Polymer-Free Batch Production and Application of Metal Foil-Based Thin-Film Strain Gauges

In the monitoring of mechanical components for lifetime prediction and detection of critical load conditions, especially strain gauges play a major role. They can be integrated into components to measure strain in the components themselves. This places special demands on the sensors used because of higher temperatures in the manufacturing phase of the components like additive manufacturing. This is why the sensors need to be polymer-free and cannot be applied with an adhesive. For this, directly deposited polymer-free sensors have been developed. In this article, the advantages of conventional polymer-foil based strain gauges (batch production) and directly deposited sensors (polymer-free) are combined by depositing the sensors on a metal foil and applying them polymer-free to metal specimens. This enables the batch production of strain gauges for use in harsh environments. Therefore, steel and aluminum foils were used as sensor carrier materials with aluminum oxide insulation layers and Platinum and NiCr sensor layers on the front side. On the back side, a tin layer was applied to enable thermocompressive bonding on the specimens leading to maximum tensile shear strengths of 10.7 MPa. After application, the sensors showed a k-factor of about 3.6 for the platinum sensors and about 2.4 for the NiCr sensors proving the functionality of the sensor concept.