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An experimental investigation of yield surfaces anisotropies
Štefan, Jan ; Parma, Slavomír ; Marek, René ; Plešek, Jiří ; Feigenbaum, H. P. ; Ciocanel, C.
This contribution is dedicated to a rigorous experimental procedure for evaluation of yield surfaces of common metallic materials. This yield surface tracing procedure employs thin-walled tubular specimens to identify individual yield points of the material under arbitrary combinations of axial load and torque. A yield point is identified on the basis of a prescribed threshold for the effective plastic strain that is being continuously and fully automatically evaluated throughout the test. The experimental results generated with this tracing method are promising, leading to shapes of the yield surfaces conform with the von Mises criterion. The proposed methodology can effectively capture the YS shape.
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Numerical calibration of material parameters of selected directional distortional hardening models with combined approach using both distorted yield surfaces and stress-strain curves
Hrubý, Zbyněk ; Plešek, Jiří ; Parma, Slavomír ; Marek, René ; Feigenbaum, H. P. ; Dafalias, Y.F.
The plastic strain induced anisotropy is a well-known phenomenon in manufacturing and directional distortional hardening represents a very promising way to capture real plastic behavior of metals. Many papers were published in the past typically extending the von Mises yield criterion with directionally dependent internal variable and defining yield point at the basis of plastic strain offset. Material parameters of these models were typically calibrated at the basis of deformed yield surfaces only, which – as revealed – could lead to certain discrepancies in simple stress-strain response. Presented paper introduces a numerical calibration approach taking both distorted yield surfaces and stress-strain curves information into account. Besides the calibration procedures, innovative applications of experimental techniques such as the acoustic emission for an acquisition of yield inception and plastic straining, convexity of the models, or numerical implementation of these models are discussed.
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