Date of Award
Master of Science in Engineering (MSE)
Mechanical and Aerospace Engineering
Inconel--Mechanical properties., Additive manufacturing.
Additive manufacturing offers the ability to produce complex structures directly from a CAD file, removing the need for complex machining or assembly. Additive manufactured lattice structures (AMLS) offer an excellent balance of light weight with high strength and energy absorption, and achieve multifunctionality unattainable in fully solid structures. Multifunctionality can be further enhanced by varying the topology arrangement of unit cells throughout an AMLS, but risks degrading the structural integrity. This study investigates the mechanical behavior of hybrid Inconel 718 AMLS with unit cell topology varied from row to row, and determines the effects of microstructure, loading direction, stacking order, and strain rate using a combination of experimental data and numerical modeling. All parameters considered are shown to influence the behavior of the AMLS. A solution treatment and aging (STA) heat treatment increased the energy absorption of the hybrid AMLS by ~30% compared to the as-built condition. The flow stress of the AMLS was consistently 7-10% higher when the structures were loaded in the transverse direction compared to the stacking direction. Increasing the strain rate from 10^-3/s to 10^3/s led to a 5-10% increase in first peak stress and affected the failure mechanisms of certain unit cell topologies, leading to shear band formation in Rhoctet topology unit cells, which does not occur under quasi-static loading. It was shown that shear band formation can be suppressed by separating adjacent rows of a shear-band forming topology with a row of unit cells of a topology which does not form shear bands. A comparison of the mechanical behavior of hybrid AMLS with uniform topology AMLS showed that in most cases, the weaker unit cell topology in the structure controls the mechanical behavior of the hybrid AMLS.
Barnes, Baxter, "Mechanical behavior of hybrid additive manufactured inconel 718 lattice structures" (2021). Theses. 367.