Study of Lüders phenomena in reactor pressure vessel steels

We have undertaken a combined experimental and modelling study of plasticity development in samples containing notches and cracks in a reactor pressure vessel steel that exhibits the Lüders phenomenon in uniaxial testing. We have used digital image correlation to study the development of plasticity in plane sided, waisted and notched samples of a mild steel that exhibits Lüders behaviour. We have developed a constitutive model for use within elastic-plastic finite element analyses of structural geometries made from materials which exhibit Lüders strain behaviour, and validated it against experimental data. The model is capable of describing plasticity development in smooth sided, waisted and notched specimens. With the assistance of the model we have determined that Lüders behaviour affects the detailed development of plasticity not only in smooth sided and waisted specimens, which is readily observed experimentally, but also in sharp notched specimens. In sharp notched specimens the plastic zone is more constrained and stress intensification higher in the presence of Lüders behaviour.