Jan 12, 2018 | By David

Researchers from Carnegie Mellon University, the University of Texas El Paso, and Washington State University recently made use of 3D printing in a project that should lead to the development of significantly improved electronic measuring equipment. The team used the aerosol jet printing technique in their work, which involved the manufacturing of a new type of strain gauge. This method creates highly porous structures, and its application enabled them to improve the sensitivity of the gauges to unprecedented levels.

One of the unsung heroes of the engineering world, strain gauges are used in the measurement of all kinds of things, from weighing cars at weighing stations to monitoring the forces on a bridge or on the wing of an aircraft. When a force is applied to a strain gauge, this causes it to deform. This structural deformation leads to a change in the electrical resistance of the material, and this change enables the exact amount of strain that the structure is undergoing to be measured.

Strain gauges tend to be made of solid material, and there is a common standard in their performance known as the Poisson Ratio. This ratio generally represents the limit to how sensitive a solid strain gauge can be. The Poisson Ratio of a material describes how much a material will contract in one direction, when it is stretched in another direction. The maximum Poisson Ratio that a solid material can have is about 0.5. With the aerosol jet 3D printing method, however, the team was able to create a porous film structure. The solid material is dotted with a huge number of tiny holes, which alter the way that the structure performs and increases its potential Possion Ratio.

Aerosol jet printing uses digitally-controlled aerodynamic focusing, to precisely deposit electronic ink on a substrate. Through this controlled sintering of nano-particles, the 3D printing process enables the exact porosity of a solid structure to be determined. The use of aerosol jet printing enabled the team to to optimize the amount of structural contraction of the film that is being used in the strain gauge. The more the film contracts, the more sensitive it will be to deformation and thus the more accurately it can measure the strain.

"Because of the porosity of the film, we are seeing an effective Poisson Ratio of approximately 0.7, which means we have about a 40 percent increase in the lateral contraction for a given deformation of the film," says researcher Rahul Panat, an associate professor of mechanical engineering at Carnegie Mellon University. "That makes the strain gauge much more sensitive to measurement."

(example of scale of aerosol jet printed electronics)

Not only did the aerosol jet 3D printing technique enable the team to reach new levels of sensitivity in the creation of strain gauges, it also improved the performance of the electronic equipment in high-temperature conditions. Conventional solid strain gauges can be very susceptible to error due to the deformation effects caused by heating. The new 3D printed devices, however, were entirely resistant to this thermal interference. This makes them even more accurate and increases their range of potential uses.

(example of a 3D printed strain gauge)

"The reason why a material will show thermal strain is because material naturally expands when it is heated," says Panat. "In our case, the overall expansion of the porous film because of heat alone is much smaller than if it were a solid film. The films created with this new technique do not expand that much, so we are significantly reducing the error in high-temperature applications."

The team’s research was detailed in a paper entitled "3-D Printed High Performance Strain Sensors for High Temperature Applications," which was published in the Journal of Applied Physics.



Posted in 3D Printing Application



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