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June 19, 2014

Supermaterial with the weight and density of aerogel but 10,000 times the stiffness and enabling super solar sails in the 2030-2040 timeframe

Engineers at MIT and Lawrence Livermore National Laboratory (LLNL) have devised a way to translate that airy, yet remarkably strong, structure down to the microscale — designing a system that could be fabricated from a variety of materials, such as metals or polymers, and that may set new records for stiffness for a given weight.

The design is based on the use of microlattices with nanoscale features, combining great stiffness and strength with ultralow density, the authors say. The actual production of such materials is made possible by a high-precision 3-D printing process called projection microstereolithography, as a result of the joint research collaboration between the Fang and Spadaccini groups since 2008.

“We found that for a material as light and sparse as aerogel [a kind of glass foam], we see a mechanical stiffness that’s comparable to that of solid rubber, and 400 times stronger than a counterpart of similar density. Such samples can easily withstand a load of more than 160,000 times their own weight,” says Fang, the Brit and Alex d’Arbeloff Career Development Associate Professor in Engineering Design. So far, the researchers at MIT and LLNL have tested the process using three engineering materials — metal, ceramic, and polymer — and all showed the same properties of being stiff at light weight.

The material has the same weight and density as aerogel -- a material so light it's called 'frozen smoke' -- but with 10,000 times more stiffness. This material could have a profound impact on the aerospace and automotive industries as well as other applications where lightweight, high-stiffness and high-strength materials are needed.

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.

"We have fabricated an extreme, lightweight material by making these thin-film hollow tubes," said Spadaccini, who also leads LLNL's Center for Engineered Materials, Manufacturing and Optimization. "But it was all enabled by the original polymer template structure."

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.

The LLNL-MIT teams' new materials are 100 times stiffer than other ultra-lightweight lattice materials previously reported in academic journals.



Science - Ultralight, ultrastiff mechanical metamaterials



The mechanical properties of ordinary materials degrade substantially with reduced density because their structural elements bend under applied load. We report a class of microarchitected materials that maintain a nearly constant stiffness per unit mass density, even at ultralow density. This performance derives from a network of nearly isotropic microscale unit cells with high structural connectivity and nanoscale features, whose structural members are designed to carry loads in tension or compression. Production of these microlattices, with polymers, metals, or ceramics as constituent materials, is made possible by projection microstereolithography (an additive micromanufacturing technique) combined with nanoscale coating and postprocessing. We found that these materials exhibit ultrastiff properties across more than three orders of magnitude in density, regardless of the constituent material.


22 pages of supplemental material

Spiderfab is being developed to use robots to assemble structures in space. Spiderfab on orbit assembly can reduce the mass of space structures by 30 times. Supermaterial that is far lighter, stiffer and stronger with very low weight could further increase the size of solar sails and space telescopes that could be built with the same weight of material.

Spiderfab with regular materials could enable solar sails that are over 1000 meters in diameter.
Spiderfab with superlight yet strong materials could enable solar sails that are over 2000 meters in diameter using the same number of launches.

SpaceX's goal is to to recover a Falcon 9 first stage with a touchdown on land by the end of the year. The company would then re-launch the stage next year on a demonstration flight. The company's engineers are also working on the more difficult problem of trying to recover the Falcon 9's second stage, which reaches a much higher altitude.

Musk predicted that instead of flying into space a handful of times per year as we do now, humans would eventually be able to fly to space multiples times per day. "I think 20 years for thousands of flights," Musk said in response to a question about increasing annual launch rates. "And I think we could probably get to the hundreds-of-flights level in 12 to 15 years."

An extremely lightweight 62-mile-wide (100 kilometers) sail unfurled close to the sun could make an interstellar voyage in 1,000 years, said Les Johnson, deputy manager of NASA's Advanced Concepts Office at the space agency's Marshall Space Flight Center.

Thousands of inexpensive launches, spiderfab construction and lighter and stronger materials could mean making a 100 kilometer solar sail in about 2030

Such an early interstellar solar would be able to go 4.5 light years in about 1000 years (0.5% the speed of light)
315 AU in 1 year.

It would enable the exploration and positioning of payloads around the solar system even out to the inner Oort cloud in a reasonable amount of time.

The Suns gravitational lens is at 550 AU. It would be very useful to have space telescope arrays that utilize various gravitational lens positions.

Kuiper Belt 30-50 AU.
The Oort cloud is thought to occupy a vast space from somewhere between 2,000 and 5,000 AU (0.03 and 0.08 ly) to as far as 50,000 AU (0.79 ly) from the Sun. Some estimates place the outer edge at between 100,000 and 200,000 AU (1.58 and 3.16 ly). The region can be subdivided into a spherical outer Oort cloud of 20,000–50,000 AU (0.32–0.79 ly), and a doughnut-shaped inner Oort cloud of 2,000–20,000 AU (0.03–0.32 ly).



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