Study On Failure Of Clinch-adhesive Joints Between Steel And Aluminum Based On Strain Rate Effect

In recent years,the promotion and application of steel-aluminum hybrid car bodies have brought higher challenges to the body joining process,and the joining process of dissimilar materials has also become a research hotspot.The connection technologies between steel and aluminum dissimilar materials include riveting,bonding and clinching-adhesive,etc.Among them,the clinching-adhesive technology is a combination of bonding and riveting,which retains the advantages of both,avoids their own defects,and is conducive to ensure the mechanical properties of the joint.At present,the research of clinch-adhesive joints mainly focuses on the forming process and the analysis of the failure process under quasi-static conditions,but the body connection joint is often subjected to impact load during service,which affects the damage mechanism of the joint.In this paper,the mechanical properties of clinchadhesive joints were studied from experiment and simulation by considering the effect of strain rate on steel,aluminum,adhesive and clinch-adhesive joints.First,the constitutive models of Q235 steel,6061-T6 aluminum alloy and adhesive with respect to the strain rate effect were studied.The Johnson-Cook constitutive model and its failure criterion were used to characterize the dynamic mechanical behavior of Q235 steel and 6061-T6 aluminum alloy.To account for the strain rate effect of the adhesive and its failure behavior,an elastoplastic material model was employed.Based on experiments and numerical simulations,the relevant parameters were fitted and the accuracy of the adhesive and steel-aluminum material models were verified.Afterwards,clinch-adhesive joints were prepared,and the influence of strain rate effect on the mechanical properties of clinch-adhesive joints was studied.Based on the characteristics of the drawing conditions,a cross-drawing fixture for the steelaluminum riveting specimen was designed and manufactured.Using high-speed hydraulic servo material testing machine and high-speed DIC equipment,clinchadhesive joints were tested under three working conditions（pull-shear condition,peeling condition and drawing condition）and three speeds（1 m/s,5 m/s and 10 m/s）.Based on the failure mode and load-displacement curve,the damage mechanism of clinch-adhesive joints at different strain rates was analyzed.Finally,a fine finite element model and a simplified finite element model of clinchadhesive joints considering the strain rate effect were established,and the failure behavior of the joint under different strain rates was simulated.The finite element software ABAQUS was used to establish a fine finite element model of clinch-adhesive joints,and the stress state of each part of the joint was simulated with a detailed mesh.In the finite element software LS-DYNA,a simplified finite element model of clinchadhesive joints was established by using the octahedral solid element,and the force transmission characteristics of the joint were simulated with a small number of meshes.Based on the octahedral solid element and the TIEBREAK contact,a simplified twostage failure finite element model of clinch-adhesive joints considering the strain rate effect was established,and the complete failure behavior of the joint was simulated.The last,the simulation results are compared with the experimental results.Based on the above research,a fine finite element model and a simplified finite element model that can simulate the failure behavior of clinch-adhesive joints under different strain rates were established;the damage mechanism of clinch-adhesive joints under different strain rates was analyzed;the application of simplified finite element model in failure simulation of clinch-adhesive joints was promoted.