Study On The Properties Of Modified Underwater Carbon Fiber Composite Repair Adhesive

With the advancement of China’s construction of a maritime power,especially the clear proposal in the 14th Five Year Plan of China to break through a batch of key core technologies in the fields of marine engineering,marine resources,marine environment,and cultivate and strengthen marine engineering equipment.The demand for lightweight composite materials in marine engineering equipment is increasing.Due to the complex usage environment,composite materials are prone to damage and equipment failure in marine engineering applications.Therefore,repairing underwater composite material structures is particularly important.At present,there are some resin systems on the market that can be used for underwater bonding,but the existing underwater epoxy resin adhesive has poor water resistance and low use strength,especially when curing with water,it will cause incomplete curing and poor performance.In order to improve the low strength of traditional underwater epoxy resin adhesives,this article starts with improving the strength of the adhesive layer,improving the adhesive bonding performance,and studying its repair performance in underwater composite material structures.This article uses epoxy resin as the matrix material and adopts the method of gas-phase Si O₂ modification to prepare an underwater epoxy resin.Non isothermal differential scanning calorimetry（DSC）was used to test,the characteristic curing temperature of the gas phase Si O₂modified underwater epoxy resin adhesive was calculated by extrapolation,the apparent activation energy of the curing system was calculated by Kissinger and Ozawa methods,and the reaction mechanism of the curing system was studied by infrared characteristic spectrum.The effect of different contents of gas-phase Si O₂ on the mechanical properties of gas-phase Si O₂ modified underwater epoxy resin adhesive was studied.When the content of gas-phase Si O₂ is 1%,the mechanical properties of gas-phase Si O₂ modified underwater epoxy resin adhesive are the best.The tensile strength,tensile modulus,bending strength,bending modulus,and bonding strength cured in air are 65.51 MPa,3.98 GPa,150.65 MPa,4.13 GPa,and 10.51MPa,respectively;The tensile strength,tensile modulus,flexural strength,flexural modulus,and adhesive strength solidified in water are 60.81 MPa,3.87 GPa,145.35 MPa,4.05 GPa,and9.06 MPa,respectively.In order to further improve the strength of gas-phase Si O₂ modified underwater epoxy resin adhesive,a gas-phase Si O₂/SCF modified underwater epoxy resin adhesive was prepared using short carbon fibers as the reinforcing phase.The effect of different content of chopped carbon fibers on the mechanical properties of gas-phase Si O₂/SCF modified underwater epoxy resin adhesive was studied through mechanical property testing.When the content of short cut carbon fibers is 0.15%,the mechanical properties of gas-phase Si O₂/SCF modified underwater epoxy resin adhesive are the best.The tensile strength,tensile modulus,and bonding strength cured in air are 72.09 MPa,4.11 GPa,and 11.74 MPa,respectively;The tensile strength,tensile modulus,and adhesive strength solidified in water are 66.62 MPa,3.97 GPa,and 10.73 MPa,respectively.The thermal mechanical properties of gas-phase Si O₂/SCF modified underwater epoxy resin adhesive were tested using DMA.The energy storage modulus does not significantly degrade with the increase of immersion time in water,and the gas-phase Si O₂/SCF modified underwater epoxy resin adhesive has good moisture resistance.The damaged structure of carbon fiber composite material was repaired using carbon fiber patch and gas-phase Si O₂/SCF modified underwater epoxy resin adhesive using carbon fiber adhesive patch technology.When the length of the carbon fiber patch was 20 mm,the mechanical properties of the repaired specimen were the best,and the repair rates in air,water,and seawater reached 81.02%,74.62%,and 71.80%of the undamaged specimen,respectively.The gas-phase Si O₂/SCF modified underwater epoxy resin adhesive has good underwater repair performance and high repair efficiency.