Research And Detection Of Low-speed Impact Of Composite Materials Based On Vibration Characteristics

Carbon fiber composite laminates are widely used in aerospace,shipping and transportation due to the advantage of their strong specific strength,specific stiffness,low density and corrosion resistance.In use and maintenance,the structure will be damaged due to the impact of birds and waves.Low velocity impact damage has the characteristics of high probability,high concealment and large danger coefficient,which seriously affects the stability and reliability of the structure.In this paper,numerical simulation and experimental methods are used to study the vibration characteristics and low velocity impact damage of laminated plates,so as to provide an effective solution for improving the impact resistance of structures.The BP neural network algorithm was optimized by genetic algorithm to predict the damage area of the laminate with different ply structures,so as to lay the foundation for damage detection online monitoring.In this paper,the dynamic signal testing system is used to test the modal vibration characteristics of four point simply supported no-destructive laminate plates,and analysis the influence of the laminate structure on the vibration characteristics of laminated plates.It is found that the position of the measurement points has little effect on the natural frequency of the laminate,and the ply structure has an effect on the natural frequency,among which the percentage of 45^?fiber layers have a great effect on the natural frequencies.In this paper,3D-MCT failure criterion is proposed to study the dynamic impact damage of laminated plates.ABAQUS software is used to simulate the impact process of 3D solid laminated plate,and a drop hammer impact test platform is built and tested according to ASTM/D7136 test standard.The accuracy and reliability of the 3D-MCT criterion model in simulating dynamic impact are verified by comparing the test data with the finite element simulation results.Based on the 3D-MCT failure criterion,the dynamic impact damage of laminated plates is simulated,and the damage evolution mechanism of laminated plates in the impact process is revealed.In this paper,three kinds of typical laminates are designed,which include[0]_{1 6},[0/90]_{4 s},[0/90/45/-45]_2s.The results show when the impact energy is small,there will be invisible damage,such as delamination failure;when the impact energy increases gradually,there will be visible damage,such as delamination,matrix cracking and even fiber fracture.The impact resistance of 45^?fiber[0/90/45/-45]_2scomposite laminates is best.Compared with the pure 0^?laminates and[0/90]_4sorthotropic laminates,the damage strength of the composite laminates are increased by 307%and 110%respectively.During the process of impact,the interlaminar damage occurred in the center of the laminate and gradually spread from the inside to the outside.In order to better analyze the relationship between the damage area and the natural frequency of the laminates with different ply structures,this paper uses the method of experiment and finite element to obtain the natural frequency of the laminates with different ply damage area,and optimizes the BP neural network based on genetic algorithm to predict the damage area model of the laminates with different ply structures.The experimental data verify the rationality of BP neural network model based on genetic algorithm.