A recent article published in the journal Additive manufacturing demonstrated topology (TO) optimization of three-dimensional (3D) printed concrete for construction.
Study: Topology optimization for 3D printing concrete with various manufacturing constraints. Image Credit: Zapp2Photo/Shutterstock.com
Additive manufacturing (AM) / 3D printing enables the fabrication of complex designs in a layer-by-layer process with greater design flexibility in geometry. AM is used in different industrial applications, such as automotive, biomedicine and aerospace.
Recently, AM has gained considerable attention for enabling free-form designs and automation in the architecture, engineering, and construction (AEC) industry. Among the various AM strategies, 3D concrete printing (3DCP) is rapidly gaining importance in the AEC industry for building large-scale structures by extruding cement-based materials. For example, 3DCP has been used to build 3D printed concrete walls, lattice-like pillars, and custom columns.
TO optimizes the structural layout under the prescribed design conditions. Structurally inefficient areas in a design are phased out using an iterative procedure to refine the design. Different methods including Solid Isotropic Material with Penalization (SIMP) method, Homogenization method, Bidirectional ESO (BESO) method, Level set method, Movable morphable component (MMC) method and evolutionary structural optimization (ESO) method, are currently used. for the TO of the works.
The freedom of design allowed by AM is compatible with the TO concept. Thus, the integration between TO and 3DCP can help fabricate structurally efficient and spatially intriguing structures for large-scale construction. However, 3DCP-TO integration also presents several challenges, which must be addressed before its implementation.
For example, cantilever structures can lose their self-supporting ability due to gravitational force if their cantilever angle, which typically ranges from 70oh at 90oh depending on the application, exceeds the maximum limit. Similarly, printed structures exhibit anisotropic structural behavior and their surfaces are vulnerable to cracking due to shrinkage due to the nature of 3DCP.
Additionally, compatible reinforcement strategies including micro-cable and fiber reinforcement, lattice reinforcement, and bar penetration should be explored to incorporate reinforcements in tensile areas. In addition, 3DCP requires continuous printing to avoid nozzle blockage due to material solidification, since simultaneous stop and start operation is extremely difficult in printers with nozzle motion systems and nozzle motion systems. separate material supply.
These manufacturing constraints are typically resolved during the post-processing stage, requiring additional design effort and significant modifications, which affect the structural efficiency of the topology-optimized design. Thus, an explicit TO framework incorporating different 3DCP manufacturing constraints is needed to successfully facilitate integration between these domains.
In this study, an integrated TO framework was proposed to meet the different constraints of 3DCP fabrication. A freestanding design was generated by introducing a layer-by-layer sensitivity scheme to replicate the layer-by-layer printing process.
The BESO procedure was used in this study because of its compatibility with image processing strategies using good computational efficiency and binary variables. Numerical studies have been performed to evaluate the efficiency and robustness of the proposed algorithm based on the reference cantilever example widely used in TO studies. In the experimental section, the feasibility of the algorithm in practical applications was tested by fabricating a TO chair using 3DCP.
Various print patterns were specified and the generated patterns were kept continuous and vertically aligned with each iteration. The geometric continuity of each layer was ensured by the implementation of an innovative continuous extrusion constraint, which led to uninterrupted extrusion and movement of the nozzle during the 3DCP manufacturing process.
The domain segmentation of the TO structure, which is analogous to the concept of modular construction, has been proposed to allow favorable impression direction in each segment and modular construction. The 3DCP anisotropic behavior was also simulated in the TO framework by considering a transverse isotropic material model in finite element analysis (FEA).
An innovative BESO TO framework has been demonstrated that addresses several 3DCP manufacturing constraints. The 3DCP overhang angle limit was satisfied by the per-layer sensitivity scheme. Vertical alignment of the optimized design has been guaranteed along the print direction, leading to a self-supporting structure in the orientation defined by the user. Alternative solutions with similar performance have been obtained using the self-support constraint.
The overflow limit was circumvented by domain segmentation. The anisotropy of the 3DCP process was effectively simulated in the optimization process using the transverse isotropic material model. Although the anisotropy of 3DCP printing has caused variations in the optimized designs, the main structural elements remain unchanged.
Implementing a new continuous extrusion constraint in the TO framework has made the continuous print operation easier. The shortest possible routes were located based on the minimum distance principle and the connected component labeling algorithm.
The optimized design achieved overall geometric continuity with interconnected two-dimensional (2D) geometry in every layer. The continuous extrusion constraint succeeded in connecting the isolated areas of each layer without significantly affecting the structural performance of the designs.
The combination of the continuous toolpath algorithm and the continuous extrusion constraint enabled the fabrication of a topology-optimized design with good efficiency and print quality. However, low volume fraction designs have been modified during post-processing to meet the nozzle size constraint.
The topology-optimized chair was successfully printed based on the proposed algorithm, which demonstrated the robustness of the algorithm to meet different 3D manufacturing constraints in a real-world design environment.
To sum up, the results of this study effectively demonstrated the TO for 3DCP with different manufacturing constraints. A constraint constraint can be integrated into the TO framework in future studies to achieve a more accurate simulation.
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Bi, M., Xia, L., Tran, P. et al. Topology optimization for 3D printing concrete with various manufacturing constraints. Additive manufacturing 2022. https://www.sciencedirect.com/science/article/pii/S221486042200375X?via%3Dihub