Based on the two-dimensional plane stress wrinkling model of an elastic-plastic annular plate and a bifurcation functional from Hill's general theory of uniqueness in polar coordinates, the critical conditions for the elastic and plastic wrinkling of the flange of a circular blank during the deep-drawing process are obtained to improve previous results of the literature. The influence of a blank-holder on wrinkling and on the number of waves generated can also be quantitatively predicted. A closed-form solution for the critical drawing stress is developed, based on the Tresca yield criterion, along with the assumption of perfectly plastic material. A nonlinear plastic stress field and the deformation theory of plasticity are used. It is demonstrated that using the large deflection theory for a strain tensor with neglecting nonlinear terms has the same result as the small deflection theory.

In this paper derivation of the second differentiation of a general yield surface by implicit time stepping method along with its consistent elastic-plastic modulus is studied. Moreover, the explicit, trapezoidal implicit and fully implicit time stepping schemes are compared in rate-dependant plasticity. It is shown that implementing fully implicit time stepping scheme in rate-dependant plasticity predicts more accurate experimental results than other schemes.

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A bstract In the current research to model anisotropic asymmetric sheet metals a new non-AFR criterion is presented. In the new model, Modified Yld2000-2d proposed by Lou et al. (2013) is considered as yield function and Yld2000-2d proposed by Barlat et al. (2003) is considered as plastic potential function. To calíbrate the presented criterion, the yield function which is a pressure dependent criterion requiers ten directional yield stresses such as uniaxial tensile stresses in three directions of 0°, 45°, 90°, uniaxial compressive yield stresses in six directions of 0°, 15°, 30°, 45°, 75°, 90° from the rolling direction along with biaxial yield stress. Moreover, the plastic potential function which is a pressure indepedent criterion needs eight experimental data points such as tensile R-values in seven directions of 0°, 15°, 30°, 45°, 60°, 75°, 90° from the rolling direction and also biaxial tensile R-value. Finally with comparing the obtained results with experimental data points, it is shown that the presented non-AFR criterion predicts compressive yield stress, biaxial tensile yield stress and R-values more accurately than Modified Yld2000-2d and it would be considered as a new criterion for anisotropic asymmetric metals. KeywordsYld2000-2d, Modified Yld2000-2d, Anisotropic asymmetric yield functions, Non-associated flow rule, Downhill Simplex Method.

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