Abstract
Concrete 3D printing (3DCP) is an additive fabrication technique poised to revolutionize the construction industry. In order to realize the full potential of 3DCP, several unique challenges must be overcome, most notably, that of structural instability during the printing process. As an extrusion process, the cementitious building material used for 3DCP must display fluid characteristics when pumped through a nozzle, but must immediately behave as a solid upon deposition in order to support its self-weight. Therefore, the yield shear stress of the material, which defines the boundary between solid and fluid behavior, plays a significant role in the design of 3D printable structures, both in terms of material selection and viable design. The work presented here seeks to better understand these relationships between material, structure, and fabrication process through the use of a computational design tool known as topology optimization, which determines mathematically the optimal material distribution within a design space under given conditions and constraints. By simulating the self-weight only loading and fixed-based boundary conditions of the 3DCP fabrication process, and by considering material yield shear stress as a constraint on design, an optimization problem can be posed for which the solution is a structure that can be successfully fabricated without collapse. To that end, a novel shear stress-constrained topology optimization algorithm was developed and used to generate optimal structural designs for 3DCP fabrication. The resulting structures demonstrate the effect of material yield shear stress on optimal design and indicate an available range of material properties suitable for 3DCP fabrication. This development of material property ranges and design sensitivities can be used for material design, for determination of available or necessary structural design conditions, or for tailoring the fabrication process to achieve printable structures.
