June 20, 2014

Researchers at Lawrence Livermore National Laboratory (LLNL) and Massachusetts Institute of Technology (MIT) have developed ultralight materials with 10,000 times more stiffness and could be 3D printed from a variety of materials, such as metals or polymers.

Stiffness and strength declines with the density of any material and their structural elements are more likely to bend under applied load. The team's metamaterials, however, exhibit ultrastiff properties across more than three orders of magnitude in density.

"These lightweight materials can withstand a load of at least 160,000 times their own weight," said team member LLNL Engineer Xiaoyu "Rayne" Zheng. "The key to this ultrahigh stiffness is that all the micro-structural elements in this material are designed to be over constrained and do not bend under applied load."

The design is based on the use of microlattices with nanoscale features, combining great stiffness and strength with ultralow density, the team says.

A visualization shows a full array of the unit cells

The observed high stiffness is shown to be true with multiple constituent materials such as polymers, metals and ceramics, according to the research team's findings. The actual production of such materials is made possible by a high-precision 3-D printing process called projection microstereolithography, which involves using a micro-mirror display chip to create high-fidelity 3D parts one layer at a time from photosensitive feedstock materials. It allows the team to rapidly generate materials with complex 3D micro-scale geometries that are otherwise challenging or in some cases, impossible to fabricate.

For example, they used polymer as a template to fabricate the microlattices, which were then coated with a thin-film of metal ranging from 200 to 500 nanometers thick. The polymer core was then thermally removed, leaving a hollow-tube metal strut, resulting in ultralight weight metal lattice materials.

A single unit of the structure developed by the team, called a stretch-dominated octet truss unit cell, made from a polymer using 3-D microstereolithography.

The team repeated the process with polymer mircolattices, but instead of coating it with metal, ceramic was used to produce a thin-film coating about 50 nanometers thick. The density of this ceramic micro-architected material is similar to aerogel.

"It's among the lightest materials in the world," LLNL Engineer Chris Spadaccini said. "However, because of its micro-architected layout, it performs with four orders of magnitude higher stiffness than aerogel at a comparable density."

Lastly, the team produced a third ultrastiff micro-architected material using a slightly different process. They loaded a polymer with ceramic nanoparticles to build a polymer-ceramic hybrid microlattice. The polymer was removed thermally, allowing the ceramic particles to densify into a solid. The new solid ceramic material also showed similar strength and stiffness properties.

"We used our additive micro-manufacturing techniques to fabricate mechanical metameterials with unprecedented combinations of properties using multiple base material constituents - polymers, metals, and ceramics," Spadaccini said.

Materials with these properties could someday be used to develop parts and components for aircraft, automobiles and space vehicles. The research team's findings are published in a June 20 article in the journal Science.

Posted in 3D Printing Applications

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gb wrote at 6/25/2014 11:01:41 AM:

close source knowledge :( we can´t learn of them http://www.sciencemag.org/content/344/6190/1373 http://www.brown.edu/Conference/ses2013/Program/Abstracts/paper413.htm and willing to sell: "... with potential applications in wide range of areas such as automotive and aerospace engineering, energy, and defense. "

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