On the use of orientation tensors to represent prepreg platelet orientation state and variability

Prepreg platelet molding compounds (PPMCs) have mesoscale (platelet scale) features that are not found in injection molding materials. Beyond the fiber orientation state, the platelet normal orientation state and the expected orientation state variabilities are desirable outputs from flow simulations of PPMC systems. However, theoretical understanding and efficient numerical molding simulation capabilities have primarily been developed for injection molding. Using exact solutions of Jeffery’s equation, two methods are developed: approximation of the second-order normal orientation tensor as a function of the second-order fiber orientation tensor and estimation of the variability in predicted orientation tensors due to scale similarity of the platelets and typical molded geometry thicknesses. These methods are validated using orientation state data obtained from computed tomography for five replicates of a PPMC bracket structure. Finally, the methods are applied as postprocessing of a fiber orientation simulation results, showing good comparison with the experimental data. The developed methods allow existing simulation capabilities to be applied to PPMCs as a reduced order model to enable efficient design iterations for PPMC manufacturing.