Vibration Characteristics Of Bond Repaired Composite In Hygrothermal Environment

Because of its excellent mechanical properties,composite laminates have gradually replaced metal materials as the main load-bearing components in aircrafts.In the design and repair of civil aircraft composite materials,according to the provisions of section 613 of CCAR25,"the influence of temperature and humidity on the design values of materials must be considered in the aircraft operation envelope".Therefore,the free vibration characteristics of composite laminates in the hygrothermal environment are analyzed.Firstly,by constructing the material constitutive equation and using ABAQUS for secondary development,the free vibration characteristics of complete composite laminates in hygrothermal environment are analyzed.It is found that the higher hygrothermal effect is,the more seriously the free vibration characteristics of the laminates are affected.The moisture absorption is greater than the influence of temperature on the free vibration characteristics of laminates.It is also found that the vibration characteristics of the composite laminates are affected more by the hygrothermal effect with more degrees of freedom constraints.Secondly,the free vibration characteristics of delaminated composite laminates in hygrothermal environment are analyzed by using the improved four laminates joint coincidence model.It is found that the influence of the constraint conditions on the vibration characteristics of the delaminated laminates are more serious than that of the complete laminates in hygrothermal environment.When the delamination area is 0%~25%,the delamination has little influence on the vibration characteristics of the delaminated laminates in hygrothermal environment.When the delamination area is more than 25%,the delamination has serious influence on the vibration characteristics of the delaminated laminates in hygrothermal environment.As the delamination position moves from the surface to the middle plane,the decreasing amplitude of each natural frequency increases gradually,among which the first order natural frequency decreases the most seriously,and the decreasing percentage of other orders natural frequency decreases gradually.The more the delaminated angle increases,the more the natural frequency falls in hygrothermal environment,when the delaminated angle increases from 30° to 70°,the drop rate of natural frequency of delaminated laminates in hygrothermal environment is the largest.Finally,the influence of repair parameters on the vibration characteristics of the bond repaired laminates under hygrothermal environment is discussed.It is found that the bond repaired laminates are more susceptible to hygrothermal effects than intact laminates.With the increase of scarf angle and damage hole diameter,the natural frequency of bond repaired laminates is more affected by the hygrothermal effect.When the hygrothermal effect is not considered,the natural frequency of the repaired laminates increases firstly and then decreases.The effect of the scarf angle on the natural frequency of the bond repaired laminates in the hygrothermal environment is more obvious than the increase of the damage hole diameter.The additional patch on the surface can improve the stiffness of the bond repaired laminates,which reduces the percentage reduction of the natural frequency of the bond repaired laminates in the hygrothermal environment,and the effect of the double additional patch is better than that of the single additional patch.