Debonding model for nonlinear Fe-SMA strips bonded with nonlinear adhesives

The application of adhesively-bonded joints for strengthening of structures using iron-based shape memory alloys (Fe-SMAs) has recently emerged in construction. Fe-SMAs and the majority of structural adhesives exhibit a pronounced nonlinear material behavior, which may result in a favorable ductile failure mechanism. The development, however, of a mechanical model to predict the structural behavior of the joint is non-trivial due to the presence of nonlinearity in the adherent and adhesive. This study aims to propose a semi-analytical and semi-numerical model for describing the mechanical behavior of Fe-SMA-to-steel adhesively bonded joints. The developed model serves three main functions: (i) estimating the bond capacity for a given interfacial fracture energy, and vice versa; (ii) processing the bond-slip (r-s) behavior directly from the load-displacement (F - A) curve, and vice versa; and (iii) delivering a numerical method to simulate the full-range mechanical behavior of the bonded joints, namely the behavior at different loading stages. The model is validated using the experimental testing of 26 Fe-SMA-to-steel lap-shear joints, as well as 24 further bonded joints subject to shear with different adherents (e.g., stainless steel strips and Nickel-Titanium SMA wires) and base materials (e.g., concrete and composite polymer). An experimental data processing protocol, on the basis of the experimentally measured force-displacement (F - A) behavior and the distributed displacement along the bond line (s - x) via the Digital Image Correlation (DIC) technique, is further proposed to assess the full-range behavior of bonded joints.