Study On The Interface Bonding Performance Between Carbon Fiber And Epoxy Resin With Molecular Dynamics Simulation

Carbon Fiber Reinforced Polymer(CFRP)has been widely used in the reinforcement and repair of civil engineering structures due to its advantages of light weight,high strength,corrosion resistance,excellent fatigue performance and ease of construction.Considering the long-term life design and the complex service environment of civil engineering structures,the durability of CFRP controlled by the bonding property of fiber/resin interface is a key factor restricting the application of CFRP.Compared with the traditional test methods,molecular dynamics simulation can study the interfacial bonding degradation mechanism from the nanoscale,but at present,it mainly focuses on obtaining the interfacial bonding degradation law.Therefore,this paper uses molecular dynamics simulation to study the degradation mechanism of the interfacial bonding properties of carbon fiber/epoxy resin under water immersion at room temperature.The main research contents and fundings are as follows:(1)Through molecular dynamics simulation,the molecular dynamics model of epoxy resin with no moisture absorption and water absorption of 1%wt and 2%wt was established,and the glass transition temperature and Young’s modulus of epoxy resin were calculated.The simulation results indicate that the glass transition temperature and Young’s modulus decrease under the effect of water,which are in good agreement with the experimental results.(2)The molecular dynamics models of unoxidized and oxidized carbon fibers were established by molecular dynamics simulation,and the surface energy of the fibers was calculated.The simulation results show that oxidation treatment can increase the surface energy of the fibers,which is consistent with the experimental results.Based on the epoxy resin and carbon fiber model,the initial molecular dynamics model of carbon fiber/epoxy resin interface was established.(3)The adsorption of epoxy in the interface was accelerated by Metadynamics enhanced sampling method,and the diffusion of water molecules was accelerated by temperature acceleration method.The equilibrated molecular dynamics model of carbon fiber/epoxy resin interface in dry and water immersion environment was obtained.Based on the equilibrium state model,the interface binding energy of carbon fiber/epoxy resin interface was calculated.The simulation results declare that the bonding property of the interface degrades under the condition of water immersion,which is in agreement with the experimental results.(4)The distribution of interfacial binding energy was studied by molecular dynamics simulation.The simulation results show that the bonding between unoxided carbon fiber and epoxy resin is mainly due to the van der Waals attraction between carbon atoms in epoxy resin and carbon fiber.The interfacial bond between oxided carbon and epoxy resin mainly derives from the van der Waals attraction between carbon atom in epoxy resin and carbon fiber as well as the Coulomb and van der Waals attraction between hydrogen atom and carbon fiber.(5)The atom distribution of epoxy resin was studied by molecular dynamics simulation.In term of the unoxidized carbon fiber/epoxy resin interface,the simulation results show that the water molecules change the distribution of atom in the van der Waals attraction region between the carbon as well as oxygen atoms of epoxy resin and carbon fiber.In the oxidized carbon fiber/epoxy resin interface,water molecules change the distribution of atom in the Coulomb attraction region between the hydrogen atom in the epoxy resin and the carbon fiber,resulting in the degradation of the bonding properties of the interface.