Study On Toughening Mechanism Of Epoxy Resin Modified By Micron Materials And Mechanical Properties Of CFRP-steel Interface

The mechanical properties of carbon fiber reinforced composites(CFRP)are superior,which is reflected in the ratio of elastic modulus to density and strength to density.Meanwhile,the manufacturing process and design of CFRP are mature,and it has great advantages in fatigue resistance and corrosion resistance,so it is widely used in the reinforcement of steel structures.The adhesive plays a role of load transfer in CFRP reinforced steel structure,so the performance of adhesive determines the quality of reinforcement.Epoxy resin,as one of the matrix of carbon fiber reinforced composites,mainly plays a role in bonding positioning and stress transfer in the composites.The performance of epoxy resin determines the performance of the composites.The product after curing of epoxy resin has a high degree of crosslinking and is prone to brittle failure under excessive load.Meanwhile,its impact resistance and fatigue load resistance are poor,and its application scope in engineering is limited.Therefore,in order to improve the quality of reinforcement and expand the application range of adhesive,it is necessary to strengthen and toughen the adhesive.Based on bisphenol A type epoxy resin E51 as matrix material,aliphatic amine and polyether amine as curing agent,adding micron material polystyrene(PS)microspheres toughening epoxy resin,analysis summary toughening agent content on the mechanical properties of modified epoxy resin,and use it to CFRP reinforcing steel structure,explore the CFRP/steel reinforcement performance.The specific work is as follows:1.The tensile properties,bending properties and impact properties of epoxy adhesive modified by micron polystyrene(PS)particles were tested,and the effect of curing time on the modified adhesive was explored.The results show that when the mass fraction of PS is 2.5%and curing time is 4d,the mechanical properties of PS/epoxy resin composites are the best,and the tensile strength,tensile elastic modulus,bending strength,bending modulus and impact strength are increased by 77%,145%,71%,35%and 22%.But the elongation at break and deflection decreased by 44%and 27%.2.The shear properties of CFRP/steel single-lap specimens made of 2.5%PS/epoxy resin composites were tested.The average shear strength of the specimens was 2.2mpa,which was lower than that of the adhesives on the market.At the same time,the effect of temperature on the adhesive was studied.The results show that the best use temperature of the modified adhesive is between 10℃ and 40℃.The microstructure was observed by scanning electron microscopy(SEM).It can be seen that the appropriate amount of PS particles effectively inhibits the growth of cracks.With the increase of mass fraction,PS particles appear agglomeration phenomenon in the resin,resulting in the decline of mechanical properties.3.Self-made adhesive was used to make CFRP fully covered adhesive to strengthen steel plate with central crack,and axial tensile test was conducted to explore the interface properties between CFRP and steel plate.Compared with three kinds of adhesive colloid commonly used in the market,the reinforcement effect is analyzed.The results show that the CFRP/steel interface bonding performance of PS adhesive is good,and only CFRP failure occurs in the specimens,which is better than that of SIKA30 and WSB adhesive,while only CFRP failure occurs in the specimens of HJY adhesive under the same conditions,so it is impossible to compare the performance differences between PS adhesive and HJY adhesive.4.Based on ABAQUS/Explicit platform,the finite element model of CFRP fully covered adhesive reinforced steel plate with central crack was established.After verification with the test,the parameters were analyzed.The results show that the failure rule of the adhesive is that it is first destroyed near the steel plate defect,then it expands to both ends and finally it is destroyed in a large area.Increasing the thickness of CFRP can improve the tensile strength of specimens.The ultimate load of specimens is related to the type of CFRP layering sequence,and the law is as follows:the less the type of CFRP layering,the greater the ultimate load of specimens.