Research On Impact Damage Of Composite Materials Based On Nonlinear Lamb Wave Mixing Mode

In recent years,as a kind of material with the advantages of high specific stiffness,high specific strength,high specific modulus,designable performance,fatigue resistance,corrosion resistance and light weight,composite materials have been widely used in aerospace,automobile,shipbuilding,chemical engineering and civil engineering.Because composite materials are often subjected to various forms of low-speed impact in the service process,such as bird impact,lightning strike,tool drop and so on,there are some small damage that can not be observed by naked eyes.Although some damage impact energy is not large,it may affect the strength and stiffness of composite structure and pose a huge potential threat to safety,so it is necessary to detect the damaged structure So as to accurately identify the degree of injury.Nonlinear ultrasonic Lamb wave mixing testing technology is a non-destructive testing technology to reflect the damage of materials.The main working principle is to evaluate the damage of materials by relying on the nonlinear acoustic phenomena such as harmonic,beam mixing and waveform distortion when ultrasonic passes through the damage.In this paper,aiming at the low-speed impact damage in composite materials,through experiments and finite element simulation The mixing nonlinear response of the composites under different impact energy was studied.The damage location of the composites was located by applying delay to the excitation signal and controlling the mixing region of the signal.Firstly,the ultrasonic wave and its classification,the wave equation,propagation characteristics and dispersion characteristics of Lamb wave in composite plate are introduced.The dispersion curve of Lamb wave in composite plate is drawn.How to identify the mode and select the appropriate frequency according to the research requirements are introduced.The mixing Lamb wave and frequency nonlinear coefficient ? are introduced to characterize the impact damage degree in composite plate.Secondly,the low-speed impact damage detection of composite materials is studied by using experimental methods.The experimental scheme is summarized,the material type is selected,the specimen preparation is completed,the low-speed impact damage is made through the drop weight impact experiment,the mixing detection system is built to adjust its parameters,and the mixing Lamb wave detection experiment is carried out.Based on the sum frequency amplitude,the different impact energy is studied The relationship between the damage and the nonlinear Lamb wave mixing response of composites under low velocity impact is studied.Then,the damage detection of composite materials under low velocity impact is studied by finite element simulation method.A finite element model including three steps of impact vibration mixing detection is constructed.The validity of the model is verified by comparing the simulation results with the experimental results.Based on the sum frequency amplitude,the relationship between the low velocity impact damage and the mixing response of nonlinear Lamb waves under different impact energy is studied.The simulation results are consistent with the experimental results.Finally,the damage location detection of composite materials under low velocity impact is studied by the finite element simulation method.Based on the previous research results,the finite element model is established,and the mixing region of the mixed Lamb wave is changed by applying a delay to the excitation signal to find the impact damage location and locate the damage point.