| With the increasingly strict requirements for energy saving and emission reduction of automobile,the lightweight of automobile body has gradually become the main direction and inevitable trend of the development of China's automobile industry.The introduction of steel aluminum hybrid body can effectively reduce the body weight on the premise of ensuring the body strength,but the connection of steel and aluminum dissimilar materials has become a major technical problem.Structural adhesive bonding has the advantages of simple process,high strength,electrochemical corrosion resistance and good bonding performance of dissimilar materials,which has become an effective connection method for steel / aluminum dissimilar materials.The quality of structural adhesive joint directly affects the safety of vehicle body.Therefore,it is necessary to study the strength influencing factors and failure behavior of structural adhesive joint.In this paper,DP590 high strength steel and 6061 aluminum alloy were used as bonding base materials.The influence of adhesive layer thickness,surface treatment and curing conditions on shear strength of steel / aluminum single lap joint was studied by experimental test method,and the optimal process parameters were obtained.Based on mat-169 material of LS DYNA,the finite element models of butt joint and thick lap joint were established,and the single lap joint of steel / aluminum sheet was studied The accuracy of the model is verified by numerical simulation and physical test.The main research results are as follows:(1)The strength variation of the adhesive layer in the range of 0.1 mm to 1 mm was studied by experiments and finite element method.The optimal thickness of adhesive layer is 0.1 mm.With the increase of adhesive layer thickness,the strength of joint decreases gradually.In the range of 0.1 mm to 0.5 mm,the peak value of peel stress decreases gradually with the increase of adhesive layer thickness,which leads to the linear decrease of joint strength.In the range of 0.5 mm to 1 mm,the shear strength of the joint decreases nonlinearly due to the influence of porosity.(2)Three surface treatment methods,cleaning,grinding and sandblasting,were compared by test methods.The results show that the mechanical properties of the joint after sandblasting are the best.The SEM observation shows that the surface of the sandblasted joint is full of petal shaped pits and scratches,which is conducive to the infiltration of structural adhesive and mechanical self-locking,so the joint shows strong mechanical properties.Compared with only cleaning the surface of the specimen,sandpaper grinding can effectively improve the joint strength,but if the mesh number of sandpaper is too high or too low,the joint strength will be reduced.(3)By comparing the mechanical properties of adhesive joint under different curing conditions,it is found that increasing the curing time is helpful for the full curing of structural adhesive when the curing is not complete,but for the fully cured bonded joint,increasing the curing time has little effect on the shear strength of the adhesive joint;increasing the curing temperature in an appropriate range can increase the curing effect of the structural adhesive However,if the temperature is too high,the rubber layer will carbonize and the joint quality will be reduced.(4)The change rule of joint strength in the range of 12.5 mm to 22.5 mm was explored by finite element method.With the increase of lap length,the maximum load of the joint is also increasing.The main reason is that with the increase of lap length,the peel stress of adhesive layer is basically unchanged,while the peak shear stress is larger and larger,and the peak distribution area is more and more wide,which leads to the stronger bearing capacity of the joint.(5)The influence of stiffness unbalance on joint strength is studied by finite element method.The simulation results show that the steel plate and aluminum plate with different yield strength have great influence on the joint strength.The higher the base metal yield strength,the greater the joint strength;and the base metal with lower yield strength has greater influence on the joint strength than the base metal with higher yield strength.With the increase of base metal yield,the distribution of shear stress gradually becomes uniform,which increases the bearing capacity of the joint... |
PDF Full Text Request