THE NONLINEAR FREQUENCY AND LARGE-AMPLITUDE OF SANDWICH COMPOSITES WITH EMBEDDED SHAPE-MEMORY ALLOY

The objective of this paper is to explore a new technique to improve d ynamic response and vibration characteristics of sandwich beams with c omposite skins and viscoelastic core by using 55-Nitinol shape memory alloy (SMA) wires. The SMA wires are embedded at the interfaces betwee n the composite skins and the viscoelastic core. The Timoshenko beam t heory including the effects of transverse shear deformation and rotary inertia was used. A coupled dynamic equations of motion with prestres s introduced due to activation (or deactivation) of SMA wires were dev eloped. Numerical results include nonlinear natural frequency of free vibration of mode I as a function of the amplitude of vibration and th e dynamic response in time domain as well as in frequency domain were presented. The transform from time domain to frequency domain was achi eved by using Fast Fourier Transform (FFT). It is observed that the no nlinear natural frequency strongly depends on the amplitude of vibrati on. As the amplitude ratio becomes small (less than 0.1) the nonlinear frequency agrees well with the linear frequency. Very significant dif ferences in dynamic responses were observed for cases when SMA wires w ere activated and SMA wires were not activated.