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S. Baumgartner, J. Stampfl:
"Nacre-inspired toughening of photopolymers by 3D-printing";
Talk: Bio-inspired Materials 2018, Potsdam; 03-19-2018 - 03-22-2018.

Additive manufacturing (AM) has developed into a promising technology for various applications and provides advantages over conventional manufacturing methods like casting or milling. Drawback of most commercially available systems are the insufficient mechanical properties and the limited resolution of the printed parts. With industry calling for tougher and stronger materials, especially for engineering applications, we developed a stereolithography (SL) process based on the principal of digital light processing (DLP), combined with direct inkjet printing. With this we are able to print highly viscous photocureable resins with high resolution and excellent surface quality and mimic the thermo-mechanical properties of natural structures like nacre by jetting thin layers of soft material into a hard matrix. In the first step of the process, a resin is cured in a material vat, forming the matrix of the printed part. In a second step, a high-resolution print head selectively places elastomer droplets onto this previous layer which then are cured during the next stereolithographic step. Those so-formed "digital materials" show promising results regarding enhancement of the thermo-mechanical properties, as first experiments indicate an increase of the strain at break and impact strength by over 50% and 40%, respectively - compared to the plain matrix material. By adding filler materials to both, the matrix and the ink formulation, an even better simulation of marine material-like behavior can be achieved. Further investigations have to be made in order to determine the influence of surface modification via inkjet, the ink amount and droplet distribution in the printed part on the toughness and overall behavior of this digital material. Also, by further developing the matrix material and finding suitable ink formulations the already promising results of the current combination might be further improved. First results show an increment of the impact resistance from 7.7 to 10.5 kJ/m² and the strain at break from 9.5% to 15% while only decreasing the tensile strength by 15% and not affecting the creep behavior at all. With this novel technology available new applications like customization of medical products or multimaterial approaches can be established.