| Multi-material car body is an effective way and development trend to realize automobile lightweight.However,the joining technology of dissimilar materials challenges the application of multi-material car body.Clinch-adhesive process is a composite joining technology consisted of the adhesive and clinch.It has the advantages of corrosion resistance,sudden fracture prevention,good mechanical properties and good sealing.It has great application potential in the design and manufacturing of steel aluminum hybrid car body.The current research mainly focuses on the clinching forming and mechanical properties of clinch joints when the adhesive is not cured or fully cured,lacking of the research on clinching in the intermediate state of adhesive curing.Moreover,the research on the constitutive model and interface model of adhesives with different curing degrees is still insufficient.In addition,there is a lack of research on the interface damage during the forming process of clinch-adhesive joints.For these reasons,AA5754 aluminum alloy,Q235 steel and Araldite 2015 epoxy resin adhesive are taken as research objects in this paper,and the forming and mechanical properties of clinch-adhesive joints are studied by finite element simulations and experiments.The main research contents of this paper are as follows:1.The curing reaction kinetics of adhesive was studied.Based on the experimental data and genetic algorithm,a non-isothermal curing kinetic model of the adhesive was established and verified by experiments.The results show that the non-isothermal curing kinetic model is in good agreement with the experiments.Moreover,the greater the difference between the initial temperature of the adhesive and the preserving temperature,the shorter the curing time required.2.Based on the fluid solid coupling method,a finite element simulation model of clinchadhesive joint forming with adhesive in the liquid state was established.The clinching process of the Q235 steel and AA5754 aluminum alloy at the beginning of curing with epoxy resin adhesive Araldite 2015 was simulated,and the forming process of clinch-adhesive joint was explored.The results show that the finite element model can accurately simulate the forming process of the clinch-adhesive joint with the adhesive in the liquid state and the upper adhesive packet formed by the extrusion of the bottom adhesive.3.The effect of the curing degree on the shear mechanical properties,failure modes,failure displacements and peak load of the clinch-adhesive joints at the beginning of curing was studied.The results show that the curing degree does not affect the failure mode,and the clicnhing failure mode is button separation.At the same time,it was found that the mechanical self-locking structure plays a major role in bearing when the curing degree is between 0 and0.57,and the tensile shear curves are similar.When the curing degree is between 0.73 and 1,the adhesive plays a major role in bearing the load,and the clinch-adhesive joints have a second peak load.The energy absorption,peak load and the second peak load of the clinchadhesive joints increase with the increase of the curing degree of the adhesive.4.A simulation model of clinch-adhesive joint forming when the adhesive is in the solid state was established.Based on the tensile tests of the dumbbell shaped adhesive specimens and the adhesive joints,the linear strengthening elasto-plastic constitutive model and interface model of the epoxy resin adhesive related to curing degree were established,and a simulation model of clinch-adhesive joint with a five layer structure of steel plate-interface-adhesiveinterface-aluminum plate was proposed.The results show that the constitutive model and interface model related to curing degree can accurately describe the influence of the curing degree on the mechanical properties of adhesives,such as Young’s modulus,yield strength and initial interface stiffness.At the same time,it was found that the curing degree during clinching mainly affects the thickness and self-locking value of the adhesive packet.Clinching when the adhesive packet is not fully cured can effectively reduce the damage of the interface.5.The influence of the curing degree of the adhesive on the forming and mechanical properties of clinch-adhesive joints and the failure process was investigated.Clinching was carried out when the adhesive is in different curing states,and tensile tests was carried out on clinch-adhesive joints when the adhesive was fully cured.The results showed that when the curing degree was 0.57,the neck of clinch-adhesive joint was damaged.The neck thickness of the clinch-adhesive joint clinched at the beginning of curing was the largest,the thickness of the adhesive packet was the smallest,and the mechanical properties were the best.At the same time,when the mechanical self-locking structure plays a major role in bearing the load,different self-locking structures can affect the failure process and clinching failure mode of clinch-adhesive joints.In conclusion,this paper has devoted efforts on joint forming in different states of adhesive.The forming process of the adhesive packet in clinch-adhesive joint with liquid adhesive was studied by simulations,the constitutive model and interface model related to adhesive curing were established,and the forming process of clinch-adhesive joint with solid adhesive was accurately simulated.The effects of curing degree during clinching and curing degree during tension on mechanical properties of clinch-adhesive joints were respectively studied.This paper provides theoretical guidance and technical reserves for expanding the application of clinch and adhesive technology in the engineering field. |
