FRACTURE AND FATIGUE OF SELECTIVE LASER SINTERED POLYMERIC LATTICE STRUCTURES

Designed cellular lattice structures can be used in many engineering applications. While typically the viscoelastic deformation behavior (stiffness and damping) is utilized in many of these applications, the strength and the fatigue behavior plays an important role for components which are exposed to long-term cyclic loading. Selective laser sintered (SLS) polyamide 12 (PA12) and thermoplastic polyurethane (TPU) materials were investigated in two various lattice structures. A bistable structure based on curved bending beams (BB) and another structure with the combination of bending and torque of the trusses (USF) was designed and produced. To cope with the complexity of the SLS generated structure, three specimen configurations with different printing directions (0° and 90°) were used. To study the bulk behavior cylindrical hollow and notched round-bar specimens, to study the cellular behavior specimens consist of single trusses and knots and specimens contain multiple lattice cells were investigated under both uniaxial and axial/torsional, monotonic and cyclic loading conditions. The monotonic tests provided not only the strength values but relevant material models for subsequent simulations. The cyclic tests were performed at low strains for a comprehensive viscoelastic characterization and at higher strains for fatigue characterization in terms of conventional and strain based S-N curves.
EXTENDED ABSTRACT