APPLICATION OF THE θ PROJECTION CONCEPT TO STRESS-CHANGE CREEP TESTS

摘要

Theta projection concept features good prediction on long term creep behavior and creep properties. This concept has been mainly applied to creep tests where stresses were maintained constant through rupture. In this paper, it was examined whether it could also be applied to the creep curve prediction even if the stress was changed during creep deformation. Using austenitic stainless steel at 700°C, two types of stress-change creep tests were performed: Stress-increase tests and stress-decrease ones. Employing the θ projection concept and the strain hardening law, creep behavior after the stress change was estimated. Results indicated that estimated creep curves in stress-increase creep tests well agreed with experiments when the creep strain due to the initial stress remained in an early part of the tertiary stage. However, the calculation overestimated the experiments in the stress-decrease tests.