Research Of Corrosion Causes And Repair Method Of B747 Cabin Floor Beam

The corrosion damage on the floor beam of B747 have not only weakened the loading area, but also reduced the structure strength. At the same time, the corrosion pit is usually the most easily place where fatigue crack nucleate. For upper chord of floor beam which suffered alternating stress, the existence of corrosion pit may result in fatigue crack producing ahead of time and reducing fatigue life of the structure. Besides, it may also cause long time unscheduled structure repair and huge economic loss.Taking B747 cabin floor beam as a research subject, according to analyzing maintenance record, the damage regular of cabin floor beam was confirmed. Based on the study of corrosion damage research result, the main damage station focus under galleys and lavatories and the main corrosion types are pit corrosion, crevice corrosion and stress corrosion.According to the mechanism of corrosion, pit corrosion, crevice corrosion, stress corrosion, the designing and maintenance defects of B747 cabin floor beam were analyzed.Based on the analysis, the floor beam damage root was concluded and provided the corrosion damage prevention & control measures, which satisfy the airplane designing principle and MSG-3 airplane maintenance theory.The general repair method about floor beam in SRM is cutting out the whole section of upper chord which need more working hours and reducing the maintenance efficiency.Starting from theory, using finite element software ABAQUS, the influence of corrosion on structure static strength and stress concentration were studied and analyzed in different degree of corrosion, the floor beam needs different repair method which provides theory for maintenance personnel. At last, one repair example was introduced.