Design, Analysis, and Fabrication of Lattice Structures for Structural and Thermal Applications

  Designing lightweight, stiff, and thermally compliant structures is an ongoing challenge  in various engineering industries, especially within aerospace. Aircraft and spacecraft are  designed to withstand extreme structural loads and thermal changes with the minimum  amount of weight possible. Advances in computational design and analysis, as well  as metal additive manufacturing (AM), have created new opportunities to design and  fabricate complex structures for loading conditions seen on aircraft and spacecraft.  

This thesis explores the application of lattice structures to various structural and thermal  aerospace applications, analyzes them under their respective loading conditions, and the  utilization of metal AM to fabricate many of the designs. Using unique lattice generation  methods and bimetallic lattice unit cell designs, multiple components and processes are  created to advance the adoption of AM for complex structures in the aerospace field.  

A lattice generation method based on the bubble-mesh method is used to create tetra hedral lattice structures with the ability to alter the following geometric parameters:  the cell size/lattice density, strut diameter, and intersection rounding. A relationship  between these parameters is evaluated and it is found that the strut diameter and  intersection rounding have the greatest structural effects on the lattice. These findings  are then used to apply these lattice structures to various aerospace components such as a  jet engine bracket, airplane bearing bracket, and an optical instrument mounting bracket.  The FEA results show that the latticed designs can withstand their respective loading  conditions. Additionally, latticed cubes are created using this lattice generation method  to understand their optimal printability. FEA is used again to explore the structural  and thermal behavior of the latticed cubes during the metal AM process. The latticed  vi  cubes are additively manufactured and will be scanned to validate the FEA results.  

The lattice generation method is then used to re-design a payload adapter to explore  a self-consuming spacecraft concept. The lattice is used to reduce the weight of the  structure, but the gaps of the lattice will be filled with propellant so it can be extracted  and used as fuel during a satellite mission. This work focuses on the structural integrity  of the latticed payload adapter, and simulations are used to understand its structural  behavior. It is then additively manufactured and tested under compression to validate  the simulations. Finally, a separate bimetallic triangular lattice unit cell is designed,  analyzed, and tested to explore bimetallic AM for fabricating controllable coefficient of  thermal expansion (CTE) structures. These bimetallic structures are created so that  their geometry and CTE of their respective materials minimize their expansion in a  specified direction. Computational and analytical models are developed to describe  this behavior, and multi-material/bimetallic AM is used to create these structures.  The structures will then undergo CTE testing and the results are used to validate the  computational and analytical models.