Physics I 15
Weird flex: Field-responsive mechanical metamaterials
WRITTEN AND DESIGNED BY JENNIFER GARLAND, APPLIED PHYSICS & MATHEMATICS, 2021
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any of today’s synthetic materials were inspired by nature. Jeffrey Grossman, a materials science and engineering professor at the Massachusetts Institute of Technology (MIT), has said that “nature is a polymer engineer gone wild.” However, even with all of the blueprints provided by nature, there is still demand for more efficient performance and increasingly technical applications. The field of metamaterials arose because scientists wanted to create materials with properties outside of nature.
To demonstrate the effects of the increase in stiffness, the cuboctahedrons were placed under a load. Under a large applied magnetic field, the lattices supported the load, but as the field decreased, the structures began to lose stiffness and collapse. This behavior is significant because the structure of the material remained the same, but its mechanical ability was altered by the field. The development of FRMMs has been largely enabled by manufacturing innovations like 3D printing, especially a method called large area projection microstereolithography (LAPμSL) that was invented at LLNL. The researchers there will continue to optimize construction, ideally figuring out a way to integrate the magnetorheological fluid with the polymer lattice instead of of the material having to manually inject it.
Mechanical metamaterials, just one of many types, are structurally tuned to respond to forces in unconventional ways. This may mean that a material widens in one direction while being stretched in the The structure perpendicular, the opposite of remained the same, but its what a rubber band does, or that a solid responds to stress like a The level of control possible mechanical ability was fluid: incompressible but not over these field-responsive stiff. Recently, a collaboration mechanical metamaterials altered by the field.” led by engineer Julie A. Jackson sets them apart from other at Lawrence Livermore National mechanical metamaterials. The Laboratory (LLNL) introduced a new class of materials stiffness response in the LNLL experiments was very quick, called field-responsive mechanical metamaterials (FRMMs) less than a second, and that behavior is reversible without whose mechanical properties can be controlled by applying damage. Instead of just creating a material with useful set a magnetic field. properties, FRMMs add a new dimension of customization controlled by a magnetic field. Because these materials may The team first 3D-printed hollow polymer tubes that be applied to protective gear like helmets, having the ability serve as the structural components of lattice shapes called to change according to environmental stimuli is critical. cuboctahedrons. Then, the hollow lattices were injected with magnetorheological fluid, which is made up of magnetic This new class of metamaterials opens the door to dynamic microparticles suspended in liquid. This fluid acts like components in a variety of areas. In addition to adaptive a normal liquid until a magnetic field is applied and the helmets, smart wearables that reduce vibrations, perhaps particles link up and align with the field, resulting in a large armor, could be on the way. Any application with movement increase in viscosity. The aligned fluid looks similar to the control could benefit, such as car seats stiffening during a spiky array of magnetized ferrofluid common in science crash. Shoe soles have already incorporated mechanical museums, but the particles in ferrofluid are on the nanometer metamaterials to improve impact absorption, and similar scale, much smaller than the microparticles. A photo of a ideas can be applied to make buildings more earthquakecuboctahedron half-filled with magnetorheological fluid resistant or jet engines more thermally stable. With more was featured on the cover of the December 2018 issue of testing, materials that stiffen up when needed most may Science Advances. soon be solidified.
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PHOTO BY WIKIPEDIA COMMONS
