An additive manufacturing research team developed a 3D printed material that shrinks rather than swells when heated. This lightweight insulation consists of a mini-grid structure that shrinks from three Cartesian directions over a wide temperature range.
According to China's 3D printing network, most solid materials swell when heated, and only a few will shrink. However, "negative thermal expansion" materials that shrink when heated can have different important uses, such as water pipes, spacecraft equipment, and fixtures that lose their accuracy under different thermal loads, including chips and high precision optical mounts. A team of scientists from Lawrence Livermore National Laboratory (LLNL) and several American universities have developed 3D printed lightweight materials that can shrink over a wide temperature range. Their research has been published in the Physical Review Letters.
The secret of the new shrink-wrapped 3D printed metamaterial developed by researchers is its dual-material mini-grid structure, which is printed in 3D from polymer and polymer/copper composites and can be bent inward. This inward bending can cause structural shrinkage when exposed to a hot environment. Most importantly, this highly adjustable contraction occurs in three Cartesian directions, and researchers believe that their 3D printed materials are the first to do so. This thermal expansion may also not occur or is positive, depending on the geometry and topology at the time of design.
The team designed a series of pyramid-shaped mini-grid structures that shrink when heated. With regard to this miniature mesh structure that can be bent and contracted, the internal struts are composed of materials with higher thermal expansion. As the struts expand, an outer frame of low expansion material forces the struts to fold into the center of the structure.
Using projection microlithography 3D printing technology, MIT's team was able to expand existing systems to make multiple materials. Under the leadership of MIT Mechanical Engineering Associate Professor Nicholas Fang, MIT scientists must ensure that materials are not contaminated and that the residue is washed off after each layer is printed.
Researchers believe that the ability of 3D printed materials to passively adapt to local temperature changes can be applied to a variety of mechanical applications where traditional applications rely on active control, such as heating and cooling. Parts of some devices become inaccurate when heated, and 3D printed materials can be used to counteract this imbalance.
According to the author of the paper, Qiming Wang, this microstructured 3D printed metamaterial can be used in dental fillings, which can easily move or break when people eat hot things. It can also be used to fill small gaps in bridges or buildings that are open-air and often undergo thermal expansion. Or it can be used in some precision equipment such as atomic force microscopy.
“Interestingly, it is made up of two different materials, beams and voids,” explains Jonathan Hopkins, assistant professor of mechanical and aerospace engineering at UCLA. "When you heat it, once a beam expands beyond the other beams, the joint between each unit cell will pull inward, causing all the lattices to pull inward. This is direct heat shrinkage, it is also Unique."
The study involved researchers from LLNL, the University of Southern California, MIT, and the University of California, Los Angeles, as part of a five-year plan for the Defense Science Office of the Defense Advanced Research Projects Agency, which focuses on controlling microstructures. material. According to Wang, the next phase of the project is to create zero-thermal expansion materials that can solve similar problems.