Study On The Mechanical Properties And Liquid-Oxygen Compatibility Of Epoxy Resin For Liquid Oxygen Tanks At Low Temperature

With the development of the space industry,the lightweight design of space vehicles is becoming more and more important.Carbon fiber reinforced resin-based composite materials have the advantages of high specific strength,high specific modulus,and corrosion resistance.They can replace traditional metal materials and be used in aerospace vehicle structures,with obvious weight reduction effects.As an important part of the space vehicle,the liquid oxygen tank bears the functions of transportation and storage of combustion aids.It has the problems of large structure and high mass ratio.The development of composite liquid oxygen tanks reduces the overall structure of the space vehicle.The importance is significant.The composite material for liquid oxygen tank needs to bear the load at low temperature,which has high requirements for its low temperature mechanical properties;at the same time,because the liquid oxygen has strong oxidation,the composite material for liquid oxygen tank must also meet the compatibility of liquid oxygen Claim.According to relevant research reports at home and abroad,epoxy resin-based composite materials are most likely to be used in liquid oxygen tanks,and the development of epoxy resin systems that can meet the requirements of liquid oxygen environments is essential.As we all know,there are many types of epoxy resins and curing agents,but the low-temperature mechanical properties and liquid oxygen compatibility of different epoxy resins and curing agents systems are not yet clear,and there is no systematic study.In view of the above problems,this article starts from two aspects of curing agent and resin,systematically studies the mechanical properties,heat resistance and liquid oxygen compatibility of different epoxy systems.Mechanical properties include normal temperature and low temperature（90K）tensile properties and bending Performance and fracture toughness,and heat resistance includes thermal weight loss analysis and glass transition temperature.It laid the foundation for the development of epoxy resin systems for composite liquid oxygen tanks.Specific research content and results include:（1）Comparative study of amine curing agents.Using TDE-85 epoxy resin as the matrix,the properties of epoxy resin cured products compounded by different amine curing agent systems and amine curing agents were studied.For the different amine curing agent systems selected,the mechanical properties of the DDM（diaminodiphenylmethane）curing system are the best,the tensile strength can reach 104.6MPa,and the fracture toughness can reach 1.07 MPa·m^0.5;DDS（diamino Diphenyl sulfone）curing system has the best heat resistance,the key temperature of 30%thermal weight loss under oxygen environment is 371.8℃,and the glass transition temperature reaches 168.1℃.（2）Comparative study of epoxy resin in low temperature environment.For four different types of epoxy resins:E51 bisphenol A epoxy resin,NPEF-170 bisphenol F epoxy resin,711 epoxy resin and multifunctional TDE-85 epoxy resin,respectively,with excellent mechanical properties DDM and DDS with excellent heat resistance are cured.The experimental results show that the mechanical properties of TDE-85 epoxy resin are the best.Among them,the tensile strength of DDM cured TDE-85 epoxy resin at room temperature is 104.6 MPa,the low-temperature bending strength is 192.4 MPa,and the low-temperature fracture toughness is 3.87 MPa·m^0.5.At the same time,due to the reduction of residual stress in the curing process of the resin matrix under low temperature environment and the denser cross-linked structure of the resin at low temperature,the mechanical properties at low temperature are improved compared to those at normal temperature,and the fracture surface under low temperature Smoother.（3）Study on the liquid oxygen compatibility of epoxy resins.Continue to use the eight resin systems in Chapter 3,focusing on liquid oxygen shock sensitivity testing,and study the impact of other physical and chemical factors on it to explore the mechanism of liquid oxygen compatibility.Experimental results show that the liquid oxygen shock sensitivity of the DDM curing system is superior to DDS.At the same time,according to the limit oxygen index test results,the flame retardant performance of the DDM curing system is relatively good.According to the test results of thermal weight loss and thermal weight gain,the critical temperature of thermal weight loss of E51 and NPEF-170 is higher and the quality improvement is less in the thermal oxygen environment,and the thermal stability and oxidation resistance are excellent.The resin’s liquid oxygen impact sensitivity is also relatively good,indicating that the resin with excellent thermal performance under the same curing system has better liquid oxygen compatibility.