Abstract
Lattice structures produced by additive manufacturing have been increasingly studied in recent years due to their potential to tailor prescribed mechanical properties. Their mechanical performances are influenced by several factors such as unit cell topology, parent material and relative density. In this study, static and dynamic behaviors of Ti6Al4V lattice structures were analyzed focusing on the criteria used to define the failure of lattices. A modified face-centered cubic (FCCm) lattice structure was designed to avoid the manufacturing problems that arise in the production of horizontal struts by laser powder bed fusion. The Gibson–Ashby curves of the FCCm lattice were obtained and it was found that relative density not only affects stiffness and strength of the structures, but also has important implications on the assumption of macroscopic yield criterion. Regarding fatigue properties, a stiffness based criterion was analyzed to improve the assessment of lattice structure failure in load bearing applications, and the influence of relative density on the stiffness evolution was studied. Apart from common normalization of S–N curves, a more accurate fatigue failure surface was developed, which is also compatible with stiffness based failure criteria. Finally, the effect of hot isostatic pressing in FCCm structures was also studied.
Highlights
Additive manufacturing (AM), and laser powder bed fusion (LPBF) of metals enables the production of exceptionally complex parts in a cost-effective manner, including architected lattice s tructures[1,2]
This study analyzed the quasi-static and dynamic mechanical properties of lattice structures based on the FCCm unit cell with different relative densities, and the interaction between macroscopic and mesoscopic variables
The quasi-static mechanical properties of FCCm lattice structures follow the expected exponential curve, and their quasi-elastic gradient and yield strength are above the ones of other bending dominated unit cells in the tested direction
Summary
Additive manufacturing (AM), and laser powder bed fusion (LPBF) of metals enables the production of exceptionally complex parts in a cost-effective manner, including architected lattice s tructures[1,2]. These structures offer a set of mechanical property combinations unavailable until few decades ago. Along with the topology of the structures, relative density is an important driving factor of their mechanical properties, defined by the proportion of the parent material within a Representative Volume Element (RVE) of the lattice structure. The effect of heat and surface treatments was extensively studied, concluding that a combination of surface treatments like chemical etching or sand blasting with Hot Isostatic Pressing (HIP) sensibly improves the lattice structures fatigue life[21,22,23]
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