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Deterioration of adhesively bonded CFRP/steel systems in salt fog environment, i.e., deicing salts and ocean environments, has to be taken into account in the design of steel strengthened structures. In the present work, monotonic and quasi-static cyclic loading were applied to CFRP-to-steel double strap joints for two kinds of CFRP laminates after being aged for a period of 5000 h to evaluate the bond behavior. The bonded joints exposed to salt fog had a different failure mode than that observed in the control specimens (0 h of exposure). The severe reduction of the maximum bond stress resulted from damage initiation that occurred in the corrosion region of the steel substrate, associated with final partial rupture on the corroded steel substrate around the edge of the bonded area: it was also correlated with reduced load carrying capacity. Results of pseudo-cyclic tests showed that the relationship between a local damage parameter (D) and normalized local dissipated energy (W d /G f) and the normalized slip increment (ΔS/ΔS ult) exhibited almost the same trend in the un-aged and aged bonded joints. The normalized slip increment can be seen as a direct indicator for the local and global damage for the un-aged and aged bonded joints. However, monotonic and quasi-static cyclic tests results revealed that the stress concentration due to local corrosion of steel substrate could lead to brittle rupture or accelerated cumulative damage once the aged bonded interface had become weaker. The bonded joints have exhibited also a smaller relative deformation capacity between CFRP and steel. [ABSTRACT FROM AUTHOR]

Pseudo-cyclic and cyclic loading were applied to CFRP-to-steel bonded joints built with two different CFRP laminates. In this paper, the strength capacity and bond-slip curves are presented and compared. The modes of failure are also described and associated with the types of material used, and the observed performances are correlated. The analysis of the results showed a threshold value for loading and amplitude level, below which the cyclic loading caused no detectable damage. For cycles above that limit, the region of the joints around the loaded end presented degradation reflected on the bond-slip stiffness and on the increase of residual deformation. It was found that the normalized dissipated energies either obtained from the bond-slip relationship or from the load-slip response had the same trend. The experimental data allowed also to establish a relationship between the damage developed within the interface and the normalized slip. A preliminary estimate of fatigue limit based on those data is suggested. [ABSTRACT FROM AUTHOR]

Effects of salt fog on CFRP-steel bonded joints were studied via simulation by accelerated cycles. CFRP-to-steel double strap joints made of two different types of laminates were subjected to salt fog cycles for 5000 h and Mode-II tests conducted to assess the degradation of their bond capacity at selected time stages of the process. Different mechanisms causing strength losses were found and analyzed. Results showed that the bond capacity of joints increased initially but was reduced at later stages. Corrosion debonding took place in the chamber between 5,000 h and 10,000 h prior to the application of external loading. Combined Attenuated Total Reflectance-Fourier transform infrared (FTIR) spectroscopy and Dynamic Mechanical Analysis (DMA) results showed that severe degradation at the interface of carbon fibers and resin only took place for one type of laminate. Galvanic corrosion was also analyzed and coupling between CFRP and steel developed due to the corrosion product depositions over the components leading to the degradation of the same type of laminate. [ABSTRACT FROM AUTHOR]