Bond behavior of CFRP sheets-to-steel shear joints with different steel surface treatments

The current study focuses on the bond behavior of CFRP sheets-to-steel double-lap shear (DLS) joints with different steel surface treatments. A total of 18 DLS joints are tested in tension. The effects of six different steel surface treatments on the mechanical response of the DLS joints are investigated. The steel surface treatments include power tool polishing with four different sandpapers in grit sizes, grit blasting and pre-coating silane coupling agent. The surface topography and roughness of the steel substrates with different treatments are evaluated from test results, and their relationship with mechanical behavior and failure modes is established qualitatively. The geometric characteristics of the surface are strongly correlated with the average ultimate loads of the DLS joints. Based on the measured load-slip curves, the bond-slip (B-S) relationship is predicted, which removes the effect of the actual deformation of the steel substrates on the slip. Regression analyses of quantifying the B-S relationship are conducted to establish the simplified B-S model applied to the CFRP sheets-to-steel bonded interface, and the effects of different steel surface treatments are considered in this model. The accuracy of the simplified B-S model is verified through comparison with the experimental results.