EXPERIMENTAL BEHAVIOUR OF CFRP-TO-STEEL BONDED INTERFACES

Strengthening of steel structures with adhesively bonded carbon fibre reinforced polymer (CFRP) plates (or laminates) has received extensive research attention over the past few years. Existing studies have revealed that debonding of the CFRP plate from the steel substrate is one of the main failure modes in such CFRP-strengthened steel structures. In order to better understand and model debonding failures, the behaviour of FRP-to-steel bonded interfaces needs to be well understood first. This paper presents a study on the full-range behaviour of CFRP-to-steel bonded interfaces through the testing of a series of single-lap bonded joints. The parameters examined include the material properties and the thickness of the adhesive layer and the axial rigidity of the CFRP plate. The test results demonstrate that the bond strength of such bonded joints depends significantly on the interfacial fracture energy among other factors. Nonlinear adhesives with a lower elastic modulus but a larger strain capacity are shown to lead to a much higher interfacial fracture energy than linear adhesives with a similar or even a higher tensile strength. The bond-slip curve is shown to have an approximately triangular shape for a linear adhesive but to have a trapezoidal shape for a nonlinear adhesive, indicating the necessity of developing different forms of bond-slip models for different adhesives. The variation of the interfacial shear stress distribution along a CFRP-to-steel interface as the applied load increases clearly illustrates the existence of an effective bond length in such bonded joints.