Investigation of Mechanical Properties, Porosity and Geometric Deviation of Lattice Structures Manufactured by Additive Manufacturing

Abstract

This thesis reports fabrication, mechanical characterization, finite element modeling, and geometric analysis of lattice structures. A net-shaped 316L stainless steel lattice structure composed of diamond unit cells was fabricated by selective laser melting (SLM). The cavities in the lattice structure were then filled by aluminum through vacuum-assisted melt infiltration to form the bimetallic composite. The bulk aluminum sample was also cast using the same casting parameters for comparison. The compressive and tensile behavior of 316L stainless steel lattice, bulk dissolvable aluminum, and 316L stainless steel/dissolvable aluminum bimetallic composite is studied. Comparison between experimental, finite element analysis (FEA), and digital image correlation (DIC) results are also performed. There is no notable difference in the tensile behavior of the lattice and bimetallic composite because of the weak bonding in the interface between the two constituents of the bimetallic composite, limiting load transfer from the 316L stainless steel lattice to the dissolvable aluminum matrix. However, the aluminum matrix is vital in the compressive behavior of the bimetallic composite. The dissolvable aluminum showed higher Young’s modulus, yield stress, and ultimate stress than the lattice and composite in both tension and compression tests, but much less elongation. Moreover, FEA and DIC have been demonstrated to be effective and efficient methods to simulate, analyze, and verify the experimental results. In addition, this thesis also provides a geometric deviation analysis of lattice-based compression and tension samples manufactured with 316L and 17-4PH stainless steel, with different volume fractions (28% and 70%) using laser powder-bed fusion (LPBF). LPBF is widely accepted for manufacturing metal parts with complicated structures. However, LPBF has inherent limitations such as internal porosities and residual stresses leading to size and shape deviations. Thus, a non- destructive characterization using X-ray microscopy was conducted to collect data. Shape, position, volume, and statistical distribution of porosities and internal defects were characterized. The data was further utilized to conduct a size and shape deviation analysis.