US researchers have used mechanical metamaterials (which have unique mechanical properties not found in nature) to develop a new material that can respond to magnetic fields from flexible to rigid, and has broad application prospects in smart wearable devices and flexible robots.
Current mechanical metamaterials have attractive characteristics such as negative thermal expansion, high strength and stiffness at low weight. But once the build is complete, its properties cannot be changed or adjusted. The new project jointly developed by Lawrence Livermore National Laboratory and the University of California, San Diego aims to use magnetic fields to create a mechanical metamaterial with dynamically adjustable mechanical properties without causing significant shape changes.
They used the so-called 4D printing technology, which is named after 3D printed objects that can change shape over time, and time is the fourth dimension. Typically, this type of structure changes shape in response to a stimulus (heat, hydration, or magnetic field).
Researchers have developed field-responsive metamaterials (FRMMs) that change their properties based on changes in the magnetic field. However, unlike typical 4D printed materials, it does not change the overall shape, but rather changes the stiffness.
The manufacturing process is to first make a mechanical metamaterial through 3D printing, which is composed of a hollow beam instead of a typical solid beam. After printing out the hollow tubular metamaterial, the magnetorheological fluid is injected into the beam core to complete the manufacture of the field-responsive metamaterial. Magnetorheological fluids consist of magnetic particles, suspended in a non-magnetic medium. When a magnetic field exists in the fluid, magnetic particles are arranged in chains along the magnetic field lines, which increases the stiffness of the fluid, thereby increasing the stiffness of the overall structure. When the magnetic field is removed, the fluid behaves as a liquid and can flow freely.
The researchers said that this magneto-mechanical effect is more than just a switching response. The stiffness of the structure can also be adjusted by the strength of the applied magnetic field. By carefully selecting the tubular structure, the mechanical properties of the field-responsive metamaterial can show tensile strengths as high as 318% in less than one second.
Researchers believe that field-responsive metamaterials can be used as variable stiffness joints in flexible robots and can be integrated into smart wearables that are flexible without magnetic fields, but when a threat is detected Properties can be changed to absorb shock or vibration.