Project Scope
Additive manufacturing (AM) is a process in which material is extruded in a layer-by-layer fashion adding material only where it is needed rather than removing unwanted material. Large-format additive manufacturing (LFAM) is a focus of AM that utilizes pelletized feedstock and single screw extrusion to create large complex geometries (>1 m3) at high deposition rates (~50 kg/hr). The use of fiber reinforced pellets in LFAM systems increases part stiffness and decreases coefficient of thermal expansion (CTE) values. The addition of fiber reinforcement material, however, introduces a high degree of anisotropy to the structure. Fiber reinforcement materials typically provide more resistance to thermal expansion (over 10x) along the longitudinal direction of the fiber than transverse. This creates a dependence of thermomechanical properties on the orientation of fiber reinforcement material within the LFAM structure. Shear force effects at the nozzle wall cause these fibers to become highly oriented in the print direction at the bead edge while fibers at the bead core remain mostly random. This nonhomogeneous distribution of fiber orientation across the microstructure results in thermomechanical properties that are dependent not only on the orientation of fiber, but also on location within the bead. This makes it difficult to accurately characterize the thermomechanical response and predict performance of LFAM printed parts. Digital image correlation (DIC) has been demonstrated as an effective technique to measure thermal-induced strain that accounts for the influence of complex microstructure on final thermomechanical properties. Understanding the relationship between the microstructure and performance of the final part will allow designers to better tailor performance to specific applications.