چكيده به لاتين
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 this thesis, 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 radial and hoop stresses 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, experimental pull-out tests were conducted at different pre-strain levels in the SMA 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.
Moreover, the effect of loading rate on the tensile properties of the SMA wires was also examined using tensile tests. According to results, increasing the loading rate led to a reduction in the tensile strength and Young’s modulus of the SMA wires.
Furthermore, Experimental pull-out tests were performed at three different loading rates with the crosshead speeds of 0.3, 25 and 400 mm/min. On the other hand, interfacial shear strength between SMA and polymer was improved in higher loading rates. Enhancement of 70% was obtained for the interfacial shear strength at 400 mm/min in comparison with 0.3 mm/min crosshead speed. Moreover, the optical microscopy was utilized to investigate the effect of the generated recovery force in the SMAs, on the compressive zone in SMA/polymer specimens.
