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LLNL: Magnetically Responsive Metamaterials Instantly Stiffen 3D Printed Structures http://bit.ly/2Alu02j Lawrence Livermore National Laboratory (LLNL) frequently does impressive work with 3D printing materials, including metamaterials. Now the lab has introduced a new class of metamaterial that can almost instantly respond and stiffen 3D printed structures when exposed to a magnetic field. LLNL calls the materials “field-responsive mechanical metamaterials” or FRMMs. They involve a viscous, magnetically responsive fluid that is injected into the hollow struts and beams of 3D printed lattices. Unlike other 4D printed materials, the FRMMs’ overall structure does not change. The fluid’s ferromagnetic particles located in the core of the beams form chains in response to the magnetic field, stiffening the fluid and the lattice structure. This happens in less than a second. The research is documented in a paper entitled “Field responsive mechanical metamaterials.“
The researchers injected a magnetorheological fluid into hollow lattice structures built on LLNL’s Large Area Projection Microstereolithography (LAPµSL) platform, which is capable of 3D printing objects with microscale features over wide areas using light and a photosensitive polymer resin. According to Mancini, the LAPµSL machine played a big role in the development of the new metamaterials, as the complex tubular structures needed to be manufactured with thin walls and be capable of keeping the fluid contained while withstanding the pressure generated during the infill process and the response to a magnetic field. The stiffening of the fluid and, in turn, the 3D printed structures, is reversible and tunable by varying the strength of the applied magnetic field.
Those applications include impact absorption, such as automotive seats that have fluid-responsive metamaterials integrated inside of them along with sensors that can detect a crash. The seats would stiffen upon impact, possibly reducing whiplash. Other applications include helmets, neck braces, housing for optical components or soft robotics. To predict how lattice structures would respond to an applied magnetic field, former LLNL researcher Mark Messner, who now works for Argonne National Laboratory, developed a model from single strut tests. Starting with a model he developed to predict the mechanical properties of non-tunable static lattice-structured materials, he added a representation of how magenetically responsive fluid affects a single lattice member under a magnetic field and incorporated the model of a single strut into designs for unit cells and lattices. He then calibrated the model to experiments Mancini performed on fluid-filled tubes similar to the struts in the lattices. The researchers used the model to optimize the topology of the lattice, finding the structures that would result in large changes in mechanical properties as the magnetic field was varied.
Mancini began the work at the University of California, Davis under her adviser, materials and engineering professor Ken Loh, who is now at the University of California, San Diego. According to Loh, the concept was partially inspired by automotive-based suspension systems. They began by investigating ways to develop flexible armor that could morph or change its mechanical properties as needed.
He also said that the researchers will explore new ways to develop a single-phase material, instead of having a liquid embedded in a solid, and higher performance-to-weight rations. Future work, he continued, “could lead to new technologies, such as flexible armor for the warfighter that stiffen instantaneously when a threat is detected.” Authors of the paper include Julie A. Jackson, Mark C. Messner, Nikola A. Dudukovic, William L. Smith, Logan Bekker, Bryan Moran, Alexandra M. Golobic, Andrew J. Pascall, Eric B. Duoss, Kenneth J. Loh and Christopher M. Spadaccini. Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below.
Printing via 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing https://3dprint.com December 27, 2018 at 02:57PM
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