Simulation of Additively Manufactured Auxetic Lattice Structures for the Estimation of Energy Absorption and Dissipation Potentials

Kurzfassung

This thesis investigates the potential of additively manufactured auxetic lattice structures for energy absorption and dissipation with a particular emphasis on their crashworthiness performance. Auxetic materials, characterized by their negative Poisson’s ratio, possess peculiar deformation mechanisms that cause lateral contraction under compression, sugesting potential advantages for energy absorption. Three thermoplastic polymers were selected to explore the influence of mechanical properties on the acquirable performance: TPU, PP, and PA12, which were characterized through mechanical testing following ISO standards for tension and compression. High Speed Sintering (HSS) manufacturing was used to produce specimens and the auxetic structures. From the test data, material models were developed and validated in LS-DYNA, progressing from simple piecewise linear plasticity (MAT_024) to an advanced compression-tension differentiated model (MAT_124). A parametric numerical investigation was carried out in order to evaluate the influence of several design variables on the energy absorption capability of the auxetics. The study included the effects of unit cell base size, relative strut thickness, loading orientation, and material selection on performance metrics such as Specific Energy Absorption (SEA), Peak Crushing Force (PCF), and Mean Crushing Force (MCF). The results demonstrated a 25% higher SEA in 3D reentrant structures loaded at 90° compared to the standard orientation, and an optimal relative thickness of 10% of the base size. Energy dissipation mechanisms were quantified by analyzing both stored elastic energy and irreversibly dissipated energy through loading-unloading simulations. PA12 presented the highest dissipation ratio (96%) due to failure, while TPU showed predominantly elastic behavior, and PP provided an intermediate performance, but the highest overall SEA. A comparative analysis later revealed superior crashworthiness in conventional lattice architectures. Similarly, 2D honeycomb and extruded reentrant structures outperformed their 3D counterparts, achieving higher SEA values, but at the cost of increased structural mass. This research establishes a methodology for the design, manufacturing, and simulation of auxetic structures for crash applications. The study provides valuable insights into their trade-offs in terms of structural performance, providing guidance for future accurate simulations of HSS 3D printed crash structures and lattices.