Discontinuous or short-fiber composites are traditionally less expensive and are normally less difficult to manufacture than continuous fiber composites, while still retaining some of the benefits of reinforcing fibers. Similarly to continuous fibers, the volume ratio influences the mechanical properties of the composite. In addition the ratio of the length and diameter of the reinforcing fibers also plays a significant role. This ratio (also known as the aspect ratio) adds another variable to the anisotropic properties of lamina plies where now not only the content of fibers but also the dimensions of the fibers themselves play a role. Short fiber reinforced composites are already used in additive manufacturing techniques; however, the amount of carbon fiber and the length of the discontinuous strands in the filaments are normally not stated or vary greatly. An investigation in conducted on how the dimensional properties of the carbon fiber, (volume fraction and aspect ratio), affect the mechanical properties of 3D printed parts. Rectangular bending samples were fabricated using a Pulse XE 3D-printer using filament rolls of varying carbon-fiber content and carbon-fiber length. The results showed that the orientation of the reinforcing fibers can play a significant role in the mechanical responses of the final product. The amount of fiber by content also influence how much of a brittle/ductile response the samples exhibited. Additionally the aspect ratio of the carbon-fiber strands appears to influence how susceptible the final products are to artifacts of the 3D-printing process. Finally it is shown how using a combination of the Halpin-Tsai model with Classical-Laminate-Composite-Theory can predict how the samples will respond based on the carbon-fiber content, aspect ratio, and print/fiber orientation. This can theoretically be used to tailor a 3D-printed products anisotropic mechanical properties based on the loading conditions expected by manipulating the reinforcing fibers.
