Creep damage assessment for notched bar specimens of a low alloy steel considering stress multiaxiality

• Creep damage assessment methods in multiaxial stress states were discussed.
• Micro-cracks were observed at the area of high multiaxiality in inelastic analyses.
• A strain-based method gives reasonable creep damage comparing with test results.
• Ductility reduction under the multiaxial state is a key factor in the assessment.

Creep damage assessment methods considering the effect of stress multiaxiality are discussed in order to evaluate creep crack initiation from stress concentrating fields. Creep tests using notched bar specimens were conducted and damaging features around the notch root were investigated. Micro damages such as small creep cracks were mainly observed around several hundred micro-meters below the surface. Creep damage assessment methods based on inelastic analyses considering the primary and secondary creep were discussed. Creep damages evaluated from creep strains taking the ductility reduction in multiaxial stress states into account were in good agreement with experimental results.