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.
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