Cyclic plastic deformation behaviour of PHT piping materials - an experimental investigation

The work presents the cyclic plastic deformation behaviour of two varieties of primary heat transport piping materials to understand the hardening/softening behaviour, load history memory, strain range effect, mean stress effect and ratcheting behaviour. Microstructural changes during cyclic deformation manifest in cyclic expansion of yield that could be used to explain the hardening/softening behaviour. Both the materials memories the prior history, however, the effect disappears after some time. Both the steels exhibit non-Masing behaviour due to inhomogeneous substructural changes. Non-Masing behaviour could be explained through cyclic expansion of yield. Engineering stress controlled ratcheting experiments were noted to be inadequate and under predict the ratcheting fatigue life. Importance of true stress controlled ratcheting experiments were discussed.