THERMODYNAMIC CHARACTERISTICS OF NITINOL-REINFORCED COMPOSITE BEAMS

The dynamic characteristics of flexible composite beams are controlled by heating sets of shape memory alloy (NITINOL) fibers embedded along the neutral axes of these beams. The activation of the shape memory effect of the fibers increases the elastic energy and enhances the stiffness of the composite beams. With such capabilities, the vibration modes of the beams can be tailored and shifted away from the excitation frequency band in order to avoid undesirable vibrations. Emphasis is placed, in the present study, on the effect of intentional electrical heating of a selected subset of the NITINOL fibers on the overall dynamics of the beams. The effect of the associated thermal energy propagating through the composite on the unintentional thermal activation of additional subsets of the NITINOL fibers is accounted for. Such an effect is not only significant but also essential to the thorough understanding of the operation of NITINOL-reinforced composites. Finite element models are developed to describe the interaction between the thermal and dynamic characteristics of the NITINOL composites as well as the interaction between the intentional and unintentional activation of the NITINOL fibers. The models are experimentally validated and close agreement is obtained between the theoretical predictions and the experimental results. The mathematical models and procedures described in this paper provide an invaluable means of predicting realistic performance of NITINOL-reinforced composites.