Misplaced Pages

This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these messages) This article provides insufficient context for those unfamiliar with the subject. Please help improve the article by providing more context for the reader. (June 2017) (Learn how and when to remove this message) This article is written like a personal reflection, personal essay, or argumentative essay that states a Misplaced Pages editor's personal feelings or presents an original argument about a topic. Please help improve it by rewriting it in an encyclopedic style. (June 2017) (Learn how and when to remove this message) This article is an orphan, as no other articles link to it. Please introduce links to this page from related articles; try the Find link tool for suggestions. (June 2017) This article may be too technical for most readers to understand. Please help improve it to make it understandable to non-experts, without removing the technical details. (June 2017) (Learn how and when to remove this message) (Learn how and when to remove this message)

Microscale structural metamaterials are synthetic structures that are aimed to yield specific desired mechanical advantages. These designs are often inspired by natural cellular materials such as plant and bone tissue which have superior mechanical efficiency due to their low weight to stiffness ratios.

Synthesis

Projection microstereolithography

This is a layer-by-layer additive printing technology which allows for the creation of arbitrary 3-D structures. Together with nanoscale coating techniques, microstereolithography can create ultralow density, complex microlattices.

The process usually involves a dynamically reconfigurable digital photomask. A 3-D model is decomposed into a series of 2-D planes, the pattern of which is transmitted to the photomask. When shined through by UV light, the mask will transmit the image of the planes onto a lens which subsequently project it onto a photosensitive polymer resin such as 1,6-hexanediol diacrylate (HDDA) causing the liquid to cure in the light exposed areas. These process is repeated for each layer and assembled together to form a 3-D system. Non-polymer lattices can also be created from this process by additional processing. For instance, metallic structures can be created by electroless plating onto the base structure followed by removal of the polymer through thermal heating. Similar deposition techniques can also be used to create ceramic structures.

Continuous liquid interface printing (CLIP)

This technique is an improvement of the layer-by-layer lithography. Additive manufacturing can be time-consuming and create flawed structures. In conventional 3-D printing, oxygen inhibition often causes incomplete curing and bulky surfaces during photosensitive polymerization. By introducing controlled levels of oxygen, efficient initiation and propagation of continuous polymer chains will result. CLIP proceeds via projecting a continuous sequence of UV images (generated by a digital light-processing imaging unit) through an oxygen-permeable, UV-transparent window below a liquid resin bath. Above a permeable window, there is an oxygen inhibition “dead-zone” maintained by a liquid interface. Above the dead zone, the curing part is continuously drawn out of the resin bath, thereby creating suction forces that constantly renew reactive liquid resin. Unlike convention stereolithography which uses step-by-step processing, CLIP employs a continuous flow.

Type

At low relative density limits, these structures display coupled density to stiffness and strength relationships: ${\displaystyle E/E_{s}\propto (\rho /\rho _{s})^{n}}$ and ${\displaystyle \sigma _{y}/\sigma _{ys}\propto (\rho /\rho _{s})^{n}}$ where E is the Young’s modulus, y is the yield stress, ρ is the density and subscript s denotes the bulk value of the specified property.

Stretch-dominated

Stretch dominated structures such as octet tress structure have reduced density to stiffness coupling with n around 1 over many magnitudes of density. This allows for the creation of structural metamaterials which are both ultralight, strong, and energy-absorbing, with elastic behavior up to and 50% compression strain. Often these structures are highly isotropic, with their behavior constant over different loading directions.

Bend-dominated

Bend dominated structures are usually such as tetrakaidecahedron structure have higher n values that result in non-linear density-to-stiffness ratio, since loading on these crystals are shear rather than tensile as in their stretch-dominated counterpart. However, these structures can also be highly compressive. For instance, 3-D simple cubic bulk graphene aerogels created using layer-by-layer lithography showed lightweight, highly conductive and supercompressible (up to 90% compressive strain) properties.

References

1. Zhen, Xiaoyu; Lee, Howon; Weisgrabber, Todd H. (20 June 2014). "Ultralight, ultrastiff mechanical metamaterials" (PDF). Science. 344 (6190): 1373–1377. Bibcode:2014Sci...344.1373Z. doi:10.1126/science.1252291. hdl:1721.1/88084. PMID 24948733. S2CID 8438316.
2. Tumbleston, John; Shirvanyants, David; Ermoshkin, Nikita (20 March 2015). "Continuous liquid interface production of 3D objects". Science. 347 (6228): 1349–1352. Bibcode:2015Sci...347.1349T. doi:10.1126/science.aaa2397. PMID 25780246. S2CID 7623328.
3. Meza, Lucas R.; Das, Satyajit; Greer, Julia R. (12 September 2014). "Strong, lightweight, and recoverable three-dimensional ceramic nanolattices" (PDF). Science. 345 (6202): 1322–1326. Bibcode:2014Sci...345.1322M. doi:10.1126/science.1255908. PMID 25214624. S2CID 31887166.
4. Zhu, Cheng; Han, Yong-Jin T.; Duoss, Eric B. (22 April 2015). "Highly compressible 3D periodic graphene aerogel microlattices". Nat. Commun. 6 (6962): 6962. Bibcode:2015NatCo...6.6962Z. doi:10.1038/ncomms7962. PMC 4421818. PMID 25902277.

• 3D printing processes
• Metamaterials