Study On Forming Simulation Of Vehicle-used 6016 Aluminum Alloy

Nowadays,Automotive Lightweight has become the trend of automotive development around the world.Aluminum alloy is one of the most widely used lightweight materials because of its light weight,high strength and good corrosion resistance,etc.However,duo to the formability of aluminum alloy is worse than that of steel and the structural complexity of the cover,wrinkling and fracture are tend to happen during forming.Thus,during the process design of metal forming,it's very important to consider the failure behavior of the structure under the condition of large deformation.In this paper,the GTN(Gurson-Tvergaard-Needleman)model coupled with Hill'48 anisotropic yield criteria was implemented by establishing a user defined subroutine under the framework of LS-DYNA/Explicit finite element code.And,combined with finite element analysis technique,the damage evolution and failure behavior of 6016 Aluminum alloy sheet metal during forming has been studied.In this paper,the main work and conclusions are as follows:(1)Firstly,the basic theory and its numerical analysis method of GTN damage model has been elaborated,then,the Hill'48 anisotropic yield criteria was introduced and the user defined subroutine was established under the framework of LS-DYNA/Explicit.Finally,the correctness of the subroutine is verified by unit test,and the influence of anisotropy on the results of sheet metal forming was studied by a numerical example of round cup drawing.The results show that the anisotropy has a big influence on the mechanical properties and damage evolution of the material.(2)In order to avoid blind assignment of the value of GTN parameters,the influence of changing values was studied by a numerical example of plate tensile test.In addition,the sensitivity of mesh size was also conducted.The results show that:(1)changing the value ofNf,N? andNs have a great influence on the damage evolution and the load-displacement curve;(2)cf and ? describes the coalescence of voids,when changing the value of cf and ?,it only affect the final stage of damage evolution,and it has a significant influence on the fracture mode and the necking of the specimen;(3)Mesh size also has great influence on fracture mode and necking of the specimen,when mesh size reduced to 0.2mm,the calculated results are tend to be stable.(3)Then,the GTN damage parameters were identified by comparing the numerical and experimental tensile results of 6016 aluminum alloy.Using traditional inverse calibration method of regarding the force versus displacement curve as the only judgment criteria,a group of GTN parameters was determined,and also taking into account of the fracture and the necking behavior,another group of GTN parameters was determined.Then the two groups of GTN parameters were applied to the tensile process simulation of 6016 aluminum alloy in turn.The results showed that the first group of GTN parameter cannot accurately reflect the actual fracture and the necking behavior,while using the second group of GTN parameters,the simulation results are in good agreement with the experimental results.(4)Ultimately,the Hill'48-GTN model,Mises-GTN model and different mesh size were applied to study the damage evolution of the 6016 aluminum alloy sheet metal during Erichsen forming.After comparing the numerical results,the above conclusions were validated,those are:(1)The load-displacement curve and the fracture calculated by Hill'48-GTN model were in good agreement with the experiment results,thus the GTN model which considered the anisotropy of material can make the calculation result more reasonable;(2)The GTN parameters identified by also taking into account of the fracture and the necking behavior can accurately reflect the actual fracture;(3)Mesh size also has great influence on the fracture,the mesh size should be small as possible if the conditions permit.