Designing bioinspired composite reinforcement architectures via 3D magnetic printing

Abstract

Discontinuous fibre composites represent a class of materials that are strong, lightweight and have remarkable fracture toughness. These advantages partially explain the abundance and variety of discontinuous fibre composites that have evolved in the natural world. Many natural structures out-perform the conventional synthetic counterparts due, in part, to the more elaborate reinforcement architectures that occur in natural composites. Here we present an additive manufacturing approach that combines real-time colloidal assembly with existing additive manufacturing technologies to create highly programmable discontinuous fibre composites. This technology, termed as '3D magnetic printing', has enabled us to recreate complex bioinspired reinforcement architectures that deliver enhanced material performance compared with monolithic structures. Further, we demonstrate that we can now design and evolve elaborate reinforcement architectures that are not found in nature, demonstrating a high level of possible customization in discontinuous fibre composites with arbitrary geometries.

Figure 1. Bioinspired composites with microstructured architectures can be recreated with 3D magnetic printing.

(a) The Haliotidae sp. abalone shell exhibits a layered structure of calcite prisms topping in-plane aragonite platelets (nacre). Reprinted from ref. (reproduced with permission from Wiley-VCH). This architecture is (b) simplified and (c) 3D magnetic printed. (d) The dactyl club of the peacock mantis shrimp exhibits a cholesteric architecture of mineralized chitin fibres. Reprinted from ref. (reproduced with permission from Elsevier). This architecture is (e) simplified and (f) 3D magnetic printed. (g) The mammalian cortical bone exhibits concentric plywood structures of lamellae-reinforced osteons. Reprinted from ref. (reproduced with permission from Elsevier). This architecture is (h) simplified and (i) 3D magnetic printed. All printed microstructures are acrylate-urethane co-polymers reinforced by 15 volume percent alumina platelets. Scale bar, 5 μm in a; 25 μm in c; 15 μm in d; 50 μm (black) and 20 μm (white) in f; 200 μm in g; and 5 mm (black) and 25 μm (white) in i.

Figure 2. The 3D magnetic printing process.

(a) The 3D magnetic-printer setup uses a digital light processor (DLP) to photo-polymerize resin with ultra-violet (UV) while a magnetic field is simultaneously applied via electromagnetic solenoids. (b) The 3D magnetic printing process systematically aligns and selectively polymerizes groupings of voxels programmed to have specific reinforcement orientation within each layer of printed material based upon a shifting field. The build plate peels after a layer is complete to print additional layers. (c) With 3D magnetic printing, detailed reinforcement micro-architectures can be printed from design files including this example of the golden rectangle which exhibits clear feature sizes as low as 90 μm. Scale bar, 2 mm, 500 and 50 μm in c from left to right.

Figure 3. Mechanical properties of 3D magnetic printed composites.

(a) Schematic of an individual voxel indicating the two strong and one weak axes of a polymer voxel containing fully oriented ceramic microplatelets. (b) Tensile tests were conducted on printed composites with monolithic reinforcement orientation. Printed composites with voxels containing ceramic microparticles aligned parallel to the principal stresses exhibited higher stiffness (+29%), higher hardness (+23%) and higher strain at rupture (+100%) as compared with composites with voxels exhibiting perpendicular alignment. (c) The hierarchy of a 3D magnetic-printed block with a concentric square pattern is schematically shown. (d) The block is produced with 3D magnetic printing (the block is 2.2 × 2.2 cm and 3 mm thick) and subjected to hardness mapping. Scale bar, 4 mm in d.

Figure 4. Mechanical analysis of printed composites with circular defects.

(a) Samples with circular defects are 3D magnetic printed with programmable reinforcement architectures including ‘osteon-inspired' microstructures with concentric reinforcement orientation and ‘monolithic' microstructures as shown in b. (b) ‘Osteon-inspired' microstructures are predicted to exhibit less relative strain (ɛ_rel) compared with misaligned ‘monolithic' microstructures. (c) Tensile tests of printed composites with circular defects show that ‘osteon-inspired' architectures out-perform all but the perfectly aligned ‘monolithic' sample. As the ‘osteon-inspired' architecture is symmetric, the load can be applied at any angle relative to the microstructure to obtain similar performance. Scale bar, 5 mm in a.

Figure 5. Crack steering with 3D magnetic printed architectures.

3D magnetic-printed architectures with islands that match and contrast the reinforcement orientation of the bulk film. Intricate micro-architectures are found to be capable of crack steering (lengthening the crack). Scale bar, 4 mm.