Three-Dimensional Architected Carbon Composites via Additive Manufacturing

The design of modern composite materials, as used in a wide range of engineering applications, is largely derived from a traditional framework based on laminates. While resulting in desirable strength and stiffness properties, the laminate-based structure leads to a high degree of anisotropy and unique failure modalities like interlaminar failure, limiting the performance of these composites under complex loading conditions. Meanwhile, recent work in the field of architected materials has yielded a thorough understanding of geometry-dependent material behavior, enabling the development of highly robust architectures with tunable (an)isotropy. In particular, the framework of architected interpenetrating phase composites (IPCs), i.e., two-phase materials consisting of an architected structure surrounded by a matrix, has led to the development of strong, resilient, and damage-resistant materials. However, such advances have focused primarily on describing the response of polymer-polymer composites due to the ubiquity of polymer-based freeform fabrication methods, with performances that hinder the applicability of IPC-based architectures to many real-world applications.<br/><br/>Here, we establish a facile and scalable fabrication method based on desktop 3D-printing followed by pyrolysis to create carbon-based, three-dimensional architected interpenetrating phase composite (IPC) materials. This fabrication method yields centimeter-scale pyrolytic carbon specimens with feature sizes smaller than 100 microns, enabling a true separation of scales. Moreover, the freeform fabrication enabled by 3D printing allows for geometries of arbitrary complexity to be fabricated, carbonized, and subsequently infiltrated, creating scalable carbon-based IPCs.<br/><br/>To understand the effect of morphology on the mechanical behavior of carbon-based 3D architected IPCs, we fabricate and test samples with periodic and aperiodic microstructures, determining their uniaxial compressive response with particular emphasis on the non-linear and failure regimes. Using X-ray computed tomography (XCT), we visualize the evolution of damage in the composite and show that the presence of a load-bearing matrix contributes to a high-strength, high-toughness, stable failure behavior. Together with computational models, we use the XCT reconstructions to understand how the development of a 3D, highly tortuous pathway for stress delays or prevents catastrophic failure of the traditionally brittle architecture phase, resulting in energy dissipation performance of the composite that is 1.6 times higher than the sum of its constituent parts, reaching a specific energy absorption comparable with automotive-grade wound fiber tubes. Altogether, this work broadens our established understanding of the link between architecture and mechanics in composite materials and provides an avenue for the additive manufacturing-based fabrication of centimeter-scale carbon-based composites with sub-millimeter feature sizes.