Additive Manufacturing of High Temperature Strain Gauges

Abstract

Additive manufacturing (AM) is quickly leading a new revolution in manufacturing. Aerosol ink jet printing (AJP) is a non-contact printing method that allows for printing on irregular substrates. When paired nanoparticulate ink, the method can print electrical traces and sensors. AJP stands to surpass current thin film technologies by flexibly printing on complex geometries. This thesis details the preliminary work towards employing AJP to create sensors operating in harsh environments. Specifically, the development of materials required to enable printed circuits functioning at temperatures exceeding 1000˚C (1850 ˚F). The high temperature corrosion behavior of devices created from nanoparticles is explored from starting with the synthesis of the nanoparticles themselves. Inks suitable for AJP are formed from the nanoparticles. The inks are subsequently printed into strain gauge designs, sintered to bulk, and tested for conductivity. A technique to create core shell nanoparticles is demonstrated in efforts to make the ink materials more resistant to side reactions during the sintering phase. An additional design aspect is introduced in the form of sol gels to solve the corrosion challenges presented. Sol gels were developed to create ceramic thin films to insulate the manufactured sensors, provide an engineered surface, and encapsulation layer for the devices. Sol gel chemistry is a wet chemical approach for forming ceramics that is also found to be compatible with AJP processes. Only a few sensors produced were suitable for electrical characterization. This was due to side reactions in the sintering process as well as insufficient adhesion of the printed traces to the substrate. The resistive path of the sensor was 31 kohms, which was outside of the testing range for strain gauges. The elevated resistance of these samples is due to impurities and defects in the printed patterns. The findings of this thesis are useful for generating the next generation devices for use in harsh environments. The materials established here can be altered by differing processing techniques to eliminate the barriers to achieving integrated strain gauges by additive manufacturing.