On the location of a neck formation during the tension of cylindrical specimens

A.V. Osintsev, A. Plotnikov, E.M. Morozov, E.Y. Lubkova


Numerical simulation of necking in tension cylindrical sample with simplified elastic-plastic material properties and large deformations. For experimental verification of the calculated data was carried out by sample testing tensile check deformations on the surface of the sample in real time by the method of digital image correlation.Numerical simulations of the neck formation during tension of cylindrical specimens have been carried out in an approach of simplified elastoplastic properties of the material and large strains. The results have been compared to those of a similar simulation done in another computation code. Regularities of the strain localization and neck development, dependence of the neck location on elastoplastic properties of material, in particular, on strain hardening modulus are illustrated. Tensile tests of cylindrical samples of different types and sizes have been carried out. It has been shown that in the samples of the same type and sizes made of the same material, the neck is formed dominantly on the same place. Strain diagrams of materials obtained in tests are transformed into true stress — strain diagrams. These diagrams have been used as models of the elastoplastic behavior of materials in simulations of the neck formation on models imitating the experimental samples. A qualitative agreement of the test and numerical simulation results have been obtained. In simulations of the neck formation, in some cases the formation of a pair of symmetrically located necks have been found. This prediction was verified in tensile stress experiments with real time registration of deformation by the method of digital image correlation. It has been found that following the stage of uniform straining, two symmetrically located regions of concentration of transverse strains are formed. Eventually one of these regions breaks up, while the second one gives rise to a neck, which in turn results in the failure of the sample.

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