Identification Method Of Low-energy Impact Location For Aeronautical Composite Structures

Carbon fiber reinforced polymer?CFRP?composite material has been widely used in aerospace structures due to its outstanding physical properties.Fiber reinforced composite materials in its life cycle,that is,manufacturing,applying and maintaining process will inevitably be affected by the impact of external objects.Low-energy impact on the composite structure can introduce the occurrence of barely visible impact damage?BVID?which can bring about a decline in bearing capacity and structural damage.These damages are difficult to be detected through visible detection and may induce a high risk of losing structural effectiveness and result in structural failure.This damage will bring unimaginable consequences.It is one of the key problems to be solved in structural health technology that the location of the impact source can be determined accurately after the impact occurs and the basis for further inspection can be provided.Aiming at the low-energy impact localization problem,this paper studies the time domain,frequency domain and energy attenuation respectively.The main research contents are as follows.?1?Lamb wave signal processing technology,including Lamb wave generation,collection and analysis,is studied for carbon fiber reinforced laminates.Lamb wave group velocity calculation method can be determined based on Mindlin plate theory and Raleigh-Lamb theory,according to the characteristics of Lamb wave propagation,namely dispersion characteristics and multimode propagation mode.Previous studies certified that the high order mode of Lame wave is cut off when the frequency thickness product is lower than1KHz·m,and only low order A0 and S0 are then present.In the case of transverse impact,most of the energy of Lamb wave is transmitted through anti-symmetric mode.The frequency of the signal induced by low-speed and low-energy impact is low.A method of using A₀ mode of Lamb wave to study low-speed impact localization is proposed.?2?In order to extract TOA effectively,Db wavelet is used to denoise,decompose and reconstruct the strain signal in time domain.Group velocity is obtained according to Lamb dispersion curve.The impact source can be acquired by triangulation technology.In order to solve the problem of solving complex nonlinear equations in triangulation technology,a hybrid optimization algorithm based on particle swarm optimization?PSO?and genetic algorithm?GA?is proposed to ensure the accuracy of solving nonlinear equations.If the algorithm which solve nonlinear equation is not good,there will be large errors,and easy to appear abnormal values.To solve this problem,an algorithm based on strain gauge and four-point circular arc location is proposed and verified by experiments??3?Aiming at the impact localization problem in frequency domain,a localization method based on data drive and FBG sensor is proposed.The strain signal induced by low-energy impact is collected by FBG sensors.Research on strain signal acquisition by FBG sensor is carried out.When FBG sensor is embedded,it is advisable to extract the fiber by the end-face extraction method during the sample preparation,because the end-face extraction method can effectively improve the survival rate of the embedded fiber.The dynamic strain signal that induced by low energy impact is obtained by the fiber Bragg grating?FBG?sensor.The amplitude of the first K order natural frequency is extracted by Fast Fourier Transform?FFT?.The amplitude data is normalized,and then establish k-order vector matrix model is established.It is proposed that k-order sum of squares of deviations can be used as the basis to predict positioning.Two different validation tests were performed.The experimental model was made of different layers.The templates were formed by the autoclave.The size of the first plate is 300mm×400mm×2.5mm,it possesses a stacking sequence[0/45/90/-45]2s.The gratings are placed along the fiber direction?45°,-45°?on the upper surface of the second layer and the fourth layer.As for the another stacking sequence of[0/90]_4s,its size is 400 mm×400 mm×2 mm.Four FBG sensors are pasted on the surface of the laminate along the fiber direction of 45°.Experiments were conducted with impact of different energy levels.The results show that proposed method by author is feasible.?4?The energy attenuation factors causing strain wave propagation in CFRP laminates are studied.The wave attenuation caused by damping and the stability of energy attenuation are studied theoretically,and the inverse localization model of energy attenuation is established.In the process of experiment validation,strain gauges were used to collect impact signal,and the distance and amplitude of different impact points were obtained.Least square method was used to fit the experimental data,then the fitting curve and attenuation factor are obtained.Aiming at the problem of localization error,the concept of error ratio neighborhood is proposed.The experiment proves that the confidence of the impact source falling in the error ratio neighborhood is 0.98.