Session: 03-01-02: Annual Conference-Wide Symposium on Additive Manufacturing

Paper Number: 149078

149078 - Investigating the Mechanical Behavior of 3d-Printed Inconel 718 Hexagonal Honeycomb Structures: A Comprehensive Study 

To fully unlock the creative possibilities offered by 3D printing for metal, it is imperative to comprehend the impact of process parameters and applied heat treatment on the mechanical behavior of complex cellular structures. Specifically, we aim to explore how current optimized printing parameters, involving high speeds within the part's inner space and lower speeds with increased energy input at the part's exterior, interact as individual element thicknesses in these structures approach the submillimeter scale. This comprehensive study endeavors to examine the impact of heat treatment, geometry (element thickness), and load direction on the compressive performance of Inconel 718 (INC718) laser powder bed fused (LPBF-ed) hexagonal honeycomb specimens. Honeycomb samples of different wall thicknesses (0.4 mm, 0.6 mm, and 0.8 mm) and flat sheets of equivalent thickness were printed. The flat sheets were machined into miniature tensile specimens to study the parent material behavior. Subsequently, half of the printed specimens were stress-relieved, while the second half was solution annealed and age hardened. Electron backscatter diffraction tests were conducted to investigate the effects of heat treatment and element thickness on the resulting microstructure. A miniature tensile tester was employed to assess the influence of heat treatment, element thickness, and loading orientation on parent material mechanical behavior. Finally, quasi-static compression tests were conducted along the three perpendicular major axes of the honeycomb samples, evaluating mechanical performance and energy-absorbing characteristics (plateau stress, specific absorbed energy, Ideality, and efficiency) for each study set. Observations on the stress-relieved samples revealed three distinct microstructure zones across submillimeter element thicknesses, linked to variations in printing parameters and heat field distribution. The percentage contribution of each zone to the overall thickness varied with the element thickness, resulting in a variable parent material behavior. Loading orientation also proved influential. When compressed in the plane of the honeycomb, the studied structures showed excellent energy absorbing characteristics compared to other 3D-printed metallic cellular structures. Stress-strain behavior was bending-dominated in one direction and bending-stretch dominated in the other, with no initial stress peaks. Solution annealing followed by age hardening heat treatment is anticipated to further improve the mechanical behavior and energy absorbing characteristics. The coupling between element thickness/ orientation and material behavior challenges the conventional analytical models in explaining the mechanical performance of 3D printed cellular structures and requires including it in any optimization process. This research extends beyond the established paradigms, contributing vital insights to the dynamic field of additive manufacturing.

Presenting Author: George Z. Voyiadjis Louisiana State University

Presenting Author Biography: George Z. Voyiadjis is the Boyd Professor at the Louisiana State University, in the Department of Civil and Environmental Engineering. This is the highest professorial rank awarded by the Louisiana State University System. He is also the holder of the Freeport-MacMoRan Endowed Chair in Engineering. He joined the faculty of Louisiana State University in 1980. He is currently the Chair of the Department of Civil and Environmental Engineering. He holds this position since February of 2001. He also served from 1992 to 1994 as the Acting Associate Dean of the Graduate School. He currently also serves since 2012 as the Director of the Louisiana State University Center for GeoInformatics (LSU C4G).
http://c4g.lsu.edu//
Voyiadjis is a Foreign Member of the Academia Europaea (Physics & Engineering Sciences), the European Academy of Sciences, and the European Academy of Sciences and Arts (Technical and Environmental Sciences). He is also a Foreign Member of both the Polish Academy of Sciences, Division IV (Technical Sciences) and the National Academy of Engineering of Korea. He is the recipient of the 2008 Nathan M. Newmark Medal of the American Society of Civil Engineers and the 2012 Khan International Medal for outstanding life-long Contribution to the field of Plasticity. He was also the recipient of the of the ICDM2 Lifetime Achievement Medal for his significant contribution to Continuum Damage Mechanics, presented to him during the Second International Conference on Damage Mechanics (ICDM2), Troyes, France July 8-11, 2015. This is sponsored by the International Journal of Damage Mechanics and is held every three years. In 2022 he was the recipient of the American Society of Mechanical Engineers, ASME, Nadai Medal, of the Materials Division. He received the 2023 Blaise Pascal Medal for Engineering from the European Academy of Sciences. He recently received the American Society of Civil Engineers’ Engineering Mechanics Institute the 2024 Theodore von Karman Medal.

Authors:

George Z. Voyiadjis Louisiana State University
Reem Abo Znemah Louisiana State University
Paul Wood Derby University