The Nonlinear Frequency and Large Amplitude of Sandwich Composites with Embedded Shape Memory Alloy

Abstract

The objective of this paper is to explore a new technique to improve dynamic response and vibration characteristics of sandwich beams with composite skins and viscoelastic core by using 55-Nitinol shape memory alloy (SMA) wires. The SMA wires are embedded at the interfaces between the composite skins and the viscoelastic core. The Timoshenko beam theory including the effects of transverse shear deformation and rotary inertia was used. A coupled dynamic equations of motion with prestress introduced due to activation (or deactivation) of SMA wires were developed. Numerical results include nonlinear niatural frequency of free vibration of mode I as a function of the amplitude of vibration and the dynamic response in time domain as well as in frequency domain were presented. The transform from time domain to frequency domain was achieved by using Fast Fourier Transform (FFT). It is observed that the nonlinear natural frequency strongly depends on the amplitude of vibration. As the amplitude ratio becomes small (less than 0.1) the nonlinear frequency agrees well with the linear frequency. Very significant differences in dynamic responses were observed for cases when SMA wires were activated and SMA wires were not activated.