Influence of multiple debonding defects on the behaviour of mechanically anchored CFRP-to-steel joints

Carbon fibre-reinforced polymer (CFRP) externally bonded reinforcement (EBR) is commonly used to improve the strength of degraded steel structures. However, the CFRP composite is prone to debond from the substrate prematurely. To prevent its debonding, the use of mechanical anchorages is a primary option. Since controlling the adherence beneath the mechanical anchorage is difficult, it is important to better understand the bond performance of CFRP-to-steel interfaces in the presence of multiple debonding defects. To study this topic, a new numerical approach based on the finite difference method (FDM) is proposed and developed. Its validation is achieved by comparing results with a commercial finite element software package. Two different debonding defects are considered, localized and randomly dispersed, and four different ratios between the debonded and bonded areas are considered. Moreover, brittle and ductile adhesives are assumed, which result in triangular and trapezoidal bond-slip relationships, respectively. The results mainly showed that the combination of brittle adhesives and localized debonding defects leads to lower maximum load degradations than those found with dispersed debonding defects. Also, the friction angle is identified as the parameter with the highest influence on the bond performance of the mechanically anchored CFRP-to-steel joints.