Study On Propagation Characters Of Ultrasonic Wave And Defect Detection Of Composite Structures Based On Laser Ultrasonic Technology

Fiber reinforced composite materials and structures have been widely used in aerospace,marine and other engineering fields due to their excellent mechanical bearing capacity and multi-functional characteristics.However,such materials are prone to form damage and defects in the process of preparation and service,thus weakening their relevant mechanical properties and increasing the risk of early failure of structures in service.For composite materials and structures with increasing engineering demand,it is very important to carry out nondestructive testing and regular maintenance in their manufacturing and use process.Compared with the traditional non-destructive testing methods,laser ultrasonic testing has the advantages of non-contact,high resolution,high detection accuracy,high degree of automation and so on.At present,the research of this technology at home and abroad,especially the application of laser ultrasonic testing technology in composite materials and structures,is still in its infancy.In this paper,based on the theory of elasticity and thermo-mechanical coupling,the finite element numerical method is used to study the laser ultrasonic propagation characteristics and defect identification method of composite materials and structures.Firstly,the basic theory of laser excited ultrasound is introduced,and the related theories such as elasticity,equivalent heat source model of laser irradiation,thermal coupling and numerical calculation methods so on are briefly described.Based on this,the process of ultrasonic propagation of carbon fiber composite laminates excited by laser is simulated by means of complete thermo mechanical coupling method.The propagation characteristics of ultrasonic wave in different directions of composite laminates are analyzed.The influence of laminate thickness and laying mode on the propagation characteristics of ultrasonic wave is discussed.The simulation results are compared with those in previous literature to verify the model.Secondly,aiming at the composite laminates with in-plane,interlaminar and mixed defects,the propagation characteristics and defect detection methods of laser ultrasonic are studied.For the type of in-plane defect,the influence of defect size on damage identification result is analyzed,the defect location and shape are realized,and the influence of coupling effect on detection result when multiple in-plane defects coexist is discussed;for the type of in-plane defect,the judgment method and depth location method of in-plane defect are discussed;for the mixed defect,the defect location of the structure containing in-plane defect and interlayer defect is simulated and realized.Finally,the laser ultrasonic propagation characteristics of the honeycomb structure,pyramid lattice structure and two-way corrugated sandwich structure of carbon fiber composite with defects are studied,and the effect of laser ultrasonic testing on such structures is discussed and compared.