Experimental and theoretical study on mechanical behaviors of CFRP–steel interface

Abstract

The performance of the CFRP–steel interface is crucial to the reinforcement efficiency of the steel structures strengthened by using externally pasted CFRP sheet method; while it is influenced significantly by adhesive properties and geometrical characteristics of joints. The present study aims to optimize the adhesive layer of the CFRP–steel interface and establish a theoretical model of predicting the interfacial behaviors of the optimized CFRP–steel joints. A commercially available adhesive was modified by addition of Nano-SiO2 ranged from 0 to 7wt% to ascertain the optimal content of Nano-SiO2. A series of tensile tests were carried out on dog-bone adhesive specimens, single-lap shear specimens and CFRP–steel double-lap joints to obtain the mechanical properties of the adhesive at different content of nanofiller and the corresponding bond–slip laws in the unmodified and modified CFRP–steel interfaces. Accordingly, theoretical models were derived to predict the load capacity of the joints and the bond stress distribution along the CFRP–steel interface during different loading phases. The results show that the mechanical properties of the adhesive are improved with the addition of nano-SiO2 up to 1.4 wt%. When the content of nano-SiO2 rises from 1.4 to 7 wt%, the tensile and shear strengths as well as the tensile modulus decline gradually whereas the ductility keeps growing with a lower growth rate. These indicate the nano-SiO2 content of 1.4 wt% is favorable. Both the peak stress and the load capacity of the CFRP–steel joint increase with the adhesive thickness varying from 0.5 to 1 mm. The bond–slip law of the unmodified CFRP–steel interface can be simplified to be bilinear, regardless of the adhesive thickness and curing duration. In contrast, the modified interface presents a trilinear curve due to the special plastic plateau caused by the filling of nano-SiO2. Consequently, a larger fracture toughness and a higher load capacity can be reached by the optimized joints. The theoretical results are in agreement with the experimental phenomena and results. The modified adhesive is beneficial to utilize the CFRP material better and improve the reinforcement efficiency.