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Abstract The degradation mechanisms of bonded joints between CFRP laminates and steel substrates under severe environmental conditions require more durability data and studies to increase the database and better understand their causes. Studies on bond properties of double-strap CFRP-to-steel bonded joints with two different composite materials as well as adhesive coupons subjected to freeze-thaw cycles for 10,000 h were conducted to reduce that gap. In addition, the equivalent to the number of thermal cycles and their slips induced in the CFRP laminates was replicated by an equivalent (mechanical) loading-unloading history condition imposed by a static tensile machine. The mechanical properties of the adhesive coupons and the strength capacity of the bonded joints were only slightly changed by the artificial aging. It was confirmed that the interfacial bond strength between CFRP and adhesive is critically related to the maximum shear stress and failure mode. The interfacial bond strength between adhesive and steel degraded with the aging. However, the equivalent thermal cyclic bond stress caused no detectable damage on the bond because only the interfacial elastic regime was actually mobilized, which confirmed that pure thermal cycles aging, per se , at the level imposed, have a low impact on the degradation of CFRP-to-steel bonded joints. [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]

Carbon Fiber Reinforced Polymer (CFRP) composites have a large potential for strengthening and retrofitting steel parts but due to their premature debonding from steel, further data and research are still required for wider application in such situations. In the present paper, the bond characteristics of CFRP-to-steel joints in pull-pull loaded conditions were studied. Monotonic loading of the double strap joints with different bond lengths was applied and the failure modes and interfacial bond-slip curves were obtained. A tri-linear bond-slip model is proposed and it was derived from the experimental data. A closed-form solution approach is also proposed based on the tri-linear bond-slip model. The strength of the CFRP-to-steel interface, the distribution of the relative displacements between bonded materials, the strains developed in the CFRP laminate and the bond stresses along the interface are reported and the closed-form solution is compared with the experimental results. Two cases are selected for presentation: (i) one with the bond length greater than the effective bond length; and, inversely, (ii) one with bond length which is shorter than the effective bond length. The results predicted by the closed-form solutions are shown to be accurate enough when compared to the experiments. [ABSTRACT FROM AUTHOR]

Mechanical anchorage devices have the potential to efficiently improve the bond behavior of Carbon Fiber-Reinforced Polymers (CFRP) Externally Bonded (EB) onto steel with an adhesive. Existing relevant studies, however, have been very limited. Against this background, experimental and numerical studies on the double overlapped CFRP-to-steel bonded joints with an end mechanical anchorage were carried out in the present study. Two types of CFRP laminates (i.e. , SIKA CFRP and the other type made in Harbin Institute of Technology – HIT) were used in the bond tests, with or without end mechanical anchorage devices. The test results showed that the end mechanical anchorage had marginal effect on the bond-slip relationship between EB CFRP and steel as well as debonding load, but could increase the ultimate load. It was also found that CFRP laminate from HIT had a better bond performance than that from SIKA, in terms of both debonding load and ultimate load. Using ABAQUS, Finite Element (FE) model was established on such bonded joints and the accuracy was verified with test results. The verified FE model was adopted in a parametric study to further clarify the effect of key parameters on the bond behavior of such bonded joints. [ABSTRACT FROM AUTHOR]