Behaviour of Steel-CFRP Adhesively Bonded Connections under Thermal Loading

by Ankit Agarwal

Institution: University of New South Wales
Department: Civil & Environmental Engineering
Year: 2014
Keywords: Freeze-thaw; Steel-CFRP joint; Thermo-mechanical loading; Adhesive
Record ID: 1069420
Full text PDF: http://handle.unsw.edu.au/1959.4/53842


The long term durability of CFRP strengthened steel structures is a key parameter for their safe use and effective design. Strengthened members can be subjected to different environmental conditions and loading scenarios during their service life, the effect of which on the failure mechanism of the strengthened members require fundamental investigations. This research presents experimental and theoretical investigations on the effects of freeze-thaw cycling and wet thermo-mechanical loading on the bond strength and failure mode of steel-CFRP adhesive joints. The influence of these conditions on the mechanical properties of pure epoxy is also investigated to give insight into the structural behaviour and also provide data for the theoretical model. The results show that the freeze-thaw cycling decreases the bond strength of the joint by about 28% and leads to variations in the failure mode. A reduction in the initial elastic modulus of the pure epoxy was also observed. The results of the wet thermo-cyclic exposure combined with sustained loading show that these conditions have little impact on the bonding strength when applied separately. However, when applied simultaneously, the mechanical properties of the epoxy and the bond strength of the joints are significantly reduced with failure observed at less than 30% of the static strength and at the temperature range well below the glass transition temperature of the adhesive. A simple shear stress-slip model is developed to analyse single-lap joints, in which the effects of freeze-thaw and thermal cycling are introduced in terms of reduced elastic modulus of the adhesive. The predicted failure load correlates well with the experimental data. A more accurate high order model is also developed that is combined with fracture mechanics and can account for the shear deformability of the adhesive layer and considers normal interfacial stresses. A new methodology to evaluate the effects of freeze-thaw cycling is proposed, which considers the effect of moisture swelling, thermal expansion and change in material properties. Finally, parametric studies are conducted and the results are presented in terms of bond strength, interfacial stresses and deformations.