Mixed-mode debonding mechanisms of Fe-SMA and CFRP bonded joints

Adhesively bonding iron-based shape memory alloy (Fe-SMA) offers a solution to strengthen fatigue-prone metallic structures and prolong their service life. However, adhesive joints being susceptible to debonding failure, static failure was studied in Mode I, Mode II, and mixed-mode conditions, both experimentally and theoretically. The Fe-SMA material behaviour on the debonding mechanism was shown to be influential, reducing the bond capacity compared to carbon fibre reinforced composites (CFRP) strengthening material. So far the study of static joint failure was mainly confined to the debonding under the controlled lap-shear test conditions, a very common test for joint characterization and not on a component scale. The interaction between the structure end the repair was assumed negligible with the focus being on the interaction between the adhesive and adherend. In this manuscript, the static mixed-mode debonding is approached experimentally and theoretically at component scale. The residual tensile strength of a fully separated structural steel or aluminium element repaired with bonded Fe-SMA or CFRP strips of different width is measured. The repair eccentricity induced bending of the structural element is considered. Analytical and finite element modelling of the structural component are validated with the experiment and allow to perform the mode separation. It is shown that the deformation of the structural element affects the mode mixity. When the repair strip stiffness is high relative to the structural components stiffness, the Mode I contribution increased, negatively affecting the component residual strength. However, this effect was shown to be less important for Fe-SMA repair strips due to their material nonlinearity. These bonded repair were thus shown to be more resilient than their CFRP counterpart.