Study On Nonlinear Lamb Wave Method For Damage Assessment Of Composite Structures

In modern engineering,composite materials have been widely used in various fields.Because of its sensitivity to the impact of foreign objects,in improper use or in harsh environments,composites may suffer from various forms of invisible and difficult to identify damage,which requires early understanding of damage in composites.Traditional linear Lamb waves have low sensitivity to small injuries and are difficult to meet the requirements for damage monitoring.On the basis of analyzing nonlinear Lamb wave propagation theory,the application of nonlinear Lamb wave in damage monitoring of composite materials is studied by taking epoxy resin composite plate as the research object.The specific work of this paper is as follows:(1)The concept and content of structural health monitoring are introduced,and the methods of Lamb wave monitoring and the application of nonlinear Lamb wave in structural health monitoring are discussed.On this basis,the domestic and foreign research status of Lamb wave is expounded.The research content and significance of this paper are introduced.(2)The propagation law and characteristics of nonlinear Lamb wave are studied in theory.The source of second harmonic generation is analyzed.Then two necessary conditions for generating cumulative second harmonic are given.Finally,the excitation and sensing methods of Lamb wave are given.(3)The damage monitoring mechanism of nonlinear Lamb wave is studied,and the calculation formula of nonlinear characteristic parameters is derived,which can quantitatively characterize the nonlinear degree of materials.Finally,the mean filtering and frequency domain signal analysis method are used to process the signal,so as to obtain the fundamental and second harmonic amplitude of the signal.(4)The sensitivity of nonlinear Lamb wave to damage is studied.The S0 mode Lamb wave is used to study the damage.The results show that the nonlinear Lamb wave has a good sensitivity to the micro damage in the structure.When the structure is damaged,the nonlinear characteristic parameter value will increase significantly.At the same time,when the damage degree is gradually deepened,the nonlinear characteristic parameter value will also increase,which makes the foundation work for the next step of damage location.(5)Based on sensor networks,the localization of crack damage in one and two-dimensional plane is studied.The results show that there is a certain corresponding relationship between the damage location and the nonlinear characteristic parameters,which proves that the nonlinear Lamb wave technology can be used for micro damage monitoring and evaluation.