Flow Curve Evaluation by Optic Strain Measurements and Force Balance at the Most Critical Section in the Neck Region of a Tensile Specimen

Abstract

Although higher strains can be reached during a tensile test of a ductile metal, only a small portion of this Information could be extracted from this ordinary tension test: Instability In the form of necking which prevents the mathematical evaluation of stresses and strains based on the elementary measurements, Is the basic obstacle. In this study, optic strain measurements around the most strained cross section of a tensile specimen, together with the force measurements, Is used to obtain the flow curve of the material up to strains of tensile rupture. GOM-Aramis System Is utilized as the optic strain measurement system. The measured strains are assumed to be totally plastic, making It possible to compute directly the yield stresses corresponding to the strains attained at the most strained point. Obtained flow curves are compared with the flow curves from the classical tension tests done by the help of precise tangible extensometers. Further comparisons with the result of hydraulic bulge tests and simulation of the tension test shows the applicability and reliability of the approach. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA. Weinheim.