The usual elastoplastic characterization of metals consists of determining the experimental tensile true stresstrue strain curve (true curve) and of correcting it for the post-necking triaxiality, in order to obtain an estimation of the equivalent Mises (flow) stress-strain curve. However, especially in the industry, the elongation-based engineering curve is often used because of its simplicity, opposed to the cross section-based true curve, which, instead, is less simple to be measured, unless either measurements of the shrinking specimen area and/or digital image correlation for local strains are used.A new methodology is proposed here for translating the engineering curves into the true curves via materialindependent mathematical tools named MVB functions, which only depend on the necking initiation strain and on the aspect ratio of the undeformed cross specimen. The true curves delivered by the MVB functions can be then translated into the flow curves via the MLR correction, proposed by the authors in 2004. The MVB functions are found to work properly for various specimens with round, square and thick/thin rectangular cross sections, provided that the specimens slenderness (ratio of length to section area) is large enough to prevent the neckinginduced stress triaxiality to overlap with the triaxiality induced by the specimen shoulders.Nine arbitrary hardening laws are adopted for checking the validity of the MVB functions by finite elements, encompassing very different combinations of early/medium/late necking strains and low/medium/high hardening slopes. The flow curves of the above arbitrary materials are obtained as Ludwik functions, which, beyond the necking onset, become linear true curves corrected via the MLR function. It is worth noting that such hypothesis about the flow curves, widely supported by literature data, also imposes a remarkable constraint to the way the curvature of the flow curve and, then, the hardening itself, may evolve in the post-necking range.The material independency of the relationships between engineering curves and true curves nicely complies with the evidence that the necking evolution is a purely geometric phenomenon, as it was also found in previous works.The experimental validation is provided by in-house tests and by literature data referred to round and thin sheet specimens.

Tensile testing of metals: relationship between macroscopic engineering data and hardening variables at the semi-local scale

Mirone G.
;
Barbagallo R.
2019

Abstract

The usual elastoplastic characterization of metals consists of determining the experimental tensile true stresstrue strain curve (true curve) and of correcting it for the post-necking triaxiality, in order to obtain an estimation of the equivalent Mises (flow) stress-strain curve. However, especially in the industry, the elongation-based engineering curve is often used because of its simplicity, opposed to the cross section-based true curve, which, instead, is less simple to be measured, unless either measurements of the shrinking specimen area and/or digital image correlation for local strains are used.A new methodology is proposed here for translating the engineering curves into the true curves via materialindependent mathematical tools named MVB functions, which only depend on the necking initiation strain and on the aspect ratio of the undeformed cross specimen. The true curves delivered by the MVB functions can be then translated into the flow curves via the MLR correction, proposed by the authors in 2004. The MVB functions are found to work properly for various specimens with round, square and thick/thin rectangular cross sections, provided that the specimens slenderness (ratio of length to section area) is large enough to prevent the neckinginduced stress triaxiality to overlap with the triaxiality induced by the specimen shoulders.Nine arbitrary hardening laws are adopted for checking the validity of the MVB functions by finite elements, encompassing very different combinations of early/medium/late necking strains and low/medium/high hardening slopes. The flow curves of the above arbitrary materials are obtained as Ludwik functions, which, beyond the necking onset, become linear true curves corrected via the MLR function. It is worth noting that such hypothesis about the flow curves, widely supported by literature data, also imposes a remarkable constraint to the way the curvature of the flow curve and, then, the hardening itself, may evolve in the post-necking range.The material independency of the relationships between engineering curves and true curves nicely complies with the evidence that the necking evolution is a purely geometric phenomenon, as it was also found in previous works.The experimental validation is provided by in-house tests and by literature data referred to round and thin sheet specimens.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.11769/372229
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