Date on Master's Thesis/Doctoral Dissertation

7-2017

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Mechanical Engineering

Committee Chair

Murphy, Kevin

Committee Co-Chair (if applicable)

Berfield, Tom

Committee Member

Berfield, Tom

Committee Member

Starr, Tom

Committee Member

Yang, Li

Committee Member

Gornet, Tim

Author's Keywords

addtive manufacturing; lattice structures; direct metal laser sintering; maraging steel

Abstract

This study involves the evaluation of lattice specimens fabricated using additive manufacturing as well as investigation of the influence of unit cell connection geometry. Lattice topologies of face-centered cells and body-centered cells were modeled, investigated using finite element analysis (FEA) for each specimen, manufactured using direct metal laser sintering (DMLS) with maraging steel powder, and mechanically tested. The strut diameter of each topology was altered to yield four different mass reductions from a solid cube, ranging from 55%-90% mass reduction. Three iterations of 1000mm3 lattice specimens were investigated. The first iteration consisted 0.5mm plates on the top and bottom of the lattice tested only in compression. While the mechanical testing results yielded increasing stiffness to increasing strut diameter, the results were poor in comparison to FEA results, ranging from only 7% to 20% of FEA stiffness results. A second iteration was modeled to enable the testing of specimens in either compression or tension as well as the use of an extensometer during testing. The results for the second iteration of specimens improved from first iteration and showed that as strut diameter is increased, the stiffness and effective modulus of each unit cell increases. All stiffness results from the second iteration specimens were greater than that of FEA results, ranging from 150% to 215% of FEA stiffness in tension and 125% to 400% of FEA stiffness in compression. The final iteration of specimens would add fillets at the strut-additional mass connections. The most mass added to a unit cell was only a 4% increase in mass. But, with added mass came an increase in both stiffness and effective modulus in most parts.

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