Experimental Study of Multiaxial Stress State on Creep Rupture Life and Ductility of P91 Steel

Many high-temperature components developed using uniaxial creep data are now experiencing multiaxial stress states due to geometrical changes, material behavior and loading environment conditions. In order to evaluate the service life of such components under multiaxial stress conditions, it is important to predict the creep rupture life. In this work, the notched bar creep testing has been performed at 600 degrees C on the ex-service P91 material. Notched bar creep testing has been performed on blunt and medium notched bar with notch acuities, (a/R) of 1.5 and 5, respectively. The von Mises skeletal stress could be used to adequately depict the test data for uniaxial and notched bar specimens. The cavity growth model was used to determine the effect of the multiaxial state of stress on creep ductility. At high triaxiality, the Spindler and Cocks and Ashby models agree reasonably well with the test data, but the Cocks and Ashby model overpredicts at low triaxiality. Fractographical examination of the notched bar specimens reveals an intergranular ductile failure mechanism in the case of a blunt notch and a mixed mode failure appearance in the case of a medium notch.

Automated summary

Many high-temperature components initially developed based on uniaxial creep data are now subjected to multiaxial stress states due to various factors. In order to evaluate the service life of such components under multiaxial stress conditions, predicting creep rupture life is crucial. Testing on notched bars at different notch acuities has provided valuable insights into the effects of multiaxial stress on creep ductility.