High Temperature Mechanical Performances Of Composite Material Based On E-51 Epoxy Resin Modification

Epoxy resin(EP)has been widely used as the matrix of CFRP composites in aviation industry due to its excellent adhesion and outstanding mechanical performances,whereas it has the operating temperature below 60?,limiting its application to devices whose operating temperatures as high as 200?.Hence,it is of great significance to undertake an overall investigation of EP modification as well as the research of high-temperature resistant composite laminates preparation methods for the benefit of composite service temperature augmentation.Tetrafunctional-epoxy resin(E-1762)and bismaleimide resin(BMI)were applied as modifiers to be mixed with DGEBA(E-51).Thermo-chemical properties,such as T_g and viscosity,were determined by DSC test and rheological test over different mass of modifiers.Both the elastic modulus and hardness were determined at temperatures over the range of 20to 140?by nano-indentation tests.The transition of phase structure for different modified system was characterized by scanning electron microscopy,and the curing reaction was predicted by using the curing kinetics theory.As for molding process,the optimized semi-impregnation processing was applied to prepare carbon fiber/modified resin composite laminates.Both the bending properties and interlaminar shear properties for laminates were investigated at temperatures over the range of 20 to 180?.The best modification method would be carried out by an overall consideration of the thermo-chemical and mechical perfomances,combining SEM microstructure characterization and mechanism analysis.Results show that the best modified method is E-51:E-1762=1:1,the curing agent is DDS,the best additive agents are AGE phr14%with DMP-30 phr10%,and the best molding processing is semi-impregnation.The thermo-chemical analysis results show that under this optimal modification,the temperature of glass transition T_g is 207?,exhibiting an increase of65.7%.The nano-identation results indicate that the hardness and modulus have been 380MPa and 1000 MPa respectively at the temperature of 140?,increased by 383%and 67%when compared to the unmodified one.The results of high-temperature mechanical experiments show that the flexural strength and interlaminar shear strength remain at 600MPa and 40 MPa respectively at 140?,which indicates the operating temperature of laminates has increased from 60?to 140?under the optimal modification.Combining the curing kinetics theory,the curing reaction level of E-51:E-1762=1:1 modified system is 0.9,consistenting with that of unmodified E-51,which reveals the curing process:acylamino and amidogen break into rings leading to the formation of curing network.The fracture morphologies of resin illustrate that the modification mechanism of E-51/E-1762 system is chemical copolymerization,while for E-51/BMI system is physical mixing,thus the modification system of E-51/E-1762 has good compatibility and low reaction activation energy,exerting a postive effect for elevating operating temperature.The fracture morphologies of laminates illustrate that the damage mechanism at high temperature exhibits differences before and after modification.Under high temperature environment,the unmodified system presents ductile fracture,while the modified system presents brittle fracture.The improved bonding ability of fiber and matrix at high temperature enhances the mechanical properties.