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Numerical Evaluation Of A Material-independent Necking Shape Factor


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G La Rosa, G Mirone & A Risitano


Numerical evaluation of a material-independent necking shape factor G. La Rosa, G. Mirone, A. Risitano Dipartimento di Ingegneria Industriale e Meccanica, Facolta di Ingegneria di Catania, Italy Abstract The best degree of approximation for the determination of a ductile material hardening curve today is represented by the Bridgman method. This procedure requires measurements of the necking curvature radius other than the load and the neck diameter, and in literature it is usually carried out without dealing with the increasing porosity of the material. The obtained curve is approximate because refers to values of the equivalent stress and strain averaged onto the entire neck section and, when it is evaluated without any void measurement, because of the difference between the apparent and the effective resisting cross section. Furthermore, it has been shown that the response of this method is strongly dependent on the initial specimen shape, showing a certain lack of precision in the triaxiality estimation. In this work a new method for the evaluation of the flow stress-equivalent plastic strain curve has been used, adopting some of the hypotheses from the Bridgman theory, but eliminating the need of curvature radii measurements. The relationships found between some variables characteristic of the plastic behavior are almost independent from the materials except for their Consider6 strain, and the derived characterization method proposed is also independent of the initial specimen shape. Introduction In previous works of the authors, [12, 131, a method for correction of the true curves, accounting for the necking induced triaxiality, was derived from finite elements calculations in which tensile tests were simulated.