Abstract: With the increasing application of composite materials in civil aircraft main bearing structures, study of the failure mode and load transfer rule in critical joint structures such like wing-fuselage joint is being more and more important. However, the research on the main bearing joint structures containing damage is still insufficient. As a potential critical failure mode, the study of fastener missing is of great significance to further understand the mechanical performance of composite wing root joint structure and ensure the safety of civil aircraft structure. Taking the stringer joint structure in composite wing root of civil aircraft as the research object, the intact specimen and specimen with critical fastener missing were designed and manufactured respectively. The influence of critical fastener missing on specimen stiffness, strain distribution and bolt load distribution was studied by means of test and simulation. The results show that after the critical fastener (located at the 1^st row) missing, the joint stiffness of wing root is not significantly changed. The values of strain gages located at the 1^st row change within 5%, and the values of strain gages located at the 2^nd ~4^th rows near the missing fastener increase significantly, with the maximum of 22.1%, 13.4%, 9.1% respectively. The loads of bolts located at the 1^st ~3^rd rows near the missing fastener increase significantly, with the maximum of 15%, 18%, 12% respectively, and the loads of bolts in other locates increase between 5%~10%. The missing of critical fastener has little effect on the load distribution of horizontal T-type fitting and butt plate.

Key words: composite material, wing root joint, stringer joint, fastener missing