Three-dimensional strength and stiffness optimization of coated structures with lattice infill

Additive manufacturing (AM) offers a design freedom to fabricate high performance parts, such as a solid outer shell with a porous infill (coated structure), to enhance strength-to-weight ratio. The goal of this article is to describe and analyze how to develop a strength-based optimization to design the topology and infill microstructures density by minimizing the failure load subjected to weight constraint. To establish the coated structure, the material and coating indicators are obtained using double smoothing and projection of design variable. Additionally, three characteristic parameters are utilized to represent the lattice geometry. Two lattices, including octet-truss lattice and cubic lattice, are considered for the infill region. The strength-based optimization is developed based on Hill's yield criterion, and the element failure indices are aggregated to a single function using the p-mean approach. The proposed design methodology has been successfully applied to different numerical test cases, which showed that performing strength-based optimization led to a smoother boundary at the re-entrant corner and achieving a lower failure load. Numerical evaluation also demonstrated that, in contrast to solely considering characteristic parameters to design lattice, considering additional material and coating indicators during the design process resulted in optimized topology as well as infill microstructures material distribution.