Study On The Vibration Test And Lumped Parameter Modeling Of Fiber Reinforced Composite Plate Under Thermal Environment

Fiber reinforced composites and its thin plate structures have the advantages of lightweight,high specific strength,high specific modulus and strong designability.Its good damping capacity can restrain the vibration level of the structures and improve the ability to withstand cyclic and impact loads.Currently,composite thin-walled components are widely used in aeroengine,advanced aircraft,high-speed trains,wind power generation and other cutting-edge fields.In engineering practice,composite structures in aircraft and engines usually work at high temperatures of several hundred or even thousands degrees Celsius,which will not only affect its bearing capacity and strength limit,but also affect its vibration characteristics.Especially,the higher temperature will change the material parameters,and cause the variation of its stiffness and the energy dissipation mechanism of damping more complex.The influence of thermal environment on the vibration characteristics of composite structures brings great difficulties and challenges to the traditional testing and modeling methods.Therefore,it is of great theoretical significance and practical value to study the vibration test and lumped parameter modeling of fiber reinforced composite thin plates in thermal environment,which also provides important data and theoretical support for the prediction and analysis of vibration characteristics,suppression and optimization of composite structures under thermal environment.This paper is divided into three parts:(1)The vibration characteristics of T300 carbon fiber/resin composite plate are tested at different high temperatures.A vibration test system of fiber reinforced composite thin plate under thermal environment is built with consideration of the base excitation load,and the natural frequencise,modal dampings and vibration responses of composite thin plate under different temperature environments are observed by frequency sweeping and frequency fixing test.Meanwhile,its modal shapes under the corresponding thermal environment are measured based on the laser scanning technology.In addition,a set of aerodynamic load device is designed to test the vibration responses of composite thin plate specimens subjected to impulse excitation under thermal environment,and the natural frequencies,modal damping ratios and resonant responses are identified based on VMD method.The test results show that the natural frequencies of composite thin plate decrease with the increase of temperature.Inversely,its modal dampings and resonance responses increase gradually.It is further verified that thermal environment has a great influence on the vibration characteristics of fiber reinforced composite thin plates.(2)According to the DOFs division criterion of half-wave number,the fiber reinforced composite thin plate is divided into a spring-damper-mass model,and considering the effect of additional thermal stiffness,a lumped parameter model with temperature-dependence is established.Meanwhile,the solving process of vibration characteristics of composite plates is elaborated based on this model.Then,the stiffness and damping lumped parameters under different temperatures are identified based on the vibration test results,stretching and Kronecker operation.Also,the corresponding modeling process is proposed.Finally,a modeling example of T300 carbon fiber/resin composite thin plate is used to verify the validity and correctness of this modeling method.The factors of the number of modes used in the modeling process and the iteration step size of additional thermal stiffness which effect the accuracy and efficiency of the lumped parameter model are also discussed.(3)The vibration characteristics of two different types of CF120 fiber reinforced composite thin paltes under different temperatures and heating times are tested,that show its vibration characteristics under thermal environment indeed occur degradation for a long time.Then,considering the effect of dynamic performance degradation,and introducing temperature change ΔT and heating time th into lumped parameters,a lumped parameter model of composite thin plates with consideration of dynamic property degradation is established.Meanwhile,the solving process of vibration characteristics of composite plates is elaborated based on this model.In addition,the additional thermal stiffness and damping lumped parameters are identified based on PSO algorithm and test results.And the corresponding modeling process is proposed.Finally,the validity of the model is verified by an example.The particle swarm number and learning factor of PSO algorithm,which affect the accuracy and efficiency of the model,are also discussed.