| The fiber-reinforced composite material has many advantages,such as high specific strength,high specific modulus,good thermal stability,and damping capacity.Nowadays they have been gradually used in aeronautics,astronautics,automobile,apparatus and other industrial fields.In engineering practice,there are a large number of the fiber-reinforced composite materials and its thin plate structures made of the types of material,such as solar panels,aircraft engine fan blades and large wind turbine blades.With their structures more and more complicated,the working environment is becoming more and more severe,which caused failure problems are more prominent,such as the vibration exceed the standard,wear and tear,and fatigue failure.Therefore,the researches on advanced testing method of vibration characteristics of the fiber-reinforced composite plates have very important theoretical significance and practical value,which they will be of help to theoretical modeling,simulated calculation,response prediction,vibration reduction optimization design,vibration mechanism,damage detection and etc.This study is mainly classified to four chapters:(1)A vibration testing platform of fiber-reinforced composite thin plate was designed and developed,and the practical application was studied.Firstly,the laser linear scanning vibration measurement system based on Lab VIEW was developed.Then,the corresponding exciting platform was also designed.And,the development task of laser scanning vibration measuring platform for composite thin plate was completed.Finally,TC300 carbon fiber/resin composite plate was taken as the research object,and its potential nonlinear vibration phenomena were characterized by the proposed test methods.And,five kinds of nonlinear vibration phenomena of composite thin plate were obtained based on the testing platform.(2)The natural characteristics of fiber-reinforced composite thin plates were studied on laser linear scanning method.Firstly,laser linear scanning method was proposed to efficiently measure modal shapes of fiber-reinforced composite thin plate with high preciseness,and the laser scanning frame model of the composite plate was established,and the extraction principle of modal shape data,laser scanning rate selection criterion was explained in details to clarify the theoretical principle of laser linear scanning method.Then,by a study case,the first 7 modal shapes of TC300 carbon fiber/resin composite thin plate were measured by laser linear scanning method,and through the comparing with the results obtained by the traditional experimental modal method and finite element method,its effectiveness and reliability have been verified.Finally,the influences of constraint boundary condition,excitation level,and laser scanning rate,scanning spacing,scanning path mode,the fiber angles and fiber material damage on modal shape results were discussed.(3)The time-domain and frequency-domain test method for nonlinear damping of fiber-reinforced composite thin plate was proposed.Firstly,by using Hilbert transform technique,the expression of nonlinear damping of the composite structure with amplitude dependence system was derived.Then,based on refined resonance method,the expression of nonlinear damping of the composite plate with amplitude dependence was derived.Finally,the reasonable and standard test procedures were summarized,and the real measurement of TC300 carbon fiber/resin composite thin plate was carried out.It was proved that the proposed two methods can effectively obtain its damping parameters under different excitation levels,thus they can be used to quantitatively evaluate nonlinear damping characteristic of composite structure with amplitude dependence.(4)The damage location detection of fiber-reinforced composite thin plate was studies by curvature modal shape scanning method.Firstly,when the extraction principle of modal shape data was illustrated,two-dimensional five-spot-tripling surface smoothing method was proposed,so that a quantitative index for damage location detection of fiber-reinforced composite thin plate,i.e.,the damage location index can be derived.Then,the Matlab calculation program was written,and the specific damage location detection procedures of composite plate based on laser scanning method are also proposed.Finally,T300 fiber/epoxy composite plate was taken as a study object,and damage detection experiment was performed.It proved that the above method can detect fiber breakage position of such composite plate with high accuracy,and this method and the related experimental system can provide a new idea for damage detection and identification of composite structures. |
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