Research On Parameter Degradation And Identification Of Cracked Damaged Composite Materials

Composite materials are an important trend in the development of new materials today.They usually represent the forefront of development in the field of materials,and have a huge boost to technological progress and industrial development.Composite materials are artificially compounded by a variety of performance materials,mainly composed of two parts:fiber material and matrix material,so it has the advantages of each material component and reduces the disadvantages of the component,and has extremely high specific stiffness and specific strength.Wear resistance,corrosion resistance,strong design and other advantages,so it is widely used in aerospace,civil engineering equipment,automobiles and other fields.At the same time,unavoidable damage will also occur in a relatively harsh working environment,such as Matrix cracks,fiber breaks,local degumming of fiber and matrix interface,and delamination damage of laminate structure,etc.The existence of damage causes the material properties to change both mathematically and physically.However,due to the anisotropic characteristics of composite materials and the diversity of damage modes,the research on the structural performance of composite laminates with local damage is extremely complicated.And difficulties.This paper takes the fiber-reinforced composite material with crack damage as the research object,establishes a damage model for the degradation of the elastic parameters of the composite material,and at the same time analyzes the damage evolution of the damaged composite material laminated structure under the condition of tensile displacement load and under different damage levels.In-depth research is carried out on the parameter identification of,and finally the influence of damage on the inherent characteristics and vibration response of the material is analyzed through the fitting formula.The specific research content is as follows:(1)Deduction of the parameter degradation of the composite laminate structure containing crack damage by theory and study its failure load.First,based on the basic principles of fracture mechanics and the mesomechanics mixing rate model,damage variables are introduced,and the damage model is established by classical laminate theory,so as to solve the change law of the equivalent modulus of the composite laminate structure under the damage state.Then,use the finite element analysis software ABAQUS to connect with the VUMAT user subroutine,write the corresponding failure criteria and damage state variables,and establish the finite element model of the composite thin plate with damage.Finally,simulation is used to simulate the failure and fracture of the composite laminate structure with damage under the condition of tensile displacement load.The damage evolution law of the fiber and matrix around the damage location is studied,and the damage diameter of the notch and the layering method on the composite material are analyzed.The influence law of the final failure load.(2)Taking the fiber-reinforced composite laminates containing damage as the research object,the material parameters in the damaged state are obtained through the method of parameter identification.First,the composite material laminates with different damage lengths and different damage depths are obtained through artificial processing and damage,and the material sheet hammering test system under the cantilever boundary conditions is built,and the hammering test is used to determine the frequency range.Then,set up a sweep frequency test system to accurately test the natural frequency of the material under different damage conditions.Finally,based on the combination of theory and experimental test data,the differential evolution algorithm is used to identify material parameters with different degrees of damage,and the parameters are fitted with the damaged structural parameters,so as to obtain the fitting formula of the material parameters and the damage parameters.And the law of change.(3)Use the fitting formula to study the inherent characteristics and vibration response of fiber-reinforced composite laminates with damage.First,the natural frequency and mode shape of the composite thin plate with damage are theoretically calculated by the fitting formula,and the results are verified by the ABAQUS simulation software.Then,the vibration equation of the material under the boundary conditions of the cantilever is established,and the vibration time-domain response of the material subjected to harmonic excitation is solved by the Newmark-β numerical integration method,and the influence of different damages on the vibration response of the material is analyzed.Finally,the finite element software simulation analysis is used to verify the results,and the frequency response function of the composite material and the change law of damage parameters are obtained through the harmonic response analysis.