Determination of the bond-slip behavior of CFRP-to-steel bonded interfaces using digital image correlation

The bond-slip behavior between carbon fiber reinforced polymer (CFRP) plates and steel is crucial for predicting the structural behavior of CFRP-strengthened steel members. In this paper, the CFRP-to-steel bonded joints with different bond lengths and adhesive thicknesses were tested to investigate the bond-slip behavior of CFRP-to-steel bonded interfaces. The digital image correlation (DIC) technique was used to measure the displacement and strain data. The test results, including the failure mode, ultimate load, displacement distribution, and CFRP strain distribution, are presented and discussed. The non-linear bond-slip curves of CFRP-to-steel bonded interfaces are determined by a fitting procedure for CFRP strain distributions. A bilinear bond-slip relationship is further proposed to simplify the non-linear bond-slip curve. The test results indicate that the adhesive thickness has an influence on the failure mode, ultimate load, and bond-slip behavior. Similar to a CFRP-to-concrete bonded interface, an effective bond length also exists for a CFRP-to-steel bonded interface. The development of the interfacial shear stress is analyzed based on the determined non-linear and bilinear bond-slip curves. Finally, two theoretical models are employed for the prediction of the ultimate load, effective bond length and bond-slip curve. This study shows that the DIC method is suitable for investigating the bond-slip behavior of CFRP-to-steel bonded joints.