Mechanical behaviour of composite spring with embedded shape memory alloy

Abstract

Closed-form solutions from complementary strain energy are derived for the spring stiffnesses of circular mid-surface symmetric composite and composite/shape memory alloy springs under uniaxial line loading. A three dimensional finite element model is established to investigate the mechanical behaviours of the springs. Homogenization technique and rule of mixtures are employed to evaluate material properties of the shape memory alloy wire/epoxy layers. The methods for determining the mechanical properties of the shape memory alloy wire/epoxy layers are discussed. Quasi-static compressive tests are performed to determine the spring stiffnesses of the springs at three temperatures. Satisfactory correlation between the predicted and experimental results is obtained. The effects of temperature and compressive Young's moudus of the E-glass fibre/epoxy composite on the spring stiffness of the springs are presented. Design charts have been created, the relationship between the spring stiffnesses and the geometric parameters of the springs are discussed. Modal tests are carried out to evaluate the damping ratio and fundamental natural frequency of these springs at various temperatures. A finite element model is built to study the effect of temperature to the dynamics behaviour of these springs and compared with experiment. Correlation curves of spring stiffnesses and the fundamental natural frequency-to-temperature ratio of the springs are established and good correlations are observed.