Study On Interfacial Bonding Of Repairable Epoxy Resin And Its Composites

Thermosetting resin matrix carbon fiber reinforced composites are widely used in aerospace,wind turbine blades,rail transit and many other fields because of their comprehensive performance advantages such as light weight,high specific strength,high specific modulus and corrosion resistance.Traditional thermosetting composites are difficult to reshape after curing,and the interface is very difficult to repair after debonding.In view of these difficulties,the vigorous development of bond exchange reaction resin provides a new direction for the interface connection and repair of composites.In this paper,Vitrimer repairable resin with dynamic cross-linking network and its composites are taken as the research object.Systematic research is carried out on its basic properties,interface connection process,interface properties and constitutive behavior.Firstly,the basic mechanical properties of the repairable resin were tested,and the basic performance parameters of the resin were obtained.The degradation law of repairable resin in ethylene glycol was studied,and 180℃ was determined as the configuration temperature of connecting fluid for subsequent experiments.The adhesive ability between repairable resin and carbon fiber was tested by microdrop pull-out test,which proved that its interfacial shear strength is not lower than that of traditional resin.Further,the interfacial bonding of resin was studied by using the method of ethylene glycol intervening in ester bond exchange reaction.The influence of temperature,time and resin content in the connection liquid on the interface connection strength is studied.Firstly,180℃ is determined as the best connection temperature.At the same time,it is found that the interface strength increases with the increase of connection time,first increases rapidly and then tends to be stable with the increase of resin content.Finally,the resin connection scheme of 180℃/4h/10.71%is determined.In the subsequent test,It is found that the interfacial tensile strength and shear strength were better than the traditional bonding scheme.Finally,the ethylene glycol assisted connection method is extended to the connection of repairable resin matrix carbon fiber composites.Through the comparison of single lap test with other three connection processes,it is proved that this method has obvious advantages.After repeated connection test,it is found that the interface still has 85%strength after three connections.The single lap experiment is simulated and analyzed by finite element method,and the cohesive parameters are obtained.Through the double cantilever beam(DCB)experiment of composite interface,the mode-I delamination resistance curve(R curve)and the law of interface bridging traction separation are obtained.The effect of resin content in the bonding solution on the interfacial properties was studied.It is found that with the increase of resin content,its influence mechanism can not only increase the initial fracture toughness,but also slow down the attenuation rate of bridging stress,so as to achieve higher steady-state fracture toughness,but it has little effect on the bridging peak stress.Finally,it is found that the fracture toughness of 50%mass fraction liquid bonding interface has reached the level of composite interlayer interface,which is only lower than that of interlayer interface in terms of bridging stress,but its stress attenuation is more slow.So it shows great potential value.