Notched specimens thermo-mechanical fatigue of a 1CrMoV turbine steel

Abstract

Isothermal (N-LCF) and thermo-mechanical fatigue (N-TMF) tests have been performed on circumferentially notched bars made of 1CrMoV. The main purpose of the investigation has been to evaluate the suitability of uniaxial fatigue data for the damage assessment of components with stress raising features. Service-cycle N-TMF tests (with low strain rates and long hold periods at peak temperature) reproduced at the notch root the strain and temperature histories of corresponding uniaxial TMF tests performed in previous studies. It is therefore possible to directly compare the notch root endurances with uniaxial data lines. The experimental results have been complemented by detailed finite element calculations and metallurgical analysis from post-test inspections. Under the assumption of a very short crack initiation length, the endurances of the notched tests can be rationalized from the uniaxial data. Measurements of short crack growth within the notch near field have been analysed using stress-strain loops in the notch near field calculated by finite elements. For the same surface equivalent strain range short crack growth is slower in notched tests than in uniaxial tests and is faster in the present N-TMF tests as compared with the N-LCF tests.