Aerosol Jet Printed Strain Gauge and Temperature Compensated Strain Gauge Design

Abstract

Aerosol jet printing (AJP) is a non-contact, computer aided design (CAD) based printing that allows for an aerosol stream, being focused by a sheath gas, to print patterns on non-planar surfaces based on the specified vector path. By being able to aerosolize metal nanoparticles and sintering the nanoparticles, the patterns printed by AJP can be used as sensors. In this thesis, strain gauges were printed using AJP. The strain gauges were printed using an ink containing silver nanoparticles and after the printing process the printed samples were sintered to make the strain gauge conductive. The underlying working principles of strain gauges and gauge factors are explored and an equation was developed to characterize the change in resistance in a strain gauge. A numerical model was also created in COMSOL to validate and complement the derived equations. The printed silver strain gauges were characterized and tested alongside standard, off-the-shelf, constantan strain gauges. Multiple sensors were printed but only 10 fell within the data acquisition resistance range of 110 – 130 ohms. The 10 prototypes that fell within the acceptable resistance range were subjected to tensile testing. Due to variability in the machine printing process, the printed sensors were not consistent in terms of resistance and gauge factor. These challenges as well as potential solutions are discussed in this thesis. Some of the printed sensors behaved linearly and matched the performance of the standard strain gauges with only minor, explainable discrepancies. One of the printed sensors was loaded until failure and failed at a strain of 1.6%. With the flexibility to easily change the design of the strain gauges, a new design for temperature compensation in uniaxial stress states was created and simulated using the numerical COMSOL model. This new design utilizes the poisson’s ratio of the part on which the strain gauge has been mounted. The flexibility and customization that aerosol-jet printed sensors provide presents a potential for customized strain monitoring in mechanical parts. Optimization of the printing and data acquisition processes is required to attain the reliability required to make this an ideal sensing alternative.