Materials

New metamaterial could let a car be its own airbag

New metamaterial could let a c...
A new metamaterial, recreated here using K'Nex, can change its softness and hardness in response to low-level stress
A new metamaterial, recreated here using K'Nex, can change its softness and hardness in response to low-level stress
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A new metamaterial, recreated here using K'Nex, can change its softness and hardness in response to low-level stress
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A new metamaterial, recreated here using K'Nex, can change its softness and hardness in response to low-level stress

Rubber and steel are at different ends of the spectrum when it comes to hardness, and wherever an object falls on that scale is typically where it will stay. But researchers at the University of Michigan have now developed a metamaterial that can change the stiffness of its surface, from hard to soft and back, in response to a small amount of stress.

As artificial materials that can be finely tuned for a specific purpose, metamaterials can do some pretty incredible things that you won't find in nature. Interestingly, what they're made of doesn't seem to matter: instead, their attributes stem from their structure, and by manipulating that, engineers can develop metamaterials that could replace optic lenses, make objects effectively invisible, or create vehicle parts that are both very strong and very light.

The University of Michigan team says its new metamaterial specializes in switching its surface between hard and soft states. Applying a small amount of strain allows that stiffness to be changed by several orders of magnitude, without damaging or weakening the material itself.

"The novel aspect of this metamaterial is that its surface can change between hard and soft," says Xiaoming Mao, lead author of the study. "Usually, it's hard to change the stiffness of a traditional material. It's either hard or soft after the material is made."

The new material's geometry is composed of a lattice of tiny struts connected with hinges, and by applying low-level stress in the form of twisting the material, the lattice changes the topological properties of the material, causing it to become either harder or softer as required. Since the hinges absorb the stress, the change can be done over and over without causing damage to the main structure.

The researchers suggest some fairly exciting potential applications for such a material. Reusable rockets could stay rigid for take-off but transition for a softer landing, and bicycle tires could adjust their own hardness to best suit whatever surface you're riding over. In cars, rather than stashing an airbag into the steering wheel, the wheel itself could soften up in the event of an accident.

"When you're driving a car, you want the car to be stiff and to support a load," says Mao. "During a collision, you want components to become softer to absorb the energy from the collision and protect the passenger in the car."

The research is published in the journal Nature Communications.

Source: University of Michigan

4 comments
Bob Stuart
A steel tape measure is a beam with two main stiffness modes that most people are already familiar with. A surface just needs more such elements.
Kpar
I foresee ultra-lightweight airline seating- more leg room! I love it!
Also, more comfortable office chairs, and lighter launch couches on spacecraft.
StWils
Right now this metamaterial is just an interesting lab toy. How soon will they have some actually practical model applications? Also, what about manufacturing costs & issues, life span, performance & end-of-life recycling? One very interesting application would be as one or more layers in composite armor, similar to the Chobham armor in U.S. Abrams & British tanks. Such a layer acts as a separator to de-couple the wave fronts of an impacting round and deflects & dissipates an explosion.
Ralf Biernacki
As always, SciFi writers were here first. I recognize this metamaterial as /twing/, described by Larry Niven in Protector (1973) and in other novels set in the Ringworld universe. He got it almost exactly right---and while I have no hard proof, I believe Larry was the first to come up with the concept of a metamaterial in the first place. Twing was just one of several, as he called them, "artificial molecules" in his works.