Study Of The Mechanical Performance And Analysis Of The Failure Behavior For Adhesivly Bonded Joints Between CFRP And Steel DC04

With the widely application of carbon fiber reinforced plastics(CFRP)in automotive lightweighting,connection design between carbon fiber composites body parts and heterogeneous materials such as steel become an urgent problem to be solved.Adhesive bonding has become an effective choice for heterogeneous connection of carbon fiber composites because of the simple process,high connection efficiency,and it is conducive to reduce manufacturing costs and energy consumption.In the bonded structure,the material properties of the structural adhesive and load conditions have important influence on the mechanical properties and failure behavior of the bonded joint.This thesis is designed for the bonded connection of heterogeneous materials between CFRP and low carbon steel.By experimental test and finite element numerical simulation method,the effects of material properties,tensile shear and three-point bending load conditions on the ultimate load,stress distribution and failure behavior of single bonded joints were studied.The main research results are as follows:(1)The mechanical properties of existing structural adhesives are diverse and have large dispersibility.By comparing the advantages and disadvantages of the test results of different test standardse,the uniaxial tension,T-peeling and thick adherent shear test is determined to measure the mechanical properties of two kinds of structural adhesives,which provide effective material parameters for the numerical simulation model of adhesive joints.The reliability of performance parameters is verified in numerical simulation.(2)For the asymmetric stiffness single lap joints constituted of composite laminates and DC04 steel,the mechanical properties of adhesive joints with different bonding length were tested systematically under tensile and three-point bending conditions.The relationship between the joint failure load,the joint stiffness and the bonding length were established.The influence of different loading modes on the mechanical properties of joints was obtained.(3)Based on the bilinear cohesive constitutive,the mechanical behavior model of the adhesive layer is established.Combined with the composite laminates theory,the numerical simulation model of the single-lap joint of the composite material is established by the finite element method.The carrying capacity and tensile failure displacement calculated by the model are in good agreement with the experimental results.Moreover,the progressive damage of the crack in the single lap joint is effectively predicted by the numerical calculation model.(4)Based on the established numerical simulation model,the stress concentration phenomenon and the failure process of the crack initiation and propagation of the adhesive layer under different bonding lengths were studied.The damage law of single-lap joint with asymmetric stiffnessis adherent was obtained.The results show that the peel strength limit of structural adhesive is the main factor that affects the failure of joint shear.