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By using a two‑step nickel‑catalyzed templating-pyrolysis process, Jianchao Ye et al. manufactured hollow tube‑in‑tube sandwich carbon structures from solid beams of 3D‑printed polymers. Using this processing route, the authors achieved a super stiff lattice structure where the inner and outer tubes are connected through a network of struts. The deformation behavior of this structure was characterized using in‑situ compression tests on a 50×50×125μm micropillar using a 100μm-diameter flat-ended conical diamond probe. The pillars were deformed to 10%, 30% and 50% strain with a strain rate of 10-3 s−1 using a displacement‑controlled feedback mode. The tube‑in‑tube morphology makes this structure ten times stiffer than other carbon tube lattices in the ultra‑low‑density regime (≤10mg cm−3). Furthermore, it showed excellent deformation recoverability at large strains and superior specific damping properties. A key finding of this work is that the stiffness of the structure increases with decreasing density. This is due to the processing route, in which the diameter of the outer tubes becomes inversely proportional to the density. A larger outer tube diameter leads to a higher moment of inertia and corresponding flexural modulus. The stronger tube‑tube junctions make the structure efficient in resisting and transmitting an applied load. This is an impressive novel material that should also inspire other new lightweight, super‑strong, shock-absorbing, and low‑cost structural materials.
The in‑situ experimental work was conducted using the Hysitron PI 88 SEM PicoIndenter with an extended range flexure, which provides a maximum displacement of 150µm.