A new breakthrough in the journal Additive manufacturing shows a concrete specimen that was inspired by Bouligand hierarchical architectures to develop 3D concrete printing. During drop weight impact testing, the impact performance of 3D printed concrete samples with or without steel fibers was evaluated.
To study: 3D concrete printing of a bio-inspired Bouligand structure: A study on impact resistance. Image Credit: Maxfield Weakley / Shutterstock.com
The study of 3D printing technology based on extrusion on mechanical characteristics has focused on static behavior, with little emphasis on dynamic responses.
A popular 3D concrete painting
Three-dimensional concrete printing (3DCP), also known as additive manufacturing (AM) of concrete, has gained popularity in the construction industry in recent years. Compared with traditional cast molding, extrusion-based 3DCP uses a layer-by-layer deposition method, allowing the fabrication of concrete structures with complicated geometry, reduced dependence on labor, and increased labor. construction productivity.
Nevertheless, the rapid growth of 3DCP is preceded by certain limitations, such as the directional effects on the mechanical characteristics of 3D printed concrete samples, then known as mechanical anisotropy, the complexity of achieving efficient processing. in-process reinforcement during the printing process; and a shortage of experienced workers capable of integrating civil and robotic work.
Biomimicry in the field of AM is becoming more and more popular, equivalent to optimizing mathematical topology, as learning organisms from nature can improve the physical properties and characteristics of things while optimizing the arrangement of things. materials.
The notion of bio-inspired architecture has recently been applied to the design and development stages of 3DCP, where the mechanical and structural qualities of 3D printed concrete elements can be improved while reducing the use of materials.
Great mechanical characteristics
Improvement of the mechanical characteristics of structural concrete with biomimetic helical patterns in 3DCP. These cracking modes helped control the propagation of fractures at the interface between the cement paste filaments formed, resulting in improved power dissipation and durability.
Cracks could form through the substances rather than through the interfaces of the layers in the samples with significant pitch slopes. In addition, the results of their tests showed that increasing the pitch angle improved the modulus of failure and the breaking force in the Bouligand structure.
The Bouligand structure as an inspiration
The Bouligand structure (helical sequence) observed in the cocksfoot club of mantis shrimp is an example. The mantis shrimp’s dactyl appendages allow it to powerfully smash its peeled prey using maximum strike speeds and high generation force. The ability of the dactyl appendage to withstand immense punching force is what makes it so amazing.
Further Reading: Biomimicry Offers Flexible Energy Storage Solution for Portable Electronics
This is due to the helical arrangement of the dactyl club, in which segments of locally parallel chitin fibrils are superimposed, with the top layer standing out at a specific angle from the bottom layer. In most cases, the starting cracks propagate in the direction of rotation of the fibrils in the helical formation, causing twisting and deflection of the cracks, which increases the crack area per volume.
This improves energy dissipation and stress relaxation within the helical structure without inducing catastrophic failure, which explains the increased resistance to fracture of the cocksfoot.
Due to the technological challenge of including traditional steel reinforcement, 3DCP research has added steel fibers in the printing process to improve the mechanical qualities of printable concrete.
Result of the research
The impact length was relatively short for all samples printed without steel fibers, and the maximum applied load ranged from approximately 3 to 4 kN; the degree of energy absorption to cause the specimens to break into two separate parts was low. The maximum impact force and energy absorption were only marginally influenced by the difference in pitch angle.
Under the impact test, the steel fiber reinforced printing samples, the one with the one-way printing design, exhibited a clearly different reaction from these other samples with the helical pattern. The duration of the impact was approximately 1ms, which was significantly shorter than the others. It had a significantly lower peak impact force of about 4 kN than the others (8-13 kN). In addition, it had a significantly lower degree of energy absorption (4 Joules) than the other specimens.
The steel fiber samples show a high peak force of 8N, the highest of any sample. The substantial difference in peak force could be due to the varying orientations of the fibers, which made the transmission of stresses between the cement matrix and the steel fiber more difficult.
Advancement in 3D concrete printing
On the other hand, different impact energy levels can result in a different load rate given to the concrete samples, due to the differences in impactor weight and drop weight resulting in varying impact speed. This will most likely alter the way cracks develop in the fracture zone, which should be reduced in future studies by using a uniform impact energy level.
In addition, new strategies for strengthening the connection of bonded filaments between layers using steel fibers are recommended to increase the performance of the mechanical properties of fiber-reinforced concrete 3D printed with a Bouligand structure.
Liu, J., et al. (2021). 3D concrete printing of a bio-inspired Bouligand structure: A study on impact resistance. Available online December 3, 2021. https://www.sciencedirect.com/science/article/pii/S2214860421006916?via%3Dihub