Metrological characterization of porosity graded β-Ti21S triply periodic minimal surface cellular structure manufactured by laser powder bed fusion

Abstract

The design of a functionally graded porous structure (FGPS) for use in prosthetic devices is crucial for meeting both mechanical and biological requirements. One of the most commonly used cellular structures in FGPS is the triply periodic minimal surface (TPMS) structure due to its ability to be defined by implicit equations, which allows for smooth transitions between layers. This study evaluates the feasibility of using a novel β-Ti21S alloy to fabricate TPMS-based FGPS. This beta titanium alloy exhibits low elastic modulus (53 GPa) and good mechanical properties in as-built condition. Two TPMS FGPSs with relative density gradients of 0.17, 0.34, 0.50, 0.66, and 0.83 and unit cell sizes of 2.5 mm and 4 mm were designed and fabricated using laser powder bed fusion (LPBF). The as-manufactured structures were analyzed using scanning electron microscopy (SEM) and X-ray micro-computed tomography (μ-CT), and the results were compared to the design. The analysis revealed that the pore size and ligament thickness were undersized by less than 5%. Compression tests showed that the stabilized elastic modulus was 4.1 GPa for the TPMS with a 2.5 mm unit cell size and 10.7 GPa for the TPMS with a 4 mm unit cell size. A finite element simulation was performed to predict the specimen’s elastic properties, and a lumped model based on lattice homogenized properties was proposed and its limitations were explored.

On the Porosity-Dependent Permeability and Conductivity of Triply Periodic Minimal Surface Based Porous Media

“…TPMS split the space in two disjoint but intertwined regions [2]. This enables the construction of complex but highly symmetric porous structures for which the porosity may even be continuously varied in space in order to optimize the physical properties to a target application [1,3,4]. There are two ways to construct a bulk structure from a given TPMS.…”

“…It was also shown that sheet networks for multimorphology geometries had higher elastic stiffnesses than solid networks. In another recent study on functionally graded gyroid TPMS structures Emanuelli et al [4] investigated the influence of density gradients on the static and cyclic compressive elastic moduli of additively manufactured b-Ti21S samples. They demonstrated that these elastic properties could be tailored to those of various kinds of bone tissues for future design of implants.…”