Hydroforming of thin-walled hollow extrusions has become popular with automotive and materials industries for making complex structural components. Because most of the hydroformed parts are made with steel, very little research has been done on the hydroforming of extruded aluminum tubes, which are lighter and environmentally friendly. As for any forming operation, computer modeling, using finite element analysis (FEA), is today a common tool used at the design stage of the process. However, in order to obtain realistic predictions, accurate material descriptions (constitutive models) will be needed. In this work, several material models have been developed for accurate simulation of metal forming processes, specifically hydroforming of extruded aluminum tubes.; A Taylor-type polycrystalline model, based on a rate-independent single crystal yield surface and rigid plasticity, has been developed and implemented into ABAQUS/Explicit finite element (FE) code using VUMAT. It has served directly as a constitutive law in the FE to calculate the crystallographic texture evolution during the hydroforming of an extruded aluminum tube. Initial crystallographic texture measured with OIM and uniaxial tensile test results are input to this FEA model. Although very accurate in representing the material anisotropy, finite element analysis based on direct use of a polycrystal model is extremely CPU-intensive, making it unfeasible for design purposes.; To develop the most accurate phenomenological model for forming of extruded aluminum tubes, this polycrystal model was used to predict the anisotropy coefficients of Barlat's Yld96 yield function. This phenomenological anisotropic yield function was also implemented into ABAQUS/Implicit finite element code, using UMAT, for simulation of bulging and hydroforming of a 6061-T4 extruded aluminum tubes. It was shown that compared with von Mises and Hill's 1948 yield function, the Yld96 material model's predictions are in better agreement with experimental results.; In order to take into account the anisotropic hardening of aluminum tubes a new flow potential, as a function of the anisotropy coefficients and deviatoric stresses, was proposed. The evolution of the anisotropy coefficients was proposed to be a linear function of the strain path, with its proportionality constant determined from experimental measurements. This model was also implemented into ABAQUS/Implicit code and shown to be capable of predicting deformation strains very accurately. It is concluded that in the absence of experimental results or reliable data, the anisotropic model could be used at early design stage to evaluate the accuracy of the phenomenological models' predictions.
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