Anton Köllner

An analytical framework for harnessing buckling instabilities in metamaterial lattices is presented. The framework comprises systematic procedures where mechanical rigid-link--spring models are generically constructed and analysed in combination with a path-following solver. The nonlinear mechanical response of lattices is tailored through specifically derived cross-sectional modifications making use of explicit incremental relationships between buckling loads and stiffness parameters employed within an optimisation routine. The resulting post-buckling behaviour is tuned by triggering more favourable deformation modes, alongside requiring buckling loads to be sufficiently separated to suppress deleterious modal interaction phenomena. The framework is verified through nonlinear finite element simulations. The present approach is demonstrated to provide an efficient and robust procedure for developing improved lattice designs that produce enhanced mechanical performance under large deformations.

The additive manufacturing of natural fibre-reinforced polymers is a pivotal method in developing sustainable engineering solutions. Using the fused filament fabrication method, the current study investigates the additive manufacturing of hemp-reinforced polybutylene succinate (PBS) alongside its mechanical characterization. Two types of hemp reinforcement are considered: short fibres (max. length smaller than 2 mm) and long fibres (max. length smaller than 10 mm), which are compared against non-reinforced (pure) PBS. A detailed analysis is performed regarding the determination of suitable 3D printing parameters (overlap, temperature, nozzle diameter). In a comprehensive experimental study, additionally to general analyses regarding the influence of hemp reinforcement on the mechanical behaviour, the effect of printing parameters is determined and discussed. Introducing an overlap in the additive manufacturing of the specimens results in improved mechanical performance. The study highlights that the Young’s modulus of PBS can be improved by 63% by introducing hemp fibres in conjunction with overlap. In contrast, hemp fibre reinforcement reduces the tensile strength of PBS, while this effect is less pronounced considering overlap in the additive manufacturing process.