Optimal design of fiber reinforced composite structures and their direct ink write fabrication

The majority of the current structural optimization software does not accommodate manufacturing constraints. Therefore, substantial modifications are imposed upon optimized designs to make them manufacturable and hence nonoptimal. We propose to optimize the design of composite structures that are amenable to Additive Manufacturing (AM). The printing process chosen in our study is based on Direct Ink Writing (DIW) in which short carbon fibers in a thermoset resin are extruded through a moving nozzle to build up a structure. Since the fibers are primarily aligned in the flow direction of the extrudate, the DIW printing trajectory influences the material properties of the composite structure. To accommodate this, the extrudate trajectory follows the contours of parameterized level-set functions. The parametrization allows us to prescribe the material properties and impose many DIW manufacturing constraints such as no-overlap, no-sag, minimum radius of curvature and continuity of the toolpaths. Ultimately, we obtain optimal manufacturable toolpaths that start and finish at a boundary. To minimize the fabrication time, we formulate the linking sequence of the toolpaths as a traveling salesman problem which we solve to obtain the shortest continuous toolpath per layer. Several examples illustrate the optimization procedure. Validation is also performed.