Colloquia

Summary

This study considered the design, manufacturing, testing, and characterisation of a novel lattice structure dedicated to biomedical purposes. A literature study was conducted which defined the specific application of orthopaedic hip implants. Moreover, an additive manufacturing process and a base material were selected. This narrowed the research further down to the manufacturing of CoCrMo cellular lattice structures produced through L-PBF designated for orthopaedic hip implants. Subsequently, further literature on an number of aspects was considered which defined the research gaps. Ultimately, a decision on a specific research gap, defined the main research question: ’what cellular TPMS lattice topology made with CoCrMo through L-PBF, exhibits auxetic behaviour?’. This defined the initiation of the design and-manufacturing phase. Conceptualisation of, through literature inspired lattice structures resulted in a number of suitable models. A selection procedure by quantitively measuring the Poisson ratios of the models through FEA simulation followed. This resulted in four final model variations including a sample with a thickness gradient in the build direction of the printer. Five samples per model were 3D printed employing an Acontiy Midi+ L-PBF system and subsequently removed from the build plate by wire EDM. Based on the geometrical accuracy of the printed samples with the CAD model, the samples were distributed to compressive testing, characterisation, or reserve. A total of 12 samples and 2 reserves were compressive tested. This allowed for the approximation of the Poisson ratio through video analysis. Further, the mechanical properties of yield strength, ultimate compressive strength, Young’s modulus, and the energy absorption capacity were determine. Post-print analysis, microscopic characterisation, and pyrometer data gave further insights on the severity of manufacturing defects and how these affected the compressive behaviour and the mechanical response. This led to the definition of the repetitive defect of bridged voids. Next to that, in the compression of the thickness gradient a plasticity recovery was identified after initial densification.

Overall, this study provided a foundation for further development and integration of this novel TPMS lattice structures in artificial orthopaedic (hip) implants. A comparison with data from literature and reference properties belonging to femoral bone was made. This concluded the breakthrough that this study has presented in the niche of L-PBF-produced, CoCrMo, TPMS lattice structures.