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S. Baumgartner, J. Stampfl:
"Digital Toughening: Miming nacre-like structures via 3D-printing";
Talk: 5th Bioinspired Materials 2020, Irsee/Online; 03-16-2020 - 03-19-2020.

Additive manufacturing (AM) has been a hot topic in various fields of application for the past decades. While most discussions go on about what technologies to substitute with AM, the more general question should be how to use its qualities for enhancing the manufacturing possibilities. In contrast to the obvious advantages of 3D printing, such as nearly unlimited freedom of design, less waste material and just-in-time production, the weak points of most commercially available AM technologies are the mechanical properties of the printed parts. Especially photopolymers, which are used for stereolithography (SL), are rather brittle. Looking into nature, one can find different strategies to overcome the lack of toughness of certain materials and structures. Shells of marine animals, as an example, often consist of complex organic/inorganic structures, which form materials of extraordinary toughness. The different phases on their own often show poor mechanical properties, whereas the combination exhibits tough behavior. By varying the Young´s Modulus of the separate phases, crack propagation can be hindered. Up to now, it has not been possible to copy those materials in a larger scale. We took the hierarchical structure of nacre as an example and built a hybrid printing system, consisting of a SL-unit and an inkjet printhead. Using the layer-by-layer approach of 3D printing, the goal was to mimic the nacre structure of brittle platelets, separated by soft, thin layers of organic material. To achieve this, a brittle matrix material is cured via a stereolithography process. An inkjet printhead then selectively places droplets of an elastomeric material in between those layers. In first studies with different acrylic polymer materials, we could show, that introducing those thin discrete layers of softer material lead to a significant increase in impact strength and toughness, 40% and 50% respectively, compared to the plain matrix material. In this study, we are evaluating the possibilities for ceramic/composite materials where the matrix material is highly filled with up to 54 vol. % of ceramic powder. In a first approach, tricalcium phosphate (TCP) and calcium carbonate are used as filler materials. With this, is possible to further imitate the organic/inorganic structure of nacre, and build up parts beyond the micro scale.

3D-printing, Digital Materials, Toughening