Architectural design in stretch-formed microtruss composites

Structural coatings of nanocrystalline metal can significantly enhance the mechanical properties of microtruss cellular materials, creating new types of cellular composites. This study investigated the optimal architectural design under a compressive load for stretch-formed low carbon steel cores reinforced with ∼20 nm grain size nanocrystalline Ni–35 wt%Fe. During stretch-forming, the struts in the starting perforated low carbon steel sheet are elongated and thinned as higher internal truss angles are formed, leading to an optimal internal truss angle. While a nanocrystalline coating enhances the weight specific mechanical properties of an optimally designed conventional microtruss, the resulting composite microtruss becomes sub-optimal since the optimal internal truss angle changes with coating thickness. A strut design framework was therefore developed to determine the optimal truss angle for a given combination of starting material, reinforcing material, sheet geometry, and coating thickness.