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J. Stögerer, S. Baumgartner, J. Stampfl:
"Multi-material Toughening of Composites in Polymer 3D-Printing";
Talk: EUROMAT 2021, Wien; 09-13-2021 - 09-17-2021.

3D-Printing is an increasingly used manufacturing method enabling the accurate production of almost any desired geometries. In polymer 3D-printing, mainly light-curable photopolymers based on acrylates and methacrylates are utilized in a layer-by-layer process. These substances provide high spatial resolution and good curing. Although produced parts exhibit high strength and stiffness offering good load bearing, end products are inherently brittle. Thus, low fracture toughness is a fundamental problem limiting industrial applications. One approach to tackle brittleness is the application of the material inhomogeneity effect. Two materials with significantly different mechanical properties (i.e., Young´s modulus and yield strength) are applied to produce a laminated part. While strong and brittle material layers provide high stiffness, soft yielding layers provide toughness. Mechanical properties are adapted via constant alteration of material layers. An increase in fracture toughness can be achieved through very thin soft material layers, thus without deteriorating stiffness significantly. Applying this concept, inherently brittle polymer composites built in a stereolithography process are adapted. A hybrid 3D-printing device combining stereolithography and inkjet printing structures samples of two different materials with strongly varying mechanical properties in a layer-wise manner. Two groups (i.e., hybrid material group A and control group B solely consisting of resin) of single edge notched bending specimens and Dynstat impact test specimens are produced. Fracture mechanical analysis reveals a significant increase of about 50% in Dynstat impact strength of group A compared to group B. Moreover, group A specimens exhibit a decrease in yield strength of about 20% compared to group B and clear plastic deformation before fracture while group B parts show completely linear elastic fracture behaviour in 3-point bending tests. The material inhomogeneity effect concept is successfully implemented in a 3D-printing process to increase fracture mechanical behaviour remarkably.

3D-Printing, Toughening, Composites, Hybrid Printing