Active control of NITINOL-reinforced composite beams

Abstract

The static and dynamic characteristics of flexible fiberglass composite beams are controlled by activating optimal sets of a shape-memory alloy (NITINOL) wires, which are embedded along the neutral axes of these beams. The underlying phenomena influencing the behavior of this class of composite structural members are presented. The individual contributions of the fiberglass-resin laminate, the NITINOL wires, and the shape-memory effect to the overall performance of the composite beam are determined at different operating temperatures and initial preloads of the wires. The static deflection, stiffness, and buckling characteristics of the fiberglass beams are measured with and without the NITINOL reinforcement. Also, the modes of vibration and modal damping ratios are monitored for various operating conditions. With properly designed NITINOL reinforcement, it is shown that the beams can become stiffer and less susceptible to buckling. The modes of vibrations of the activated NITINOL-reinforced composite beams can also be shifted, to higher frequency bands, relative to those of the unactivated or unreinforced beams. Finite-element models are developed to describe the static, dynamic, and thermal interaction between the NITINOL wires and the fiberglass-resin laminates. Close agreement is obtained between theoretical predictions and experimental results. With such tunable characteristics, the NITINOL-reinforced composite beams have proven successful in attenuating the vibrations induced by cross flows. Experiments are conducted on 30-cm-long and 0.156-cm-thick reinforced beams mounted in a clamped-clamped arrangement inside a wind tunnel. The effect of varying the flow speed or the induced vibration is determined with and without the activation of the NITINOL wires. The results indicate that vibration attenuations in excess of 60% were attained near and at resonance. [Work supported under grant from ARO.]