3D printing of TPMS microlattice: indentation characterisation and numerical analysis

Mechanical metamaterials are emerging as an important tool in many engineering applications, where microarchitectured lattices have advantages of high strength-to-weight ratios, energy absorption capabilities and versatility in designed mechanical behaviours. Whilst a variety of microarchitectured lattices have been previously investigated for their mechanical properties, they have been mostly constrained to strut and plate-based designs and subjected to additional post-processing to modify their functionality. In this work, we demonstrate a novel approach utilising the two-photon polymerisation (2PP) method to generate complex, defect-free microarchitectured lattices. Unlike traditional methods, our technique allows for the direct fabrication of shell-based triply periodic minimal surfaces (TPMS) without requiring any additional post-processing. We utilise gyroid and diamond TPMS unit cells to perform uniaxial micro-compression testing to characterise their mechanical properties. In doing so, we gain insights into the mechanical behaviours of microlattices, with the finding that diamond cells possess superior stiffness and energy absorption potential compared to gyroid cells. To unravel the size-dependency property alterations at this scale, we further analyse a variety of bending beam samples and observed a strain rate-dependent mechanical behaviour attributable to the material's viscoelastic nature. We employ finite element analysis to enhance our understanding of the deformation mechanisms inherent in TPMS topologies, finding good agreement with measured mechanical properties. This work establishes a comprehensive framework that spans from design and geometry characterisation to robust microstructure testing using indentation, combined with comprehensive numerical simulation.