High temperature static and dynamic strain response of PdCr thin film strain gauge prepared on Ni-based superalloy

Abstract

Thin film resistance strain gauges are being developed to monitor the in-situ static and dynamic strain of engine blades in aerospace propulsion and power generation system. In this work, the palladium chromium thin film strain gauge, which consists of four layers: graded buffer layer, insulating layer, strain sensitive element and protective layer, is prepared on Ni-based superalloy by vacuum sputtering deposition technique. The static and dynamic strain responses are investigated from room temperature up to 800 °C. The results of static testing demonstrate that the resistance of the gauge exhibits a linear change dependent on strain and displays excellent repeatability. The gauge factor shows temperature dependence, which is calibrated to be 1.78, 1.94, 2.03 and 2.13 at 25, 400, 600 and 800 °C, respectively. For dynamic strain response, the resistance of palladium chromium thin film strain gauge varies periodically, which keeps the same frequency with the K465 test bar vibrates driven by the shaker system at the resonance frequency. The results indicate that PdCr thin film strain gauge has a fast response enough to monitor the dynamic strain change. Then, the dynamic strain can be derived from the dynamic variation of resistance of the thin film strain gauge up to 800 °C. Therefore, palladium chromium thin film strain gauge provides an effective approach for the measurement of in-situ static and dynamic strain of engine blades in aerospace propulsion.