NITINOL-reinforced plates: Part III. Dynamic characteristics

Abstract

The dynamic characteristics of NITINOL-reinforced composite plates are controlled by heating sets of NITINOL fibers embedded inside these plates. The activation of the shape memory effect of these NITINOL fibers increases the elastic energy, enchances the stiffness of the composite plates and modifies their modal characteristics. One of the objectives of the resulting modal modification is to shift the modes of vibration of the plates away from the excitation frequencies in order to avoid undesirable resonances. In this way, the modal characteristics can be tailored in response to the external disturbances acting on the plates. The classical finite element approach is used to form the equations of motion of the assembly of NITINOL-reinforced plate elements and the appropriate boundary conditions are then applied. The solution of the eigenvalues of the resulting homogeneous equations gives the natural frequencies of the NITINOLreinforced plate as influenced by the properties of the composite matrix and the NITINOL fibers. It is important to note that these properties are influenced by the temperature distribution inside the composite plate which is developed by virtue of activating and de-activating the NITINOL fibers. Emphasis is placed on the effect of intentional electrical heating of a selected subset of the NITINOL fibers on the overall dynamics of the plates. 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 the NITINOL-reinforced plates.