Imagine a material with 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.
Lawrence Livermore and Massachusetts Institute of Technology (MIT) researchers have developed a material with these properties using additive micro-manufacturing processes. The research team's findings are published in a June 20 article in the journal Science.
Titled "Ultralight, Ultrastiff Mechanical Metamaterials," the article describes the team's development of micro-architected metamaterials -- artificial materials with properties not found in nature -- that maintain a nearly constant stiffness per unit mass density, even at ultralow density. Materials with these properties could someday be used to develop parts and components for aircraft, automobiles and space vehicles.
Most lightweight cellular materials have mechanical properties that degrade substantially with reduced density because 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 LLNL Engineer Xiaoyu "Rayne" Zheng, lead author of the Science article. "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 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.
"Our micro-architected materials have properties that are governed by their geometric layout at the microscale, as opposed to chemical composition," said LLNL Engineer Chris Spadaccini, corresponding author of the article, who led the joint research team. "We fabricated these materials with projection micro-stereolithography."
This additive micro-manufacturing process 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.
"Now we can print a stiff and resilient material using a desktop machine," said MIT professor and key collaborator Nicholas Fang. "This allows us to rapidly make many sample pieces and see how they behave mechanically."
The team was able to build microlattices out of polymers, metals and ceramics.
Internal damage in fiber-reinforced composites, materials used in structures of modern airplanes and automobiles, is difficult to detect and nearly impossible to repair by conventional methods. A small, internal crack can quickly develop into irreversible damage from delamination, a process in which the layers separate. This remains one of the most significant factors limiting more widespread use of composite materials.
However, fiber-composite materials can now heal autonomously through a new self-healing system, developed by researchers in the Beckman Institute's Autonomous Materials Systems (AMS) Group at the University of Illinois at Urbana-Champaign, led by professors Nancy Sottos, Scott White, and Jeff Moore.
Sottos, White, Moore, and their team created 3D vascular networks—patterns of microchannels filled with healing chemistries—that thread through a fiber-reinforced composite. When damage occurs, the networks within the material break apart and allow the healing chemistries to mix and polymerize, autonomously healing the material, over multiple cycles. These results were detailed in a paper titled "Continuous self-healing life cycle in vascularized structural composites," published in Advanced Materials.
"This is the first demonstration of repeated healing in a fiber-reinforced composite system," said Scott White, aerospace engineering professor and co-corresponding author. "Self-healing has been done before in polymers with different techniques and networks, but they couldn't be translated to fiber-reinforced composites. The missing link was the development of the vascularization technique."
"The beauty of this self-healing approach is, we don't have to probe the structure and say, this is where the damage occurred and then repair it ourselves," said Jason Patrick, a Ph.D. candidate in civil engineering and lead author.
Gregory
Mark co-owns Aeromotions, which builds computer-controlled racecar
wings. To make those wings both strong and lightweight, they use carbon
fiber. No surprise there—it's the material of choice for many advanced
motorsports parts. The problem is that making custom racecar parts out
of carbon fiber is daunting. The only real method available is CNC
machining, an expensive and difficult process that requires laying
pieces by hand.
To improve the process, Mark looked to
3D printing. But nothing on the market could print the material, and no
available materials could print pieces strong enough for his purposes.
So Mark devised his own solution: the MarkForged Mark One, the world's
first carbon fiber 3D printer.
Mark debuted his Boston
area-based startup MarkForged at SolidWorks World 2014 in San Diego with
a working prototype. The Mark One can print in carbon fiber,
fiberglass, nylon and PLA (a thermoplastic).
"We took
the idea of 3D printing, that process of laying things down strand by
strand, and we used it as a manufacturing process to make composite
parts," he told PopMech. "We say it's like regular 3D printers do the
form. We do form and function."
What you notice first
about MarkForged's printer is its amazing simplicity. With an anodized
aluminum unibody and a translucent printing bed, it looks like the Mac
of 3D printing. The Mark One employs kinematic coupling for consistent
bed leveling, meaning you won't need to worry about making sure the bed
is leveled correctly after each print. It's also compact, measuring 22.6
inches wide, 14.2 inches tall, and 12.7 inches deep—a good desktop
size.
