Experimental evaluation of the dynamic bond strength between CFRP sheets and steel under direct tensile loads

The efficiency and the adequacy of bonding carbon fibre reinforced polymer (CFRP) composites to strengthen/repair steel elements largely depend on the bond between the steel elements and the CFRP composite. To ensure high performance and safer strengthening/repair procedures, it is important to provide sufficient bond between the patching system and the steel by choosing a suitable adhesive. Although strengthened/repaired structures are more likely to be subjected to dynamic loadings, the effect of different loading rates on the adhesion bond between CFRP sheets and steel has not been examined to date. This paper presents an experimental investigation of the assessment of the adhesive strength between CFRP and steel under various dynamic rates (3.34×10^-5, 3.35, 4.43 and 5 m/s) by utilising pull-off tests. The values from samples with one CFRP layer are higher than those with three layers for both Araldite 420 and MBrace saturant adhesives due to CFRP delamination. The loading rate affects the failure mode of samples with one CFRP layer for both Araldite 420 and MBrace saturant adhesives and remarkable changes are clearly shown at dynamic compared to static loadings. Conversely, the failure mode does not change for samples with three CFRP layers and remains CFRP delamination at all rates. Overall, the increase in pull-off strength is about 100% on average within the dynamic loading rates tested.