Dynamic analysis and experimental testing of thin-walled structures driven by shear tube actuators

The objective of this research is to experimentally and analytically investigate the structural dynamic behavior of thin-walled structures driven by shear actuators. A finite element analysis to predict the torsional structural dynamic response of thin-walled structures actuated by piezoelectric induced-shear tube actuators is developed and validated. This analysis is intended as a tool to aid the design of a proposed helicopter rotor blade anti-icing system. Proof of concept icing experiments were conducted for the proposed anti-icing system. Coupled constitutive equations for a PZT shear tube (shear stress-strain relationship) are required for accurate prediction of the frequency response of the piezoelectric actuator. The model predicts the actuator frequency response behavior accurately up to the second torsional modal frequency of the piezoelectric tube. Structural dynamic analysis of the piezoelectric shear tube actuator driving thin-walled aluminum tubes is performed. Two different tubes, 0.15 and 3.65 m in length respectively, are driven by a shear tube actuator. The two aluminum tubes have a 35 mm outer radius and are 1 mm thick. Experimental frequency response tests were conducted up to 15 KHz for the thin-walled 0.15 m long aluminum tube and 3.5 KHz for the 3.65 m long aluminum tube. The frequency response of the shorter aluminum tube is accurately predicted up to its fourth modal frequency. The frequency response for the longer aluminum tube is accurately predicted up to its seventh natural frequency. An ultrasonic frequency test (1 MHz) is also conducted on a 3.65 m aluminum tube. Electromagnetic transducers (EMAT) are used to visualize the horizontal shear waves generated by the shear tube actuator on the surface of the aluminum tube. Minimal decay in the generated horizontal shear waves is measured by the EMAT. The validated analytical tool is used to perform a preliminary design procedure of a piezoelectric actuator system for rotor blade anti-icing. An aluminum D-spar cross-section similar to the one of the Bell UH-1 helicopter is studied under the effects of a shear piezoelectric actuation system (6.7 m span). For a power consumption of 325 W, nodal strains up to 29 μ-strains (0.75 MPa) are reached by a system of four shear actuators driven at the fourth torsional natural frequency of the structure.