Ultra light, uber strong

Lawrence Livermore engineer Xiaoyu ‘Rayne’ Zheng.

Photo: Julie Russell/LLNL

RESEARCH journal Science reports a team of researchers from MIT and Lawrence Livermore National Laboratory (LLNL) have developed new ultra-lightweight materials that are as light as aerogel, but 10 000 times stiffer.

The team sees the materials being used in planes, cars and trains and predict the end material could still be 100 times stronger than the current experimental versions.

Called metamaterials, these artificial materials gain strength from their geometric structure, not their chemical composition, and is “microarchitected” using projection micro-stereolithography, an additive micromanufacturing technique combined with nano­scale coating and postprocessing.

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.

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.

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 nanometres 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 Optimisation.

The abstract in Science states the microarchitected materials maintain a nearly constant stiffness per unit mass density, even at ultra-low density, unlike ordinary materials in which mechanical properties degrade quickly with reduced density when their structural elements are bend.

“These lightweight materials can withstand a load of at least 160 000 times their own weight,” LLNL engineer Xiaoyu “Rayne” Zheng told Gizmag.

“The key to this ultra-high 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 team sees the materials being used in planes, cars and trains and predict the end material could still be 100 times stronger than the current experimental versions.

Called metamaterials, these artificial materials gain strength from their geometric structure, not their chemical composition, and is “microarchitected” using projection micro-stereolithography, an additive micromanufacturing technique combined with nanoscale coating and postprocessing.

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.

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.

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.

“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 Optimisation.

The abstract in “Science” states the microarchitected materials maintain a nearly constant stiffness per unit mass density, even at ultralow density, unlike ordinary materials in which mechanical properties degrade quickly with reduced density when their structural elements are bend.

“These lightweight materials can withstand a load of at least 160 000 times their own weight,” LLNL Engineer Xiaoyu “Rayne” Zheng told Gizmag.

“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.”