Research on Piezoelectric Sensor for Micro Friction Measurement Based on Torque Amplification

The accurate measurement of surface friction resistance is crucial in the design of hypersonic vehicles, given its significant impact on the overall performance. To fulfill the stringent requirements of high sensitivity and resistance to normal force interference during testing, the present study introduces a novel approach for directly measuring surface micro friction force. This approach utilizes torque amplification principles based on the torsion characteristics of quartz wafer. First, a detailed analysis is conducted to investigate the relationship between sensor stress and the measured force. This examination reveals the governing stress law on the wafer surface. Subsequently, by leveraging the force-to-electric conversion principle of quartz crystal, an accurate charge output model is established for the wafer when subjected to an input force. Simulation analysis is performed to validate the obtained results and to further explore the charge output behavior of the wafer under normal surface pressure. Second, the design of the surface friction measurement structure is meticulously carried out. This measurement structure is then subjected to rigorous static calibration and positive pressure interference verification experiments to ensure its reliability and accuracy. Finally, the dynamic performance of the test structure is obtained through hammering experiments. The experimental results show that both the linear error and repeatability error of the output are below 1%. The measurement error is less than 0.9%. Class A uncertainty is less than 2.9%. The first natural frequency is 2428 Hz. The experiment on normal pressure interference reveals minimal impact on friction measurement results, and the error is less than 1.7%. The proposed method enhances the measurement techniques for assessing aircraft surface friction resistance during wind tunnel tests, thereby offering valuable technical support for the advancement of the aerospace industry.