A theoretical and experimental investigation on the stress distribution in the interface of pre-strained SMA wire/polymer composites

Abstract

The major concern in using the shape memory alloy (SMA) wires embedded in a polymer matrix is the possibility of debonding between SMA and the surrounding polymer due to the SMA phase transition recovery stress. Hence, it is important to examine the distribution of stresses in the SMA wire and the surrounding matrix. In the present study, using the principle of the minimum complementary energy a new analytical model was developed to determine the axial, radial, and shear stresses along the SMA/polymer interface. By considering the Poisson's effect and shear stress in the present analytical model, while ignored in the classical shear-lag model, more accurate results were obtained. Furthermore, by considering the effects of the SMA wire pre-strain, actuating temperature, recovery stress and thermal expansion, a novel relationship was also presented for calculating the maximum interfacial shear stress. To show the effect of the SMA wire pre-strain on the distribution of stresses throughout the SMA/epoxy interface, pull-out tests were conducted at different pre-strain levels in the SAM wire. Results showed applying the pre-strain in the SMA wire followed by a thermal activation enhanced the debonding load between the SMA wire and epoxy matrix and caused a significant variation in the stress distribution.