Additive Manufacturing of Heterogeneous Composites for Biomimetic Robots



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Printing complex objects from computer-aided design models is a unique capability of additive manufacturing (AM). Developing this ability to print heterogeneous materials with diverse mechanical properties will advance AM beyond the current capabilities, eliminating the need for assembly and post-processing, and promoting the efficient design of multifunctional complex objects with minimum time and cost. Considering this concept, we aim to investigate this technology to fabricate biologically inspired structures, actuators, and robots. In this dissertation, first, an inexpensive 3D printer is developed for a single step fabrication of a novel bioinspired joint system, consisting of dissimilar materials with high strength and high strain. The joint consists of thermoplastic parts reinforced with metal fibers that resemble bones and soft elastomer that mimics soft tissue. An open-source 3D printer is modified to print thermoplastic with continuous fibers (copper and steel), where the metal fibers act as reinforcement within a polymer matrix (PLA and PETG). The influence of different wire materials and polymer matrixes on the tensile modulus and ultimate tensile strength is studied. The properties of the samples are predicted analytically using several models and compared with experimental results. Highly stretchable elastomer is directly 3D printed and simultaneously cured by heating. Moreover, a cost effective multi-material AM (modified FDM and DIW) is developed that maintained high elasticity and sufficient strength for printing components that mimic the musculoskeletal system. In the second part of the study, the main focus is on the highly elastic materials, sacrificial materials, and actuation units to further develop the fabrication of highly elastic soft structures. Silicone thinner is used to tailor the mechanical properties of the soft material, and it is shown that the addition of the thinner to the silicone reduces the tensile modulus and improves the elongation to break. By adding 20% volume thinner to the silicone, the 3D printed silicone samples reached to 1260% elongation without breaking, which is the highest among all the 3D printed elastomers previously reported. However, this strain is not achieved in the cyclic tensile test, instead, the maximum strain was 600 % where the sample failed after 40 cycles. To create hollow channels during 3D printing of silicone, carbohydrate glasses are introduced as sacrificial materials. Few configurations of fluidic actuators that are commonly used in soft robots are developed by forming channels in the silicone elastomer via 3D printed sacrificial carbohydrate structures. The last part is the design and development of biomimetic structures (jellyfish, modular joint and starfish structures) by the existing method of robot manufacturing and proposed AM techniques. The primary focus on this part is on the design, development, and analysis of the heterogeneous structures of biomimetic robots. Therefore, a complete fabrication process for each of the robotic structure is identified and used to make multiple functional prototypes. All the demonstrated biomimetic systems are actuated by embedding twisted and coiled polymer (TCP) muscle during or after the fabrication process or assembled. The flexibility of the TCP enables the soft robot to bend, twist, and change shape while it is embedded in the structure. 6-Ply and 4-Ply silver-coated nylon (TCP) muscle geometries were studied and used for the design and development of the jellyfish and starfish like robots. The capabilities offered by these biomimetic robots are extensively characterized such as: (i) swimming, (ii) multidirectional bending, and (iii) producing morphing shapes. Extensive evaluations of these capabilities with functional prototypes demonstrate that integration TCP with elastomer is viable for creating biomimetic robots.



Additive manufacturing, Three-dimensional printing, Biomimetic materials, Robots