Bond characteristics between high/ultra-high strength steel and ultra-high modulus CFRP laminates

With the increasing applications of high and ultra-high strength steel (HSS/UHSS) in engineering structures, there is a need to address rehabilitation and strengthening of such steel grades using carbon fibre reinforced polymer (CFRP). The bond between HSS/UHSS and CFRP is vital to ensure the efficiency of the strengthening. The existing bond study was focused on mild steel as substrate, with very limited work on HSS up to the grade of S690. Since HSS/UHSSs are designed to undergo much higher loading in service, much higher shear stress is expected in the adhesive layer, leading to a higher chance of premature debonding. In this paper, the bond between HSS/UHSS plates and ultra-high modulus (UHM) CFRP laminates under static tensile loading is studied experimentally, numerically and theoretically. Both single-sided and double-sided schemes were adopted. The numerical simulation using LS-DYNA software package was implemented and a reasonable agreement with the experimental results is found. A theoretical bond model was developed to relate the bond strength to the imposed strain in the steel member outside the bonded region.