# Analysis of a Preliminary Design Approach for Conformal Lattice Structures
## 4 Conclusions  
In this manuscript, the modeling, size optimization, and structural linear analysis of conformal lattice structures were presented. In particular, the work aimed to provide design tools that require a low process time and low computational power in a preliminary design phase, thanks to the implementation of the design, optimization, and geometric modeling in a single environment and to the 1D analysis that is faster than solid FEA. A geometric design approach based on the deformation of the wireframe of a regular lattice structure through the NURBS-FFD method was proposed. The possibility of performing size optimization and structural linear analysis based on the beam theory in the same environment was explored. An automated process was then developed for importing the geometrical information and constructing FE models inside the Patran/Nastran and Ansys commercial FEA software. This method promotes the design, optimization, and structural analysis of conformal cellular structures and facilitates further real-time geometrical modification through the control points of the NURBS-FFD control volume inside the same environment. At the same time, limitations are still present; the NURBS-FFD approach offers a fixed topology of the control volume, and the graphic interface can appear confusing when dealing with volumes described by many control points. Furthermore, the proposed size optimization approach and the validation methods are limited to beam-based lattice structures with a restriction on the minimum slenderness ratio. As a case study, the central part of a piston rod was filled with four different lattice structures, based on the SC, BCC, WG, and DA unit cells, two of them with thick struts to highlight the limitation of the beam structural size optimization and structural linear analysis. It was shown how bending behavior in conformal lattice structures not only depends on the Maxwell criterion but also on the load direction with respect to the main axes of the cell, as was seen for the SC structure. It was highlighted that the constraints of the size optimization algorithm should include not only the size limitations of the manufacturing process but also the minimum slenderness ratio to use the beam theory correctly and the maximum slenderness ratio to prevent buckling effects. In conclusion, it is expected that for beam-based lattice structures, the beam theory tends to be more conservative than experimental results in terms of stiffness, and therefore, the solutions have an advantage in terms of safety, which can be useful in the AM field since irregularities and defects of the parts negatively affect the mechanical performance. As future works, new case studies will be used to validate the NURBS-FFD method, and other unit cells will be introduced, such as strut-TPMS. Dealing with size optimization, the algorithm could be modified to interact with field approaches for structural optimization and other size optimization strategies. Concerning the modeling method, an enhanced version able to provide a lattice structure with smooth connections between the beams and between the lattice and the solid model is going to be developed. Finally, experimental tests for validating the numerical results are needed. Conceptualization, P.D.F., S.R., A.C., G.S., R.M., and G.C. ; Formal analysis, P.D.F. and S.R. ; Funding acquisition, G.S. and A.C.; Investigation, P.D.F., S.R., and D.B.B. ; Methodology, P.D.F., S.R., A.C., D.B.B., and G.S. ; Supervision, A.C., G.S., G.C., R.M., and S.R. ; Writing--original draft, P.D.F., and S.R. ; Writing--review and editing, P.D.F., S.R., A.C., and G.S. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was partially funded by the Regional Operational Programme F.S.E.