Bond behavior of superelastic shape memory alloys to CFRP composites

Shape memory alloys (SMA) have been embedded in fiber reinforced polymers (FRP) to increase the energy dissipation and actively tune the properties of the composites. The effectiveness of the system relies on an effective bond between the SMA wires and the composites through the epoxy interface. In this research pull-out specimens were tested to investigate the bond behavior of superelastic NiTi SMA (Nitinol) wires to carbon fiber reinforced polymers (CFRP). A total of 45 pull-out specimens were tested monotonically up to failure. The test parameters considered include the wire diameter and embedment length. A digital image correlation (DIC) system was used to measure the full field strains and displacements. The results indicate that the development length required to achieve complete transformation of the SMA wires is greater than that required to develop the upper plateau stress of the SMA. A 3-D, non-linear finite element model was developed to predict the pull-out behavior. A parametric study was conducted to quantify the parameters of a bond-slip model. The influence of the interface stiffness, κ, maximum interface shear stress, τ_max, and total fracture energy, G was considered. The numerical model was validated by comparison with the experimental results.