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The integration of endless fiber reinforced composites in additive manufacturing enables the automated production of materials with high mechanical properties such as strength. The current state of the art utilizing print heads with separate fiber and matrix feeds showed that, without active infiltration, the fiber infiltration is poor or not possible for thermoplastics with low flowability (high viscosity). In this work, the improvement of the print head technology and the investigated infiltration effect lead to a significantly higher infiltration. The material selection of thermoplastic matrix (PA6) and fiber reinforcement (carbon fiber) were adjusted for the new process parameters. The selection of the fiber matrix combination was conducted using the interfacial tension calculations at room temperature. The polar and dispersive surface energy of two different carbon fibers as well as the wetting of PA6 polymer melts on carbon fibers and on aluminum carriers were investigated. The calculation of composite properties using material data of the matrix and fiber was used to determine the process windows for specific parameters such as layer height, layer width and nozzle size. Furthermore, the mechanical properties and the cost of the composite can be determined in relationship with the materials used and the fiber volume content. The composition of the fiber sizing and the influence of high processing temperatures was characterized using TGA, FTIR spectroscopy and XPS analysis. The processing parameters and rheological behavior of PA6 thermoplastic resins and mixtures were investigated, and a mixture of 75 wt.% Ultramid B3k and wt.25% of Ultramid B50l from BASF was used for the composite fabrication by material extrusion. The optimization of the extrusion process enables the production of filaments with higher flowability (low zero viscosity), with the fiber infiltration improved by the adjusted rheological behavior. Samples for mechanical and optical analysis were fabricated using the self developed print head and three different types of carbon fibers. Three point bending properties were investigated as a function of layer height and printing temperature; tensile properties of single composite strands fabricated with different printing temperatures and multilayer composite were also characterized. The fiber volume content and the porosity were evaluated in crosssectional analyses. The investigated material combinations, optimization of process parameters and the fiber roving infiltration effect in the print head leads to higher mechanical properties and lower porosity in the composite.

additive manufacturing; 3D printing; composite

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The engineering and utilization of biocomposites is a research field of major scientific and industrial interest worldwide. The biocomposite area is extensive and spans from structured and solid biocomposites (e.g., reinforced bioabsorbable polymers), films (e.g., antimicrobial barriers), to soft biocomposites (e.g., use of alginates, collagen and nanocellulose as components in bioinks for 3D bioprinting). Key aspects in this respect are the appropriate engineering and production of biomaterials, nanofibres, bioplastics, their functionalization enabling intelligent and active materials, processes for effective manufacturing of biocomposites and the corresponding characterization for understanding their properties. The current Special Issue emphasizes the bio-technological engineering of novel biomaterials and biocomposites, considering also important safety aspects in the production and use of bio- and nanomaterials.

Encapsulation --- 3D Printing --- Surface modification --- Microbiology --- Cellulose --- Biocompatibility --- Scaffolds

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Three-dimensional printing. --- 3-D printing --- 3D printing --- 3DP (Three-dimensional printing) --- Additive manufacturing

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This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contact

soft robot --- soft actuator --- soft sensor --- continuum manipulator --- fiber jamming --- growing --- 3D printing --- learning-based modeling

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Three-dimensional printing is a futuristic technology capable of transforming the ways in which we make components and devices. It is almost certain that this technique will find its niche in the manufacturing sector in the very near future. In view of the growing importance of 3D printing, this book addresses key issues related to emerging science and technology in this area. Detailed and informative articles are presented in relation to a wide variety of materials, including those based on critical engineering metals such as aluminum, magnesium, titanium and composites. Advances in various techniques, such as electron beam melting and selective laser melting are discussed. Of key importance in the area of materials science is the end properties of the materials following processing. Accordingly, the articles presented critically discuss the effects of microstructural features such as porosity, forming defects and the heat treatment induced effects on the mechanical properties. Applications covered in these articles are targeted at the aerospace, automobile, defense and aerospace sectors. Overall, the information presented in this book is of significant importance for academic and industrial-based researchers who wish to inform themselves regarding this upcoming highly promising manufacturing technique.

composites --- laser metal deposition --- additive manufacturing --- titanium --- selective laser melting --- magnesium --- aluminum --- 3D printing --- electron beam melting