Controlled 2D and 3D Self-assembly of short fibers for additive manufacturing

A common issue with thermosetting resins is the relatively weak mechanical properties of the pure polymer materials. Thus, 3D-printed parts using thermoset chemistries are restricted to rapid prototyping. For thermoset 3D manufacturing to be useful in user-end parts, reinforcements must be incorporated to improve mechanical properties such as modulus and strength. Carbon and glass continuous mats or short fibers are examples of reinforcement materials commonly used in traditional composite manufacturing. However, fiber mats are difficult to incorporate into 3D printing technologies, and short fiber is limited to very low loadings in resins for printing. Here we present an inexpensive method of aligning and consolidating short fibers into different shapes, such as discs, spheres, triangles, and needles. The method consists of flow-induced self-assembly of fibers using complex flow fields. The self-assembled shapes are shown to depend on the length of the short fibers, the concentration of fibers, and flow field parameters. We envision that the self-assembled shapes can be used in VAT polymerization methods via placement and consolidation. 3D printed test specimens are discussed and the results are compared to neat resin and traditional composite manufacturing methods.