Damping Characteristics Analysis And Loss Factor Identification Of Fiber-Reinforced Composite Thin Plate

Fiber-reinforced composite has excellent mechanical properties,good thermal stability and capability on weight reduction,which is widely used in the area of aeronautics,astronautics,automotive,naval vessel and weapon industry.Currently,there are a large number of such composite thin walled structures,such as solar panels,aircraft engine fan blades,large wind turbine blades and etc.Damping is a key parameter for such type of composite,but because of the complex structure and the complexity of the load,which has significant influence by fiber orientation,interface condition of fiber/matrix,material preparation process and environmental temperature.At the same time,it is also closely related to the external excitation frequency,excitation amplitude and so on.So the analysis of damping characteristics has a great degree of uncertainty.In addition,the damping parameters of this type of composites exhibit nonlinear characteristics.It is closely related to external excitation energy,excitation frequency and other factors.And the macro structure also exhibits the damping characteristics depend on the external excitation amplitude and frequency which called frequency dependent and amplitude dependent.This poses a great challenge to the traditional vibration testing methods based on linear equivalence.Until now,a complete and effective damping characteristic analysis method has not yet been established in academic circles.In this paper,the damping characteristics of fiber reinforced composite thin plate and the identification method of its loss factor are studied,and it can be divided into three parts:(1)The linear damping parameters of the composite thin plate structure are analyzed and predicted based on the Ritz method and the complex modulus method which considering the influence of the fiber direction.And the influence of elastic modulus,loss factor and ratio of length to width on damping is also discussed.The Matlab program is written and the damping ratio of composite thin plate is obtained by two methods.In order to verify the correctness of the method,the experimental verification is further carried out.The error between the calculated results and the test results based of the Ritz method is within 18%,and the error between the calculated results and the test results based on the complex modulus method is within 14%,which verifies the correctness of the analysis method.(2)The time domain analysis method and frequency domain analysis method for nonlinear damping of fiber reinforced composite plates are presented.Firstly,theoretical analysis signals are constructed based on nonlinear compression transform,and the expression of nonlinear damping of composite structure system is derived,and the theoretical principle of obtaining nonlinear damping parameter from time domain test angle is defined.The damping parameters of composite plate under different attenuation time are obtained by the proposed method;this method can be used to quantitatively evaluate the different excitation amplitude and frequency characteristics of the nonlinear damping composite structure.Meanwhile,the nonlinear damping of fiber reinforced composite thin plate with amplitude dependence is analyzed by frequency domain based on strain energy density function method.Research shows the theoretical and experimental results are in agreement with the time domain analysis.With the increase of excitation amplitude,the damping of fiber reinforced composite thin plate gradually increases.(3)The identification method of the linear and nonlinear loss factors of fiber reinforced composites is studied and experimental verification is also carried out.Firstly the damping model is established based on fiber reinforced composite thin plate.Then,the loss factor of fiber reinforced composites is identified by the least square method;and the identification process of loss factor of fiber reinforced composite thin plate is presented;and TC300 carbon/epoxy composite plate is taken as a research object,and its loss factors are identified.Finally,with the comparing between the measured damping results obtained in this paper and the calculated damping results based on the Adams-Bacon model with the same loss factor,the corresponding maximum deviation between them is less than 15%,so the correctness of such identification method has been verified indirectly.