Abstract: For the honeycomb structure with facesheet/core debonding composed by composite laminate and Nomex core, numerical analysis under different hygrothermal environment was carried out to investigate the influence of facesheet/core debonding on the natural frequency of composite honeycomb structure. Based on the piecewise shear deformation theory, considering the displacement difference between the upper facesheet and the core in the debonding area after deformation, the governing equation of motion of honeycomb structure was solved by using the equivalence of hygrothermal expansion. Finite element model of composite honeycomb structure with facesheet/core debonding by four-edge clamped support was established. The effects of temperature, humidity and combined humidity and temperature on the natural frequencies of honeycomb structure with different facesheet/core debonding area were discussed, respectively. The results of the example show that when the moisture concentration is between 0.5% and 0.75%, the honeycomb structure with 25% debonding area first appears buckling effect. Under the same hygrothermal environment, with the expansion of debonding area, the first three natural frequencies of composite honeycomb structure decrease gradually, and the influence on the first natural frequency is the greatest. When the hygrothermal stress reaches a certain degree, the increase of debonding area will cause the honeycomb structure to reach the state of hygrothermal buckling earlier, and the effect of buckling will gradually extend from low-order frequency to high-order frequency. Under the combined effect of temperature and humidity, the natural frequency of honeycomb structure with 18% debonding area is most seriously affected by the environment.

Key words: composite honeycomb structure, facesheet/core debonding, hygrothermal environment, buckling, natural frequency