Researchers will apply molecular simulations to build predictive models of fiber/epoxy ink microstructure during embedded 3D printing by building mesoscale models of ink composites, simulating inks in flow, predicting fiber response, and relating the mesoscopic predictions to macroscopic flow conditions during FRE-3D printing. They will also deploy digital twins of the FRE-3D print process to optimize printing of high-performance fiber-reinforced composites by replicating the FRE-3D extrusion process in macroscopic flow simulations to better understand how process parameters translate to local flow conditions inside the nozzle and relate processing parameters to fiber orientation and aggregation to enable real-time process control.