Additive Manufacturing and Cellular/Lattice Structures: Designs, Realization and Applications: Cellular/Lattice Structures II
Sponsored by: TMS Additive Manufacturing Committee, TMS Materials Characterization Committee
Program Organizers: Li Yang, University of Louisville; Allison Beese, Pennsylvania State University; John Carpenter, Los Alamos National Laboratory; Carolyn Seepersad, Georgia Tech; Miguel Aguilo, Morphorm LLC

Monday 2:00 PM
October 10, 2022
Room: 305
Location: David L. Lawrence Convention Center

Session Chair: John Carpenter, Los Alamos National Laboratory


2:00 PM  
Prediction of Mechanical Properties of Ceramic Honeycombs by Polarimetry Measurements of Epoxy Resin Prototypes.: David Koellner1; Bastien Tolve-Granier2; Swantje Simon1; Ken-ichi Kakimoto3; Tobias Fey1; 1Friedrich-Alexander-Universität Erlangen-Nürnberg; 2Science and Technologies Faculty of Limoges; 3Nagoya Institute of Technology
    We present a non-destructive approach to determine the cellular ceramics compressive strength and fracture behavior. For this, we correlate the photoelastic stresses of polymer (epoxy) prototypes with the mechanical properties of ceramics (alumina). Regular and inverse epoxy honeycombs are 3-D printed via stereolithography with varying structure angle from -35° to 35°, with negative angles forming an auxetic and positive hexagonal lattice. Photoelastic measurements under mechanical loading reveal regions of excess stress, which directly corresponds to the initial fracture points of the ceramic honeycombs. The photoelastic stress distribution is much more homogeneous for angles of smaller magnitude, which is reflected in highly increased compressive strengths up to 446 ± 156 MPa at 0°. By adapting the geometric structural model from Gibson and Ashby, we show that we can use a non-destructive technique to determine the compressive strength of alumina honeycombs from the median photoelastic stress measured on similar epoxy honeycomb structures.

2:20 PM  
Specific Energy Absorption of 3D Printed Octet-Truss Lattice Structures with Hollow Struts: Matthew Bolan1; Alexander Bardelcik1; 1University of Guelph
    In this work, we investigate the energy absorption properties of octet-truss lattice structures suitable for custom 3D printed personal protection equipment (PPE) applications. High resolution SLA 3D printing was used to produce 3”x3”x3” octet-truss lattice structures with solid and hollow strut members. An extremely ductile polymer (~180% total elongation) was used for these structures, which resulted in no strut failure up to the onset of densification during compression testing of these structures. The relative density of the structures varied from ~0.05 to ~0.5, which was due to variations in strut length (or unit cell density) and strut radius. Although the compressive energy absorption was excellent for the solid strut structures, the specific energy absorption (SEA) was relatively low when compared to expanded poly styrene (EPS), the standard helmet energy absorbing material. The hollow strut lattice structures showed improved SEA performance and potential for increased adoption within custom PPE.

2:40 PM  Invited
Performance of Titanium Alloy Lattice Structures in Quasi-static and High Strain Rate Environments: John Carpenter1; B. Brown2; N.S. Johnson3; Donald Brown1; David Jones1; Borys Drach4; Jonathan Pegues5; Manyalibo Matthews6; 1Los Alamos National Laboratory; 2Kansas City National Security Campus; 3SLAC National Accelerator Laboratory; 4New Mexico State University; 5Sandia National Laboratories; 6Lawrence Livermore National Laboratory
    Additively manufactured metal lattices are uniquely positioned to address current and emerging lightweight needs through unprecedented design freedom and manufacturing responsiveness. In this talk, the results of in situ, diffraction-based quasi-static compression studies on lattice structures fabricated out of Ti5553 are presented and connected with predictive FE-based modeling. It was found that incorporation of CT-based surface roughness and diffraction-based residual stress measurements are required in order to develop a predictive mechanical model. In addition, high strain rate tests on Ti5553 lattice structures built using Renishaw and SLM systems will be presented in a case study on the impact of differing AM technologies on dynamic performance. The combined results presented are used to help mature our understanding of the process-structure-property-performance relationships in metal lattice structures.

3:00 PM  
Evaluation of Structural Robustness in Additively Manufactured Lattice Structures: Mrinaal Lorengo1; Ji Ma1; 1University of Virginia
    In structural engineering, robustness is defined as insensitivity to an initial failure. Thus, when a robust structure is damaged, the initial failure will not cause progressive collapses which can save both costs and lives. In this research, the robustness of various lattice structures was analyzed to identify ideal lattices for damage tolerant structures. For this purpose, a quantitative metric to measure robustness was developed and then applied in this study. Stretching dominated, bending dominated, and augmented bending dominated lattices were evaluated using this previously developed metric. Lattices additively manufactured via metal powder bed fusion were also used, with undamaged and damaged samples subjected to compression testing to validate simulated results. The developed metric shows bending dominated lattices are more robust, likely due to better accommodating new bending moments caused by damage. This research adds another aspect to lattice structure design by showcasing a quantitative method for assessing damage tolerance.

3:20 PM Break

3:40 PM  
Progressive Nature of Failure of 3D Lattices under Compressive, Shear and Hydrostatic Loads : Sahar Choukir1; Chandra Veer Singh1; 1University of Toronto
    3D lattices can possess unusual mechanical properties. Limited studies delve into post-yield behavior of lattices under multiple loading conditions. Insights into the response of these complex structures under uniaxial compressive load, shear load and hydrostatic pressure are necessary to build innovative engineering materials with tunable properties. Via finite element simulations, the progressive failure of polymeric and metallic 3D lattices with different topologies were investigated. The results enable the systemic characterization of the mechanical response of these structures for both a brittle and a ductile material system for specific load-bearing and energy absorption applications. These findings provide a comparative study of the brittle versus ductile behavior of strut, sheet and triply periodic minimal surface based cellular structures and pave the way to structural design of damage tolerant lattices.

4:00 PM  
The Effects of Powder Feedstock and Process Parameter on the Material Characteristics of Ti6Al4V Thin Wall Features Fabricated by Laser Powder Bed Fusion Additive Manufacturing: Naresh Koju1; Jonah Hermes1; Sumit Paul1; Li Yang1; 1University of Louisville
    In this work, three different types of Ti6Al4V powder feedstock of different particle size ranges (small, medium and coarse) were utilized to fabricate thin wall lightweight features using laser powder bed fusion additive manufacturing (L-PBF-AM) using different process parameter settings. Thin wall features of varying dimensions from 0.1mm to 0.5mm were fabricated. The resulting sample sets allow for the analysis of the compound powder feedstock-process-geometry-material (PPG-M) characteristics for lightweight features fabricated by L-PBF-AM, which has not been previously explored. Various material characteristics, including porosity, grain size, geometry quality and mechanical properties of the thin wall samples were experimentally determined and analyzed. The results clearly demonstrated the significance of the compound PPG-M relationships for lightweight structures, which calls for further studies to “re-establish” knowledge base for L-PBF-AM materials at small dimension scales.