Crack shape evolution of surface flaws under fatigue loading of austenitic pipes

Abstract

From the results of fatigue crack growth and fracture tests of a Ni-Fe base superalloy (Incoloy 908), an improved fatigue life analysis model has been derived from the framework of Newman and Raju. For a plate geometry with an initial semi-elliptical surface crack in its thickness direction, the new model can predict the evolution of crack aspect ratio for a wide range of initial crack geometry for Incoloy 908 that has been considered as the primary candidate for the ITER central solenoid conduit. The improved model is applied to the ITER central solenoid magnet life prediction. The model predicted the conduit fatigue lives that are about two times the values obtained by assuming the constant aspect ratio during the crack growth, for both free-standing and bucked against central solenoid designs. Therefore, we recommend the improved model for the best estimate design analysis of future magnet conduit.