A recent study published in Communications Materials introduced a modular assembly approach to scaling up lightweight, rigid, and programmable pyrolytic carbon (PyC) lattice structures. Researchers explored three assembly mechanisms—adhesive, Lego-adhesive, and mechanical interlocking—and demonstrated the practical applications of their method by using assembled PyC lattices as the core of an aerospace sandwich structure.
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Background
Three-dimensional (3D) architectured structures like PyC lattices hold significant promise for engineering applications in aerospace, marine, and civil infrastructure fields. These structures are valued for their high strength-to-weight ratio, exceptional energy absorption, lightweight composition, low density, and design flexibility.
Despite these advantages, most research to date has focused on sub-millimeter PyC lattices. Practical engineering applications, however, often require larger structures ranging from centimeters to meters. Two main limitations constrain the size of PyC lattices: the build volume of 3D printers and the dimensions of tube furnaces.
Additionally, as lattice size increases, structural strength tends to reduce, creating challenges for large-scale manufacturing. To address these issues, the study proposed a novel approach to assembling millimeter-scale PyC lattices to create larger structures while preserving their outstanding properties.
Methods
The researchers used computer-aided design (CAD) software to design polymer structures, which were then printed using a commercial 3D printer with a photo-curable acrylate-based resin. The lattices were uniformly configured with unit cells repeated in three dimensions.
To optimize mechanical properties, pyrolysis temperatures were varied between 315 °C and 1050 °C. Pre-treatment of the as-printed lattices involved partial carbonization in a vacuum tube furnace under argon at 200 °C for four hours to remove moisture. The final temperature (ranging from 315 °C to 1050 °C) was maintained for an additional four hours, followed by cooling to room temperature.
The researchers also fabricated carbon fiber-reinforced polymer (CFRP) composite face sheets using unidirectional carbon and 105/206 epoxy resin. Each face sheet comprised four layers with a [90/0/90/0] layup configuration. These were vacuum-bagged under 0.1 MPa for 12 hours to minimize voids and partially cured. Full curing occurred over a week at room temperature. Afterward, the sheets were cut into 50×50 mm pieces and attached to conventional honeycomb or PyC cores with a strong epoxy adhesive.
Mechanical properties were evaluated through uniaxial compression and quasi-static indentation tests.
Results and Discussion
The polymer-to-PyC transformation occurred most significantly between 300 °C and 400 °C. As the final pyrolysis temperature increased, the weight and volume of the PyC lattices decreased, leading to improved mechanical performance. For instance, specific strength increased by 116 %, 180 %, and 182 %, while specific modulus improved by 68 %, 98 %, and 120 % for lattices pyrolyzed at 315 °C, 325 °C, and 350 °C, respectively.
Over-pyrolyzed lattices exhibited higher strength and stiffness but significantly reduced ductility compared to partially pyrolyzed lattices. To strike a balance between strength and ductility, lattices pyrolyzed at 325 °C were selected as building blocks for large-scale PyC lattices.
Among the three assembly mechanisms explored—adhesive, Lego-adhesive, and mechanical self-interlocking—the mechanical interlocking method produced PyC lattices with the highest specific strength and modulus. Remarkably, these interlocked lattices even outperformed intact, single-unit PyC lattices of comparable size.
In contrast, lattices assembled using adhesive demonstrated the lowest specific strength and modulus. This reduction in performance stemmed from structural integrity issues, specifically the half-thickness load-bearing struts at the connecting sides, combined with the additional weight introduced by the adhesive.
To demonstrate the feasibility of scaling up PyC lattice structures, the researchers assembled nine individual PyC building blocks into an innovative core (configured as a 4,4,1 assembly) for sandwich composite structures. These composites featured top and bottom CFRP face sheets. When compared to a baseline sandwich composite structure incorporating a conventional aramid paper honeycomb core of identical dimensions, the innovative PyC lattice core exhibited superior indentation resistance and enhanced energy absorption capabilities.
Conclusion
The study successfully demonstrated the design and assembly of stiff, lightweight, and programmable PyC lattice structures using millimeter-scale building blocks. Mechanical interlocking emerged as the most effective, efficient, and cost-friendly assembly method, offering better performance than non-assembled lattices of comparable size.
Additionally, the researchers created a centimeter-sized, curved PyC structure in the shape of "SU," which proved capable of withstanding transverse shear loads, illustrating its versatility. Such structures could be valuable in bioengineering and other advanced applications.
However, future research should focus on assessing the long-term durability and fatigue performance of different joint mechanisms to further validate the modular assembly approach.
Journal Reference
Naderi, A., Lin, W., Tarafdar, A., Zhang, T., Wang, Y. (2025). Stiff, lightweight, and programmable architectured pyrolytic carbon lattices via modular assembling. Communications Materials. DOI: 10.1038/s43246-025-00739-w, https://www.nature.com/articles/s43246-025-00739-w
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