Vibration Characteristic Analysis Of Composite Honeycomb Structure Under Hygrothermal Environment

Composite honeycomb structure has been widely used in aircraft secondary loadcarrying construction,like radomes,rudder surfaces and wing rib,because of its incomparable advantages of metal structures.However,due to the special material and construction characteristics of honeycomb structure,its performance is very sensitive to the changes of hygrothermal environment.Therefore,in order to design the honeycomb structure and meet the requirements of it's relevant Instructions for Continued Airworthiness,the expected environmental conditions in service,such as temperature and humidity,must be fully considered.Based on this,this paper takes the honeycomb structure composed by composite laminate and Nomex honeycomb core as the research object,and uses the method of theoretical qualitative prediction combined with simulation quantitative analysis to explore the influence of hygrothermal environment on its vibration characteristics.Firstly,based on the piecewise shear deformation theory,the vibration governing equation of honeycomb structure was solved by considering the equivalence of temperature and humidity.A detailed model of composite honeycomb structure with four-edge clamped support was established by using finite element software ABAQUS.The effects of temperature,moisture concentration,and combined temperature and humidity on the vibration characteristic of honeycomb thin plate and thick plate were discussed respectively.It is found that for the change of the natural frequencies of honeycomb structure,every 0.1% increase of moisture concentration is more sensitive than 10 K increase of temperature.Under the same humid and thermal environment,the natural frequencies of the thick plate structure is larger than that of the thin plate.The coupling effect of temperature and humidity has a greater effect on the natural frequency of honeycomb structure than the superposition of temperature and humidity when they act alone.Secondly,considering that sandwich plate theory has relatively high calculation efficiency on the premise of ensuring the accuracy of calculation,this equivalent model were used to analyze the vibration characteristic of composite honeycomb structure with facesheet/core debonding under hygrothermal environment.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;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.The effect of debonding at the center of the honeycomb structure on the reduction of the overall stiffness of the structure is the greatest;When the coupling effect of temperature and humidity,the debonding damage at the edge of honeycomb structure is more affected by the buckling effect than the damage at the center.Finally,according to the SRM(Structure Repair Manual)of civil airliner,the effect of lap length and surface additional patches on the vibration characteristic of steppedscarf repair of honeycomb structure under hygrothermal environment were discussed.It is found that the increase of the lap length will reduce the overall stiffness of the repair structure,resulting in a reduction in the natural frequency;Compared with the first-order natural frequency,the increase of lap length makes the reduction ratio of the second-order and the third-order natural frequency more obviously affected by the hygrothermal environment.When the number of additional patches on the surface increases from 0 to 2,the first-order natural frequency of the scarf repair of honeycomb structure continues to decrease,and the decrease is approximately proportional to the number of additional patches.