Dynamically responsive scaffolds produced by additive manufacturing

Abstract

Additive manufacturing (AM) and design methodology of compliant mechanisms, topology optimisation, lattice structures, metamaterials, etc. allows for the production of complex customised components with very specific properties. One of these types of components is dynamically responsive scaffolds (DRS), made of thin geometric structures that adjust mechanical behaviour to the required loading and direction. This work presents design, numerical simulation, production, and testing of DRS structures as two-dimensional scaffoldings. The scaffoldings were printed in different directions to compare the isotropic behaviour of the AM samples for tensile tests. The methodology for DRS physical testing was demonstrated. The auxetic behaviour of the samples were also studied. Auxetic behaviour will be highly beneficial for DRS as it would allow the DRS to distribute the force more evenly in the event of an impact on the scaffolding. Three series of experiments and numerical simulations were done. First, the scaffoldings were produced from ABS (acrylonitrile butadiene styrene) filament using fused deposition modelling (FDM) system to obtain a basic understanding of DRS mechanical behaviour. Second, the polyamide (PA 2200) specimens were produced with selective laser sintering (SLS) machine. The SLS scaffolding specimens were tensile tested that gave a reading on the tensile force experienced by the specimens during elongation. The data from the tensile tests were then processed into force-over-displacement graphs, and the results were studied. Videos of the tensile tests were also taken to examine the deformation of the specimens as they elongated. Finally, two of the most promising designs were selected and fabricated in a metallic material (Ti6Al4V alloy) by laser powder bed fusion (L-PBF). The physical testing and numerical simulations of Ti6Al4V DRS samples were compared and discussed. This study aims to lay a foundation for the development of DRS, which could one day be used as medical implants that require specific mechanical properties and behaviour that would otherwise not be possible. An essential application for designed DRS could be a cranial implant that can grow with the patient removing the need for future surgeries to replace the implant due to the growth of the skull until it is fully developed. The compliance of the scaffolding, the stiffness, and the support perpendicular to the growth direction make designed DRS especially promising for this application.