Study On Damage Characteristics And Identification Methods Of Composite Laminates

As a new type of material,composite material has the characteristics of high specific strength,high specific stiffness,impact resistance,light weight and corrosion resistance.Its mechanical strength and modulus can exceed that of many alloying metallic materials while being lighter than that of alloying metallic materials.Due to the manufacturing process problems of composite laminates and external impact during service,some internal lamination and fiber/matrix damage will inevitably occur.Such damage is difficult to be detected by the appearance of composite laminates,and even if detected,it is difficult to assess the extent of the damage.Therefore,it is necessary to find a method to determine the damage location and evaluate the damage degree of composite laminates reasonably,and provide guidance for the design of composite laminates at the same time.The damage characteristics and identification methods of composite laminates are studied by using curvature method.Firstly,S4R5 thin shell element in Abaqus was used to simulate composite laminated plates,and the stiffness matrix and mass matrix of a single element were extracted,and the mass matrix and stiffness matrix were assembled in Matlab.Then the dynamic characteristics of the composite laminate model were calculated,and the stiffness matrix controlling plane strain,bending strain and transverse shear were separated.Through matrix perturbation method and stiffness attenuation method,the influence law of different attribute stiffness on the dynamic characteristics of composite laminates is analyzed,and the stiffness attribute that has a great influence on the curvature of vibration mode is determined.The damage is equivalent to the attenuation of the stiffness of the attribute,so that the damage location can be identified and the damage identification principle is further discussed.Then the dynamic problem of laminated plates can not be simulated by shell elements and is transformed into a static problem for analysis.Based on the classical theory of composite laminates,the mechanical properties of laminates are studied,and the theory of laminates penetration/non-penetration is established.According to the established theory,the influence of position layering with bending direction unchanged/bending direction changing on the stiffness,curvature and strain of the lamination position of the lamination plate is analyzed,so as to realize the identification of different damage types and damage positions.Finally,C3D20 R was used to build laminated composite plate models with layered damage and fiber/matrix damage respectively to verify the validity of the theory.Firstly,the influence of lamination position with bending direction unchanged/bending direction changing on lamination position stiffness,curvature and vibration frequency is analyzed,and then the influence of fiber/matrix damage on lamination position stiffness,curvature and vibration frequency is analyzed.By comparing the effects of these two types of damage on the mechanical properties of laminated plates,the methods to distinguish these two types of damage and how to improve the identification accuracy of layered damage are given.The strain law of the lamination position of the lamination plate is analyzed and the method to evaluate the damage degree of the lamination is proposed.