Fracture Mechanisms In CFRP/Steel Composite Laminates Reinforced With Multi-scale Short Fibers

Carbon fiber reinforced composites have the characteristics of high strength,high modulus,high temperature resistance,friction resistance,electrical conductivity,thermal conductivity and corrosion resistance,which have been widely used in reinforcement and repair of steel structures.However,in the CFRP/steel composite structure,the bonding layer is a weak area,and the strength of the bonding layer directly determines the overall strength of the carbon fiber/steel composite structure.In this paper,the surface of the steel plate was grooved and sandblasted.The self-made aramid chopped fiber film and carbon nanotube pretreatment technology were used to add multi-scale short fibers into the adhesive layer.The strength of the bonding layer of CFRP/steel composite structure was enhanced based on the bridging reinforcement of short fibers.The main research contents are as follows:(1)The surface of the steel was roughened by sandblasting technology,and the steel surface was pretreated by the carbon nanotube pretreatment technology.An ENF specimen of carbon nanotube reinforced carbon fiber/steel composite structure was prepared.The test results of ENF specimen shows that the failure mode of the bonding interface is mainly the failure of the bonding layer.The average load value of these specimens is 1209.8N and the fracture energy is 1313.3 J/m~2.Compared with the pure resin adhesive layer,carbon nanotubes can increase the peak load and fracture energy by 28.6%and 51.4%,respectively.(2)The ENF specimens of carbon fiber/steel composite structure were prepared by using surface grooving technology to roughen the steel surface,using self-made aramid chopped fiber film and surface wetting technology to add aramid chopped fiber into the resin bonding layer.The test results of ENF specimen shows that the average load is 1050.1N and the fracture toughness is 1221.3J/m~2because aramid chopped fiber can be embedded in the surface of grooved steel and carbon fiber.Compared with the pure resin adhesive layer,the addition of aramid chopped fiber film in the adhesive layer can increase the peak load and breaking energy by 57.1%and 106.5%,respectively.(3)Based on the aramid chopped fiber reinforced carbon fiber/steel composite structure,the carbon nanotubes were added into the adhesive layer to prepare the aramid chopped fiber/carbon nanotube mixed structure reinforced carbon fiber/steel composite structure ENF specimens.The test results of ENF specimen shows that the failure form of the ENF specimens is mainly the failure of the bonding layer,indicating that the mixed use of aramid chopped fiber and carbon nanotubes can further improve the bonding strength.The average load value of these specimens is 1284.6N and the fracture energy is 1960.9 J/m~2.Compared with the specimen with only short aramid fiber film added to the adhesive layer,the peak load and breaking energy were increased by 22.3%and 60.6%,respectively.(4)Different lengths of short aramid fibers and different concentrations of carbon nanotube pretreatment solutions will affect the arrangement of the fibers in the bonding layer and the reinforcement mechanism.In response to this problem,the effects of three different lengths of short aramid fiber and three different concentrations of carbon nanotube pretreatment solution on the bonding layer were studied in this paper.The result shows that the reinforcement effect of the 6mm short aramid fiber film on the grooved steel surface is the best,and the reinforcement effect of the carbon nanotube pretreatment solution with a mass fraction of 0.5%is the best;for sandblasted steel surfaces,carbon nanotubes with a mass fraction of 1%are the most effective.