Variable stiffness functionally graded TPU materials with TPMS lattice structures for FDM 3D printing: design, simulation and experimental validation

Recent advances in additive manufacturing and digital materials science are giving rise to entirely new approaches to the development of function-oriented structural materials with specified technical characteristics. In the field of lower limb prosthetics, the challenge of ensuring uniform stress distribution in the “stump–prosthesis” system remains. Pressure redistribution can be achieved through the introduction of innovative, next-generation materials. The development of functionally graded polymeric materials, which combine high strength, variable stiffness, reduced mass, and adaptive properties, is of particular relevance. This work examines a step-by-step process for creating a functionally graded polymeric material based on TPU A95 using FDM printing. An analysis was conducted of existing topologies based on triple periodic minimal surfaces and classical geometric structures. The limiting porosity values for FDM technology were evaluated by increasing the wall thickness of the lattice structures from 0.5 to 2.5 mm, which corresponded to a decrease in porosity from 90 % to 10 %. Numerical modeling and experimental verification were performed for three types of lattice topologies: Gyroid, Schwarz Primitive and Honeycomb structures at 75 % and 40 % porosity. The mechanical behavior was evaluated using the finite element method, followed by a comparison of the results with data from cyclic compression tests. It was found that the Gyroid structure exhibits the most favorable combination of specific stiffness and uniform stress distribution due to the isotropic character of deformation. For this topology, the discrepancy between numerical and experimental results did not exceed 8 –12 % at low porosity. Honeycomb structures exhibited pronounced anisotropy and reduced resistance to transverse loads, while for the Schwarz Primitive and Honeycomb architectures at high porosity, increased deviations in the calculated data were identified, which is associated with technology-induced defects in FDM printing.

1. Ministry of Science and Higher Education of the Russian Federation - No 075-15-2024-562