An engineering research team at the University of Southern California has developed a material that is able to contract when heated. This is their first step in achieving a material that won’t react to heat.
Most materials expand when they are subjected to heat, so creating a material that won’t react to heat is definitely a challenge. Structures such as bridges and buildings require expansion joints built in so that when the structure expands, it will not suffer any damage. As for combined materials that are mismatched, one material may expand faster than the other, and cause the combination to crack.
According to Qiming Wang, assistant professor in the Sonny Astani Department of Civil and Environmental Engineering, “We wanted to solve all these thermal mismatch problems. Imagine if you can design some material that has zero expansion, no expansion at all.”
This project, which is in collaboration with Christopher Spadaccini of the Lawrence Livermore National Laboratory and Associate Professor Nicholas Fang from the Massachusetts Institute of Technology, was sponsored by the National Science Foundation Manufacturing Machines and Equipment program as well as the DARPA Materials with Controlled Microstructural Architectures program.
3D Printing Process
To be able to develop a composite material that contracts when heated, Wang designed a manufacturing technique that lets the user 3D-print a structure that consists of more than one special material. First, thin layers of liquid will be solidified via UV light one layer at a time while switching between the different materials. By doing so, this will create a 3D structure of varied designs with as much materials as needed.
For the contracting material, Wang designed a 3D lattice structure that consists of beams that are oriented at certain angles so as to maximize the expansion behaviour of the material. Since the two materials expand at different rates, the beams of the structure will be pulled inward and therefore making the whole structure contract.
“Overall, the structure will contract in volume, rather than expand in volume,” Wang explained. “That’s the basic mechanism.”
By using different materials and different lattice arrangements, the research team hopes to customize expansion and contraction rates, and create a material that doesn’t expand at all. This development will certainly help improve the safety as well as physical possibilities of bridges and buildings and cities around the world.