Modeling of smart composite box beams with nonlinear induced strain

A new smart composite box beam model is developed to investigate the behavior of helicopter rotor blades built around the active box beam. Piezoelectric actuators and sensors are surface bonded on the walls of the composite box beam. The new theory, based on a refined higher order displacement field of a plate with eccentricity, is a three-dimensional model which approximates the elasticity solution so that the box beam cross-sectional properties are not reduced to one-dimensional beam parameters. Both in-plane and out-of-plane warpings are included automatically in the formulation. The formulations also include nonlinear induced strain effects of piezoelectric actuators. The procedure is implemented using finite element method. The developed theory is used to model the load carrying member of helicopter rotor blades with moderately thick-walled sections. Static analysis of the smart box beam under varying degrees of actuation has been performed. Very good overall agreement is observed with available experimental data for thin-walled sections without embedded actuators. The results show that piezoelectric actuation significantly reduces the deflection along the box beam span and therefore can be used to control the magnitude of rotor blade vibrations. The nonlinear actuation effect is found to be closely related to the material stiffness of the primary structure.