LLNL researchers invent 3D printed metamaterial that stiffens with magnetic field

Lawrence Livermore National Laboratory (LLNL) researchers invented a new metamaterial consisting of hollow 3D printed lattice structures filled with ferrofluid that instantly stiffens when exposed to magnetic fields. This creation is exactly as cool as it sounds because its potential uses range from soft robotics and optic housing to smart armor that’s not dissimilar to Batman’s electro-stiffening “memory cloth” cape in The Dark Knight.

The research team led by LLNL engineer Julie Jackson Mancini set out to create tunable metamaterials, specifically field-responsive mechanical metamaterials (FRMMs). They employed the use of the not-at-all oxymoronic Large Area Projection Microstereolithography (LAPµSL) platform that specializes in 3D printing microscale features over a large space; such technical requirements were needed to produce the thin walls of the complex tubular lattice structures necessary for their tests. After 3D printing, the lattices were injected with magnetorheological fluid, so the walls had to be strong enough to handle the loading pressure and extra weight of the ferrofluid but also flexible enough to be able to detect and measure changes in stiffness when a magnetic field was applied.

Most metamaterials with dynamic mechanical properties need minutes or hours to undergo their changes. Not so for the FRMM which has a response time of less than a second. When a specific magnetic field is applied, the magnetic molecules in the ferrofluid align into chains that instantly stiffen the lattice structures. “In this paper we really wanted to focus on the new concept of metamaterials with tunable properties," said Mancini. “It’s been shown that through structure, metamaterials can create mechanical properties that sometimes don’t exist in nature or can be highly designed, but once you build the structure you’re stuck with those properties. A next evolution of these metamaterials is something that can adapt its mechanical properties in response to an external stimulus. Those exist, but they respond by changing shape or color and the time it takes to get a response can be on the order of minutes or hours. With our FRMM’s, the overall form doesn’t change and the response is very quick, which sets it apart from these other materials.”The magnetic field can also be tuned to invoke various mechanical properties besides just stiffness, as Mancini explains, “What’s really important is it’s not just an on and off response, by adjusting the magnetic field strength applied we can get a wide range of mechanical properties. The idea of on-the-fly, remote tunability opens the door to a lot of applications.” Yeah, like Batsuits. But also advanced suspension systems and aerospace components that could benefit from very fast, precise movements that don’t require clunky servos.

The team is now working to meld the two materials into a single-phase material that won’t require the manual ferrofluid injection step. Professor Ken Loh, one of the research team members, commented that future development of the technology “could lead to new technologies, such as flexible armor for the warfighter that stiffens instantaneously when a threat is detected.” Tell me that’s not a sly reference to Batman.