A Study On Strength Of Adhesive Bonded Joints For Vehicle Structures

In recent years,with the development of automobile lightweight technology,the materials used in automobiles have been diversified in the direction of light metal materials and composite materials,which achieves the lightweight effect but presents the connection problem between dissimilar materials.As a new structural connection technology,bonding has been widely concerned by engineers because of its good connection properties of dissimilar material s,and the adhesive connection also has the advantages of relieving stress concentration,improving sealing and anti-fatigue performance.Usually,automotive adhesives are used for sealing,shock absorption and structural reinforcement,but they are rarely used in semi-loaded parts or load-bearing parts.The main reason is that the strength properties of bonded joints are affected by many factors,and reliable prediction methods and comprehensive systematic research are still little.Therefore,it is urgent to study the static strength mechanical properties of bonded joints,explore the inherent laws,and propose effective prediction methods to guide and promote the application of structural adhesive bonding technology in automobiles.In this paper,the static strength mechanical properties of structural adhesive joints for vehicles are studies through experiments,simulation and theoretical modeling.The main work contents and conclusions are as follows:1.Analyzed the mechanism of adhesive bonding,establi shed the basic process flow of bonding joints,discussed the main factors affecting the connection of structural adhesives,and summarized the basic types,force analysis and failure modes of bonded joints.Provided a theoretical basis for the experimental preparation and analysis of bonded joints,and also laid the foundation for the scientific analysis of the intrinsic factors and strength of bonded joints.2.Based on two types of joints commonly used in automobiles-single lap joints and T-type joints,combined with different adhesives,adherends and glue distribution form,the joint tensile test was carried out.The test results were analyzed from the aspects of the adhesive bearing form,the properties of the adherend,the failure form,the performance of the adhesive,and the mixed glue distribution form.The results show ed that the ability of the adhesive layer to carry the peeling stress is far weaker than the ability to withstand the shear stress;the connection performance of the flexible adhesive is superior to the brittle adhesive;at the same time,the condition of the adhesive layer at the end of the T-bonded joint is critical to the bearing capacity of the joint,by optimizing the force form of the end layer,the joint strength will be greatly improved.3.The finite element model of bonded jo ints was established based on the cohesive model theory,and the validity was verified by the test results.The results show ed that the cohesive model simulation can accurately fit the tensile failure proce ss of joints with ideal or ideal failure modes.The influence of different adhesives and adherends on joint strength and joint failure process were successfully analyzed through the damage variable.A single lap layer mises stress analysis model was established considering the shear deformation of the adherend and suitable for balanced or unbalanced,multi-adhesive mixed distribution,and the validity of the analytical model to predict joint strength by mises yield criterion was verified.The result showed that the analytical model can accurately solve the mises stress distribution of the adhesive joint layer;the strength prediction model based on the analytical model can achieve conservative strength for different lap length and adherend thickness,the different adhesive and sticking type single lap joint,but it is not suitable for the prediction of the strength of different adhesive layer thickness.4.Combined with experimental design and regression analysis,the influence degree of each factor on the performance of bonded joints was discussed.The strength and quality prediction model of bonded joints with multi-factor influence were established.Finally,the joint strength-quality multi-objective optimization design was carried out.The research showed that the lap length is the most important factor affecting the strength of the single lap joint.The t hickness of the bonded parts is the most important factor affecting the quality of the joint.An effective method to predict the strength of bonded joints considering multiple factors is provided by t he approximate model method based on orthogonal test.The multi-objective optimization design method based on genetic algorithm provides a feasible solution for multi-factor joint optimization design in engineering.