Architected materials that consist of periodic arrangements of nodes and struts are lightweight and can exhibit combinations of properties (such as negative Poisson ratios) that do not occur in conventional solids. Architected materials reported previously are usually constructed from identical ‘unit cells’ arranged so that they all have the same orientation. As a result, when loaded beyond the yield point, localized bands of high stress emerge, causing catastrophic collapse of the mechanical strength of the material. This ‘post-yielding collapse’ is analogous to the rapid decreases in stress associated with dislocation slip in metallic single crystals. Here we use the hardening mechanisms found in crystalline materials to develop architected materials that are robust and damage-tolerant, by mimicking the microscale structure of crystalline materials—such as grain boundaries, precipitates and phases. The crystal-inspired mesoscale structures in our architected materials are as important for their mechanical properties as are crystallographic microstructures in metallic alloys. Our approach combines the hardening principles of metallurgy and architected materials, enabling the design of materials with desired properties.
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The datasets generated and analysed during this study are available from the corresponding author on reasonable request.
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M.-S.P. thanks A. Rollett, F. Dunne, C. Gourlay and S. Holdsworth for discussions, T. Walton and P. Hooper for fabricating some lattices, A. Piglione for providing an SEM image of γ/γ′ microstructure, and an Engineering Alloys Fellowship awarded by the Department of Materials, Imperial College London. M.-S.P. also thanks M. M. Attallah and D. M. Dimiduk for providing the original versions of Fig. 1b, f. I.T. is grateful for funding through EPSRC grants EP/P006566/1 and EP/L02513/1, and the Royal Academy of Engineering.
Nature thanks C. Niordson, N. Pugno and the other anonymous reviewer(s) for their contribution to the peer review of this work.
A patent developed on the basis of the approach proposed in this study has been filed, managed by Imperial Innovations.
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Extended data figures and tables
a, Unit cell of the fcc lattice. b, A macro-lattice cube consisting of 8 × 8 × 8 macro-unit cells. c–e, The rotation sequence to form a twin meta-grain.
Extended Data Fig. 2 Different numbers of meta-grains within the same global volume (40 mm × 40 mm × 40 mm).
a, A single meta-grain. b, c, Two twinned meta-grains, with (b) and without (c) the outer frame. d–h, Four (d), eight (e), 16 (f), 18 (g) and 27 (h) meta-grains. The locations of the boundaries are highlighted.
a–c, Materials consisting of two (a), eight (b) and 16 (c) meta-grains.
a, Stress–strain curves of architected materials consisting of different numbers of meta-grains. b, The flow stress σf of architected materials containing meta-grains at a given nominal strain of 40% increases as the size of the meta-grains decreases.
a, Model of eight meta-grains. b, c, The orientations of lattices (with respect to the global X, Y and Z co-ordinates) in the four meta-grains in the top (b) and bottom (c) layers.
Extended Data Fig. 6 Deformation behaviour of an architected material containing eight meta-grains separated by incoherent high-angle boundaries.
a, b, Macro-lattice fabricated from 316L stainless steel (a) and an elasto-plastic polymer (b). c, d, Stress–strain constitutive behaviour of the macro-lattices fabricated from the steel (c) and polymer (d).
a, Meta-precipitate lattice (orange) embedded in the matrix. b, Cubic morphology and locations of meta-precipitates inside the fcc meta-phase. c, fcc unit cell of the matrix. d, Face-centred tetragonal unit cell of the meta-precipitate.
This material contains 25 meta-precipitates.
a, Single fcc-phase meta-grain. b, Single bcc-phase meta-grain. c, A cube of meta-polygrains (left panel) consisting of two meta-phases: fcc (top and bottom layers; middle panel) and bcc (middle layer; right panel).
a, Unit cell. b, hcp-inspired meta-phase.
Red lines represent the helical movements of basal nodes; for clarity, only the movement of basal nodes on the top plane are shown.
Finite-element method simulation of an architected material containing two twinned meta-grains mimicking twinned bi-crystals. Colour represents the degrees of true strain during compression
Experimental record of the deformation behaviour of an architected hexagonal lattice during a compression loading–unloading cycle
Finite-element method simulation of the deformation behaviour of an architected hexagonal lattice during a compression loading–unloading cycle. Colour represents the degrees of true strain during deformation
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Pham, MS., Liu, C., Todd, I. et al. Damage-tolerant architected materials inspired by crystal microstructure. Nature 565, 305–311 (2019). https://doi.org/10.1038/s41586-018-0850-3
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