新型“超材料”有望让整车都变为“安全气囊”

橡胶和钢材在硬度上属于两个极端,但是密歇根大学的研究人员们,却已经开发出了一种新型“超材料”。尽管人造材料可以精确调整到某种固定的性状,但超材料却可以做到一些很不可思议的事情,它的神奇之处是可以对少量压力做出反应,改变自身表面的硬度(由硬到软,再变回来),并且多次改变也不会对主结构造成损坏。这种新材料可以在许多领域得到应用,比如可重复使用的火箭(刚性起飞、软接触着陆),可以自行调节软硬度的自行车轮胎(以最好的状态应对各种表面)。

http://newatlas.com/metamaterial-changes-hard-soft/47528/

New metamaterial could let a car be its own airbag

A new metamaterial, recreated here using K'Nex, can change its softness and hardness in response to...

A new metamaterial, recreated here using K'Nex, can change its softness and hardness in response to low-level stress(Credit: University of Michigan)

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.

The University of Michigan researchers demonstrate the metamaterial using the K'Nex construction system in the video below.


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