Mechanical Properties Of CFRP-Aluminum Adhesive Joint With Equivalent Stiffness

With the extensive application of lightweight and high-strength polymer-based composites,the connection between composites and metal has drawn much attention.Among them,the adhesive bonded method has become one of the research focus because of its unique advantages such as high bonding efficiency and small damage to composites.In this thesis,Carbon Fiber Reinforced Polymer(CFRP)/metal single-lap adhesive joint has been studied,by means of finite element simulations and experiments,to reveal the influence of stiffness relationship between CFRP and aluminum on the mechanical performance of adhesive joints.The main research contents include:Laminates with different tensile stiffness and flexural stiffness were designed by tailoring the number,angle and sequence of the p lies that make up the CFRP composite laminates.And then corresponding finite element models were established to analyze the influence of tensile and flexural stiffness ratio on stress value and distribution of the joints.Results showed that the increase of tensile stiffness ratio reduced the shear stress of adhesive layer and the normal stress on the surface of laminate.As the tensile stiffness ratio increased from 0.49 to 1.27,the shear stress of adhesive decreased by 28.19%,from 46.57 MPa to 33.44 MPa.And the tensile stress of laminate decreased by 37.93%,from 608.41 MPa to 377.64 MPa.Similarly,the increase of flexural stiffness ratio reduced the shear stress in adhesive layer,the peel stress and the normal stress on the surface of laminate.As the flexural stiffness ratio increased from 0.90 to 1.85,the shear stress of adhesive decreased by 16.79%,from 45.20 MPa to 37.61 MPa.The peeling stress of adhesive decreased by 14.82%,from 36.30 MPa to 30.92 MPa.And the tensile stress of laminate decreased by 31.43%,from 675.27 MPa to 463.01 MPa.According to the result of ply design,CFRP composite laminates were prepared by mould pressure process.And then CFRP/aluminum single-lap adhesive joints were made and their tensile properties were tested.Digital Ima ge Correlation(DIC)was used to collect the deformation information of each part of the joint during testing,and the real-time strain of the structure was obtained by post-processing on computer.The experimental results showed that the tensile properties of the bonded joints can be improved to some extent by increasing tensile stiffness ratio and flexural stiffness ratio of CFRP laminates to aluminum plates.Basing on finite element analysis and experiments,the following conclusions can be drawn: the change of tensile stiffness ratio and flexural stiffness ratio of CFRP laminates to aluminum plates will significantly change the stress value and distribution of single lap joints,and then influences the tensile strength of the joints.The increase of tensile and flexural stiffness ratio of CFRP laminate to aluminum plate will improve the whole stiffness of the single-lap adhesive joint,and reduce the stress level of the joint,and thereby improve the mechanical performance of the joint.