Study On The Salt-fog Aging Properties Of C/BMI Composites And Its Repaired Structures

C/BMI composite material is a high-performance composite with excellent thermal stability and mechanical properties,which has been widely used in aero vehicles as primary and secondary structures.The composite structures of the aero vehicles would be damaged by the salt-fog environment during its long-term service in the marine environment.That could strongly reduce the safety and combat capacity of the aero vehicles.The composite bonding repair is an effective method to rapidly repair the damaged structures in the combat.In this paper,T300/QY8911 composites used on aircraft were the research objects.The influence of the damaged-hole diameters and some parameters of the heterogeneous repair method,for example,the numbers,the angels,and the lengths of the patches,on its mechanical performance were investigated.And the salt-fog aging behavior of C/BMI composites before and after repaired was studied.The results indicate that the tensile strength and modulus of the T300/QY8911 composites decrease with the damaged-hole diameter increasing.When the hole diameter is 5 mm,it is reduced to 68.2% and 51.3%,respectively.And when the hole diameter is 15 mm,it is reduced to 96.9% and 75.1%,respectively.The double-lap repair has the best repair effect comparing with single-lap repair and step-lap repair.Corresponding to the ?5 mm and ?15 mm damaged structures,the best length of the repairing patch is 30 mm and 60 mm,respectively.And the tensile strength and modulus can be recovering to about 100% and 130% as the intact sample.The influence of the salt-fog ageing on the mechanical performances of the parent plate,the repairing patch,adhesion films,and the repaired structures was investigated.The results show that the parent-plates(with and without damaged holes)and the repaired structures have an excellent salt-fog resistance,whose tensile strength don?t reduce when they were exposed in salt-fog for 6 months and 3months,respectively.There is some degradation to the mechanical properties of repairing patches and adhesion films when they were aged just for 2 months in salt-fog environment.The tensile strength value of the repairing patch reduces to 96.1% of the initial patch and the shear strength of the adhesion film is depressed to 86.2%.In conclusion,the adhesive bonding repair has an excellent repairing effect on the C/BMI composites when using the C/EP composites as repair materials.And the salt-fog resistance of the repaired structures is also excellent.