Curing effects on steel/CFRP double strap joints under combined mechanical load, temperature and humidity

This paper examines the effects of curing conditions on the performance of steel/CFRP double strap joints subjected to combined loading, cyclic temperature and humidity. A series of joints, cured respectively at an elevated temperature (120 °C) and room temperature (about 23 °C) were exposed to different combined environmental and loading conditions. It was found that curing at an elevated temperature had no effects on the joint ultimate strength tested at room temperature. However, at 50 °C, the joints cured at 120 °C showed almost no strength reduction, in comparison to those cured at room temperature with a 50% strength reduction. Curing at elevated temperature also helped to improve the time-to-failure of joints: joints cured at room temperature failed within less than 2 h when exposed to the environmental conditions, while joints cured at 120 °C could survive up to 270 h, dependent on the applied load levels. Partial safety factors proposed in design guidelines for FRP composites under environmental effects were used to evaluate the experimental results obtained, suggesting a very critical degradation of joint mechanical properties due to the environmental effects investigated in this study.

► Detailed comparative study on environmental, loading and curing effects.
► Harsh environments represented by cyclic temperature and humidity, combined with loading.
► Curing effects on durability of the adhesively-bonded system is quantified.
► Creep response under cyclic temperature and humidity received up to 270 h.
► Time-to-failure in a harsh environment quantified as a function of load level.