American researchers used mechanical metamaterials (with unique mechanical properties that do not exist in nature) to develop a new type of material that can change from flexible to rigid in response to a magnetic field, and has broad application prospects in smart wearable devices and flexible robots.
Current mechanical metamaterials have attractive properties such as negative thermal expansion, high strength and high stiffness at low weight. But once the construction is completed, its properties cannot be changed or adjusted. The new project jointly launched by Lawrence Livermore National Laboratory in the United States 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 the 3D printed objects can change shape with time, time is the fourth dimension. Typically, this type of structure changes shape in response to stimuli (heat, hydration, or magnetic fields).
The field-responsive metamaterial (FRMM) developed by the researchers can change its properties according to changes in the magnetic field. However, unlike typical 4D printing materials, it does not change the overall shape, but rather the stiffness.
The manufacturing process is to first make a mechanical metamaterial by 3D printing, which is composed of hollow beams instead of typical solid beams. 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 fluid is composed of magnetic particles, suspended in a non-magnetic medium. When there is a magnetic field in the fluid, the magnetic particles are arranged in chains along the magnetic field lines, increasing the rigidity of the fluid, thereby simultaneously increasing the rigidity of the overall structure. When the magnetic field is removed, the fluid appears as a liquid and can flow freely.
The researchers say that this magnetomechanical effect is not just a switch 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 up to 318% tensile stiffness in less than a second.
Researchers believe that field-responsive metamaterials can be used as variable stiffness joints in flexible robots and can be integrated into smart wearable devices that are flexible without magnetic fields, but when threats are detected The properties can be changed to absorb shock or vibration. (Reporter Feng Weidong)
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