obtained from simple shear flow, deviated significantly from that based on the local flow kinematics.
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