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Measuring true stress–strain curve over a large-strain-range is essential to understand mechanical behavior and simulate non-linear plastic deformation. The digital image correlation (DIC) technique, a non-contact full-field optical measurement technique, is a promising candidate to obtain a long-range true stress–strain curve experimentally. This paper proposes a method for measuring true stress–strain curves over a large-strain-range during tensile testing using DIC. The wide-strain-range true stress–strain curves of dual-phase and low carbon steels were extracted on the transverse direction in the neck region. The axial strain on the neck section was estimated by averaging the inhomogeneous deformation on the cross-section of the tensile specimen. The true stress was calculated from the engineering stress and the cross-sectional area of the neck. The validity of the proposed method was assessed by comparing the experimental load–displacement responses during tensile testing with the finite element method (FEM) simulation results. The stress and strain on the neck section estimated using the FEM and DIC, respectively, were proven to satisfy the uniaxial condition and successfully obtained. The experimental results agree well with the FEM results. The proposed concept can be applied to various deformation modes for accurately measuring long-range true stress–strain curves.

In this study, a suitable method to simulate pipe-manufacturing processes (i.e., bending, unbending, and flattening) was developed to reproduce the process and the mechanical properties of the pipe. To verify the reliability of the strain distribution and plastic deformation behavior predicted by the proposed method, experimentally-derived strain by digital image correlation (DIC) and finite element analyses were employed. Hardness and tensile tests were performed on bent-flattened specimens. The finite element method confirmed that the proposed method can predict the yield strength of pipes.