A comparison of the influence of nonlinear and linear creep on the behaviour of FRP-bonded metallic beams at warm temperatures

This study investigates whether it is necessary to consider nonlinear (rather than linear) adhesive viscoelasticity when considering the behaviour of an FRP-bonded metallic beam at warm service temperatures (25 °C, 30 °C and 40 °C). The paper presents finite element analyses that compare the effects of nonlinear and linear creep in the bonded joint for two different FRP-strengthened metallic beams (steel and cast-iron). This modelling work incorporates a viscoelastic adhesive constitutive model determined using a dynamic mechanical analyser for a commonly used ambient cure structural epoxy adhesive. The nonlinear viscoelastic behaviour of the strengthening adhesive was characterised using time-temperature superposition combined with the parallel rheological framework model. The study found that a model incorporating nonlinear viscoelastic creep only leads to a slightly larger joint slip (maximum 1.0% after 1 year) and a slightly lower CFRP axial stress (maximum 2.4% after 1 year), compared to an equivalent model using linear creep. This has a limited impact on the structural performance for the cases studied. In most cases, the simpler linear viscoelastic constitutive model is sufficient to analyse the behaviour of the FRP-bonded metallic beam in a warm environment.