| Auto lightweight is the demand of energy saving,environmental protection and economic development.Due to its own series of excellent properties,aluminum alloy is used as the current best lightweight material.In the stamping process of aluminum alloy automobile body panels,complex panels shape often leads to generation of defects such as cracking and wrinkling,which affects the stamping properties and service life of panels,and restricts the application of aluminum alloy sheet for automobile.Therefore,it is necessary to study the deformation mechanism,stamping condition and fracture problem of aluminum alloy sheet for automobile during stamping process.Which can provide a theoretical basis and guidance for further application of aluminum alloy sheet in automobile.In this paper,6016 aluminum alloy sheet for automobile is chosen as the research object.Researching the deformation mechanism and stamping condition and fracture problem of 6016 aluminum alloy sheet by experimental method and numerical simulation of finite element and meshless.The main work of this paper is as follows:(1)The deformation mechanism of aluminum alloy sheet at different strain rates conditions was studied by standard tensile test and high speed tensile test.It is found that the dynamic deformation mechanical properties of 6016 aluminum alloy sheet have certain sensitivity to strain rate,but this strain rate sensitivity is not regular.Then obtaining the dynamic deformation constitutive equation of aluminum alloy sheet by fitting experimental data.(2)Under different pressure and different pulling speed conditions,the dynamic friction coefficient of aluminum alloy sheet during stamping process was tested by friction coefficient test.The experimental results show that the friction coefficient is changed and affected by sheet stamping speed and mold pressure during stamping process of aluminum alloy sheet.When the pressure and speed are 5 ~ 15 MPa and 10 ~ 110 mm / s,the friction coefficient fluctuates between 0.07 ~ 0.15.In order to study the applicability of dynamic friction coefficient,a numerical model of aluminum alloy hood inner was established.Which used dynamic friction coefficient as a boundary condition and calculated by finite element method.The calculation results were verified experimentally.It shows that the numerical simulation results are in good agreement with the experimental results.Which proves the dynamic friction coefficient obtained by this paper is accurate.(3)Fracture behavior of 6016 aluminum alloy sheet under different stress conditions was studied by zero scale shear,standard drawing,5mm notch tensile and expansion test.Based on experimental data,the parameters of Gissmo fracture criterion model were identified by an inverse method.The results show that the critical fracture strain values of aluminum alloy sheet deformation are not same under different stress conditions.The numerical models of non-zero shear,7.5mm notch tensile and expansion model were established and input the Gissmo fracture criterion model parameters.These models were calculated by finite element and meshless method and verified by experiments.It shows that the meshless method results more accord with experimental verification results.Which proves the rationality of Gissmo fracture criterion model parameters obtained in this paper and the accuracy of meshless analysis method for calculating the fracture problem of aluminum alloy sheet.(4)A numerical model of aluminum alloy automobile hood inner was established and calculated by meshfree coupled finite element method,which input the dynamic constitutive equation and dynamic friction coefficient and Gissmo fracture criterion model parameters of aluminum alloy obtained in this paper.The numerical simulation results were verified experimentally.It shows that there is no crack but generates corrugated wrinkles in the same area for numerical simulation results and experimental results.Which proves the dynamic constitutive equation,dynamic friction coefficient and Gissmo fracture criterion model parameters of aluminum alloy obtained in this paper are suitable for analyzing the sheet stamping process of aluminum alloy. |
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