Lawrence Livermore National Laboratory (LLNL) researchers are known for continually pioneering research in 3D printing. Now the LLNL researchers have developed and introduced a new class of 3D printed metamaterials which can change their mechanical properties like stiffness when exposed to a magnetic field. This new development will have far reaching implications on applications like next-generation helmets, wearable armour, etc.
3D Printed Metamaterials
The 3D printed structure is manually injected with “field-responsive mechanical metamaterials” (FRMMs) into the hollow struts and beams of its lattices. The injected fluid contains ferromagnetic particles which form a chain when exposed to a magnetic field. This chain stiffens the fluid and in turn the entire lattice structure. The response is rapid and happens in less than a second.
This is unlike 4D printing, where the overall structure changes shape. This change takes a considerable time and the mechanical properties also remain the same.
Talking about the research, lead author Julie (Jackson) Mancini, said “In this paper we really wanted to focus on the new concept of metamaterials with tuneable properties, and even though it’s a little more of a manual fabrication process, it still highlights what can be done, and that’s what I think is really exciting. It’s been shown that through the structure, metamaterials can create mechanical properties that sometimes don’t exist in nature or can be highly designed, but once you build the structure you’re stuck with those properties.”
She continued, “The next evolution of these metamaterials is something that can adapt its mechanical properties in response to an external stimulus. Those exist, but they respond by changing shape or colour and the time it takes to get a response can be on the order of minutes or hours. With our FRMM’s, the overall form doesn’t change and the response is very quick, which sets it apart from these other materials.”
Injection of Field-Responsive Mechanical 3D Printed Metamaterials
The process involves infusion of the magnetorheological (MR fluid or MRF) fluid into the hollow lattice structures.
“A magnetorheological fluid (MR fluid, or MRF) is a smart fluid which responds to a magnetic field by rapidly increasing its apparent viscosity, to a point where it becomes a viscoelastic solid.”
This was achieved on LLNL’s Large Area Projection Microstereolithography (LAPµSL) platform, which is capable of 3D printing objects at the microscale level. This system works similar to regular Stereolithography 3D printing where a photosensitive polymer is cured using a light source.
According to Mancini, “The new form of dynamically tuneable metamaterial owes a lot of its success to the LAPµSL machine, because the complex tubular lattice structures had to be manufactured with thin walls relative the overall size of the structure, and capable of keeping the fluid contained while withstanding the pressure generated during the infill process and the response to a magnetic field.”
Once the MR fluid is inserted inside the structure, a magnetic field is applied externally. This causes the fluid to stiffen and the entire structure rapidly increases its mechanical strength. This change is reversible and is highly tuneable/manageable by varying the strength of the applied magnetic field.
Applications of 3D Printed Metamaterials
As per Mancini, the newly developed technology could be useful in a range of application including impact absorption which can be used in automotive seats. In case of a crash, the automotive seats which will have fluid–responsive metamaterials integrated inside along with sensors to detect a crash, and seats would stiffen on impact, potentially reducing passenger motion that can cause whiplash. It also could be applied to next-generation helmets or neck braces, housing for optical components and soft robotics, among many other applications.
Mancini added, “What’s really important is it’s not just an on and off response, by adjusting the magnetic field strength applied we can get a wide range of mechanical properties, the idea of on-the-fly, remote tune-ability opens the door to a lot of applications.”
Future Work on 3D Printed Metamaterials
According to Keh Loh, an engineering professor at the University of California, San Diego, and who advised Mancini during her Master’s degree, said, “The concept was partly inspired by automotive-based suspension systems and started out by looking at ways to develop flexible armour capable of morphing or changing its mechanical properties as needed. One of the criteria is to achieve a fast response, and magnetic fields and MR materials offer that capability.”
Loh added, “Researchers will look into new ways to develop a single-phase material, instead of having a liquid embedded in -to- solid, and higher performance weight ratios, adding that future work. This could lead to new technologies, such as flexible armour for the soldiers that stiffen instantaneously when a threat is detected.”
Lead author, Julie Mancini will continue working towards printing structures with the magnetic fields responsive fluid built-in to eliminate the manual in-filling stage and on increasing the overall size of the structures.
The Laboratory Directed Research and Development program funded the research. The research titled “Field responsive mechanical metamaterials” appears on the cover of the journal Science Advances, published online. The paper is authored by Julie Mancini and co-authored by Nikola Dudukovic, William Smith, Logan Bekker, et al.
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