Full-range stress–strain behaviour of contemporary pipeline steels: Part I. Model description

The stress–strain relationship of contemporary pipeline steels is often approximated by the relatively simple Ramberg–Osgood equation. However, these steels often show a more complex post-yield behaviour, which can result in significant errors. To address this limitation for cases where an accurate full-range description is needed, the authors developed a new ‘UGent’ stress–strain model which has two independent strain-hardening exponents. This paper compares the UGent model with the Ramberg–Osgood model for a wide range of experimental data, by means of least-squares curve fitting. A significant improvement is observed for contemporary pipeline steels with a yield-to-tensile ratio above 0.80. These steels typically exhibit two distinct stages of strain hardening. In contrast to the Ramberg–Osgood model, both stages are successfully described by the UGent model. A companion paper (Part II) discusses how to find appropriate model parameter values for the UGent model.

► Contemporary pipeline steels often show two strain-hardening stages.
► This phenomenon is progressively apparent as Y/T exceeds 0.80.
► Both stages cannot be simultaneously described by the Ramberg–Osgood model.
► A new “UGent” model provides significantly better descriptions.
► The improvement becomes more pronounced as Y/T increases.